Health physics最新文献

Abstract: Many medical facilities across the United States use ionizing-radiation-producing machines and radioactive materials for diagnostic and therapeutic purposes on a regular basis. While institutions are required to ensure full-term fetal doses are below the regulatory limit, clear guidance on how pre-declaration fetal doses should be estimated is not available. This paper provides a process that can be used to estimate the pre-declaration fetal dose and provides a predictive screening tool for licensees to use to recommend workload adjustments prior to actual fetal dosimetry results that could exceed the institutions derived investigation levels. The evaluation process presented herein serves as a guide for medical licensees when performing fetal dose evaluations for declared pregnant workers.

Abstract: In the present study, we are presenting the results of radium content, radon concentration, and radon exhalation rates (both mass and area) for 32 soil samples collected from different locations of Abi-Adi Town, Ethiopia, by using the sealed can technique containing a LR-115 Type-II plastic detector. The values of radium content from soil samples were found to vary from 35.26 Bq kg -1 to 101.78 Bq kg -1 , with a mean value of 70.25 Bq kg -1 . The mass and area exhalation rates of radon were found to be from 2.72 × 10 -6 Bq kg -1 d -1 to 7.87 × 10 -6 Bq kg -1 d -1 and from 0.76 × 10 -4 Bq m -2 d -1 to 2.20 × 10 -4 Bq m -2 d -1 , with a mean value of 5.43 × 10 -6 Bq kg -1 d -1 and 1.52 × 10 -4 Bq m -2 d -1 , respectively. The outdoor and indoor annual effective dose equivalent varied from 0.24 mSv y -1 to 0.68 mSv y -1 and from 0.06 mSv y -1 to 0.17 mSv y -1 with a mean value of 0.37 mSv y -1 and 0.09 mSv y -1 , respectively. The working level varied from 2.50 mWL to 7.21 mWL with a mean value of 3.94 mWL. From the results of this study, we found that there was a positive correlation between radium content and radon exhalation rates in soil samples. The radium content values determined in soil samples are less than the permissible value of 370 Bq kg -1 recommended by Organization for Economic Cooperation and Developments as acceptable for safe use. Thus, results reveal that the area under investigation is safe as far as the health hazards of radon are concerned.

Abstract: The objective of this paper is to derive basic restrictions for induced internal electric field and reference levels for external magnetic flux density for a class of periodic non-sinusoidal waveforms as multiples of the existing limits applicable to sinusoidal waveforms in current exposure standards. The Law of Electrostimulation and the Spatially Extended Nonlinear Node computational model were used to derive peripheral nerve stimulation thresholds of the internal electric field for both non-sinusoidal and sinusoidal waveforms. Threshold ratios (non-sinusoidal to sinusoidal) permitted basic restrictions and reference levels to be derived as multiples of the sinusoidal ones. Intercomparisons of threshold ratios from both models suggest that they are in agreement for flat-topped flux density waveforms with fast rise-times relative to the period but showed a discrepancy for the continuous sinusoid. Results from the computational model were used to establish the threshold ratios used in the conversion. Resulting non-sinusoidal basic restrictions and reference levels were found to have the same functional relationship with frequency as the sinusoidal ones, consisting of two ranges: a flat rheobase and a frequency-dependent (basic restriction) or inverse frequency-dependent (reference level) portion that intersects the rheobase at a transition frequency that is waveform-dependent. Above the transition frequency, the non-sinusoidal basic restriction was found to be inversely related to the flux density rise-time, resulting in an increased limit for fast-rising waveforms. The transition frequencies of fast-rising waveforms were found to be lowered relative to the sinusoidal one. Above the same transition frequency, the non-sinusoidal reference level is flat with frequency and was found to be approximately 79% lower than the sinusoidal one.

Abstract: This study elucidated the radiation response characteristics of a Gafchromic radiochromic film subjected to low photon doses of ≤50 mSv, which corresponds to the annual whole body effective dose limit for radiation workers in Canada. Radiochromic films are investigated for possible use as a complementary tool for the Canadian Armed Forces that can be worn in addition to their existing personal dosimetry to quickly assess personal radiation dose received from radiological hazards without reliance on electronics. The films were exposed to varying photon energies emanating from x-ray generators and radioisotopes, specifically cesium-137, cobalt-60, and americium-241. The resultant radiation-induced film darkening was quantitatively assessed employing three analytical methodologies: net optical density analysis, UV/Visible spectroscopic analysis, and Fourier Transform Infrared spectroscopic analysis. Ideally, a film dosimeter necessitates a pronounced chromatic alteration and the capability to accurately quantify doses ≤50 mSv where net optical density analysis was identified as the optimal modality for interpreting the film darkening into a dose approximation. This new approach established a lower detection threshold of 7.6 mSv for the films when exposed to cesium-137 radiation. Notably, the film exhibited a linear dose response relationship in terms of net optical density; however, a photon energy-dependent variability was observed within the 0-100 mSv dose range. In conclusion, these Gafchromic radiochromic films present a promising candidate for military dosimetry applications. They offer a real-time, visual dose response that can be discerned by military personnel or analyzed using mobile spectroscopic instrumentation. Moreover, these films demonstrate proficiency in the accurate quantification of photon doses ≤50 mSv. Future investigations will evaluate the film's performance under heterogeneous and indeterminate radiation environments, as well as the impact of environmental conditions on the film's performance.

Abstract: Three topics related to ANSI/HPS Standard N13.56, Sampling and Monitoring Releases of Airborne Radioactivity in the Workplace, are discussed. First, due to the omission of consideration of the activity's half-life in the standard's continuous particulate air monitor (CPAM) quantitative method, it is possible for concentration estimates produced by that calculation to be underestimated. Second, the concentration estimate found in air grab sampling, as discussed in the standard, is not, as claimed, an average unless the activity is "long-lived" (negligible decay during sampling). It is nonetheless possible for this calculation to produce a concentration estimate that is not significantly different from the average, depending on both the half-life of the activity and the sampling time. Third, the issue of when to change the filter for the CPAM method is addressed.

Abstract: This work investigates the low photon radiation dose (≤50 mSv) response of commercially available radiochromic films as a potential field dosimeter that could be used by the Canadian Armed Forces to complement their existing personal radiation dosimeters. The films were exposed to various photon energies from x-ray devices and radioisotopes (cesium-137, cobalt-60, and americium-241), and their radiation signal was read using three methods: net optical density, UV/visible spectroscopy, and Fourier transform infrared spectroscopy. A complimentary film dosimeter for field usage should, for military use, display a visual color change and detect doses ≤50 mSv. Given the film's radiochromic properties, it was determined that the net optical density method was the most optimal read-out method, which ascertained a minimum detection dose limit of 4.5 mSv under exposure to a clinical orthovoltage operated at 100 kVp. The film presented an overall linear relationship between net optical density and radiation dose; however, they also portrayed a photon energy-dependent response between 0-100 mSv. Overall, the radiochromic films presented a real-time visual dose signal that could be interpreted rapidly in a mobile laboratory and possessed the ability to detect photon doses ≤50 mSv below the vendor's recommended limits, making it a suitable option as a complementary, disposable, military dosimetric tool. Future work includes the investigation of the film's response under multi- and unknown source environments and environmental-dependent factors such as UV/sunlight exposure and extreme temperatures.

Abstract: A glow-curve analysis code was previously developed in C++ to analyze thermoluminescent dosimeter glow curves using automated peak detection while applying a first-order kinetics model. A newer version of this code was implemented to improve the automated peak detection and curve fitting models. The Stochastic Gradient Descent Algorithm was introduced to replace the prior approach of taking first and second-order derivatives for peak detection. Additionally, early stopping mechanisms were invoked to improve the previously used Levenberg-Marquardt Algorithm employed for curve fitting. The two software versions were compared through glow curve analysis of different thermoluminescent dosimeter materials and calculation of the corresponding figures of merit. Overall improvements were shown, namely an increase in the number of peaks detected and a reduction of the mean figure of merit by approximately 46%.

Abstract: A former uranium recovery facility located in northwestern New Mexico currently serves as a uranium mill tailings site undergoing reclamation and decommissioning. High velocity winds are common in the area, causing soil erosion via aeolian processes. Strong winds may carry soil for several kilometers, which is redeposited downwind. This study estimates the potential for impact on remediation efforts caused by downwind contamination from soil-bound 226 Ra resuspension. The study was performed by measuring the mass of soil moving onsite to determine horizontal saltating flux over the period of 3 mo. Previous frameworks relating dimensional flux were used to estimate suspension flux from site-massed saltating flux. Using concentrations of soil-bound radionuclides and meteorological data collected onsite, a modified Gaussian plume model estimating downwind deposition of contaminants was constructed. The highest deposition rate calculated, 6.81 × 10 -15 Bq cm -2 s -1 , suggests approximately 4.3 million years of deposition are required to exceed the criterion for release, a far longer timespan than the expected remediation and release of the site in 2030. Based on the results, estimated impacts of windblown soil contamination were determined to be negligible.

Abstract: The objective of this note was to study the measurement uncertainties at each step of Yttrium-90 radioembolization. We studied the measurement uncertainty contribution from the dose calibrator accuracy during the initial dose assay, the survey meter accuracy, and the operator's reading uncertainties during the dose rate measurements. The propagation of these uncertainties was calculated to determine the final dose delivery uncertainty for various prescribed doses. The percentage of final dose delivered could be affected significantly by the uncertainties associated with operation at each step of dose assay and dose rate measurements, especially for low prescribed doses.

Abstract: An electret detector is a piece of dielectric material film charged or polarized by a specific charging method to induce a quasi-permanent electric field. Electret films perform unique characteristics for production and applications in many areas of science and technology, especially in health physics dosimetry. A charged electret detector, when placed in an ionized environment, collects negative or positive ions depending on its original charging state, which reduces its original charge. The number of charges reduced in the ionized field is usually proportional to the absorbed radiation dose. In this paper, the state-of-the-art information on the type of electrets, production methods, some applications in particular in health physics dosimetry, and relevant concepts are reviewed.