Measurement of the neutron fluence on the spallation source at Dubna

Abstract

A ²³²Th activation sample was exposed directly to the spallation neutrons produced by 1GeV proton colliding with a lead target and other samples of ¹⁹⁷Au, ²⁰⁹Bi, ⁵⁹Co, ¹¹⁵In and ¹⁸¹Ta were irradiated by moderated neutrons after passing through 6 cm of paraffin. Different (n, γ) and (n, xn) reaction products in ²³²Th, ¹⁹⁷Au and ²⁰⁹Bi samples are analyzed by gamma-ray spectrometry to measure the neutron fluence at the positions of the samples. For this purpose a histogram of 'flat' spectrum averaged neutron cross-sections in over thirty given energy groups was determined from the PREPRO-2000 software. Results of measurements are compared with Monte-Carlo simulations by the Dubna CASCADE code. Experimental values for both spallation and moderated neutron fluences are in reasonable agreement with the CASCADE code. Thus, the experimentally measured fluence of moderated neutrons was used to infer the 'one group' reaction cross-sections of ²⁰⁹Bi (n, xn) reactions for x = 6 to 9.