Determination of the cross section of 39 K(n, p) 39 Ar reaction induced by D-D neutrons with neutron activation and noble gas mass spectrometry techniques

Abstract The cross-sections of 39 K(n, p) 39 Ar at the 2-3 MeV energy play an important role in nuclear structure reasearch and 40 Ar/ 39 Ar geochronology application. Due to the limitations of n- 3 He coincidence technology and counting instruments, the published data from the literature are before 1967, and the existing data are scarce and of significant divergence. Meanwhile, there are large discrepancies between the measured and evaluation results. By taking advantage of the high sensitivity and resolution noble gas mass spectrometer at Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS), the cross-section of 39 K(n, p) 39 Ar were measured by the methods of combined neutron activity analysis and noble gas mass spectrometry techniques, and the uncertainties were discussed in detail. The cross-section of 39 K(n, p) 39 Ar were measured as 103.84 ± 16.33, 109.76 ± 15.88, 150.27 ± 24.19 mb, at 2.56 ± 0.08, 2.69 ± 0.08, 2.96 ± 0.12 MeV energies respectively. The measured data filled the data gaps and provided more accurate data support for 40 Ar/ 39 Ar dating. Furthermore the theoretical excitation function of 39 K(n, p) 39 Ar was calculated using TALYS-1.97 computer codes. Then the experimentally determined cross-sections were analyzed by comparing with literature data available in EXFOR database and evaluated nuclear data in ENDF/B-VIII.0, JEFF-3.2, TENDL-2021, BROND-3.1, and JENDL-5 databases. According to comparative results, the measured cross-sections of 39 K(n, p) 39 Ar exhibit a rapid energy-dependent increase between 2-3 MeV, aligning with higher literature values and resolving previous discrepancies. Compared with the previously reported data, the precision of determined cross-sections in this work have great improvement. The comparison of measured data indicates that the combined detection method of neutron activity analysis and noble gas mass spectrometry techniques is suitable for measuring cross-sections of long-life product nuclei nuclear reaction and the application of 40 Ar/ 39 Ar geochronology with D-D neutron source.