ELECTRON EYE-LENS OPERATIONAL DOSE COEFFICIENTS.

In 2012, the International Commission on Radiological Protection issued a recommendation for a reduced annual eye-lens dose limit in the face of mounting evidence of the risk of cataract induction. This led to worldwide research efforts in various areas including the dose simulation in realistic eye-models, the production of dosimeters and the elaboration of protection and operation fluence to eye-lens dose coefficients. In this last case, much efforts have been expanded with regards to photon operational coefficients for Hp (3) but much less for electron radiation. In this work, Hp (3) coefficients for electrons are presented following simulations using MCNP and compared to those that are available in the literature. It is found that, at energies of 1 MeV and less, Hp (3) coefficients depend strongly on the selected electron transport options and on the dose tally volume. The effect of these differences is demonstrated for two beta emitters.

A COMPARISON OF BETA SKIN DOSES CALCULATED WITH VARSKIN 5.35.3 AND MCNP5.

The computer code VARSKIN, version 5.3, is widely used to calculate superficial dose caused by the routine handling of radioactive substances or in skin contamination incidents. It allows a variety of source configurations, points, volume, surface and syringe-like (cylindrical) and a variety of exposure situations such as direct skin contact or exposure through clothing. However, there is a need for more benchmarking data of VARSKIN, especially for beta particles, with complex irradiation geometries. Dose calculations using MCNP5 and VARSKIN 5.3 for a variety of mass-less point beta-emitting sources were performed. Both programs gave comparable results that are in good agreement with published dose rate conversion factors for sources on contact with the skin or with fabric. However, important differences appear, with VARSKIN 5.3 values as much as 40% below the Monte Carlo results, when an air gap of a few mm is introduced between the fabric and skin.

SINGLE ANODE TRIPLE GEM TISSUE EQUIVALENT PROPORTIONAL COUNTER AS THE BASIS FOR A PERSONAL NEUTRON DOSIMETER.

This paper reports on a tissue-equivalent proportional counter (TEPC) based on a triple gas electron multiplier structure, with a single pad readout, as a basis for a personal neutron dosimeter. Its dosimetric response was studied using the 252Cf neutron source at the Health Physics Generator Facility of the Canadian Nuclear Laboratories. Measured lineal energy spectra were found to be in agreement with numerical simulations performed with Monte Carlo N-Particle eXtended (MCNPX). Both simulations and measurements showed that the mean pathlength of secondary charged particles in the TEPC gas was best represented by the thickness of the drift region of the device. It was determined that the Cauchy Theorem, used to calculate the mean chord length in spherical and cylindrical TEPCs, overestimated the simulated mean chord length by nearly a factor of two. Important operational characteristics of the device were investigated, including gas gain, sensitivity and dosimetric response, as functions of tissue-equivalent gas pressure. This work demonstrates that the proposed design can serve as the basis for a personal neutron dosimeter device, which would satisfy the angular dosimetric response criteria of the personal dosimeter standard IEC61526.

Multiple Methods for Assessing the Dose to Skin Exposed to Radioactive Contamination.

There is the possibility for a worker at a nuclear installation, such as a nuclear power reactor, a fuel production facility or a medical facility, to come in contact with radioactive contaminants. When such an event occurs, the first order of business is to care for the worker by promptly initiating a decontamination process. Usually, the radiation protection personnel performs a G-M pancake probe measurement of the contamination in situ and collects part or all of the radioactive contamination for further laboratory analysis. The health physicist on duty must then perform, using the available information, a skin dose assessment that will go into the worker's permanent dose record. The contamination situations are often complex and the dose assessment can be laborious. This article compares five dose assessment methods that involve analysis, new technologies and new software. The five methods are applied to 13 actual contamination incidents consisting of direct skin contact, contamination on clothing and contamination on clothing in the presence of an air gap between the clothing and the skin. This work shows that, for the cases studied, the methods provided dose estimates that were usually within 12% (1σ) of each other, for those cases where absolute activity information for every radionuclide was available. One method, which relies simply on a G-M pancake probe measurement, appeared to be particularly useful in situations where a contamination sample could not be recovered for laboratory analysis.

Correction and verification of AECL Bonner Sphere response matrix based on mono-energetic neutron calibration performed at NPL.

The AECL Bonner Sphere Spectrometer (BSS) was taken to National Physical Laboratory (NPL) for calibration in mono-energetic neutron fields and bare (252)Cf neutron fields. The mono-energetic radiations were performed using ISO-8529 prescribed neutron energies: 0.071, 0.144, 0.565, 1.2, 5 and 17 MeV. A central SP9 proportional counter was also evaluated at the NPL thermal neutron calibration facility in order to assess an effective pressure of (3)He inside the counter, i.e. number density of (3)He atoms. Based on these measurements and methods outlined by Thomas and Soochak, a new BSS response matrix was generated. The response matrix is then verified by unfolding spectra corresponding to various neutron fields. Those are NPL bare (252)Cf source, National Institute of Standards and Technology bare and heavy water moderated (252)Cf source and (241)AmBe calibration source located at National Research Council. A good agreement was observed with expected neutron fluence rates, as well as derived dosimetric quantities, such as International Commission on Radiological Protection-74 ambient dose equivalent.

Measurements of neutron energy spectra from 7Li(p,n)7Be reaction with Bonner sphere spectrometer, Nested Neutron Spectrometer and ROSPEC.

Neutron spectrometry measurements were carried out at the McMaster Accelerator Laboratory (MAL), which is equipped with a 3-MV Van de Graaff-type accelerator. Protons were accelerated onto a thick natural lithium target inducing the (7)Li(p,n)(7)Be threshold reaction. Depending on the proton energy, slightly different poly-energetic neutron fields were produced. Neutron spectra were measured at two incident proton energies: 2.15 and 2.24 MeV, which produced poly-energetic neutrons with maximum kinetic energies of 401 and 511 keV, respectively. Measurements were performed at a distance of 1.5 m from the target in the forward direction with three different instruments: Bonner sphere spectrometer, Nested Neutron Spectrometer and ROtational proton recoil SPECtrometer.

Neutron spectrometry and dosimetry study at two research nuclear reactors using Bonner sphere spectrometer (BSS), rotational spectrometer (ROSPEC) and cylindrical nested neutron spectrometer (NNS).

Neutron spectrometry and subsequent dosimetry measurements were undertaken at the McMaster Nuclear Reactor (MNR) and AECL Chalk River National Research Universal (NRU) Reactor. The instruments used were a Bonner sphere spectrometer (BSS), a cylindrical nested neutron spectrometer (NNS) and a commercially available rotational proton recoil spectrometer. The purposes of these measurements were to: (1) compare the results obtained by three different neutron measuring instruments and (2) quantify neutron fields of interest. The results showed vastly different neutron spectral shapes for the two different reactors. This is not surprising, considering the type of the reactors and the locations where the measurements were performed. MNR is a heavily shielded light water moderated reactor, while NRU is a heavy water moderated reactor. The measurements at MNR were taken at the base of the reactor pool, where a large amount of water and concrete shielding is present, while measurements at NRU were taken at the top of the reactor (TOR) plate, where there is only heavy water and steel between the reactor core and the measuring instrument. As a result, a large component of the thermal neutron fluence was measured at MNR, while a negligible amount of thermal neutrons was measured at NRU. The neutron ambient dose rates at NRU TOR were measured to be between 0.03 and 0.06 mSv h⁻¹, while at MNR, these values were between 0.07 and 2.8 mSv h⁻¹ inside the beam port and <0.2 mSv h⁻¹ between two operating beam ports. The conservative uncertainty of these values is 15 %. The conservative uncertainty of the measured integral neutron fluence is 5 %. It was also found that BSS over-responded slightly due to a non-calibrated response matrix.

Detection of bremsstrahlung radiation of 90Sr-90Y for emergency lung counting.

This study explores the possibility of developing a field-deployable (90)Sr detector for rapid lung counting in emergency situations. The detection of beta-emitters (90)Sr and its daughter (90)Y inside the human lung via bremsstrahlung radiation was performed using a 3″ × 3″ NaI(Tl) crystal detector and a polyethylene-encapsulated source to emulate human lung tissue. The simulation results show that this method is a viable technique for detecting (90)Sr with a minimum detectable activity (MDA) of 1.07 × 10(4) Bq, using a realistic dual-shielded detector system in a 0.25-µGy h(-1) background field for a 100-s scan. The MDA is sufficiently sensitive to meet the requirement for emergency lung counting of Type S (90)Sr intake. The experimental data were verified using Monte Carlo calculations, including an estimate for internal bremsstrahlung, and an optimisation of the detector geometry was performed. Optimisations in background reduction techniques and in the electronic acquisition systems are suggested.

A neutron spectrometer using nested moderators.

The design, simulation results and measurements of a new neutron energy spectrometer are presented. The device, which may be called NNS, for Nested Neutron Spectrometer, works under the same principles as a Bonner Sphere Spectrometer (BSS) System, i.e. whereby a thermal neutron detector is surrounded by a polyethylene moderator. However, the moderator is cylindrical in shape. The different thicknesses of moderator are created by inserting one cylinder into another, much like nested Russian dolls. This design results in a much lighter instrument that is also easier to use in the field. Simulations and measurements show that, despite its shape, the device can be made to offer a near angular isotropic response to neutrons and that unfolded neutron spectra are in agreement with those obtained with a more traditional BSS.

Neutron microdosimetric response of a gas electron multiplier.

A new high-sensitivity tissue equivalent proportional counter (TEPC) on the basis of the gas electron multiplier (GEM) detector used in high-energy physics experiments has been designed, constructed and tested in a variety of neutron fields. The GEM-TEPC makes use of a lithographically produced strip readout system to achieve the equivalent of a large number of miniature TEPC detector elements. This new device could be used as the basis of an electronic personal dosemeter for gamma and neutron mixed radiation fields.

Monte Carlo determination of age-dependent steady-state dose to red bone marrow and bone from 14C exposure.

Monte Carlo simulations were carried out to calculate the age-dependent dose from the beta decay of 14C to marrow and bone on the basis of a steady-state specific-activity model. A model of the trabecular cavity containing spherical fat cells in a square lattice surrounded by haemopoietic tissue was employed. The age-dependent 14C dose to haemopoietic (red) marrow was estimated taking account of the change in the fat cell size with fat fraction. Allowances were made for the change in the percentage cellularity and distribution of active marrow in the whole skeleton as a function of age. Age-dependent changes in trabecular cavity size and bone composition were found to have only a small effect on dose. Dose rates were estimated under steady-state conditions, for food ingested with a 14C specific activity of 1 Bq g(-1) of C. The equivalent dose rate to the haemopoietic tissue of a 20 year-old adult is 77 microSv a(-1), and 39 microSv a(-1) for a 3-month-old infant. Similarly, the equivalent dose rate to the bone surfaces of an adult is 48 microSv a(-1), and 38 microSv a(-1) for an infant. Therefore, the equivalent dose rate to marrow and bone stem cells increases with age under steady state conditions.

Classical microdosimetry in radiation protection dosimetry and monitoring.

Classical microdosimetry concerns the measurement and analysis of the spectrum of radiation energy deposition events in simulated microscopic tissue-equivalent sites. Over the past three decades, classical microdosimetry has been extensively applied for the direct measurement of dosimetric quantities, such as the ambient dose equivalent, and for the spectroscopic properties of tissue-equivalent proportional counters that have led to methods of mixed-field analysis and particle identification. This paper reviews some of the special applications of classical microdosimetry such as the determination of kerma coefficients, differential dosimetry and aviation dosimetry. Also reviewed are some of the technological innovations related to the application of microdosimetry in operational health physics and in particular the development of multi-element proportional counters and detectors based on gas microstrip technology.

Dose to the cell nucleus from exposure to tritiated pump oil or formaldehyde.

A Monte Carlo simulation of tritium decays in a cell composed of two parts, a nucleus and surrounding cytoplasm, was developed to evaluate the beta-radiation dose to the nucleus. A dose modifying factor (DMF), which is a ratio of the average nuclear dose to the whole-tissue dose, after skin-contact exposure of rats to tritiated pump oil or tritiated formaldehyde was estimated. Biokinetic data characterizing the retention of tritium in liver were available in the form of tritium-specific activities and biological half-times for tritiated water and five macromolecular species (DNA, RNA, acid-soluble fraction, acid-insoluble protein, and lipids). The spatial distribution of tissue-free water and macromolecular species in the nucleus and cytoplasm of rat liver cells was based on published data. In the case of exposure to tritiated pump oil, tritium incorporated into lipids provides the largest percentage (60%) of the absorbed dose to the nucleus. For the tritiated-formaldehyde exposure, the tritium dose to the nucleus is overwhelmingly contributed by tritiated water (58%) and in acid-insoluble proteins (40%). For both these tritiated organic exposures, the tritium-labeled DNA has a negligible effect on the DMF. The DMF for the tritiated pump oil and formaldehyde exposures was estimated as 0.81 and 1.05, respectively: the DMF of both exposures was close to unity. Given the other uncertainties in tritium dosimetry, our results suggest that for these skin-contact exposures a uniform distribution of tritium in tissue is an adequate assumption for dosimetry.

Photon-counting radiography with the gas microstrip detector.

We have built a proof of-concept photon-counting x-ray imaging system using a Xe:CH4 gas microstrip detector (GMD) as the image receptor, and have used this system to demonstrate several advantages of photon counting over energy integration. Our experiments spanned x-ray spectra from 10 to 50 kVp and Xe:CH4 pressures from 1 to 4 atm. When photon counting is done, the energy deposited in the detector by each incident photon can be measured on adjacent anode strips and a centroid calculation can be used to provide spatial resolution significantly better than the anode strip pitch. We measured > 11 lp mm(-1) at 13 kVp with our 200 microm pitch detector, and 8.2 lp mm(-1) at 50 kVp. The energy resolution of our GMD is 5.2% at 59.6 keV, and the space-charge limited counting rate is >2 x 10(6) mm(-2) s(-1) at 3 atm for a 30 kVp beam.

Taste, temperature, and presentation predict satisfaction with foodservices in a Canadian continuing-care hospital.

OBJECTIVE: To identify food, service, and patient variables associated with high satisfaction with foodservices in a continuing-care hospital that serves, primarily, geriatric patients and patients undergoing physical rehabilitation. DESIGN: Survey questionnaire concerning eight aspects of food and foodservice as well as type of diet and major patient descriptors. SUBJECTS: All patients from geriatric continuing-care units, geriatric rehabilitation units, and physical rehabilitation units at Saint-Vincent Pavilion were considered potential respondents. A convenience sample of 65 clients met the established inclusion criteria and were willing to participate. Patients had to be able to communicate their views, and the clinical nursing staff judged all respondents to be cognitively able to provide opinions concerning food and foodservice. The mean age of subjects was 67 years, the mean length of stay in the hospital was 2 years, and 60% of the subjects were women (n = 39). STATISTICAL ANALYSES: Spearman rank correlations, univariate analyses (t tests for continuously distributed data, chi 2 tests for categorical data), and multivariate analyses (regular and logistic regression). RESULTS: In general, patients questioned were extremely positive about the quality and quantity of food and foodservices at this continuing-care/rehabilitation hospital. Type of diet and patient characteristics were not differentially associated with high levels of overall satisfaction with foodservices (as assessed by a general satisfaction question). Univariate analyses revealed that all aspects of foodservices (except quantity of food) were significantly correlated with overall satisfaction. Multivariate analyses showed that satisfaction with presentation of meal was the best predictor of overall satisfaction and that clients who were very satisfied with the taste of food and were very satisfied that cold food was cold enough were the most satisfied overall. Knowledge of key variables as assessed by multivariate analyses (ie, taste and coldness) predicted whether clients were very satisfied overall 80% of the time. APPLICATIONS: Surveys are usefull tools for assessing the ways in which clients view the food and services provided by dietitians. Dietitians in continuing-care settings need to focus on a few specific characteristics related to what is eaten and how food is presented, rather than on patient-specific variables, when trying to maximize satisfaction with hospital food. The information in this study can be used as a baseline against which future data can be compared. The survey contributes to a continuing quality assurance process that allows dietitians to track the effect of changes that are made to food and foodservices and to monitor areas that require modification.

Puréed diet: prevalence and reported reasons for use in a long-term care hospital.

Although puréed diets are thought to be widely used for patients in long-term care facilities, there is little specific information concerning prevalence and reasons for the actual use of this diet texture. At Saint-Vincent Hospital, a 516 bed, long-term care and rehabilitation facility, 25.9% of the chronic-care population (n = 424) were on a puréed diet. Those who received puréed diets tended to be older (83.5 years versus 75.4 years, P < 0.001) and were more likely to be female (82.7% versus 70.8% P < 0.006), than the total population of long-term care patients. A greater percentage of patients receiving a puréed diet had dementia (43.0% versus 30.6%, P < 0.02), and fewer had cerebrovascular accident as a primary diagnosis (22.6% versus 33.9%, P < 0.05), than the total population of long-term care patients at this hospital. Following data collection, reasons for patients being on a puréed diet were grouped into five categories. The most popular categories were "Physiological/Mechanical" and "Cognitive" problems.