The γ-ray spectroscopy studies of low-spin structures in 210Bi and 206Tl using cold neutron capture reactions

The γ-coincidence studies of low-spin structures of 210Bi and 206Tl are presented. The 210Bi nucleus, populated in thermal neutron capture reaction, was investigated using EXILL HPGe array at Institut Laue-Langevin in Grenoble. The experimental results were compared to the shell-model calculations allowing to draw the conclusions on the nature of the low-spin excitations populated below the neutron binding energy in 210Bi (4.6 MeV). It has been found that some levels cannot be described by the valence proton and neutron couplings, but may arise from couplings of valence particles to the 3- octupole phonon of the doubly magic 208Pb core. Moreover, preliminary results of a low-spin structure measurements of 206Tl by the γ-coincidence technique, making use of the 205Tl(n,γ)206Tl reaction at the FIPPS prompt γ-ray spectroscopy facility of ILL are shown. The population of a large number of excited states of 206Tl above the ground state up to the neutron binding energy (at 6.5 MeV), within a few units of spin is expected. The analysis involving double and triple γ-coincidences and γγ-angular correlations will allow to significantly extend the experimental information on the energy and spin-parity of the levels in 206Tl. This will help shedding light on the proton-hole and neutron-hole couplings near the doubly magic core 208Pb.

CALCULATION OF NUCLEAR LEVEL DENSITY PARAMETERS OF SOME LIGHT DEFORMED MEDICAL RADIONUCLIDES USING COLLECTIVE EXCITATION MODES OF OBSERVED NUCLEAR SPECTRA

In this study the nuclear energy level density based on nuclear collective excitation mechanism has been identified in terms of the low-lying collective level bands near the neutron binding energy. Nuclear level density parameters of some light deformed medical radionuclides used widely in medical applications have been calculated by using different collective excitation modes of observed nuclear spectra. The calculated parameters have been used successfully in estimation of the neutron-capture cross section basic data for the production of new medical radionuclides. The investigated radionuclides have been considered in the region of mass number 40<A<100. The method used in the present work assumes equidistance spacing of the collective coupled state bands of the interest radionuclides. The present calculated results have been compared with the compiled values from the literatures for s-wave neutron resonance data.

COMMENT ON A FREQUENT ERROR IN CALCULATIONS OF THE Γn/Γf RATIO

In the last decade some 20–30 publications in leading journals appeared in which cross sections for production of super-heavy elements are calculated with an erroneous formula for the Γn/Γf ratio. The erroneous treatment of shell structure corrections leads to an energy-dependent fission barrier that is inserted to the expression for the fission width Γf. In this approach the shell effect in the residual nucleus that emitted the neutron is ignored. We give examples of calculations that illustrate the deviations of the erroneous formula from the correct one. The errors reach several orders of magnitude, especially for low excitation energies and those compound nuclei for which large ground-state shell effect exceeds the neutron binding energy.