Fusion cross-section measurements with deuterons of low energy

Abstract

A knowledge of the energy dependence of the cross-section for collisions between two deutrons leading to a triton and a proton, is of interest both to nuclear theory and to calculations of the rate of thermonuclear reactions. Until now reliable values were only available down to about 13 keV and thus the contributions by the large number of slower particles in a distribution could not be assessed. The purpose of the work was to extend this range to lower energies which involves the measurement of very small cross-sections. The method of measuring the fusion cross-sections made use of an intense ion beam and of th e observation of the fast protons from the reaction norm al to the beam over an angle 2 π . The beam intensity was raised by avoiding an ion focusing system and using a simple extraction electrode with equal gas pressure in the ion source and gas target. Observation over a large angle was achieved by depositing a scintillation detector on a light guide which surrounded the target chamber. From calorimetric measurements of the beam current and measurements of the counting rate, relative cross-sections were obtained for deuteron energies up to 15 keV where absolute cross-sections are well known. In this w ay absolute values of the cross-section were found from 15 keV down to 4 keV, where a value of 9 x 10 -33 cm 2 was measured. Although the results are consistent with Gamow’s relation, the cross-section in the lower energy range is slightly larger than expected.