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Total fusion (TF) excitation function has been measured for the system 7Li + 64Ni at the energies near the Coulomb barrier of the system. The evaporation residue (ER) cross sections have been estimated through the online detection of characteristic γ-rays of the ERs. The summed ER cross sections yielding the experimental TF cross section have been compared with the theoretical one dimensional barrier penetration model (1DBPM) prediction. The measured and the model cross sections are very close to each other at above barrier energies. However, an enhancement of the experimental TF cross section with respect to the 1DBPM prediction is observed at below barrier energies. Coupled channels (CC) calculation with inelastic excitations alone could not explain the enhancement. The origin of the enhancement is identified as due to the enhanced population of the αxn channels.

Total fusion excitation function has been measured for the reaction of weakly bound 6Li projectile on medium mass 64Ni target at energies near the Coulomb barrier of the system. Online characteristic γ-ray detection method has been used to identify and determine the cross sections of the residues. No suppression of total fusion cross section (σTF) is observed at above barrier energies. But enhancement of measured cross section with respect to the one-dimensional barrier penetration model (1-DBPM) calculation is observed at below barrier energies. The enhancement can not be explained by coupled channels calculation with dominant projectile and target excitations as well as one-neutron stripping reaction.

One neutron stripping cross sections ( σ - 1 n ) are measured in 9 Be+ 159 Tb system in the energy range E cm /V B ∼ 0.79–1.24 using offline gamma counting technique. The CRC model calculations including the ground state and the 2 + resonance state of 8 Be, carried out using the FRESCO code, give a reasonable description of the measured data. In addition, comparisons of reduced 1n-stripping cross sections- σ red with 9 Be for different target nuclei (A ∼ 150–200), and σ red for 9 Be, 6 Li with 159 Tb target are presented. While no strong target dependence is observed with 9 Be projectile, σ red ( 9 Be) is significantly larger than that for 6 Li, which is consistent with the Q-value for transfer reactions and breakup threshold energy of projectiles. [ABSTRACT FROM AUTHOR]

In this paper, the design and test results of a front-end cryogenic amplifier for a bolometer detector are presented. The amplifier is implemented with two low-noise Si JFETs, where the first FET is configured as a source follower amplifier and the second FET provides a high dynamic resistance to keep the voltage gain very close to unity. A 3 dB bandwidth over a wide range from DC to 10 MHz is achieved in this design. The input voltage noise density is ~ 1.9 nV/√Hz at 300 K, which further reduces to 1.6 nV/√Hz at 120 K. The flicker corner frequency observed is below 50 Hz. [ABSTRACT FROM AUTHOR]

This paper reports the detailed noise characterization, investigation of various noise sources, and its mitigation to improve the performance of a cryogenic bolometer detector for the TIN.TIN experiment. The noise spectrum has been measured for a sapphire bolometer test setup with an indigenously developed neutron transmutation doped Ge sensor in the cryogen free dilution refrigerator system at Mumbai. The effect of external noise, arising either from ground loops in the system or from the diagnostic and control electronics of the cryostat, on the performance of the bolometer is assessed. A systematic comparison of the influence of different noise pickups on the bolometer resolution is also presented. The best-achieved resolution (σE) at 15 mK is ∼15 keV for heater pulses and appears to be mainly limited by the noise due to the pulse tube cryocooler. [ABSTRACT FROM AUTHOR]

Presents Mössbauer and magnetization studies in Fe[sub3-x]Ru[subx]Si. Behavior of alloys; Description of the approach of magnetization to saturation; Characteristics of Mössbauer spectra.

We demonstrate here an efficient photoconductive THz source with low electrical power consumption. We have increased the maximum THz radiation power emitted from SI-GaAs based photoconductive emitters (PCEs) by two orders of magnitude. By irradiating the SI-GaAs substrate with Carbon-ions up to 2 μm deep, we have created lot of defects and decreased the lifetime of photo-excited carriers inside the substrate. Depending on the irradiation dose, we find 1 to 2 orders of magnitude decrease in total current flowing in the substrate, resulting in subsequent decrease of heat dissipation in the device. This has resulted in increasing maximum cut-off of the applied voltage across PCE electrodes to operate the device without thermal breakdown from ~35V to >150V for the 25 μm electrode gaps. At optimum operating conditions, carbon irradiated (1014 ions/cm2) PCEs give THz pulses with power about 100 times higher in comparison to the usual PCEs on SI-GaAs and electrical to THz power conversion efficiency has improved by a factor of ~800. [ABSTRACT FROM AUTHOR]

The feasibility study for searching neutrinoless double beta decay in 124Sn using cryogenic bolometer has been initiated. For this purpose, a custom-built cryogen-free dilution refrigerator, having a large cooling power of 1.4 mW at 120 mK, has been installed at TIFR, India. This paper describes the design, installation and performance of a cryogen-free dilution refrigerator (CFDR-1200). The performance of CFDR-1200 has been analysed using Takano’s model developed for conventional (wet) dilution refrigerators. [ABSTRACT FROM AUTHOR]

This report presents a theoretical study of an electrostatic charge state analyzer, having one of its electrodes inclined and the other one straight with respect to the beam axis. This type of analyzer can be used in studying the charge state distribution of the postfoil beam, with a resolution better than that of the conventional parallel plate geometry. Even at high beam energies (>5 MeV/A) this analyzer, unlike the conventional one, would be useful with a reasonable bias and moderate drift length. [ABSTRACT FROM AUTHOR]

Prompt gamma-ray spectroscopy of fission fragments produced in the heavy-ion induced fusion-fission reaction 208Pb(18O, f) at E = 90 MeV has been performed. The relative isotopic yields of the fission fragments and the fragment mass distribution have been studied. Structures in the mass distribution have been discussed in the light of earlier results. Relative yields of several odd-A isotopes of Mo, Ru, Pd, and Cd and the odd-A isotones with N = 62 and 64 have been studied along with the yields of the neighboring even-Z, even-N fragments and correlated to nuclear structural effects. The average total neutron multiplicity during fission has been measured to be 5.48d±0.59. The level schemes of the two neutron-rich nuclei 110Pd and 116Cd have been studied from γ-ray triple coincidence data. A large number of transitions, previously reported only from β-decay studies, have been observed in 1 110Pd for the first time. The yrast band in 116Cd has been extended up to spin (16+). In addition, a rotational sequence built upon an excited 5- state in 116Cd has been observed up to (13-). The level schemes have been discussed in the context of existing results, both experimental and theoretical, in the literature. [ABSTRACT FROM AUTHOR]

Background: The barrier distribution function is an important observable in low-energy nucleus-nucleus collisions because it carries the distinct signature of the channel-coupling effect that is dominant at low energies. It can be derived from the fusion excitation function as well as from the back-angle quasi-elastic excitation function. The barrier distribution functions derived from the two complimentary measurements, in general, appear to peak at an energy close to the Coulomb barrier for strongly bound systems. But for weakly bound projectiles, like 6Li, a relative shift is observed between the distributions. Purpose: The present work investigates the barrier distribution functions from fusion as well as from the back-angle quasi-elastic excitation function for the 6Li + 64Ni system. The purpose is to look for the existence of a shift, if any, between the two measured distribution functions, as reported for 6Li collision with heavy targets. A detailed coupled-channel calculation to probe the behavior of the distribution functions and their relative shift has been attempted. Measurement: A simultaneous measurement of fusion and back-angle quasi-elastic excitation functions for the system 6Li + 64Ni was performed. The fusion excitation function was measured for the energy range of 11 to 28 MeV while the quasi-elastic excitation function measurement extended from 11 to 20 MeV. The barrier distribution functions were subsequently extracted from both the excitation functions and compared. Results: A small shift of around 450 keV peak to peak is observed between the barrier distribution functions derived from the complementary measurements. Detailed coupled channel and coupled reaction channel calculations reproduced both the excitation functions and barrier distributions. The shift of about 550 keV resulted from the model predictions corroborate the experimentally observed value for 6Li + 64Ni system. Conclusions: The coupling to inelastic channels are found to be sufficient to describe the fusion-barrier distribution. The positive Q-value one-proton and one-neutron stripping channels, leading to three-body final states, on the other hand, play dominant roles in reproducing the barrier distribution from the back-angle quasi-elastic excitation function. [ABSTRACT FROM AUTHOR]

Negative parity high-spin states of 107Cd have been investigated using the reaction 94Zr(18O,5n), from the γ-ray coincidence events recorded by the Indian National Gamma Array. A magnetic dipole (M1) band structure was established for the first time in this nucleus decaying to the low-spin states via several paths. Lifetimes of five in-band levels in this band have been measured using the Doppler shift attenuation method. The experimentally deduced B(M1) values are found to decrease with increasing spin. The experimental observations, interpreted by the tilted axis cranking calculations, suggest that the M1 band is developed from the shears mechanism based on the 5qp configuration π(g9/2-2) ⊗ ν(h11/2g7/2²), which is then crossed by another 5qp configuration π(g9/2-2) ⊗ ν(h11/2³). The semiclassical model of the shears mechanism also reasonably reproduces the decreasing trend of the observed B(M1) values as a function of spin, supporting the above interpretation. The present work highlights the unique coexistence of both magnetic and antimagnetic (observed by us earlier) rotation bands in one nucleus arising from the same proton configuration, but different neutron configurations. [ABSTRACT FROM AUTHOR]

The total fusion (TF) excitation function for a 6Li projectile with a 64Ni target has been measured using the online characteristic γ ray detection method at energies around the Coulomb barrier. The complete fusion (CF) excitation function for the system is subsequently estimated from the dominating neutron evaporation channels with the help of statistical model predictions. The CF cross sections exhibit a suppression of about 13% compared to the one-dimensional barrier penetration model (1DBPM) at above-barrier energies, but no suppression is observed for TF cross sections. The observation does corroborate the estimated suppression for 6Li on 59Co target, but does not corroborate the recently proposed universal suppression factor for the 6Li projectile. The result supports the conjecture of reduced suppression of CF cross sections with decreasing target mass. At energies below the barrier, both the TF and the CF cross sections are enhanced. The observed enhancement of the CF process can be explained by channel coupling (CC), but the enhancement in TF cross sections is significantly higher than the CC predictions. [ABSTRACT FROM AUTHOR]

Fusion and quasi-elastic scattering measurements have been carried out for 6,7Li + 197Au systems in the energy range E/Vb ~ 0.7 to 1.5. Coupled-channel calculations including coupling to inelastic states of the target and projectiles are able to explain an enhancement in measured fusion cross sections at energies below the barrier. At energies above the barrier the complete fusion cross sections are found to be suppressed compared to the coupled-channel predictions for both systems. A systematic comparison of fusion cross sections of the weakly bound stable nuclei 6,7Li and halo nuclei 6,8He on a 197Au target is presented. Barrier distributions from quasi-elastic scattering are seen to shift towards higher energies with respect to fusion after inclusion of the breakup-α channel for both 6Li and 7Li. [ABSTRACT FROM AUTHOR]