High Levels Of Background Radiation Research Articles

Combined X-ray absorption and SEM–EDX spectroscopic analysis for the speciation of thorium in soil

Mobility and bioavailability of radionuclides in the environment strongly depend on their aqueous speciation, adsorption behavior and the solubility of relevant solid phases. In the present context, we focus on naturally occurring Th-232 at a location in central Sri Lanka presenting high background radiation levels. Four different soil samples were characterized using X-ray Absorption Spectroscopy (XAS) at the Th L3-edge (16.3 keV), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy. X-ray Absorption Near Edge Structure (XANES) spectra are applied as a fingerprint indication for Th existing in different chemical environments. Linear combination fitting (LCF) of the Extended X-ray Absorption Fine Structure (EXAFS) data involving reference Th-monazite (phosphate) and thorianite (oxide) compounds suggested that Th is mostly present as Th-phosphate (76 ± 2%) and Th-oxide (24 ± 2%), even though minor amounts of thorite (silicate) were also detected by SEM–EDX. Further studies on selected individual particles using micro-focus X-ray Fluorescence (μ-XRF) and micro-X-ray Absorption Spectroscopy (μ-XAS) along with SEM–EDX elemental mapping provided information about the nature of Th-bearing mineral particles regarding mixed phases. This is the first study providing quantitative and XAS based speciation information on Th-mineral phases in soil samples from Sri Lanka.

INTERNAL EXPOSURE FROM INDOOR RADON, THORON AND THEIR PROGENY IN RESIDENCE AROUND HIGH BACKGROUND RADIATION AREA, PHANG NGA PROVINCE, THAILAND.

A passive integrating discriminative radon-thoron monitor (Raduet) and a radon-thoron progeny monitor with a solid-state nuclear tracking detector were used for estimating indoor radon, thoron and their progeny concentrations in residential areas around the old mines of southern Thailand. Exposure to high background radiation levels from natural 238U and 232Th in the tin mine areas or active fault areas may increase the risk of lung cancer in the respiratory system when considering the health effects of the surrounding inhabitants. In this study, radon thoron and their progeny concentrations from inhalation in the study site have been assessed in dose at volunteer houses to confirm radiation effects. The annual effective doses due to inhalation of radon-thoron, radon progeny and thoron progeny using the ICRP latest dose conversion factors were estimated to be 3.0-4.6, 2.5-3.7 and 0.4-1.0mSv, respectively, and as 5.9-9.0mSv in total.

Determination of Activity Concentration of Natural Radionuclides and Radiation Hazards' Assessment of Building Materials in High Background Radiation Areas of Homa and Ruri, Kenya.

The areas around Homa and Ruri hills in Homa Bay County in Kenya are associated with high background radiation levels. The activity concentration of the natural radionuclides (226Ra, 232Th, and 40K) in earthen building materials used in the areas of Homa and Ruri hills has been measured using a NaI (Tl) detector in this work. The measured values of radioactivity concentrations are used to estimate the associated radiological risk. The earthen building material samples from Ruri registered relatively high 232Th concentration values averaging 1094 ± 55 Bq/kg, nearly three times those of the samples from Homa. 226Ra level was not significantly different in both regions with Homa reporting 129 ± 10 Bq/kg and Ruri 111 ± 6 Bq/kg. 40K was however higher in the samples from Homa by an approximate factor of 2 relative to those from Ruri where the activity concentration was 489 ± 24 Bq/kg. The radium equivalents for 226Ra, 232Th, and 40K in the samples from Ruri were 111 ± 9, 1564 ± 125, and 38 ± 3 Bq/kg, while in Homa, the values were 129 ± 10, 570 ± 46, and 69 ± 5 Bq/kg, respectively. The calculated value of total radium equivalent in Ruri was 1713 ± 137 Bq/kg which was two times higher than that of Homa. 232Th contributed about 74% and 91% to the total radium equivalent in Homa and Ruri, respectively; thus, it was the one with the largest contribution to radiation exposure in both regions. The average indoor annual effective dose rates were 1.74 ± 0.14 and 3.78 ± 0.30 mSv/y in Homa and Ruri, respectively, both of which were above the recommended safety limit of 1 mSv/y.

Design and simulation of landmines detection system based on fast neutron analysis

A landmine detection system based on D-T sealed neutron generator was set up to verify the validity of fast neutron analysis (FNA) for landmine detection. The results of experiment and MCNP5 simulation prove that the capacity of FNA for landmine detection is greatly limited due to its high background radiation levels. Inspired by previous efforts, the application of tagged neutron method (TNM) for landmine detection was investigated and modeled by MCNPX code. The gamma spectra of graphite sample were compared at different time windows. The appropriate selection of time window is effective for the landmine location and the background suppression. The influence of the soil humidity was studied for the landmine buried at different depths. The simulation results showed that the peak area ratio of C/Si and C/O can be used to effectively identify explosive materials in the detection area.

Investigating the expression level of NF-KB and HIF1A genes among the inhabitants of two different background radiation areas in Ramsar, Iran

This study investigated the fluctuation of NF-KB and HIF-1a gene expression between inhabitants of a high-level background radiation area (HBRA) and a normal-level background radiation area (NBRA) of Ramsar, Iran. Sixty participants with the mean age of 48 ± 15 years were selected and divided into two groups. The group receiving a dose of ≤1.5 mGy/year (NBRA) was considered the control group and the target group (HBRA) received a dose of >1.5 mGy/year. These two groups were from neighbor regions to minimize socioeconomic differences between the participants. Blood samples were collected from each group and NF-KB and HIF-1a expression levels were compared using quantitative real-time PCR (qPCR) based on the stem loop method. The effects of residency duration in the respective areas and gender on the expression of NF-KB and HIF-1a was also examined. The HIF-1a expression level was statistically lower in the HLBRA region (P < 0.0002), while NF-KB expression was upregulated (P < 0.0001). Although the under-expression of HIF-1a in response to dose rate was significant in females (P < 0.0004), it was not different in males (P = 0.74), indicating a significant difference between sexes (P = 0.0047). The upregulation of NF-KB expression related to dose level was also significant for the female group (P < 0.0001), whereas it was not for the male group (P = 0.72). Notably and as expected, there was a significant relation between longer residency in the HBRA and HIF-1A under-expression (P < 0.026), while there was no effect of increasing residency time for NF-KB over-expression level (P = 0.29). The dwellers of the HBRA those noted that despite receiving an elevated radiation level were seemingly good in general health, showed some alterations in their molecular mechanisms, specifically HIF-1a and NF-KB expression levels. It is not clear if this is indicative of a beneficial adaptive response and more research is recommended.

A Glance at the Errors of Some Studies on the Health Effects of High Background Natural Radiation Areas

There is no place on the Earth, the planet we live on, where the natural background radiation level is zero. Since the birth and even in our fetal stage, we have been exposed to different sources of natural radiation. Life, in fact, evolved in a radiation environment that was much more harsh than today. Earth serves as a source of terrestrial radiation. Uranium, thorium, and radium are among the radioactive materials that naturally exist in soil and rock. Moreover, the air, we breathe, contains radon, a colorless, odorless, radioactive gas that is created naturally by the radioactive decay of uranium and radium. The crucial importance of the studies on the health effects of living in areas with high levels of background radiation for understanding the biological impact of exposure to low doses of ionizing radiation is well documented. Despite the undeniable need for accurate information about the health effects of exposure to high levels of background radiation, many published papers suffer from methodological and other common types of errors. In this paper, we review three articles published on high background radiation areas. The first paper has addressed the frequencies of unstable (dicentrics& rings), stable (translocations & inversions), and other types of chromosome aberration in adult men from both high background radiation areas of Kerala and areas with normal background radiation. The second paper has addressed different aspects of the world’s high background natural radiation areas. Finally, the third paper has tried to address the role of background radiation on males to females’ ratio at birth. The author has mainly referred to the studies performed on the impact of radiation exposures from nuclear testing (worldwide) and Chernobyl fallout (in Europe).The major shortcomings of these three papers, especially methodological errors, which affected the accuracy of their findings and conclusions are discussed.

Compact laser radar based on a subnanosecond laser diode transmitter and a two-dimensional CMOS single-photon receiver

A pulsed TOF laser radar utilizing the single-photon detection mode has been implemented, and its performance is characterized. The transmitter employs a QW double-heterostructure laser diode producing 0.6 nJ/100 ps laser pulses at a central wavelength of ∼810 nm. The detector is a single-chip IC manufactured in the standard 0.35-μm HV CMOS process, including a 9×9 single-photon avalanche diode (SPAD) array and a 10-channel time-to-digital converter (TDC) circuit. Both the SPAD array and the TDC circuit support a time gating feature allowing photon detection to occur only within a predefined time window. The SPAD array also supports a 3×3 SPADs subarray selection feature to respond to the laser spot wandering effect due to the paraxial optics and to reduce background radiation-induced detections. The characterization results demonstrate a distance measurement accuracy of +/−0.5 mm to a target at 34 m having 11% reflectivity. The signal detection rate is 28% at a laser pulsing rate of 100 kHz. The single-shot precision of the laser radar is ∼20 mm (FWHM). The deteriorating impact of high-level background radiation conditions on the SNR is demonstrated, as also is a scheme to improve this by means of detector time gating.

Review on studies in natural background radiation

The environment around us is radioactive due to background radiation emitted from the sky, earth's crust, food, water, and building materials. The human body gets exposed to radiation doses of about 82%, which are out of control; they arise from background radiation sources such as terrestrial, cosmic, and exposure to internal radiation. The background dose from cosmic radiation depends on the altitude, and regions with high altitude have high radiation doses. Natural radioactivity is present in the earth and is present in the different environment geological formations in the rocks and soils. Gamma radiation emitted from naturally occurring radioisotopes, such as 40K and the radionuclides from the 232Th and 238U series and their decay products which exist as trace levels in all ground formations, represents the main external source of irradiation to the human body. Their concentrations in rocks, soils, and sands depend on the local geology of each region in the world. Naturally occurring radioactive materials have terrestrial-origin radionuclides since the creation of the earth. The dose rate of background radiation increases because of the existence of some quarries and springs in some regions which are called high-level background radiation regions. The type of construction materials used in houses can be affecting the dose rate of background radiations. Study of radioactivity in the environment is important to monitor the levels of radiation to which human is exposed directly or indirectly. Recently, several international studies have been done and different values were measured. In this article, a review and literature survey of background radiations such as terrestrial, cosmic, and food radiation was carried out.

Visual Detection of Cesium Ions in Domestic Water Supply or Seawater using a Nano-optode

Abstract Cesium, in particular radioactive Cs 137 is currently a significant environmental problem in Japan following the incident at the Fukushima-Daiichi nuclear power plant caused by the Great East Japan earthquake. Although radioscopes and gamma ray cameras have been developing to visualize radioactive species or contamination, it is not necessarily a simple matter to locate sources of contamination under high levels of background radiation. However, supramolecular approaches for environmental sensing of analyses are useful in the design of high-resolution molecular sensors. Here, we have developed an optical imaging technique for cesium ions involving an optode system in environmental water. An optode membrane was prepared incorporating a calix[6]arene derivative, which showed excellent selectivity toward cesium ions in aqueous solutions, even in water supplied for domestic use or seawater. Furthermore, this membrane was fabricated using nanoparticles with a diameter of ca. 100 nm. The nano-optode also gave an excellent response to cesium ions. Therefore, this optode provides a higher spatial resolution than existing radioscopes and gamma ray cameras under high level radioactive environments.

Surface temperature measurements from a stator vane doublet in a turbine afterburner flame using a YAG:Tm thermographic phosphor

Phosphor thermometry measurements in turbine engine environments can be difficult because of high background radiation levels. To address this challenge, luminescence lifetime-based phosphor thermometry measurements were obtained using thulium-doped Y3Al5O12 (YAG:Tm) to take advantage of the emission wavelengths at 365 nm (1D2 → 3H6 transition) and at 456 nm (1D2 → 3F4 transition). At these wavelengths, turbine engine radiation background is reduced compared with emission from longer wavelength phosphors. Temperature measurements of YAG:Tm coatings were demonstrated using decay of both the 365 and 456 nm emission bands in a furnace environment up to 1400 °C. To demonstrate that reliable surface temperatures based on short-wavelength YAG:Tm emission could be obtained from the surface of an actual engine component in a high gas velocity, highly radiative environment, measurements were obtained from a YAG:Tm-coated Honeywell stator vane doublet placed in the afterburner flame exhaust stream of the augmenter-equipped General Electric J85 turbojet test engine at the University of Tennessee Space Institute (UTSI). Using a probe designed for engine insertion, spot temperature measurements were obtained by measuring luminescence decay times over a range of steady state throttle settings as well as during an engine throttle acceleration. YAG:Tm phosphor thermometry measurements of the stator vane surface in the afterburner exhaust stream using the decay of the 456 nm emission band were successfully obtained at temperatures up to almost 1300 °C. Phosphor thermometry measurements acquired with the engine probe using the decay of the 365 nm emission band were not successful at usefully high temperatures because the probe design allowed transmission of intense unfiltered silica Raman scattering that produced photomultiplier tube saturation with extended recovery times. Recommendations are made for probe modifications that will enable temperature measurements using the 365 nm emission band decay, which will be beneficial in environments with strong reflections of combustor radiation.

Evaluation of excess life time cancer risk from gamma dose rates in Jhelum valley

Human beings are continuously exposed to the radiations coming from outside and inside their bodies. Outside and inside radiations are coming from ground, building materials, food, air, the universe and even elements within human own bodies. According to UNSCEAR 2000 report, background radiations deliver an average effective dose of 2.4 mSv per person worldwide. Sustained exposure from high background radiation levels may pose substantial health threats to general public. In the current study we are presenting the results of ambient outdoor gamma dose rates measured for Jhelum valley of the state of Azad Kashmir. This study has been carried out by using Ludlum micrometer-19 which is an active and portable detector. Effects of different parameters of interest on the measured values of gamma dose rates have been investigated. For the region under investigation, minimum and maximum indoor gamma dose rates were found as 610 ± 4.05 μGy·y−1 and 1372 ± 2.7 μGy·y−1, respectively, whilst minimum and maximum outdoor gamma dose rates were found as 495 ± 4.49 μGy·y−1 and 1296 ± 2.78 μGy·y−1, respectively. Overall arithmetic mean (A.M) and geometric mean (G.M) values of gamma dose rates for indoor and outdoor measurements were found as 940 ± 3.26 μGy·y−1, 892 ± 3.35 μGy·y−1 and 928 ± 3.28 μGy·y−1, 880 ± 3.37 μGy·y−1 respectively. Excess life time cancer risk (ELCR) for indoor exposure ranges from 1.057 × 10−3 to 2.377 × 10−3 with an average value of 1.629 × 10−3. For outdoor exposure, ELCR varies from 0.352 × 10−3 to 0.792 × 10−3 with mean value of 0.543 × 10−3. Average values of indoor gamma doses were found to be greater than the world population-weighted average for indoor gamma dose rates (780 μGy·y−1 or 89 nGy h−1).

A review on natural background radiation

The world is naturally radioactive and approximately 82% of human-absorbed radiation doses, which are out of control, arise from natural sources such as cosmic, terrestrial, and exposure from inhalation or intake radiation sources. In recent years, several international studies have been carried out, which have reported different values regarding the effect of background radiation on human health. Gamma radiation emitted from natural sources (background radiation) is largely due to primordial radionuclides, mainly 232Th and 238U series, and their decay products, as well as 40K, which exist at trace levels in the earth's crust. Their concentrations in soil, sands, and rocks depend on the local geology of each region in the world. Naturally occurring radioactive materials generally contain terrestrial-origin radionuclides, left over since the creation of the earth. In addition, the existence of some springs and quarries increases the dose rate of background radiation in some regions that are known as high level background radiation regions. The type of building materials used in houses can also affect the dose rate of background radiations. The present review article was carried out to consider all of the natural radiations, including cosmic, terrestrial, and food radiation.

Annual intakes of 226Ra, 228Ra and 40K in staple foodstuffs from a high background radiation area in the southwest region of Cameroon

Concentrations of naturally occurring radionuclides 226Ra, 228Ra and 40K were determined in five most consumed vegetables in a high-level background radiation area (HLBRA) in the southwest region of Cameroon. A total of 25 foodstuff samples collected from Akongo, Ngombas, Awanda, Bikoué and Lolodorf rural districts were analyzed by gamma spectrometry. The average activity concentration values of 226Ra, 228Ra and 40K were respectively 2.30, 1.50 and 140.40 Bq kg−1 fresh-weights. The effective dose for individual consumption of the investigated foodstuff types was calculated on an estimated annual intake of such diets in the study area. The estimated total daily effective doses from the ingestion of the investigated foodstuffs for each studied long-life natural radionuclide were respectively 0.41 μSv for 226Ra, 0.84 μSv for 228Ra and 0.71 μSv for 40K. The total annual effective dose was estimated at 0.70 mSv y−1. 228Ra (44%) and 40K (36%) were found to be the main sources for internal irradiation which is very likely due to the specific uptake of these radionuclides by the studied plants.

Natural Radiation Induced Developmental Disability: An Avian Model

AbstractRadiation exposure during gestation causes mutation in the fetus leading to birth defects in the newborn. On a survey of the coastal villages of Kanyakumari District, Tamilnadu, India, high levels of background radiation were detected, which was suggestive of inducing mutations, and congenital abnormalities in the exposed population. To substantiate the dangerous impact of such natural radioactive emissions, we have established an avian model of irradiation-induced birth defect in chicks hatched from eggs exposed to natural radioactive beach sand. The hatched experimental chicks exhibited severe locomotor disability and extreme malformations. Our study proves for the first time, that natural beach sand radiation induces severe developmental abnormalities. The results of this experiment brings to light, the importance of radiation-protection during gestation and also the need for monitoring and cleaning of radioactive sand deposits in beaches all over the world.

Background radiation and individual dosimetry in the costal area of Tamil Nadu, India

South coast of India is known as the high-level background radiation area (HBRA) mainly due to beach sands that contain natural radionuclides as components of the mineral monazite. The rich deposit of monazite is unevenly distributed along the coastal belt of Tamil Nadu and Kerala. An HBRA site that laid in 2×7 m along the sea was found in the beach of Chinnavillai, Tamil Nadu, where the maximum ambient dose equivalent reached as high as 162.7 mSv y(-1). From the sands collected at the HBRA spot, the high-purity germanium semi-conductor detector identified six nuclides of thorium series, four nuclides of uranium series and two nuclides belonging to actinium series. The highest radioactivity observed was 43.7 Bq g(-1) of Th-228. The individual dose of five inhabitants in Chinnavillai, as measured by the radiophotoluminescence glass dosimetry system, demonstrated the average dose of 7.17 mSv y(-1) ranging from 2.79 to 14.17 mSv y(-1).

Survey of Radioiodine Therapy Safety Practices Highlights the Need for User-Friendly Recommendations

Fetuses whose mothers are treated with radioiodine after approximately 10–12 weeks of pregnancy are at high risk of developing iatrogenic hypothyroidism (1). Other than this well-documented occurrence, there is no evidence of harm to others from radiation originating from patients treated with radioiodine. Given that radioiodine is concentrated in breast milk and radioiodine has been documented to be taken up by the thyroid in nursing newborns whose mothers were given diagnostic activities of radioiodine (2), discontinuing lactation before radioiodine therapy and avoiding breastfeeding after radioiodine treatment is justified despite the lack of a case report of infantile hypothyroidism ascribed to radioiodine ingestion from breastfeeding. Aside from circumstances relating to pregnancy and lactation, the harm that a radioiodine-treated patient could inflict upon another person while following common sense instructions appears to be low. Patients, who themselves receive a much higher dose of radiation because they ingest the full radioiodine treatment, suffer relatively few side effects. For the most part these occur in tissues that actively take up the radionuclide, and the adverse effects occur in a dose-dependent manner (3). This provides some reassurance that the small amount of radiation exposure to the public from those who receive radioiodine treatment is unlikely to cause harm, even if the treated patients ignore nearly all of the radiation safety instructions they receive. On the other hand, it is known that thyroidal exposure to higher levels of radiation, especially in children, can result in harm (4) and by extrapolation with a linear no-threshold dose–response relationship, one may assume that exposure to low levels of radiation might result in some harm. Thus, this theoretical possibility of increased harm at any increase of radiation exposure beyond background radiation, combined with no evidence of benefit of radiation exposure to the public, has led to the practice of keeping radiation exposure to others As Low As Reasonably Achievable (ALARA). High levels of radiation exposure are dangerous. It has been estimated that half of the people receiving a dose to the whole body over a few minutes to a few hours of between 3500 and 5000 mSv would die within 30 days (multiple mSv by 100 to convert to mrem). Similarly, high-dose exposure (starting somewhere between 100 and 1000 mSv) over a relatively short period of time, is associated with the development of a number of malignancies. Conversely, the average yearly radiation exposure from natural sources to an individual in the United States is approximately 3 mSv. Radon gas accounts for two thirds of this exposure, while cosmic, terrestrial, and internal radiation account for the remainder. No adverse health effects have been demonstrated from these levels of natural radiation exposure. In addition, artificial sources of radiation from medical, commercial, and industrial activities contribute another 0.6 mSv, for a total average yearly radiation exposure of 3.6 mSv. Doses (in mSv) from common medical imaging procedures include the following: bitewing dental x-ray, 0.004; chest x-ray (posterior-anterior), 0.02; lateral lumbar spine x-ray, 0.3; mammography, 0.7; lung ventilation/perfusion scan, 1.5; barium swallow, 1.5; technetium-99m bone scan, 4.4; barium enema, 7; 2-deoxy2[F-18]fluoro-d-glucose positron emission tomography scan, 7; chest or abdominal computed tomography scan, 8-10; and coronary angiogram, 5–16. A personalized annual radiation dose estimate can be calculated at the website http:// www.epa.gov/radiation/understand/calculate.html. Although radiation may cause cancers at high doses and dose rates, currently there are no data that unequivocally establish the occurrence of cancer following exposure to low doses or dose rates (e.g., below about 100 mSv). People living in areas with high levels of background radiation (>10 mSv per year) such as Denver, Colorado, have shown no adverse biological effects. Keep these millisievert values in mind as you read the next paragraph. Effective May 29, 1997, and updated on July 29, 2009, the Nuclear Regulatory Commission (NRC) revised Federal Regulation 10 CFR 35.75, which permits NRC-licensed facilities to release a patient treated with radioiodine from their control if the total effective dose equivalent to any other individual from exposure to the released individual is not likely to exceed 5 mSv. Further, a licensee must provide the released individual, or the individual’s parent or guardian, with instructions (including written instructions) on actions

Development of Land Mine Detector System Based on the Measurements of Capture γ-Rays with Anticoincidence and Coincidence Methods

In this paper, we describe a detector system for finding land mines in the soil using 10.83 and 2.22 MeV capture γ-ray detections by neutron capture reactions with nitrogen and hydrogen, respectively. There are certain difficulties in land mine detection, including high background radiation levels during measurement and a low detection efficiency of high-energy γ-rays. To overcome these difficulties, a methodology involving simultaneous measurements using anticoincidence and coincidence methods and a combination of BGO and NaI(Tl) scintillators is proposed. The background radiation level is suppressed using this methodology and the detection efficiency of high-energy γ-rays is improved. Consequently, it should be possible to detect land mines buried in the soil with a high efficiency.

High background radiation investigated by gamma spectrometry of the soil in the southwestern region of Cameroon

The aim of this work is to determine the radioactivity concentration of 226Ra, 232Th and 40K in sub-surface (0–5 cm) soil samples collected from Awanda, Bikoué, Ngombas in the southwestern region of Cameroon, to assess their contribution to the external dose exposure relative to the United Nation Scientific Committee on Effects of Atomic Radiation (UNSCEAR) data. An HPGe p-type detector coupled to a multichannel analyzer was used to perform measurements and data processing. The activity concentrations of 226Ra varied from 0.06 ± 0.01 to 0.27 ± 0.02 kBq kg −1 with a mean value of 0.13 ± 0.01 kBq kg −1 wet weight. The activity concentrations of 232Th varied from 0.10 ± 0.01 to 0.70 ± 0.05 kBq kg −1 with a mean value of 0.39 ± 0.03 kBq kg −1 wet weight, and 40K concentrations varied from 0.37 ± 0.02 to 1.53 ± 0.11 kBq kg −1 with a mean value of 0.85 ± 0.07 kBq kg −1 wet weight, respectively. The mean value of outdoor annual effective doses were estimated to be 0.48 mSv y −1, 0.39 mSv y −1 and 0.38 mSv y −1 from Ngombas, Awanda and Bikoué, respectively. The studied areas can be said to have a high background radiation level.

Recent Progress in the Design of a Tomographic Device for Measurements of the Three-Dimensional Pin-Power Distribution in Irradiated Nuclear Fuel Assemblies

A tomographic technique for determination of the thermal power distribution in nuclear fuel assemblies is under development. The purpose is to provide an experimental validation tool for core simulation codes. Such codes are essential for the operation of nuclear power reactors, and validation is important in the process of improving and developing the codes as well as the fuel.The tomographic method is nonintrusive and offers large amounts of data within a normal revision shutdown. In earlier experimental investigations using a test platform, the method proved useful, demonstrating results of satisfying quality. However, the measuring setup also revealed nonfeasible properties related to transport, decontamination, and background radiation shielding.In this paper, the design of a new measuring device is presented. It is based on experiences from the test platform, but its size and weight make it advantageous regarding transports and decontamination. Moreover, the design inherently allows for more efficient background shielding.The latter has been investigated in a detailed study using the MCNP simulation code. The results confirm the high levels of background radiation observed in the test platform. It is also concluded that the shielding properties in the new design are sufficient.

The radioprotective properties of fungal melanin are a function of its chemical composition, stable radical presence and spatial arrangement

Melanized microorganisms are often found in environments with very high background radiation levels such as in nuclear reactor cooling pools and the destroyed reactor in Chernobyl. These findings and the laboratory observations of the resistance of melanized fungi to ionizing radiation suggest a role for this pigment in radioprotection. We hypothesized that the radioprotective properties of melanin in microorganisms result from a combination of physical shielding and quenching of cytotoxic free radicals. We have investigated the radioprotective properties of melanin by subjecting the human pathogenic fungi Cryptococcus neoformans and Histoplasma capsulatum in their melanized and non-melanized forms to sublethal and lethal doses of radiation of up to 8 kGy. The contribution of chemical composition, free radical presence, spatial arrangement, and Compton scattering to the radioprotective properties of melanin was investigated by high-performance liquid chromatography, electron spin resonance, transmission electron microscopy, and autoradiographic techniques. Melanin protected fungi against ionizing radiation and its radioprotective properties were a function of its chemical composition, free radical quenching, and spherical spatial arrangement.