A fast neutron coincidence spectrometer of high efficiency has been constructed applicable to the approximate energy range of 1 Mev to 20 Mev. Design considerations and the working model are discussed.

To illustrate the operation of such an instrument, the line spectra of the gamma‐rays from Co60 and of 3.3‐ Mev D‐D Neutrons are presented. Discrimination between gamma‐rays and neutrons is obtained by utilizing the difference in the time of flight of the two particles. In conclusion possible improvements are suggested.

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Segel, Swartz and Owen, to be published.
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The carbon nuclei in the scintillator are shown to produce negligibly small pulses as the result of neutron scattering (reference 4).
8.
A solution of p‐terphenyl and diphenyl hexatriene in commercial phenyl‐cyclohexane was tested in one counter but was not found superior to the standard xylene solution.
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To be described in a future communication.
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12.
The instrument resolution is somewhat better than is indicated by this figure. It has been shown that many neutrons enter the primary counter after scattering in the lead shielding, resulting in a spread of the distribution and enhancing the number of small pulses in the primary counter (see reference 2).
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