Measurement of Neutron Flux with Lithium Borate Loaded Emulsions

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Abstract
Methods for the incorporation of lithium borate in nonelectron sensitive nuclear emulsions have been investigated from the viewpoint of emulsion stability and high B10 and Li6 pick‐up for use in the estimation of low neutron flux. Ilford C‐2 plates loaded by absorption from 10 percent lithium borate solution buffered with lithium carbonate and containing 3 percent by volume of glycerine or diethylene glycol pick‐up an equilibrium concentration of 34 mg per cc of boron and 12 mg per cc of lithium ions, respectively. Isothermal absorption curves indicate that the borate and lithium ions migrate into the gelatin—AgBr mixture at different rates. Higher concentrations of B‐ and Li‐ nuclei in the emulsion can be introduced by the method of evaporation loading. Methods for evaluating the boron and lithium concentration in the emulsion are described. Quantitative recording of tracks from the B10(n,α)Li7 and the Li6(n,α)H3 reactions can be maintained for periods of about 3 months; which provides a convenient means of estimating low slow‐neutron flux for purposes of health monitoring, or investigations of spontaneous fission processes, and for the evaluation of the cosmic radiation neutron background. The flux at sea level arising from cosmic radiation is of the order of 230 slow neutrons per cm2 per day, (ranging from 160 to 300 with change of exposure conditions). At an elevation of 3500 m, the flux shows a 10‐fold increase.
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