Search

Self-powered (s-p) detectors are useful for incore neutron measurements in nuclear reactors because of their small size, ruggedness and simplicity. In one type of detector, a delayed current results from the beta activity induced in the device by the neutron flux while a second type gives an instantaneous response due to the compton electrons produced by the gammas released following the capture of neutrons in the device. To test these physical models and more importantly, to point the way to improvements in design without having to resort to excessive experimentation, a Monte-Carlo model was constructed to allow computations to be made of the response of both types of detector. The calculations were performed for Rh and V delayed and Co instantaneous detectors with emitter diameters of .051 cm and insulator thickness of .025 cm in all cases. The agreement with experiment was fairly good and the small discrepancies which occur are discussed in the paper.

For optimum operation of fast breeder reactors, knowledge of the incore power and breeding distributions is desirable. Because of the high temperature liquid sodium environment in the breeders, an activation method rather than a technique involving ion chambers seems to be the most appropriate experimental technique at present. An activation system has been worked out in which 1/16" BeO balls containing oxides of 235U and 238U are inserted into the reactor for activation and withdrawn to be counted in a Ge(Li) counter. Measurements of the activated fission and 239Np gamma-rays yield the desired information. Parameters and procedures are obtained based on a specific fast Demonstration Breeder design. However, only slight modification would be required for the application to other breeders.

Elastic scattering of 100 MeV protons by 3He and 4He has been measured over a wide range of angles. Analysis of the small-angle results was carried out using a superposition of nucleon-nucleon amplitudes computed with both modern and old phase shifts. No significant differences were found in the accuracy of the predictions resulting from the two sets, but in both cases the 3He results were better than those of 4He. The peaking evident in the backward p–4He scattering but not seen in heavy nuclei has been interpreted in terms of an exchange interaction using an optical model analysis.

To the Editor:— Doctor Goldwater's points are well taken. The vehicle must be taken into account, and in the usual commercial preparation of the esters of 2,4-D the vehicle is usually a petroleum solvent plus an emulsifier, but these are usually listed as inert ingredients by the manufacturer. Dr. R. B. Hurl of Marysville, Ohio, wrote to us and raised the question about the possible role of the petroleum solvent and the emulsifier in the causation of the peripheral neuropathy. Dr. Hurl suggested that "perhaps it is safer to say that certain proprietary ester formulations of 2,4-D have caused peripheral neuropathy." We agree with this point of view, since the essential point of our article was that undue exposure to a commercial preparation of an ester of 2,4-D was followed by peripheral neuropathy. In one instance we were able to obtain the label from the container of the 2,4-D preparation.