Measurement of the neutron fluence on the spallation source at Dubna

A 232 Th activation sample was exposed directly to the spallation neutrons produced by 1GeV proton colliding with a lead target and other samples of 197 Au, 209 Bi, 59 Co, 115 In and 181 Ta were irradiated by moderated neutrons after passing through 6 cm of paraffin. Different (n, γ) and (n, xn) reaction products in 232 Th, 197 Au and 209 Bi 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 209 Bi (n, xn) reactions for x = 6 to 9.