Standartization of (166m)Ho in a coincidence system by software and determination of its gamma emission probabilities

Abstract

This works presents a new standardization of the radionuclide (166m)Ho that was carried out at Nuclear Metrology Laboratory (LMN) at IPEN. (166m)Ho decays with 1133 years of half-life by beta emission followed by a cascade of gamma-rays in a range of 73 to 1427 keV, and these characteristics makes it a good secondary standard to the calibration of gamma spectrometers. Previously calibrated with a standard 4 Pi(PC)Beta-Gama coincidence system, the same samples were now measured in the Software Coincidence System (SCS), where the data analyses can be done after the measurements, using a software developed at LMN as well. The SCS is composed of a 4Pi geometry proportional counter operated at 0.1MPa coupled to one NaI(Tl) crystal, positioned above the PC counter, and to a HPGe detector, positioned below the PC counter. The signals from all detectors are digitalized and their pulses height and time of occurrence are recorded on computer files. After the standardization, the emission probabilities per decay of the most intense gamma-rays in the (166m)Ho decay were determined by means of a HPGe spectrometer system, which was calibrated with standard sources previously calibrated in the 4 Pi(PC)Beta-Gama coincidence system, and the results were compared with the literature. All the uncertainties were treated by the covariance analysis method.