Photoneutron Cross Sections

Abstract

The neutron yields resulting from photoneutron reactions have been measured as a function of betatron energy from threshold to 23 Mev for 22 elements. These yield curves have been analyzed by the photon difference method to give the total cross section 0 = (cr&, "+0&,»+2cr&, 2") as a function of photon energy.Whenever possible, this cross section has been resolved into its components using threshold considerations and subsidiary data. Some general conclusions based on the new results are presented regarding the systematics of (y, n) reactions. Based on part on a thesis presented for the Ph. D. degree at the University of Saskatchewan by R. Montalbetti. f On leave of absence from Departamento de Fisica, Universidade de Sao Paulo, Sao Paulo, Brazil. 'Other neutron emitting cross section are energetically forbidden in the energy region covered in this experiment. s J. Goldernberg and L. Katz, LPhys. Rev. 89, 1300 (1953)g discuss the validity of such subtractions. ' G.

The Photodisintegration of Nuclei with Z Between 9 and 30

“…The result of this fit is shown in Figure 1. The agreement with the experiment of Nathans and Halpern (1954) is excellent. The low energy peak is at 17 MeV according to this fit, and this leads, using Danos's theory, to a Qo of 0·67±0·n barn.…”

“…The data of Nathans and Halpern (1954) on the 51V(y, n)50V reaction show some evidence for giant resonance splitting. With this in mind, an attempt was made to fit the experimental cross section values obtained by Nathans and Halpern with the sum of a pair of Breit-Wigner resonance curves of equal height.…”

“…which may be expected, an energy value was assumed for the higher energy peak. The systematic study of (y, n) reactions by Montalbetti, Katz, and Goldemberg (1953) was used as a guide in the choice of this value. However, the ratio of energies /iwb//iwa is the significant number in this result.…”

High Power Polarized Positron Source

“…For Tungsten, the gammas with energy E< 6.19 MeV can not generate neutrons [7], [8]; for reaction of ( γ γ γ γ , 2n) the threshold is 13.6 MeV (W). For some materials thresholds could be found in [11] (see references there).…”

Calorimetric calibration of an ionization chamber for determination of x-ray total beam energy

“…Th e prob ab ility for a ('Y ,n) 1'cac Lioll was tak en as thc triple product of tJlC a tomic d ensity of lead (2 .91 X 1.O 2l atoms/g), tll e rcaction cross sectioH (cm 2 ) and lhe effcc tive le ng th of the cylindcr (g /cm 2 ). '1'Jlc cross sec tioll was taken f1'01n refcre nce [10] be low 18 1 [ev a nd from refcr c nce [11] at hi gh er , T he amo un t of energy sto red by t he lead crystal when lead atoms arc displaced to interstitial sites by X-rays and secondary electrons in t he cyli ncler ca n be shown to be negligible: The CJ OSS scction for atomic displaceme nt in lead is of t hc order of 3X lO-21 em' fo r X-rays and !O~" em' for clect rons, and each displaced atom \liU in turn displace no more t han fi ve additional atoms [7J. Each displ acement results in the storage of less t han 25 cv.…”