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Multinucleon transfer reactions were measured in interactions of 28Si with 90,94Zr at a near barrier energy using recoil mass separator, Heavy Ion Reaction Analyzer (HIRA) at Inter University Accelerator Centre (IUAC), New Delhi. The effects of shell closure, positive Q-value transfer channels on the relative strengths of ground state and excited state transfer in multinucleon transfer processes were investigated. The kinematic coincidence technique was employed to reduce the background. The m/q ambiguity was resolved by time of flight (TOF) technique. Based on the Q-value considerations, it was observed that pickup channels were predominantly of neutron transfer, whereas, stripping channels were mainly of proton transfer. A 14-element BGO array was used to extract the relative strength of excited state transfer. In interactions of 28Si with 90Zr, it was observed that the ground state and excited states competes for populating all the transfer channels. In reactions of 28Si with 94Zr, nearly similar behavior was observed except for two-neutron pickup channel, where excited state transfer was dominant and four-neutron pickup channel where ground state transfer was dominant. [ABSTRACT FROM AUTHOR]

A Coulomb-excitation measurement to study low-energy electromagnetic properties of 45Sc has been performed at the IUAC facility in New Delhi, India using a 70 MeV 32S projectile from the 15UD tandem accelerator. The preliminary value of the reduced transition probability B(E2, 11/2- ! 7/2-) and the resulting lifetime for the 11/2- state at 1237 keV were determined using the GOSIA code. [ABSTRACT FROM AUTHOR]

In order to gain further information on the electromagnetic properties of the low-lying states in 45Sc, a Coulomb excitation measurement was carried out at the IUAC, New Delhi. The 45Sc target nuclei were Coulomb excited by the 70 MeV 32S beam from the 15UD tandem accelerator. The -rays depopulating Coulomb excited states in 45Sc were detected by four Clover detectors in coincidence with the forward scattered ions. The main aim of the experiment was to determine the B(E3; 7=2- → 3=2+) and B(E3; 7=2- → 5=2+) transition probabilities, as well as the transitional electromagnetic matrix elements for low-lying intruder states. [ABSTRACT FROM AUTHOR]

Recoil mass spectrometers (RMS) are ideal instruments for identifying weakly populated reaction products in the forward angle from heavy-ion reactions amidst an intense beam background. The Heavy Ion Reaction Analyzer (HIRA) at the Nuclear Science Centre (NSC), New Delhi, is one of the few operating first generation RMSs. The features of and physics studies pursued using HIRA are covered in the paper. With the augmentation of the accelerator facilities at NSC, a second generation RMS combined with a gas-filled separator is planned. The design details of the new facility, Hybrid Recoil Mass Analyzer (HYRA), are presented. HYRA will be operated either stand-alone or in conjunction with a Large Gamma Array (LGA) at its target position. Physics studies planned with these forthcoming facilities are outlined.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The 100 element neutron detector array facility, National Array of Neutron Detectors (NAND) has been installed at Inter University Accelerator Centre (IUAC), New Delhi for experiments in heavy-ion reaction studies. The detector array consists of 100 organic liquid scintillators, each of size 5" × 5" coupled to 5 in. diameter photomultiplier. The liquid cells are mounted at 175 cm from the target with full array covering 3.3% of 4 π solid angle. We present an overview of the design and implementation of various subsystems of the array. Description of the mechanical structure, development of detectors and nuclear electronics for signal processing, data acquisition, characterization of detectors and test results are presented. Results on the performance characteristics of the array are given based on the offline tests using radioactive sources and commissioning test by in-beam experiments. The system demonstrates good n − γ discrimination and time-of-flight performance. [ABSTRACT FROM AUTHOR]

Neutron multiplicity excitation function has been measured for the 30Si+197Au reaction populating the 227Np compound nucleus at excitation energies in the range 44.1-78.8 MeV using the National Array of Neutron Detector facility of Inter University Accelerator Centre, New Delhi. Measured pre-scission neutron multiplicity values are analyzed using a statistical model incorporating Krammer's fission width due to the dissipative drag in nuclear fission, shell corrections in fission barrier and level density, collective enhancement of level density, and K-orientation effect. The present work demonstrates that a strong fission hindrance is essential to reproduce the experimental pre-scission neutrons, whereas the temperature dependent dissipation coefficient as observed in a few recent measurements is not required to reproduce the experimental νpre data. No substantial effect of collective enhancement of nuclear level density and tilting away effect of compound nucleus spin on neutron emission prior to the scission configuration was observed unlike fission of preactinides. [ABSTRACT FROM AUTHOR]

Measurements on multinucleon transfer reactions for 28Si+90,94Zr systems were performed at sub- and near-barrier energies. The fact that 90Zr has a closed neutron shell (N = 50) and 94Zr has four neutrons outside the closed shell, allows us to investigate the effects of shell closure and pairing correlation on multinucleon transfer mechanism. The experiment was performed with pulsed 28Si beam using the Heavy Ion Reaction Analyzer (HIRA) at Inter University Accelerator Centre (IUAC), New Delhi. Based on the Q-value considerations, it turned out that pickup channels were neutron transfer whereas stripping channels were proton transfer. For the 28Si+90Zr system, the values of the slope parameter for two-neutron pickup turned out to be less than that for one-neutron pickup. The values of the slope parameter were almost the same for two-, three-, and four-neutron pickup channels in the case of the 28Si+94Zr system. The transfer probabilities in the case of the 28Si+94Zr system were much larger than those for the 28Si+90Zr system, further supporting the fact that there is a correlation between the transfer channels and sub-barrier fusion cross-section enhancement. An odd-even staggering was observed in the extracted transfer probabilities at the barrier radius implying the role of pairing correlation in transfer reactions. [ABSTRACT FROM AUTHOR]

Abstract: A multi-detector gamma-ray spectrometer named the Indian National Gamma Array (INGA) has been set up at the Inter University Accelerator Centre, New Delhi, for nuclear structure studies. The array is designed to incorporate twenty four Compton-suppressed Clover germanium detectors with a total photopeak efficiency . The spectrometer along with sub-systems developed in-house like, mechanical support structure, high voltage power supplies, automatic liquid nitrogen filling system, front-end electronics and data acquisition system are described. The mechanical support structure facilitates the use of the Clover Germanium array with a recoil mass separator. The array has been used in a number of nuclear spectroscopic investigations. The in-beam and off-beam performance of the array are reported. [Copyright &y& Elsevier]

In the present work, the pre- and post-scission neutron multiplicities were measured for the reaction 18O+186W at different excitation energies populating the compound nucleus 204Pb, using the National Array of Neutron Detectors (NAND) facility at IUAC, New Delhi, India. Here, we investigated the entrance channel effect on the nuclear dissipation involved in the heavy ion fusion-fission dynamics. The statistical model analysis was performed using the code vecstat. The prescribed reaction 18O+186W had similar value of the mass asymmetry as the system 16O+181Ta studied earlier, populating the compound nucleus 197Tl. Specifically, we observed the similar behavior from both the systems against the nuclear dissipation, with the similar value of the mass asymmetry. The role of the entrance channel parameters on the nuclear dissipation was also discussed in the present work. [ABSTRACT FROM AUTHOR]