Narrow Results

A three-body model proposed earlier (S. Kumar and V. S. Bhasin, Phys. Rev.C65, 034007 (2002)) to set up the wave function of ¹¹Li is extended to investigate structural properties of ¹¹Li like matter radius, momentum distributions of the halo neutrons and the core(c), and n–n and n–c correlations. The energies and widths of experimentally observed resonant states of ¹¹Li in continuum have been calculated by employing the complex scaling method. The model is further extended to study the β-decay of ¹¹Li to the decay modes: (i) deuteron + ⁹Li channel and (ii) ¹¹Be* (18.3 MeV) state. The results obtained are found to be in reasonably good agreement with the experimental data.

β-decay half-lives around ⁷⁸Ni and ¹³²Sn are studied with proton-neutron Quasiparticle Random Phase Approximation on the basis of Skyrme-Hartree-Fock (SHF) method. We take into account tensor force correlation in calculating the ground and excited states and find it improves the half-life of ¹³²Sn. However, the Q value is still underestimated. We also discuss that half-lives do not strongly depend on type of particle-particle interaction in isospin T = 0 channel.

The variation of β-decay lifetime of the ground state of various isotope chains display a systematic behavior with respect to the ratio of the number of valence neutron particles or holes and the maximum possible number of neutron particles or holes in that shell. Lifetimes, depending on the particle or hole nature of the protons and neutrons, as well as whether they belong to the same shell or not, are found to exhibit similar increasing or decreasing trends and display similar behavior with respect to variation of the above-mentioned ratio.

The Mott polarimetry for T-violation (MTV) experiment tests time-reversal symmetry in polarized nuclear $\beta$-decay by measuring an electron’s transverse polarization as a form of angular asymmetry in Mott scattering using a thin metal foil. A Mott scattering analyzer system developed using a tracking detector to measure scattering angles offers better event selectivity than conventional counter experiments. In this paper, we describe a pilot experiment conducted at KEK-TRIAC using a prototype system with a polarized ⁸Li beam. The experiment confirmed the sound performance of our Mott analyzer system to measure T-violating triple correlation (R correlation), and therefore recommends its use in higher-precision experiments at the TRIUMF-ISAC.

Using the Hartree–Fock–Bogoliubov mean-field theory, the ground-state structural and decay properties of Nd isotopes are investigated from the proton-rich side up to the neutron drip-line. Quantities such as binding energies per nucleon, one and two-neutron separation energies, rms charge radii, and quadrupole deformation parameters have been calculated. Compared with the relativistic mean-field results, the present calculations are in better agreement with the available experimental data. The results show clearly the signature of a shape transition at $N=90$ and an abrupt increase in the deformation near the neutron drip-line. Further, the possible decay modes like alpha, cluster and $\beta$-decay are analyzed in a unified fission model and phenomenological formulas. Overall, a good agreement is achieved between the calculated and experimental $Q$-values and half-lives wherever available. The most likely decay modes are thus identified throughout the isotopic chain.

We try to give a comparison of the calculated Gamow–Teller $\beta$-decay half-lives for ${}^{43}\mathrm{\text{K}}$, ${}^{47}\mathrm{\text{Ca}}$ and ${}^{85}\mathrm{\text{Sr}}$ nuclei with the experimental ones obtained from ($\gamma$,p), ($\gamma$,n) and (n,$\gamma$) reactions, respectively. The calculations are performed within the framework of quasi-particle phonon nuclear model. The nucleon–nucleon interaction potential is included according to Pyatov’s restoration method. The calculated decay half-lives are also compared with available experimental data in the literature.

We study the change in internal rotational energy in the transformation of protons to neutrons in the $\beta$-decay reactions that take place in the collapse of the iron core of massive stars that precede Type II supernova explosions. We consider an ensemble of electrons, protons, neutrons and neutrinos undergoing $\beta$-decay reactions, treat the protons and neutrons as triatomic rotors, evaluate the equilibrium constant to obtain the change in rotational energy during the proton-to-neutron transformation. We estimate such change for a variety of conditions, and compare with the energy released in a supernova explosion.

In this paper, the nuclear structure and some prospective decay properties of the ${}^{128-208}$Sm${}_{62}$ elements are studied. This is accomplished by using an axially deformed oscillator basis and the Relativistic Mean Field model (RMF) with PK1 and NL-SH force parameters. The bulk characteristics are carefully examined, including the binding energy (B.E./A), nuclear radii,quadrupole deformation parameter(${\beta }_2$), two neutron separation energy ($S_{2n}$), and differential change of two neutron separation energy ($d{S}_{2n}$). Estimates are also made for the half-lives of the Sm isotopes for $\alpha$-decay, $\beta$-decay and spontaneous fission (SF). Both our computed Q-values and empirically measurable Q-values are used to determine the $\alpha$-decay half-life periods using the MUDL and AKRE formulae. The results we anticipate could be useful for experiments and future perspective.

TETRA long neutron counter has proven to be an unique tool to identify and to measure delayed neutron emission from photo-fission fragments produced at ALTO ISOL facility. TETRA uses robust technology based on ³He filled-counters operating in the proportional mode. The cross-section of the reaction (n, ³He) is very larger for the thermal neutron energy range. Thus, β-delayed neutrons are moderated and can be detected with a high efficiency. However, due to the moderation process, information on the initial neutron energy is typically lost. Energy of emitted neutrons is needed for detailed description of the process of delayed (multi) neutron emission from neutron rich nuclei. In the present paper we discuss one of a method which can be used to recover information on the initial neutron energy.

Total Absorption Spectrometers are characterized by high efficiency detection of γ-ray radiation, which is due to their large volume and nearly 4π solid angle coverage. This high efficiency, used in the study of β-decay of unstable nuclei, allows for the total detection of the deexcitation path of daughter nuclei. This makes total absorption spectroscopy an ideal technique to establish true β-decay feeding patterns, which helps determine β-strength distributions as well as to understanding decay heat and the anti-neutrino spectrum emitted from nuclear reactors. The Modular Total Absorption Spectrometer (MTAS) constructed at the Holifield Radioactive Ion Beam Facility has been used to study the β decay of over 70 fission products. The measurements were focused on nuclei abundantly produced in the reactor core. In this contribution we present aspects of the analysis of the β-decay of ⁸⁹Rb measured with the MTAS detector.

Precision measurements of β-decays in nuclei, muons and neutrons allow to search for non V-A contributions in weak interactions and to set limits on parameters relevant to theoretical models beyond standard theory. Novel experiments are possible in particular at presently operating stable beam facilities and at new radioactive beam facilities such as the ISAC facility at TRIUMF, the upcoming RIKEN cyclotron facility in Japan, the new proposed FRIB (RIA) facility and the newly available facility TRIµP at KVI. EURISOL is the most powerful and versatile planned radioactive beam facility.

New shell model Hamiltonians, which give successful description of spin responses in nuclei, are applied to astrophysical processes in stars induced by nuclear weak interactions. Neutrino-nucleus reactions in supernova explosions, electron capture reactions in stellar core-collapse process and β-decays in r-process are discussed.

The roles of nuclear weak processes in stars are discussed. Neutrino-nucleus reactions on ¹²C, ⁵⁶Fe and ⁴⁰Ar are studied with new shell-model Hamiltonians. New cross sections, which give good account of experimental data, are applied to nucleosynthesis of light elements in supernova explosions. Effects of ν-oscillations are investigated, and the abundance ratio of ⁷Li/¹¹B is pointed out to be sensitive to the ν mass hierarchy. Then, e-capture and β-decay rates in sd-shell nuclei are evaluated at stellar environments, and applied to study cooling of O-Ne-Mg core stars by nuclear URCA processes. The fate of 8-10 M_❿ stars is sensitive to the cooling of the core. Finally, β-decay half-lives of r-process waiting-point nuclei with N=126 are evaluated by shell-model calculations taking into account both the Gamow–Teller and first-forbidden transitions. The half-lives obtained are short compared with standard FRDM values.

This The β- decay of ^70-74Co and other species in the vicinity of ⁷⁸Ni has been investigated following the relativistic fission of a ²³⁸U primary beam at the Radioactive Ion Beam Factory facility in RIKEN, as part of the EURICA campaign. Extremely neutron-rich nuclei from Mn to Cu were produced and stopped in a state-of-the-art β-decay spectroscopy setup after their in-flight identification. The unprecedented high intensity of the primary beam, I = 10 pnA, ensures the access to a broad number of low-lying excited states in their daughters. In the present contribution, specific details on the setup and the experimental techniques employed are described. As well, the preliminary results are discussed.