A comparative study of the effect of true coincidence summing (TCS) on the full-energy peak efficiency calibration of a clover HPGe detector, for direct and add-back modes of operation, has been done at different source-to-detector distances (d). The detector response was simulated using the Geant4 toolkit. The TCS correction factors determined by both experimental and analytical methods have been found to agree well with each other. The clover detector in add-back mode exhibits larger summing corrections than the direct mode for the same distance d. The distance d below which the summing correction becomes significant for the add-back mode of measurement is found to be higher than the corresponding distance for the direct mode of measurement for a clover detector.

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The true coincidence summing (TCS) correction factor for a Broad Energy Germanium (BEGe) detector has been calculated at far and close geometry measurement using multi-energetic radioactive γ-ray sources ^60Co, ^133Ba and ^152Eu. The correction factors were calculated using experimental method and analytical method. Photopeak efficiency and total efficiency required to calculate the correction factor were obtained using Geant4 Monte Carlo simulation code. A few standard as well as fabricated mono-energetic sources were also included in the γ-ray efficiency measurements. The simulated efficiencies of mono-energetic γ-ray sources were matched to experimental γ-ray efficiencies by optimizing the detector parameters. The same parameters were used to obtain the photopeak and total efficiency for γ-ray of our interest and coincident γ-ray. Analytical correction factors and experimental correction factors were found in good agreement with each other.

The true coincidence summing correction factor for a Broad Energy Germanium detector has been calculated at far and close geometry set-up using radioactive γ-ray sources. The correction factors were calculated using both experimental and analytical methods. Geant4 simulation was done to calculate the full-energy peak and total efficiencies of the detector. Standard, as well as fabricated mono-energetic γ-ray sources, were used for the γ-ray efficiency measurements. The simulated efficiencies of mono-energetic γ-ray sources were matched to the experimental γ-ray efficiencies by optimizing the detector parameters. The same parameters were used to obtain the full-energy peak and total efficiencies for γ-rays of current interest. Analytical and experimental correction factors were found to agree well with each other. The coincidence summing effect is found to be significant for source-to-detector distances less than 5 cm.

The true coincidence summing effect on the full-energy peak efficiency calibration of an unsuppressed clover HPGe detector has been studied. Standard multi-energetic and mono-energetic gamma-ray sources were used to determine the full-energy peak efficiency of the detector as a function of the gamma-ray energies at different source-to-detector distances. The true coincidence summing correction factors for the full-energy peak efficiency of the detector has been determined, in the add-back and direct modes of the detector, using both experimental and analytical methods. Geant4 simulations were performed to obtain the full-energy peak efficiency and total efficiency of the detector for different gamma-ray energies. The simulated efficiencies were used to calculate the correction factors using the analytical method. The correction factors obtained from both analytical and experimental methods were found to be in good agreement with each other. The clover detector in add-back mode exhibits larger summing corrections compared to the direct mode for the same source-to-detector distances. For the add-back mode, the coincidence summing effect is not significant for source-to-detector distances ~ 13 cm or above, whereas, for the direct mode, measurements can be performed for source-to-detector distances ~ 5 cm or above without considering the coincidence summing effect.

Elastic scattering angular distribution for weakly bound nucleus $^{6}$Li on the deformed rare earth $^{159}$Tb target nucleus has been measured at energies around the Coulomb barrier. The elastic scattering cross sections for this reaction consist of inelastic contributions from low lying excited states of $^{159}$Tb. The pure elastic cross-sections have been extracted from the admixture of elastic and inelastic data. The optical model potential parameters for the system have been obtained from the extracted pure elastic scattering cross sections. Coupled channel calculations have been performed with this set of potential parameters, to compare the theoretical and experimental inelastic scattering cross sections. The work has been extended to obtain the spectroscopic factor for $^{158}$Tb+n configuration from the experimental 1n-pickup data.

Fusion cross-sections have been measured for the asymmetric system 16O+165Ho at energies near and deep below the Coulomb barrier with an aim to investigate the occurrence of fusion hindrance for the system. Fusion cross sections down to ~ 700 nb have been measured using the off-beam gamma-ray technique. The fusion cross sections have been compared with the coupled channel calculations. Although the onset of fusion hindrance could not be observed experimentally, an indication of a small deviation of the experimental fusion cross-sections with respect to the calculated cross-sections could be observed at the lowest energy measured. However, the energy onset of fusion hindrance has been obtained from the extrapolation technique and is found to be about 2 MeV below the lowest energy of the present measurement.

*Saikat Bhattacharjee, Ashish Gupta, Rajkumar Santra, D. Chattopadhyay, N. Deshmukh, A. Mukherjee, S. Gupta, S.K. Pandit, V.V. Parkar, K. Ramachandran, K. Mahata, A. Shrivastava, Rebecca Pachuau and S.Rathi Saha Institute of Nuclear Physics, 1/AF, Bidhan Nagar, Kolkata-700064 and HBNI, Mumbai Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, INDIA Deptartment of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai 400085, INDIA Vivekanand Education Society’s College of Arts, Science & Commerce Mumbai 400 071, INDIA . * email: saikat.bhattacharjee@saha.ac.in