Summary: Several aspects of the procedure and corrections for the calibration of encapsulated radium sources at NBS have recently been investigated. It was found that a chamber equipped with a guard-ring type electrode system allowing the use of a vibrating reed electrometer as a current detector provides more versatility and precision than the gold-leaf electroscope now in use for routine calibrations. Absorption corrections for the U.S. primary national radium standards have been determined for the NBS chamber: 0.78 percent for standard 5440 and 1.01 percent for standard 5437. The Owen-Naylor integral equation for absorption of rays in the walls of cylindrical radium sources has been evaluated by a power series expansion of the integrand. Absorption coefficients and correction factors for platinum and Moael metal (materials commonly used for source capsules) have been computed for the NBS chamber.
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Several aspects of the procedure and corrections for the calibration of encapsulated radium sources at NBS have recently been investigated. It was found that a chamber equipped with a guard-ring type electrode system allowing the use of a vibrating reed electrometer as a current detector provides more versatility and precision than the gold-leaf electroscope now in use for routine calibrations. Absorption corrections for the U.S. primary national radium standards have been determined for the NBS chamber: 0.78 percent for standard 5440 and 1.01 percent for standard 5437. The Owen-Naylor integral equation for absorption of rays in the walls of cylindrical radium sources has been evaluated by a power series expansion of the integrand. Absorption coefficients and correction factors for platinum and Moael metal (materials commonly used for source capsules) have been computed for the NBS chamber.
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