Nuclear Cross Sections for 270-Mev Neutrons

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Abstract
The total cross sections of eleven different elements were measured for the neutrons resulting from the bombardment of a 2-in. Be target by the 350-Mev protons of the 184-in. cyclotron. Bismuth fission ionization chambers served as the neutron detectors and had an estimated mean neutron detection energy of 270 Mev for the measurements. The attenuating materials were placed inside the concrete shielding and the monitor was placed to one side of the attenuators. The detector was placed about 30 ft. from the attenuators in line with the target and the attenuators. Collimators in the concrete shielding and a concrete block immediately behind the attenuating materials limited the detection of neutrons scattered through small angles to 20 min. "Poor" geometry cross sections of carbon, copper, and lead were measured by placing a shallow fission chamber behind attenuators of large cross-sectional area over which the neutron flux was uniform. The inelastic cross section is at least half the total for all three elements.

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