Measurement Of Absorbed Dose Rate Research Articles

Gölcük/Isparta ve Yakın Çevresinde Yer Alan Kayaçların Doğal Radyoaktivite Özelliklerinin İncelenmesi

This study was carried out in the Gölcük (Isparta) volcanic region, which is among the youngest eruptive volcanoes of Turkey. The aim of this study is to measure the radioactivity concentration values in the rocks developed due to explosive volcanism in the region, to interpret these values for the region, and to evaluate the effects of the concentration values on human health and environmental effects. Uranium (U), Thorium (Th), Potassium (K), and absorbed dose rate measurements were taken at a total of 452 points on the volcanic and pyroclastic rocks in the region using Gamma-ray spectrometry and in situ measurement technique. Distribution maps of the measurements were created and high radioactivity values were observed throughout the region. While the obtained U values varied between 10 and 350 Bq/kg, it was observed that the Th values reached 420 Bq/kg. High concentration values were observed in similar regions in both concentration distribution maps. The potassium value measured for the region reaches 2200 Bq/kg. It is thought that the high U and K values obtained as a result of the measurements may be due to the potassic-ultrapotassic characters of the volcanic-origin rocks in the region. The dose rate absorbed in the air reaches 480 nGy/h, which is approximately eight times the world average (60 nGy/h) determined by UNSCEAR. Therefore, there is a possibility that the living things living in this environment may be negatively affected by this situation.

Active Dosimetry with the Ability to Distinguish Pulsed and Non-Pulsed Dose Rate Contributions

This paper presents the concept of an active dosimetry system and its operational regime for pulsed radiation dose rate measurements. The plastic scintillator is suggested to be used for absorbed dose rate measurements. As long as the detector can be considered tissue equivalent, the energy weighting of pile-up events in terms of the dose is achieved. The real-time distinction of pulsed and non-pulsed dose rate contributions is based on the time structure of a single interaction and requires only basic information about the beam time structure (pulses duration and period). The detector connected to a fully digital signal processing board creates an active dosimetry system with adjustable parameters. Such a system was used for absorbed dose rate measurements in pulsed photon field mimicking radiation field outside the bunker of a medical LINAC, but also in the presence of a constant radiation component. The results show a linear dependence of a pulsed radiation contribution on the accelerator current in the investigated range of the total dose rate up to 8 μGy/h.

DOSIMETRY WITH THE ABILITY TO DISTINGUISH PULSED AND NON-PULSED DOSE CONTRIBUTIONS

The concept of an active dosimetry system for pulsed radiation dose rate measurements is presented. Real-time distinction of pulsed and non-pulsed radiation contributions is based on the time structure of a single interaction. A fast tissue equivalent plastic scintillator is exploited to minimize the pile-up effect influence on absorbed energy measurements. Being connected to a fully digital signal processing board, the detector creates an active dosimetry system with adjustable parameters. With this system, absorbed dose rate measurements were carried out in a photon field with a time structure mimicking a radiotherapeutic beam, but also in the presence of a constant radiation field. Measurements show a linear dependence of a pulsed radiation contribution on the accelerator current in the investigated range of the total dose rate up to 8 μGy h-1. While increasing the accelerator current by 1 μA, the pulsed radiation dose rate grows by (26.2±0.9) nGy h-1 when considering pile-up events.

Determination of Absorbed Dose Results from Radioactive Waste Sampling and Assay

There has been great concern about the health risks associated with exposure to radioactivity present in soil, thus in this present study, absorbed dose rate measurements were carried out at some selected samples of contaminated soil. The purpose is to examine to what extent such measurements can be used to delineate the effect radiation to the workers and to assess the radiation risk of radioactive waste management personnel by calculating the annual dose of external radiation exposure and the amount of radioactive dose absorbed by the workers. Ladlum detector used to measure the exposure dose rate (µR/h). The germanium system was used to analyze the samples collected from the decontamination processes, the activity concentration ranged from (1026.21 to 25961.5) Bq/kg. The value of the annual dos rate vary between (5.55E-05 to.40E-03) Sv/h.

Air Absorbed Dose Rate Measurements and External Dose Assessment by Car-Borne Survey in the Gold Mining Areas of Betare-Oya, Eastern-Cameroon

In order to assess radiological exposure of the public due to natural occurring radioactive materials from gold mining areas of Betare-Oya and vicinity, Eastern Cameroon, a preliminary study was carried out in 2015 for laboratory measurements of activity concentrations of primordial radionuclides. In terms of annual effective dose, results revealed a mean value of 0.34 mSv y-1. However, it was necessary to make air absorbed dose rate contour map for a detailed evaluation of external dose. For this purpose, a car-borne survey using a 3-in × 3-in NaI(Tl) scintillation spectrometer was carried out in Betare-Oya and vicinity. Absorbed dose rates in air ranged from 23 to 80 nGy h-1 with a mean value of 44 ± 7 nGy h-1. The average values of activity concentrations in soil of 40K, 238U and 232Th were 197 ± 21 Bq kg-1, 37 ± 13 Bq kg-1 and 32 ± 7 Bq kg-1 respectively. 232Th was found to be the main contributor to the absorbed dose rate in air from outdoor terrestrial radiation in the study areas with a mean value of 43%. External annual effective dose ranged from 0.17 to 0.60 mSv y-1 with a mean value of 0.33 ± 0.05 mSv y-1, in agreement with the result (0.34 mSv y-1) of the previous study performed in the same areas using gamma spectrometry in laboratory for radioactivity measurements in soil samples. This survey first and widely revealed an aspect of natural radiation exposures in soil mining areas of Eastern Cameroon.

NPL's new absorbed dose standard for the calibration of HDR 192Ir brachytherapy sources

A novel graphite calorimeter for absorbed dose rate measurements close to high dose rate (HDR) 192Ir brachytherapy sources has been designed and built at the UK National Physical Laboratory (NPL). The graphite calorimeter allows a more direct calibration of HDR 192Ir sources in terms of absorbed dose rate to water at a distance of 1 cm, , compared with the current air kerma-based calibration method, where is determined as the product of the measured air kerma strength and the dose rate constant, Λ, resulting in overall standard uncertainties of up to 5%. With the new absorbed dose standard, can be measured directly with standard uncertainties between 0.7% and 1.0%, depending on the operating mode of the calorimeter. A Nucletron microSelectron-v1 Classic HDR 192Ir source was calibrated with the calorimeter in terms of . The same source was also calibrated with NPL's HDR 192Ir air kerma primary standard in terms of reference air kerma rate. Combining both measurements yielded the experimentally determined dose rate constant of the 192Ir source.

Workplace Monitoring During Interventional Cardiology Procedures

Interventional cardiologists are at greater risk from radiation exposure as a result of the procedures they undertake than most other medical specialists. A study was performed to evaluate operator dose during interventional cardiology procedures and to establish methods of operator dose reduction with a radiation protective device. Different procedure technique and use of protective tools can explain big difference in the annual equivalent dose received by the professionals. Strategies to prevent and monitor radiation exposure, advanced protective shielding and effective radiation monitoring methods should be applied. Keywords—absorbed dose rate measurements, annual equivalent dose, protective device.

TU‐D‐AUD C‐05: Development of a Novel Absorbed Dose to Water Calorimeter‐Based Standard for HDR Ir‐192 Brachytherapy

Purpose: To study parameters affecting the design of a new standard for absorbed dose to water for high dose rate iridium‐192 brachytherapy sources based on 4 °C stagnant water calorimetry. Method and Materials: The absorbed dose rate of a Nucleotron microSelectron‐HDR brachytherapy source was measured for sources with nominal air kerma strength Sk,air 21000 and 38000 U at several source‐detector separations dsrc‐det ranging between 25–30 mm. The irradiation time was adjusted to ensure a minimum dose of 1 Gy delivered to the measurement point. The heat‐loss correction was calculated using COMSOL MULTIPHYSICS™ and is defined as the ratio of the temperature in the calorimeter under ideal conditions to realistic conditions. Results: The heat‐loss corrected dose rate measurements had a standard deviation of 1.5%, while the agreement between our measurements and the calculated dose rate results obtained using the TG‐43 formalism was within 6.5%. The effects of convection were calculated to be negligible as the glass vessel serves as a convective barrier significantly decoupling the water velocity in the interior and exterior of the vessel (differences in velocity reaching one to two orders of magnitude). It was found that small uncertainties on dsrc‐det significantly affects the shape of the drift curve, while varying the exact value of SK,air, irradiation time, and differences in initial source temperature at the time of insertion into calorimeter have minimal effects. Differences between the shape of experimental and calculated drift curves can be used to optimize the calculation parameters. Conclusion: Feasibility of water calorimetry for absolute dosimetry for HDR brachytherapy sources has been shown both numerically and experimentally. We believe absolute absorbed dose rate measurements with uncertainties significantly better than 5% are possible. Revisions to experimental designs are underway to improve the robustness of setup and improve the repeatability and uncertainty on measurements.

Absorbed dose measurements of a handheld 50 kVP X-ray source in water with thermoluminescence dosemeters

Absorbed dose rate measurements of a 50 kV(p) handheld X-ray probe source in a water phantom are described. The X-ray generator is capable of currents of up to 40 microA, and is designed for cranial brachytherapy and intraoperative applications with applicators. The measurements were performed in a computer-controlled water phantom in which both the source and the detectors are mounted. Two different LiF thermoluminescence dosemeter (TLD) phosphors were employed for the measurements, MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P). Two small ionisation chambers (0.02 and 0.0053 cm(3)) were also employed. The TLDs and chambers were positioned in watertight mounts made of water-equivalent plastic. The chambers were calibrated in terms of air-kerma rate, and conventional protocols were used to convert the measurements to absorbed dose rate. The TLDs were calibrated at National Institute of Standards and Technology (NIST) in terms of absorbed dose rate using a (60)Co teletherapy beam and narrow-spectrum X-ray beams. For the latter, absorbed dose was inferred from air-kerma rate using calculated air-kerma-to-dose conversion factors. The reference points of the various detectors were taken as the center of the TLD volumes and the entrance windows of the ionisation chambers. Measurements were made at distances of 3-45 mm from the detector reference point to the source center. In addition, energy dependence of response measurements of the TLDs used was made using NIST reference narrow spectrum X-ray beams. Measurement results showed reasonable agreement in absorbed dose rate determined from the energy dependence corrected TLD readings and from the ionisation chambers. Volume averaging effects of the TLDs at very close distances to the source were also evident.

Outdoor absorbed dose rate in air in relation to airborne natural radioactivity and meteorological conditions at Bucharest (Romania)

The results of environmental absorbed dose rate measurements performed over a 3-year period (1996-1999) at the Bucharest Environmental Radioactivity Surveillance Station are presented. The outdoor absorbed dose rate levels were analyzed in connection to airborne natural radioactivity and meteorological parameters, such as precipitation, air temperature and pressure.The minimum values were recorded in winter and the maximum values at the end of summer or beginning of autumn, mainly as a consequence of changes in weather and soil conditions (rain, ground moisture, snow cover).Significant statistical correlations were obtained between the outdoor absorbed dose rate and the air temperature and atmospheric pressure, respectively.

Performance characteristics of the MIT fission converter based epithermal neutron beam

A pre-clinical characterization of the first fission converter based epithermal neutron beam (FCB) designed for boron neutron capture therapy (BNCT) has been performed. Calculated design parameters describing the physical performance of the aluminium and Teflon® filtered beam were confirmed from neutron fluence and absorbed dose rate measurements performed with activation foils and paired ionization chambers. The facility currently provides an epithermal neutron flux of 4.6 × 109 n cm−2 s−1 in-air at the patient position that makes it the most intense BNCT source in the world. This epithermal neutron flux is accompanied by very low specific photon and fast neutron absorbed doses of 3.5 ± 0.5 and 1.4 ± 0.2 × 10−13 Gy cm2, respectively. A therapeutic dose rate of 1.7 RBE Gy min−1 is achievable at the advantage depth of 97 mm when boronated phenylalanine (BPA) is used as the delivery agent, giving an average therapeutic ratio of 5.7. In clinical trials of normal tissue tolerance when using the FCB, the effective prescribed dose is due principally to neutron interactions with the nonselectively absorbed BPA present in brain. If an advanced compound is considered, the dose to brain would instead be predominately from the photon kerma induced by thermal neutron capture in hydrogen and advantage parameters of 0.88 Gy min−1, 121 mm and 10.8 would be realized for the therapeutic dose rate, advantage depth and therapeutic ratio, respectively. This study confirms the success of a new approach to producing a high intensity, high purity epithermal neutron source that attains near optimal physical performance and which is well suited to exploit the next generation of boron delivery agents.