X-γ同時計数法によるRIの崩壊率の絶対測定(第3報)

抄録

The arrangement and characteristics of the x-gamma ray coincidence-counting system and the method of standardizing the disintegration rate of ⁸⁸Y and ⁵⁴Mn sources were previously reported. In the present paper, the absolute disintegration rate of a ⁵⁵Fe source is determined by modifying the x-gamma ray coincidence-counting method. The absolute disintegration rate of a ⁵⁵Fe source emitting only x-rays has, ordinarily, been measured by the 4πX counting method. In this report, the calibration of a ⁵⁵Fe source by the x-gamma ray coincidence method is attempted. The prin-e ciple of this idea is as follows: a known amount of ⁵⁷Co or ⁵⁴Mn isotope, which emitts both x- and gamma-rays, is added to a ⁵⁵Fe source separately, the radioactivity of each mixed source is counted with x-gamma ray coincidence equipment, and then the absolute disintegration rate of the ⁵⁵Fe isotope is calculated by analyzing the counting results, The 55Fe solution used in this experiment was a standard solution supplied by Radio-Chemical Center (U. K.). The ⁵⁷Co and ⁵⁴Mn isotopes, were produced by irradiating highly-pure nickel sheet with a high energy gamma ray beam from the linac at JAERI, and by irradiating electrolytic iron with fast neutrons in JRR-3, respectively. The absolute disintegration rates of ⁵⁷Co and 54Mn sources were well defined by the x-gamma ray coincidence method decribed in previous papers, and then either ⁵⁷Co or ⁵⁴Mn master solution was, mixed with the standard solution of ⁵⁵Fe. The counting sources were prepared by dropping and evaporating the solution on a thin mylar film, and the radioactivity of these sources were measured with the x-gamma ray coincidence counting system. It is found that the agreement between ⁵⁷Co. and ⁵⁴Mn tracer method of absolute counting for ⁵⁵Fe was good.