Radiological complexity of nuclear facilities: an information complexity approach to workplace monitoring

Nuclear energy is crucial for achieving net-zero carbon emissions. A big challenge in the nuclear sector is ensuring the safety of radiation workers and the environment, while being cost-effective. Workplace monitoring is key to protecting workers from risks of ionising radiation. Traditional monitoring involves radiological surveillance via installed radiation monitors, continuously recording measurements like radiation fields and airborne particulate radioactivity concentrations, especially where sudden radiation changes could significantly impact workers. However, this approach struggles to detect incremental changes over a long period of time in the radiological measurements of the facility. To address this limitation, we propose abstracting a nuclear facility as a complex system. We then quantify the information complexity of the facility's radiological measurements using an entropic metric. Our findings indicate that the inferences and interpretations from our abstraction have a firm basis for interpretation and can enhance current workplace monitoring systems. We suggest the implementation of a radiological complexity-based alarm system to complement existing radiation level-based systems. The abstraction synthesized here is independent of the type of nuclear facility, and hence is a general approach to workplace monitoring at a nuclear facility.

Development and establishment of a parallel plate ionization chamber as a transfer standard for measurement of dose to tissue in beta radiation fields

A parallel-plate ionization chamber (PPC) with a nominal volume of 8.16 cm³ was developed based on theoretically simulated design parameters. Its purpose is to serve as a transfer standard for dosimetry in a beta radiation field. The entrance window of the PPC consists of an aluminized Mylar sheet with a thickness of 1.4 mg/cm2. The collecting and guard electrodes are created by applying a graphite coating on a Poly Methyl Methacrylate (PMMA) substrate with a thickness of 5 mm. The nominal sheet resistance of the graphite-coated PMMA substrate was measured using a four-probe technique and found to be approximately 800 Ω per square (Ω/□). Dosimetric characterization of the PPC was performed in the ISO 6980 reference beta radiation field, utilizing 90Sr-90Y and 85Kr beta radiation sources. The assessment included studies on short-term stability, linearity, current-to-voltage characteristics, stabilization time, and leakage current. The PPC was calibrated and established as a transfer standard using the 'Extrapolation Ionization Chamber,' recognized as an absolute standard for dose to tissue in 90Sr-90Y and 85Kr beta sources within the laboratory. The calibration coefficient of the PPC indicates an energy dependence of 0.6 % for 90Sr-90Y and 85Kr beta sources.

Measurement of energy and directional distribution of neutron ambient dose equivalent for the 7Li(p,n)7Be reaction

Double differential neutron fluence distributions were measured in the 7Li(p,n)7Be reaction for proton beam energies 7, 9 and 12 MeV. Seven liquid scintillator based detectors were employed to measure neutron fluence distributions using the Time of Flight technique. Neutron ambient dose equivalents were determined from the measured fluence distribution using ICRP (International Commission on Radiological Protection) recommended fluence to dose equivalent conversion coefficients. Neutron dose equivalents were also measured using a conventional BF3 detector based REM counter. Ambient dose equivalent measured by the REM counter is found to be in agreement with that determined from the neutron fluence spectra within their uncertainties. Angular distributions of the ambient dose equivalents were also determined from the measured fluence distributions at different angles.

Proton induced activation studies in the carbon steel composites

The number of accelerator installations has increased significantly in the last decade and requirements are consistently increasing. In these facilities neutrons and high energy charge particle induced reactions are possible with the metallic enclosures made up of natural Fe or steel composites used as structural components or shielding materials. Present study aims to generate a dose rate profile of the induced activations and quantify the induced radionuclide concentrations in the low carbon steel composites. A comparison of the radionuclide concentrations generated in the metallic Fe and SS-304 composite is also presented for a judicious material selection to minimise the radiation concerns.

Generation of map on natural environmental background absorbed dose rate in India

A systematic mapping of natural absorbed dose rate was carried out to assess the existing exposure situation in India. The mammoth nationwide survey covered the entire terrestrial region of the country comprising of 45127 sampling grids (grid size 36 km²) with more than 100,000 data points. The data was processed using Geographic Information System. This study is based on established national and international approaches to provide linkage with conventional geochemical mapping of soil. Majority (93%) of the absorbed dose rate data was collected using handheld radiation survey meters and remaining were measured using environmental Thermo Luminescent Dosimeters. The mean absorbed dose rate of the entire country including several mineralized regions, was found to be 96 ± 21 nGy/h. The median, Geometric Mean and Geometric Standard Deviation values of absorbed dose rate were 94, 94 and 1.2 nGy/h, respectively. Among the High Background Radiation Areas of the country, absorbed dose rate varied from 700 to 9562 nGy/h in Karunagappally area of Kollam district, Kerala. The absorbed dose rate in the present nationwide study is comparable with the global database.

Clinical outcome of anterior cruciate ligament reconstruction with modified transtibial and anteromedial portal

Arthroscopic ACL reconstruction is the current standard care of treatment for anterior cruciate ligament (ACL) injuries. Modified transtibial (mTT) and anteromedial portal (AMP) techniques aim at the anatomical placement of femoral tunnel. Controversy existed in the literature with regard to the outcome of these techniques. Hence, we designed a retrospective comparative study to analyse the clinical and functional outcomes of mTT and AMP techniques. We hypothesized that there would be no difference between the clinical and functional outcomes in mTT and AMP techniques. This retrospective observational study was conducted in consecutive patients who underwent arthroscopic ACL reconstruction using semitendinosus-gracilis (STG) quadrupled graft in our tertiary care centre with a minimum follow-up of two years. Out of 69 patients, 37 had undergone ACL reconstruction by mTT technique and remaining by AMP technique. All the patients were assessed clinically by anterior drawer, Lachman's, pivot shift and single-legged hop test. Lysholm Knee Scoring Scale and International Knee Documentation Committee (IKDC) subjective knee evaluation score were used for the functional status. Knee instability was assessed objectively by KT-1000 arthrometer. There was no statistically significant difference in baseline demographic characteristics between mTT and AMP groups. At the end of 2 years, no statistically significant difference was noted in the anterior drawer and Lachman's test. Though not significant, IKDC scores and Lysholm's scores showed a better outcome in the AMP group when compared to the mTT group. AMP group showed significantly better outcome with KT-1000 arthrometer. Based on the results obtained, we presume that overall both mTT and AMP have similar functional outcome. However, as AMP technique offers significantly improved subjective rotational stability on pivot shift test, better hop limb symmetry index and KT 1000 readings compared to mTT, we suggest AMP over mTT.

Bifocal Stabilisation of Acute Acromioclavicular Joint Dislocation using Suture Anchor and Temporary K-Wires: A Retrospective Analysis

Introduction

The acromioclavicular joint (ACJ) is a major link connecting the upper limb to the torso. The acromioclavicular and coracoclavicular (CC) ligaments help in stabilising the joint. We feel it is prudent to address both these ligament injuries, to achieve optimum result. This study was undertaken to analyse the results of a simple frugal surgical technique we used to deal with this injury considering stabilisation for both these ligaments.

Materials and methods

In this retrospective study, skeletally mature patients with Type III, IV or V ACJ dislocations who underwent open reduction and stabilisation of the joint with temporary K-wires, repair of the capsule and augmentation of CC ligaments with suture anchors were included. Clinico-radiological and functional outcome was evaluated. Functional assessment of the upper limb was analysed using the Disabilities of Arm, Shoulder, and Hand Score (DASH), Constant shoulder score (CSS) and Oxford shoulder score (OSS).

Results

Clinical and radiological evaluation of the 32 patients who had completed two years from the index surgery, was done. Out of the 37 patients included initially, five were lost in follow-up. Majority of the subjects included were males and type V was the most common injury. Mean pre-operative CC distance on the affected side was 13.92±4.94mm. In the immediate post-operative radiograph, it was 7.63±2.08mm and in the final follow- up was 9.36±2.75mm. Measurements were taken by two independent investigators and inter, and intra-observer reliability were analysed by Interclass correlation coefficient. Excellent functional outcome was noted despite the 1.81±1.50mm average loss of correction. At final follow-up, mean DASH score was 4.67±4.18, Oxford shoulder score was 44.06±2.44 and Constant shoulder score was 86.37±5.81. The severity of the injury had no significant effect on the functional outcome post our method of stabilisation and rehabilitation.

Conclusion

Bifocal fixation restores the multidirectional stability of the disrupted ACJ. Adequate radiological reduction, good functional outcome and simplicity of execution make this technique an undemanding one for use in regular practice.

Hydrogeochemical characterization and evaluation of subsurface water quality in the Proterozoic Cuddapah Basin, Andhra Pradesh, India

In the current survey, different hydrogeochemical processes governing the geochemistry of aquifers, the usefulness of groundwater for regular consumption, and agricultural purposes were evaluated around the Tummalapalle area. One hundred forty-four borehole locations were chosen to characterize the major physicochemical components of the aquifer water. The analysis results of pH inferred that the groundwater is nominally acidic to basic, and pH ranged from 6.6 to 8.4. The average concentrations of TDS, Ca²⁺, Mg²⁺, total hardness (TH), HCO₃^-, and total alkalinity (TA) are within the allowable limits of potable water quality as prescribed by the Bureau of Indian Standards (BIS) and WHO. However, the average concentrations of Na⁺, K⁺, Cl^-, and SO₄^2- were all below the permissible limit. All samples were analyzed with the help of Piper and Chadha charts to determine the dominant hydrogeochemical components of groundwater. The dominance of cations in groundwater in this region is in the sequence of Ca²⁺  > Na⁺  > Mg²⁺  > K⁺, followed by anions HCO₃^-  > Cl^-  > SO₄^2-. The Gibbs plot analysis suggested the predominance of rock aquifer interaction as the major hydrogeochemical process governing groundwater geochemistry in this region. The water quality index (WQI) of all groundwater samples in the Tummalapalle region was estimated, with 55% of the samples being potable grade. The different irrigation indices were analyzed for the groundwater samples to estimate their desirability for agriculture. The maximum number of water samples was found to be well-suited for cultivation.

STUDY OF EFFECTIVENESS OF SHELTERING FROM RADIATION EXPOSURE DUE TO ACCIDENTAL RELEASE OF RADIOACTIVITY

Sheltering is one of the important protective actions as a part of emergency response during the early phases of an accident-mostly precautionary in nature. Sheltering via structural shielding reduces the direct exposure from plume/cloud shine and ground shine doses as well as the airborne radioactivity concentration and hence inhalation dose. The present study was aimed at estimating the shielding factor in the case of Indian houses for external exposure pathways using the FLUKA Monte Carlo based radiation transport code. Furthermore, the dose reduction factor due to exposure from the inhalation pathway was estimated using an indoor aerosol model. These factors were assessed for the three major types of dwellings, and they provided important inputs for decision-making for sheltering or evacuation in case of any sudden release of radionuclides into the environment.

Dose distribution to a random walker moving in a two-dimensional surface around a radioactive source

BACKGROUND

Modeling of dose distribution of randomly moving population around a radioactive source is a complex problem.

OBJECTIVE

The objective is to develop a model and solution techniques to estimate radiation absorbed dose to the population randomly moving around a radioactive source.

METHODS

The problem is formulated using a second-order partial differential equation; different moments of the dose distribution function are defined related to physically realizable quantities, and solutions are obtained using standard moments methods. Alternatively, numerical simulations are performed to estimate the radiation doses using Monte Carlo approach for individual positions and random motions of the people around the source.

RESULTS

A good agreement is found between average doses obtained from moments method and numerical simulations. A typical application of this model to different exposure conditions shows that the average dose is highly dependent on the population density. The study results show that average dose decreases with increase in the population density and movement area of random walker.

SIGNIFICANCE

This mathematical model can be used as a rapid assessment tool by the emergency planners in resource optimization by providing quick estimates of likely exposures for triage and emergency response.

Simulation study on radiation fields around targets to apply CR-39 for photo-neutron measurement in electron accelerator near the threshold energy

Photo-neutron production in electron accelerator near the threshold energy has been studied by Monte Carlo simulation using the FLUKA code. A pencil beam of 10 MeV electron was incident normally on W, Ta, Pb and Bi targets and a CR-39 detector attached to the target was used as scoring region. In the simulation, photon and neutron spectra, yield and their spatial distribution, fast neutron fluence above 100 keV, total dose and neutron dose deposition were estimated for these metallic targets. The photon emission was found to be forward peaked whereas the neutron emission was isotropic in nature. The photon yield was found to be 5 to 6 orders of magnitude higher than that of neutrons. In W and Ta, the photon yield is maximum for 1.5 mm thickness whereas for Pb and Bi, the photon yield is highest at 2 and 2.5 mm respectively. The total neutron yield was highest for W and lowest for Pb whereas highest number of fast neutrons above 100 keV was for W followed by Bi, Pb and Ta. Production of significant number of fast neutrons above 100 keV suggests the possibility of the use of CR-39 detector for measurement of these neutrons. The total dose deposition was found to be highest for Bi followed by Pb, Ta and W whereas the neutron dose equivalent was highest for W followed by Pb, Bi and Ta. This simulation study will be useful for neutron dosimetry, estimation of source term, implementation of CR-39 for measurement and other radiation protection aspects in the vicinity of an electron accelerator.

Application of multipoint dose rate measurement for radioactive inventory estimation in waste drums

Dose-to-Curie (DTC) conversion is a fast and simple method for quantification of radionuclide content in solid waste packages with a prior knowledge of waste matrix and radionuclide composition of the waste stream. A dose to curie conversion factor generated based on an assumed radioactivity distribution in the package is used for conversion of the measured dose rate to activity. The difference between the radionuclide distribution for drum from field and the assumed distribution is a major source of error in activity estimation using this technique. In this work, the systematic error of DTC method, due to the spatial variation of a single hot-spot in 200 L solid waste drum is subjected to systematic analysis using Monte-Carlo simulation. Data analysis was carried out with 1920 source locations within the drum and up to sixteen measurement points for dose rates around the drum. The span of error obtained for different configurations of detectors were compared to optimise the waste drum assay system. The general trends observed in simulation were found to be in good agreement with the experimental measurements done using a ¹³⁷Cs (318.2 MBq) standard source placed at selected locations. The results presented here clearly establish the advantage of multipoint dose rate measurement to improve the accuracy in activity estimation using DTC method.

Evaluation of influential correction factors applicable for absolute beta dosimetry of 85Kr, 90Sr-90Y and 106Ru-106Rh beta emitters

Extrapolation ionization chamber is normally used for absolute measurement of absorbed dose to tissue and in standardization of beta particle emitting sources in particular. However, in this technique, several correction factors are applied to the measured ionization current to evaluate the true value of the dose to the tissue from beta radiation. These correction factors are described in ISO 6980-2:2004. Out of these, ion recombination correction factor (k_sat) and ambient air density correction factor (k_ad) are evaluated experimentally during measurement of ionization current. Other significant correction factors are backscatter correction factor (k_ba), correction factor for perturbation in electron spectrum due to ionization chamber side wall scatter (k_pe), correction factor for difference in attenuation of beta spectrum due to change in ambience condition (k_abs) and correction factor for radial non-uniformity of dose inside detector volume (k_ra). Experimental evaluation of correction factors k_ba, k_pe and k_abs are not easily achievable. In the present work four significant correction factors k_ba, k_pe, k_abs and k_ra are derived theoretically by Monte Carlo particle transport simulation. These correction factors are evaluated for beta emission spectrum of ⁸⁵Kr, ⁹⁰Sr-⁹⁰Y and ¹⁰⁶Ru-¹⁰⁶Rh radioactive sources.

DEVELOPMENT OF NACL-BASED OPTICALLY STIMULATED LUMINESCENT PHOSPHORS FOR THE POSSIBLE APPLICATIONS IN DOSIMETRY

New highly sensitive optically stimulated luminescent phosphors with NaCl moiety and dopants Ca,Cu,P/Mg,Cu,P are developed. These phosphors show very high optically stimulated luminescence (OSL) sensitivity. The dose response for NaCl:Ca,Cu,P is linear up to 1.2 Gy and for NaCl:Mg,Cu,P is slightly sub linear from 0.2 Gy. These phosphors show 30% fading during first 4 and later signal gets stabilised with no further signal loss. These sensitive phosphors will find applications in radiation dosimetry using OSL.

Study of optically stimulated luminescence and calculation of trapping parameters of K2Ca2(SO4)3:Eu nanophosphor

K₂Ca₂(SO₄)₃:Eu nanophosphor was synthesized by chemical coprecipitation method and annealed at different temperatures from 400 to 900 °C. The nanophosphor annealed at 600 °C showed cubic structure with crystallite size ~25 nm. TEM shows morphology of K₂Ca₂(SO₄)₃:Eu nanophosphor was in the form of nanorods having diameter ~20 nm and length of ~100-200 nm. These samples were irradiated with gamma radiation for the doses varying from 10 mGy to 10 kGy and their Thermoluminescence (TL) and continuous-wave optically stimulated luminescence (CW-OSL) have been studied. CW-OSL response was found to be maximal for the sample annealed at 600 °C. The TL glow curve of the nanophosphor apparently showed a major peak at around 160 °C accompanied by three low intensity peaks at ~75, 215 and 285 °C. The traps responsible for all the TL peaks in K₂Ca₂(SO₄)₃:Eu were also found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response suggested that the traps associated with low temperature peaks are responsible for fast decay and the traps associated with the higher temperature peaks are responsible for slow decay of the OSL signal. OSL response showed linear behavior up to 1 kGy and saturated with further increase in the gamma dose. The wide OSL response makes studied K₂Ca₂(SO₄)₃:Eu nanophosphor a good candidate for high dose measurement.

DOSE ASSESSMENT FOR ATMOSPHERIC DISCHARGE OF LONG-LIVED RADIONUCLIDES IN NUCLEAR POWER PLANT DECOMMISSIONING

Decommissioning of nuclear power plants is a multistage process involving complex operations like radiological characterization, decontamination and dismantling of plant equipment, demolition of structures, and processing and disposal of waste. Radioactive effluents released into the environment may result in exposure of population through various exposure pathways. The present study estimates the public dose due to atmospheric discharge of important radionuclides during proposed decommissioning activities of Indian Pressurized Heavy Water Reactors. This study shows that major dose contributing radionuclides are 60Co followed by 94Nb, 134Cs, 154Eu, 152Eu, 133Ba, 99Tc, 93Mo and 41Ca. It is found that infant dose is higher than adult dose and major fraction of total dose (~98%) is through ground shine and ingestion; other pathways such as inhalation and plume shine contribute only a small fraction. This study will be helpful in carrying out radiological impact assessment for decommissioning operations which is an important regulatory requirement.

Determination of calibration matrix for HPGe-based in vivo monitoring system for estimation of 241Am in lungs and liver

The detection of internal contamination may be carried out by direct or indirect methods. The lung counting technique using an array of High Purity Germanium (HPGe) detectors is one of such direct detection methods. It is known from the literature that the estimation of activity by organ counting can lead to erroneous results if an amount of activity is possessed by an adjacent organ. In the case of HPGe-based lung monitoring, the estimation could be misleading if the activity is possessed by the liver, which is a proximal organ. In such cases the measured activity should be modified using cross-talk coefficients which account for the contribution from adjacent organs. The determination of cross-talk coefficients for ²⁴¹Am was carried out by placing the detectors over inactive lungs of an Lawrence Livermore National Laboratory phantom when the source activity was contained in the liver and vice versa. A calibration matrix was formulated with calibration coefficients as diagonal elements and cross-talk coefficients as off-diagonal elements. The measured activities may be modified by matrix multiplication with the inverse of the calibration matrix to nullify the contribution from adjacent organs. The current work has empirically determined the fitting equations which relate calibration and cross-talk coefficients for lungs and liver measurement geometries with muscle-equivalent chest wall thickness (MEQ-CWT) values. The values of these coefficients were determined for an average MEQ-CWT of 1.77 cm for lungs and 1.33 cm for liver. The calculations showed that the activity contribution from liver to lungs was 29% higher than that of lungs to liver. A verification exercise was conducted to demonstrate this method. For the given calibration source, the percent overestimation was reduced for lung activity, while the liver activity was slightly underestimated. In the case of old exposure follow-up monitoring cases, the ²⁴¹Am activity built up in liver could interfere with the lung monitoring results and this method using the calibration matrix may be used for estimation of more accurate results.

Effective dose conversion coefficient for gamma ray exposure from an overhead plume

The external radiation exposure from an overhead plume containing gamma emitting radionuclides can contribute substantial dose to the ground receptor during normal operations as well as accidental release conditions of nuclear facilities. In order to estimate the effective dose conversion coefficients (DCCs) directly, a finite plume Monte Carlo model along with the reference phantom at the ground receptor location needs to be implemented. In the present study, a comprehensive simulation of radiation transport from the Gaussian plume source to the ICRP reference adult voxel phantoms (receptor) is carried out using the FLUKA Monte Carlo code. The organ absorbed doses as well as the effective DCCs of the adult reference phantom are computed for different meteorological parameters and downwind distances. To illustrate the application of this model, an overhead Gaussian plume containing two different gamma emitting radionuclides, ¹³⁵Xe and ⁴¹Ar are considered. From these simulations, the ratio of the effective dose rate to the kerma rate are estimated as 0.6 Sv Gy^-1 and 0.65 Sv Gy^-1 for the exposure from ¹³⁵Xe and ⁴¹Ar, respectively. This ratio is constant irrespective of the meteorological conditions and cloud models. Further results show that the effective DCCs as a function of the downwind distance vary by an order of magnitude for an unstable weather category; however, the variations are very small in the case of a stable category. This study demonstrates an accurate method for calculating the effective dose to the ground receptor from an external plume which can be further applied for any radionuclide under any meteorological condition.

Standardisation of Rhenium-188 and determination of calibration factors for secondary standard and radionuclide calibrator

The use of Rhenium-188 for various therapeutic applications in the field of nuclear medicine has increased in recent years due to its favourable properties like decay scheme, cost effective availability and easy chemistry. Two independent measuring setups were used to standardise ¹⁸⁸Re radioactive solution. The modus operandi of standardisation was 4πβ-γ coincidence technique where the beta detection was done by proportional counting and liquid scintillation counting and the gamma detection was done by using NaI(Tl) detectors. The secondary standard, high pressure ionisation chamber type Centronic IG12, 20A was calibrated with the standardised ¹⁸⁸Re solution and the sensitivity coefficient (pA MBq^-1) was determined. To enhance the accuracy of the commercial radionuclide calibrator and to ensure that patients receive optimum dose of these radiopharmaceuticals, calibration number of the Capintec CRC-15β radionuclide calibrator was also verified. This paper presents the standardisation of ¹⁸⁸Re radioactive solution by primary methods and calibration of BARC secondary standard ionisation chamber system and a Capintec CRC-15β radionuclide calibrator.

WALL THICKNESS OPTIMISATION OF AN IONISATION CHAMBER FOR DIRECTIONAL DOSE EQUIVALENT RATE MEASUREMENT AT LOW AND MEDIUM PHOTON ENERGIES

A thin and plane wall ionisation chamber having 900 cc volume was designed and fabricated to study the calibration coefficient dependency on ionisation chamber wall thickness for directional dose equivalent rate (Ḣ'(d)) at various low and medium energy X-ray beam qualities. Optimised wall thickness was established through measurements to achieve a near flat energy response using the developed ionisation chamber. The measurement shows that in the energy range 12-213 keV, the average calibration coefficient for directional dose equivalent rate lies within ±10% for wall thickness 1.2 mg/cm2 and 480 mg/cm2 (4 mm poly methyl methacrylate) for skin and eye lens dose monitoring, respectively. The study could be useful for the estimation of skin and eye lens doses for the paramedical staff and patient during the interventional radiology and interventional cardiology procedures by monitoring the directional dose equivalent rate.

DEVELOPMENT OF AN IONIZATION CHAMBER FOR LOW AND MEDIUM ENERGY PHOTON DOSIMETRY

Measurement of dose due to low and medium energy X-ray using an ionization chamber needs special considerations as the wall thickness of the detector plays an important role in signal generation. A thin and plane wall ionization chamber having 900 cc volume was developed to study its calibration coefficient with air kerma (Kair) rate and ambient dose equivalent (H*(10)) rate at various X-ray beam qualities generated from a dosimetry grade X-ray machine. Optimized ionization chamber wall thickness was determined through measurements where a flat energy response of the ionization chamber could be established. The measurement shows that the air kerma rate based calibration coefficient for ionization chamber varies up to 45% and ambient dose equivalent rate based calibration coefficient varies up to 20% for wall thickness 1.2-1200 mg/cm2 in the energy range 17.6-213 keV.

Evaluation of Uncertainties in lung measurements of actinides due to counting statistics

Counting statistics is an important parameter that can introduce uncertainties in the lung activity measurements of actinides in radiation workers. Evaluation of uncertainties due to counting statistics is practically difficult as it requires monitoring various radiation workers having different levels of lung actinide content, multiple times, each for 50 min of monitoring period. However, different activities in lungs can be simulated by combining uncontaminated male data with LLNL phantom data acquired with ²⁴¹Am and natural uranium lung sets at various short periods. Therefore, multiple measurements were carried out on realistic thorax LLNL phantom with ²⁴¹Am and natural uranium lung sets for 15-600 s. The mean counts with the phantom at various time intervals, corresponds to different actinide activities in lungs, assuming they are obtained for 50 min of monitoring interval. Using propagation of error, standard deviations were evaluated for combined phantom and uncontaminated adult male data. The combined standard deviations and mean phantom counts are used to evaluate scattering factors (SFs) for uncertainties due to counting statistics for Phoswich and HPGe array detectors. The SFs due to counting statistics are found to be the function of lung activities of radionuclides as well as energies and yields of the photons emitted by radionuclides. SFs are found to increase with decrease in lung activity. For similar yields photons, SFs are found to be lower for higher energy photons compared to lower energy photons. For photons of similar energies, the SFs are lower when yield is higher compared to lower yield photons.

PHASE DEPENDENT OPTICALLY STIMULATED LUMINESCENCE IN CU-DOPED Sr4Si3O8Cl4

Phase dependent optically stimulated luminescence (OSL) is studied in Cu-doped Sr4Si3O8Cl4. The Study shows that samples in which amount of contributing strontium metasilicate phase in Cu-doped Sr4Si3O8Cl4 is less, show intense OSL while those samples in which strontium metasilicate phase is more show weak OSL. The observed Cu luminescence is also found to be phase dependent. Sample in which Sr4Si3O8Cl4 phase is dominant, the observed Cu luminescence is around 350 nm whereas an additional longer wavelength band around 450 nm is observed when the strontium metasilicate phase is present in significant amount. The relatively phase pure, Cu-doped Sr4Si3O8Cl4 shows good OSL properties. The sensitivity of such material is 3.89 times more compared to commercial Al2O3:C (Landauer Inc.). High sensitivity, good linearity and reusability, along with low fading make this material as good OSL phosphor and may find applications in OSL based radiation dosimetry.

PHOTOLUMINESCENCE, THERMOLUMINESCENCE AND OPTICALLY STIMULATED LUMINESCENCE STUDIES IN ZINC-BASED FLUOROPERVOSKITES

The optically stimulated luminescence, thermoluminescence and photoluminescence in various Cu and Ag doped zinc based fluoropervoskites are studied. In all the samples, photoluminescence of Cu+ and Ag+ is observed which could be attributed to 3d94 s1←→3d10 and 4d95 s1←→5d10 transitions, respectively. The observed emission is double humped and the main emission band shifts to the lower wavelength side with increasing ionic size of the alkali ion. All the studied fluoropervoskites show reasonable OSL sensitivity. Highest sensitivity is observed for Cu doped ZnNaF3 and is 25% compared to commercial Al2O3:C. Weak thermoluminescence is observed in all samples. In all Ag doped samples the TL peak is observed at 200°C whereas for Cu doped samples peak is observed at 150°C, and correlated with the OSL. The samples show good linear dose response in the 10 mGy-1.2 Gy range and show good reusability characteristics. This study will lead to the development of zinc-based fluoropervoskite phosphors for the radiation dosimetry using OSL.

DEEP, SHALLOW AND EYE LENS DOSES FROM 106Ru/106Rh-A COMPARSION

106Ru/106Rh is unique amongst other commonly used beta sources such as 147Pm, 85Kr, 204Tl, 32P, natU and 90Sr/90Y in the sense that it is capable of simultaneously delivering shallow/skin, eye lens and deep/whole body doses (WBDs) and they differ from each other substantially. In view of this, the investigation of various quantities defined for individual monitoring is possible and this makes 106Ru/106Rh beta source, a classical example in radiation protection and dosimetry. This led us to estimate skin, eye lens and WBDs for 106Ru/106Rh beta source. Optically stimulated luminescence based ultra-thin α-Al2O3:C disc dosimeters were used in the present study. Typical values (relative) of the eye lens and whole body/deep doses with respective to the skin dose (100%) were experimentally measured as ~66 ± 4.6% and 17 ± 3.9%, respectively. The study shows that 106Ru/106Rh beta source is capable of delivering even WBD which is not the case with other beta sources.

Optically stimulated luminescence study in rare earth doped SrBPO5

Optically stimulated luminescence (OSL) was studied in rare earth doped SrBPO₅ for the possible applications in radiation dosimetry using optically stimulated luminescence. The study shows that the sensitivity of the Eu doped SrBPO₅ shows good OSL and the sensitivity is comparable to that of Al₂O₃:C. It is observed that annealing has a profound effect on the OSL sensitivity. Slowly cooled Eu doped sample shows highest sensitivity and is 77% compared to that Al₂O₃:C whereas lowest sensitivity is observed in the quenched sample. Other properties like good linearity and low fading will make this phosphor suitable for the applications in radiation dosimetry using OSL.

Evaluation of uncertainties in lung measurement of actinides due to non-uniform distribution of activity in lungs

Various parameters can introduce uncertainties in the lung activity measurements of actinides. In this study, uncertainties due to non-uniform distribution of activity in the lungs are evaluated. To study the effect of non-uniform distribution, lungs of ICRP male thorax voxel and resized phantoms are divided into upper and lower parts of both right and left lungs as well as into anterior and posterior lung regions. Simulation of uniform and non-uniform distribution of activity in lungs is carried out using thorax voxel phantoms in FLUKA for Phoswich and an array of three HPGe detectors for 18-238keV photons. Source sampling for non-uniform distribution of activity is carried out by selecting the source points by varying the weightage to 0.4, 0.5, 0.6 and 1 in different parts of lungs. Uncertainties in lung activity estimation at different energies are quantified in the form of scattering factors (SFs) which are geometric standard deviations. The SFs due to non-uniform distribution of activity of the order of 0.4-0.6 in different parts of the lungs are found to be ~ 1.25 for Phoswich and HPGe array detectors above 18keV.

METHODOLOGY FOR THE ASSESSMENT OF INGESTED ACTINIDES FROM MONTE CARLO SIMULATION OF VOXEL PHANTOM

In case of internal contamination of actinides by ingestion pathway, activity will be transferred to various regions of the alimentary tract over a period of time. In this article, counting efficiencies (CEs) of Phoswich and an array of HPGe detectors are estimated for source in alimentary tract of voxel phantom. The phantom as well as Phoswich, and an array of three HPGe detectors are incorporated in Monte Carlo code 'FLUKA'. Human alimentary tract model is solved using default parameters to identify different compartments where activity will accumulate after an ingestion intake of 1 Bq as a function of time. Accordingly, CEs are evaluated on 0.5-5 d post ingestion intake for the source distributed in the contents of alimentary tract for photon energies in 18-238 keV range representing sources of actinides. The assessment of ingested activity of actinides from abdomen measurements is discussed. Higher CEs are observed with Phoswich detector compared with HPGe array due to its large size and high effective Z. Also, the CEs observed on Days 1-5 using both the detectors are found to decrease by 16-75 % with respect to the CE on half day. Thus, there is need to use CEs according to the observed activity distribution post ingestion intake. The contribution in the abdomen measurements due to source in the lungs and vice versa is also studied for intake by both inhalation and ingestion pathways. The contribution of source in the liver is found to be ∼30-50 % in chest and 75 % in abdomen measurements.

Effect of Al(3+) co-doping on the luminescence properties of Cu doped Na2SiF6

Studies were carried out to assess the correlation between thermoluminescence (TL) and optically stimulated luminescence (OSL) of this phosphor. It was observed that the OSL and TL glow curve consists of a wide distribution of traps having different photo-ionization cross-sections, trap depths and frequency factors. In case of Al doped sample, some of the traps up to 200°C are assumed to act as a source traps for the observance of OSL due to thermal transfer of charge carriers into the deep traps beyond 480°C. This suggests that Al impurities play an important role in the thermal transfer OSL process. As most of the work on this phenomenon is done on natural materials (mainly quartz) in which aluminum is a natural impurity, this study will explain the role of Al in this phenomenon.

Measurement of eye lens dose for Varian On-Board Imaging with different cone-beam computed tomography acquisition techniques

The objective of this work was to measure patient eye lens dose for different cone-beam computed tomography (CBCT) acquisition protocols of Varian's On-Board Imaging (OBI) system using optically stimulated luminescence dosimeter (OSLD) and to study the variation in eye lens dose with patient geometry and distance of isocenter to the eye lens. During the experimental measurements, OSLD was placed on the patient between the eyebrows of both eyes in line of nose during CBCT image acquisition to measure eye lens doses. The eye lens dose measurements were carried out for three different cone-beam acquisition protocols (standard dose head, low-dose head [LDH], and high-quality head [HQH]) of Varian OBI. Measured doses were correlated with patient geometry and distance between isocenter and eye lens. Measured eye lens doses for standard head and HQH protocols were in the range of 1.8-3.2 mGy and 4.5-9.9 mGy, respectively. However, the measured eye lens dose for the LDH protocol was in the range of 0.3-0.7 mGy. The measured data indicate that eye lens dose to patient depends on the selected imaging protocol. It was also observed that eye lens dose does not depend on patient geometry but strongly depends on distance between eye lens and treatment field isocenter. However, undoubted advantages of imaging system should not be counterbalanced by inappropriate selection of imaging protocol, especially for very intense imaging protocol.

A new highly sensitive low-Z LiF-based OSL phosphor for radiation dosimetry

A new low-Z lithium fluoride-based optical stimulated luminescent (OSL) phosphor is developed. The phosphor shows good OSL properties, and its sensitivity is comparable with that of the commercial Al2O3:C (Landauer, Inc.) phosphor. For the luminescence averaged over initial 3 s, blue stimulated luminescence (BSL) and green stimulated luminescence (GSL) sensitivities were found to be 0.27 and 4 times, respectively, than that of Al2O3:C (Landauer, Inc.). The BSL decay is fast, and the whole signal decays within 3 s; the GSL decay is relatively slow, and the signal decays in 25 s. The fast decay, good sensitivity, good linearity and its near tissue equivalence (Zeff ∼8.14) will make this phosphor suitable for radiation dosimetry particularly in personnel as well as in medical dosimetry.

Performance demonstration of 4πβ(LS)-γ coincidence counting system for standardization of radionuclides with complex decay scheme

A standardization of (134)Cs and (131)I was carried out in order to demonstrate the performance and applicability of the 4πβ(LS)-γ coincidence counting system for standardization of radionuclides with complex decay scheme. The coincidence analyzer, capable of analyzing coincidence between beta and two gamma windows simultaneously, was developed and used for the standardization. The use of this dual coincidence analyzer has reduced the total experimental time by half. The activity concentrations obtained using the 4πβ(LS)-γ coincidence counting system, a 4πβ(PC)-γ coincidence counting system, and the CIEMAT/NIST method are in excellent agreement with each other within uncertainty limits and hence demonstrates its performance for standardization of radionuclides decaying with complex decay scheme. Hence use of this 4πβ(LS)-γ coincidence counting system can be an alternative method suitable to standardize radionuclides with complex decay scheme with acceptable precision.

Assessment of uncertainties in the lung activity measurement of low-energy photon emitters using Monte Carlo simulation of ICRP male thorax voxel phantom

Assessment of intake due to long-lived actinides by inhalation pathway is carried out by lung monitoring of the radiation workers inside totally shielded steel room using sensitive detection systems such as Phoswich and an array of HPGe detectors. In this paper, uncertainties in the lung activity estimation due to positional errors, chest wall thickness (CWT) and detector background variation are evaluated. First, calibration factors (CFs) of Phoswich and an array of three HPGe detectors are estimated by incorporating ICRP male thorax voxel phantom and detectors in Monte Carlo code 'FLUKA'. CFs are estimated for the uniform source distribution in lungs of the phantom for various photon energies. The variation in the CFs for positional errors of ±0.5, 1 and 1.5 cm in horizontal and vertical direction along the chest are studied. The positional errors are also evaluated by resizing the voxel phantom. Combined uncertainties are estimated at different energies using the uncertainties due to CWT, detector positioning, detector background variation of an uncontaminated adult person and counting statistics in the form of scattering factors (SFs). SFs are found to decrease with increase in energy. With HPGe array, highest SF of 1.84 is found at 18 keV. It reduces to 1.36 at 238 keV.

A primary standard for the measurement of alpha and beta particle surface emission rate from large area reference sources

A large area windowless gas flow multi wire proportional counting system for the calibration of large area reference sources has been developed as a primary standard at Bhabha Atomic Research Centre (BARC). The counting system consists of a multi wire proportional counter (MWPC), vacuum system, gas flow system and pulse processing units. The MWPC detector assembly consists of a vacuum tight aluminum enclosure, multi wire grid and sliding source tray. Various detector characteristics like operating characteristics curve, Fe-55 spectrum for beta discriminator threshold setting and dead time of the measurement system were studied and determined in order to achieve an optimized detection capability. The surface emission rates of different source strengths were measured and their relative combined standard uncertainties were determined. Large Area Sources Comparison Exercise (LASCE) was organized by International Committee on Radionuclide Metrology (ICRM) working group and coordinated by National Institute for Ionising Radiation Metrology (ENEA), Italy, to demonstrate equivalence of surface emission rate measurements at the international platform. BARC participated in the programme and the results of LASCE are also discussed in this paper.