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A comparative study of elastic scattering of low-energy electrons by boron, aluminum and gallium trihalides The transmission of normally incident electrons through aluminum, which has been vacuum deposited on a 75-A aluminum oxide insulator has been measured for electrons of energy between 1 eV and 4 keY. Currents to the top layer (65 to 525 A) and to the metallic bottom layer underlying the insulator were monitored with operational amplifiers in obtaining the transmission characteristic. Below 50 eV the transmission is apparently controlled by the aluminum oxide insulator. Above this energy the absorption increases rapidly until the entire beam current is absorbed in the top layer. At still higher energies the current to the top layer decreases through zero to a value of -1 (normalized). The energy at which the top current goes to zero was found to increase as the thickness of the top layer was increased. These data were analyzed to yield the electron stopping power which was found to vary from about 3.1 eV! A at 300 eV to about 4.5 eV! A at 950 eV when the raw data were corrected for nuclear scattering by a modified version of the Yang scattering theory.

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This paper is on the subject of neutron dose measurements using activation detectors. It is well-written-succinct and clear. In it, the authors pointed out the basic difficulties of neutron dosimetry: the wide range of possible neutron energies, the great dependence of dose on neutron energy and the lack of suitable dosimeters or nuclear reactions to cover the large energy span. The authors, then, proposed an ingenious method of producing a "man-made" reaction which has an effective threshold in the keV region. This was accomplished by shielding 239Pu with a certain thickness of '"B to simulate a "low threshold" fast neutron detector. The authors, then, incorporated this detector into a system of other well-chosen detectors to achieve a computer detector system capable of measuring neutrons from thermal to 20 MeV. The resulting product was the "boron-ball" which contained the fission detectors at its centre. Details and formulae for using this detector system were provided by the authors. This product was subsequently used widely in many nuclear establishments although its popularity has waned.

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