Photoneutron

Kh. B. Mezhiborskaya, Photoneutron Method ofDeterminingBeryllium, Consultants Bureau Enterprises, Inc., New York, 1961. 

B. L. Berman, Atlas of Photoneutron Cross Sections Obtained with Monoenergetic Photons, Lawrence Livermore National Laboratory, Report UCRL 78482, 1976. 

PHOTONUCLEAR REACTION. A nuclear reaction induced by a photon. In some cases the reaction probably takes place via a compound nucleus formed by absorption of the photon followed by distribution of its energy among the nuclear constituents. One or more nuclear particles then "evaporate from the nuclear surface, or occasionally the nucleus undergoes pliotofissioii. In other cases the photon apparently interacts directly with a single nucleon, which is ejected as a photoneutron or photoproton without appreciable excitation of the rest of the nucleus. 

A number of investigators have examined the production of radioactivity resulting from photoneutron reactions induced by high-energy electrons. Meyer (15) has reviewed these data and showed that the induced radioactivity, 72, in specific activity per unit dose (picocuries per gram of element times megarad) is reasonably well represented by Equation 1. 

Figure 2. Threshold energies for photoneutron, photoproton, and phototriton reactions as a...

Table I. Photoneutron, Photoproton, and Phototriton Threshold Energies Below 10 m.e.v. (2)...

Fig. 48. Energy spectrum of the photoneutrons emitted by Cu, after Byerly and Stephens. The continuous curve is calculated on the statistical model.

Fig. 31 was presented by E. Vogt who compares the predictions of the theory of Lane, Thomas, and Wigner with the photoneutron results of Watten-BERG in 1947 [ANL—ynl] ... 

Fig. 28. The cross-section for the production of photoneutrons in Ag, Ta, W, Pb, and U as a function of photon energy. Up to 13.5 Mev, the curves are estimated. [Figure from Jones and Terwilliger Phys. Rev. 91, 699 (1953).]...

The hard y-ray activity (about 3 Mev) aftel shutdown, however, depends on the yield and decay of specific.fission product chains. These have been measured by the photoneutron threshold reacfioii in heaVy. water. The average lifetime and yield of the y rays of energies higher than this value are ... 

The radioisotope program has been supplemented lately by the stable isotope program and by the facilities for neutron irradiation either in one of the reactors or, by means of a photoneutron source, in any properly equipped laboratory. 

Photoneutrons are neutrons produced by some nuclei during or after irradiation with 7 rays. 

Photoneutrons are produced at considerable flux densities in the heavy metal of the bremsstrahlung converter. For example, in the linear accelerator used by the authors, a thermal neutron flux density of some 10 °cm s has been produced in the tantalum converter during normal operation (30MeV, 150 pA). This appears a relatively poor flux density compared to that of a standard nuclear research reactor. Nevertheless, in advantageous cases trace analyses can be performed. For example, routine analyses of several elements in air-dust samples were carried out by activation with photoneutrons (see below). Normally, however, the photoneutron flux is analytically negligible, whether as an analytical tool or as a source of interference. 

Since all buckling measurements are lower thiui those predicted theoretically, some effort has been devoted to a search for possible systematic experimental causes for the discrepancy. Effects of various loadings near the tank edge, as well as effects due to photoneutron production by shortlived fission products have been measured but do not account for the variation. 

Secondary Source Rods Gamma and neutron The photoneutron somce material used in the secondary somce rods is an equal volume mixture of antimony and beryllium (Sb-Be). Extensive shielding is provided for refuelling activities. 

No. Light water has sufficient heavy water contamination to provide adequate photoneutrons for... 

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