Cross sections of the14N(n, p)14C reaction at 24.5, 53.5 and 144 keV

Abstract

Abstract. We have measured the 14N(n, p)14C reaction cross section at 24.5, 53.5 and 144 keV to be 2,04+0.16 mbarns, 2.08_+0.23 mbarns and 2.07+0.27 mbarns, respectively. The measured values indicate that this reaction could have a large influence on the process of element formation in the Universe. PACS: 25.40.FqEstimates of the role played by the 14N(n,p)14C reaction in the process of element formation in the Universe are given in [1,2]. They are based on reaction cross section measurements using semiconductor detectors. Discrepancies in these previous measurements call for a new measurement with a different neutron source and method of proton registration.The measurements were performed using beams of filtered neutrons from the WWR reactor at the INR in Ukraine. A beam of quasimonoenergy neutrons with an average energy of E= 24.5 + 1 keV was obtained by using an iron-aluminium-sulphuir-boron filter set. Similarly, a silicon-boron-sulphur filter yielded a neutron beam of E= 53.5 + 1.4 keV, and a silicon-boron-titanium filter produced a beam of E = 144 __+ 24 keV.We used a two-section ionization chamber with two grids in each section to separate charged particles of different types [3] in these measurements. Adenine (CsNsHs) and lithium fluoride targets of the same size were placed in separate sections of the chamber. The targets were prepared by vacuum evaporation on aluminium backings. The targets were set at the "grazing angle" of about 4 ~ to the beam axis. In this way, the reaction products were detected eliminating the angular distribution effects. The chamber was filled with an Ar+4%CO 2 gas mixture at 0.8 atm. Signals from the chamber were recorded by a multi-parameter data acquisition and handling system [4]. Both sections of the chamber were identical and the energies of the registered particles were calibrated using e-particles from 234U and 238U~ e-particles and tritons from the 6Li(n, t)4He reaction, and protons from the 14N(t/, p)14C reaction.The cross sections were calculated using the formula:where nLi is the number of nuclei/cm 2 of 6Li in the LiF target; n N is the number of nuclei/cm 2 of 14N in the adenine target;N N is the total number of protons/s from the adenine target and gaseous nitrogen in the chamber;NLi is the total number of tritons/s from the lithium target;K~ is the correction for the presence of nitrogen in the gas filling the chamber; K 2 is the correction for beam scattering from the aluminium target backing and the electrode between the targets; au is the well established cross section of the 6Li(n, t)4He reaction [5].In all measurements the same pair of adenine and lithium targets was used. The ratio (nLi/nN)=O.0177• was measured at the thermal energy in a separate experiment at the WWR reactor in Kiev. The thermal neutron cross section of the 14N(rt, p)14C reaction was measured with the IBR-30 booster of JINR, Dubna, and found to be (1.83 + 0.07) barns [6]. The values for N N and NL~ were found after subtracting the background. The background induced by off-energy neutrons w...

Trojan Horse Investigation for AGB Stellar Nucleosynthesis

“…Measurements performed from thermal neutron energy up to 35 keV [144,145] found clear evidence for a 1/v behavior of the 14 N(n,p) 14 C reaction cross section up to approximately 30 keV and their results for the stellar reaction rate at kT = 525 keV are also approximately a factor of 3 higher than reported by [143]. Measurements with quasimonoenergetic neutrons at 25 keV from [146] are in fair agreement with the results from [144,145] and with the estimates from the inverse reaction, since again the same thermal value was used for the normalization. Another direct measurement of the 14 N(n,p) 14 C stellar cross section at kT = 525 keV was done by [147].…”