Gamma-Ray Spectra of the Los Alamos Reactors

Abstract

The gamma-rays emitted from a ${\mathrm{U}}^{235}$ slug at the center of the Los Alamos water boiler and from the core of the "fast reactor" were analyzed with a magnetic Compton spectrometer during the period that each reactor operated at a constant power level (30 kilowatts for the water boiler and 25 kilowatts for the fast reactor). An absolute gamma-ray spectrum (neglecting line structure) was determined for each reactor in an energy range from about 0.5 Mev to 12 Mev. In both cases, the number of photons emitted per unit energy interval decreased exponentially with photon energies so that the value at 8 Mev was less by a factor of ${10}^4$ than the value at 0.5 Mev. The average quantum energy for this type of spectrum was approximately 1 Mev. The total energy release of gamma-radiation from the ${\mathrm{U}}^{235}$ slug (diameter 2.22 cm, length 0.426 cm, weight 28.5 g, 95 percent purity) occured at a rate of about 2×${10}^{13}$ Mev/sec.