Measurement of (n,γ) cross sections of Na-22 and Co-58

Measurement of (n,γ) cross sections of Na-22 and Co-58

Physica 29 1196 Farinelli, U. Martini, M. 1963 LETTER TO THE EDITOR Measurement of (n, y) cross sections of Na-22 and Co-58 The cross sections for ...

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Physica 29 1196

Farinelli, U. Martini, M. 1963

LETTER TO THE EDITOR

Measurement of (n, y) cross sections of Na-22 and Co-58 The cross sections for the absorption of pile neutrons in the two radioactive nuclides Co-58 and Na-22 have been measured by a source depletion method. For each of the two isotopes, two sources were prepared; the ratio of their activities was determined by y-counting. One of the sources was then irradiated for a certain time in the thermal neutron flux of the Ispra 1 reactor. The ratio of the activities of the two sources was again measured after irradiation. If r is the value found for this ratio before irradiation, r' after irradiation, the cross section 11 for the absorption of pile neutrons by the radioactive nuclei is easily found to be:

r

In-

r'

a = ---J(I) dt

where the integral at the denominator is the integrated neutron flux, in neutrons/ems, to which the irradiated sample was submitted; this expression is independent of source decay and history of irradiation. The integrated neutron flux was measured by irradiating a Co foil together with the sample, and by determining its activity both absolutely, by fast y - y coincidence technique, and relatively to a known Co-60 standard. Corrections for spurious activations were evaluated by irradiating dummy sources together with the radioactive samples. In the case of Co-58, the possible formation of new Co-58 by (n, p) reactions in the Ni-58 present in the source was also taken into account by irradiating a Ni sample with the experiment. This correction was found to be negligible. Several irradiations were performed, since in order to have a good sensitity in the measurement, the integrated flux should be of the order of 1111. The results found were: 3150 90000

± ±

150 10000

barns for Co-58 barns for Na-22

The result for Co-58 is consistently higher than that reported by C. H. Hogg and

L. D. Weber (Trans. Am. Nuclear Soc. 3, 1960); no previous measurement of the N a-22 cross section is known to the authors. Received 29-7-63 U.

FARINELLI

M. MARTINI

Comitato Nazionale per l'energia nucle are Laboratorio Fisica e Calcolo Rea ttorl Casaccia (Rama) - Italia

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