LARCalc, a tool to estimate sex- and age-specific lifetime attributable risk in populations after nuclear power plant fallout.

A tool called LARCalc, for calculating the radiological consequences of accidental large scale nuclear power plant releases based on estimates of 137Cs ground deposition, is presented. LARCalc is based on a previously developed models that has been further developed and packaged into an easy-to-use decision support tool for training of decision makers. The software visualises the radiological impact of accidental nuclear power plant releases and the effects of various protective measures. It is thus intended as a rapid alternative for planning protective measures in emergency preparedness management. The tool predicts projected cumulative effective dose, projected lifetime attributable cancer risk, and residual dose for some default accidental release scenarios. Furthermore, it can predict the residual dose and avertable cumulative lifetime attributable risk (LAR) resulting from various protective measures such as evacuation and decontamination. It can also be used to predict the avertable collective dose and the increase in cancer incidence within the specified population. This study presents the theoretical models and updates to the previous models, and examples of different nuclear fallout scenarios and subsequent protective actions to illustrate the potential use of LARCalc.

Average uranium bedrock concentration in Swedish municipalities predicts male lung cancer incidence rate when adjusted for smoking prevalence: Indication of a cumulative radon induced detriment.

Bedrock U has been used as a proxy for local indoor radon exposure. A preliminary assessment of cancer incidence rate in a cohort of 809,939 adult males living in 9 different Swedish counties in 1986 has been used to correlate the cumulative lung cancer and total cancer (excluding lung) incidence rates between 1986 and 2020, respectively with the municipality average value of bedrock U concentration obtained from Swedish geological Survey (SGU). To control for regional difference in tobacco smoking, data on county average smoking prevalence, obtained from a survey conducted by the Public Health Agency of Sweden from 2001 to 2004, was used. Regression analysis shows that there is a significant positive correlation between smoking prevalence adjusted lung cancer incidence rate in males and the municipality bedrock U concentration (R2 = 0.273 with a slope 5.0 ±â€¯0.87·10-3 ppm-1). The correlation is even more significant (R2 = 0.759 with a slope = 4.8 ±â€¯0.25·10-3 ppm-1) when assessed on population weighted cancer incidence data binned in nine intervals of municipality average bedrock U concentration (ranging from 0.97 to 4.9 ppm). When assessing the corresponding correlations for total cancer incidence rate (excluding cancer of the lung) with adjustment for smoking prevalence, there appears to be no or little correlation with bedrock U concentration (R2 = 0.031). We conclude that an expanded future study needs age-standardized cancer incidence data to obtain a more consistent exposure-response model. Such model could be used to predict future lung cancer cases based on geological survey maps of bedrock U as an alternative to laborious indoor radon measurements, and to discern what future lung cancer rates can be expected for a population nearing zero smoking prevalence, with and without radon prevention.

Time-dependence of decontamination efficiency after a fallout of gamma-emitting radionuclides in suburban areas: a theoretical outlook on topsoil removal.

Decontamination of urban areas may be necessary in the case of extensive fallout of radioactive material after a nuclear accident, as removal of contaminated soil and vegetation will significantly reduce doses for the residents in an area affected by fallout. Experience from Japan shows that cleanup operations of urban areas may take years despite investment in ample resources. The time delay between the initial fallout and completion of the decontamination measures allows natural and physical processes to affect the results. The efficiency of the decontamination will therefore depend significantly on time. Radioecological modeling and computer simulation of urban topography with one-story houses were applied in this study to estimate action-influenced time-integrated dose reductions (TDR) of contaminated topsoil removal as a function of time after the fallout. Results indicate that the TDR decreases gradually after the fallout depending on the vertical migration rate of radiocesium and, to some extent, the initial 134Cs/137Cs ratio. Delaying the topsoil removal from 1 to 10 years will result in a TDR decrease by more than a factor of two. Removing the topsoil within one year after fallout results typically in an averted effective dose between 34 and 80 mSv per MBq m-2 deposition of 137Cs for residents in wooden houses. The corresponding values for residents in brick houses are about 50% lower due to higher shielding. Additional modeling is needed to estimate how age and sex influence the averted detriment to affected cohorts. In addition, more in-depth knowledge of how the efficiency of topsoil removal in practice compares with hypothetical models and the effect of incomplete removal of radiocesium is needed to improve calculations of TDR values.

In vivo measurement of pre-operational spallation source workers: baseline body burden levels and detection limits of relevant gamma emitters using high-resolution gamma spectrometry.

As a measure to prepare for long-term internal dose monitoring of workers at the European Spallation Source (ESS) in Lund, Sweden, operated by the European Research Infrastructure Consortium (ERIC), as well as to enhance emergency preparedness against accidental releases, a series of in vivo measurements were conducted using a high-resolution HPGe detector with a 123% relative efficiency (1.332 MeV). This study describes the whole-body counting set-up, calibration procedure, and subsequent validation measurements using conventional NaI(Tl)-scanning-bed geometry on a selection of workers from the ESS. Detection limits for the relevant gamma emitters 7Be, 172Hf, and 182Ta were determined to be 65 Bq, 130 Bq, and 22 Bq, respectively, using a 2400 s acquisition time. The baseline measurements suggest that care must be taken to ensure that the fluctuations in the presence of radon daughters 214Bi and 214Pb are minimised by, for example, ensuring a minimum air exchange between the measuring room and the ambient air, and by demanding that the measured subjects change clothes and shower before measurement. Furthermore, in a monitoring program for internal doses to spallation source workers, the presence of radionuclides originating from non-work-related sources (such as 226Ra from private water wells or 137Cs from intakes of Chernobyl contaminated foodstuffs), or radionuclides from previous work history (such as 60Co within the nuclear power industry), must be considered.

OSL PROPERTIES IN VARIOUS FORMS OF KCl AND NaCl SAMPLES AFTER EXPOSURE TO IONIZING RADIATION.

The aim of this work was to investigate the optically-stimulated luminescence (OSL) properties of potassium chloride (KCl) and its potential use in radiation dosimetry. The optimal condition for OSL readout with blue light stimulation were designated using a commercially available Risø TL/OSL reader. KCl was studied in three sample forms: crystals, powder and pellets. The following OSL characteristics were determined: signal reproducibility, OSL measurement-induced sensitivity changes, temperature dependence of OSL and signal stability over time. The results show a high reproducibility of KCl samples and strong sensitivity changes, which can be corrected for by using a test-dose. The long-term OSL studies confirmed the occurrence of both inverse fading and fading phenomena in KCl. In addition, a comparison with corresponding measurements using sodium chloride (NaCl) were carried out. Although it was confirmed that NaCl is more suitable for dosimetry, there might be benefits of combining NaCl with KCl for more accurate absorbed dose determinations.

UNCERTAINTY ON RADIATION DOSES ESTIMATED BY BIOLOGICAL AND RETROSPECTIVE PHYSICAL METHODS.

Biological and physical retrospective dosimetry are recognised as key techniques to provide individual estimates of dose following unplanned exposures to ionising radiation. Whilst there has been a relatively large amount of recent development in the biological and physical procedures, development of statistical analysis techniques has failed to keep pace. The aim of this paper is to review the current state of the art in uncertainty analysis techniques across the 'EURADOS Working Group 10-Retrospective dosimetry' members, to give concrete examples of implementation of the techniques recommended in the international standards, and to further promote the use of Monte Carlo techniques to support characterisation of uncertainties. It is concluded that sufficient techniques are available and in use by most laboratories for acute, whole body exposures to highly penetrating radiation, but further work will be required to ensure that statistical analysis is always wholly sufficient for the more complex exposure scenarios.

Optically stimulated luminescence (OSL) dosimetry in irradiated alumina substrates from mobile phone resistors.

In this study the dosimetric properties of alumina (Al2O3) substrates found in resistors retrieved from mobile phones were investigated. Measurements of the decline of optically stimulated luminescence (OSL) generated following exposure of these substrates to ionising radiation showed that 16% of the signal could still be detected after 2 years (735 days). Further, the magnitude of the regenerative dose (calibration dose; D i) had no impact on the accuracy of dose estimates. Therefore, it is recommended that the D i be set as low as is practicable, so as to accelerate data retrieval. The critical dose, D CL, and dose limit of detection, D DL, taking into account the uncertainty in the dose-response relation as well as the uncertainty in the background signal, was estimated to be 7 and 13 mGy, respectively, 1 h after exposure. It is concluded that given the significant long-term component of fading, an absorbed dose of 0.5 Gy might still be detectable up to 6 years after the exposure. Thus, OSL from alumina substrates can be used for dosimetry for time periods far in excess of those previously thought.

The influence of 134Cs on the 137Cs gamma-spectrometric peak-to-valley ratio and improvement of the peak-to-valley method by limiting the detector field of view.

The peak-to-valley method was investigated under laboratory conditions and in situ with respect to both 134Cs perturbation of the 137Cs valley and use of collimation. The 134Cs perturbation is significant down to 134Cs:137Cs activity ratios of 1:100. In these cases the full energy peaks from 134Cs (796 and 802keV) and associated valley should be used instead of the peak and valley from the 137Cs 662keV peak. Use of collimators in situ outside Fukushima Daiichi significantly increased PTV for 134Cs.

A rotating-slit-collimator-based gamma radiation mapper.

For situations with radioactive material out of control where it may be physically difficult or prohibited to access areas close to the source, measurements from distance may be the only way to assess the radiation environment. Using collimated detectors will provide means to locate the direction of the radiation from the source. To investigate the possibilities of mapping gamma emitting radioactive material in a closed non-enterable area, a tentative system for mapping radioactive materials from a distance was built. The system used a computer controlled cylindrical rotating slit collimator with a high purity germanium detector placed in the cylinder. The system could be placed on a car-towed trailer, with the centre of the detector about 1.4 m above ground. Mapping was accomplished by the use of a specially developed image reconstruction algorithm that requires measurements from two or more locations around the area to be investigated. The imaging capability of the system was tested by mapping an area, 25 by 25 m2, containing three 330 MBq 137Cs point sources. Using four locations outside the area with about 20 min measuring time in each location and applying the image reconstruction algorithm on the deconvoluted data, the system indicated the three source locations with an uncertainty of 1-3 m. The results demonstrated the potential of using collimated mobile gamma radiometry combined with image reconstruction to localize gamma sources inside non-accessible areas.

Peak-to-valley ratios for three different HPGe detectors for the assessment of 137Cs deposition on the ground and the impact of the detector field-of-view.

The peak-to-valley (PTV) method was investigated experimentally comparing PTV ratios for three HPGe detectors, with complementary Monte Carlo simulations of scatter in air for larger source-detector distances. The measured PTV ratios for 137Cs in air were similar for three different detectors for incident angles between 0 and 90°. The study indicated that the PTV method can differentiate between surface and shallow depth sources if the detector field of view is limited to a radius of less than 3.5m.

SILICON DIODE AS AN ALPHA PARTICLE DETECTOR AND SPECTROMETER FOR DIRECT FIELD MEASUREMENTS.

A windowless silicon (Si) diode (4 mm(2)) was evaluated as alpha particle detector and spectrometer for field measurements. It was irradiated with alpha particles from a (241)Am (2.3 kBq) and a (210)Po (9 kBq) source at source-detector distances (SDD) of 0.5, 1.0 and 1.8 cm. The energy resolution in terms of full width at half maximum was 281, 148 and 113 keV for SDD of 0.5, 1.0 and 1.8 cm, respectively. The minimum detectable activity increased from 0.08 to 0.83 Bq when the SDD increased from 0.5 to 1.8 cm. The detector has the potential for several alpha spectrometric applications, such as monitoring for wound, skin and surface contamination at nuclear fuel facilities, nuclear power plants and facilities handling radioactive waste. Other areas are environmental surveys following releases of actinides at accidents in nuclear power plants and in connection with other radiological or nuclear scenarios.

A PHANTOM FOR DETERMINATION OF CALIBRATION COEFFICIENTS AND MINIMUM DETECTABLE ACTIVITIES USING A DUAL-HEAD GAMMA CAMERA FOR INTERNAL CONTAMINATION MONITORING FOLLOWING RADIATION EMERGENCY SITUATIONS.

The purpose of this study was to derive calibration coefficients (in terms of cps kBq(-1)) and minimum detectable activities, MDA, (in terms of kBq and corresponding dose rate) for the dual head gamma camera part of an SPECT/CT-instrument when used for in vivo internal contamination measurements in radiation emergency situations. A cylindrical-conical PMMA phantom with diameters in the range of 7-30 cm was developed in order to simulate different body parts and individuals of different sizes. A series of planar gamma camera investigations were conducted using an SPECT/CT modality with the collimators removed for (131)I and (137)Cs, radionuclides potentially associated with radiation emergencies. Energy windows of 337-391 and 490-690 keV were selected for (131)I and (137)Cs, respectively. The measurements show that the calibration coefficients for (137)Cs range from 10 to 19 cps kBq(-1) with MDA values in the range of 0.29-0.55 kBq for phantom diameters of 10-30 cm. The corresponding values for (131)I are 12-37 cps kBq(-1) with MDA values of 0.08-0.26 kBq. An internal dosimetry computer program was used for the estimation of minimum detectable dose rates. A thyroid uptake of 0.1 kBq (131)I (representing MDA) corresponds to an effective dose rate of 0.6 µSv d(-1) A (137)Cs source position representing the colon with an MDA of 0.55 kBq corresponds to an effective dose rate was 1 µSv y(-1) This method using a simple phantom for the determination of calibration coefficients, and MDA levels can be implemented within the emergency preparedness plans in hospitals with nuclear medicine departments. The derived data will help to quickly estimate the internal contamination of humans following radiation emergencies.

CAN AN ENERGY-COMPENSATED SOLID-STATE X-RAY DETECTOR BE USED FOR RADIATION PROTECTION APPLICATIONS AT HIGHER PHOTON ENERGIES?

The objective of this study was to investigate the characteristics of a solid-state detector commonly available at hospitals for parallel use as a real-time personal radiation monitor following radiation emergency situations. A solid-state detector probe with an inherent filtration (R100, RTI Electronics AB, Mölndal, Sweden) was chosen for evaluation. The energy dependence and the linearity in signal response with kerma in air were examined, and the detector was exposed to both X-ray beams using a conventional X-ray unit with effective photon energies ranging between 28.5 and 48.9 keV and to gamma rays 1.17 and 1.33 MeV from (60)Co. The R100 exhibited ∼1.7 times over-response at the lowest X-ray energy relative to the (60)Co source. The detector demonstrated a linear response (R(2) = 1) when irradiated with (60)Co to air kerma values in the range of 20-200 mGy. The conclusion is that high-energy photons such as those from (60)Co can be detected by the R100 with an energy response within a factor of <2 over the energy range examined and that the detector can provide real-time dose measurements following nuclear or radiological events.

Experimentally determined vs. Monte Carlo simulated peak-to-valley ratios for a well-characterised n-type HPGe detector.

Measurements and simulations to investigate the contributing factors to the peak-to-valley (PTV) ratio have been both experimentally determined as well as Monte Carlo simulated for a well-characterised HPGe n-type detector together with a Cs-137 gamma source encapsulated in thin polystyrene. Measurements were carried out in a low-background gamma counting facility at Lund University. The results of the PTV ratio have been compared to distinguish what components or variables in the setup that significantly influence the ratio. In addition to manufacture specifications, the detector components have been examined using planar X-ray, source scanning and computer tomography in order to determine and verify component dimensions when necessary. In spite of these efforts a discrepancy of approximately 25% for thin absorbers in the PTV ratio between measurements and calculations is observed. However, this discrepancy becomes less significant for larger absorbing layers of copper (>1mm). This indicates that it would be difficult to achieve a field calibration for in-situ gamma spectrometry using the PTV ratio that could position a Cs-137 source in soil depth shallower than corresponding 1mm layer of copper. The results also showed that when building a detector in simulations part by part, the inner dead layer, and the contact pin are of great importance for the accuracy of the PTV ratio simulations.

Household salt for retrospective dose assessments using OSL: signal integrity and its dependence on containment, sample collection, and signal readout.

The aim of this work was to determine how a latent optically stimulated luminescence (OSL) signal in irradiated household salt is preserved under various ambient conditions, from the time of exposure to the time of signal readout. The following parameters were examined: optical fading in fluorescent light and under darkroom conditions (red light), thermal stability of the OSL signal during storage in a light-tight container, optical fading in representative container types, and sensitization effects of the OSL signal in exposed household salt. Furthermore, the influence of grain mixing within the saltshaker or salt container was studied by determining the dose gradient within typical salt packages. Finally, the signal integrity of salt irradiated under field conditions in a village in Belarus contaminated by Chernobyl fallout was investigated. The results show that the OSL signal in household salt is preserved in large cardboard box containers, but not in white plastic salt containers or in small portion bags used in, e.g., fast food restaurants. Furthermore, the continuous wave blue OSL signal in household salt does not fade significantly during storage up to 140 days. On the contrary, the signal appears to slowly increase during storage ("inverse fading"). Field tests of two different salt containers (with and without black tape to block light) located in Belarussian households confirmed that the signal is preserved in white plastic salt containers when they are covered with extra light-shielding material.

Retrospective dosimetry using OSL of tooth enamel and dental repair materials irradiated under wet and dry conditions.

Following a radiological or nuclear emergency event, there is a need for quick and reliable dose estimations of potentially exposed people. In situations where dosimeters are not readily available, the dose estimations must be carried out using alternative methods. In the present study, the optically stimulated luminescence (OSL) properties of tooth enamel and different dental repair materials have been examined. Specimens of the materials were exposed to gamma and beta radiation in different types of liquid environments to mimic the actual irradiation situation in the mouth. Measurements were taken using a Risø TL/OSL reader, and irradiations were made using a (90)Sr/(90)Y source and a linear accelerator (6 MV photons). Results show that the OSL signal from tooth enamel decreases substantially when the enamel is kept in a wet environment. Thus, tooth enamel is not reliable for retrospective dose assessment without further studies of the phenomenon. Dental repair materials, on the other hand, do not exhibit the same effect when exposed to liquids. In addition, dose-response and fading measurements of the dental repair materials show promising results, making these materials highly interesting for retrospective dosimetry. The minimum detectable dose for the dental repair materials has been estimated to be 20-185 mGy.

Optimizing a readout protocol for low dose retrospective OSL-dosimetry using household salt.

The authors' aim has been to find a single aliquot regenerative dose (SAR) protocol that accurately recovers an unknown absorbed dose in the region between 1-250 mGy in household salt. The main investigation has been conducted on a specific mine salt (>98.5% NaCl) intended for household use, using optical stimulation by blue LED (λ = 462 nm). The most accurate dose recovery for this brand of salt is found to be achieved when using Peak Signal Summing (PSS) of the OSL-decay and a preheat temperature of 200°C after the test dose. A SAR protocol for the household salt with preset values of regenerative doses (R1--R5) and a test dose (TED) of 17 mGy is also suggested here. Under laboratory conditions, the suggested protocol recovers unknown absorbed doses in this particular brand within 5% (2 SD) in the dose range between 1-250 mGy. This is a very promising result for low dose applications of household salt as a retrospective dosimeter after a nuclear or radiological event.

Gafchromic film as a fast visual indicator of radiation exposure of first responders.

Three types of Gafchromic films have been studied to investigate their potential for use as a visually readable dosemeter for persons acting as first responders in connection with radiological or nuclear emergencies. The two most sensitive film types show a pronounced variation in sensitivity by photon energy and are therefore not suitable for use in cases of unknown exposures. The third film type tested (RTQA2), which is intended for quality control in radiation therapy has a sensitivity that is independent of the radiation quality, and is therefore considered as the most optimal for visual reading in situ. Tests carried out on a group of 10 human observers showed that absorbed doses down to 40 mGy can be detected by the eye. Read by a portable densitometer, qualitative absorbed dose estimates down to 9 mGy can be achieved. The colour change is obtained instantaneously, giving first responders immediate information about the presence of beta-, gamma- and X-ray radiation.

Visualisation and quantification of lung content of radionuclides associated with nuclear and radiological emergencies.

In a situation when radionuclides accidentally or deliberately are dispersed in the environment, there is a need for rapid investigation of the internal contamination in exposed individuals. In this work, the possibilities of visualising and quantifying uptakes of different radionuclides in the lung region of an adult individual using gamma camera systems have been examined, mainly on a two-headed stationary clinical gamma camera. An anthropomorphic phantom was used to mimic acute lung uptakes in three different body sizes. The gamma camera was calibrated with the lung inserts filled with a homogeneous solution of 99Tc(m), 46Sc and ³²P, or with point sources of ²4¹Am, 57Co, 85Sr, ¹³7Cs and 9°Sr/9°Y. It was found that for the stationary gamma camera the minimum detectable activity in the lungs using a 5-min acquisition time ranged from 0.53 kBq for 46Sc to 50 kBq for ³²P. Furthermore, the point sources of ¹³7Cs, 6°Co and 9°Sr/9°Y (0.16, 0.80 and 2.2 MBq, respectively) located in the lung insert of the phantom, could be clearly visualised, exhibiting distinct intensity maxima. It is thus concluded that gamma camera systems can be useful for rapid assessment of acute intakes of radionuclides associated with emergency preparedness, both in terms of localisation and quantification.

Household salt as a retrospective dosemeter using optically stimulated luminescence.

The aim of this work was to investigate the potential of a selection of household salts (NaCl) as a retrospective dosemeter for ionising radiation using optically stimulated luminescence (OSL). The OSL-response of five brands of salt to an absorbed dose in the range from 1 mGy to 9 Gy was investigated using a Risø TL/OSL-15 reader and a (60)Co beam, allowing low dose-rate irradiations. The salt was optically stimulated with blue light (lambda = 470 +/- 30 nm) at a constant stimulation power (CW-OSL) of 20 mW cm(-2). A linear dose response relationship was found in the dose range from 1 mGy to about 100 mGy and above that level, the relationship becomes moderately supra-linear, at least up to 9 Gy. Depending on the sensitivity and background signal, the minimum detectable absorbed dose (MDD) for the household salt when kept at sealed conditions varied from 0.2 to 1.0 mGy, for the household salts investigated. In addition to its widespread abundance and availability, the low MDD suggests that household salt should seriously be considered as an emergency dosemeter. However, the OSL-properties of NaCl under normal household usage need to be more properly investigated as well as the variation in sensitivity by the quality of the radiation. A further optimisation of the read-out sequence for various brands of commercially available salt may further improve the sensitivity, in terms of luminescence yield, and the signal reproducibility.