Impact of the 138,139La radiative strength functions and nuclear level densities on the galactic production of 138La

[摘要] ENGLISH ABSTRACT: 138La is a very long-lived and low abundant p-isotope. Most p-nuclei withZ > 54 are thought to be produced through photodisintegration of s- andr-process seed nuclei. However, this p-process cannot satisfactorily explain theobserved abundance of 138La, and more exotic processes, such as ve + 138Ba →138La + e− have to be considered. This v-process can reproduce the observedsolar abundance of 138La, but the significance of the p-process cannot be ruled out due to very high uncertainties in its predicted reaction rates. These errorshave been discussed to be mainly due to the unavailability of the experimentalnuclear level densities and radiative strength functions of 138,139La, which arecritical ingredients for astrophysical reaction rate calculations based on theHauser-Feshbach approach.Thus, nuclear physics measurements are necessary to place the nuclear propertieson a strong footing, in order to make statements regarding the importanceof p- and v-processes. In this research project the experimental nuclear leveldensities and radiative strength functions of 138,139La were measured belowthe neutron thresholds. From this new experimental data, the Maxwellianaveraged cross sections for the 137La(n, y) and 138La(n, y) reactions, at thep-process temperature of 2.5⇥109 K, were computed with the TALYS code.Using these reaction rates the nucleosynthesis calculations in the O/Ne-richlayers of Type II supernovae were performed. The results imply that the standardp-process still under-produces 138La, which puts the v-process on a verystrong footing as the main production process for 138La.

[发布机构] Stellenbosch University