Photoproduction of Alpha Particles from Several Metallic Elements

Abstract

Photoproduction of alpha particles from copper has been investigated by using 22-Mev bremsstrahlung to irradiate a "sandwich" consisting of a thin copper foil (2.75 mg/${\mathrm{cm}}^2$) placed between two Ilford E-1, 100-micron thick nuclear emulsions. The observed yield was (3.9±0.6)×${10}^4$ alpha particles per moleroentgen. The energy distribution of the alpha particles has a maximum near 8 Mev. In addition, photoproduced alpha particles from thin foils of eleven elements, including copper, have been detected by means of their tracks in nuclear emulsions. "Sandwiches" containing two target foils on either side of a lead stopping foil were exposed to 21.5-Mev bremsstrahlung hardened by 147.4 g/${\mathrm{cm}}^2$ of graphite. The photo-alpha yields observed with the hardened spectrum are given in terms of unhardened bremsstrahlung, having been multiplied by the calculated ratio of effective photons in the two spectra. These yields, in units of ${10}^4$ alphas per mole-roentgen, are: Al-1.3, V-0.4, Fe-1.9, Co-2.3, Ni-3.9, Cu-2.6, ${\mathrm{Cu}}^{63}$-3.6, Zn-8.2, Nb-0.5, Rh-0.3, Ag-0.17, and In-0.09. For the seven elements having $Z\le 30$, there seems to be a correlation between the yield and the difference between the alpha and neutron binding energies.