R. Dams

MEAN FISSION NEUTRON CROSS SECTIONS FOR THE REACTIONS

The mean fission neutron cross sections of the Nb(n, <x)°»Y, Nb(n, α)βΥ and Nb(n, 2n)»Nb reactions were determined experimentally from the absolute Y, Y and Nb activities induced in irradiated niobium pentoxide. For this purpose a separation method for yttrium from niobium was developed using fluoride and oxalate precipitations. Niobium was purified from tantalum by anion exchange and homogeneous precipitation methods. The Y and Nb activities were measured by gamma spectrometry and the Y activity by means of a calibrated Geiger Müller tube. For the cross sections of the reactions Nb(n, α)»Y and Nb (η, α)«Y respective values of 22.1 + 0.3 and 58.5 ± 2.2 /¿barn were found. For the cross section of the reaction Nb (n, 2n) Nb a value of 420 + 7 //barn was obtained.

sup 93

Summary The mean fission neutron cross sections of the 127I(n, p)127mTe; 127I(n, p)127Te and 127I(n, 2n)126I reactions were determined experimentally from the absolute 127mTe, 127Te and 128I activities induced in irradiated potassium iodide. For this purpose a quantitative separation method for tellurium from iodine was developed using liquid-liquid extraction of iodine and precipitation of tellurium by means of hydrazine hydrate. The absolute tellurium activity was measured with a calibrated Geiger-Müller tube whereas the iodine activity was measured by gamma spectrometry. For the cross sections of the reactions 127I(n, p)127mTe and 127I(n, p)127Te respective values of 11.1 ± 0.2 μbarn and 7.62 ± 0.11 μbarn were obtained. For the cross section of the reaction 127I(n, 2n)126I a value of 0.647 + 0.010 μbarn was found.

Nb(n,

The cross-section for the reaction 1 8 1 T a (n, p) 1 8 1 H f averaged over the fission neutron spectrum was determined experimentally from the 1 8 1 H f activity induced in irradiated T a 2 0 5 . The T a 2 O s target was purified by liquid-liquid extraction with methylisobutylcetone from a H 2 S 0 4 H F solution. The induced 1 8 1 H f activity was separated and purified using anion exchange in hydrochloricoxalic acid medium. The 1 8 1 H f activity was measured by fast-slow coincidence spectrometry. A value of 1.2 ± 0.3 Mbarn was obtained for the cross-section.