Standardization of 125I by photon-photon coincidence counting and efficiency extrapolation

The standardization of ¹²⁵I by photon-photon coincidence counting and the determination of the activity by a linear efficiency extrapolation is described. The variation of the efficiencies is realized by symmetrically changing the distance between the source and two movable photon detectors with thin NaI(Tl) crystals. Experimental results, data evaluation and the accuracy of the method are discussed.     

Long term monitoring of 137Cs in foodstuffs in the Czech Republic

This work presents the results of ¹³⁷Cs content long-term monitoring (1986–2007) in selected groups of foodstuffs. The data in the period of 1992–2007 were roughly log-normally distributed (beef, pork, milk). The more detailed statistical evaluation in this period of time was performed. Maximum likelihood method was used for estimation of the mean values. Several methods for decreasing the detection limits of ¹³⁷Cs (detector efficiency, sample preparation, counting containers) are listed and compared.     

Spatial distributions of 137Cs and 239+240Pu in surface seawater within the Exclusive Economic Zone of East Coast Peninsular Malaysia

The studies of ¹³⁷Cs and ^239+240Pu distributions in surface seawater at South China Sea within the Exclusive Economic Zone (EEZ) of Peninsular Malaysia were carried out in June 2008. The analysis results will serve as additional information to the expanded baseline data for Malaysia’s marine environment. Thirty locations from extended study area were identified in the EEZ from which large volumes of surface seawater samples were collected. Different co-precipitation techniques were employed to concentrate cesium and plutonium separately. A known amount of ¹³⁴Cs and ²⁴²Pu tracers were used as yield determinant. The precipitate slurry was collected and oven dried at 60 ^oC for 1–2 days. Cesium precipitate was fine-ground and counted using gamma-ray spectrometry system at 661.62 keV, while plutonium was separated from other radionuclides using anion exchange, electrodeposited and counted using alpha spectrometry. The activity concentrations of ¹³⁷Cs and ^239+240Pu were in the range of 3.40–5.89 Bq/m³ and 2.3–7.9 mBq/m³, respectively. The ^239+240Pu/¹³⁷Cs ratios indicate that there are no new inputs of these radionuclides into the area.     

Soil sampling and 137Cs analysis of the chernobyl fallout in Greece

A total of 1242 samples of soil, collected over Greece, during the period May–November 1986, were counted and analysed for ¹³⁷Cs from Chernobyl fallout. The counting was performed using a NaI detector on-line to a microcomputer; moreover, 252 of the samples were also analysed using Ge detectors, for inter-comparison and also for the assessment of other long-lived isotopes in the fallout. The results show that ¹³⁷Cs fallout from Chernobyl presents a remarkable geographical variability. The evaluated ground activity due to ¹³⁷Cs deposition ranges between 0.01 and 137 kBq/m².     

Atmospheric input of 137Cs and 239,240Pu isotopes in Korea after the Fukushima nuclear power plant accident

Caesium isotopes (¹³⁴Cs and ¹³⁷Cs) and ^239,240Pu in rainwater and dry deposition have been analyzed by Korea Research Institute of Standards and Science (KRISS) since the Fukushima nuclear power plant (NPP) accident in March 2011. The concentrations of ^239,240Pu and ¹³⁷Cs in the rainwater are 2.6±1.0 to 15±3 µBq/kg and 0.01 to 0.36 mBq/kg, respectively. The concentrations are concordant to those observed before the Fukushima NPP accident, on the other hand, the monthly depositional flux of ^239,240Pu and ¹³⁷Cs are much lower than the amounts observed after Fukushima NPP accident and in Monaco in 1998–2001. This confirms that the Fukushima NPP accident caused no significant impact in Korea.     

Standardization of 134Cs by three methods.

The nuclide 34Cs decays by beta-emission followed by gamma-deexcitation to 134Ba with a half-life T(1/2) = 2.065 a. It has been standardized by three methods: liquid scintillation counting (LSC), 4pi beta-gamma coincidence counting and 4pi gamma counting. In the LSC measurements, the CIEMAT/NIST method was used to calculate the efficiency. For the coincidence measurements, a conventional 4pi beta (proportional counter)-gamma(NaI) system was used. For the 4pi gamma standardization, a well-type Nal(Tl) detector was modeled with the Monte Carlo package PENELOPE, and the counting efficiency obtained by calculation. Results of the three methods agree within 0.65%.     

Study of activation cross sections of proton induced reactions on barium: Production of 131Ba→131Cs

In the frame of a systematic study of charged particle production routes of the therapeutic radioisotope ¹³¹Cs, excitation functions of the ^natBa(p,x)^135,132mgLa, ^{ind135m,cum133m,cum133mg,cum131mg}Ba and ^{136mg,134mg,132,cum129}Cs reactions were measured in the 30?70 MeV energy range using stacked foil irradiation technique, activation method and gamma spectroscopy. Comparisons with new results of the ALICE-IPPE and EMPIRE-II codes and with existing data obtained with TALYS code are shown. From the measured cross section data integral yields were calculated and compared with experimental integral yield data reported in the literature. Potential use of proton induced reactions on Ba for production of ¹³¹Cs is discussed.     

信号核素134Cs诱发体细胞和生殖细胞畸变效应比较研究

对１３４Ｃｓ诱发体细胞和生殖细胞的畸变效应进行了比较研究。方法观察内污染不同放射性活度１３４Ｃｓ时诱发同体骨髓细胞和精原细胞染色体畸变的量效关系，以及同一放射性活度１３４Ｃｓ作用不同时间诱发上述两种细胞的染色体畸变产额。结果研究发现，１３４Ｃｓ内照射诱发的骨髓细胞染色体畸变产额显著高于精原细胞，而其诱发的染色体畸变类型均以染色单体型畸变为主。结论由不同放射性活度１３４Ｃｓ所诱发的染色体畸变产额而言，骨髓细胞要比精原细胞高出１．５～５倍。     

Standardization of radionuclide by beta(LS)-gamma coincidence counting using the geometry-efficiency variation method.

A liquid scintillation counting method consisting of three photomultiplier tubes for beta counters and a NaI(Tl) gamma counter has been developed for the standardization of radionuclides with the beta-gamma coincidence technique. The beta detection efficiency functions are obtained by means of a geometry-variation method developed in the present work; an array of beta detectors is moved uniformly at the same time from a centrally located counting vial to 50 mm. The method has been applied in the standardization of 60Co and 134Cs. Unquenched liquid scintillation samples with nominal count rates from 1000 to 6000 s-1 were prepared. The observed beta detection efficiencies with this method are from 90 to 45% in the case of 60Co, and from 84 to 50% for 134Cs. The output of each beta channel is summed together and compared with gamma data by the coincidence analyzer. The dead time of each counting channel is adjusted to be 20 micros, sufficiently long to suppress the afterpulses in the beta counting channel. The activity of each sample is determined by using the Cox and Isham formula. The obtained results are in good agreement with KRISS certified values.     

Feasibility studies on iterative methods of fuel burnup estimation using gamma-ray spectrometry

The aim of this work is to establish a method for spent fuel burnup estimation using non-destructive γ-ray spectrometry without the need for detailed data on fuel irradiation history. The methods thus developed are based on an iterative approach by comparison between the measured and the calculated fission product activities or activity ratios. Good agreement is obtained among the burnup values deduced from ¹³⁷Cs activities, ¹³⁴Cs/¹³⁷Cs activity ratios, and ¹⁴⁰La activities.     

Standardization and determination of the total internal conversion coefficient of In-111

The standardization of ¹¹¹In by means of a 4πβ-γ coincidence system, composed of a proportional counter in 4π geometry, coupled to a 20% relative efficiency HPGe crystal, for measuring gamma-rays is presented. The data acquisition was performed by means of the software coincidence system (SCS) and the activity was determined by the extrapolation technique. Two gamma-ray windows were selected: at 171 keV and 245 keV total absorption peaks, allowing the determination of the total internal conversion coefficient for these two gamma transitions. The results were compared with those available in the literature.     

The efficiency variation method for 4πβ−γ coincidence counting by ink-jet printing

In order to vary the counting efficiencies in the 4πβ−γ coincidence extrapolation technique, a radioactive source was coated directly with varying amounts of an electrical conducting pigment using an ink-jet printer. This method can be used to efficiently prepare the multiple sources needed to generate efficiency extrapolation curves, and was successfully applied to the standardization of a ⁵⁴Mn source.     

Absolute radioactivity measurement of 60Co, 134Cs and 166mHo by 4πβ−γ anti-coincidence method

A 4πβ−γ anti-coincidence system has been developed for absolute radioactivity measurements with a HPGe γ-spectrometer used as the γ-ray detector and a 4πβ proportional counter as the β detector. The activity of ⁶⁰Co, ¹³⁴Cs and ^166mHo have been measured with the combined standard uncertainties of 0.24%, 0.33% and 0.44%, respectively. Compared with the results of the National Institute of Metrology and 4πβ−γ coincidence counting system of the China Institute of Atomic Energy, the agreement of the results of ⁶⁰Co and ¹³⁴Cs is satisfactory. For ^166mHo, the results obtained using other methods by most national and international labs lack sufficient accuracy due to the complex decay scheme of this radio-nuclide. It is also concluded that the result of anti-coincidence measurement is independent of β efficiency.     

Dosimetric differences between intraoperative and postoperative plans using Cs-131 in transrectal ultrasound–guided brachytherapy for prostatic carcinoma

The aim of the study was to investigate the differences between intraoperative and postoperative dosimetry for transrectal ultrasound–guided transperineal prostate implants using cesium-131 (¹³¹Cs). Between 2006 and 2010, 166 patients implanted with ¹³¹Cs had both intraoperative and postoperative dosimetry studies. All cases were monotherapy and doses of 115 were prescribed to the prostate. The dosimetric properties (D₉₀, V₁₅₀, and V₁₀₀ for the prostate) of the studies were compared. Two conformity indices were also calculated and compared. Finally, the prostate was automatically sectioned into 6 sectors (anterior and posterior sectors at the base, midgland, and apex) and the intraoperative and postoperative dosimetry was compared in each individual sector. Postoperative dosimetry showed statistically significant changes (p < 0.01) in every dosimetric value except V₁₅₀. In each significant case, the postoperative plans showed lower dose coverage. The conformity indexes also showed a bimodal frequency distribution with the index indicating poorer dose conformity in the postoperative plans. Sector analysis revealed less dose coverage postoperatively in the base and apex sectors with an increase in dose to the posterior midgland sector. Postoperative dosimetry overall and in specific sectors of the prostate differs significantly from intraoperative planning. Care must be taken during the intraoperative planning stage to ensure complete dose coverage of the prostate with the understanding that the final postoperative dosimetry will show less dose coverage.     

Geochronology of Lake Baikal from Pb and Cs radioisotopes

Two box cores of near surface sediments were obtained from Lake Baikal in Southeastern Siberia, Russia. The cores were taken from the northern and southern basins of the lake during a joint American–Russian research expedition in the summer of 1994. The cores were analyzed for ²¹⁰Pb, ¹³⁷Cs and total organic carbon (TOC). Organic carbon is an indicator of photosynthetic production by phytoplankton, taking place primarily in the euphotic zone of the water column. Accumulation rates of TOC may be used as indicators of paleo-productivity when sedimentation rates are determined using the ²¹⁰Pb dating method and combined with both the density of sediment and organic carbon content. Accordingly, the lake is characterized by changes in accumulations of TOC, which may be linked to rates of sedimentation. Accumulations of TOC and sedimentation rates were higher in the southern basin site than in the northern basin site. The southern station core was taken from an area in close proximity to the Selenga River delta, which carries 50% of the water input to Lake Baikal. Productivity should thus be higher in this region due to the high nutrient input and sediment accumulation higher due to influx of riverine sediment input. Traces of ¹³⁷Cs (an anthropogenic product) were found in both cores. However, activities of ¹³⁷Cs were significantly higher in the southern basin, likely due to the input of the Selenga River in the southern region, which extends to a region in Mongolia in close proximity to the area of the Chinese atomic-bomb atmospheric testing of the 1970s. Application of a quantitative inverse model to the ²¹⁰Pb profiles yielded the following results: (i) station 12, near the Selenga Delta, had an accumulation rate of about 0.38 cm/y in 1957 but this rate was halved by 1980 to about 0.22 cm/y and has been roughly steady since that time; ¹³⁷Cs values are consistent with the age-to-depth determination from ²¹⁰Pb for station 12; (ii) since about 1960, station 5A in the northern basin had an accumulation rate lower by a factor 2–4 than that of the station near the Selenga Delta; the ¹³⁷Cs values are consistent with the ²¹⁰Pb age-to-depth determination for station 5A; (iii) the ¹³⁷Cs activities for station 12 systematically increase with time towards the present day and are about a factor 6–10 higher than ¹³⁷Cs activities recorded for station 5A, which do not show a corresponding systematic increase with time.     

137Cs contamination of Techa river flood plain in Brodokalmak settlement

¹³⁷Cs contamination of the Techa river flood plain inside the Brodokalmak settlement has been mapped. The collimated scintillated detector technique was used for ¹³⁷Cs deposit measurements. The ¹³⁷Cs contamination is very heterogeneous. A comparison of this technique with the traditional sample method was performed at selected locations. The sampling data are in good agreement with in-situ data. Soil surface activity of ⁹⁰Sr was determined from the samples. It was shown that ¹³⁷Cs contamination correlates with ⁹⁰Sr contamination within the flood plain of the settlement.     

Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry

A comparison of the coincidence summing correction methods is presented. Since there are several ways for computing these corrections, each method has advantages and drawbacks that could be compared. This part of the comparison was restricted to point sources. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing correction factors for several energies of ¹⁵²Eu and ¹³⁴Cs, and three source-to-detector distances. They are presented and discussed.     

Standardization and measurement of gamma-ray probability per decay of 177Lu

The procedure followed by the Nuclear Metrology Laboratory (LMN), at the Nuclear and Energy Research Institute (IPEN), for the primary standardization of ¹⁷⁷Lu is described. This radionuclide is widely used in radiopharmacy due to its convenient half-life and emitted beta ray energies. The ¹⁷⁷Lu solution was supplied during an international comparison sponsored by BIPM in 2009 and the primary standardization has been accomplished by the 4πβ-γ coincidence method using a proportional counter in 4π geometry coupled with two NaI(Tl) scintillation counters. The beta efficiency was varied by placing Collodion and aluminum absorbers over and under the radioactive source. The ¹⁷⁷Lu calibrated sources were also measured in a previously calibrated HPGe spectrometer, in order to obtain the emission probability per decay for the selected gamma-ray transitions. The experimental extrapolation curves were also compared with Monte Carlo simulations by means of code ESQUEMA developed at the LMN.     

Geochronology of Lake Baikal from 210Pb and 137Cs radioisotopes

Two box cores of near surface sediments were obtained from Lake Baikal in Southeastern Siberia, Russia. The cores were taken from the northern and southern basins of the lake during a joint American–Russian research expedition in the summer of 1994. The cores were analyzed for ²¹⁰Pb, ¹³⁷Cs and total organic carbon (TOC). Organic carbon is an indicator of photosynthetic production by phytoplankton, taking place primarily in the euphotic zone of the water column. Accumulation rates of TOC may be used as indicators of paleo-productivity when sedimentation rates are determined using the ²¹⁰Pb dating method and combined with both the density of sediment and organic carbon content. Accordingly, the lake is characterized by changes in accumulations of TOC, which may be linked to rates of sedimentation. Accumulations of TOC and sedimentation rates were higher in the southern basin site than in the northern basin site. The southern station core was taken from an area in close proximity to the Selenga River delta, which carries 50% of the water input to Lake Baikal. Productivity should thus be higher in this region due to the high nutrient input and sediment accumulation higher due to influx of riverine sediment input. Traces of ¹³⁷Cs (an anthropogenic product) were found in both cores. However, activities of ¹³⁷Cs were significantly higher in the southern basin, likely due to the input of the Selenga River in the southern region, which extends to a region in Mongolia in close proximity to the area of the Chinese atomic-bomb atmospheric testing of the 1970s. Application of a quantitative inverse model to the ²¹⁰Pb profiles yielded the following results: (i) station 12, near the Selenga Delta, had an accumulation rate of about 0.38 cm/y in 1957 but this rate was halved by 1980 to about 0.22 cm/y and has been roughly steady since that time; ¹³⁷Cs values are consistent with the age-to-depth determination from ²¹⁰Pb for station 12; (ii) since about 1960, station 5A in the northern basin had an accumulation rate lower by a factor 2–4 than that of the station near the Selenga Delta; the ¹³⁷Cs values are consistent with the ²¹⁰Pb age-to-depth determination for station 5A; (iii) the ¹³⁷Cs activities for station 12 systematically increase with time towards the present day and are about a factor 6–10 higher than ¹³⁷Cs activities recorded for station 5A, which do not show a corresponding systematic increase with time.