/ Experiment-Nucl nucl-ex/9608002

Measurement of neutron capture on Ca-48 at thermal and thermonuclear energies

Beer, H. (Karlsruhe U., EKP) ; Coceva, C. (ENEA, Bologna) ; Sedyshev, P.V. (Dubna, JINR) ; Popov, Yu.P. (Dubna, JINR) ; Herndl, H. (Vienna, Tech. U.) ; Hofinger, R. (Vienna, Tech. U.) ; Mohr, P. (Vienna, Tech. U.) ; Oberhummer, H. (Vienna, Tech. U.)

Published in: Phys.Rev.
Year: 1996
Vol.: C54
Page No: 2014-2022
Pages: 15

Abstract: At the Karlsruhe pulsed 3.75\,MV Van de Graaff accelerator the thermonuclear $~{48}$Ca(n,$\gamma$)$~{49}$Ca(8.72\,min) cross section was measured by the fast cyclic activation technique via the 3084.5\,keV $\gamma$-ray line of the $~{49}$Ca-decay. Samples of CaCO$_3$ enriched in $~{48}$Ca by 77.87\,\% were irradiated between two gold foils which served as capture standards. The capture cross-section was measured at the neutron energies 25, 151, 176, and 218\,keV, respectively. Additionally, the thermal capture cross-section was measured at the reactor BR1 in Mol, Belgium, via the prompt and decay $\gamma$-ray lines using the same target material. The $~{48}$Ca(n,$\gamma$)$~{49}$Ca cross-section in the thermonuclear and thermal energy range has been calculated using the direct-capture model combined with folding potentials. The potential strengths are adjusted to the scattering length and the binding energies of the final states in $~{49}$Ca. The small coherent elastic cross section of $~{48}$Ca+n is explained through the nuclear Ramsauer effect. Spectroscopic factors of $~{49}$Ca have been extracted from the thermal capture cross-section with better accuracy than from a recent (d,p) experiment. Within the uncertainties both results are in agreement. The non-resonant thermal and thermonuclear experimental data for this reaction can be reproduced using the direct-capture model. A possible interference with a resonant contribution is discussed. The neutron spectroscopic factors of $~{49}$Ca determined from shell-model calculations are compared with the values extracted from the experimental cross sections for $~{48}$Ca(d,p)$~{49}$Ca and $~{48}$Ca(n,$\gamma$)$~{49}$Ca.

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