Standardization of 65Zn by sum-peak method.

A commercial solution of (65)Zn was standardized by the sum peak-method using a planar HPGe detector. The activity results were compared with measurements made with a well type 4πγ ionization chamber, which is traceable to BIPM.RI (II)-K2.Zn-65 key-comparison performed in 2002. The sum-peak value was 42.79 kBq/g and the ionization chamber value was 42.74 kBq/g both at the reference date. The uncertainty obtained in the sum peak standardization was 0.25% (k=1), and in the ionization chamber was 0.85% (k=1). The results showed that sum-peak method can be used in (65)Zn standardization and this method is easier, simpler and more practical than others methods.

An approach based on the SIR measurement model for determining the ionization chamber efficiency curves, and a study of 65Zn and 201Tl photon emission intensities.

The measurement model used to determine ionization chamber efficiency curves accounts from the outset for impurity corrections and beta spectrum shapes. The curves are represented by exponentials of polynomials whose coefficients are adjusted using non-linear least-squares minimization. The curves are validated by comparing with SIR key comparison reference values (KCRVs) and other published curves. The associated covariance matrix is also evaluated. Deviations from model predictions for 65Zn and 201Tl using recommended nuclear data are studied.

Standardisation of 54Mn and 65Zn using a software coincidence counting system.

The activities of 54Mn and 65Zn have been determined by 4pi(PC)-gamma coincidence counting, with efficiency variation performed by the conventional method of altering the self-absorption in the sources as well as by the computer discrimination method. The standardisation of 65Zn presents some complications requiring optimisation of the gamma-ray energy window settings to achieve a linear efficiency-extrapolation curve. Determination of these optimal settings by the conventional coincidence method is a tedious task. These difficulties have been reduced by the utilisation of a software coincidence counting system that records time and amplitude information of individual pulses from coincidence measurements, where the coincidence parameters are set after the data collection process has completed, facilitating multiple data evaluations on a single data set. The optimal gamma-ray energy window settings for the 65Zn standardisation were derived from the results of the 54Mn standardisation, as well as from studies of the 65Zn data itself. The setting of the PC channel thresholds for K and both (K+L) electrons is also discussed. The results are compared with those attained using conventional coincidence counting.

Standardization and nuclear decay data of 65Zn.

Standardization by means of 4pibeta-gamma coincidence counting was applied to calibrate a 65Zn solution within the scope of EUROMET project no. 721. The activity result was combined with gamma-ray spectrometry measurements to investigate the photon emission probabilities. The half-life of 65Zn was measured with improved accuracy by means of 4pi ionization chamber measuring systems that were also used for secondary activity determination. In addition, we tested a new secondary standardization procedure by means of liquid scintillation counting.

Experimental verification of the half-life of 65Zn.

The half-life of 65Zn was determined experimentally and compared with literature values. Two ampoules of a 65Zn solution were measured at regular intervals in two ionisation chambers over a period corresponding to nearly two half-lives. The result of 243.8+/-0.3 days is in agreement with the value of 244.0+/-0.2 days obtained by De Roost et al. (Z. Phys. 250 (1975) 395) at the same institute (previously called CBNM) in 1972. Moreover, this half-life is supported by most of the other measurements reported in the literature.

Standardization of 65Zn.

Two absolute methods were used for standardizing the 65Zn solution received within the framework of the 2002-2003 full-scale BIPM comparison. The first method was the 4piPC-gamma-coincidence with efficiency extrapolation. The measurement conditions were adjusted so that the slope of the extrapolation curve was absent, which ensured that the measurement result did not depend on the positron branch intensity. When using the second method, the KX-gamma-coincidence counting with two NaI(Tl) scintillation crystals of different thicknesses, extrapolation was not needed, but a correction for the positron branch was necessary. It is shown that the 4piPC-gamma-coincidence method has a significantly larger uncertainty, and it is necessary to pay attention to the uncertainty component connected with setting the gamma-channel mode, which is characteristic for 65Zn only.

Standardization of 65Zn by 4piPC-gamma coincidence counting method with efficiency extrapolation.

A 65Zn solution was standardized by the 4piPC-gamma efficiency-extrapolation coincidence counting method. Theoretical aspects of coincidence equations, efficiency equations and linearity conditions are reviewed. Experimental measurements were performed for two low level discrimination thresholds for the PC channel (counting K+L or K X-rays or Auger electrons from EC decay) and for three different settings of the gamma window. Requirements on gamma channel set-up for linear extrapolation were established by using a Pb absorber or by proper gamma window setting. The measured activity values were discussed and found in good agreement with those obtained with a calibrated ionization chamber.