Calibration of ¹³³Ba by Sum-Peak Method

A calibration laboratory should have several methods of measurement in order to ensure robustness on the values applied. The National Laboratory for Metrology of Ionizing Radiation, (LNMRI IRD), provides gamma sources of radionuclide in various geometries and standardized in activity with reduced uncertainties. Some absolute and relative methods of calibrations could be used routinely. Relative methods require standards to determine the activity of sample to be calibrated, while the absolute methods do not need, simply make the counting and the calculation of the activity is obtained directly. The great advantage of calibrations of radionuclides by absolute method is the accuracy and low uncertainties. ¹³³Ba is a radionuclide enough used in research laboratories and calibration of detectors for environmental analysis and, according to the scheme, it decays 100% by electron capture and emits about 14 energy gamma and X-ray lines, forming several coincidences. However, the classical methods of absolute measurement, as coincidence 4 πβ-γ have difficulty to calibrate ¹³³Ba due to its complex decay scheme. The sum-peak method, developed by Brickman, could allow this calibration. It is used for radionuclide calibration that emits at least two photons in coincidence. Therefore, it was developed a methodology that combines gamma spectrometry technique with sum-peak method to standardize ¹³³Ba samples. Activity results obtained proved compatible, with uncertainties of less than 1%, and, when compared with other methods of calibration, sum-peak demonstrated the feasibility of this methodology, particularly, for simplicity and effectiveness. (author)