Level density andγ-decay properties of closed shell Pb nuclei

Abstract

The level densities and γ-ray strength functions of 205−208 Pb have been measured with the Oslo method, utilizing the ( 3 He, 3 He ′ γ) and ( 3 He, αγ) reactions on the target nuclei 206 Pb and 208 Pb. The extracted level densities are consistent with known discrete levels at low excitation energies. The entropies and temperatures in the micro-canonical ensemble have been deduced from the experimental level density. An average entropy difference of ∆S ∼ 0.9k B has been observed between 205 Pb and 206 Pb. The γ-ray strength functions in 205−208 Pb have been extracted and compared with two models; however, none of them describe the data adequately. Intermediate structures have been observed in the γ-ray strength functions for γ-ray energies below neutron threshold in all the analyzed Pb nuclei. These structures become less pronounced while moving from the doubly-magic nucleus 208 Pb to 205 Pb.

Microscopic calculations of the characteristics of radiative nuclear reactions for double-magic nuclei

“…The results obtained confirm the necessity of using consistent microscopic approaches for calculations of radiative nuclear characteristics in double-magic nuclei. Also, due to comparison of the two sets of experimental data [13] and [16], it was possible to conclude that the nature of the PSF values observed in [16] at E < 4.84 MeV for 208 Pb should be only caused by the transitions between excited states.…”

“…In Fig. 2, the E1 PSF for 208 Pb is compared with the experimental data obtained within the Oslo method [13]. As it can be seen in contrast to the phenomenological model EGLO and microscopic CRPA, the CTBA approach, i.e.…”

“…Thus, one can think that the excitations observed in [13] at E < 4.84 MeV are only caused by transitions between excited states. However, it is necessary to underline that the mechanisms of the reactions used in [13] and [16] are very different and the use of energy-independent smoothing parameter may be too approximate. …”

“…3) : 1) the PSF data from [13] where the transitions between ground and excited states as well as between excited states could be measured and 2) the data [16] for the B(E1) values for the transitions between only ground and excited states. It is necessary to compare both sets of data with approximately the same smoothing.…”

Gamma strength functions and level densities from high-resolution inelastic proton scattering at very forward angles

“…3 (blue diamonds) and compared to data derived with the Oslo method from a 208 Pb( 3 He, 3 He γ ) experiment [14,15] in comparison to the reanalysed [23] results from the Oslo experiment [22]. The inlet shows an expanded view of the lowenergy region 5-8 MeV.…”