High-rate Gamma Spectrometry Using a LaBr3(Ce) Scintillator with a Fast Pulse Shaping.

ABSTRACT: The performance of a LaBr3(Ce) gamma spectrometer at high count rates was investigated up to an input count rate of 1.3 Mcps. In order to make its pulse processing faster, a preamplifier provided by the detector manufacturer was eliminated, and the signal from the photomultiplier tube was fed directly to a digital pulse processing system. To accomplish both fast pulse processing and good energy resolution, the pulse-shaping parameters were optimized at a low count rate of 1.5 kcps, and then measurements were carried out at various count rates. Input count rates ranging from 1.5 kcps to 21 kcps were produced using a set of 137Cs resin sources, while higher rates between 45 kcps and 1.3 Mcps were produced using a 1.2-GBq 137Cs source. The spectrometer showed an excellent performance for the input rate up to 150 kcps, while the dead time increased rapidly for the input rates above 150 kcps. The system dead time has been improved greatly by eliminating the preamplifier.

Optimization and characterization of a coincidence beta-ray spectrometer.

Aimed at beta spectrometry and dosimetry for mixed beta-gamma fields, a Si-plastic scintillator coincidence beta-ray spectrometer has been developed. The spectrometer collects pure beta-ray spectra by rejecting the gamma-ray detection events through coincidence. Both pulse height and arrival time of each detection event were recorded in list mode by a compact digital processing system. Spectral measurements were carried out using mixed beta-gamma fields from 90Sr/90Y and 137Cs sources for various beta and gamma count rates to evaluate the system performance. Coincidence beta spectra were collected for four fixed beta count rates (7.3-241 cps) from 90Sr/90Y while the gamma count rate from 137Cs was varied from 500 to 8000 cps. The coincidence beta spectrum was stable and unperturbed by the gamma detection events for most measurements while notable perturbation was observed in the low energy region when the beta to gamma count ratio is very low.

Isolation of the effects of alpha-related components from total effects of radium at low doses.

PURPOSE: Radium is the most common source of alpha radiation exposure to humans and non-human species in the environment but the dosimetry is complicated by the decay chain which involves gamma exposure due to radon daughters. This paper seeks to determine the separate contributions of alpha and gamma doses to the total dose and total direct and non-targeted effect in a fish and a human cell line. MATERIALS AND METHODS: This study aimed to isolate the effect of alpha particles following exposure to low doses of radium in cells, and their progeny which received no further exposure. This was initially done by comparing the survival values of a human keratinocyte cell line (HaCaT) and an embryonic Chinook salmon cell line (CHSE-214) exposed to gamma radiation, from survival of the same cell lines exposed to mixed alpha and gamma radiation through exposure to Ra-226 and its decay products. A Monte Carlo simulation was later performed to determine the contributions of radium decay products including radon daughters. RESULTS: The human cell line showed increased radioresistance when exposed to low doses of alpha particles. In contrast the fish cell line, which demonstrated radioresistance to low dose gamma radiation, showed increased lethality when exposed to low doses of alpha particles. Significant and complex levels of non-targeted effects were induced in progeny of irradiated cells. The simulation showed that gamma and beta decay products did not contribute significant dose and the highest beta dose was below the threshold for inducing non-targeted effects. CONCLUSIONS: The results confirm the need to consider the dose-response relationship when developing radiation weighting factors for low dose exposures, as well as the need to be aware of possible cell line and species differences.

One-Decade-Spanning transgenerational effects of historic radiation dose in wild populations of bank voles exposed to radioactive contamination following the chernobyl nuclear disaster.

The concept of historic radiation doses associated with accidental radioactive releases and their role in leading to radiation-induced non-targeted effects on affected wild animals are currently being evaluated. Previous research studying Fukushima butterfly, Chernobyl bird and fruit fly populations shows that the effects are transgenerational, underlined by the principles of genomic instability, and varied from one species to another. To further expand on the responses of and their sensitivity in different taxonomically distinct groups, the present study sought to reconstruct historic radiation doses and delineate their effects on bank voles (Clethrionomys glareolus) found within a 400-km radius of the Chernobyl Nuclear Power Plant meltdown site. Historic dose reconstruction from the whole-body dose rates for the bank vole samples for their parental generation at the time of radioactive release was performed. Relationships between the historic doses and cytogenetic aberrations and embryonic lethality were examined via graphical presentations. Results suggest that genomic instability develops at the historic dose range of 20-51 mGy while a radioadaptive response develops at the historic dose range of 51-356 mGy. The Linear No-Threshold (LNT) relationship was absent at historic doses of lower than 356 mGy at all generations. However, LNT was apparent when the very high historic dose of 10.28 Gy in one sampling year was factored into the dose response curve for the bank vole generation 21-22. It is worth being reminded that natural mutation accumulation and other environmental stressors outside the realm of dose effects could contribute to the observed effects in a multiple-stressor environment. Nevertheless, the consistent development of genomic instability and radio-adaptive response across generations and sampling sites unearths the utmost fundamental radiobiological principle of transgenerational non-targeted effects. As a result, it calls for better attention and regulation from global governing bodies of environmental health protection.

Effects of historic radiation dose on the frequency of sex-linked recessive lethals in Drosophila populations following the Chernobyl nuclear accident.

Contrary to the effects of high doses of radiation, the effects of low doses of radiation are still being investigated. Low doses and their non-targeted effects in particular are of special interest for researchers. The accident that occurred at the Chernobyl Nuclear Power Plant (NPP) gives researchers the opportunity to view these effects outside of a laboratory environment. For this paper, the relationship between low historic radiation doses and the persistent genetic damage observed in populations of fruit flies (Drosophila melanogaster) around the Chernobyl NPP over 3 years will be investigated. Data from Zainullin et al. (1992) on the frequency of sex-linked recessive lethals (SLRLs) in D. melanogaster around the Chernobyl NPP. To calculate the absorbed historic external dose, a method based on the Gaussian plume model was used to find the external dose from both plume shine and ground shine. The dose attributed to the ground shine dose made a greater contribution to the overall absorbed external historic radiation dose than the plume shine dose. For earlier generations of Drosophila living in the radioactive contaminated sites, the SLRL frequencies appeared to correlate with the dose in a linear no-threshold relationship. The later descendent generations appeared to have developed a radio-adaptive-like response. This work contributes to the understanding of historic dose effects on wildlife health following the accidental release of high mount of radioactive materials into the environment.

Transgenerational effects of historic radiation dose in pale grass blue butterflies around Fukushima following the Fukushima Dai-ichi Nuclear Power Plant meltdown accident.

Low dose radiation effects have been investigated in Chernobyl for many years but there is uncertainty about initial doses received by many animal species. However, the Fukushima Dai-ichi Nuclear Power Plant accident opens an opportunity to study the effects of the initial low historic dose on directly exposed species and their progeny during a time where the contaminating radionuclides are decaying. In this paper, it is proposed that historic acute exposure and its resulting non-targeted effects (NTEs) may be partially involved in the high mortality/abnormality rates seen across generations of pale grass blue butterflies (Zizeeria maha) around Fukushima. Data from Hiyama et al. (2012) on the morphological abnormality frequencies in Z. maha collected around Fukushima and their progeny were used in this paper. Two dose reconstruction methods based on the Gaussian plume model were used to determine the external absorbed dose to the first exposed generation from both ground shine and plume shine. One method involved the use of the dose rate recorded at the time of collection and only took Cs-137 into account. The other involved using release rates and atmospheric conditions to determine the doses and considered Cs-137 and Cs-134. The reconstructed doses were plotted against the mortality rates and abnormality frequencies across generations. The mortality rates of the progeny from irradiated progenitors increased linearly with the increasing historic radiation doses reconstructed using both Cs-137 and Cs-134 sources. Additionally, a higher level of morphological abnormalities was observed in progeny than in the progenitors. The mean abnormality frequencies also increased throughout generations. As these results are a sign of NTEs being involved, it can be suggested that increasing mutation levels across generations may result, in part, from NTEs induced by the initial low dose received by the first exposed generation. However, continual accumulation of mutations over generations in their natural contaminated habitats remains a likely contributor into the observed outcome.

Development of an advanced two-dimensional microdosimetric detector based on THick Gas Electron Multipliers.

PURPOSE: The THick Gas Electron Multiplier (THGEM)-based tissue-equivalent proportional counter (TEPC) has been proven to be useful for microdosimetry due to its flexibility in varying the gaseous sensitive volume and achieving high multiplication gain. Aiming at measuring the spatial distribution of radiation dose for mixed neutron-gamma fields, an advanced two-dimensional (2D) THGEM-TEPC was designed and constructed at McMaster University which will enable us to overcome the operational limitation of the classical TEPCs, particularly for high-dose rate fields. Compared to the traditional TEPCs, anode wire electrodes were replaced by a THGEM layer, which not only enhances the gas multiplication gain but also offers a flexible and convenient fabrication for building 2D detectors. METHOD & MATERIALS: The 2D THGEM TEPC consists of an array of 3 × 3 sensitive volumes, equivalent to nine individual TEPCs, each of which has a dimension of 5 mm diameter and length. Taking the overall cost, size and flexibility into account, to process nine detector signals simultaneously, a multi-input digital pulse processing system was developed by using modern microcontrollers, each of which is coupled with a 12-bit sampling ADC. RESULTS: Using the McMaster Tandetron 7 Li(p,n) accelerator neutron source, both fundamental detector performance, as well as neutron dosimetric response of the 2D THGEM-TEPC, has been extensively investigated and compared to the data acquired by a standard spherical TEPC. It was shown that the microdosimetric response and the measured absorbed dose rate of the 2D THGEM detector developed in this study are comparable to the standard 1/2" TEPC which is commercially available. CONCLUSION: This study proved that the 2D TEPC based on the THGEM technology can be effectively used in microdosimetry studies and is a promising detector for measuring the absorbed dose rate distribution over an area in mixed radiation fields. This unique small gas cavity detector opens new possibilities in applications for high-intensity mixed radiation fields as well as in nanodosimetry.

A Pilot Study Measuring Aluminum in Bone in Alzheimer's Disease and control Subjects Using in vivo Neutron Activation Analysis.

Aluminum, being the most abundant metal in the earth's crust, is widely distributed in the environment, and is routinely taken up by the human body through ingestion and inhalation. Aluminum is not considered an essential element and it can be toxic in high concentrations. Most of the body burden of aluminum is stored in the bones. Aluminum has been postulated to be involved in the causality of Alzheimer's disease. A system for non-invasive measurement of bone aluminum using the in vivo neutron activation analysis technique has been developed and previously reported in the literature by our group. The results are reported as ratio of Al to Ca in order to eliminate the variations in beam parameters and geometry as well as the physical variations among the subjects such as size of the hand and bone structure. This pilot study included 30 subjects, 15 diagnosed with Alzheimer's disease in mild and moderate stages and 15 control subjects, all of whom were 60 years of age or older. The mean value of aluminum for the control group was 2.7±8.2µg Al/g Ca (inverse-variance weighted mean 3.5±0.9µg Al/g Ca) and for the Alzheimer's disease subjects was 12.5±13.1µg Al/g Ca (inverse-variance weighted mean 7.6±0.6µg Al/g Ca). The difference between the mean of the Alzheimer's disease group and the mean of the control group was 9.8±15.9µg Al/g Ca, with a p-value of 0.02. An age-dependent linear increase in bone aluminum concentration was observed for all subjects. The difference in serum aluminum levels between the two groups did not reach significance.

Ultra-Violet Light Emission from HPV-G Cells Irradiated with Low Let Radiation From (90)Y; Consequences for Radiation Induced Bystander Effects.

In this study, we aimed to establish the emission of UV photons when HPV-G cells and associated materials (such as the cell substrate and cell growth media) are exposed to low LET radiation. The potential role of UV photons in the secondary triggering of biological processes led us to hypothesize that the emission and absorption of photons at this wavelength explain some radiation induced "bystander effects" that have previously been thought to be chemically mediated. Cells were plated in Petri-dishes of two different sizes, having different thicknesses of polystyrene (PS) substrate, and were exposed to ß-radiation from (90)Y produced by the McMaster Nuclear Reactor. UV measurements were performed using a single photon counting system employing an interference-type filter for selection of a narrow wavelength range, 340±5 nm, of photons. Exposure of the cell substrates (which were made of polystyrene) determined that UV photons were being emitted as a consequence of ß particle irradiation of the Petri-dishes. For a tightly collimated ß-particle beam exposure, we observed 167 photons in the detector per unit µCi in the shielded source for a 1.76 mm thick substrate and 158 photons/µCi for a 0.878 mm thick substrate. A unit µCi source activity was equivalent to an exposure to the substrate of 18 ß-particles/cm(2) in this case. The presence of cells and medium in a Petri-dish was found to significantly increase (up to a maximum of 250%) the measured number of photons in a narrow band of wavelengths of 340±5 nm (i.e. UVA) as compared to the signal from an empty control Petri-dish. When coloured growth medium was added to the cells, it reduced the measured count rate, while the addition of transparent medium in equal volume increased the count rate, compared to cells alone. We attribute this to the fact that emission, scattering and absorption of light by cells and media are all variables in the experiment. Under collimated irradiation conditions, it was observed that increasing cell density in medium of fixed volume resulted in a decrease in the observed light output. This followed a roughly exponential decline. We suggest that this may be due to increased scattering at the cell boundary and absorption of the UV in the cells. We conclude that we have measured UVA emitted by cells, cell medium and cell substrates as a consequence of their irradiation by low LET ß-particle radiation. We suggest that these secondary UV photons could lead to effects in non-targetted cells. Some effects that had previously been attributed to a chemically mediated "bystander effect" may in fact be due to secondary UV emission. Some radiation bystander effect studies may require re-interpretation as this phenomenon of UV emission is further investigated.

In vivo quantification of bone-fluorine by delayed neutron activation analysis: a pilot study of hand-bone-fluorine levels in a Canadian population.

Humans can be exposed to fluorine (F) through their diet, occupation, environment and oral dental care products. Fluorine, at proper dosages, is believed to have positive effects by reducing the incidence of dental caries, but fluorine toxicity can occur when people are exposed to excessive quantities of fluorine. In this paper we present the results of a small pilot in vivo study on 33 participants living in Southwestern Ontario, Canada. The mean age of participants was 45 ± 18 years with a range of 20-87 years. The observed calcium normalized hand-bone-fluorine concentrations in this small pilot study ranged from 1.1 to 8.8 mg F/g Ca. Every person measured in this study had levels of fluorine in bone above the detection limit of the system. The average fluorine concentration in bone was found to be 3.5 ± 0.4 mg F/g Ca. No difference was observed in average concentration for men and women. In addition, a significant correlation (r(2) = 0.55, p < 0.001) was observed between hand-bone-fluorine content and age. The amount of fluorine was found to increase at a rate of 0.084 ± 0.014 mg F/g Ca per year. There was no significant difference observed in this small group of subjects between the accumulation rates in men and women. To the best of our knowledge, this is the first time data from in vivo measurement of fluorine content in humans by neutron activation analysis have been presented. The data determined by this technique were found to be consistent with results from ex vivo studies from other countries. We suggest that the data demonstrate that this low risk non-invasive diagnostic technique will permit the routine assessment of bone-fluorine content with potential application in the study of clinical bone-related diseases. This small study demonstrated that people in Southern Ontario are exposed to fluoride in measureable quantities, and that fluoride can be seen to accumulate in bone with age. However, all volunteers were found to have levels below those expected with clinical fluorosis, and only one older subject was found to have levels comparable with preclinical exposure.

Effect of fluorescent whitening agent on the transcription of cell damage-related genes in zebrafish embryos.

7-Diethylamino-4-methylcoumarin (DEMC) is a fluorescent whitening agent (FWAs). There have been some studies on DEMC's protective effects against biological activity but there are few papers about the in vivo toxicity of DEMC. In this study, we used wild-type zebrafish embryos 3 days post fertilization (dpf). Test solutions with DEMC concentrations were negative control (without vehicle), 0 (with vehicle, 0.01% v/v ethanol), 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 and 2 ppm. Embryos and larvae were counted for survival rate and hatching rate. Heart rates were also counted at 2.5 and 3.0 dpf. At 3.0 dpf, quantitative RT-PCR was performed with some samples (0, 0.25, 0.75 and 1.25 ppm) to determine the toxic effect to DEMC by detecting the expression levels of toxic-responsive genes. We used 11 genes, which included oxidative stress-related genes [sod(Mn), sod(Cu,Zn) and hsp70], mitochondrial metabolism-related genes (coxI, pyc, cyt and cyclinG1) and apoptosis-related genes (c-jun, bcl2, bax and p53). High-concentration DEMC-treated groups showed significant different survival rate, hatching rate and heart rate compared with low-concentration DEMC-treated groups. The LC50 of this chemical, 0.959 ppm, was calculated. We also confirmed that some genes in the DEMC exposure groups showed significantly up-regulations in expression levels compared with control groups. We concluded that the fluorescence agent, DEMC, has possible developmental toxicities and alteration effect of gene expression, which are related to oxidative stress, mitochondrial metabolism and apoptosis in zebrafish embryos.

Effect of dose rate on the radiation-induced bystander response.

Radiation-induced biological bystander effects have become a well-established phenomenon associated with the interaction of radiation with cells. These so-called bystander effects have been seen across a variety of end points for both high and low linear energy transfer (LET) radiations, utilizing a variety of dose rates and radiation sources. In this study, the effect of dose rate and different low LET sources on the bystander cell survival fraction (SF) was examined. The cell line investigated was the human keratinocyte HPV-G. The bystander response was measured via clonogenic assay after medium transfer protocol. Cells were irradiated using (60)Co gamma-rays and 20 MeV electrons at doses of 0.5, 5 and 10 Gy with varying dose rates. Both gamma and electron irradiation decreased recipient SF at 0.5 Gy and 5 Gy, respectively. Subsequent recovery of the SF to control levels for 10 Gy was observed. There was no dose rate dependence for (60)Co irradiation. A significant difference in the survival fraction was observed for electron irradiation at 10 Gy and a high dose rate. Furthermore, survival fractions were compared between (60)Co and 20 MeV electron irradiations. This showed a significant increase in the survival fraction 'recovery' at 10 Gy for a (60)Co dose rate of 1.1 Gy min(-1) compared to 20 MeV electrons at 1.0 Gy min(-1). No such difference was observed when comparing at higher dose rates. Lastly, increases in survival fraction at 10 Gy were abolished and the SF decreased by the plating of increased numbers of recipient cells. Such evidence may help gain insight into the nature and mechanism(s) surrounding bystander signal production, how these phenomena are tested and their eventual application in a clinical setting.

Effective target size for the induction of bystander effects in medium transfer experiments.

Although radiation-induced bystander effects are frequently observed biological phenomena, the mechanism for these effects has not been fully determined. The target-hit theory and related concepts from microdosimetry provide a convenient formalism to help identify the nature of the targets responsible for initiating the emission of diffusible factors in medium transfer experiments. We used the microdosimetric models proposed by Stewart et al. (Radiat. Res. 165, 460-469, 2006) to analyze the results of published medium transfer experiments for gamma-ray doses in the range of 0.04 mGy to 5 Gy. The analysis suggests that the effective size of the target responsible for initiating signal emission in HPV-G human keratinocyte donor cells is approximately 2 microm.

A dose threshold for a medium transfer bystander effect for a human skin cell line.

The existence of radiation-induced bystander effects mediated by diffusible factors is now accepted, but the mechanisms and precise behavior at low doses remain unclear. We exposed cells to gamma-ray doses in the range 0.04 mGy-5 Gy, harvested the culture medium, and transferred it to unirradiated reporter cells. Calcium fluxes and clonogenic survival were measured in the recipients. We show evidence for a dose threshold around 2 mGy for the human skin cell line used with a suggestion of increased survival below that dose. Similar experiments using direct gamma irradiation showed no reduction in survival until the dose exceeded 7 mGy. Preliminary data for neutrons where the gamma-ray dose was kept below the bystander threshold do not show a significant bystander effect in the dose range 1-33 mGy. A lack of a bystander response with neutrons occurred at around 1 Gy, where significant cell killing from direct irradiation was observed. The result may have implications for understanding the role of bystander effects at low doses.

Effects of chemical carcinogens and physicochemical factors on the UV spectrophotometric determination of DNA.

The ultraviolet (UV) absorbance ratio of 260/280 nm has been used as an indicator of DNA purity. However, the A260/A280 ratio may be beyond the normal range (1.8-1.9) due to physicochemical alterations produced by pH and temperature, and carcinogenic chemical modification. When the pH of the DNA solution buffer increased from 3 to 11, the A260/A280 ratio changed significantly from 1.5 to 2.2 in mixtures of DNA bases [A:T:C:G = 28.5:28.5: 21.5:21.5, i.e., (A + T)/(all four bases) = 57%, expressed as mole percent], of deoxyribonucleosides (adenosine:thymidine:cytidine:guanosine= 28.5:28.5:21.5:21.5, as mole percent), or of deoxyribonucleotides (dAMP:dTMP:dGMP:dCMP = 28.5:28.5:21.5:21.5, as mole percent) examined. The A260/A280 ratio increased with RNA contamination and exceeded 1.9 when RNA concentration was >30%, as mole percent. In contrast, the A260/A280 ratio was linearly reduced by increasing the protein concentration. Phenol (>0.02%) contamination also reduced the A260/A280 ratio to below 1.8. Benzo[a]pyrene diol epoxide (BPDE), a reactive carcinogen metabolite of benzo[a]pyrene (BaP), decreased the A260/A280 ratio correlated with the degree to which it modified the DNA. These results suggest that the UV A260/A280 ratio is significantly affected by pH and the presence of contaminating species of macromolecules and chemicals.