Efficiency Tracing Method Research Articles

Photon emission probabilities of 176Lu

An aqueous solution containing dissolved lutetium nitrate with a natural isotopic composition was measured by means of gamma-ray spectrometry to determine emission probabilities of photons which are emitted as a consequence of the decay of the primordial isotope 176Lu. The geometry and matrix of the sample were taken into account in terms of efficiency transfer factors computed with the aid of the upgraded Monte Carlo simulation software GESPECOR. A combination of these results, with the activity determination via liquid scintillation counting using the CIEMAT/NIST efficiency tracing method, yields absolute values of PX(54.61keV)=0.095(4), PX(55.79keV)=0.168(5), Pγ(88.36keV)=0.149(5), Pγ(201.83keV)=0.777(9) and Pγ(306.84keV)=0.929(9). In addition, the upper limit of the probability for a potential electron-capture decay of 176Lu was improved using additional high resolution gamma-ray spectra taken with a planar HPGe detector.

Activity determination and nuclear decay data of 177Lu

The activity concentration of a 177Lu solution was measured within the scope of the international comparison CCRI(II)-K2.Lu-177, starting in 2009. At PTB, the solution was measured by means of 4πβ–γ coincidence counting using a proportional counter and a NaI detector. In addition, liquid scintillation counting using the CIEMAT/NIST efficiency tracing method as well as the triple-to-double coincidence ratio (TDCR) method was applied. The efficiency computation for the TDCR method was realized by means of the MICELLE2 program, applying a stochastic model for the computation of electron emission spectra.The activity concentrations derived from the three methods were found to be in good agreement and the relative standard uncertainty of the combined result was found to be 0.19%.At PTB, the combined result was used to calibrate a 4π ionization chamber for future calibrations of this isotope which is frequently used in nuclear medicine.In addition, activity standardizations were combined with gamma-ray spectrometry to determine photon emission probabilities. To this end, the comparison solution as well as another 177Lu solution was used. The results are in good agreement with previous measurements at PTB but show a considerable discrepancy to recently published values from Deepa et al. (2011).The decay curve of a third solution was followed by liquid scintillation counting for about 66 days to determine the half-life of 177Lu, which was found to be T1/2=6.639(9)d.

CCRI(II) activity comparison of 241Pu: CCRI(II)-K2.Pu-241

In 2010, seven laboratories took part in the CCRI(II) key comparison of activity concentration measurements of 241Pu, CCRI(II)-K2.Pu-241, using seven different methods. The spread of all results except one is 4 × 10−2 in relative terms. The results based on the CIEMAT/NIST efficiency tracing method are shown to be dependent on the beta spectrum shape selected and further work is proposed.The key comparison reference value has been determined as the arithmetic mean of six independent results based on four different methods. The results of the comparison have been analyzed with respect to the key comparison reference value. The degrees of equivalence relative to the key comparison reference value have been approved by the CCRI(II) and are published in the BIPM key comparison database.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Standardization of 131I: Implementation of CIEMAT/NIST method at BARC, India

The CIEMAT/NIST efficiency tracing method using 3H standard was implemented at Radiation Safety Systems Division, Bhabha Atomic Research Centre (BARC) for the standardization of 131I radioactive solution. Measurements were also carried out using the 4 π β– γ coincidence counting system maintained as a primary standard at the laboratory. The implementation of the CIEMAT/NIST method was verified by comparing the activity concentration obtained in the laboratory with that of the average value of the APMP intercomparison ( Yunoki et al., in progress, (APMP.RI(II)-K2.I-131)). The results obtained by the laboratory is linked to the CIPM Key Comparison Reference Value (KCRV) through the equivalent activity value of National Metrology Institute of Japan (NMIJ) ( Yunoki et al., in progress, (APMP.RI(II)-K2.I-131)), which was the pilot laboratory for the intercomparison. The procedure employed to standardize 131I by the CIEMAT/NIST efficiency tracing technique is presented. The activity concentrations obtained have been normalized with the activity concentration measured by NMIJ to maintain confidentiality of results until the Draft-A report is accepted by all participants. The normalized activity concentrations obtained with the CIEMAT/NIST method was 0.9985±0.0035 kBq/g and using 4 π β– γ coincidence counting method was 0.9909±0.0046 kBq/g as on 20 March 2009, 0 h UTC. The normalized activity concentration measured by the NMIJ was 1±0.0024 kBq/g. The normalized average of the activity concentrations of all the participating laboratories was 1.004±0.028 kBq/g. The results obtained in the laboratory are comparable with the other international standards within the uncertainty limits.

Application of a free parameter model to plastic scintillation samples

In liquid scintillation (LS) counting, the CIEMAT/NIST efficiency tracing method and the triple-to-double coincidence ratio (TDCR) method have proved their worth for reliable activity measurements of a number of radionuclides. In this paper, an extended approach to apply a free-parameter model to samples containing a mixture of solid plastic scintillation microspheres and radioactive aqueous solutions is presented.Several beta-emitting radionuclides were measured in a TDCR system at PTB. For the application of the free parameter model, the energy loss in the aqueous phase must be taken into account, since this portion of the particle energy does not contribute to the creation of scintillation light. The energy deposit in the aqueous phase is determined by means of Monte Carlo calculations applying the PENELOPE software package. To this end, great efforts were made to model the geometry of the samples. Finally, a new geometry parameter was defined, which was determined by means of a tracer radionuclide with known activity. This makes the analysis of experimental TDCR data of other radionuclides possible. The deviations between the determined activity concentrations and reference values were found to be lower than 3%.The outcome of this research work is also important for a better understanding of liquid scintillation counting. In particular the influence of (inverse) micelles, i.e. the aqueous spaces embedded in the organic scintillation cocktail, can be investigated. The new approach makes clear that it is important to take the energy loss in the aqueous phase into account. In particular for radionuclides emitting low-energy electrons (e.g. M-Auger electrons from 125I), this effect can be very important.

Determining the activity of 241Pu by liquid scintillation counting

Liquid scintillation counting (LSC) is one of the most widely used methods for determining the activity of 241Pu. One of the main challenges of this counting method is the efficiency calibration of the system for the low beta energies of 241Pu (E max = 20.8 keV). In this paper we compare the two most frequently used methods, the CIEMAT/NIST efficiency tracing (CNET) method and the experimental quench correction curve method. Both methods proved to be reliable, and agree within their uncertainties, for the expected quenching conditions of the sources.

Beta shape-factor function and activity determination of 241Pu

The Physikalisch-Technische Bundesanstalt (PTB) investigated the low-energy beta emitter (241)Pu within the scope of an international key comparison on the activity concentration of the same solution. The activity concentration was measured by means of liquid scintillation counters with two and three photomultiplier tubes (PMT). The counting efficiencies were determined with two established techniques, which are based on a free parameter model. The free parameter is determined via (3)H-efficiency tracing in systems with two PMTs, or it is derived from the triple-to-double coincidence ratio (TDCR) in a system with three PMTs. Both methods require an accurate computation of the beta emission spectrum of the first-forbidden (non-unique) transition. In this work, the experimental outcome of a recent measurement from Loidl et al. (2010) with cryogenic magnetic calorimeters was used to determine a shape-factor function. The computed beta spectrum is in good agreement with the measured data when the shape-factor function C(W)=1-1.9582W+0.96078 W(2) and an end-point energy E(β,max)=21.6 keV are used. The activity concentrations determined with the two methods agree well when using the new shape-factor function, whereas a considerable discrepancy is found when assuming C(W)=1, as for an allowed beta transition. Consequently, the difference between the efficiency tracing method and the TDCR method, as observed by other researchers, could be resolved.

Activity determination and nuclear decay data of 113mCd

The radionuclide (113m)Cd was extracted from a Cd component, which has been irradiated in a research reactor during its routine operation. A validated separation procedure was then used to obtain a (113m)Cd solution of high radiochemical purity. The solution was measured by means of liquid scintillation counting for activity determination. To this end, the CIEMAT/NIST efficiency tracing method as well as the triple-to-double coincidence (TDCR) counting technique were used. Measurements in a low-background gamma-ray spectrometer were applied to identify any potential photon-emitting impurities and to measure the 263.7 keV photons from the isomer transition. A gamma emission probability of 0.01839(29)% was determined for this line. The liquid scintillation measurements were also used to evaluate the half-life of (113m)Cd. The decay was followed for about 11 months and a half-life T(1/2)=13.97(13) years was obtained.

Study of the influence of the liquid scintillator in the Compton efficiency tracing method

The principle of the Compton source efficiency tracing method (CET) in liquid scintillation counting (LSC) is to use, as a tracer, a Compton electron source temporarily created inside the source being measured. The tracer source and the source to measure have thus exactly the same chemical composition. A main advantage anticipated for this measurement method is its low sensitivity to the kB factor and insensitivity to the chemical composition and quenching of the source, which would obviate the necessity to develop a reference liquid scintillator cocktail in the framework of an international reference system for the measurement of pure-beta emitters by LSC. We took the opportunity of a tritiated water international activity measurement in comparison to prepare LS sources using various commercial liquid scintillator cocktails. Tritium is assumed to be a good candidate for testing the LSC activity measurement method, as the detection efficiency is rather low and the effect of the ionization quenching parameter, kB, on the detection efficiency calculation by the TDCR method is known to be important. The sources were measured using a TDCR counter equipped with a Compton spectrometer in order to apply the CET method. The measurements are analyzed using both the TDCR method and CET method in order to deduce the optimal calculation parameters. The detection efficiency range covered by these experiments is from 0.4 to 0.6, allowing a good test of the validity of the physical assumptions included in the calculation model. The paper will conclude on the advantages and drawbacks of using this CET method in the framework of an international reference system for low-energy pure-beta radionuclides.

Determination of 93Zr decay scheme and half-life

This study describes a new determination of the decay scheme and half-life of 93Zr. A pure 93Zr solution was obtained after chemical separation from the dissolution of an irradiated zircaloy sample. The concentration of 93Zr in the solution was measured by mass spectrometry, with an isotopic dilution technique. The activity of the solution was measured by liquid scintillation counting, using an efficiency tracing method. The measurement of the activity concentration of 93Nb m by X-ray spectrometry, allowed the determination of the 93Zr decay scheme and the calculation of the 93Zr detection efficiency. This leads to the calculation of the decay probability of 93Zr toward 93Nb m of (0.73±0.06) and to a half-life of 93Zr of (1.64±0.06)×10 6 years. These values are discussed in comparison with the evaluated values available in the literature.

The Compton source efficiency tracing method in liquid scintillation counting: A new standardization method using a TDCR counter with a Compton spectrometer

We describe a new standardization method in liquid scintillation counting based on the use of a temporary virtual tracer source created inside the scintillator by Compton interaction. The Compton tracer source is measured by the triple coincidence liquid scintillation counter after selection of the Compton events by a gamma-ray detector. The paper describes the principle of the method, the experimental setup and presents the results obtained by this method for the standardization of a 3H solution. These results are compared with those obtained using the classical triple to double coincidence ratio method. Possible application of this new method for international comparisons is addressed.

A simple counting technique for measuring mixtures of two pure β-emitting radionuclides

A simple counting technique to measure mixtures of two pure β-emitting radionuclides is described. The method is based on elements of two liquid scintillation techniques that are widely used to measure single-radionuclide solutions, namely the triple-to-double coincidence ratio (TDCR) efficiency calculation technique and the CIEMAT/NIST efficiency tracing method. Double- and triple-coincidence count rates, together with the figure-of-merit P determined from an external tracer, are used to extract the component activities of a source. A simulation was used to gauge the effect of counting statistics on the method's ability to extract a mixture composition under normal counting conditions and to validate derived uncertainty formulas based on counting statistics. The method is demonstrated experimentally for various mixture combinations of 14C and 63Ni. It is shown that the accuracy of the technique can be enhanced by improving the determination of the figure-of-merit.

Implementation of CIEMAT/NIST LSC efficiency tracing method in KRISS: 204T1 standardization

The CIEMAT/NIST efficiency tracing method has been widely used for radionuclide standardization. The method consists of the theoretical calculations of counting efficiencies and the experimental data obtained from a commercially available double photomultiplier detector. We have recently implemented the technique using 3H as a tracer. Our implementation of the method was validated by participating into an international comparison of activity measurements of a solution of 204T1. We report in this paper the procedure employed to implement the technique and compare our measurement result of 204T1 activity with that of the international comparison.

Primary standardisation of 204Tl using the efficiency tracing method

The electron-capture and β −-emitting radionuclide 204Tl has been known from previous experience to show discrepancies between different methods of standardisation. Source preparation is also difficult due to the complex chemistry of thallium. The Bureau International des Poids et Mesures (BIPM) intercomparison held in 1997, showed discrepancies of up to 10% between measurements of solid sources and liquid scintillation methods. These problems have been the subject of a BIPM CCRI(II) working group since 1999. This paper presents the results from a primary standardisation of a 204Tl solution using 4π β− γ coincidence counting and liquid scintillation counting. The tracer technique was used for the 4 πβ − γ coincidence counting, where 204Tl was traced with 134Cs and 60Co. The extrapolation to 100% β-efficiency was performed by three different approaches: foiling, adding carrier and measuring sources of different initial masses. The results showed that tracing with 60Co and using external foiling gave the same result as obtained by liquid scintillation counting. A comparison of the results achieved by the different methods of measurement, tracers and methods for extrapolation is presented and discussed in this paper.

Determination of Radon Concentration in Water Using Liquid Scintillation Counter

It has been confirmed that, in the measurement of radon-in-water using liquid scintillation counting, the direct method is preferred to the extraction method, since the former is simple technique. With a counting time of 60 minutes, the minimum detectable radon concentration by the extraction method and the direct method were found to be 0.03 Bq/kg and 1 Bq/kg, respectively. The minimum detectable radon concentration of 1 Bq/kg attained by the direct method is sufficient to check the radon concentration in drinking water below the Maximum Contaminant Level (11.1 Bq/L) proposed by the U. S. Environmental Protection Agency. The total net counting rates were estimated by the zero level extrapolating method. The optimized window values of the 3 efficiency tracing points were 50 keV - ∞, 75 keV - ∞ and 100 keV - ∞. The efficiency tracing method has been proved useful with LSCs that are currently available in Japan.

Construction and implementation of the NIST triple-to-double coincidence ratio (TDCR) spectrometer

A description of the triple-to-double coincidence ratio (TDCR) spectrometer recently constructed at NIST and results of tests to assess its operating characteristics are presented. Measured activities for previously calibrated solutions of 3H (tritiated water) and 63Ni agreed with certified activity values to within 0.04% and 0.2%, respectively. Agreement between measurements of solutions containing 90Y using the TDCR and the CIEMAT/NIST efficiency tracing method was achieved to within 0.7% and within the respective experimental uncertainties. A difference of 5.3% was observed between TDCR measurements and the certified massic activity value for a calibrated solution containing 54Mn, but because of the large uncertainty on the TDCR result (3.6% relative standard uncertainty), the values agree to within the experimental uncertainties. Agreement to within experimental uncertainties (2%) for 103Pd was achieved with the TDCR and CIEMAT/NIST methods, but not between TDCR and isothermal calorimetric measurements. TDCR results for a 204Tl solution were in excellent agreement (maximum difference of 0.2% with any other method, with combined standard uncertainty of 0.45% on TDCR result) with results obtained using three other methods.

Standardisation of 89Sr using three different methods

Three independent methods were used to standardise a 89Sr solution within the frame of an international comparison organised by BIPM/CCRI(II): 4 π liquid scintillation (LS) spectrometry, based on the CIEMAT/NIST efficiency tracing method, and direct activity measurements with a windowless 4 π CsI(Tl)-sandwich spectrometer and a 4 π pressurised gas proportional counter. Quantitative solid point-like sources were prepared paying special attention during the source drying phase. The impurities in the original solution were measured and corrected for in the results of all three methods. The activity concentration of 89Sr was found to be 26.21±0.08 kBq g −1. A new half-life value for 89Sr of 50.61±0.05 days was determined from the LS measurements. The measurement methods, including the impurity measurements, are described and the results compared, considering the advantages and disadvantages of each method.

Standardization of 89Sr at the National Office of Measures

Strontium-89 is an important radiotherapy nuclide in bone palliation. The standardization of 89Sr has been performed at the National Office of Measures (OMH) within the frame of the BIPM CCRI(II)-K2.Sr-89 key comparison. The activity concentration of the 89Sr solution was measured by two different methods. The conventional 4 πβ counting technique was used with two proportional counting measurement systems. The 4 πβ– γ-coincidence efficiency tracing method was used with a 4 πβ– γ-coincidence measurement system using 24Na as the tracer radionuclide. The β efficiencies of each of these counting techniques were nearly 100%. The combined uncertainties of the activity concentration determined by these absolute methods are 0.3%. The general agreement of results between the two methods was 0.5%. The measurement equipment, evaluation methods and results of activity concentration measurements with their uncertainty budgets are reported.

The standardization of 188W/ 188Re by 4 πβ liquid scintillation spectrometry with the CIEMAT/NIST 3H-standard efficiency tracing method

The massic activity of a solution containing 188W in equilibrium with its daughter, 188Re, has been standardized by the National Institute of Standards and Technology using 4 πβ liquid scintillation counting with efficiency tracing using the CIEMAT/NIST method. Confirmatory measurements were carried out with γ-ray spectrometry using high purity germanium detectors and a 4 πγ NaI(Tl) system. A calibration factor of 1.68 MBq pA −1 ±0.03 MBq pA −1 (expanded, k=2, uncertainty) for the 188W in the solution was determined, along with correction factors for activity determinations using Capintec dose calibrators. A half-life value of 69.78 d±0.05 d (standard uncertainty) was determined by measurement in the NIST 4 πγ ionization chamber and is consistent with currently recommended values.

The measurement of activity contained in a 32P stainless-steel stent by destructive assay

Destructive assays of stainless-steel stents containing 32P were performed. Prior to assay, 24 stents were intercompared on a NaI(Tl) well-type crystal. A subset of stents were then digested in a suitable carrier solution by the addition of concentrated hydrofluoric acid. The final solution was measured by the CIEMAT/NIST tritium efficiency tracing method for liquid scintillation counting. A separate experiment was performed which indicated no loss of activity during stent digestion. Expanded ( k=2) uncertainties on stent activity ranged from 1.0% to 2.6%.