Development of a Low-Background Neutron Autoradiographic Technique

The cellular distribution of10 B in tissue is of interest in neutron capture therapy, since the efficacy of the ¹⁰ B( n,α) ⁷ Li reaction is dependent on localization within cells. Experimental results showed that air nitrogen in conjunction with emulsion of greater than optimum thickness was responsible for high background encountered in previous attempts to develop a technique capable of determining intracellular distribution in human tissues. Irradiation of slides coated with liquid emulsion, with thermal neutrons ( 6.23× 10¹⁰ cm⁻²) in a CO2 atmosphere, gave a heavy-particle background of 2 tracks per microscopic field ( 1.77× 10⁻⁴ cm⁺²). If a tissue section 5 microns thick, containing 60 μg of10 B per gram of tissue (roughly the maximum amount tolerable to human tissues), is irradiated with the same fluence, the number of countable α-tracks per field from the ¹⁰ B( n,α)⁷ Li reaction would be 25.6 o...