Heavy Ion Physics and Its Applications

The following sections are included:

• Preface

• Opening Address

• Contents

The recent upgrading of the Heavy Ion Research Facility Lanzhou (HIRFL) is briefly introduced with an emphasis on the development of Radioactive Ion Beam Line Lanzhou (RIBLL) at the accelerator. The progresses in the physics research in IMP are reviewed including the studies of hot nuclei and synthesis and studies of nuclei far from stability.

Some recent results on the production of hard photons in intermediate energy heavy-ion reactions are reported. The topics covered are the use of hard photons as a means to study the energy dissipation mechanism in peripheral heavy ion reactions and the observation of second chance or thermal hard photons.

Using the relativistic transport model that includes explicitly the kaon degree of freedom, we investigate kaon flow, i.e., the average kaon transverse momentum as a function of rapidity, and the associated flow parameter in both Au+Au collisions at 1 GeV/nucleon and Ni+Ni collisions at 1.93 GeV/nucleon. We use four different assumptions for the kaon potential in nuclear matter, i.e, without potential, the potential based on the mean-field approximation to an effective chiral Lagrangian, the potential obtained in impulse approximation using the KN scattering length, and the potential containing only the repulsive vector interaction. It is found that the pattern of kaon flow in heavy-ion collisions is sensitive to the kaon potential used in the model and thus provides a useful means for studying kaon properties in nuclear medium.

Angular distribution of neutral pions emitted in multiplicity-selected collisions of 0.8 GeV/u Au+Au and of 2 GeV/u Ni+Ni will be reported. Contrary to the baryonic flow and squeeze-out, which is due to the compression, similar azimuthal asymmetries in the meson's emission might have its origin in the absorption or rescattering of mesons by the spectator matter in the reaction plane. New experimental data for π^o with low transverse momenta, anticorrelation of π⁺and baryonic flows and squeeze-out like pattern observed for π^o with high transverse momenta will be compared with the qualitative predictions of both scenario. Change in the data obtained by us for two colliding systems with their different masses and different beam energies seems to indicate a need for another ‘dynamic’ scenario able to describe whole set of experimental findings about pionic flow in relativistic heavy ion collisions.

Using the FOPI facility at GSI, charged particles (1 ≤ Z ≤ 6) produced in Au + Au reactions at 150 A MeV have been measured at laboratory angles 1.2° < θ_LAB < 30°. Highly stopped collisions have been selected by imposing the ratio of the total longitudinal momentum to the collected charge within an event to be small. For these events, the cluster (Z ≥ 3) emissions are characterised by narrow rapidity distributions centred around mid-rapidity, hence typical of highly central collisions. The relevance of this selection method is confirmed by QMD simulations which indicate that such a criterion is able to select mean impact parameters of 1.8 fm. The centre-of-mass polar angle distributions of the clusters emitted in these central reactions are found peaking at large angles (70°-90°), thus indicating a transversally enhanced flow of fragments. Auto-correlation biases distorting the net amplitude of the effect have been examined through experimental approach and simulations. The prominent transverse emission subsists with a magnitude of at least 30%. Comparison with theoretical predictions is briefly presented.

We study elementary processes for production of dileptons from nucleons, either through N N bremsstrahlung or through photon-induced reactions. We emphasize the dependence of the expected cross-sections of the electromagnetic formfactor of the nucleon in the time-like regime and point out that the mentioned reactions can provide important information on the validity of vector meson dominance for the nucleon. We also study the off-shell dependence of the formfactors.

The complete version of constrained correlation dynamics of SU(N) gauge theories in temporal gauge and canonical form has been formulated in three steps. (1) With the aid of generating-functional technique and in the framework of correlation dynamics, a closed set of equations of motion for correlation Green's functions have been established. (2) Gauge constraint conditions are analysed by means of Dirac theory. The algebraic representations of Gauss law and Ward identities are given. In accordance with the truncation approximations of correlation dynamics, the conserved Gauss law and Ward identities due to residual gauge invariance are shifted to intial value problems. (3) The equations of motion for multi-time correlation Green's functions have been transformed into those for equal-time correlation Green's functions. In two-body truncation approximation, a tractable set of equations of motion, Gauss law, and Ward identities are given explicitly.

The relative yield of decay modes of projectile remnant as a function of < Z_bound > has been first time analysed from ALADIN data of (600 MeV/nucleon) Au + Cu reactions, and it is in consistent with the corresponding theoretical results of the Incomplete-Fusion-Fragmentation Model. Both the experimental and the theoretical results of the relative yield of decay modes, of the Campi plot and the theoretical results of thermodynamical temperature plot, show satisfactorily the competition and transformation processes of the decay modes of projectile remnant with decreasing of < Z_bound >.

Results of some recent studies of nuclear reactions and nuclear structure by the use of the antisymmetrized molecular dynamics (AMD) are reported. Fragmentation problems in heavy ion collisions and proton inelastic scattering to continuum are discussed. An improved description of the particle emmision process in AMD is also briefly explained. As for the structure problem, characteristic structure change of Li, Be, B, and C isotopes with the increase of the neutron number is discussed. Around neutron drip lines, clustering structure is predicted for Be and B, while large oblate deformation with neutron skin is predicted for C.

We present the Boltzmann-Langevin approach which provides a description of the strongly out of equilibrium dynamics encountered in the course of violent heavy-ion collisions. After having introduced the Boltzmann-Langevin model we present some applications to situations where fluctuations are expected to play an important role : the production of kaons at very low beam energy, well below the nucleon-nucleon threshold and the study of nuclear multifragmentation.

The concept that quantum chaos is a kind of statistical relaxation process within a finite time for quantum systems with discrete spectrum is first introduced. Then nuclear statistical theories on both fluctuations and mean properties are discussed as consequences of chaotic motions in nuclei.

Precise variational solutions for few-nucleon and few-cluster systems are obtainable by using combinations of correlated Gaussians as a trial wave function. This facilitates a fully analytical calculation of the matrix elements. The nonlinear parameters of the trial function are selected by a stochastic technique. The method has proved very efficient, virtually exact, and seems feasible for any few-body bound-state problems. The method has been extended to describe various light nuclei including exotic nuclei as a multicluster system comprising α, t, h, p and n.

We propose to introduce a new stochastic process in antisymmetrized molecular dynamics in order to describe the phenomena caused by the wave packet spreading such as the nucleon emission process from a hot nucleus. We give the fluctuations originating from the width of the nucleon wave packet to the nucleon stochastically. We show by calculating the liquid gas phase equilibrium that we can recover the quantum mechanical statistical property of the nucleus for the particle emission process. This improvement also has large effects in the fragmentation in heavy ion collisions such as ⁴⁰Ca+⁴⁰Ca system at 35 MeV/u. In usual AMD the reaction is almost always binary, while the yield of intermediate mass fragments increases after the incorporation of the effect of the wave packet width.

In order to treat low-energy heavy-ion reactions, we make an extension of quantum molecular dynamics method. A phenomenological Pauli-potential is introduced into effective interactions to approximate the nature of the Fermion many-body system. We treat the widths of nucleon wave-packets as time-dependent dynamical variables. With these modifications, our model can describe the ground-state properties in wide mass range. Improvements due to the extension are also obtained in the nucleus-nucleus collision calculations.

A two-body correlation transport theory (TBCTT) for describing the dynamical process in heavy ion collision (HIC) has been established by means of coupling the equation of motion for coherent single particle states with two-body correlation dynamics (TBCD). This model contains the time-dependent mean field effect, two-body correlation, all orders of interactions as well as fermionic effect. It is capable of describing the time-evolution of nonuniform nuclear matter, fluctuation effects and the dynamical formation of fragments in HIC. The calculation results show that this model can really be used to describe the dynamical process in HIC.

The RVUU model has been used to study the dynamical processes of both pion and kaon produced in heavy ion collisions. We include the nuclear medium effect on kaon and pion in the model, and simulate pion production and subthreshold kaon production processes in heavy ion collisions at 1 GeV/nucleon. The calculated results show that the attractive pion optical potential changes final-state pion momentum spectrum, enhancing the yield of pions with low transverse momenta. At the same time it also apparently increases kaon abundance and modifies kaon momentum distribution.

Fission is a powerful tool for studying the primary reaction mechanisms in nucleus-nucleus collisions involving at least one fissionable nucleus. This is well shown when an additional information on the violence of the collision is provided by a totally independent observable such as the neutron multiplicity. The mass asymmetry in the entrance channel and the impact parameter are shown to have a decisive influence on the fate of the collision leading to either fusion or a two-body deeply inelastic reaction, analogous to what is known at lower bombarding energies. The experimental approach allows also to single out electromagnetic fission of U after interaction with Au and to provide some characteristics of such a process.

The formation and decay of excited nuclei with masses around A = 200 are studied for excitation energy, ε* ranging from 0 to 6 MeV/u. In case of multifragment emission, we find that:

- the life-time of the excited nucleus before breaking is equal to 100-150 fm/c for ε* values around 5 MeV/u

- the emission time (i.e. the interval between the emission of two fragments) evolves from a large value (τ>500 fm/c, sequential decay) when ε* equals 2-3 MeV/u to a very small value (τ<50 fm/c, simultaneous decay) for ε* values around 5 MeV/u.

- toroidal shapes are reached for the decay of the long-lived primary configurations.

The excitation function for complete vaporization has been measured for the system ³⁶Ar + ⁵⁸Ni over a broad range of bombarding energies. A kinematical analysis was used to select incomplete fusion and binary dissipative processes. In both cases, excitation energies of the primary hot outgoing partners formed in these collisions have been reconstructed. Excitation energies exceeding 16 A.MeV are found to be reached.

CHIMERA is a multi-element detector array made of 1192 Si-Csl telescopes covering the 94% of the whole solid angle that is planned to fully operate in 1998 by using the Superconducing Cyclotron beams at the LNS of Catania. Besides the usual charge identification, due to simultaneous TOF measurements, CHIMERA allows a mass identification. The high granularity reduces drastically the multiple firing and make it possible to perform an event by event analysis as required in multifragmentation process studies. We will discuss some results of simulations concerning the problem of the complete event recostruction, in connection with the specific performances of the detector.

Fission of hot nuclei after incomplete fusion in asymmetric heavy-ion collisions has been investigated at the 4π - array FOBOS. Binary decay as well as ternary intermediate mass fragment accompanied fission has been observed. The broadening of the fragment mass distribution with increasing excitation energy is connected with the occurrence of asymmetric mass splits approaching intermediate masses at one side and heavy residues at the other. Correlations of fission fragments with intermediate mass fragments as well as light charged particles have been studied. The results obtained up to now are discussed in terms of time scales and fission dynamics.

The unstable light nuclei emitted in the interaction of ⁴⁰Ar on ¹⁹⁷Au have been detected at energy of 25MeV/u by using particle-particle correlation measurement at small relative angle. Their in-plane and out-of-plane emission was measured for three bins of experimentally estimated impact parameter. The enhanced in-plane emission for mid-rapidity unstable nuclei is observed. This enhanced in-plane emission becomes stronger with increasing of impact parameter, but changes small with the mass of unstable nuclei. The in-plane enhancement decreases slightly with the energy of excited state of unstable nuclei. For projectile-like unstable nuclei, the in-plane emission dominates as expected.

Hard photons and high energy protons from Ar and Xe induced reactions at 44 MeV/u were analysed in a series of experiments performed with the detector MEDEA. A careful analysis shows a strong correlation between hard γ and fast protons giving an unambiguous signature of the n-p first chance bremsstrahlung hypothesis. Some preliminary results on the emission of fast protons are reported.

The paper presents the threefold massive events produced in 25-A-MeV ⁴⁰Ar + ¹¹⁵In, ¹⁰³Rh and ⁹³Nb reactions. In these massive events the fragments emitted with angles larger than 36° were detected by ten parallel-plate, position-sensitive avalanche counters, each with a detection area of 25 × 20 cm². For these events total kinetic energies (TKE), a yield ratio of threefold fragmentation (3-F) to fission P₃₂, several distributions in fragment mass, velocity, relative angle among them, and so on, were obtained. From the ratio of each fragment mass to the mass of the compound nucleus in the threefold massive events, a simple empirical expression could roughly reproduce it. Using a simple space-time model to fit the relative angular correlations, the time difference between the two scission points in the threefold mass splitting process for the Ar + In system was derived. A systematics of P₃₂ versus Z²/A for hot nuclei was performed.

Inelastic and deep inelastic collisions induced by heavy ions at low incident energy display energy fluctuations in the differential excitation functions even if the outgoing particle spectra are integrated over an energy range corresponding to a large number of final states^1-9] .The properties of these fluctuations are reviewed and discussed in terms of the recent developments of the Partially Overlapping Molecular Level Model (POMLM)^2,7,8,10] and of the previous theories^11-15]. New results on angular cross-correlation functions are presented.

Complete fusion of massive nuclei is considered in the framework of the dinuclear system concept and the macroscopic dynamical model. The competition between complete fusion and quasifission in the massive dinuclear systems is discussed. The reality of the dinuclear system concept is demonstrated for symmetric and asymmetric reactions. The synthesis of superheavy nuclei is discussed in the framework of this concept

The following sections are included:

• Nuclear Structure of Superheavy Elements – Experiments and Predictions 1995.

• Approaching the pb-Limit at SHIP/GSI.

• Production Cross Sections of SHE

• The Discovery of Elements 110 to 111

• Towards a Fast, Direct Reaction Mechanism – Heavy Clusters, Compactness and Precompound n-Emission

• Outlook to Future Experiments to Synthesize SHE Beyond Element 111

• Acknowledgement

• References

The experimental techniques used for decay studies of the very neutron decicient isotopes such as ²⁰Mg, ³⁶Ca, ³⁷Ca, ⁹⁴Ag, ¹⁰⁰In, ¹⁰¹Sn and ¹¹⁴Ba are discussed. Particular emphasis is put on the discussion of the projectile fragment separator online to the accelerator SIS and the isotope separator online to the accelerator UNILAC.

Secondary beams of ⁵⁸Ni, ¹⁹⁷Au, and ²⁰⁹Bi fragments have been produced at energies of 200-370 A-MeV by projectile fragmentation, separated with the fragment separator FRS and injected into the storage–cooler ring ESR for mass and half-life measurements. Radioactive beams have also been generated by completely stripping all electrons from ¹⁶³Dy and ¹⁸⁷Re ions to investigate the resulting bound-state β decay. For these studies the revolution frequencies and beam intensities of the stored and cooled unstable nuclei were measured via Schottky spectroscopy. In the ⁵⁸Ni case the achieved relative momentum spread of 9-10⁻⁷ (FWHM) allowed us to resolve the ground and isomeric states of cooled ⁵²Mn and ⁵³Fe. The circulating beams were fully ionized which rendered possible, for the first time, to measure pure β⁺ branches of ground states (⁵²Fe⁹, ⁵³Fe⁹) and the sum of pure β⁺ and γ branches of isomers (⁵²Mn^m, ⁵³Fe^m). In the experiment with the heavier fragments the main goal was to study nuclei which are members of α-decay chains with unknown masses. We systematically mapped the “mass surface” in the holmium to polonium region from nuclei close to stability up to nuclei with unknown masses as far as their half-lives are ≳ 0.5 min. Relative accuracies for the measured mass values in the order of 1.10⁻⁶ and below can be achieved. Via a-decay energies from the literature the “mass surface” up to the proton drip-line can be accessed. Due to the high sensitivity of the Schottky diagnosis also small number of daughter nuclei of stored ions with half-lives up to years can be detected. In this way ¹⁸⁷Re was identified as a second case of bound-state β-decay.

The status of the on-going analysis of these experiments is presented.

¹⁹Na, a nuclide on proton drip line was studied by p + ²⁰Ne reaction. A new proton activity at laboratory energy of 1.10 ± 0.08 MeV with half- life of 33 ±25 ms was observed. Based on proton energy, half-life and reaction channel analyses, this new proton activity was tentatively assigned to β-delayed proton decay of ¹⁹Na. The lifetime for direct proton emission of ¹⁹Na has been theoretically estimated. Further study is needed to reslove the contradiction between experimental results and theoretical estimation.

The Projected Shell Model (PSM) of Hara and Sun is reviewed. This is a shell model developed for the medium to heavy systems. Although the model can be applied to a variety of collective modes, its current numerical code is primarily designed to study nuclear structure of well deformed systems, in high and low spin states. We will give a general discussion of the model and its relationship with the algebraic approaches such as the Fermion Dynamical Symmetry Model, and also show various applications to the physics of high spin spectroscopy, level statistics (or “quantum chaos”), and △I = 4 bifurcation.

The hybrid-VT model and the complex scaling method are fully applied to studies on the three-body structure of weakly-bound and resonance states of light nuclei near the neutron dripline. The recent studies are presented for ⁶He (⁴He+n+n), ¹⁰He (⁸He+n+n) and ¹¹Li (⁹Li+n+n). For ⁶He, all possible bound and resonance states are investigated within p-shell-dominance configurations of two valence neutrons. The ground and first excited resonance states are obtained with a very good correspondence to experiments. Other three resonance states are additionally predicted. For ¹¹Li, the analysis has been done with the use of the reliable interaction obtained from the study on resonances in ¹⁰Li. However, there still remains a lack of the binding energy by about 1 MeV. We study a coupled-channel model of (⁹Li+n+n)+(⁹Li^*+n+n) by taking into account the core nucleus excitations of ⁹Li^*. Its preliminary result shows that the main part of the lack is removed by the J^π=O⁺-paring excitation of ⁹Li*. It is further discussed that the ground resonance state of ¹⁰He observed recently can be understood consistently with the ¹¹Li bound ground state in the same two-body interaction, where the ⁸He-n folding potential is weaken due to removal of a p_3/2-orbtial proton in comparison with the ⁹Li-n one.

The configuration of most excited superdeformed bands in the mass A = 150 region can be understood in terms of simple particle-hole excitations with respect to a superdeformed core. The transition energies of many identical bands are related to those in nearby nuclei. Recent lifetime measurements with the Eurogam array have addressed the question of whether the deformation of these identical bands are also the same. Evidence that collective octupole vibrational states also play a role in excited bands in ¹⁵²Dy is also presented.

Using a triaxial-particle-rotor model, we have calculated the quadrupole and dipole transition energies, kinematic and dynamic moments of inertia, electromagnetic transition probabilities and the relative intensity of the E2 γ-transitions for SD bands in ¹⁹⁵Tl. A strong perturbation effect of rotation on transition energies and M1 and E2 transitions of superdeformed states is investigated. The total Ml transitions, enhanced by internal conversion, are expected to compete strongly with E2 γ-ray at low spins in SD ¹⁹⁵Tl nucleus.

Excitation functions of dissipative reaction products in ¹⁹F+⁵¹V reaction at 102. 25 MeV to 109. 50 MeV have been measured with identified Z and A numbers simultaneously. The corresponding energy coherence widths Γ were extracted by means of the energy autocorrelation function method. The Γ dependence on the mass number A and on the degree of freedom of neutron excess N/Z are presented for the first time.

High spin states of the odd-odd ¹⁶²Lu nucleus have been studied via ¹⁴⁷Sm(¹⁹F, ⁴nγ) reaction at 95MeV beam energy. Level scheme for yrast band based on π[h_11/2]v[i_13/2] quasiparticle configuration was established up to Iπ=(23⁻) for the first time. This band shows the signature inversion in energy before backbending generally appeared in this mass region. It is stressed that the signature splitting in ¹⁶²Lu is larger than that in ¹⁶⁰Tm nucleus.

High spin states of ¹¹⁷Xe have been investigated by means of in-beam γ-ray spectroscopy using the reaction ⁹²Mo(²⁸Si, 2pn) at beam energies of 100 to 120 MeV. The previously known vh_11/2 bands are confirmed and the vg_7/2 favored signature band is extended up to 47/2^*, in which two band crossings are observed at ħ ω = 0.33 and 0.44 MeV, respectively. Two new positive-parity bands have been established, one of which decays into the vh_11/2 yrast band via enhanced El transitions, implying the existence of octupole correlations in ¹¹⁷Xe. A new transition cascade with irregular level spacings is also observed.

The high-spin states of ¹⁹⁸Bi have been studied in the reaction ¹⁸⁷Re (¹⁶O, 5n)¹⁹⁸Bi at ¹⁶O energies from 85 to 105 MeV. In-beam measurements of γ-ray excitation functions, γ-γ-t coincidences and γ-ray angular distributions were carried out with 6 BGO(AC)HPGe detectors and one intrinsic Ge planar detector. A level scheme for ¹⁹⁸Bi with 26 γ rays was established for the first time, including a 15⁺ isomer with a measured half-life of 8.0±3.6 ns. The level structure of ¹⁹⁸Bi was qualitatively interpreted by using semi-empirical methods.

The following sections are included:

• RI Beam Factory Project
  • Facility plan
  • Experimental Opportunities in Nuclear Physics
  • Present status and recent developments

• Spectroscopy of exotic nuclei
  • Magnetic moments of nuclei far from the stability
  • Excitation of halo neutron

• Decoupling of Proton and Neutron Distribution
  • Neutron skin in Na isotopes
  • Measurements of proton distribution at MUSES
  • Other experimental opportunity in MUSES

• Acknowledgment

The charge exchange reaction ⁶He(p,n)⁶Li was measured in reverse kinematics with secondary beams and a proton target. The angular distributions of the Gamow-Teller transition to the ground state and of the Fermi transition to the isobaric analog state were obtained. The ratio of these cross sections is a measure of the relative strength of the exchange interaction V_στ and V_σ. This ratio is found compatible with existing systematics for 2 neutron excess nuclei, and no clear signiture for the halo structure was found.

Enhanced shell effects at double closure far off stability have been a long standing question. Doubly magic nuclei have been searched for intensively during the last decade. Binding energy, shape, decay-mode and simple excited configurations in this class of nuclei provide characteristic data from where residual interactions can be established and shell-model calculations extended to new areas of the chart of nuclides. Regarding the nucleosynthesis, the ⁷⁸Ni isotope is the first N=50 isotope encountered in the rapid neutron capture. For this waiting point nucleus, β-decay half-life and n-capture cross section are to be known in order to improve our understanding of the r-process and to reproduce the mass abundances as they have been measured in the solar system…

A new generation recoil mass spectrometer to be on-line with the new radioactive ion beam facility at Oak Ridge National Laboratory is described. The new RMS is composed of a momentum achromat in front of a typical RMS. Its unique qualities are high electrical rigidity, large solid angle, high beam rejection, and high mass resolution. When used with large detector arrays, these characteristics will extend the range of cross-sections to be explored in recoil mass-γ-γ-coincidence studies to several orders of magnitude smaller than present limits. Some of the broad, new regions of inaccessible exotic nuclei very far from stability out to the proton drip line opened up for study by this RMS and RIB are described. New detectors for the target and focal plane of the RMS are presented. With stable beams on a stable target, radioactive ion beams at the focal plane can have energies up to 5 MeV/A. Thus, the RMS with stable beams on target can provide a wide range of radioactive beams at the focal plane for nuclear reactions and Coulomb re-excitation.

The first experiments made at GANIL with the neutron detector Demon are described and their preliminary results presented.

We present the application of the relativistic mean field theory under the axial deformation assumption for even-even nuclei ranging from Z-8 to Z-50 up to the proton and neutron driplines. We perform the constraint calculations on the quadrupole moment and obtain all possible ground state configurations from the energy curves. To show one more capability of the RMF theory and get rid of the ambiguity between shape coexistence and triaxial deformation, we also present constraint calculations using the triaxial symmetry assumption for a selected set of isotopes…

The radioactive nuclear beam facility built at the HI-13 tandem accelerator of China Institute of Atomic Energy is described. It is designed to yield low energy ⁶He, ⁷Be, ⁸Li ¹¹C, ¹²B, ¹³N, ¹⁵O and ¹⁷F secondary beams with intensities of 10⁴-10⁶ pps and to study some reactions of nuclear physical and astrophysical interest. The experimental results in producing several species of secondary beams are summarized. The differential cross section for the ⁷Be(d, n)⁸B reaction at E_c.m = 5.8 MeV has been measured using ⁷Be beam. The ⁸B ions were detected in full geometry with a two dimensional position sensitive △E-E counter telescope. The reaction cross section was determined to be 58±4 mb. The angular distribution data were analyzed with distorted-wave Born approximation calculation. The data are of importance to determine the astrophysical the S₁₇ factor of the ⁷Be(p,γ)⁸B reaction.

A versatile radioactive tracer technique, ‘multitracer’, has been developed at RIKEN. It enables efficient simultaneous tracing of a number of elements under accurately same experimental conditions in various chemical, environmental, and biological systems. Its principle and features are presented with a few examples of application. Metal foil targets (typically Au, Ag, Ge, Cu and Fe) are irradiated with C, N, or O ions accelerated up to 135 MeV/nucleon by RIKEN Ring Cyclotron. Fragmentation of the target nuclei results in varieties of radioactive nuclides useful as tracers. Radiochemical procedures have been developed to remove the target material leaving the nuclides as “multitracer” solutions containing various radionuclides. So far, more than 50 elements have been traced with the technique. Several examples of application of multitracers are described focusing on studies of metabolism of trace elements in rats and mice.

The high sensitivity of Accelerator Mass Spectrometry can be usefully exploited for on-line measurements of low cross sections of astrophysical interest. The utilization of this technique for the case of the reaction ⁷Be(p,γ)⁸B is discussed.

A summary of research into biological effects of heavy ions in IMP is introduced in the paper. It includes biological effects of medium energy ion penetration and ultra-low energy ion implantation on living samples. Their main contents are influence of ions on germination and growth, cytologic observation and investigation of physical mechanisms. In addition, comparative research between penetration and implantation using medium energy ions is involved. Its results show that the deeper implantation using medium energy ions could, perhaps, serve for site-chosen mutation.

Electronic excitation-induced transition process from crystalline state to amorphous state in yttrium iron garnet (YIG)Y₃Fe₅O₁₂ irradiated by energetic Ar ions has been investigated by means of sample-tilting X-ray diffraction and optical absorption spectroscopy. Electronic energy loss threshold and critical irradiation dose of damage creation have been determined. These values are Se_th= 2.9 MeV/μm and D_Cri = 1 × 10¹⁴ Ar/cm² respectively. This threshold of damage creation is five times lower than electronic energy loss threshold of the chemical etching of latent track. And for the first time the nearly compelete amorphous state was observed at Se=8.3 MeV/μm with irradiation dose equal or more than 1×10¹⁴ /cm².

This was a very satisfying meeting with many excellent talks. There was a genuinely pleasant and relaxed atmosphere conducive to lively scientific discussions. I certainly have learned a lot, and if I have one regret, it concerns the many parallel sessions that made it impossible to attend all talks, a shortcoming that I as the summary speaker painfully felt. In the tradition of the Lanzhou conferences on Heavy Ion Physics and its Application the symposium covered a wide range of topics consumerate with the broad interests of the Lanzhou Institute of Modern Physics…

The following sections are included:

• List of Participants