PHOTONEUTRON YIELDS FROM NATURAL MAGNESIUM

Published measurements of the cross sections for the ($\ensuremath{\gamma}, n$) reaction in natural Mg and in ${\mathrm{Mg}}^{25}$ are in disagreement in the energy region where the other Mg isotopes do not contribute to the cross section of the natural sample, and imply a most unusual cross-section curve for the ${\mathrm{Mg}}^{26}$ isotope at slightly higher energies. A new measurement of the cross section for natural Mg is reported which disagrees strongly with the published data, but agrees with the ${\mathrm{Mg}}^{25}$ values, and implies a not-surprising cross-section curve for ${\mathrm{Mg}}^{26}$. The origin of the disagreement in the natural-sample cross-section values is unknown.