[en] Highlights: • Authors measured the backscattered photons to determine Z_eff of composite samples. • Backscattered photons generated by 661.6 keV photons from weak Cs-137 gamma source. • Ratio of thickness to intensity of backscattered saturated peak used to infer Z_eff. • Present experimental technique is used to determine Z_eff ≤ 30 of composite sample. • Method can be used to determine the Z_eff of biological samples using weak source. The effective atomic number (Z_eff) of composite materials has been determined by measuring the backscattered gamma photons at 180°. A 661.6 keV gamma photons from ¹³⁷Cs radioactive source are allowed to scatter at an angle of 180° from the sample. The backscattered photons at 180° from the sample are detected with “2 × 2″ NaI(Tl) scintillation gamma ray spectrometer coupled to 16 K Multi Channel Analyzer (MCA). It is observed experimentally that the intensity of backscattered photons increases initially with increasing the thickness of the target and then it becomes saturated above a certain thickness. By knowing the saturated thickness values for known atomic number of the elemental targets, the Z_eff of composite materials has been determined. The experimentally measured Z_eff values have been compared with theoretical values predicted by direct method, power law method and AutoZ_eff code.

[en] In the present investigations, the fusion cross-sections for the formation of ²⁰⁰Pb compound nucleus (CN) using ¹⁶O + ¹⁸⁴W, ³⁰Si + ¹⁷⁰Er, and ⁴⁰Ar + ¹⁶⁰Gd nuclear reactions at energies above the Coulomb barrier were calculated to understand the effect of entrance channel mass asymmetry (α) on the fusion reactions;the Skyrme energy density formalism (SEDF) was used for this calculation. The SEDF uses the Hartree-Fock-Bogolyubov (HFB) computational program with Skyrme forces such as SkM^*, SLy4, and SLy5 to obtain the nucleus-nucleus potential parameters for the above reactions. Using the SEDF model with SkM^*, SLy4, and SLy5 interaction forces, the theoretical fusion cross-sections were determined above the barrier energy and compared with the available experimental fusion cross-sections. The results show a close agreement between the theoretical and experimental values for all selected systems at energies well above the barrier. However, near the barrier energies, the theoretical values were observed to be higher than the experimental values. (authors)

[en] It is well known that the nuclear dynamics at different stages of fusion-fission process can be understood using heavy ion reactions. The dynamics of a fused system can be studied by measuring neutrons, charged particles, high energy gamma radiations and evaporation residues (ERs). It is also known that the excess of pre-scission particles in comparison with standard statistical model predictions indicates that the fission process in heavy ion reaction is delayed. Already two groups have measured the ER cross sections of ²²⁴Th and found that measured data not only disagree with one another but also observe unpredicted oscillating nature at higher excitation energies. In view of these, we have undertaken this work. The objective of which is to understand fission hindrance in ²²⁴Th by measuring ER cross sections and spin distributions. To understand the role of excess two neutrons in ER cross sections and spin distributions, the highly excited ²²⁴Th compound nucleus was formed using ¹⁸O + ²⁰⁶Pb system in addition to ¹⁶O + ²⁰⁸Pb system

[en] Thermal neutron flux (Φ_th) of Americium-Beryllium (Am-Be) neutron source has been measured by adopting the foil activation method. The neutrons emitted from Am-Be source are used to activate the Indium-115 (¹¹⁵In) foil. The gamma radiations emitted from the activated isomer ^116m1In are measured with NaI(Tl) and HPGe detectors. The thermal neutron flux is measured by adopting the cadmium (Cd) foil difference technique in which the Cd foil placed in front of the source to prevent the thermal neutrons from entering into the indium foil. The neutron flux is determined by measuring the gamma radiation emitted from indium foil using a low and high energy resolution NaI(Tl) and HPGe detectors respectively. The measured thermal neutron flux obtained from both detectors has been compared and found that the Φ_th does not depend on the resolution and type of the detectors used in the present investigations. (author)

[en] Several investigators have used various methods such as electron scattering method, muonic X-ray method, mirror nucleus method, Levenberg-Marquart method to determine the nuclear radius parameter. In the present investigation we have performed a simple laboratory experiment to determine the nuclear radius parameter of the medium Z elements using Nal(TI) detector spectrometer. Neutrons emitting from Am-Be neutron source are made to interact with pure water medium to produce (n, γ) reaction. The nuclear radius parameter ro value from the present experiment is found to be 1.04 Fermi

[en] Transfer reaction is an important tool to probe the structure of a nucleus. The occupancy of nucleons in a nucleus can be understood using the Spectroscopic Factor (S.F.). The stripping (d,p) and pick up (p,d) reactions are used to determine the spectroscopic factor and comparison would validate the nuclear shell model. In this investigations, SF values for the 21 nuclei using the finite range DWBA method has been determined. Comparison of the spectroscopic factor values with those determined experimentally indicate good agreement within uncertainties

[en] Heavy ion induced nuclear reaction is a well established probe to understand the nuclear dynamics at different stages of fusion-fission process. The dynamics of fusion-fission process can be understood by studying the emitted neutrons, charged particles, gamma rays and the evaporation residues (ERs) from the fissioning nucleus. During this observation the excess of pre-scission particles in comparison with standard statistical model predictions creates the interesting reason is that the fission process in heavy ion nuclear reaction is delayed. We have undertaken this work using dedicated well advanced facilities available at IUAC, New Delhi. The measurement of ERs for the two reactions were carried out using the HYbrid Recoil mass Analyzer (HYRA) coupled with the TIFR 4pi-spin spectrometer at IUAC, New Delhi

[en] The effect of solid state and chemical environments on K-edge of atom of target was studied by several investigators using monochromatic gamma radiations as well as synchrotron radiation. Very few investigators have used the advantage of continuous spectrum of external Bremsstrahlung radiation to study the effect of solid state and chemical environments on K-edge. In the present investigations, the external Bremsstrahlung has been used to determine the K-edge of high Z target by adopting a novel method

[en] In the present work our aim is to measure the mass-gated neutron multiplicity for ³²S + ^184,186W reactions forming the fissioning nuclei ^216,218Th. In above reactions, out of two fissioning nuclei, ²¹⁶Th has shell closure (N=126) configuration while the other one ²¹⁸Th is non-shell-closed nucleus. Besides, the present investigation would also facilitate to study the fission fragments (FF) mass distribution in these reactions. In the present paper, we report some of the preliminary results of the analysis

[en] It is well known that measurements of evaporation residues (ERs) excitation functions at energies near fusion barrier would provide the information not only about the fission process but also about viscosity of nuclear fluid. In the present work we have used the IUAC facilities to study the nuclear fission hindrance in ²²⁴Th compound nucleus formed by ¹⁶O+²⁰⁸Pb and ¹⁸O+²⁰⁶Pb systems. We have measured ER cross sections using Hybrid Recoil mass Analyzer (HYRA) facility and spin distributions of ER using TIFR 4π spin spectrometer placed in beam hall-2 at IUAC. Measurement was carried out for both systems in the energy range E_Beam = 85 to 125 MeV. The beam with energy range 85 to 125 MeV was selected using Pelletron and Pelletron+LINAC facilities. Experimentally measured ER cross section in arbitrary units is shown. As ERs cross section probability is very low and ranges the kinetic energy of the recoil ERs also low, measurement of the ERs cross section and the ER gated spin distribution was very challenging task during the experiment. However, with optimized gas pressure and the appropriate voltage at the focal plane detector, it was possible to detect the ERs effectively