Report for General Research January 8, to April 30, 1951 (Alpha - Neutron Volume)
An experimental, gamma-sensitive, coaxial radioelectric cell has been tested by the Control Section. It was found to be as precise as the rotating sample gamma counter but much faster and simpler to operate. A gamma-sensitive, radioelectric cell of improved design has been constructed for the 'Y' Section. A neutron sensitive radioelectric cell has been tested over a range of pressures with various filling gases and with several combinations of hydrogenous electrode backings. Neutron to gamma discrimination ratios as high as 2,000 to 1 were obtained, A multiple electrode, alpha radiation, radioelectric cell using coated plastic electrodes gave increased current output, but the electrode life was quite short. Preliminary life tests indicated that aluminum electroscope foil would give excellent electrode life and techniques were worked out for making good electrodes of both aluminum and of gold electroscope foil. The vacuum-pressure gas system has been redesigned and completely rebuilt (p. 5) The fast-neutron scintillation counter is much smaller and lighter than a B-wall proportional counter and a large moderator. The former is more efficient for polonium-beryllium neutron sources but is less efficient for radium-beryllium neutron sources or for polonium sources producing lower energy neutrons The fast neutron scintillation counter would thus be very useful if the neutron to gamma discrimination ratio could be markedly improved. Preliminary experiments indicate that this ratio can be improved by carefully tailoring the frequency response characteristics of the amplifier used. Phosphors are also being investigated from the standpoint of improving this ratio. Preliminary attempts to detect neutrons by measuring the neutron-capture gamma of cadmium were unsuccessful. However, the conversion gamma from alpha-beryllium neutron sources can be detected with high efficiency; and this might be used to determine the neutron flux from such sources even in the presence of high backgrounds of lower energy gammas (p. 8). Maximum efficiency is obtained for polonium-beryllium neutron sources when the beryllium powder contains a minimum of oxide, when the polonium is 'shot' into the source container and when the curie-to gram-of-beryllium ratio is in the range of 5 to 11 (p. 11). Four mock-fission neutron sources have been prepared in an attempt to improve the efficiency which can be obtained by the evaporation technique (p. 13). A polonium-boron neutron source of unusually high efficiency has been made by the evaporative procedure. Two further attempts to prepare polonium-boron neutron sources by volatilization gave low efficiency (p. 14). Polonium, satisfactory for making neutron sources, has been reclaimed from large volumes of hydrochloric acid containing high concentrations of contaminating ions (p. 15). Work has continued on the problem of determining the total energy emitted from a covered alpha source. The effective thickness of a tantalum hold-down apparently, increases with time. If a source does not contaminate acetone after 24 hours immersion, it can be considered as being satisfactorily sealed. It is believed that a satisfactory seal of a tantalum hold-down to a gold plated source can be obtained by using a gold foil ring between the hold-down and the source, clamping to give pressure, and heating in a vacuum (P. 16).
- Research Organization:
- MOUND (Mound Plant, Miamisburg, OH)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AT-33-1-GEN-53
- OSTI ID:
- 957458
- Report Number(s):
- MLM-563; MLM-MU-51-66-0022; TRN: US200916%%180
- Resource Relation:
- Related Information: Classification cancelled 5/28/2009.
- Country of Publication:
- United States
- Language:
- English
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