Neutron Cross Sections for Some Threshold Reactions

Three neutron reactions leading to production of the rare gases Ar41 and Xe135 have been in­ vestigated. Single crystal samples of KF, CaF2 , and BaF2 were irradiated in the Berlin reactor and the target-free absolute activities of the rare gas isotopes measured by a /^-/-coincidence method. The calculated cross sections are K41 (n,p)Ar41: o = ( 2 ,73±0,41) mb; o0= (98,6± 14,8) mb; Ca44(n,a)Ar41: o = (61,1 ±9,2 ) ^b; 0„=(64 ,7± 9,7) mb; Ba138(n,a)Xe135: o = ( 1,9 ± 0 ,3 ) fib', o0= ( 4 ,9 ± 0,7) mb. The first set of values are valid for a fission-neutron spectrum. The second set are calculated cross sections for the high energy plateau. They can be considered as valid for 15 MeV neutrons.