Fission and Properties of Neutron-Rich Nuclei

The following Sections are included:

• Program Committee And Advisory Committee

• Preface

• Contents

We know two kind of stellar explosion events; shock induced explosions of core collapsing massive stars known as type II supernovae, and accretion induced thermonuclear explosions such as type Ia supernovae, X-ray bursts, and novae in accreting binary systems. The type II supernova shock front causes rapid increase of density and temperature conditions in the stellar material initiating fast neutron or gamma induced nucleosynthesis processes such as the r-process and the p-process which contribute to the heavy element abundance distribution in our universe. Thermonuclear stellar explosions on the other hand are driven by nuclear ignition of dense stellar material at highly electron degenerate conditions. The ignition conditions are defined by the reaction rates of heavy ion fusion processes of stellar core material for type Ia supernovae, or by rapid nuclear fusion processes such as the hot CNO cycles or the rp-process in the stellar atmosphere of freshly accreted matter. This paper will provide a summary of the nucleosynthesis signatures of the rapid nucleosynthesis processes in stellar explosions and will highlight their impact on the associated energy release and the production of heavy elements as observed in our galaxy.

Stable nuclei are well described with closed-shell or "magic" nuclei as key benchmarks. In exotic nuclei, canonical shell closures can break down and new shell gaps may appear. Nucleon knockout reactions in the vicinity of the "Island of Inversion" and inelastic proton scattering in the chain of silicon isotopes have been performed at the National Superconducting Cyclotron Laboratory at Michigan State University to track the changes in the shell structure of neutron-rich nuclei around N = 20 and N = 28.

We report on a study of exotic nuclei around doubly magic ¹³²Sn in terms of the shell model employing a realistic effective interaction derived from the CD-Bonn nucleon-nucleon potential. The short-range repulsion of the latter is renormalized by constructing a smooth low-momentum potential, V_low–k, that is used directly as input for the calculation of the effective interaction. In this paper, we focus attention on nuclei beyond the N = 82 shell closure, in particular on ¹³⁴Sn and ¹³⁶Sb which, with an N/Z ratio of 1.68 and 1.67, respectively, are at present the most exotic nuclei in the ¹³²Sn region for which information exists on excited states.

Neutron- rich nuclei above the doubly magic ¹³²Sn near neutron drip-line are of recent interest. The masses and weak interaction rates are particularly useful for astrophysical r-process studies. The present work addresses some of the important issues in the light of the shell model. Large basis untruncated shell model calculations have been done for the A=138 neutron - rich nuclei in proton (gdsh) and neutron (hfpi) valence space above the ¹³²Sn core using the OXBASH code. Two (1+2) body nuclear Hamiltonians, viz.; realistic CWG and empirical SMPN in this model space have been used. Untruncated shell model calculations for 6 valence nucleons in this large basis space usually involve matrices of large dimensions. Calculated ground state binding energies, level spectra and other spectroscopic properties have been compared with the available experimental data. Matrix elements of the two interactions are compared to gain insight into the N-N interaction in this exotic domain.

We study fusion reactions of various systems using the density-constrained time-dependent Hartree-Fock (TDHF) formalism. In this formalism the fusion barriers are directly obtained from TDHF dynamics. In addition, we incorporate the entrance channel alignments of deformed nuclei due to dynamical Coulomb excitation. We show that alignment leads to a fusion barrier distribution and alters the naive picture for defining which energies are actually sub-barrier.

An extended SU(3) shell model that explicitly includes unique-parity levels is introduced. Shell-model calculations for a group of N~Z upper-fp shell nuclei are performed where valence nucleons beyond the N=Z=28 core occupy levels of the normal parity upper-fp shell (f_5/2,p_3/2,p_1/2) and the unique parity g_9/2 intruder configuration. More detailed analyses are done for the ⁶⁴Ge and ⁶⁸Se isotopes where levels of the upper fp shell are handled within the framework of an m-scheme basis and its pseudo-SU(3) counterpart, and respectively, the g_9/2 as a single level and as a member for the complete gds shell. The second of these approaches, namely, the extended SU(3) picture, allows one to better probe the effects of deformation and to account for many key properties of the system by using a highly truncated model space.

We have studied the ground state properties of Zr and Pb isotopes up to the neutron drip line on the basis of Hartree-Fock method with Skyrme forces allowing for deformation (DHF). The DHF calculations with Ska forces predict the existence of stability island (or peninsula) around the isotope ¹⁵²Zr, which is stable against one and two neutrons emission. It is demostrated that extremely neutron-rich Pb isotopes may have abnormally large deformation parameters β ~ 0.6 for proton and neutron density distributions. It is also shown that for superdeformed Pb isotopes the calculated values of root mean square radii are abnormally large. The stability of ^266-288Pb with respect to one-neutron emission is predicted.

High spin states of ^137,138Cs have been studied by measuring γ – γ – γ coincidences from the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. The high-spin level scheme of the N=83 neutron-rich Cs (Z=55) isotope, ¹³⁸Cs, built on 6^- isomeric state, has been established for the first time up to a 4626 keV level, assigned (16⁺). The level scheme of ¹³⁷Cs has been expanded up to a 5495 keV level, assigned (31/2^-). Spins, parities, and configurations are assigned based on the agreement between experimental level energies and shell model calculations and level systematics. Similarities are observed in the N=82 isotones, ¹³⁷Cs and ¹³⁵I up to 17/2⁺ as well as in the N=83 isotones, ¹³⁸Cs and ¹³⁶I up to 12^-. The shell-model calculations indicate the important role played by interactions between the excitation of the valence protons outside the Z=50 major shell and the f_7/2 valence neutron outside the N=82 major shell.

New experimental information has been obtained on the μs isomeric cascade in the very neutron-rich ¹³⁶Sb using γ-ray and conversion-electron spectroscopy at the Lohengrin fission-product spectrometer of the Institut Laue-Langevin, Grenoble. Two new transitions have been observed and their multipolarities determined, resolving the question of the origin of the isomerism. The new level scheme is in good agreement with predictions of a realistic shell-model calculation. Microsecond isomers in deformed neutron-rich fission fragments have also been studied in ¹⁰⁷Mo and ¹⁰⁷Tc with the Lohengrin spectrometer. These studies have been complemented by prompt γ-ray spectroscopy of these nuclei, plus the neighboring ¹⁰⁵Mo, following the spontaneous fission of a ²⁴⁸Cm source inside EUROGAM2. Simple quasiparticle-rotor model calculations are able to reproduce the experimental level schemes and decay patterns.

The Rare ISotopes INvestigation project combines the fragment recoil separator at GSI with a high-efficiency Germanium array. The project focuses on studies of shell evolution far off stability, pn-pairing, symmetries and nuclear shapes utilizing projectile fragmentation beams. Highlights from a few recent experiments performed at RISING are reported.

Magic numbers are a key feature in finite Fermion systems since they are strongly related to the underlying mean field. The study of the evolution of the shells far from stability is therefore of high interest since such information can be linked to the shape and symmetry of the nuclear mean field. The study of nuclei with large neutron/proton ratio allow to probe the density dependence of the effective interaction. Changes of the nuclear density and size in nuclei with increasing N/Z ratios are expected to lead to different nuclear symmetries and excitations. Recently it has also been shown that the tensor force play an important role in breaking and creating magic numbers being a key element of the shell evolution along the nuclear chart. A tremendous effort is presently going on through a systematic exploration of new regions of the chart of nuclei as well as through the developments of high intensity stable and radioactive ion beam facilities. In this contribution I will discuss some selected examples which show the big potential of stable beams using "unconventional" reactions for the study of the properties of the nuclear many body system.

Results of two experimental campaigns are presented investigating shell structure in neutron-rich nuclei near ⁵⁴Ca and ¹³²Sn, respectively. In the first experiment excited states in ⁵⁵Ti were investigated at the middle focus of the GSI FRS via one-neutron knock-out from ⁵⁶Ti. Longitudinal momentum distributions were measured inclusively and in coincidence with a newly discovered gamma-ray at 955 keV detected by the MINIBALL gamma-ray detector array. From the momentum distributions the νp_1/2 single-particle structure of the ground state was determined for the first time while the excited state at 955 keV is identified as the νp_3/2 single-particle state. Secondly, results from the Coulomb excitation of neutron-rich nuclei ^122,124,126Cd, ^{138,140,142,144}Xe are presented. These experiments were performed at the REX-ISOLDE accelerator at CERN also using the MINIBALL array. The obtained B(E2)-values follow the expected systematic behavior that correlates the energy of the first excited 2⁺ state with the B(E2)-values and also agree well with the results of theoretical predictions.

The structure of neutron-rich Fe isotopes near N=40 is addressed in terms of the results obtained from the ⁶⁴Ni + ²³⁸U deep-inelastic reaction. The results are interpreted within the scope of the shell model, and the role of the g_9/2 neutron orbital in these nuclei is discussed.

Recent spectroscopic studies of the heaviest actinides (Z≂100) have led to the identification of K isomers in these nuclei. These states, with their "pure" intrinsic configurations, probe energies of single-particle levels and the extent of the gaps therein. This information is crucial for quantitative tests of divergent model predictions of magic gaps in superheavy nuclei. K isomers and their decay properties have been established in ^254,252No, ²⁵⁰Fm and ^248,246Cm. These results, along with their implications for various theoretical approaches, are presented.

To pursue the investigation of a new territory of nuclei with extreme N/Z called "terra incognita" several projects, all aiming at the increase by several orders of magnitude of the RIB intensities are now under discussions worldwide.

The main goal of SPIRAL2 is clearly to extend our knowledge of the limit of existence and the structure of nuclei deeply in the medium and heavy mass region (A=60 to 140) which is to day an almost unexplored continent.

SPIRAL 2 is based on a high power, CW, superconducting driver LINAC, delivering 5 mA of deuteron beams at 40MeV (200KW) directed on a C converter+ Uranium target and producing therefore more 5×l0¹³fissions/s. The expected radioactive beams intensities for exotic species in the mass range from A=60 to A=140, of the order of l0⁶ to 10¹⁰pps will surpass by two order of magnitude any existing facilities in the world. These unstable atoms will be available at energies between few KeV/n to 15 MeV/n. The same driver will accelerate high intensity (100μA to 1 mA), heavier ions up to Ar and later on up to Xe at 14 MeV/n producing also proton rich exotic nuclei. The heavy ions capabilities as well as the very large intensities of this driver may open unique opportunities in the field of Super Heavy Elements.

The investments costs is of 136 M€ and personnel costs reach 60 M€, for the period 2006-2013. Funding from EU 7^th framework and from others partnership countries are expected to contribute for about 20% to this budget. The status of the construction will be outlined.

Based on Letter of intents process, large international collaborations are proposing innovative new instrumentation and methods for the for SPIRAL2 facility. Scientific and technical R&D programs in collaboration with EU and International partners will be presented.

The project of the international Facility for Antiproton and Ion Research (FAIR), co-located to the GSI facility in Darmstadt, has been officially started on November 7, 2007. The current plans of the facility and the planned research program will be described.

An investment of about 1 billion € will permit new physics programs in the areas of low and medium energy antiproton research, heavy ion physics complementary to LHC, as well as in nuclear structure and astrophysics. The facility will comprise about a dozen accelerators and storage rings, which will enable simultaneous operations of up to four different beams.

Many interesting investigations across a range of physics can be undertaken if intense beams of radioactive beams are available. The intensity of these beams is directly related to the power that the production target can support. Some technical challenges of using such high powered targets at TRIUMF will be discussed along with some of the experimental highlights.

As a new-generation facility for radioactive isotope (RI) beam, RIKEN RI Beam Factory (RIBF) is dedicated to provide beams of various nuclei very far from the stability valley with high-power driver accelerators. The accelerator complex has already started operation, and the first result of new isotope production has been performed in 2007 with primary uranium beams at 345 MeV/nucleon. Research opportunities with RI beams, especially for the ones with intermediate energies, are discussed by taking examples of experimental results at RIKEN by RI beams in the last decades.

Michigan State University's NSCL (National Superconducting Cyclotron Laboratory) is funded by the U.S. National Science Foundation to operate the premier rare isotope user facility in the U.S. Beams of rare isotopes at NSCL are produced via projectile fragmentation or fission and separated in-flight. The current NSCL facility capabilities and main research directions will be outlined. The laboratory is currently expanding its capabilities by building an efficient gas-stopping and reacceleration capability initially up to 3.2 MeV per nucleon. For the longer term future, NSCL is proposing to replace the existing superconducting cyclotrons with a 200 MeV superconducting heavy-ion linac.

No abstract received.

The Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory hosts a dedicated user program in nuclear physics using exotic beams. Vigorous and innovative research programs concentrating on nuclear astrophysics, nuclear structure and nuclear reactions are based at HRIBF, along with a Center of Excellence for Stewardship Science operated by Rutgers University and UNIRIB consortium. Recent work has concentrated on investigation of exotic nuclei beyond the N=50 and N=82 closed shells. HRIBF was developed out of an existing accelerator complex at ORNL at a modest initial cost. Projects to improve facility efficiency and reliability are underway. However, HRIBF will require additional investments to remain productive and competitive over the decade between now and the completion of the long-planned next-generation U.S. exotic beam facility. There are several additional ways in which a modest upgrade could substantially improve HRIBF performance and operation. The most promising and cost-effective of these appears to be addition of a high-power electron accelerator for production of neutron-rich species by photofission.

After a brief survey of research work that has been done in Dubna using the secondary beams of the ACCULINNA separator, new data recently obtained for ⁹He are discussed. Results obtained in a new series of experiments dedicated to ⁸He and ¹⁰He are presented.

No abstract received.

We are studying the gamma ray and neutron multiplicity of various fission processes, beginning with the spontaneous fission of ²⁵²Cf, for a variety of basic and applied science purposes. The Livermore-Berkeley Array for Collaborative Experiments (LiBerACE) consists of six high-purity germanium Clover detectors (HPGe) each enclosed by an array of 16 bismuth-germanate (BGO) detectors. These detectors were arranged in a cubic pattern around a 1 μCi ²⁵²Cf source to attempt to cover as much solid angle of gamma ray emission as possible with a high level of segmentation. The single-gamma detector response function is determined at several energies by tagging in a HPGe detector on the photopeak of one of two gamma rays in two-gamma ray calibration sources and observing the multiplicity of the remainder of the array. Summing these single-gamma responses in groups yields the response function of the array to higher multiplicity events, which are convolved with multiplicity distributions from theoretical models and compared to the measured results to test the models' validity.

Fragment mass and total kinetic energy distributions in the proton-induced fission of ²³²Th, ²³³U and ²³⁸U at beam energies of 10.0, 11.5 and 13.0 MeV have been measured by a double time-of-flight method. The yields at the fragment mass number A ~ 132 with the spherical shells of N = 82 and Z = 50 in the asymmetric fission mode increase with excitation energy of the compound nucleus compared with those at A ~ 143 with the deformed shell of N = 86 – 88 in p + ²³²Th. In contrast, such excitation energy dependence of the yields is not observed in p + ^233,238U. The excitation energy dependence of the spherical and deformed shells seems to be sensitively related with the shell structure effects based on not the neutron number but the proton number of the fissioning nuclide.

Multi-modal fission of actinide nuclei is investigated with a dynamical approach using the multi-dimensional Langevin equation. We adopt the potential energy taking account of the microscopic energy which depends on the excitation energy. We calculate the mass and the total kinetic energy distributions of the fission fragments for ²⁶⁴Fm and ²³⁶U. In order to classify the events into fission modes, it is essential to utilize the information from the Langevin calculation. The obtained results for ²³⁶U are consistent with the experimental data. Numerical properties of the Langevin equation are discussed from the mathematical view point of the stochastic differential equation.

Analysis of the modern experimental data requires the description of the fine details and peculiar features of the fission processes. In order to refine the interpretation, the nuclear potential energy surface is taken into consideration. This surface displays the multi-valley structure of binary fission configurations and tripartion as well.

The influence of low energy charged particles on the barrier penetrability is considered and the possibility of the resonance (parametric) enhancement is discussed.

For the system ¹²⁴Sn+⁶⁴Ni system at 35 MeV/nucleon we investigated ternary processes in the framework of the Constrained Molecular Dynamics approach (CoMD). The agreement between experimental data and the model are satisfactory by reproducing also different time scales as evidenced in previous works. The same approach predicts the existence of more complex dynamical processes leading to the target like disassembly. Some result of an analysis on the experimental data devoted to evidence the existence of this process are presented.

A compact high resolution, isobar separator, based on the Multi-pass-Time-of-Flight (MTOF) principle, is being built by the University Radioactive Ion Beam (UNIRIB) Consortium. MTOF as a spectroscopy tool will have the capability to suppress a contaminating nuclear species with a relative mass difference of M/dM > 40,000 by a factor of ≫ 100. MTOF has high transmission (20% - 50%), is not chemistry dependent and fast (2-10 milliseconds of analysis time per ion bunch of ~ 10⁴ ions). The commissioning of and first experiments with MTOF will take place at the UNISOR mass separator of HRIBF, which acts as a low resolving power pre-separator. At this location, MTOF will provide isobarically pure samples of nuclei for decay spectroscopy produced in fusion-evaporation reactions with stable beams from the 25-MV tandem accelerator or by fission of UC. MTOF is capable of providing isobarically pure samples of all masses. Initially, our experimental program will focus on the region around ¹⁰⁰Sn.

The development of high quality radioactive beams has made possible the measurement of transfer reactions in inverse kinematics on unstable nuclei. Measurement of (d,p) reactions on neutron-rich nuclei yield data on the evolution of nuclear structure away from stability, and are of astrophysical interest. Experimentally, (d,p) reactions on heavy (Z=50) fission fragments are complicated by the strongly inverse kinematics, and relatively low beam intensities. Consequently, ejectile detection with high resolution in position and energy, a high dynamic range and a high solid angular coverage is required. The Oak Ridge Rutgers University Barrel Array (ORRUBA) is a new silicon detector array optimized for the measurement of (d,p) reactions in inverse kinematics.

An array of 24 Compton-suppressed Clover detectors, covering 25% of total solid angle with ~5% total photopeak detection efficiency, is currently under installation at the Inter University Accelerator Centre, New Delhi. The array, known as Indian National Gamma Array (INGA) would be rotated among the three accelerator centres in Delhi, Mumbai and Kolkata. At IUAC, the array would be used together with the recoil separator HYRA. The past experiences and the future experimental program with INGA are reported.

A source of ²³⁹U was produced by the ²³⁸U(n,γ)²³⁹U reactions and was purified by radiochemistry. Disintegration rates were determined by 4π counting in a liquid scintillation spectrometer, and gamma emission rates were determined by counting liquid samples with well-characterized HPGe spectrometers. The prominent 74.7-keV γ ray was found to occur in 53.9(5)% of the decays, and this value was used to obtain intensities for L and K x-rays and γ rays from 31 to 1102 keV.

Results of the experiments aimed at the study of fission and quasi-fission processes in the reactions ³⁶S+²³⁸U, ⁴⁸Ca+^144,154Sm, ¹⁶⁸Er, ²⁰⁸Pb, ²³⁸U, ²⁴⁴Pu, ²⁴⁸Cm; ⁵⁰Ti+²⁰⁸Pb, ²⁴⁴Pu;⁵⁸Fe+²⁰⁸Pb, ²⁴⁴Pu, ²⁴⁸Cm, and ⁶⁴Ni+¹⁸⁶W, ²⁴²Pu leading to the formation of heavy and super-heavy systems with Z=82-122 are presented. Cross sections, mass-energy and angular distributions for fission and quasifission fragments have been studied at energies close and below the Coulomb barrier. The influence of the reaction entrance channel properties as mass asymmetry, deformations and neutron excess, shell effects in the interacting nuclei and producing compound nucleus the mechanism of the fusion-fission and the competitive process of quasi-fission are discussed.

An overview of present experimental investigation of superheavy elements is given. Using cold fusion reactions which are based on lead and bismuth targets, relatively neutron deficient isotopes of the elements from 107 to 113 were synthesized at GSI in Darmstadt, Germany, and/or at RIKEN in Wako, Japan. In hot fusion reactions of ⁴⁸Ca projectiles with actinide targets more neutron rich isotopes of the elements from 112 to 116 and even 118 were produced at FLNR in Dubna, Russia. Recently, part of these data which represent the first identification of nuclei located on the predicted island of SHEs were confirmed in two independent experiments. The data are compared with theoretical descriptions.

No abstract received.

No abstract recevied.

The deformation energy of ²⁹⁴118 is calculated by using the Yukawa-plus-exponential model and the shell and pairing corrections based on the two-center shell model. The α valley of ¹⁰⁶Te is clearly seen on the PES. The half-lives of α-emitters are determined by means of the analytical superasymmetric fission model, the universal curve, and a semiempirical formula based on fission theory (semFIS). The increased deviations in the neighbourhood of magic numbers of nucleons, present in other relationships, are smoothed out by semFIS, leading to the best fit with experimental results. The experimental lifetimes of 142 transuranium α-emitters including superheavies are compared with theoretical results.

Recent microscopic calculation based on the density functional theory predicts long-lived superheavy elements in a variety of shapes, including spherical, axial and triaxial configurations. Only when N=184 is approached one expects superheavy nuclei that are spherical in their ground states. Magic islands of extra-stability have been predicted to be around Z=114, 124 or, 126 with N=184, and Z=120, with N=172. However, the question of whether the fission-survived superheavy nuclei with high Z and N would live long enough for detection or, undergo alpha-decay in a very short time remains open. In this talk I shall present results of our calculations of alpha-decay half lives of heavy and superheavy nuclei. Calculations, carried out in a WKB framework using density-dependent M3Y interaction, have been found to reproduce the experimental data quite well. Fission survived Sg nuclei with Z=106, N=162 is predicted to have the highest alpha-decay half life (~3.2 hrs) in the Z=106-108, N=160-164 region called, small island/peninsula. Neutron-rich (N >170) superheavy nuclei with Z >118 are found to have half-lives of the order of microseconds or, less.

The analysis of quasiparticle spectra in heaviest A ~ 250 nuclei with spectroscopic data provides an additional constraint for the choice of effective interaction for the description of superheavy nuclei. It strongly suggest that within the relativistic mean field (RMF) theory only the parametrizations which predict Z = 120 and N = 172 as shell closures are reliable for superheavy nuclei. The influence of the central depression in the density distribution of spherical superheavy nuclei on the shell structure is studied. Large central depression produces large shell gaps at Z = 120 and N = 172. The shell gaps at Z = 126 and N = 184 are favored by a flat density distribution in the central part of nucleus.

Two measurements of P_CN, the fusion probability, are described. In the first measurement, the value of P_CN was deduced for a typical cold fusion reaction, the ⁵⁰Ti + ²⁰⁸Pb reaction, by analysis of the fission fragment angular distributions. In the second measurement, P_CN was deduced, using the DNS model, from experimental measurements of the capture and EVR cross sections for the ¹²⁴Sn + ⁹⁶Zr reaction. Comparison of the deduced values of P_CN with various theoretical models of the synthesis of the heaviest nuclei are made.

Several g factors of excited states of moderately neutron-rich ²⁵²Cf fission fragments were measured using the IPAC method from data gathered with the GAMMASPHERE array. These results shine new light onto two regions of the nuclear chart very sensitive to the number of valence nucleons. The results for ¹⁰¹Zr and ^103,105Mo focus on the single particle properties of nuclei in a region characterised by rapid shape changes and the emergence of triaxiality, and were found consistent with a particle–rotor picture. The g factors of ^138,140,142Xe constitute an excellent test of single–particle properties near the N=82 shell closure. The measured g factors are in excellent agreement with recent shell-model and QRPA calculations.

Triple gamma coincidences from a ²⁵²Cf spontaneous fission source were measured at Gammasphere. Angular correlations of the gamma rays emitted from the fission fragments, which were stopped in an unmagnetized iron foil, were obtained using a new method. The hyperfine fields in the iron lattice cause an attenuation of the observed angular correlations in some cases. This attenuation of the correlation allows the g-factor of excited states in the fission fragments to be measured.

Magnetic moments provide a microscopic description of the structure of wave functions of nuclear states. The advent of radioactive beam has opened the possibility of exploring nuclear properties in nuclei far from stability where new phenomena, not described by extant theoretical models, might become observable. Over the last few years, techniques have been developed to extend the measurements of g factors of low-lying excited states with lifetimes of picoseconds to these regions of the periodic table. The transient field technique, coupled to Coulomb excitation of beams in inverse kinematics, represents an approach with broad applicability. The experiments are difficult and each nucleus imposes new challenges. The first two experiments, one on proton-rich ⁷⁶Kr carried out at the LBNL and one on neutron-rich ¹³²Te nuclei performed at the HRIBF laboratory at ORNL, will be described. The future direction of such measurements will be discussed in the context of the existing and planned radioactive beam facilities.

This paper reports a new a-priori approach to the calibration of attenuations observed in Recoil-in-Vacuum angular distribution experiments which should allow extraction of g-factors for states of picosecond (ps) lifetime in many nuclei, of both odd-A and even-A without the need for extensive experimentally based calibration. The methods used and results for Ge and Mo isotopes are discussed, with outline applications to both on-line beam/target Coulomb excitation and fission fragment experiments.

JYFLTRAP project has produced of the order of 200 atomic masses with the precision of few keV or better. Many of these studies have been performed on medium mass neutron-rich nuclei produced in proton induced fission. They have revealed information on the evolution of shell gaps, appearance of shape changes as well as contributed to the better knowledge of the mass surface.

New experimental results are presented on the fission characteristics of ²³⁸U(n, f) in the threshold region from E_n = 0.9 to 2.0 MeV and the prompt neutron spectrum from fission of ²³⁶U* induced by neutrons at E_n = 0.5 MeV. Fission properties in the vibrational resonance in the fission cross-section of ²³⁸U at E_n = 0.9 MeV have been investigated for the first time ever. Possible evidence of an angular dependence of the fission neutron spectrum and indications for the observation of scission neutrons is presented. Improved modeling of the neutron emission in spontaneous and neutron-induced fission has resulted in a better understanding of the experimental data, if scission neutrons are included.

A new approach to determine the independent yields of fission products mass separated by IGISOL has been developed. It is based on identifying and detecting fission product ions by direct counting after separation in the purification trap of the JYFLTRAP system with a typical mass resolving power of 10⁵. Due to the ion production mechanism of IGISOL only directly produced ions are detected and hence independent yields measured. A satisfactory agreement with previous measurements was found for independent yields of Rb and Cs isotopes in 50 MeV proton induced fission.

The use of radioactive beams in inverse kinematics dramatically increased the number of isotopes which can be studied at excitation energies ranging from a few to several hundred MeV. Since this method is not subject to target restrictions, long isotopic and isotonic chains could be investigated, and hence, studies of the evolution of fission fragment charge yields, of total kinetic energies, as well as of the time scale of nuclear fission of highly excited compound nuclei with proton and neutron number of the fissioning nucleus, are possible.

Calculations for existing and future radioactive beam facilities predict that many neutron-rich medium-mass secondary beams could be produced in greatest intensity using fission of a ²³⁸U primary beam. However, these predictions are uncertain due to the limited isotopic production cross section data available for ²³⁸U energies of 50–500 MeV/u. To address this issue, fission of an 80–MeV/u ²³⁸U beam following abrasion by a Be target has been studied at the National Superconducting Cyclotron Laboratory at Michigan State University. Recoiling fragments were spatially separated from the primary beam and identified using the A1900 fragment separator with magnetic rigidity varied in steps from 2.5–3.9 T m. In addition to standard particle identification techniques, gamma decays originating from known microsecond isomers were used to provide independent isotopic identification. A search for new neutron-rich nuclides was performed and has shown evidence for production of ¹²⁵Pd. Comparison of experimental results with theoretical models are presented.

Taking advantage of the intense, pulsed neutron source at WNR/LANSCE, we have measured the energy distribution and the number of prompt neutrons emitted in the neutron-induced fission of ^235,238U and ²³⁷Np over the broad incident neutron energy range from 1 to 200 MeV. The mean kinetic fission neutron energy was extracted as a function of the incident-neutron energy. We confirm here the observation, for these reactions, of a dip around the second-chance fission threshold, which is explained by the lower kinetic energy of the pre-fission neutrons and a decrease in the energy of the fission neutrons. This observation is reproduced by Los Alamos model as implemented at Bruyères-le-Châtel. The measured mean fission neutron energy for incident neutrons above 15 MeV is significantly lower than that predicted by the model, however. At present we are applying these techniques to neutron emission from ²³⁹Pu, and we are beginning measurements of the gamma-rays emitted in fission for all of these isotopes.

Neutron capture cross section measurements on actinides are complicated by the presence of neutron-induced fission. An efficient fission tagging detector used in coincidence with the Detector for Advanced Neutron Capture Experiments (DANCE) provides a powerful tool in undertaking simultaneous measurements of (n,γ) and (n,f) cross sections. Preliminary results on ²³⁵U(n,γ) and (n,f) and ^242mAm(n,f) cross sections measured with DANCE and a custom fission-tagging parallel plate avalanche counter (PPAC) are presented. Additional measurements of γ-ray cluster multiplicity distributions for neutron-induced fission of ²³⁵U and ^242mAm and spontaneous fission of ²⁵²Cf are shown, as well as γ-ray energy and average γ-ray energy distributions.

The neutron-induced fission cross sections of ^239–242Pu were measured at the Los Alamos Neutron Science Center. The prime interest is the ^240,242Pu(n,f) cross sections in support of the Global Nuclear Energy Partnership (GNEP). Since the ^240,242Pu samples contain low levels of the fissile ²³⁹Pu and ²⁴¹Pu isotopes, these cross sections were measured as well for correction purposes. The experimental results are compared to calculations using the EMPIRE-II nuclear reaction code. By fitting the theoretical cross sections to the experimental ones information about the fission barrier parameters, as well as (n,xn) cross sections can be deduced. In this paper we present the experimental cross sections, as well as our first attempt to calculate the cross sections using EMPIRE-II in the 0.1-20 MeV range.

Fission excitation functions have been measured for a chain of neighboring compound nuclei from ²⁰⁷Po to ²¹²Po. We present a new analysis which provides a determination of the fission barriers and ground state shell effects with nearly spectroscopic accuracy. The accuracy achieved in this analysis may lead to a future detailed exploration of the saddle mass surface and its spectroscopy.

The fission cross sections relative to ²³⁵U have been measured for ²⁴⁰Pu, ²⁴³Am, ^natW, and ²⁰⁹Bi in a "shape experiment" for a wide energy range of incident neutrons from 0.6 MeV to 200 MeV at the GNEIS facility. The measurements were performed using a multiplate ionization chamber and time-of-flight techniques. The newest ²³⁵U fission cross section evaluation and evaluated data files in ENDF/B-VII.0 were used for cross section normalizing. The results obtained in this measurement are presented in comparison with other data.

Proton even-odd staggering in fission fragment yields and its relation with energy dissipated in the fission process are investigated with respect to symmetric and asymmetric charge splits. Thermal-neutron and electromagnetic induced fission provide different fissioning systems in a range of incident energies, allowing a systematic study of this even-odd effect in the fragment yields. These data show evidence for a smaller or absent dependence of the even-odd effect at symmetry on the fissility of the fissioning system. This behaviour is still to be explained in the present picture of the fission process.

The STARS/LiBerACE collaboration has been exploring the surrogate technique with success in the actinide region. This method uses a direct reaction to measure the decay probability of the same compound nucleus produced via a neutron-induced channel. This paper serves as an overview of these activities. Using the STARS array at 88-inch Cyclotron at Lawrence Berkeley National Laboratory we have explored the following surrogate reactions: ²³⁴U(α, α′f), ²³⁵U(³He,αf), ²³⁶U(α, α′f), ²³⁸U(α, α′f), ²³⁸U(³He,αf), ²³⁸U(³He,tf) surrogates for ²³³U(n, f), ²³³U(n, f), ²³⁵U(n, f), ²³⁷U(n, f), ²³⁶U(n, f), and ²³⁷Np(n, f), respectively.

We apply the coupled-channels technique to study the hindrance of fusion which has been observed at extreme sub-barrier energies in ⁶⁴Ni+⁶⁴Ni and ¹⁶O+²⁰⁸Pb collisions. The calculated fusion cross section is sensitive at extreme subbarrier energies to the ion-ion potential for overlapping nuclei but we are not able to reproduce the low-energy data when we apply a conventional Woods-Saxon or proximity type potential in the calculations. The data can, however, be explained quite well by applying the M3Y double-folding potential which has been corrected for the effect of the nuclear incompressibility. The correction is made by including a repulsive contact interaction in the double-folding procedure. This produces a thicker Coulomb barrier and rather shallow pocket in the entrance channel potential, and these two features make it possible to explain the fusion data at the lowest energies.

High-spin states in ¹³⁹Pm have been studied via the ¹¹⁶Cd(²⁷Al, 4n)¹³⁹Pm reaction at a beam energy of 120 MeV. γγ-coincidences were recorded using the Gamma Detector Array (GDA), consisting of 12 Compton suppressed HPGe detectors. A total of 60 new γ-rays have been assigned to ¹³⁹Pm on the basis of coincidence data. A total of 53 new levels have been proposed in the present work. Four new bands have been identified and all the earlier reported bands, other than the yrast band, have been extended up to higher spin and excitation energy. Spin-parity assignments for most of the newly proposed levels have been made using the measured DCO ratios for the strong transitions. Lifetimes of levels in the yrast band have been measured by the Doppler Shift Attenuation Method (DSAM). The observed level structure is discussed.

The low-lying level pattern of the shape transitional nucleus ¹⁵⁰Sm may be viewed either as vibrational phonon multiplets or as K-bands of a softly deformed rotor. The decay pattern of the excited levels is used to analyze the preference for one of the two alternatives. This is further studied in a calculation in the microscopic approach of Dynamic Pairing-Plus-Quadrupole Model and in the Interacting boson model. A correspondence is demonstrated of the effect of the control parameter of the two models on the nuclear structure. Preference for the K-band structure is indicated, which enables better agreement with E2 transition data, in contrast to the conclusion drawn in a recent study.

We discuss a method for a direct measurement of the astrophysical S-factor for neutron-less nuclear reactions induced in laser plasmas. A very preliminary experiment to test the concepts supporting our theoretical predictions was performed at the ENEA ABC-facility. The target material, shoot during a facility tuning up activity*, was provided by LNS**. The preliminary results are reviewed as well as some theoretical predictions.

The lack of a drop in the excitation energy ratios and the anomaly of E(2⁺) energies in the even A Cd isotopes near the r-process waiting point nuclei of ¹³⁰Cd also are observed in the even A Hg isotopes near ²⁰⁶Hg with N=126. Because shape coexistence exists in Hg isotopes, Cd isotopes near N=82 are proposed to have the similar shape coexistence. In the present work, it is shown that the state mixing of ground and excited bands can reproduce level energies observed in Hg and Cd isotopes. Experimental Q_β values of ¹³⁰Cd and ¹³²Sn are on the extrapolated lines without unusual raising or lowering. Therefore, it is concluded that shell quenching is not required to explain the band structures of neutron-rich Cd isotopes.

New high-spin levels have been identified in the nucleus ¹²⁰Pd from analysis of the coincidence gamma rays observed in the ²³⁸U(α, fγγγ) reaction. Recoiling fragments were detected with the Rochester heavy-ion detector array, CHICO, in coincidence with gamma-rays using Gammasphere. An A=110-130 mass-gated γ – γ – γ cube from this experiment was constructed and analyzed for coincident gamma-rays in several nuclei near A=120. New results for neutron-rich ¹¹⁸Pd and ¹²⁰Pd have been obtained. The ¹²⁰Pd level scheme was extended to spin of 10⁺ by building on the new low-energy gamma rays identified in decay studies of ¹²⁰Rh. The details of the ¹¹⁸Pd level scheme derived from this work are compared to previous work. The systematics of the yrast levels in even-even Pd and Cd isotopes are presented and the symmetry of energy levels around N = 68 is discussed. A new 10⁺ level in ¹²⁴Cd has been observed. The population intensity of even-even neutron-rich Cd isotopes is deduced, indicating that nuclides near ¹²⁰Cd are preferentially populated following alpha-induced fission of ²³⁸U.

The investigation of the limits of nuclear existence is fundamental to the understanding of nuclear forces and structure. The limits of binding for very neutron-rich nuclei and the location of the neutron dripline are established experimentally only for the lightest elements. We report on the discovery of the new neutron-rich isotopes ⁴⁰Mg, ^42,43Al, and ⁴⁴Si. These rare isotopes were produced at the National Superconducting Cyclotron Laboratory by fragmentation of a 141 MeV/u ⁴⁸Ca beam on a tungsten target. The combination of the A1900 fragment separator together with the analysis beam line of the S800 spectrograph provided a two-stage fragment separation with exceptional selectivity. The observation of the odd-odd nucleus ⁴²Al, which was predicted to be unbound by FRDM [1] and HFB-8 [2] models, is the first indication that the neutron drip line may be located significantly further towards heavier isotopes in this mass region than it is currently believed.

The investigation of the N=20 isotopes of Ne,Na and Mg highlighted the dramatic change in structure with increasing isospin, namely the neutrons filling of the f_7/2 orbital ahead of the d_3/2 orbital. This anomalous behavior is strongly linked to the change of shell gaps with increasing isopsin. In this talk we discuss the level structure of neutron rich ^28-30Na approaching the 'island the inversion' obtained via β-delayed γ-spectroscopy. This systematic analysis allows us to better understand the influence of neutron excess in favoring intruder configurations.

We have investigated the structure of neutron-rich Z=19 Potassium isotopes at and beyond the N=28 closed neutron shell. The procedure involved a combination of two sets of data, from the fragment spectrometer to identify new γ transitions and γ-γ coincidence data to establish the level structure. In ⁴⁸K we identified the lowest excitations which involve a proton hole in πs_1/2 and πd_3/2 orbitals and found a new 7 ns isomer, analog of the 7/2^- isomer in ⁴⁷K.

The existence of a sudden onset of deformation at N ≈ 60 has long been established, but the nature of this transition remains disputed. Laser spectroscopy of the yttrium chain of isotopes has been performed to provide a range of nuclear measurements from A = 92 to A = 102. For three of the nuclear states measured, however, the extracted quantities depend on unconfirmed spin assignments. The consequencies of alternative assignments are presented here.

Fusion-evaporation reactions forming compound nuclei with A ~ 200 have been used to populate high-spin excitations in nuclei near the line of stability as fragments following fission of the compound system. Several examples are invoked to illustrate the power of prompt γ-ray spectroscopy of fission fragments from compound nuclei. This technique is compared to results from complementary methods, such as Coulomb excitation and deep-inelastic processes. All these complementary methods help bridge the gap in the systematics in areas between the neutron-deficient and neutron-rich nuclei. Moreover, many of the nuclei studied in these methods are located near shell closures where the experimental results can be compared with predictions from existing shell-model calculations or motivate such calculations in the future.

The fusion-evaporation reactions ⁹Be(¹¹B,2p) and ⁹Be(⁹Be,2p) were used to populate ¹⁸N and ¹⁶C. The mean lifetime of the first excited state in ¹⁸N was measured to be 582(165) ps (B(M1)=0.036(10) W.u.). The observed ground state spin inversion in the N=11 isotones ¹⁷C, ¹⁸N, and ¹⁹O is attributed to the increased importance of the quadrupole relative to the pairing interaction. The mean lifetime of the 2⁺₁ state in ¹⁶C has been measured to be 11.7(20) ps corresponding to a B(E2; 2⁺₁ → 0⁺) value of 4.15(73) e²fm⁴ (1.73(30) W.u.), consistent with other even-even closed shell nuclei. Our result does not support an interpretation for "decoupled" valence neutrons.

The isomer spectroscopy on nuclei in vicinity of the doubly-magic ¹³²Sn was performed with use of the RISING array at the GSI Darmstadt. Two reactions were used to produce nuclei in this region: the fragmentation of ¹³⁶Xe beam at 750 A·MeV and the fission of ²³⁸U beam at 650 A·MeV. Decays of about 20 isomeric states have been detected. Here we report in more detail on the observation of the 8⁺, π(g_9/2)^-2 isomer in ¹³⁰Cd. Comparison to shell model predictions reveals good agreement and no indication of the N = 82 shell quenching.

We present a semi-empirical approach to predict masses of nuclei far from stability on both sides of stability (neutron-rich and proton-rich). The approach is based on the parameterization of important nuclear structure aspects as a function of F-spin.

Spectroscopic observations of metal-poor stars along with meteoritic data suggest that an additional nucleosynthesis mechanism besides the r- and s- processes is necessary to be able to explain some of the abundances in those stars and in the solar system. Although it has recently been postulated that a light element primary process (LEPP) creating 10-30% of the abundance of elements Z ≤ 47 satisfies the abundance requirements, the nature and location of such process is not known with certainty. Different ideas about the astrophysical nature of the LEPP and current open questions are presented.

The ⁸²Ge, ⁸⁴Se, ¹³²Sn, ¹³⁰Sn, and ¹³⁴Te (d,p) reactions have been measured with ≈4-5-MeV-A rare isotope beams and CD₂ targets at the HRIBF at ORNL. Energies and spectroscopic strengths have been measured for excitations in ⁸³Ge and ⁸⁵Se. Direct neutron capture calculations on ⁸²Ge are presented. Preliminary results for single-neutron excitations in ¹³¹Sn, ¹³³Sn, and ¹³⁵Te are reported.

The presence of isomeric levels with half lives in the microsecond range has been identified in ^{125,126,127,128}Cd These Cd isotopes were produced from the fragmentation of a 120-MeV/nucleon ¹³⁶Xe beam and uniquely identified through their time-of-fight, energy loss, and total kinetic energy. Gamma rays from these isomeric levels were measured with an array of Ge detectors that were gated for a period of 15 μs y a particle implantation trigger. The gamma rays found for the ^125,127Cd isomers appear to be consistent with expected yrast structures observed in lighter, odd-mass Ce isotopes. The appearance of isomers at the point where N/Z exceeds 1.6 is interpreted as an indication of the onset of a weakened neutron-neutron and proton-neutron interaction.

From γ-γ-γ coincidence studies of prompt γ rays in the spontaneous fission from ²⁵²Cf with Gammasphere, two sets of ΔI = 1 doublet bands assigned odd-parities were identified in ^108,110,112Ru. γ-γ (θ) angular correlation data were analyzed to assign multipolarities of the depopulating transitions and spins of the bandheads. The above assignments and the decay pattern of the levels uniquely support the odd-parity assignment of the doublet bands. By checking characteristic conditions for generating chiral symmetry breaking and the fingerprints as expected for observations of chiral doublet bands in the nuclei, and based on the Tilted Axis Cranking calculations, the Δ I = 1 odd-parity doublet bands identified in ^110,112Ru are assigned zero and one phonon chiral vibration bands built on υ h_11/2 × (d_5/2g_7/2)^-1 configuration.

Several examples of extensive weakening of K selection rules for gamma transitions in deformed nuclei are known. When Y₃² deformation-driving orbitals, (those of opposite parity for which the sum or difference of projection Ω is 2) straddle the Fermi energy there arises a Y₃² octupole deformation tendency in addition to the familiar Y₂⁰, Y₂² and Y₃⁰ shape deformation terms. In the region around ¹⁷⁶Hf a K=2 bandhead sometimes comes near or below the K=2⁺ quasi-gamma bandhead, and an octupole E3 decay-out branch is enhanced by one or two orders of magnitude over the Weisskopf single-proton value. For this region we suggest that octupole Y₃² shape deformation may play a significant role in K-mixing. In the ¹⁰⁸Ru region, in the heart of quadrupole triaxiality, the K=2⁺ quasi-gamma bandheads come quite low, and no octupole K=2^- or 3^- are to be seen at comparable energies. However, "K-forbidden" E1 transitions out of odd-parity bands to ground band are common, of a strength comparable to low-energy rotational E1 in the region of pear-shaped nuclei above ¹³²Sn and ²⁰⁸Pb. The presence of such E1 transitions arises from a cross term between quadrupole and octupole shape deformation or softness.

We present a new technique for measuring angular correlations between γ-rays emitted by the fragments from the spontaneous fission of ²⁵²Cf and measured with Gammasphere. For states with short lifetimes (≤10ps), these correlations can be used to determine the spin and parity of unknown levels. For states with long lifetimes, the technique can be used to determine the g-factor of the level in question by measuring the attenuation of the correlation caused by rotation of the nucleus about the randomly oriented domains in an un-magnetized iron foil. Applying our new method to our set of triple coincidence data, we have been able to assign spins to new levels in ^108,110,112Ru. Mixing ratio and g-factor measurements are also discussed.

The level structures of ^105,108Mo and ¹¹²Ru have been carefully investigated by measuring prompt γ – γ – γ coincident measurements of neutron-rich nuclei populated in the spontaneous fission of ²⁵²Cf. In ¹⁰⁵Mo five new collective bands are observed. The three bands are proposed as single-neutron excitation bands built on the 3/2⁺[411], 1/2⁺[411] and 5/2⁺[413] Nilsson orbitals, respectively. The other two bands are candidates for one-phonon K = 9/2 and two-phonon K = 13/2 γ-vibrational bands, respectively. This is the first observation of such γ-vibrational collective band structures in odd-A nuclei. In ¹⁰⁸Mo and ¹¹²Ru, the one-phonon γ-vibrational bands have been extended and two-phonon γ-vibrational bands have been identified for the first time.

The oblate–prolate shape coexistence phenomena in N=Z nuclei, ⁶⁸Se and ⁷²Kr, are investigated using the adiabatic self-consistent collective coordinate (ASCC) method and the pairing-plus-quadrupole (P+Q) Hamiltonian including the quadrupole pairing interaction. The one-dimensional collective path is extracted from the time-dependent Hartree–Fock–Bogoliubov (TDHFB) phase space of large dimensions in a self-consistent way, and the collective Hamiltonian is microscopically derived. Excitation spectra and E2 transition probabilities are calculated by requantizing the collective Hamiltonian. Basic properties of the shape coexistence phenomena are reproduced. It is found that shape mixing decreases as angular momentum increases. It is also shown that effects of time-odd mean-fields associated with the quadrupole pairing significantly increase the collective mass (inertial function) of the large amplitude collective motion.

The neutrinoless double beta decay can yield the neutrino mass, if the neutrino is a Majorana particle. In the Standard Model, the neutrinoless double beta decay is not allowed but it is allowed in most Grand Unified Theories (GUT's). The neutrino must be identical with its antiparticle and must have a mass to allow the neutrinoless double beta decay. Apart of one claim that the neutrinoless double beta decay in ⁷⁶Ge is measured, one has only upper limits for this transition probability. But even the upper limits allow to give upper limits for the electron Majorana neutrino mass and upper limits for parameters of GUT's and the minimal R-parity violating supersymmetric model. One further can give lower limits for the vector boson mediating mainly the right-handed weak interaction and the heavy mainly right-handed Majorana neutrino in left-right symmetric GUT's. For that one has to assume that the specific mechanism is the leading one for the neutrinoless double decay and one has to be able to calculate reliably the corresponding nuclear matrix elements. In the present contribution, one discusses the accuracy of the present status of calculating the nuclear matrix elements.

We briefly review the continuum mechanical approach to the excitation of collective modes in homogenous nuclear matter. The main point of this treatment is that nuclear matter around the saturation density displays characteristics analogous to a linear elastic continuum. Giant resonances are discussed as typical cases of elastic disturbances in nuclear matter. Within such a macroscopic approach it is possible to understand the gross properties of isoscalar electric and magnetic resonances. We sketch also how this framework can be extended to the case of inhomogenous nuclear matter.

The full extent of available magnetic moments of ground states of Cu isotopes, including recent results, covers a wide and interesting range including the double magic shell closures at N, Z = 28, 28 and 40,28. Significant physics, presenting challenges to theory, is briefly reviewed.

Significant progress have been made over the last decade in experimental investigation of the ⁷⁸Ni and its neighbors. Nuclear decay studies achieved lifetime measurement of the doubly-magic ⁷⁸Ni and provided excitation energies of low lying levels up to ⁷⁶Ni, establishing the "baseline" systematics of the nuclear structure knowledge for this region of nuclear chart. Perspective studies which will build on this research are presented. One major goal is determine, if ⁷⁸Ni is a good double closed-shell nucleus. The answer to this question may have profound consequences for astrophysics and also our understanding of the nuclear models describing properties of very neutron rich nuclei.

The β and β-delayed neutron decay properties of ^83,84,85Ga were measured at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. For ⁸³Ga we establish an extensive decay schème in the β and βn branches including observing for the first time the 247-keV transition between the νs_1/2 first excited state and the νd_5/2 ground state in ⁸³Ge. The β-delayed neutron probability was found to be 69.5(2.3)%, significantly higher than the currently "accepted" value. For ⁸⁴Ga, we assign a 624-keV γ ray as depopulating the state in ⁸⁴Ge, indicating that the states for the N = 52 isotones continue to decrease in energy below mid-shell. This transition has also been observed with limited statistics in the decay of ⁸⁵Ga. The lowering of these states cannot be explained within the context of current shell model spaces/interactions and may require weakening of the ⁷⁸Ni core.

Collective properties of low-lying states in the neutron-rich ^67,69,71,73Cu isotopes were investigated by Coulomb excitation with radioactive beams produced at ISOLDE and postaccelerated by REX-ISOLDE up to 2.99 MeV/A. Experimental B(E2; ½^- → 3/2^-_g.s.), B(E2;5/2^- → 3/2^-_g.s.) and B(E2;7/2^- → 3/2^-_g.s.) were determined in all four investigated isotopes. Results show that the low-lying level schemes of these nuclei are governed by three different configurations: the expected proton single-particle excitations, core-coupled states and a surprisingly low-lying collective mode.

A decay spectroscopy experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU) to measure the lowenergy excited states in ^71-75Ni populated via the β-decay of ^71-75Co. Data collected from this experiment provided enough statistics to establish γ-γ coincidence relations leading to partial level schemes for ⁷¹Ni and ⁷³Ni. The main goal of this experiment was to investigate the changes in excitation energy of the 5/2^- state relative to 9/2⁺ ground state as well as search for the 1/2^- isomeric state in odd-mass nickel isotopes approaching ⁷⁸Ni. Systematics in shell model calculations using realistic interactions for odd mass ^69-77Ni reveal a steady increase in energy spacing between the 1/2^- level and 9/2⁺ ground state but an almost constant energy separation between the 5/2^- and 1/2^- excited states. In this experiment the positions of the 5/2^- states in ⁷¹Ni and ⁷³Ni have tentatively been established.

Isobarically purified and re-accelerated ISOL beams have been used at the Holifield Radioactive Ion Beam Facility (HRIBF) of Oak Ridge National Laboratory to study the β and β-delayed neutron decay properties of ^76–79Cu. The β-delayed neutron probabilities of ⁷⁶Cu and ⁷⁷Cu were deduced from comparison of the intensities of γ rays in the Zn daughter isotopes and found to be 6.9(0.4)% and 36(3)%, respectively. For ⁷⁷Cu we have also identified 14 γ rays associated with this decay and obtained level schemes for the β and βn daughters. For ⁷⁸Cu, we observe the yrast decay sequence transitions up to the 6⁺ state with no population of the 8⁺ isomer. In the decay of the r-process critical nuclide ⁷⁹Cu we observed for the first time a γ ray at 730 keV associated with the known to ground state transition in ⁷⁸Zn.

In the framework of the Hartree-Fock method with Skyrme forces (Ska, SkM*, Sly4) allowing for deformations the location of proton and neutron drip-lines and the characteristics of the neutron-deficient and the neutron-rich isotopes Fe, Ni and Zn are investigated. The calculations predict a big jump of deformation parameter up to β ~ 0.4 for Ni isotopes in the neighborhood of N=62. The manifestation of magic numbers for the isotopes ⁴⁸Ni, ⁵⁶Ni, ⁷⁸Ni as well as for ¹¹⁰Ni, which is stable against neutron emission, is discussed.

The nuclear structure of ¹²⁴Xe is studied in the microscopic Dynamic Pairing plus Quadrupole model, adopted for light mass nuclei, and the empirical Interacting Boson model (IBM-1). The absolute B(E2) values in g-band and K^π=2+ band are compared with recent experiment. Also recently identified K^π=4+ band is studied in the two models.

Eight new high spin states and 23 new γ transitions were identified in ¹⁰⁰Zr from spontaneous fission of ²⁵²Cf by using Gammasphere. A near spherical excited band was extended up to 12⁺. And half-life of the 2⁺ state in ¹⁰⁴Zr was measured by use of the new technique of the half-life measurement which compares the prompt and delayed cascades with similar energies. Then half-life of the 2⁺ state in ¹⁰⁴Zr is 2.0(3) ns. The B(E2) and quadrupole deformation (β₂) are 0.40(6) and 0.47(7), respectively. ¹⁰⁴Zr is the most deformed 2⁺ state among medium and heavy even-even nuclei, except for ¹⁰²Sr.

Significant advantages can be obtained through the application of digital electronics to nuclear physics experiments by replacing the traditional timing and shaping circuits by numerical algorithms implemented in real time. One example demonstrating the power of digital techniques is the achievement of a low-energy threshold, <50 keV, for the detection of beta-decay electrons in a thick Si detector. Such a low beta detection threshold would dramatically improve the detection efficiency in standard beta decay correlation experiments.

The structure of Tc nuclei is extended to more neutron-rich regions based on the measurements of prompt gamma rays from the spontaneous fission of ²⁵²Cf at Gammasphere. The level scheme of N = 67 neutron-rich (Z = 43) ¹¹⁰Tc is established for the first time and that of ¹¹¹Tc is considerably expanded. The ground band of ¹¹¹Tc reaches the band-crossing region and the new observation of the weakly populated α = - 1/2 member of the band provides important information of signature splitting. The systematics of band crossings in the isotopic and isotonic chains and a CSM calculation suggest that the band-crossing of the ground band of ¹¹¹Tc be due to alignment of a pair of h_11/2 neutrons. The best fit to signature splitting, branching ratios and excitations of the ground band of ¹¹¹Tc by RTRP model calculations result in a shape of ε₂ = 0.32 and γ = -26º for this nucleus. Its triaxiality is larger than that of ^107,109Tc, which indicates increasing triaxiality in Tc isotopes with increasing neutron number. The identification of the weakly populated 'K+2 satellite' band provides strong evidence for the large triaxiality of ¹¹¹Tc. In ¹¹⁰Tc, the four lowest-lying levels observed are very similar to those in ¹⁰⁸Tc. At an excitation of 478.9 keV above the lowest state observed, ten states of a ΔI=1 band are observed. This band of ¹¹⁰Tc is very analogous to the ΔI=1 bands in ^106,108Tc but it has greater and reversal signature splitting at higher spins.

The calculation of β decay properties often only includes the Gamow-Teller allowed decays. Theory indicates that nuclei above Z=28, N=50 may need to include first forbidden decays as well in the calculations of β decay properties. An experiment will be conducted at the HRIBF of ORNL to investigate branching ratios of first forbidden decays in ^86,88,90,92Br to Kr isotopes since nearly pure Br beams are available at the HRIBF.

Yield measurements from proton-induced fission have been performed on various targets. In general, the low-density uranium carbide targets produce higher yields than a high-density UC₂ target and a uranium boride target. Higher yields expected in the mass 80-90 region from the thorium oxide target were not realized.

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