Direct determination of the astrophysical reaction rate of ¹⁴¹ Pr( <i>γ</i> , n) ¹⁴⁰ Pr at the SSRF-SLEGS

Context . The 141 Pr( γ , n) cross-section is critical to the nucleosynthesis of p -nuclides 136,138 Ce in thermonuclear supernovae and in massive stars. The photonuclear reaction of 141 Pr( γ , n) provides a new method for producing 140 Pr radioisotopes for positron emission tomography tracing in nuclear medicine. Aims . We aim to perform an accurate measurement of the 141 Pr( γ , n) 140 Pr cross-section over a sufficiently wide range of gamma energies of the p -process and deduce the 140 Pr(n, γ ) 141 Pr cross-section with γ SF and TALYS-SMLO models. We determined the astrophysical reaction rate of 141 Pr( γ , n) 140 Pr at the temperature range of 0.2–10 GK based on the new measurement cross-section of the 141 Pr( γ , n) 140 Pr reaction. Methods . We performed a new measurement of the 141 Pr photoneutron cross-section at the Shanghai Laser Electron Gamma Source of the Shanghai Synchrotron Radiation Facility using quasi-monoenergetic laser Compton scattered γ -ray beams. The neutrons emitted by the 141 Pr target were detected by the flat-efficiency detector array, while the γ beam transmitted by the 141 Pr target were attenuated by a copper absorber and then measured by a bismuth germanate detector in order to reconstruct the γ spectrum incident on the target. Results . The cross-section data of 141 Pr( γ , n) were acquired using an unfolding iteration method with an uncertainty of less than 4%, and the inconsistencies between the available experimental data and evaluation libraries were discussed. The inverse reaction cross-section of 140 Pr(n, γ ) and the reaction rates for the 141 Pr( γ , n) reaction were derived over the astrophysically relevant temperature range of the p -process nucleosynthesis model. The photodisintegration decay constants of the 141 Pr( γ , n) reaction for stellar temperatures between 0.2 GK and 10 GK are provided in a tabular form and by an analytical fitting expression. The λ γ n ( 141 Pr) = 0.013 ± 0.001 s −1 at a typical p -process temperature of T = 2.5 GK was also computed. Conclusions . The photodisintegration decay constants of the 141 Pr( γ , n) reaction deviate significantly from previous theoretical predictions, and the uncertainties are significantly reduced in the direct measurement.