Evaluation of 133Xe and 133Xem decay data

This paper presents the decay data evaluation of ¹³³Xe and ¹³³Xe^m, which includes the most recent available data, such as half-life results and gamma-ray intensities that have not been considered in previous evaluations. The adopted internal conversion coefficients (ICC) have been calculated using the ‘Frozen Orbital’ approximation and are compared here to recent measured values. Recent Q-value tabulations, recommended gamma-ray energies for calibrations, as well as new evaluated gamma-ray intensities for the 81- and 233-keV lines (37.0 (3)% and 10.16 (13)%, respectively) are also presented in this evaluation. Atomic radiation emission probabilities (X-ray and Auger electron) associated with nuclear radiations have been deduced and also included in this work.     

Evaluation of 233Pa decay data.

An evaluation of the complete scheme and data for (233)Pa decay, including results of the recent measurements, is presented. Several data evaluation procedures were used in the analysis of the half-life data. The half-life has been determined to be 26.971+/-0.013 days. All the gamma-ray emission probabilities ever published have been examined, and the gamma-ray emission probability for the reference 312-keV gamma line is recommended as 38.35+/-0.28%. The calculated internal conversion coefficients and their uncertainties have been used to obtain the complete decay intensity balance. Other decay characteristics have been calculated using the ENSDF analysis program. Finally, a new (233)Pa decay scheme has been built.     

A simple method for the absolute determination of uranium enrichment by high-resolution gamma spectrometry.

A simple method for the determination of uranium enrichment using high-resolution gamma spectrometry is presented in this paper. The method relies solely on the gamma-ray emission probabilities of 235U and 234mPa, and an iterative procedure for the least squares fit of a polynomial to a set of experimentally determined data. To ensure the reliability of the 234mPa gamma-ray emission probabilities employed, a new determination of these probabilities was carried out using a combination of gamma spectrometry and Cerenkov counting of a purified 234Th solution. Using these new data, a maximum difference of approximately 5% has been found between the experimental and declared uranium enrichment in a set of solid and liquid samples containing uranium compounds.     

Determination of gamma-ray emission probabilities per decay of Ga-68

The measurement of the gamma-ray emission probabilities per decay of 1077 keV of ⁶⁸Ga is presented. The standardization system consists of a gas-flow proportional counter in 4π geometry coupled to an HPGe detector for the gamma-ray detection. The gamma-ray emission probabilities per decay were measured in an HPGe gamma-ray spectrometer. The weaker gamma-ray intensities of ⁶⁸Ga were measured in a relative way, making use of an uncalibrated ampoule of ⁶⁸Ge–⁶⁸Ga in radioactive equilibrium, and considering the absolute result from the 1077 keV gamma-ray.     

Evaluation the decay data of 153Gd

¹⁵³Gd decays to the excited states of ¹⁵³Eu through the electron capture decay mode. The evaluation of the complete decay scheme and data of ¹⁵³Gd including the recent new measurements are presented in this report. The limitation of relative statistical weight method (LRSW) was applied to average numbers throughout the evaluation. The uncertainty assigned to the average value was always greater than or equal to the smallest uncertainty of the values used to calculate the average. The half-life is determined to be 239.47±0.07 days. All known measured γ-ray relative emission probabilities have been examined. And the γ-ray emission probability of the reference γ line of 97.431 keV is recommended to be 29.5±0.5%. The calculated internal conversion coefficients and their uncertainties have been used to obtain the complete decay intensity balance. The other decay characteristics are calculated using the ENSDF analysis program. Finally the new ¹⁵³Gd decay scheme was re-built.     

Determination of the emission probabilities of the principal gamma-rays for 134Cs to a high precision.

While multi-gamma-ray emitting nuclides such as 75Se, 134Cs and 152Eu have reasonably well-defined decay scheme, some inconsistencies still remain. Detailed evaluations and weighted-mean analyses result in the recommendation of gamma-ray emission probabilities with small uncertainties, although significant deviations exist in the measured values. Therefore, the gamma-ray emission probabilities of 134Cs have been measured to a high precision after an extremely accurate calibration of detection efficiency. The resulting data agree extremely well with the evaluated values in IAEA-TECDOC-619 (IAEA, X-ray and gamma-ray standards for detector calibration, IAEA-TECDOC-619, IAEA, Vienna, 1991).     

Disintegration rate,gamma-ray emission probabilities and metastable half-life measurements of 67Ga

The procedure for determining the ⁶⁷Ga disintegration rate by a primary method is described. The proposed triple 4πβ–γ coincidence system consists of a thin window gas-flow 4π proportional counter (PC) coupled to a NaI(Tl) scintillator and a HPGe crystal. Independent pulse height and occurrence time information is provided for the three detector outputs by means of a Software Coincidence System. Separate spectrometry measurements with a n-type reversed electrode coaxial Ge detector (REGe) were performed for obtaining gamma-ray emission probabilities per decay. Accurate values of disintegration rate, gamma-ray emission probabilities and the metastable half-life were achieved.     

Photon emission probabilities and decay percentages in 185Os and 186Re decays

The K x-rays and gamma-ray intensities in the decays of ¹⁸⁵Os and ¹⁸⁶Re have been measured precisely using three well-calibrated HPGe detectors. These intensity results have been used to evaluate photon emission probabilities and β⁻ and EC percentages feeding to different levels of daughter nuclei populated in the decays of ¹⁸⁵Os and ¹⁸⁶Re. The intensities of various components of K x-rays in the decay of ¹⁸⁵Os are being reported for the first time.     

Standardization and decay data of 169Yb

The specific activity of a ¹⁶⁹Yb solution was determined at the PTB by 4πEC-γ-coincidence measurements and by 4πγ-counting with a relative standard uncertainty of 0.1%. Based on a simplified decay scheme with 21 gamma transitions, relative gamma-ray emission probabilities measured at the PTB and data from other authors, a consistent set of decay data for the decay of ¹⁶⁹Yb was calculated. The absolute emission probability of the 198 keV gamma rays was determined to be (0.3591±0.0013) photons per disintegration.     

Emission probabilities of γ-rays associated with the decay of 229Th and its daughters

As an aid in the quantitative assay of ²²⁹Th by means of γ-ray spectrometry, we have made precise measurements of the emission probabilities of several γ rays from the decay of ²²⁹Th and seven from the decay of its daughters in the energy range from 40 to 808 keV. The decay-rate calibration of an isotopically separated source was obtained from the total α-emission rate as determined with an Au-Si surface-barrier detector gated to accept only the α particles from ²²⁹Th. The geometry of this detector was measured with a ²⁴⁹Cf source calibrated on a low-geometry proportional counter. The γ-ray emission rates were measured on calibrated Ge detectors for this calibrated ²²⁹Th source. The relative γ intensities were also measured for a chemically separated ²²⁹Th source, which allowed an assessment of the contributions from the daughter activities. The percentage uncertainties in the measured γ-emission probabilities range from 1.3 to 4.0%. Our results differ significantly from those of two recently published measurements. A comparison of these three sets of results is given.     

Evaluation of 225Ac decay data.

Evaluation of the complete decay scheme and data for (225)Ac including new measurements are presented in this report; literature data available up to March 2006 are included. The half-life is determined to be 10.0+/-0.1 days. All known measured gamma-ray relative intensities have been examined; the gamma-ray emission probability of the reference gamma-ray line of 150.04 keV is recommended to be 0.693+/-0.012%. The calculated internal conversion coefficients and their uncertainties have been used to obtain the complete decay intensity balance. The other decay characteristics are calculated using the ENSDF analysis program. Finally, the new decay scheme for (225)Ac is presented.     

Alpha-particle emission probabilities for 239Pu and 240Pu

Tabulated emission probabilities [e.g. IAEA (1986)] for the α-particle decay of the nuclide ²³⁹Pu appear to require revision in the light of measurements reported here. Although the sum of the probabilities of the two most intense lines, α₀ and α₁₃, has been listed as ca 88% since the work of Baranov et al. (1963). However, the individual probabilities measured for these lines were 70.73 and 17.56%, and these values differ significantly from those appearing in reference tables [e.g. IAEA (1986)]. In earlier measurements, the incomplete resolution of two peaks only ∼13 keV apart, or the effects of conversion electrons in producting energy-summing effects may have given rise to systematic errors depending on the type of apparatus used.Measurements have been carried out under low geometry with a very thin source of purified ²³⁹Pu and, for comparison, another of ²⁴⁰Pu. Emission probabilities were obtained from the energy spectra using a computer programme to find a best-fit to the peaks with analytical expressions. The programme is based on an iterative Simplex procedure to find a minimum of Chi-squared. A careful evaluation of the variances provides estimates of the relative uncertainty (at the 2σ level) of each emission probability which are, in all cases, <2% of the measured values.     

Alpha-particle emission probabilities in the decay of 238U

²³⁸U decays by alpha-particle emission to ²³⁴Th. No direct measurements of alpha-particle emission probabilities (P_α) of this nuclide have been reported since 1961, and recommended values for P_α have remained unchanged for years, until recent evaluations suggested new values. This work presents the results of new measurements made with Si detectors and sources of natural uranium. The results obtained for the analysis of twenty spectra are: P_α0=0.7754±0.0050, P_α50=0.2233±0.0050 and P_α163=0.0013±0.0003.     

Determination of precise gamma-ray emission probabilities for 88Rb.

Precise gamma-ray emission probabilities of 88Rb have been measured by 4pi beta-gamma coincidence using a live-timed two-dimensional data-acquisition system. The absolute emission probabilities of the 898.1, 1836.1 and 2677.9 keV gamma rays were determined from the absolute gamma-ray intensities and the disintegration rates to be 14.68+/-0.13%, 22.73+/-0.15% and 2.123+/-0.021%, respectively. The relative intensities were measured for the weak gamma rays by a gamma-ray spectrometer, and the 88Rb decay scheme was determined from these results.     

Activity standardization and nuclear decay data of 109Cd.

The activity of a (109)Cd solution has been accurately determined without using (109)Cd nuclear decay data such as emission probabilities. An ampoule containing this calibrated (109)Cd solution was sent to the Bureau International des Poids et Mesures to include the activity result in the database of the International Reference System (SIR). The emission rate of conversion electrons was measured by means of pressurized proportional counters as well as by a liquid scintillation spectrometer. The combination of the results with the photon emission rate measured with the aid of gamma-ray spectrometers yields the activity concentration. The measurement results were also used to deduce emission probabilities with high accuracy. For the 88 keV transition, a photon emission probability of p(gamma)=0.03663(33) and a total internal conversion coefficient of alpha(t)=26.30(25) were determined.     

Measurement of the gamma-ray probability per decay of 42K.

In the present work, the gamma-ray emission probabilities per decay of 42K transitions have been measured. The activity measurement was carried out in a 4pi (PC)beta-gamma coincidence system. The gamma-ray measurements were performed in a HPGe system. All the uncertainties involved were treated rigorously, by means of covariance analysis. The value of the 1524 keV gamma-ray intensity per decay of 42K obtained in the present work was (0.1813+/-0.0014). This result is compared to the data from other authors.     

Determination of the absolute alpha-particle emission probabilities of 237Np

In the framework of the EUROMET project No. 416, decay scheme data of ²³⁷Np were measured by α-particle spectrometry. Emission probabilities of α-particles and γ-rays were determined in the past at IRMM. After improvements of the detector system and the electron bending magnet the α-particle measurements have been repeated. As a result, the absolute emission probabilities of 20 α-particle transitions were obtained with a significant lower uncertainty. Among those transitions already known, five new were found.     

Analysis of the 237Np-233Pa photon spectrum using the full response function method.

A study has been made of X- and gamma-ray emission from 237Np in equilibrium with 233Pa using the full response function method. This analysis process is characterised by photon spectrometry in which the entire spectrum is modelled in a pseudo-empirical way by means of elementary functions describing the total absorption and escape peaks, the Compton diffusion internal and external to the detector and the peaks resulting from detection of internal conversion electrons. This method has been applied to determine the L X-, K X- and gamma-rays emission probabilities in 237Np and 233Pa decay studies.     

Decay scheme study of 126Sn and 126Sb

To study the decay scheme of ¹²⁶Sn, two samples of a purified solution were measured by gamma-ray spectrometry and the relative photon emission intensities were determined. The ¹²⁶Sb^m isomeric branching ratio was derived to be 18.6 (6) %. The maximum beta energy of the ¹²⁶Sn decay was checked by liquid scintillation. The Kβ/Kα intensity ratio of Sb was determined being 0.226 (11). These new experimental results were used to re-examine the whole decay scheme of ¹²⁶Sn and its daughters.     

Extension of the TDCR model to compute counting efficiencies for radionuclides with complex decay schemes

The triple-to-double coincidence ratio (TDCR) method is frequently used to measure the activity of radionuclides decaying by pure β emission or electron capture (EC). Some radionuclides with more complex decays have also been studied, but accurate calculations of decay branches which are accompanied by many coincident γ transitions have not yet been investigated.This paper describes recent extensions of the model to make efficiency computations for more complex decay schemes possible. In particular, the MICELLE2 program that applies a stochastic approach of the free parameter model was extended. With an improved code, efficiencies for β⁻, β⁺ and EC branches with up to seven coincident γ transitions can be calculated. Moreover, a new parametrization for the computation of electron stopping powers has been implemented to compute the ionization quenching function of 10 commercial scintillation cocktails.In order to demonstrate the capabilities of the TDCR method, the following radionuclides are discussed: ^166mHo (complex β⁻/γ), ⁵⁹Fe (complex β⁻/γ), ⁶⁴Cu (β⁻, β⁺, EC and EC/γ) and ²²⁹Th in equilibrium with its progenies (decay chain with many α, β and complex β⁻/γ transitions).