IN-SITU GAMMA-RAY SPECTROMETRY FOR RADIOACTIVITY ANALYSIS OF SOIL USING NaI(Tl) AND LaBr3(Ce) DETECTORS.

In this study, the full energy peak count rates to radioactivity conversion factors of 3â€³Ø × 3″ NaI(Tl) and 2â€³Ø × 2″ LaBr3(Ce) detectors for radioactivity analysis in the soil were determined on site using a semi-empirical method with point-like gamma-ray sources. To validate the conversion factors derived for the detectors, in-situ gamma-ray measurements were performed in wide open fields with almost flat surface and compared with the sampling analysis for the radioactivity of U-series, Th-series, and 40K in the soil. As a result, radioactivity concentrations of 40K, 208Tl and 214Bi by in-situ and laboratory measurements agreed well with each other within 5%, and the MDAs for artificial radionuclides were estimated under the condition of fresh deposition considering a radiation emergency situation.

Monte Carlo simulations and analysis of transmitted gamma ray spectra through various tissue phantoms.

Studies of radiation interactions with tissue equivalent material find importance in efforts that seek to avoid unjustifiable dose to patients, also in ensuring quality control of for instance nuclear medicine imaging equipment. Use of the Monte Carlo (MC) simulation tool in such characterization processes allows for the avoidance of costly experiments involving transmitted X- and γ-ray spectrometry. Present work investigates MC simulations of γ-ray transmission through tissue equivalent solid phantoms. Use has been made of a range of radionuclide gamma ray sources, 99mTc, 131I, 137Cs, 60Co (offering photons in the energy range from a few keV up to low MeV), popularly applied in medicine and in some cases for gauging in industry, obtaining the transmission spectra following their interaction with various phantom materials and thicknesses. In validation of the model, the simulated values of mass attenuation coefficients (µ/ρ) for different phantom materials and thicknesses were found to be in good agreement with reference values (NIST, 2004) to within 1.1% for all material compositions. For all of the primary photon energies and medium thicknesses of interest herein, results show that multiple scattering peaks are generally located at energies lower than 100 keV, although for the larger phantom thicknesses it is more difficult to distinguish single, double and multiple scattering in the gamma spectra. Transmitted photon spectra investigated for water, soft tissue, breast, brain and lung tissue slab phantoms are demonstrated to be practically independent of the phantom material, while a significant difference is observed for the spectra transmitted through bone that was proved to be due to the density effect and not material composition.

In situ measurement of radioactive contamination of bottom sediments.

A gamma spectrometric method is presented for in situ radiation monitoring of bottom sediments with contaminated layer of unknown thickness to be determined. The method, based on the processing of experimental spectra using the results of their simulation by the Monte Carlo method, is proposed and tested in practice. A model for the transport of gamma radiation from deposited radionuclides 137Cs and 134Cs to a scintillation detection unit located on the upper surface of the contaminated layer of sediments is considered. The relationship between the effective radius of the contaminated site and the thickness of the layer has been studied. The thickness of the contaminated layer is determined by special analysis of experimental and thickness-dependent simulated spectra. The technique and algorithm developed are verified as a result of full-scale studies performed with the submersible gamma-spectrometer.

Design and implementation of a mobile gamma spectrometry system to in vivo measure the accumulated activity of 131I in patients with thyroid diseases.

The design and implementation of a mobile gamma spectrometry system to in vivo measure the accumulated activity of 131I in whole body and thyroid of patients with thyroid diseases are presented in this work. This system may be used for both pre-therapeutic and post-therapeutic dosimetry calculations. It consists of a detector and a movable support that allows its movement from one place to another.

Analysis of MCNP simulated gamma spectra of CdTe detectors for boron neutron capture therapy.

The next step in the boron neutron capture therapy (BNCT) is the real time imaging of the boron concentration in healthy and tumor tissue. Monte Carlo simulations are employed to predict the detector response required to realize single-photon emission computed tomography in BNCT, but have failed to correctly resemble measured data for cadmium telluride detectors. In this study we have tested the gamma production cross-section data tables of commonly used libraries in the Monte Carlo code MCNP in comparison to measurements. The cross section data table TENDL-2008-ACE is reproducing measured data best, whilst the commonly used ENDL92 and other studied libraries do not include correct tables for the gamma production from the cadmium neutron capture reaction that is occurring inside the detector. Furthermore, we have discussed the size of the annihilation peaks of spectra obtained by cadmium telluride and germanium detectors.

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.

Computational Approaches on Photon-Attenuation and Coincidence-summing Corrections for the detection of gamma-emitting radionuclides IN foods.

Source-based calibration methods used for photon attenuation and coincidence summing corrections are time consuming and require multiple certified standards that match sample geometry with varying densities. Three programs which are capable of simulating a variety of sample geometries, matrix compositions, and sample densities have been examined as alternatives. LabSOCS, ANGLE 3 and GESPECOR are effective at generating efficiency curves for food matrices with a range with different densities. The curves generated have been successfully used to determine activity in food samples.

Design of a new comprehensive continuous monitoring system for environmental radioactive aerosol.

In order to comprehensive monitoring the radioactive isotopes from nuclear facilities, we developed a dual channel spectral monitoring instrument, and realized synchronous measurement for alpha, beta and gamma radionuclides. This article focuses on how to ensure its accuracy, stability and efficiency. First is the accuracy. In order to lower the interference of environmental and detector performance variation, the zero phase shift filter was designed to ensure the accuracy of characteristic peak position. Lorenz fitting algorithm was designed to reduce the effect of spectral low-energy tailing. Multi thread processing was introduced to ensure that there was sufficient time to complete our complex algorithms. Second is the stability. The complicated measuring process was decomposed into several sub-states. A state monitoring method was set up to timely dispose the abnormal operation. Third is the efficiency. Sampling process and measurement process were designed in synchronous to save monitoring time, which is especially useful for environmental low level radioactive monitoring. Continuous test for seven days shows that the detection limit is less than 0.0003Bq/m3 for U, 239Pu, and less than 0.048Bq/m3 for beta and 137Cs.

Low-level atmospheric radioactivity measurement using a NaI(Tl) spectrometer during aerosol sampling.

In order to increase the early warning ability of the radiation monitoring network of the Czech republic, a high-volume aerosol sampler was upgraded with a NaI(Tl) probe placed directly above the aerosol filter. The paper demonstrates the possibility of using a method based on principal component regression to accurately subtract the complicated natural background caused by radon decay products. This approach yielded minimum detectable activities of 8mBq/m3, 3mBq/m3 and 7mBq/m3 for 131I, 134Cs and 137Cs, respectively, after 24h of sampling.

Monitoring 3D dose distributions in proton therapy by reconstruction using an iterative method.

The Bragg peak of protons can be determined by measuring prompt γ-rays. In this study, prompt γ-rays detected by single-photon emission computed tomography with a geometrically optimized collimation system were reconstructed by an iterative method. The falloff position by iterative method (52.48mm) was most similar to the Bragg peak (52mm) of an 80MeV proton compared with those of back-projection (54.11mm) and filtered back-projection (54.91mm) methods. Iterative method also showed better image performance than other methods.

Design and fabrication of an in situ gamma radioactivity measurement system for marine environment and its calibration with Monte Carlo method.

Simulation, design and fabrication of a sealing enclosure is carried out for a NaI(Tl) 2″×2″ detector, to be used as in situ gamma radioactivity measurement system in marine environment. Effect of sealing enclosure on performance of the system in laboratory and marine environment (distinct tank with 10m(3) volume) were studied using point sources. The marine volumetric efficiency for radiation with 1461keV energy (from (40)K) is measured with KCl volumetric liquid source diluted in distinct tank. The experimental and simulated efficiency values agreed well. Marine volumetric efficiency calibration curve is calculated for 60keV to 1461keV energy with Monte Carlo method. This curve indicates that efficiency increasing rapidly up to 140.5keV but then drops exponentially.

Determination of gamma-ray self-attenuation correction in environmental samples by combining transmission measurements and Monte Carlo simulations.

We develop a simple and widely applicable method for determining the self-attenuation correction in gamma-ray spectrometry on environmental samples. The method relies on measurements of the transmission of photons over the matrices of a calibration standard and an analysed sample. Results of this experiment are used in subsequent Monte Carlo simulations in which we first determine the linear attenuation coefficients (µ) of the two matrices and then the self-attenuation correction for the analysed sample. The method is validated by reproducing, over a wide energy range, the literature data for the µ of water. We demonstrate the use of the method on a sample of sand, for which we find that the correction is considerable below ~400keV, where many naturally occurring radionuclides emit gamma rays. At the lowest inspected energy (~60keV), one measures an activity that is by a factor of ~1.8 smaller than its true value.

Intercomparison of γ-spectrometry analysis of radionuclides between China and Japan in 2012-2013.

An intercomparison of γ-spectrometry measurement and analysis was organized by the Japan Chemical Analysis Center (JCAC), the National Institute for Radiological Protection, Chinese Center for Disease Control and Prevention (NIRP, China CDC), and the Radiation Monitoring Technical Center of Ministry of Environmental Protection, Chinese (RMTC). The main objective of this study was to assess the γ-spectrometry measurement and analysis technology. The JCAC completed the collection and preparation of soil and powdered rice samples. Three laboratories compared the measurement of seven radionuclides that included two samples of (214)Pb, (214)Bi, (208)Tl, (228)Ac, (40)K, (137)Cs, and (134)Cs with γ-spectrometry. During the studies conducted at the laboratory, the calculated value En was found to be the total uncertainty data of the reported activity. Except (134)Cs in powdered rice sample, the calculated En between each of the two laboratories was <1. The measurement results are acceptable except (134)Cs; therefore, measurement results in the three laboratories were consistent within a certain range except in the case of (134)Cs. Although there is a need to improve the accuracy of measurements and analysis of (134)Cs, an intercomparison was conducted of the tested levels on radionuclide analyzed in the three laboratories.

Assessment of radionuclides in the soil of residential areas of the Chittagong metropolitan city, Bangladesh and evaluation of associated radiological risk.

Soil samples from the three residential hubs of Chittagong city, Bangladesh were analyzed using gamma spectrometry to estimate radiation hazard due to natural radioactive sources and anthropogenic nuclide (137)Cs. The activity concentration of (226)Ra was found to be in the range 11-25 Bq.kg(-1), (232)Th in the range 38-59 Bq.kg(-1) and (40)K in the range 246-414 Bq.kg(-1). These results were used to calculate the radiological hazard parameters including Excess of Lifetime Cancer Risk (ELCR). The estimated outdoor gamma exposure rates were 40.6-63.8 nGy.h(-1). The radiation hazard index (radium equivalent activity) ranged from 90-140 Bq.kg(-1). The average value of the ELCR was found to be 0.21 × 10(-3), which is lower than the world average. Sporadic fallout of (137)Cs was observed with an average value of 2.0 Bq.kg(-1).

Assessment of intake and internal dose from iodine-131 for exposed workers handling radiopharmaceutical products.

Two methods for determination of internal dose due to (131)I intake during the preparation and handling of iodine radiopharmaceutical products have been compared. The first method was based on the measurement of (131)I in 24-hour urine samples while the second method was based on the measurement in vivo of (131)I in thyroid. The results have shown that urine analysis method can be used as a screening test but not for internal dose assessment of exposed workers. Thyroid monitoring method was found to be more reliable and accurate method for assessing internal dose from (131)I intake. In addition, the assessed internal dose showed that the annual internal effective dose for some workers was below 1 mSv with no risk classification, whereas the results of other group of workers were between 1 and 6 mSv with low risk classification. Only one worker reached 7.66 mSv with high risk classification; and this worker must be monitored individually.

Radioactivity measurements in the aquatic environment using in-situ and laboratory gamma-ray spectrometry.

The in-situ underwater gamma-ray spectrometry method is validated by inter-comparison with laboratory method. Deployments of the spectrometer KATERINA on a submarine spring and laboratory measurements of water samples with HPGe detector were performed. Efficiency calibrations, Monte Carlo simulations and the Minimum Detectable Activity (MDA) estimations were realized. MDAs varied from 0.19 to 10.4 (lab) and 0.05 to 0.35 (in-situ) Bq/L, while activity concentrations differed from 7% (for radon progenies) up to 10% (for (40)K), between the two methods.

Traceability in gamma-ray spectrometry.

The new edition of the International vocabulary of metrology-basic and general concepts and associated terms (VIM) defines metrological traceability in a different way than was defined in the previous edition. The reference to an "unbroken chain of comparisons" is replaced by a "chain of calibrations." Calibrations, unlike comparisons, render possible an interpolation of the quantity values between indicated parameters where the calibration was performed. Calibrations of software may be performed using software-measurement standards as well. Furthermore, the traceability of quantities having a minor influence on the measurement result is not mandatory. As a consequence of these modifications, the traceability of gamma-ray spectrometric results can also be attained when gamma-ray spectrometry is implemented other than as a relative method.

Toward prompt gamma spectrometry for monitoring boron distributions during extra corporal treatment of liver metastases by boron neutron capture therapy: a Monte Carlo simulation study.

A Monte Carlo calculation was carried out for boron neutron capture therapy (BNCT) of extra corporal liver phantom. The present paper describes the basis for a subsequent clinical application of the prompt gamma spectroscopy set-up aimed at in vivo monitoring of boron distribution. MCNP code was used first to validate the homogeneity in thermal neutron field in the liver phantom and simulate the gamma ray detection system (collimator and detector) in the treatment room. The gamma ray of 478 keV emitted by boron in small specific region can be detected and a mathematical formalism was used for the tomography image reconstruction.

Extension of the calibration curve for the PGRA facility in Petten.

At the boron neutron capture therapy (BNCT) facility in Petten, the Netherlands, (10)B concentrations in biological materials are measured with the prompt gamma ray analyses facility that is calibrated using certified (10)B solutions ranging from 0 to 210 ppm. For this study, newly certified (10)B solutions ranging up to 1972 ppm are added. MCNP simulations of the setup range to 5000 ppm. A second order polynomial (as already used) will fit (10)B-concentrations less than 300 ppm. Above 300 ppm a fitted third order polynomial is needed to describe the calibration curve accurately.

Radiological maps of outdoor and indoor gamma dose rates in Greek urban areas obtained by in situ gamma spectrometry.

The results obtained from 259 indoor and outdoor in situ gamma spectrometry measurements with a portable Ge detector and 707 total gamma dose rate measurements with an NaI detector in urban areas of 16 Greek islands are presented. From the in situ gamma spectra, the absorbed dose rate in air due to Uranium series, Thorium series, (40)K and (137)Cs are derived and discussed. The results obtained from the present work in conjunction with those reported previously were used for the realization of a complete indoor and outdoor gamma radiation map of Greek urban areas using in situ gamma spectrometry with portable Ge detector.