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The time-dependence of the 2.5 MeV neutron emission from JET is reliably measured using fission chambers. The absolute calibration of these chambers is required to an accuracy of 10%, or better, for a range of intensities that may cover 6 or more decades. At JET, this calibration is now achieved by using activation techniques, the most convenient of which involves fissionable materials (thorium and uranium) and delayed neutron counting. As delayed neutron counting is unfamiliar in the fusion community, particular care was taken to obtain confirmation of the results based on this method by comparison with measurements made using the conventional activation procedure (involving indium, nickel and zinc as target materials). As the activation measurements can be influenced appreciably by the weak emission of 14 MeV neutrons, this contribution was measured separately using high threshold energy activation reactions (in copper and silicon). Neutron transport calculations were employed to relate the measured local fluences of both 2.5 MeV and 14 MeV neutrons to the total yields from the plasma. Absolute calibration accuracies of 6% and 8% are claimed for 2.5 MeV and 14 MeV neutron yields, respectively; the accuracy of the 14 MeV to 2.5 MeV yield ratios is 6%.

Additional information

Authors: JARVIS O N, JET Joint Undertaking, Abingdon, Oxon. (GB);CLIPSHAM E ET AL., JET Joint Undertaking, Abingdon, Oxon. (GB);PILLON M, ENEA, Centro Ricerche Energia Frascati, Roma (IT);RAPISARDA M, ENEA, Centro Ricerche Energia Frascati, Roma (IT);VERSCHUUR K A, ECN, Petten (NL)
Bibliographic Reference: Report: JET-P(90)46 EN (1990) 42 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
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