Proficiency testing with uncertainty evaluation for measuring activities per unit mass of 134Cs and 137Cs in brown rice in Japan.

In Japan, we conducted proficiency testing of activity measurement by using high-purity germanium detectors for 134Cs and 137Cs in brown rice grains. Among 176 reported results, 86 % (for 134Cs) and 93 % (for 137Cs) of the results satisfied |En| â‰¦ 1. However, 58 reports for 134Cs and 51 reports for 137Cs had some failures in their evaluations of uncertainties. The proficiency testing was effective to improve the ability of uncertainty evaluation.

A Novel 141Ce-Based Flood Field Phantom: Assessment of Suitability for Daily Uniformity Testing in a Clinical Nuclear Medicine Department.

Daily quality control testing of a γ-camera is of the utmost importance in assessing whether the camera is suitable for clinical use. The aim of our study was to assess the suitability of a fillable 141Ce-based flood field phantom developed in-house for daily quality control testing of γ-cameras. Methods: Daily uniformity testing was performed for 113 d using the fillable 141Ce phantom and a commercially available sheet-type 57Co phantom, and the results were compared. Results: The average integral uniformity obtained by the 141Ce and 57Co phantoms was 3.24% and 2.72%, respectively, for detector 1 and 3.31% and 2.78%, respectively, for detector 2. Conclusion: The 141Ce phantom we developed is a suitable alternative to the commercially available 57Co phantom.

137Cs Dosimeter Irradiation Facilities: Calibration Frequency, Precision, and Accuracy.

Many dosimeter and instrument calibration sources, especially Cs irradiators permanently installed in facilities, are infrequently calibrated since their geometry is not subject to large variation, their mechanisms are simple, and their operation can be visibly error-free for decades. Only decay corrections are needed to know delivered doses at fixed locations once a thorough characterization of such facilities is completed. For one such Cs source, however, collected current values in a span of a few days were found to drop significantly. Malfunction of the internal positioning mechanisms through wear were found to be the cause. This paper suggests periodic source calibrations for the timely identification of source failures that could cause gross errors in dose delivery. In addition, a rigorous analysis of the magnitude of uncertainties and errors in dose delivery using a calibration source is included, which is based upon newly collected experimental data. This provides a technical basis for calibration procedures to ensure a given accuracy and precision of dose delivery.

The Current Limits for Radionuclides in Food in Japan.

After the TEPCO Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, the current limits in Japan on the radionuclide contamination of food [100 Bq kg for general foods, 50 Bq kg for milk and infant foods, and 10 Bq kg for drinking water as radioactive cesium (Cs + Cs)] were established on the basis of an effective dose of 1 mSv y, consistent with international standards to mitigate the exposure of the general public to radiation. Measures that include recalling or restriction of food have been taken in cases when these limits were violated. As a result of these efforts, the actual effective doses of radioactive cesium (Cs + Cs) in foods approximately 1 y after the FDNPP accident were below 0.01 mSv y. However, there is little information on the current status of these limits in the literature, which necessitates a comprehensive review of the information that exists. In this paper, the concept behind the introduction of these limits, the methods by which they were derived, and the results of monitoring food accordingly, are reviewed. This information will be helpful in the case of a future accident, and it will also help to enhance the understanding of the current limits and to relieve the anxieties of the general public concerning radiation exposure from radionuclides in food.

Assessment of natural radioactivity and (137)Cs in some coastal areas of the Saudi Arabian gulf.

The levels of natural radioactivity have been investigated in some Saudi Arabian Gulf coastal areas. Sampling sites were chosen according to the presence of nearby non-nuclear industrial activities such as, the two main water desalination plants in Al Khobar and Al Jubail, and Maaden phosphate complex in Ras Al Khair, to ensure that effluents discharges into the Arabian Gulf didn't enhance radioactivity in seawater and shore sediments. Seawater samples were analyzed for radium isotopes (Ra-226 & Ra-228) and measured by gamma spectrometry using high purity germanium detector, after radiochemical separation of the isotopes by co-precipitation with MnO2. Shore sediment samples were analyzed for (226)Ra, (228)Ra ((232)Th), (4)°K and (137)Cs using gamma sepectrometry. A small variation was observed in the activity concentrations of the investigated radioisotopes, and the activity levels were comparable to those reported in literature. Quality assurance and methods validation were established through the efficiency calibration of the detectors, the estimation of uncertainties, the use of blanks, the analysis of standard reference materials and the intercomparison and proficiency tests. Radiological hazards were assessed, and the annual effective dose had an average value of 0.02 mSv. On the basis of the current results, we may conclude that any radiological hazards to the public visiting these shores are not expected.

Results of an EC laboratory comparison on 4°K, 9°Sr and ¹³7Cs in dried bilberry powder.

The evaluation is presented of a laboratory comparison (LC) on (90)Sr, (40)K and (137)Cs in dried bilberries organised in 2011 by the IRMM. The activity concentrations reported by 88 participant laboratories are compared to the reference values of the new reference material IRMM-426 Wild Berries. Nine per cent and 17% of activity concentration results for (137)Cs and (40)K, respectively, deviate more than 20% from the reference values, a result worse than that obtained in previous LCs. For (90)Sr, about 88% of results lie within 30% of the reference value, better than observed in previous LCs. But only 58% of (90)Sr results are satisfactory in terms of the En criterion, indicating difficulties with a complete uncertainty estimation.

Development of certified matrix reference materials for quality assurance of screening ¹³4Cs and ¹³7Cs in food.

A certified reference material using activated alumina powder certified for activity of (134)Cs and (137)Cs was developed. The results of the verification and the certification are described. The certified reference material can be used for quality assurance of screening activity measurements of (134)Cs and (137)Cs in food/foodstuffs. Commercially available equipments were experimentally tested using the CRM and another CRM including (40)K. The results of these tests are also shown.

First participation by the NMISA in a low-level comparison: CCRI(II)-S9 exercise.

The NMISA Radioactivity Standards Laboratory participated in the CCRI(II)-S9 inter-comparison of the measurement of the activity concentration of (137)Cs and (40)K in rice material, piloted by the KRISS. The paper describes the equipment used, the measurement set-up and data analysis. The efficiency of the detector for (137)Cs and (40)K was determined by comparison against a spiked standard solution, and Monte Carlo simulations performed to estimate the difference in γ-ray escape probability between the solution standard and starch (as an approximation for milled rice) due to attenuation disparities. The uncertainty budget was estimated rather conservatively, since these were the first low-level measurements performed by the NMISA using an HPGe detector.

Quantifying and reducing the effect of calibration error on variability of PET/CT standardized uptake value measurements.

UNLABELLED: The purpose of this study was to measure the errors introduced by regular calibration of PET/CT scanners and to minimize the effect of calibration error on standardized uptake value measurements. METHODS: Global calibration factors from 2 PET/CT scanners were recorded for 3.5 and 1.8 y, comparing manufacturer-recommended protocols with modified protocols to evaluate error contributions due to operator-influenced procedures. Dose calibrator measurements were evaluated using National Institute of Standards and Technology-traceable sources. RESULTS: Dose calibrator variability was less than 1%, although there was a consistent bias. Global scaling variability was reduced from 6% to 4% for scanner 1 and from 11% to 4% for scanner 2 when quality assurance and quality control procedures were applied to the calibration protocol. When calibrations were done using a (68)Ge/(68)Ga phantom, the variability for both scanners was reduced to approximately 3%. CONCLUSION: Applying quality assurance and quality control procedures to scanner calibration reduces variability, but there is a still a residual longitudinal scanner variability of 3%-4%. The procedures proposed here reduce the impact of operator error on scanner calibration and thereby minimize longitudinal variability in standardized uptake value measurements.

TG-43 U1 based dosimetric characterization of model 67-6520 Cs-137 brachytherapy source.

PURPOSE: Brachytherapy treatment has been a cornerstone for management of various cancer sites, particularly for the treatment of gynecological malignancies. In low dose rate brachytherapy treatments, 137Cs sources have been used for several decades. A new 137Cs source design has been introduced (model 67-6520, source B3-561) by Isotope Products Laboratories (IPL) for clinical application. The goal of the present work is to implement the TG-43 U1 protocol in the characterization of the aforementioned 137Cs source. METHODS: The dosimetric characteristics of the IPL 137Cs source are measured using LiF thermoluminescent dosimeters in a Solid Water phantom material and calculated using Monte Carlo simulations with the GEANT4 code in Solid Water and liquid water. The dose rate constant, radial dose function, and two-dimensional anisotropy function of this source model were obtained following the TG-43 U1 recommendations. In addition, the primary and scatter dose separation (PSS) formalism that could be used in convolution/superposition methods to calculate dose distributions around brachytherapy sources in heterogeneous media was studied. RESULTS: The measured and calculated dose rate constants of the IPL 137Cs source in Solid Water were found to be 0.930 (+/-7.3%) and 0.928 (+/-2.6%) cGy h(-1) U(-1), respectively. The agreement between these two methods was within our experimental uncertainties. The Monte Carlo calculated value in liquid water of the dose rate constant was null set=0.948 (+/-2.6%) cGy h(-1) U(-1). Similarly, the agreement between measured and calculated radial dose functions and the anisotropy functions was found to be within +/-5%. In addition, the tabulated data that are required to characterize the source using the PSS formalism were derived. CONCLUSIONS: In this article the complete dosimetry of the newly designed 137Cs IPL source following the AAPM TG-43 U1 dosimetric protocol and the PSS formalism is provided.

Secondary charged particle equilibrium in 137Cs and 60Co reference radiation fields.

During the calibration or irradiation of dosemeters, typical irradiation geometries (collimated beams) and source-to-detector distances (1-5 m) lead to the fact that for photon energies above a few hundred keV, the secondary charged particle equilibrium is usually not ensured. The reason is that the effective beam radius at the detector position is smaller than the range of the secondary electrons produced in air whose maximum particle energy is as large as the maximum photon energy. Therefore, the International Organization for Standardization (ISO) recommends putting a build-up plate (BUP) made of polymethyl methacrylate in front of the dosemeter to be calibrated in ISO 4037-3. In this paper, the effect of the thickness of the BUP and its distance from the dosemeter at different source-to-dosemeter distances were investigated by means of measurement and calculation. It turned out that the geometrical arrangement of the source, dosemeter and BUP recommended by ISO mostly does not ensure secondary charged particle equilibrium. The consequence is to always place the BUP directly in front of the dosemeter to be calibrated or irradiated.

Simulated and measured spectral characteristics of 137Cs reference radiation beams.

137Cs sources are widely used in calibrations of radiation protection dosimeters and doserate meters. In these calibrations, conversion coefficients from the air kerma to various dose equivalent quantities are needed. These conversion quantities are functions of photon energy. In this work, Monte Carlo simulations and measurements are used for quantifying the energy distributions of the photon fluence from two 137Cs sources used for calibration purposes. The results indicate that the standard set of conversion coefficients, obtained from a monoenergetic spectrum, do not sufficiently take into account the scattered radiation (most of which is scattered by the source itself): For the large (14x15.6 mm) and small (3.5x3 mm) 137Cs sources, the simulated values for the conversion coefficients H'(0.07)/Ka and H*(10)/Ka (which were nearly equal for the both quantities) showed around 1.0 and 1.5% deviations from the ISO standard value 1.20 (for the large and small sources, respectively). Similarly, the conversion coefficient Hp(10)/Ka showed around 1.5 and 2.5% deviations from the ISO standard value 1.21 for the large and small 137Cs sources, respectively, whereas Hp(0.07)/Ka had the values 1.22 and 1.23. The amplitude of the variation of the conversion coefficients due to varying 137Cs source size did not exceed 1%. Thus, the overall uncertainty (with coverage factor k=2) due to varying source size for the average values of the conversion coefficients can be estimated as low as 0.6%.

Calibration of a portable HPGe detector using MCNP code for the determination of 137Cs in soils.

In situ gamma spectrometry provides a fast method to determine (137)Cs inventories in soils. To improve the accuracy of the estimates, one can use not only the information on the photopeak count rates but also on the peak to forward-scatter ratios. Before applying this procedure to field measurements, a calibration including several experimental simulations must be carried out in the laboratory. In this paper it is shown that Monte Carlo methods are a valuable tool to minimize the number of experimental measurements needed for the calibration.

Close-geometry efficiency calibration of p-type HPGe detectors with a Cs-134 point source.

When close-geometry detector calibration is required in gamma-ray spectrometry, single-line emitters are usually used in order to avoid true coincidence summing effects. We managed to overcome this limitation by developing a method for the determination of the efficiency of p-type HPGe detectors in close-geometry with a calibrated Cs-134 point source. No separate determination of coincidence summing correction factors is required and a single measurement furnishes the full-energy-peak efficiencies in the 475-1365 keV energy range.

Technical note: Monte Carlo derivation of TG-43 dosimetric parameters for radiation therapy resources and 3M Cs-137 sources.

In clinical brachytherapy dosimetry, a detailed dose rate distribution of the radioactive source in water is needed in order to plan for quality treatment. Two Cs-137 sources are considered in this study; the Radiation Therapy Resources 67-800 source (Radiation Therapy Resources Inc., Valencia, CA) and the 3M model 6500/6D6C source. A complete dosimetric dataset for both sources has been obtained by means of the Monte Carlo GEANT4 code. Dose rate distributions are presented in two different ways; following the TG43 formalism and in a 2D rectangular dose rate table. This 2D dose rate table is helpful for the TPS quality control and is fully consistent with the TG43 dose calculation formalism. In this work, several improvements to the previously published data for these sources have been included: the source asymmetries were taken explicitly into account in the MC calculations, TG43 data were derived directly from MC calculations, the data radial range was increased, the angular grid in the anisotropy function was increased, and TG43 data is now consistent with the along and away dose rate table as recommended by the TG43 update.

Dose mapping using MCNP5 mesh tallies.

Rensselaer Polytechnic Institute has a 69.6 GBq (1.88 Ci) (137)Cs source that is used for research, calibration of various instruments, and teaching. Recently it was calibrated using ion chambers. The source and room were also modeled in Monte Carlo N-Particle transport code (MCNP5) to determine if the use of a new feature called mesh tallies produces a dose map in the entire room that agrees with the measured results. The dose rate in the hallway, while the source is exposed, was also calculated. It was found that the dose rates calculated from the MCNP5 are in reasonable agreement with the measured results and theoretical predictions. It was also confirmed that the dose rates where the user often stays during the measurement are well below the annual limits. This project shows that the MCNP5 mesh tallies are useful tool for dose mapping in many operational radiation protection situations.

AAPM TG-43 formalism for brachytherapy dose calculation of a 137Cs tube source.

We present a development of the use of the AAPM TG-43 dose formalism applied to 137Cs gynecological implant sources. The geometry factor, radial dose function, and anisotropy function of a 137Cs source modeled after the Nuclear Associates 67-809 series stainless steel jacketed tube source were derived following the AAPM TG-43 formalism. The dose rate distribution through the center of the source using the AAPM TG-43 dose formalism is calculated and compared with the calculations obtained using the Sievert summation and Monte Carlo simulation. The three methods resulted in an agreement within less than 5%, or an isodose rate line agreement within 2 mm. We demonstrate that the AAPM TG-43 formalism can be applied to 137Cs linear sources and is capable of serving as a 137Cs dose calculation algorithm that can be used for treatment planning purpose.

Convergence of techniques for the evaluation of discrepant data.

The problem of evaluating discrepant data has been addressed by several authors over the previous 20 yr. More recently some attention has been given to the use of the median, which is expected to have better statistical 'robustness'. The various evaluation techniques should converge towards the 'true' value as the number of data in a data set increases, and the 'robustness' of each evaluation technique can then be tested by the rate at which that technique converges. Several evaluation techniques have been applied to discrepant data sets, and the results are shown to converge as the size of the data set grows. The discrepant data sets used as examples are the measured half-lives of 90Sr and 137Cs. Differences in the behaviour of the evaluation techniques are discussed, as applied to these data sets. The half-lives deduced from this study are: 90Sr 10,551+/-14 days; 137Cs 10,981+/-11 days.

Self-help countermeasure strategies for populations living within contaminated areas of Belarus, Russia and Ukraine.

Countermeasures have been effectively employed within intensive agricultural systems in areas of the Former Soviet Union (FSU) affected by the Chernobyl accident. However, ingestion doses continue to be elevated in some areas as a result of few foodstuffs which are collected from the wild or produced by the household. Forest fungi and berries, and milk from privately owned cattle are the most notable contributors to 137Cs intakes amongst these foodstuffs. In this paper we consider advice which would help affected populations to both understand the importance of these exposure routes and to reduce their exposure. In addition to the potential radiological benefits, self-help schemes are highly cost-effective and likely to have a positive psychological influence on populations living within contaminated areas of the FSU. Evidence to suggest that the transfer of radiocaesium to cow milk is considerably higher in the FSU than within western Europe and North America is discussed.

Remediation strategies for rural territories contaminated by the Chernobyl accident.

The objective of the present paper is to derive remediation strategies for rural settlements contaminated by the Chernobyl accident in which annual doses to a critical group still exceed 1 mSv. Extensive radioecological data have been collected for 70 contaminated settlements. A dose model based on these data resulted in estimates that are on average close to and a bit less than the official dose estimates ('catalogue doses') published by the responsible Ministries of Belarus, Russia and Ukraine. For eight remedial actions that can be applied on a large scale, effectiveness and costs have been assessed in light of their dependence on soil type, contamination level and on the degree of previous application of remedial actions. Remediation strategies were derived for each of the 70 settlements by choosing remedial actions with lowest costs per averted dose and with highest degree of acceptability among the farmers and local authorities until annual doses are assessed to fall below 1 mSv. The results were generalised to 11 contamination/internal-dose categories. The total numbers of rural inhabitants and privately owned cows in the three countries distributed over the categories were determined and predicted until the year 2015. Based on these data, costs and averted doses were derived for the whole affected population. The main results are (i) about 2000 Sv can be averted at relatively low costs, (ii) the emphasis on reducing external exposures should be increased, (iii) radical improvement of hay-land and meadows and application of Prussian blue to cows should be performed on a large scale if annual doses of 1 mSv are an aim to be achieved, (iv) additional remedial actions of importance are fertilising of potato fields, distribution of food monitors and restriction of mushroom consumption, and (v) for inhabitants of some settlements (in total about 8600) annual doses cannot be reduced below 1 mSv by the remedial actions considered.