N. V. S. V. Prasad

Study of transfer channel coupling and entrance channel effects for the near and sub-barrier fusion of 46Ti+64Ni, 50Ti+60Ni and 19F+93Nb systems

Abstract The fusion excitation functions for the 46 Ti+ 64 Ni , 50 Ti+ 60 Ni and 19 F+ 93 Nb systems have been measured from ∼ 10% below to 15% above the nominal Coulomb barrier, utilizing the recoil mass separator, HIRA at the Nuclear Science Centre, New Delhi. Mean spins have been deduced from the fusion cross sections by two different methods, one using the statistical model and the second by a fit to the fusion cross sections. Good agreement is found between them. It is seen that the simplified coupled-channel calculations, with couplings to the lowest surface inelastic excitations alone, do not explain both the observed fusion cross sections and mean spins in the low energy domain for all the three systems. A systematic comparison is made between the systems 46 Ti+ 64 Ni and 50 Ti+ 60 Ni which have quite different ground-state transfer Q -values ( Q gg ) for the transfer channels. The 46 Ti+ 64 Ni system shows a significant enhancement of the sub-barrier fusion cross section and mean spin as compared with the 50 Ti+ 60 Ni system, indicating the importance of the transfer channel coupling. Fusion cross section and mean spin have been studied for the near and sub-barrier fusion of the highly mass asymmetric system 19 F+ 93 Nb and compared with those for the 48 Ti+ 64 Ni system leading to the same compound nucleus via the nearly symmetric entrance channel. Since the 19 F+ 93 Nb system has a large positive Q gg for one-proton pick-up, the fusion data have been complemented by one-nucleon transfer measurements at energies around the Coulomb barrier. A simultaneous analysis of the fusion excitation functions and mean spin data indicates no significant effects that may be related to the entrance channel mass asymmetry.

The Leuven isotope separator on-line laser ion source

An element-selective laser ion source has been used to produce beams of exotic radioactive nuclei and to study their decay properties. The operational principle of the ion source is based on selective resonant laser ionization of nuclear reaction products thermalized and neutralized in a noble gas at high pressure. The ion source has been installed at the Leuven Isotope Separator On-Line (LISOL), which is coupled on-line to the cyclotron accelerator at Louvain-la-Neuve. 54,55Ni and 54,55Co isotopes were produced in light-ion-induced fusion reactions. Exotic nickel, cobalt and copper nuclei were produced in proton-induced fission of 238U. The b decay of the 68–74Ni, 67–70Co, 70–75Cu and 110–114Rh isotopes has been studied by means of β–γ and γ–γ spectroscopy. Recently, the laser ion source has been used to produce neutron-deficient rhodium and ruthenium isotopes (91–95Rh, 98Rh, 90,91Ru) near the N=Z line in heavy ion-induced fusion reactions.

Production of neutron-rich copper isotopes in 30-MeV proton-induced fission of 238U

Abstract The neutron-rich isotopes 70–76Cu have been produced in 30-MeV proton-induced fission of 238U using the Ion Guide Laser Ion Source (IGLIS) at LISOL. The production rates of the copper isotopes, and of the nickel and cobalt isotopes that were measured earlier, are compared to cross section calculations. Based on these new results an estimate for the cross section of 78Ni is given.

Short-lived fission products as a diagnostics tool for studying atom and ion behavior in a gas-based laser ion source

Abstract A striking difference between gamma spectra of neutron-rich Rh isotopes obtained with the laser ion source at the Leuven Isotope Separator On-Line facility has been observed depending on the mode of operation. Although the global production rate of 112Rhg,m nuclei decreases considerably, the ratio between the productions of 112Rhg and 112Rhm increases strongly when no laser ionisation is used. This effect is caused by 112Ru atoms which decay during gas evacuation of the ion source gas cell, thereby producing 112Rhg ions. The comparison in time behaviour of reaction produced ions, β-decay produced ions and laser produced ions makes it possible to study and characterise the different processes in the gas cell. The influence of these processes has to be considered when extracting nuclear information such as the relative feeding of different short-lived isomers and isotopes and fission cross-sections in a particular mass chain.

A modular focal plane detector system for the heavy ion reaction analyzer at NSC, New Delhi

Abstract A detector system has been developed for the focal plane of the HIRA. It consists of two independent detectors, a low-pressure multiwire proportional counter (LP-MWPC) followed by a split-anode ionization detector. Details of the design and test results are presented. Using slow preamplifiers, the position resolution is 21 mm and the time resolution is estimated to be 1.5 ns for the LP-MWPC. The ionization detector gives 2.4% energy resolution for 150 MeV “Si scattered off a gold target and the AZ/Z obtained for 28Si+27A1 is l/42 for Z= 14. Some results for fusion and transfer studies for the 48Ti+58Ni and 28Si+68Zn systems, respectively, at energies around the Coulomb barrier, are presented to highlight the performance of the detector system. 1. Introduction Recoil mass spectrometers (RMS) are versatile tools for heavy ion reaction studies [ 1,2]. Coupled to a high rejection for beam-like particles is the excellent mass resolution with large solid angle, and space and energy focusing. They are ideally suited for studying reactions which are forward peaked and have found good application in the study of fusion and transfer reactions around the Coulomb barrier, spectroscopy by residue tagging, etc. The heavy ion reaction analyzer (HIRA) at the Nuclear Science Centre is a large solid angle RMS, details of which are presented elsewhere [3]. An important part of such spec- trometers is the focal plane detector system (see Refs. [4,5] and references therein). At the focal plane, the HlRA brings to focus particles of varying values of

{beta}-decay properties of {sup 72}Ni and {sup 72}Cu

The {beta}-decay properties of {sub 28}{sup 72}Ni{sub 44} and {sub 29}{sup 72}Cu{sub 43} have been studied at the LISOL facility of Louvain-La-Neuve and at the CERN-ISOLDE facility, respectively. These neutron-rich nuclei have been produced in the proton-induced fission of {sup 238}U. Their decay schemes are presented and the lifetime T{sub 1/2}=6.63(3) s of {sup 72}Cu was measured. No {beta}-decaying isomeric state was found in {sup 72}Cu, in line with a suggested spin (2) for its ground state. Spin and parity assignments of the observed excited states in the odd-odd nucleus {sup 72}Cu are proposed and discussed in terms of coupling between the valence proton and neutrons. Comparison is made with a schematic shell-model picture of {sup 72}Cu and with large-scale shell-model calculations performed in the (2p{sub 3/2}1f{sub 5/2}2p{sub 1/2}1g{sub 9/2}) shell space outside the doubly magic {sub 28}{sup 56}Ni{sub 28} core.The {beta}-decay properties of {sub 28}{sup 72}Ni{sub 44} and {sub 29}{sup 72}Cu{sub 43} have been studied at the LISOL facility of Louvain-La-Neuve and at the CERN-ISOLDE facility, respectively. These neutron-rich nuclei have been produced in the proton-induced fission of {sup 238}U. Their decay schemes are presented and the lifetime T{sub 1/2}=6.63(3) s of {sup 72}Cu was measured. No {beta}-decaying isomeric state was found in {sup 72}Cu, in line with a suggested spin (2) for its ground state. Spin and parity assignments of the observed excited states in the odd-odd nucleus {sup 72}Cu are proposed and discussed in terms of coupling between the valence proton and neutrons. Comparison is made with a schematic shell-model picture of {sup 72}Cu and with large-scale shell-model calculations performed in the (2p{sub 3/2}1f{sub 5/2}2p{sub 1/2}1g{sub 9/2}) shell space outside the doubly magic {sub 28}{sup 56}Ni{sub 28} core.

Nuclear structure studies of neutron‐rich Cu and Zn isotopes produced by means of proton‐induced fission of 238U

The neutron-rich nuclei 72Ni and 72Cu have been produced in the proton-induced fission of 238U at the LISOL and ISOLDE facilities of Louvain-La-Neuve and CERN. Partial β-decay schemes are presented, giving some information about the nuclear structure of their daughter nuclei 72Cu and 72Zn. The lifetime of 72Cu was determined to be T1/2 = 6.63(3) s, in line with previous measurements. No β-decaying isomeric states were identified in 72Cu, in contrast to 70Cu. The spin and the parity of several states in 72Cu are tentatively assigned and a comparison is made with different shell-model predictions.

Sub-barrier few-nucleon transfer reaction and channel coupling effects in heavy ion fusion

Measurements of sub-barrier transfer reactions are reported for the systems , and using the recoil mass spectrometer HIRA in kinematic coincidence mode. The problem related to M/Q-ambiguity in measurements with mass separators has been resolved. Excellent mass resultion with a large solid angle is obtained by correction of the aberrations. Simplified coupled-channels calculations are carried out for these systems with transfer form factors extracted from the measured transfer probabilities. The surface vibration coupling is treated up to two phonon states with second-order coupling terms.