Vertical profile of Cs in soil

In this paper, a vertical distribution of ¹³⁷Cs in undisturbed soil was investigated experimentally and theoretically. Soil samples were taken from the surroundings of the city of Kragujevac in central Serbia during spring-summer of 2001. The sampling locations were chosen in such a way that the influence of soil characteristics on depth distribution of ¹³⁷Cs in soil could be investigated. Activity of ¹³⁷Cs in soil samples was measured using a HpGe detector and multi-channel analyzer. Based on vertical distribution of ¹³⁷Cs in soil which was measured for each of 10 locations, the diffusion coefficient of ¹³⁷Cs in soil was determined. In the next half-century, ¹³⁷Cs will remain as the source of the exposure. Fifteen years after the Chernobyl accident, and more than 30 years after nuclear probes, the largest activity of ¹³⁷Cs is still within 10 cm of the upper layer of the soil. This result confirms that the penetration of ¹³⁷Cs in soil is a very slow process. Experimental results were compared with two different Green functions and no major differences were found between them. While both functions fit experimental data well in the upper layer of soil, the fitting is not so good in deeper layers. Although the curves obtained by these two functions are very close to each other, there are some differences in the values of parameters acquired by them.     

Concentration of radiocaesium Cs and Cs in sediments of the Malaysian marine environment

The concentrations of ¹³⁷Cs and ¹³⁴Cs in Malaysian marine sediments were measured by gamma-ray spectrometry with a high-purity germanium (HPGe) detector connected to a multichannel analyzer. In general, the ¹³⁷Cs concentration in Malaysian marine sediments has been found to be very low and less than 5 Bq/kg dry weight with the exception of those from a few sampling locations. The concentration of ¹³⁴Cs was found to be less than the minimum detectable activity for the measuring condition used. Data reported in this paper were found to be comparable with results from within the region and thus can be used as reference data for the country.     

Natural and man-made radioactivity in soils and plants around the research reactor of Inshass

The specific radioactivities of the U-series, ²³²Th, ¹³⁷Cs and ⁴⁰K were measured in soil samples around the Inshass reactor in Cairo, using a γ-ray spectrometer with a HpGe detector. The -activity of ²³⁸U, ²³⁴U and ²³⁵U was measured in the same soil samples by surface barrier detectors after radiochemical separation and the obtained results were compared with the specific activities determined by γ-measurements. The -activity of ²³⁸Pu, ^239+240Pu, ²⁴¹Am, ²⁴²Cm and ²⁴⁴Cm was measured after radiochemical separation by surface barrier detectors for both soil and plant samples. Then β-activity of ²⁴¹Pu was measured using liquid scintillation spectrometry.     

Nuclide-dependent local and collector surface effects in sampling of radioactive deposition to ground

After the end of atmospheric nuclear weapons tests and after the Chernobyl accident, the deposition characteristics of ¹³⁷Cs changed from a predominant wet deposition to the present resuspension mechanism characterised by predominant dry deposition. To study the consequences of this change for deposition sampling, monthly deposition data from two collectors located at a distance of 600 m were compared from 1991 to 2000. On the average, the deposition rates differed by roughly a factor of two for ¹³⁷Cs, whereas for the cosmogenic ⁷Be a difference was not detectable with statistical significance. Further, a “funnel” collector with a mostly dry surface collected on the long-term average 36% less of ¹³⁷Cs, but 8% less of ⁷Be, than a “pot” collector with a continuously water-covered surface. Since for ¹³⁷Cs deposition and the bulk deposition a similar behaviour was found, a stronger sensitivity of other resuspension-derived radionuclides against local and collector surface variations can generally be expected.     

Observation of beta-ray spectra after penetrating absorbing materials.

β-Ray spectra after penetrating absorbing materials of various thicknesses were observed by the use of a scintillation-type β-ray spectrometer equipped with a flat NE-102 plastic scintillator of 5 mm thickness for sources of ⁶⁰Co, ⁹⁰Sr–⁹⁰Y, ¹³⁷Cs, ¹⁴⁷Pm and ²⁰⁴Tl. Although the spectra changed rapidly with increasing absorber thickness, the average β-ray energy was kept nearly constant for a wider range. These results are consistent in that the β-ray absorption curve becomes quasi-linear in a semi-logarithmic plot. Spectra including scattered β-rays from several materials placed behind the source were also measured for ¹³⁷Cs and ²⁰⁴Tl. It may be concluded that mean energy measurements by the use of β-ray spectrometer of this kind is useful for the identification of nuclides in radiation protection purposes even in worse source-conditions.     

Radionuclide accumulation in near-shore sediments along the Bulgarian Black Sea coast

The accumulation of radionuclides in Black Sea marine ecosystems was investigated by low level gamma spectrometry. Artificial as well as natural radionuclides were determined in bottom sediments samples from 35 reference locations along the Bulgarian Black Sea coast, evenly distributed from the Rumanian to the Turkish border including the main Black Sea resorts and rivers. The measurement of radionuclides in sea bed sediments was carried out during six consecutive seasons using a HPGe detector. The data obtained show that the nuclide concentrations depend strongly on the sediment nature. Results for sandy sediments are within close range, while those for slime and silt vary to a much greater extent. The radionuclide content in the sandy sediments of the main Black Sea resorts is at the lowest limit of the determined values. Small seasonal changes of radionuclide concentration in sandy sediments were observed while greater variations in slime and silt occur. From the data obtained ¹³⁴Cs/¹³⁷Cs and ¹³⁷Cs_meas/¹³⁷Cs_Chern ratios are calculated to determine the Chernobyl part of the measured ¹³⁷Cs. The activities determined in the sediments for natural radionuclides correspond to those cited in the literature for natural levels, showing no additional anthropogenic contamination. A data base for the nuclide concentration values was created which will enable the modeling of radionuclide transfers by estimation of their concentration variations, accumulation and influence on the marine ecosystems.     

Attenuation coefficients of soils and some building materials of Bangladesh in the energy range 276–1332 keV

The linear and mass attenuation coefficients of different types of soil, sand, building materials and heavy beach mineral samples from the Chittagong and Cox's Bazar area of Bangladesh were measured using a high-resolution HPGe detector and the γ-ray energies 276.1, 302.8, 356.0, 383.8, 661.6 and 1173.2 and 1332.5 keV emitted from point sources of ¹³³Ba, ¹³⁷Cs and ⁶⁰Co, respectively. The linear attenuation coefficients show a linear relationship with the corresponding densities of the samples studied. The variations of the mass attenuation coefficient with γ-ray energy were exponential in nature. The measured mass attenuation coefficient values were compared with measurements made in other countries for similar kinds of materials. The values are in good agreement with each other in most cases.     

Distribution of radiocesium and natural gamma emitters in pine needles in coniferious forest sites of Izmir

Using a high-resolution gamma-spectrometer system, the activity concentrations of ⁷Be, ¹³⁷Cs, ⁴⁰K and ²²⁶Ra were determined in the pine needles. Activity concentrations of the concerned radionuclides in the needle samples were as follows: ⁷Be, 24.6±2.40 to 210±7.21 Bq kg⁻¹, ⁴⁰K, 23.5±12.4 to 287±15.6 Bq kg⁻¹, ²²⁶Ra, 0.44±0.12 to 12.3±2.18 Bq kg⁻¹, and ¹³⁷Cs, 0.61±0.30 to 2.29±0.38 Bq kg⁻¹. It is found that the frequency distributions obtained for ⁷Be and ¹³⁷Cs can be fitted to a normal distribution, and for ⁴⁰K and ²²⁶Ra can be fitted to a log-normal distribution.     

On the use of mercury as a means of locating background sources in ultra low-background HPGe-detector systems

In low-level gamma-ray spectrometry, it is common to measure large samples in order to obtain low detection limits for the massic activity (in mBq/kg). These samples have significant shielding effects. In order to study whether the background sources in three ultra low-background HPGe detectors were located in the detector or in the shield, Marinelli beakers filled with hyperpure mercury were measured. Although the measurements were hampered by the presence of cosmogenically produced ¹⁹⁴Hg, information regarding the major background location of ⁴⁰K, ⁶⁰Co, ¹³⁷Cs, ²¹⁰Pb, ²²⁶Ra, ²²⁸Ra and ²²⁸Th could be obtained.     

Optimization of low activity spectrometric gamma–gamma probes for ash determination in coal stockpiles

A stockpile probe based on backscattered gamma–gamma-ray technique was tested for the determination of coal ash. A centralized tool employing a gamma-ray source of very low radioactivity (1.85 MBq) was used. This logging tool was tested using ¹³⁷Cs and ¹³³Ba sources with a 37 mm (diameter) by 75 mm NaI (TI) scintillation detector. Ten source–detector configurations were analyzed using ¹³⁷Cs, and another nine source–detector configurations are analyzed, using ¹³³Ba source, both for four geophysical models, having a borehole diameter of 90 mm. Regression analysis on the laboratory logging data for each studied configuration was carried out in order to establish calibration equations for ash prediction. The optimum configuration for the logging stockpile probe using ¹³⁷Cs source was determined to be 80 mm source to detector spacing, and 80 mm iron thickness shielding. This configuration gives the best results for ash prediction. The root mean square (rms) deviation for ash is 1.52%. The optimum configuration for the logging stockpile probe using ¹³³Ba source is determined to be 85 mm source to detector spacing, and 50 mm iron thickness shielding. This configuration gives the best results for ash prediction, where the rms deviation for ash is 1.47%.     

Distribution of radionuclides in the river sediments and coastal soils of Chittagong, Bangladesh and evaluation of the radiation hazard

The concentrations and distribution of natural and anthropogenic radioactive materials in sediments and soils from around the two major rivers and coastal area of Chittagong, Bangladesh were investigated with an aim of evaluating the environmental radioactivity and radiation hazard. In the sediment and soils in general, the concentration of ²³²Th was found to be higher than that of the ²³⁸U and the activities of ²³²Th and ²³⁸U in this area are higher than the world average. ¹³⁷Cs was observed in all the samples, ranging from 0.4 to 3.88 Bq kg⁻¹. The radium equivalent activities, emanation coefficients and radon exhalation rates were estimated for the sediment and soils; the emanation coefficients, radon exhalation rates and dose rates were found to be higher than the world average values.     

Comparison of four methods used in determination of secondary shielding requirements for a teletherapy facility: a case study of Cs room in Tanzania

The performance of four methods often used to calculate the secondary barrier requirements is evaluated for a typical ¹³⁷Cs-therapy room as a case study. The first two methods are provided by the NCRP49 and IAEA and both consider the influence of the primary, leakage and scattered radiation at a point as corrected for the workload, use and occupancy factors. A different shielding model encompasses the third method, which determines the doses as corrected for build-up effects assuming the narrow beam geometry. The fourth method is based on the calculation of the dose rates from the source activity with a relevant gamma constant. In all four methods, an appropriate transmission factor for the protective barrier in question is applied. The results show that for controlled area, the similarity in the calculated thicknesses using all four methods was nearly within 50%. For uncontrolled areas, a significant difference of magnitude up to a factor of 2.4 was found, which is mainly attributed to the non-consideration of occupancy factors in the latter two methods. Nevertheless, the non-agreement is useful to validate the specific assumptions taken for the employed shielding method. Despite being slightly high, it is concluded that the current shielding methods based on NCRP fundamentals are satisfactorily optimal in planning new therapy facilities. However for existing facilities, such as those undesigned according to the standard requirements, the combination of the four different methods with the dose rate measurements tend to offer a better cost effective shielding option. Retrospectively, additional 41-cm thick concrete is recommended for the unshielded southern barrier of the ¹³⁷Cs room. Interestingly, the recommended thickness agrees to within ±5% with that estimated by using the recently recommended method by IAEA.     

Peak efficiency calibration for attenuation corrected cylindrical sources in gamma ray spectrometry by the use of a point source

A theoretical method of determining the gamma-ray peak efficiency for a cylindrical source, based on a modified expression for point sources is derived. A term for the photon self-attenuation is included in the calculation. The method is valid for any source material as long as the source activity concentration is considered to be homogeneous. Results of this expression are checked against experimental data obtained with ²⁴¹Am, ⁵⁷Co, ¹³⁷Cs, and ⁶⁰Co sources.     

Neutron detection via bubble chambers

Research investigating the application of pressure-cycled bubble chambers to fast neutron detection is described. Experiments with a Halon-filled chamber showed clear sensitivity to an AmBe neutron source and insensitivity to a ¹³⁷Cs gamma source. Bubble formation was documented using high-speed photography, and a ceramic piezo-electric transducer element registered the acoustic signature of bubble formation. In a second set of experiments, the bubble nucleation response of a Freon-134a chamber to an AmBe neutron source was documented with high-speed photography.     

Results obtained in the metrological certification of a commercially available radionuclide calibrator

The paper presents the results obtained at IFIN-HH during a metrological certification of the commercially available radionuclide calibrator, the CURIEMENTOR2. Its performance was tested for the radionuclides: ⁵⁷Co, ^99mTc, ¹³¹I and ¹³⁷Cs. The calibration factors determined by the manufacturer and those obtained at IFIN-HH differed by less than 3.5%. New calibration factors were determined for ⁶⁰Co and ¹⁸⁸Re, which have, until now, not been distributed by the manufacturer to the users. Furthermore, the linearity of instrument response and the dependence of measuring geometry were checked and found in accordance with the international accepted standards and legal requirements.     

A new technique for processing airborne gamma ray spectrometry data for mapping low level contaminations

A new technique for processing airborne gamma ray spectrometry data has been developed. It is based on the noise adjusted singular value decomposition method introduced by Hovgaard in 1997. The new technique opens for mapping of very low contamination levels. It is tested with data from Latvia where the remaining contamination from the 1986 Chernobyl accident together with fallout from the atmospheric nuclear weapon tests includes ¹³⁷Cs at levels often well below 1 kBq/m² equivalent surface contamination. The limiting factors for obtaining reliable results are radon in the air, spectrum stability and accurate altitude measurements.     

Comparison of a digital and an analog signal processing system for neutron inelastic gamma-ray spectrometry

We compared the value of using a digital signal processing unit for gamma-ray spectroscopy with that of an analog one for in situ measurements of gamma-rays generated by inelastic neutron scattering reactions with soil elements. A large cylindrical NaI(Tl) scintillation detector, 15.24 cm high by 15.24 cm diameter was used to measure carbon (C) and oxygen (O). The performance of the systems was assessed as a function of input count rate (ICR) by monitoring the peak areas of the C, 4.43 MeV, and O, 6.13 MeV, gamma-rays. In separate experiments, the digital and the analog systems were also compared using an intense 10.3 mCi ¹³⁷Cs source to vary the ICR, and the 1.17 MeV peak area of ⁶⁰Co was used as the reference.     

Gamma spectroscopic assay of soil samples from waste dump sites in Port Harcourt, Nigeria

A lead shielded 7.6 cm×7.6 cm NaI (Tl) detector and a Canberra Multichannel Analyzer were employed for a gamma spectrometric assay of 100 soil samples from refuse dump sites in Port Harcourt city and environs. The massic activities of ⁴⁰K, ²²⁶Ra and ²²⁸Ra were determined and found to correspond to natural levels of some 10 Bq/kg. No gamma-emitting anthropogenic radionuclides were detected. The mean radium equivalent is 44.2 Bq/kg giving a dose rate of 24.6 μSv/year.     

Precise tests of internal-conversion theory

Using the 165.9-keV M1 transition in ¹³⁹La as a calibrant, we have determined the K-shell internal conversion coefficients (ICCs) for the 127.5-keV E3 transition in ¹³⁴Cs and the 661.7-keV M4 transition in ¹³⁷Ba to 0.6% precision. Unlike previous less-precise measurements of these ICCs, which differed significantly from calculated values, our results agree well with calculations that include the atomic K-shell vacancy and disagree with those that exclude it. These results, which are consistent with what we also found for ¹⁹³Ir, confirm our earlier conclusions but for different energies, multipolarities and atomic numbers.     

Gamma-ray density and thickness gauges using ultra-low activity radioisotope sourcesfillin

 Most commercial nuclear density gauges use either ¹³⁷Cs or ⁶⁰Co sources of activity between about 185 and 1850 MBq (5 and 50 mCi). In the current work, density and thickness gauges that use ultra-low activity gamma-ray sources that are exempt from licensing requirements have been investigated. Results are reported on gauges that use a 1 MBq ²²Na source for determining slurry density in the CSIRO UltraPS slurry particle size analyser and for determining belt loading in the CSIRO on-conveyor belt microwave moisture gauge.