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High-flux Prompt-Gamma Activation Analysis at FRM II, Garching

Zsolt Révay (Technische Universität München Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II))

A well-shielded, collimated HPGe gamma detector has the efficiency of 10-3 - 10-5 photopeak counts per photon, from which one can conclude that samples irradiated in a neutron beam with a fluence rate as low as 106 - 107 cm-2 s-1 should give a reasonable count rate. Why do we need strong neutron beams for this technique at all? At the Research Neutron Source Heinz Maier-Leibnitz (FRM II) in Garching, the PGAA facility operates the strongest reported neutron beam, with a flux of 6x1010 cm-2 s-1. This is a focused beam with a high divergence. When the elliptical neutron beam is not in operation, a weaker, highly uniform beam is also available with flux of 2x109 cm-2 s-1. For many typical applications of PGAA this beam is more than enough. However, the focused-beam option has made possible many new measurements. Now samples with masses less than 1 mg can be measured. The lowest cross section nuclides can also be detected in this beam: 10-6 barn is now easily available (D, N-15 etc.). Radioactive isotopes were not really measurable with this technique, because the radiation from the sample would overwhelm the induced radiation; however a series of actinides can now be measured at the PGAA facility at Garching. A few interesting applications will be presented in the talk.

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