An absolute measurement of the $^7$Li(n,n’t)$^4$He reaction cross-section between 5.0 and 14.0 MeV by tritium assaying

Swinhoe, Martyn Thomas (1978). An absolute measurement of the $^7$Li(n,n’t)$^4$He reaction cross-section between 5.0 and 14.0 MeV by tritium assaying. University of Birmingham. Ph.D.

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Abstract

In view of the world’s energy situation, it is necessary to investigate all possible means of supply. The principles of controlled thermonuclear fusion are described, together with the role of lithium and the need for nuclear data. Information on $^7$Li and the $^7$Li(n,n’t)$^4$He reaction is given. The conclusion is that the state of the data is inadequate for the CTR development programme.

In the experiment, the tritium is produced in samples- of lithium hydroxide, which are then dissolved, leaving the tritium as tritiated water. This is then measured by liquid scintillation counting in the normal way. The counting efficiency is measured as a function of quenching, with standard tritiated water. As a check on this method the $^6$Li(n,$\alpha$ t) cross-section was measured in a reactor irradiation. The result (including a self-shielding correction) was 900$\pm$52 barns, in agreement with the accepted value of 940$\pm$5 barns.

The neutron dose was measured with, an NE213 liquid scintillation detector, the efficiency of which was measured as a function of neutron energy from 1.5 to 25 MeV, using the associated particle technique.

Irradiations were carried out between 4.7 and 14.1 MeV, using the Harwell Tandem Van de Graaff and Cock-croft Walton generator. The cross-section obtained for the $^7$Li(n,n’t)$^4$He was 28% lower than the ENDF/B-IV evaluation, with standard deviation of 5%. The cross-section of $^{27}$AI(n,$\alpha$)$^{24}$ Na was measured concurrently and good agreement was obtained with the accepted value.

Other evidence is presented for this result; el astic cross section measurements from the Triangle Universities (USA), and tritium production measurements in an integral assembly at Karlsruhe (West Germany). The results from the present experiment may also improve the overall fitting of a recent R-matrix analysis to the $^7$Li nucleus.

Finally, the conclusions are that, at least, a new evaluation is required, and also more measurements are required to resolve the discrepancies especially at 14 MeV.

Type of Work:	Thesis (Doctorates > Ph.D.)
Award Type:	Doctorates > Ph.D.
Licence:	All rights reserved
College/Faculty:	Faculties (to 1997) > Faculty of Science
School or Department:	Department of Physics
Funders:	None/not applicable
Subjects:	Q Science > QC Physics
URI:	http://etheses.bham.ac.uk/id/eprint/15001

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