Neutron-CaptureγRays from Various Elements

Neutron-capture γ-ray spectra have been measured in the energy range 0.3 to 3 Mev by means of a two-crystal Compton scintillation spectrometer. The efficiency of the instrument as a function of energy was determined experimentally. The uniqueness of the 2.23-Mev γ ray following capture of a neutron by hydrogen has been confirmed, and this γ ray was used as a standard to establish the absolute intensity of γ rays from other elements.Most of the γ rays observed can be understood in terms of known levels, and many appear to be emitted in transitions from such levels to the ground state. In many cases, the information obtained complements high-energy data in establishing preferred modes of decay of the product nucleus.In sodium a very strong γ ray is emitted from the first excited state of Na²⁴ at 0.47 Mev, and another ground-state γ ray appears to be emitted from the level at 1.34 Mev. The strongest γ ray in the magnesium spectrum is an $E1$ transition between the levels at 3.41 and 0.58 Mev in Mg²⁵. The aluminum spectrum is very complex, and only a few peaks have been resolved. A ground-state transition is seen from the level at 2.27 Mev in Al²⁸.In silicon two $E1$ transitions are observed from the capturing level to the levels at 4.93 and 6.38 Mev, and a ground-state transition is seen from the first excited state at 1.28 Mev. Ground-state transitions are observed from the levels at 0.52, 1.15, and 2.18 Mev in P³². In sulfur, there is a strong ground-state γ ray from the first excited state at 0.84 Mev, and a strong $E1$ transition to this level from that at 2.34 Mev.In chlorine almost all of the observed γ rays can be understood as ground-state transitions from known levels in Cl³⁶ at 0.79, 1.16, 1.95, 2.47, and 2.87 Mev. In K⁴⁰ the decay scheme involves several level to level transitions. γ rays to the ground state are observed from the levels at 2.05 and 3.40 Mev in K⁴⁰, and possibly from the 1.18-Mev level in K⁴².The spectra from calcium and titanium are very simple. A strong γ ray occurs almost once per capture in Ca⁴⁰ from the 1.95-Mev first excited state of Ca⁴¹, and a strong γ ray from the 1.39-Mev first excited state of Ti⁴⁹ occurs almost once per capture in Ti⁴⁸.In V⁵² most of the observed γ rays are emitted by levels below 1 Mev. Ground-state transitions occur from the levels at 0.42 and 0.83 Mev. In Cr⁵⁴ a very strong γ ray to the ground state is emitted by the level at 0.84 Mev, and a weak transition may be from the 0.54-Mev level in Cr⁵³ to the ground state.γ rays to the ground state are observed from levels at 0.42 and 0.88 Mev in Ni⁵⁹. No definite identification can be made of the four γ rays observed from zinc. The Cd¹¹⁴ spectrum contains many unresolved radiations; by far the most intense is the 0.56-Mev γ ray which is emitted from the first excited state.