Abstract
To measure the activities of Fe59 and Fe55 in a composite sample a convenient differential counting method have been studied.
Calculating the photo-peak area of 1.10 and 1.29 MeV of gamma rays from Fe59, the minimum countable amount of 3.0×10-4 m. c. c. was obtained without any interference of other activities. The photo-peak was measured by a NaI (TI) crystal scintillation counter and a 256 pulse height analyser.
To measure the Fe55 activity two methods have been tried.
In the first method using a Geiger-Müller counter activities of K-X ray from Fe55 and beta and gamma rays from Fe59 was measured. Subtracting the contribution of Fe59 estimated by the suitable correction rate of beta and gamma rays from Fe59, the amount of Fe55 was deduced. As the counting efficiency of K-X ray is very low, the minimum detectable amount of Fe55 was about 5×10-2 m. c. c.
Instead of Geiger-Müller counter an 1 mm thick NaI (TI) crystal scintillation counter and a 256 pulse height analyser were used in the second method. A typical spectrum of K-X ray was obtained. Subtracting the background and the interference of higher energies the amount of Fe55 was deduced from the photo-peak area of this spectrum. The minimum detectable amount of Fe55 in the second method was found to be less than 1/10 of the minimum detectable amount in the first method.
