| Popis: |
4 He production has been measured by an isotopic dilution mass spectrometry method, for the irradiation of Be-metal samples by fast neutrons from the 9 Be(d,n) source reaction, corresponding to 7-MeV deuterons incident on a thick Be-metal target. The 58 Ni(n,p) 58g+m Co dosimetry reaction was employed as a reference standard for measurement of the neutron flux. The integral cross section for the 9 Be(n,2n) 8 Be(2 4 He) reaction ( 8 Be breaks up very quickly into two α-particles) was deduced by applying a correction of 9.4% to account for the 9 Be(n,α) 6 He reaction contribution to the total 4 He yield from neutrons on Be. The experimental integral reaction cross-section ratio of 9 Be(n,2n)2 4 He to 58 Ni(n,p) 58g+m Co in this spectrum was found to be 1.217, with an error of 3.5%. This is in good agreement with the corresponding calculated ratio of 1.161 which is based on an average of results obtained by considering four distinct representations of the 9 Be(d,n) neutron spectrum and ENDF/B-VI values for the reaction cross sections. The scatter of the calculated results amounts to 0.5%. It is small because the shapes of the response functions, R ( E ) = o ( E ) σ ( E ), for these two reactions in this neutron spectrum are very similar. The observed C/E is 0.954. This is very good agreement, considering the various uncertainties involved, including those for the differential cross sections from ENDF/B-VI. This integral measurement is sensitive to the differential reaction cross section in the range 3–6 MeV. The uncertainty attributable to the 58 Ni(n,p) 58g+m Co reaction differential cross section in this range is estimated to be 3.5%. Therefore, the results of the present investigation indicate that ENDF/B-VI represents the 9 Be(n,2n)2 4 He reaction differential cross section quite well over this energy range. |
