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Fission dynamics of 188 Pt, a neutron deficient nucleus in newly discovered mass asymmetric sub-Pb region, have been explored via fission fragments mass-angle and mass-total kinetic energy distributions, at energies around and above the barrier. The observed correlations of fragment mass and emission angle indicate the presence of fission events originating from a non-equilibrated source. Mass-total kinetic energy spectra are relatively broader and the dependence of measured mean total-kinetic-energy on fragment mass is also broader than the expected parabolic dependence for liquid drop fission behaviour, at all studied energies. The measured mean total kinetic energy values are higher than the prediction of Viola systematics. The widths of measured total kinetic energy distributions are also inconsistent with the observed systematic behaviour of compound nucleus (CN) in this mass region. These observation of mass-angle and mass-total kinetic energy distributions revealed the clear signatures of the presence of slow quasifission in the fission of 188 Pt compound nucleus. These findings indicate the role of entrance channel parameters such as mass asymmetry and charge product Z P Z T in Fusion-Fission and quasi-fission dynamics. Dynamical model calculations do not predict the presence of quasi-fission for the present reaction system. [ABSTRACT FROM AUTHOR]

Production of 155Tb radioisotope for medical purposes is still a challenge. In this regard the present study has been done using 16O beam and 146Nd target within the 3–7 MeV/nucleon energy range. The γ-ray spectrometry has been used to identify the residues produced in the reaction. The EF measurements have been done and cross-sections of 155Tb have been reported and compared with the theoretical model code PACE 4. A strong indication of the occurrence of incomplete fusion has been realized within the energy range considered. The highest cross-section of 124 ± 12 mb has been obtained at Elab 101.7 ± 0.5 MeV. [ABSTRACT FROM AUTHOR]

The fusion excitation functions of evaporation residues, populated through complete fusion and/or incomplete fusion, were measured in the 18 O+ 146 Nd system at an incident beam energy of ≈ 3–7 MeV/nucleon. These results were then compared with those obtained from the previously reported 16 O+ 148 Nd system. This comparison is particularly relevant since both systems lead to the population of the same compound nucleus, 164 Er*, in the case of complete fusion, and the same intermediate composite system, 160 Dy*, in the case of incomplete fusion. Significant enhancements in the measured excitation functions of evaporation residues populated via α -emitting channels indicate the population of such residues via incomplete fusion in addition to complete fusion. Further, a comparison of the measured data for 18 O+ 146 Nd and 16 O+ 148 Nd systems shows interesting results. The complete fusion and incomplete fusion cross-sections, reduced by three different procedures, are found to satisfactorily match each other, despite the major difference in the α - breakup threshold values of the projectiles 18 O (6.23 MeV) and 16 O (7.16 MeV). The effect of different α -breakup threshold values of the projectiles 18 O and 16 O was not observed in the comparison of incomplete fusion data for the systems 18 O+ 146 Nd and 16 O+ 148 Nd. This may be attributed to the fact that the residues populated in the exit channel are emitted from the same intermediate composite system 160 Dy* and also there is a high resemblance in the entrance channel mass asymmetry and other structural properties of these systems. [ABSTRACT FROM AUTHOR]

The present work concerns the study of fission dynamics of 48 Ti+ 232 Th reaction resulting in the superheavy composite system 280 Cn 112 at an incident energy of 280 MeV. Mass distribution studies play an important role in understanding the fusion-fission mechanism involved in the heavy-ion induced nuclear reaction. The studies related to the superheavy nucleus 280 Cn are limited till date and in order to achieve a better insight of the reaction dynamics, mass and total kinetic energy (TKE) distribution of the binary fragments populated in the reaction 48 Ti+ 232 Th has been measured at an excitation energy 63.5 MeV. Correlation between the mass and TKE and mass-angle distribution of the binary fragments have been investigated. The mass-energy distribution of the reaction fragments obtained from the analysis confirms the dominance of quasi-fission over fusion-fission. A sudden rise in the width of σ TKE 2 (M) has been observed in the mass symmetric region. This has been interpreted in terms of the mixing of fusion-fission and quasi-fission events. A deviation from the Viola systematic is observed in the measured TKE of the fragments due to the presence of quasi-fission (QF) process. Theoretical results performed to understand the experimental results in the framework of the DNS model show that the peaks in the mass distribution of the binary products around the mass numbers A = 40–60 and A = 220–240 is related with the contribution of the DIC and quasi-fission products. The contribution of the quasi-fission products to the yield of the binary fragments with the mass numbers around A = 80–110 and A = 170–200 is dominant. The contribution of the symmetric quasi-fission products to the yield of the mass symmetric region is comparable with the yield of the fusion-fission products. [ABSTRACT FROM AUTHOR]

Inter-University Accelerator Centre (IUAC) came into existence as Nuclear Science Centre in 1984. A 15UD Pelletron accelerator was installed and it started delivering accelerated charged particle beams in 1991. Various experimental research facilities were set up in parallel at the Centre. All these facilities have been and are being extensively used by scholars and researchers from various universities and institutes in India. Research activities in nuclear physics, materials science and other inter-disciplinary fields are the main thrust at the laboratory. Nuclear physics research carried out at IUAC has made an indelible mark in the understanding of nuclear structure and nuclear reaction dynamics using heavy ion beams at near and above Coulomb barrier energy region. This review article presents the details of the various experimental facilities and highlights of research contributions in nuclear reactions and nuclear structure, spanning three decades. [ABSTRACT FROM AUTHOR]

Elastic scattering angular distributions have been measured for 7 Li+ 92 , 100 Mo systems in the bombarding energy range of 0.85 to almost two times the Coulomb barrier. The measured elastic scattering angular distributions are fitted using optical model to investigate energy dependence of the real and imaginary strength parameters with phenomenological Woods-Saxon and double folding S a ~ o Paulo potentials. Both interaction potential models simulate similar patterns to energy dependence sustaining the same consequence of breakup threshold anomaly. The results of Continuum Discretized Coupled Channels (CDCC) Calculations with inclusion of the breakup coupling of the projectile compares experimental elastic scattering angular distribution better for the 7 Li+ 92 , 100 Mo systems rather than excluding breakup coupling. A systematic behaviour of total reaction cross section on target and projectile dependency has been investigated by including a wide range of target mass and tightly to weakly bound projectiles. A comparative study on obtained breakup and reaction cross sections has also been carried out for 7 Li+ 92 , 100 Mo systems. [ABSTRACT FROM AUTHOR]

Characteristics and performance of a time of flight (TOF) spectrometer developed for performing fission mass distribution studies are presented. The spectrometer contains two TOF arms based on multi-wire proportional counters (MWPCs). Each arm has two MWPCs to form a start–stop detection system for TOF measurements. The start detector has an active area of 4 × 4 cm2. The stop detector is a two-dimensional position sensitive MWPC with an active area of 16 × 11 cm2. Salient features of the MWPCs are the use of reduced sub-millimeter wire pitches of 0.635 and 0.317 mm in the electrodes along with the use of gold plated tungsten wires of diameters 10 and 20 µm. A delay line for position electrodes is prepared using chip inductors and capacitors. Ten different configurations of MWPC were investigated for the start detector, which involved the use of three and four electrode geometries, use of different wire pitches, and use of aluminized mylar for timing electrodes. Performance results close to micro-channel plate detectors have been observed with some designs of MWPC, displaying rise times better than 2 ns with an estimated inherent time resolution of ∼100 ps FWHM. A position resolution of ∼1 mm (FWHM) has been observed. Design features of the MWPCs and their test performance results are described in this article. [ABSTRACT FROM AUTHOR]

The barrier distribution of a system can be extracted from excitation function data obtained either through fusion reaction or through quasi-elastic scattering measurement. In the present work, the quasi-elastic excitation function has precisely been measured at back angle for the 28Si + 142Nd system at energies around the Coulomb barrier and the corresponding experimental barrier distribution has been extracted. The experimental data has been interpreted in the frame work of the coupled channel calculations which include couplings to different possible modes of excitations of the interacting target-projectile combination. The possible effect of the nature of projectile excitations on the derived barrier distribution has been presented. [ABSTRACT FROM AUTHOR]

In the present work, the break-up fusion or incomplete fusion (ICF) process has been studied from the forward recoil range distribution measurement for 16O + 175Lu system at ≈ 96 MeV energy. The measured forward recoil range distributions are analyzed in the framework of code SRIM. The present analysis shows clearly the role of linear momentum transfer and also the break-up of projectile 16O into its fragments (12C + 4He and/or 8Be + 8Be). Any systematic trend is not observed with the target deformation parameter (β2) dependent study of ICF. It is observed that projectile structure also affects the ICF dynamics. The projectile α-Q-value is found to be a suitable parameter which explains effectively the observed projectile structure effect on ICF. [ABSTRACT FROM AUTHOR]

The experiments were performed to study excitation functions (EFs) of evaporation residues (ERs), i.e. 103,102,101Ag, 101,100,99Pd, 101,100Rh, 97Ru, 96Tc, 95Tc, 94Tc, 93Mom, 92Nbm populated in the reactions induced by 12C on 93Nb for exploring the reaction dynamics involved at energies ≈ 47-75 MeV. The activation technique followed by offline γ-ray spectrometry has been employed to measure EFs. These measurements were simulated with other reported values available in literature as well as with theoretical predictions based on computer code PACE-2. The effect of variation of level density parameter involved in this code has also been studied. An excellent agreement was found between theoretical and experimental values in some of the fusion evaporation channels. However, significant enhancement of cross-section as observed in α-emission channels may be due to incomplete fusion (ICF) process and/or direct reaction process. To confirm the aforesaid reaction mechanism, Recoil Range Distributions (RRDs) of various ERs have been measured at ≈ 80 MeV. Moreover, an attempt is made to separate the percentage relative contributions of complete and incomplete fusion components from the analysis of the measured RRDs data. Further, the relative percentage ICF fraction, also estimated from EFs data, was found to be sensitive with the projectile energy. [ABSTRACT FROM AUTHOR]

Quasielastic scattering angular distributions have been measured for the 7Be + 9Be system at Elab = 17 , 19 and 21MeV in the angular range $ \theta_{{cm}}^{}$ = 24° - 57° . An optical model (OM) analysis of these data has been carried out in order to extract optical potential parameters and reaction cross-sections. One-proton stripping cross-sections were also measured for this system at Elab = 19 and 21MeV. These transfer angular-distribution data were compared with the finite-range distorted-wave Born approximation (FRDWBA) calculations. For the 7Li + 9Be system quasielastic scattering angular distributions were measured and emitted light charged particles were detected at Elab = 15.75 , 24.00 and 30.00MeV in the angular range $ \theta_{{cm}}^{}$ = 7° - 70° . Fusion cross-sections were obtained by reproducing the measured $ \alpha$ -evaporation spectra from the compound nucleus at backward angles with the statistical model calculations. The ratios of the experimental fusion cross-sections to the total reaction cross-sections (obtained from OM analysis) were found to be small. This result suggests that the break-up process has a strong influence on the fusion process leading to a reduction in the fusion cross-section. [ABSTRACT FROM AUTHOR]

Two large area multistep position sensitive (two dimensional) multiwire proportional counters have been developed for experiments involving study of fission dynamics using general purpose scattering chamber facility at IUAC. Both detectors have an active area of 20×10 cm2 and provide position signals in horizontal (X) and vertical (Y) planes, timing signal for time of flight measurements and energy signal giving the differential energy loss in the active volume. The design features are optimized for the detection of low energy heavy ions at very low gas pressures. Special care was taken in setting up the readout electronics, constant fraction discriminators for position signals in particular, to get optimum position and timing resolutions along with high count rate handling capability of low energy heavy ions. A custom made charge sensitive preamplifier, having lower gain and shorter decay time, has been developed for extracting the differential energy loss signal. The position and time resolutions of the detectors were determined to be 1.1 mm full width at half maximum (FWHM) and 1.7 ns FWHM, respectively. The detector could handle heavy ion count rates exceeding 20 kHz without any breakdown. Time of flight signal in combination with differential energy loss signal gives a clean separation of fission fragments from projectile and target like particles. The timing and position signals of the detectors are used for fission coincidence measurements and subsequent extraction of their mass, angular, and total kinetic energy distributions. This article describes systematic study of these fission counters in terms of efficiency, time resolution, count rate handling capability, position resolution, and the readout electronics. The detector has been operated with both five electrode geometry and four electrode geometry, and a comparison has been made in their performances. [ABSTRACT FROM AUTHOR]

With a view to study complete- and incomplete-fusion components in 159Tb , 169Tm ( 16O , x reactions, experiments have been carried out at the Inter-University Accelerator Center, New Delhi, India using the 15UD Pelletron accelerator facilities. The forward mean recoil ranges for some radio-nuclides; 168 m Lu , 167Lu , 167Yb , 166Tm produced in the 16O$ + $159Tb system at ≈ 90 MeV, and 179Re , 177Re , 177W , 178Ta and 177Hf produced in the 16O$ + $169Tm system at ≈ 87 MeV have been measured. The recoil-catcher activation technique followed by off-line γ -spectrometry has been employed in the present work. The analysis of forward mean ranges for different radio-nuclides has been done in the framework of the degree of linear momentum transfer from projectile to target nucleus by adopting break-up fusion model considerations. Different complete- and incomplete-fusion components, which may be attributed to the fusion of 16O and/or 12C and 8Be transfer from the 16O projectile to the target nucleus have been observed. An attempt has also been made to separate out the relative percentage contributions of complete- and incomplete-fusion components using experimentally measured forward recoil ranges. The complete-fusion contributions deduced from recoil range distribution are found to be consistent with the prediction of the theoretical model code PACE. The analysis of data indicates the complete- and incomplete-fusion competition for both the systems at the given energies. [ABSTRACT FROM AUTHOR]

High-spin states in 79Rb were populated in the reaction $\mathrm{^{63}Cu \ensuremath(^{19}F, p2n) ^{79}Rb}$ at E( beam) = 60 MeV. The lifetimes of the excited states of the $\pi \ensuremath g_{\frac{9}{2}}$ positive-parity yrast band and of the $\pi \ensuremath p_{\frac{3}{2}}$ negative-parity band in 79Rb were measured by the Doppler Shift Attenuation Method. The deduced transition quadrupole moments Qt are found to have a decreasing trend with rotational frequency for both the bands, consistent with those found experimentally in neighbouring nuclei. [ABSTRACT FROM AUTHOR]

High-spin states in 78Kr have been studied via the 63Cu (19F, 2p2n)78Kr reaction at a beam energy of 60 MeV using the Indian National Gamma Array (INGA). In this nucleus, lifetimes have been measured upto the I π=22+ level in the yrast positive-parity band and upto the I π=15- level in the negative-parity band using the Doppler Shift Attenuation Method (DSAM). The deduced transition quadrupole moments Qt's are found to decrease with rotational frequency for both the bands. [ABSTRACT FROM AUTHOR]

A correction to the article "Loss of Collectivity in Rb," that was published in the 11 September of 2006 issue is presented.