Studies of nuclear reactions by micro-gas analytical methods

The development of an apparatus for the measurement of amounts of helium in the range 10(^-5) to 10(^-8) is described. Studies were made of the previously unmeasured average fission neutron cross section for the reaction Fe(^56)(n, a)Cr(^53) and a value of 0.39 mb, obtained from irradiations in B. E. P. O. at Harwell and D. F.R. at Dounreay. The nuclear reactions Fe(^54)(n, p)Mn(^54) and Fe(^54) (n, a)Cr(^51) were also studied and values of the average cross section measured. The absolute fission yields of Mo(^99) and Ba(^140) in the thermal neutron fission of natural uranium were determined using helium analysis of an irradiated uranium solution containing boric acid to obtain the number of fission events. The chemical separation of the nuclides and the counting and standardization procedures are fully described. The results, of 5.94 and 5.87% for Mo(^99) and Ba(^140) respectively, and the errors involved are discussed in the light of previous values. The third section of the work was concerned with the calibration of photoneutron sources by destructive analysis of the beryllium cylinders for helium, also produced in the photo-reaction. A discussion of neutron source calibrations is included. The design, and experiments carried out with an apparatus which included a silver-palladium leak for hydrogen are described. Unfortunately this work was not completed, but suggestions are included for its conclusion.