Measurements of photon emission probabilities from the decay of 226Ra and daughters.

X- and gamma-rays spectrometric techniques have been used to determine and improve the photon emission probability data of 226Ra. These values were obtained from 226Ra spectra in radioactive equilibrium with daughters such as 222Rn, 214Bi and 214Pb in the 50-2500 keV energy range. The efficiency calibration of the coaxial and planar Ge detectors took into account correction factors for pile-up losses, attenuation and source geometry effects, and gamma-gamma and gamma-X summation losses. XK emission probabilities were successfully resolved and determined more precisely because of the ability to de-convolute complex regions of the spectrum below 90 keV combined with spectral knowledge of the interferring Pb-XK-rays. The resulting absolute intensities of the main photon emissions of 226Ra and daughters exhibit improvements (+/-0.7% for the smallest uncertainty estimated to one standard deviation) or agree with published data.     

Precise emission probabilities of gamma-rays of 159Gd.

Measurement of emission probabilities for principal gamma-rays of 159Gd with 4pibeta(ppc)-gamma(HPGe) coincidence apparatus has given precise values as indicated by uncertainties of about 1%. Improved certainties are seen when comparing the present results with emission probabilities evaluated in Nuclear Data Sheets (Helmer, 1994, p. 72) for which the uncertainties are about 24%. The improvement resulted in precise decay scheme parameters of the nuclide.     

A source for measurement of the absolute intensities of 226Ra gamma-radiation in equilibrium with decay products.

The design and production techniques of a gamma-ray spectrometric source of 226Ra in equilibrium with its daughter decay products have been developed. The radon emanation coefficient of the source did not exceed 0.1%. The 226Ra activity in the gamma-ray spectrometric source was measured relative to that in an alpha-particle spectrometric source by comparison of the intensities of the main gamma rays using a semiconductor gamma-ray spectrometer. The total uncertainty of the activity measurement results was 0.5% for a coverage factor of k = 2.     

Emission probabilities of K X- and gamma-rays following 51Cr and 67Ga decay.

Emission probabilities of K X- and gamma-rays following the decay of 51Cr and 67Ga were precisely measured with a calibrated Si(Li) detector. The photopeak efficiency of the Si(Li) semiconductor detector was determined experimentally for about 4-400 keV energy range by using standard sources. Results of this study have been compared with the theoretical values and other available experimental results in the literature. Good agreement was observed between our results, and other available experimental results and theoretically calculated values.     

Automated measurement of 224Ra and 226Ra in water.

We present a new simple approach for automated, non-destructive measurement of the alpha-emitting radium isotopes ((223)Ra, (224)Ra, and (226)Ra) in water based on the emanation of their respective radon daughters ((219)Rn, (220)Rn, and (222)Rn). The method combines the high adsorption uptake of MnO(2) Resin for radium (K(d)=2.4 x 10(4)ml/g) over a wide pH range with the simplicity of the activity registration using a commercial radon-in-air analyzer (RAD7, DURRIDGE Company, Inc). Radium is first adsorbed onto the MnO(2) Resin by passing a water sample through the resin packed in a gas-tight glass cartridge. The same cartridge is then connected to the radon analyzer via a simple tubing system to circulate air through the resin and a drying system. The efficiency of the proposed system is determined by running standards prepared in the same manner. Our results indicate that the efficiency for (226)Ra is >22% if both (218)Po and (214)Po counts are collected. This is comparable with typical efficiencies for alpha spectrometry but with much less sample preparation. We estimate that an MDA of 0.8 pCi/L for (226)Ra may be obtained with this new approach using a 1L water sample and less than 4h of counting.     

Absolute measurements of photon emission probabilities of 169Yb.

A solution of 169Yb was absolutely standardized by the 4pi(EC,X)-gamma coincidence counting method and the result was used to obtain direct measurements of gamma-ray emission probabilities with a coaxial HPGe detector. The empirical relation proposed by (Va?o, F., Gonzalez, L., Gaeta R., Gonzalez, J.A., 1975. An empirical function which relates the slope of the Ge efficiency curves and the active volume Nucl. Instr. Meth. 123, 573) was tested using the gamma spectral response above 200 keV. The half-life of 169Yb was also measured with a 4pi gamma ionization chamber.     

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).     

Procedures for the determination of 222Rn exhalation and effective 226Ra activity in soil samples.

Two methods for measuring 222Rn exhalation and effective 226Ra in soil samples were studied. In the first determination, the method employed was based on the adsorption of radon onto activated charcoal and subsequent measurement of the activity of its daughters with an HPGe (high-purity germanium) detector. In the second, vials containing an aqueous suspension of the sample, mixed with an insoluble high efficiency mineral oil scintillation cocktail, were measured using a low-level liquid scintillation counter. Studies of optimum sampling time, efficiency in both procedures, variation of 226Ra efficiency with quenching, as well as the effect of sample amount and granulometry upon the quenching parameter, were carried out. The two methods were applied to the determination of 222Rn exhalation and effective 226Ra in environmental samples.     

On the use of 225Ra as yield tracer and Ba(Ra)SO4 microprecipitation in 226Ra determination by alpha-spectrometry.

A simple procedure for the determination of 226Ra in geological samples using alpha-spectrometry is presented. The method uses 225Ra as yield tracer, and microprecipitation of Ba(Ra)SO(4) for source preparation. Extensive studies were performed in order to determine the chemical yield of the proposed procedure with precision. The method was tested on a geological reference sample, and gave satisfactory results and high reproducibility.     

Precise measurements of the gamma-ray emission probabilities of 186Re and 188Re.

Gamma-ray emission probabilities of 186Re and 188Re are important in nuclear medicine, and have been precisely measured by 4pibeta-gamma coincidence using a live-timed two-dimensional data-acquisition system. The gamma-ray emission probabilities of the 137.2 keV for 186Re and 155.1 keV for 188Re were 0.09487+/-0.00029 and 0.15425+/-0.00072, respectively.     

Determination of half-life and photon emission probabilities of (65)Zn.

A (65) Zn radioactive solution standardized by an absolute measurement method at Laboratoire National Henri Becquerel (LNHB), was sent to Bureau International des Poids et Mesures (BIPM), in order to include the results in their database. The activity value determined at BIPM was in good agreement with that stated by LNHB (the difference was 0.3%). Additional measurements of (65) Zn activity and half-life were also carried out, by using a 4pigamma ionization chamber; the half-life value proposed by this work: 244.15 (10) days, is consistent to others reported in the literature. The spectra analysis was performed by gamma-ray spectrometry with high-purity germanium detectors, with the aim to improve the accuracy of the photon emission probabilities values of this nuclide. The determined photon emission probabilities are 0.498 for the 1115 ke V gamma-ray, 0.347 and 0.0479 for the X-rays Cu-K(alpha) and Cu-K(beta); the associated uncertainties are 0.4%, 0.9% and 1.1%, respectively.     

Sequential method for the determination of uranium, thorium and 226Ra by liquid scintillation alpha spectrometry.

A new procedure for the determination of uranium, thorium and 226Ra from the same aliquot of an aqueous sample using extractant scintillators and liquid scintillation alpha spectrometry is proposed. The procedure is designed such that the same aqueous phase can be used in all the stages, with slight modifications. The procedure is thus very simple, requiring little manipulation of the sample. Testing of the procedure was performed obtaining satisfactory results and high reproducibility.     

Comparison of methods for the analysis of 226Ra in water samples.

226Ra is one of the key nuclides among the natural radionuclides from the point of view of radiation protection. For monitoring the radiation exposure risk along the water pathway it has to be measured routinely with low detection limits. Because of the properties of 226Ra and its progenies, a number of quite different methods are possible for this purpose. This paper presents a comparison of routine techniques for the determination of 226Ra in water samples as applied by the authors.     

Standardization and photon emission probabilities in the decay of 237Np/233Pa

The activity concentration of a ²³⁷Np solution was determined by 4πα counting, by alpha particle spectroscopy with defined solid angle and by liquid scintillation counting (LSC). These methods yielded results which differ by less than 0.1% from the mean, the relative standard uncertainties being 0.23% (4πα), 0.27% (LSC) and 0.5% (solid angle). X-ray and gamma-ray emission probabilities of several transitions were measured using semiconductor detectors.     

Simultaneous determination of 226Ra, 233U and 237Np by liquid scintillation spectrometry.

A method has been developed for the simultaneous determination of 226Ra, 233U and 237Np by liquid-scintillation (LS) spectrometry. This method consists of the evaluation of the alpha-spectrum that is composed of the strongly overlapping peaks of 226Ra, 233U, 237Np, 222Rn and 218Po in the energy range of 4.60-6.00 MeV and the single 214Po peak at 7.69 MeV. The alpha-peaks are analysed by a special peak fit function that considers the deviation of the alpha-peak at the low energy side from the pure Gaussian shape. First 237Np is determined using its daughter 233Pa by analysing the beta-spectrum in the range 150-570 keV. 226Ra follows from the alpha-spectrum that is measured 6 weeks after sample preparation, i.e., 226Ra is determined from the radioactive equilibrium with its short-lived daughters 222Rn, 218Po and 214Po. Finally the 233U activity results from the fitted spectrum in the range of 4.4-4.8 MeV by subtracting the activity of 226Ra and 237Np. Knowing the exact energy position of the LS-peaks an alternative evaluation consists in the accurate deconvolution of the first three peaks that are formed by 226Ra and 233U (maximum of both at channel 700), 237Np (maxima at channels 700 and 725) and 222Rn (maximum at channel 737). In these two ways 226Ra, 233U and 237Np can be determined in mutual activity ratios of 1:50 with a relative standard deviation of less than 4% for the major activity and 9% for the minor activity.     

Inter-comparison exercise for determination of 226Ra, 232Th and 40K in soil and building material

A nationwide inter-comparison exercise for the determination of activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K in soil and building material was organized by the National Institute for Radiological Protection (NIRP), CDC, China. The primary purpose of this work was to assess the accuracy and precision of γ-spectrometry analyses. Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K were determined by gamma-ray spectrometry in accordance with established inter-comparison procedures. A total of 15 laboratories participated in this programme. All participants reported their comparison results for a total of 87 data sets for three nuclides in soil and building material. The overall measurement results of samples for inter-comparison showed a good agreement with the reference values, with nearly 87% of the participants producing acceptable results. Some influential factors in measurement comparisons are also discussed in this paper on the basis of reported results.     

Measurement of the 226Th and 222Ra half-lives

The half-lives of (226)Th and (222)Ra were measured by counting alpha-particle emissions from sources as a function of time. The (226)Th sources were prepared from an open (230)U source, capturing recoil atoms after alpha-particle decay on glass disks or even directly onto a detector. Similarly, the (222)Ra sources were obtained by self-transfer of recoil atoms from (226)Th sources. The activity measurements were performed in (nearly-)2π geometry with an ion-implanted silicon detector. The decay curves were analysed in different ways, incl. moment analysis, trying to avoid the pitfalls of bias of least-squares fits to Poisson distributed data. The observed half-life values are T(1/2)((226)Th)=30.70 (3) min and T(1/2)((222)Ra)=33.6 (4) s. Literature values show some inconsistency.     

EC comparison on the determination of 226Ra, 228Ra, 234U and 238U in water among European monitoring laboratories

In anticipation of new European requirements for monitoring radioactivity concentration in drinking water, IRMM organized an interlaboratory comparison on the determination of low levels of activity concentrations (about 10–100 mBq L^?1) of the naturally occurring radionuclides ²²⁶Ra, ²²⁸Ra, ²³⁴U and ²³⁸U in three commercially available mineral waters. Using two or three different methods with traceability to the International System of Reference (SIR), the reference values of the water samples were determined prior to the proficiency test within combined standard uncertainties of the order of 3%–10%. An overview of radiochemical separation and measurement methods used by the 45 participating laboratories are given. The results of the participants are evaluated versus the reference values. Several of the participants’ results deviate by more than a factor of two from the reference values, in particular for the radium isotopes. Such erroneous analysis results may lead to a crucial omission of remedial actions on drinking water supplies or to economic loss by an unjustified action.     

Simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by using the liquid scintillation counter-suspension gel method.

A method for the simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by liquid scintillation counting was developed. Radium and lead were separated together from the samples as Ba(Ra) x PbSO4 co-precipitate, which was centrifuged and dissolved with 0.1 M EDTA solution (pH 9.0). Radium was separated as Ba(Ra)SO4 co-precipitate by adding ammonium sulfate and adjusting the pH of the solution to 4.2. Lead remaining in the solution was separated as PbSO4 precipitate by adding 9 M sulfuric acid. These Ba(Ra)SO4 and PbSO4 precipitates were purified with EDTA solution and used for measurement. To save time and to make counting samples simpler, direct counting of Ba(Ra)SO4 and PbSO4 precipitates instead of the phosphoric acid fusion method was attempted. Ba(Ra)SO4 and PbSO4 precipitates were suspended in the scintillation gel, and measured. Two liquid scintillation cocktails, Instagel XF and UltimaGold AB were used to prepare the counting samples. A mixture of water (40%), Instagel XF (40%) and UltimaGold AB (20%) formed a stable gel. Activities of 226Ra and 210Pb were calculated from the alpha spectrum of Ba(Ra)SO4 and beta spectrum of PbSO4, respectively. The long-term stability of the suspension gel was good. The analytical results of 226Ra and 210Pb in spiked groundwater samples were in good agreement with the known concentrations of 226Ra and 210Pb. The analytical values of 226Ra and 210Pb in the soil reference samples were within 11.5 and 1.6% of the relative error from the reference values, respectively.