Gamma Rays from Neutron Capture in Helium-3 and Deuteron Capture in Deuterium

Abstract

The gamma rays from the ${\mathrm{He}}^{3}(n, \ensuremath{\gamma}){\mathrm{He}}^{4}$ and the $\mathrm{D}(d, \ensuremath{\gamma}){\mathrm{He}}^{4}$ reaction have been observed. The gamma detector, a 3-in.\ifmmode\times\else\texttimes\fi{}4-in. NaI crystal, was surrounded by a plastic scintillator to eliminate the cosmic-ray background. A pileup rejection circuit was used to reduce the background from neutron induced reactions in the NaI. The cross section of the ${\mathrm{He}}^{3}(n, \ensuremath{\gamma}){\mathrm{He}}^{4}$ reaction at 4 MeV is $\ensuremath{\sigma}=5$ \ensuremath{\mu}b/sr at 90\ifmmode^\circ\else\textdegree\fi{}. The intensity ratio, $\frac{I(90\ifmmode^\circ\else\textdegree\fi{}}{I(45\ifmmode^\circ\else\textdegree\fi{})}\ensuremath{\approx}2$, agrees with that expected for electric dipole radiation ($\ensuremath{\Delta}M=0$). The $\mathrm{D}(d, \ensuremath{\gamma}){\mathrm{He}}^{4}$ reaction at 1.35 MeV has a cross section $\ensuremath{\sigma}=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}33}$ ${\mathrm{cm}}^{2}$/sr at 45\ifmmode^\circ\else\textdegree\fi{}.