Decreasing Dose Rate Research Articles

Methodological principles of searching for disposal sites of radioactively contaminated materials by geophysical methods

This article is devoted to radiometric studies at one of the sites of the Chornobyl nuclear power plant (the “Sandy Plateau” site), which is located on the south-eastern outskirts of the city of Pripyat. Radioactive substances, both artificial and natural, resulting from incidents and disasters at nuclear facilities pose the greatest danger. The disposal sites for radioactively contaminated materials considered in this work are sources of groundwater pollution. Currently, there is a problem of searching for their location for reburial in specialized stationary burial grounds, to solve which detailed complex geophysical studies are used. Various geophysical methods are considered, including micro-sensing and radiometric studies, to determine the location of burials. Particular attention is paid to the analysis and interpretation of geophysical data, as well as the economic and practical aspects of the application of these methods. As a result of the study, it was established: that when searching and studying burial sites of radioactively contaminated materials, the use of surface gamma photography makes it possible to assess the level of radioactive contamination of the upper layers of the soil (to a depth of 0.8-1 m). However, if the thickness of buried radioactively contaminated materials exceeds a certain level, which leads to weak contamination of rocks at a depth of more than 1-1.5 m, then burial objects may go undetected when using only gamma-ray imaging. In such cases, microgamma probing becomes an effective method. Increased values of exposure dose rate and the nature of microgamma sounding curves serve as indicators of the presence (increase in exposure dose rate with depth) or absence (sharp decrease in exposure dose rate with depth) of radioactively contaminated materials in the studied area.

Systematic experimental and model-based evaluation of the synergistic effects of alloy composition and damage rate on the formation of Cr-rich precipitates in Fe–Cr–Al alloys under ion irradiation

Fourteen Fe–Cr–Al alloys with systematically varied Cr and Al compositions were irradiated at 350∘C to 0.24 dpa by 10.5 MeV self-ions as model alloys for the Fe–Cr–Al (oxide dispersion strengthened: ODS) alloys being developed as accident tolerant fuel (ATF) cladding for light water reactors. Three dose rates (8×10−6, 8×10−5, and 8×10−4 dpa/s) were selected to predict the formation behavior of Cr-rich precipitates (CrRP) under neutron irradiation conditions. The effects of Cr, Al composition, and dose rate on the CrRP formation behavior were evaluated using a three-dimensional atom probe (3DAP) analysis. The results showed that the CrRP number density, volume fraction, and Cr concentration increase with increasing Cr composition, decreasing Al composition, and decreasing dose rate. Multiple regression analysis showed that in addition to these primary effects, there was an interaction between them on the CrRP volume fraction: (1) the higher the Al composition, the smaller the increase in the CrRP volume fraction with increasing Cr composition, and (2) the lower the Cr composition, the smaller the increase in the CrRP volume fraction with the decreasing Al composition and dose rate. It was also highlighted that to understand the dose rate effect on the CrRP formation behavior under neutron irradiation, it is useful to examine the irradiation time dependence, including the effective use of thermal aging data as a limit to the zero dose rate, in addition to the dose-dependency perspective. In addition to the systematic database of CrRP-related quantities established in this study, these considerations should contribute to further developing and validating numerical prediction models.

A scattering-foil free electron beam to increase dose rate for total skin electron therapy (TSET).

Electron beams are used at extended distances ranging between 300 to 700cm to uniformly cover the entirety of the patient's skin for total skin electron therapy (TSET). Even with electron beams utilizing the high dose rate total skin electron (HDTSe) mode from the Varian 23iX or TrueBeam accelerators, the dose rate is only 2500 cGy/min at source-to-surface distance (SSD)=100cm. At extended distances, the decrease in dose rate leads to long beam delivery times that can limit or even prevent the use of the treatment for patients who, in their weakened condition, may be unable to stand on their own for extended periods of time. Previously, to increase dose rate, a customized 6 MeV electron beam was created by removing the x-ray target, flattening filter, beam monitor chamber, and so forth. from the beam path (Chen, et at IJROBP 59, 2004) for TSET. Using this scattering-foil free (SFF) electron beam requires the treatment distance be extended to 700cm to achieve dose uniformity from the single beam. This room size requirement has limited the widespread use of the 6 MeV-SFF beam. This study explores an application of a dual-field technique with a 6 MeV-SFF beam to provide broad and uniform electron fields to reduce the treatment distances in order to overcome treatment room size limitations. The EGSnrc system was used to generate incident beams. Gantry angles between 6 MeV-SFF dual-fields were optimized to achieve the similar patient skin dose distribution resulting from a standard 6 MeV-HDTSe dual-field configuration. The patient skin dose comparisons were performed based on the patient treatment setup geometries using dose-volume-histograms. Similar dose coverage can be achieved between 6 MeV-SFF and 6 MeV-HDTSe beams by reducing gantry angles between dual-field geometries by 8° and 7° at treatment distances of 400 and 500cm, respectively. To achieve 95% mean dose to the first 5mm of skin depth in the torso area, the mean dose to depths of 5-10mm and 10-15mm below the skin surface was 74% (74%) and 49% (50%) of the prescribed dose when using 6 MeV-SFF (6 MeV-HDTSe) beam, respectively. The 6 MeV-SFF electron beam is feasible to provide similar TSET skin dose coverage at SSD ≥ 400cm using a dual-field technique. The dose rate of the 6 MeV-SFF beam is about 4 times that of current available 6 MeV-HDTSe beams at treatment distances of 400-500cm, which significantly shortens the treatment beam-on time and makes TSET available to patients in weakened conditions.

Impact of shield location on staff and caregiver dose rates for I-131 radiopharmaceutical therapy patients

The goal of this study is to investigate the effect of the location and width of a single lead shield on the dose rate of staff and caregivers in a hospital room with an I-131 patient. The best orientation of the patient and caregiver relative to the shield was determined based on minimizing staff and caregiver radiation dose rates. Shielded and unshielded dose rates were simulated using a Monte Carlo computer simulation and validated using real-world ionisation chamber measurements. Based on a radiation transport analysis using an adult voxel phantom published by the International Commission on Radiological Protection, placing the shield near the caregiver yielded the lowest dose rates. However, this strategy reduced the dose rate in only a tiny area of the room. Furthermore, positioning the shield near the patient in the caudal direction provided a modest dose rate reduction while shielding a large room area. Finally, increased shield width was associated with decreasing dose rates, but only a four-fold dose-rate reduction was observed for standard width shields. The recommendations of this case study may be considered as potential candidate room configurations where radiation dose rates are minimized, however these findings must be weighed against additional clinical, safety, and comfort considerations.

Improvement of the approach to definition of patient release criteria after radionuclide therapy

Current patient release criteria established in NRB-99/2009 relate to four radionuclides used in Russia that period of the document preparation. These criteria were calculated only considering the radionuclide decay. Thus, these criteria give conservative assessments which require the patient to stay in dedicated protected room (“hot” room) of the radiotherapy department for several days and do not allow to radionuclide therapy to be given in the outpatient hospital which certainly reduces the availability of this type of treatment. Consideration of the biological excretion of the radiopharmaceutical will be able to make the patient release criteria after radionuclide therapy significantly softer. Recently, new promising radionuclides and radiopharmaceuticals for therapy have appeared, the introduction of which into medical practice is obstructed by the lack of the patient release criteria. Current study is devoted to justification of improvement the approach to definition of patient release criteria after radionuclide therapy with promising and applied radiopharmaceuticals considering biological excretion of radiopharmaceutical. As examples, calculations of patient release criteria were performed for 177Lu-PSMA, 177Lu-DOTA-TATE, 131I-mIBG и Na131I. The dosimetric model used for calculation is based on the model which was used for definition of the current patient release criteria in NRB-99/2009. Additionally, the biological excretion of the radionuclide in radiopharmaceutical, which was assessed according to the published data, was considered. Two phases of biological excretion were evaluated for considered radiopharmaceuticals (fast and slow fractions). The main contribution of the radionuclide decrease in the patient’s body during the first hours after the injection is made by the fast-eliminated fraction. During 4-6 hours after the administration about 50% of these radiopharmaceuticals eliminated via urine. The calculation of patient release criteria were performed for slow-elimination fractions which characterize the decrease of radionuclide activity in the body after the patient release. The following effective half-lives were used: 177Lu-PSMA – 60 hours, 177Lu-DOTA-TATE – 100 hours, 131I-mIBG – 45 hours, Na131I – 7.5 days. The calculations demonstrate when planning a course of radionuclide therapy with four administrations of 177Lu-PSMA, the release of a patient is allowed at the dose rate of 20 μSv/h from the patient at the distance of 1 m; in case of radionuclide therapy with 177Lu-DOTA-TATE, release of a patient is allowed at the dose rate of 12 μSv/h. Considering the fast-eliminated fraction in the first hours after the administration, it can be assumed that more patients with normal renal function can undergo radionuclide therapy with 177Lu-PSMA in the outpatient hospital. Some patients after the 177Lu-PSMA administration and patients in the therapy with 177Lu-DOTA-TATE may be held in the department in the “hot” rooms for 1-2 days until the dose rate decrease to the acceptable levels. The consideration of biological excretion of radiopharmaceutical makes it possible to soften patient release criterion for 131I-mIBG by four times and for Na131I – by 10%. It will allow to release patients after radionuclide therapy earlier without reduce of radiation safety of people around the patient and will increase the capacity of radionuclide therapy department.

Exploring the impact of groundwater constituents and irradiation conditions on radiation-induced corrosion of copper

In this work, the impact of groundwater constituents and irradiation conditions on radiation induced corrosion of copper have been studied using numerical simulations based on the recently published mechanism. The simulations show that the amount of corrosion at a given total absorbed radiation dose will increase with decreasing dose rate. Furthermore, hydroxyl radical scavengers in general have a very marginal effect on the rate of corrosion while scavengers of the hydrated electron almost double the rate of corrosion. Sulfide present under relevant conditions has a significant effect on the corrosion rate and reduces the rate by 80% already at the lowest expected concentration and flux. Fe2+ present under relevant conditions does not influence the rate of corrosion significantly. Also initially dissolved oxygen has a very marginal effect on the process. Dissolved organic material scavenge hydroxyl radicals upon formation of C-centered radicals which in turn react with molecular oxygen. In systems where peroxyl radical recombination is not dominating, i.e., where there are solutes reactive towards peroxyl radicals, the presence of dissolved organic material can reduce the rate of corrosion by almost 99%. The pH and the presence of Cl−, HCO3− and SO42− have relatively small effects. In general, radiation induced corrosion is 20–40% slower at pH = 9 as compared to pH = 7.4 and the presence of HCO3− increases the rate of corrosion somewhat at pH = 9 as compared to pure water at the same pH.

New perforated radiation shield for anesthesiologists: Monte Carlo simulation of effects.

Catheterization for structural heart disease (SHD) requires fluoroscopic guidance, which exposes health care professionals to radiation exposure risk. Nevertheless, existing freestanding radiation shields for anesthesiologists are typically simple, uncomfortable rectangles. Therefore, we devised a new perforated radiation shield that allows anesthesiologists and echocardiographers to access a patient through its apertures during SHD catheterization. No report of the relevant literature has described the degree to which the anesthesiologist's radiation dose can be reduced by installing radiation shields. For estimating whole-body doses to anesthesiologists and air dose distributions in the operating room, we used a Monte Carlo system for a rapid dose-estimation system used with interventional radiology. The simulations were performed under four conditions: no radiation shield, large apertures, small apertures and without apertures. With small apertures, the doses to the lens, waist and neck surfaces were found to be comparable to those of a protective plate without an aperture, indicating that our new radiation shield copes with radiation protection and work efficiency. To simulate the air-absorbed dose distribution, results indicated that a fan-shaped area of the dose rate decrease was generated in the area behind the shield, as seen from the tube sphere. For the aperture, radiation was found to wrap around the backside of the shield, even at a height that did not match the aperture height. The data presented herein are expected to be of interest to all anesthesiologists who might be involved in SHD catheterization. The data are also expected to enhance their understanding of radiation exposure protection.

A study on the influence of dose rate on total ionizing dose effect of anti-fuse field programmable gate array—The irradiation damage is attenuated at low dose rate

The TID (total ionizing dose) in-situ experiments of LC1020B, an anti-fuse FPGA (Field Programmable Gate Array) device, were designed and carried out under different dose rates, and the influence of dose rate on the TID effect of FPGA was studied. The experimental results show that: 1) the TID irradiation failure of the FPGA under different dose rates has nothing to do with the input voltage parameter exceeding the standard. 2) with the decrease of cobalt source irradiation dose rate [171, 26.83, and 2.68 mGy(Si)/s], the TID effect failure dose threshold [168, 229, and 334 Gy(Si), respectively] of the FPGA gradually increased, showing obvious attenuation of low dose rate damage. Theoretical analysis suggests that, compared with the space charge limitation effect, the oxide charge annealing effect plays a dominant role, and longer irradiation time is beneficial to the oxide charge annealing. And based on the experimental data, an FPGA TID analytical model with power consumption current as the damage characterization parameter is established, which lays a foundation for scientific evaluation of radiation effect of anti-fuse FPGAs.

Quality Control and Mating Performance of Irradiated Glossina palpalis gambiensis Males.

Simple SummaryIn vector control programs based on the sterile insect technique (SIT), the biological quality of sterile males must be as high as possible to compete with their wild counterparts. This study evaluates the biological quality and mating performance of sterile male Glossina palpalis gambiensis produced in a mass-rearing facility in Burkina Faso. It shows that irradiation had no effect on the adult emergence rate but reduced the percentage of operational flies and male fly survival. Irradiation had no effect on mating performances, as all females were inseminated, and the sterile males competed well with unirradiated males for virgin females in walk-in field cages. However, the sterility rate induced in females was lower than expected (89.67%). This study indicates that, under experimental field cage conditions, the G. p. gambiensis males produced at the CIRDES are well-suited for use in area-wide integrated pest management (AW-IPM) programs that have an SIT component. The reduction in the sterility rate highlights the importance of regularly monitoring the biological parameters of sterile males and the radiation source.The biological quality of sterile male insects produced in a mass-rearing facility is a prerequisite for the success of the SIT, which is a component of area-wide integrated pest management (AW-IPM). Indeed, sterile male insects released in the field must have a good mating performance in order to compete with wild males, but they must also present the required level of sterility. In the present study, the biological quality of sterile male Glossina palpalis gambiensis produced in a mass-rearing insectary was assessed through quality control testing. The mating performance of irradiated males was assessed in walk-in field cages. Irradiation had no effect on adult emergence but significantly reduced the percentage of operational flies (from 89.58% to 79.87%) and male survival (from 5 to 4 days, on average). However, irradiation did not impact the sterile male insemination potential, with all females inseminated and more than 80% of the spermathecae completely filled. The rate of induced sterility in females was 89.67% due to a dose rate decrease of the radiation source. Moreover, sterile males were able to compete successfully with untreated fertile males for untreated females in walk-in field cages. This study confirmed that the flies were still competitive and stressed the importance of regularly checking the radiation source parameters.

Radiation Monitoring in the Residential Environment: Time Dependencies of Air Dose Rate and 137Cs Inventory

Background: Residential areas have some factors on the external exposure of residents, who usually spend a long time in these areas. Although various survey has been carried out by the government or the research institutions after the Fukushima Daiichi Nuclear Power Plant accident, the mechanism of radiocesium inventory in the terrestrial zone has not been cleared. To better evaluate the radiation environment, this study investigated the temporal changes in air dose rate and 137Cs inventories (Bq/m2) in residential areas and agricultural fields.Materials and Methods: Air dose rate and 137Cs inventories were investigated in residential areas located in an evacuation zone at 5–8 km from the Fukushima Daiichi Nuclear Power Plant. From December 2014 to September 2018, the air dose rate distribution was investigated through a walking survey (backpack survey), which was conducted by operators carrying a γ-ray detector on their backs. Additionally, from December 2014 to January 2021, the 137Cs inventories on paved and permeable grounds were also measured using a portable γ-ray detector.Results and Discussion: In the areas where decontamination was not performed, the air dose rate decreased faster in residential areas than in agricultural fields. Moreover, the 137Cs inventory on paved surfaces decreased with time owing to the horizontal wash-off, while the 137Cs inventory on permeable surfaces decreased dramatically owing to the decontamination activities.Conclusion: These findings suggest that the horizontal wash-off of 137Cs on paved surfaces facilitated the air dose rate decrease in residential areas to a greater extent compared with agricultural fields, in which the air dose rate decreased because of the vertical migration of 137Cs. Results of this study can explain the faster environmental restoration in a residential environment reported by previous studies.

Focused proton beam generating pseudo Bragg peak for FLASH therapy

FLASH effect refers to ultra-high dose rates and ultra-fast irradiation that could reduce normal tissue damage while maintaining tumor control. An isochronous proton cyclotron can generate high-intensity continuous beams, making it ideal for potential FLASH proton therapy. However, generating the dose Bragg peak requires an energy degrader, leading to a drastic decrease in dose rate that is inadequate for FLASH therapy. This paper proposes a shoot-through beam modality by abandoning the energy degrader to increase beam intensity significantly. However, this results in the overall path dose being too high to be accepted. We investigate using focused proton beams to concentrate the dose into a small target volume to form a pseudo-Bragg-peak dose distribution. Simulations show that it can significantly reduce the integrated entrance and exit dose compared to the original parallel beam when delivering the same dose to the target volume, sparing the surrounding healthy tissue.

Evaluation of the effect of radioactivity to the environment in wooden houses within the evacuation area at Fukushima

The accident at Fukushima Daiichi Nuclear Power Plant caused radioactive materials to spread outside the plant. To limit exposure in the area, air dose rates have been measured. When the dose rate exceeded the acceptable upper bound, the area was decontaminated by stripping the soil and washing roads. Immediately after the accident, it was not clear how much of an effect outdoor contamination had on dose rates inside houses. This paper discusses the effect of outdoor contamination on indoor air dose rates and factors influencing those dose rates based upon actual measurements taken of a wooden house standing on flat land in the area around the power plant. In addition, the effects of indoor horizontal distribution, height distribution, and decontamination are discussed using simple model simulations. As a result, the following was found, although within the range of air dose rates and location conditions measured in this study. Horizontal variation in indoor air dose rates decreases monotonically toward the centre of the house. Once decontamination has been performed, the overall dose rate decreases and variation becomes smaller. This trend is thought to be mainly due to expansion of a low-dose area. Vertical changes in indoor air dose rates are not straightforward. It is estimated that the dose rate decreases near the ground surface, then tends to increase going higher and finally decreases even higher up. This change in dose rates is thought to be due to the effect of radioactive materials permeating the soil. Recognition of the effects of these factors is important when estimating indoor air dose rates because indoor air dose rates are affected by the degree of decontamination, house size, and degree of penetration of radionuclides into the soil.

Optimizing the Schedule of PARP Inhibitors in Combination with 177Lu-DOTATATE: A Dosimetry Rationale.

177Lu-DOTATATE for neuroendocrine tumours is considered a low-toxicity treatment and may therefore be combined with other pharmaceuticals to potentiate its efficacy. One approach is to add a poly-[ADP-ribose]-polymerase (PARP) inhibitor to decrease the ability of tumour cells to repair 177Lu-induced DNA damage. To decrease the risk of side effects, the sequencing should be optimized according to the tumour-to-normal tissue enhanced dose ratio (TNED). The aim of this study was to investigate how to enhance 177Lu-DOTATATE by optimal timing of the addition of a PARP inhibitor. Biokinetic modelling was performed based on the absorbed dose to the bone marrow, kidneys and tumour; determined from SPECT/CT and planar images from 17 patients treated with 177Lu-DOTATATE. To investigate the theoretical enhanced biological effect of a PARP inhibitor during 177Lu-DOTATATE treatment, the concept of relative biological effectiveness (RBE) was used, and PARP inhibitor administration was simulated over different time intervals. The absorbed dose rate for the tumour tissue demonstrated an initial increase phase until 12 h after infusion followed by a slow decrease. In contrast, the bone marrow showed a rapid initial dose rate decrease. Twenty-eight days after infusion of 177Lu-DOTATATE, the full absorbed dose to the bone marrow and kidney was reached. Using an RBE value of 2 for both the tumour and normal tissues, the TNED was increased compared to 177Lu-DOTATATE alone. According to the modelling, the PARP inhibitor should be introduced approximately 24 h after the start of 177Lu-DOTATATE treatment and be continued for up to four weeks to optimize the TNED. Based on these results, a phase I trial assessing the combination of olaparib and 177Lu-DOTATATE in somatostatin receptor-positive tumours was launched in 2020 (NCT04375267).

Preparation of impact-resistant functional polyurea coatings and effect of γ-ray irradiation on its microstructure and performance

New polyurea coatings were synthesized using aromatic diphenylmethane diisocyanate, large molecular weight amino-terminated polyether, and appropriate additives. Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy were used to examine the effects of γ-ray irradiation with different dose rates and cumulative doses on the microstructure of the new polyurea coatings. The variations of mechanical properties of the polyurea coatings before and after irradiation were studied using an electronic universal testing machine and a split Hopkinson compression bar. FTIR spectroscopy showed that the raw materials for preparing polyurea coatings had reacted completely, and polyurea had been synthesized. An analysis of the mechanical properties showed that the mechanical behavior of the new polyurea changed gradually from rubbery under a quasi-static load to glassy under a dynamic load, showing excellent impact resistance. The characteristic absorption peaks of the FTIR spectrum of polyurea did not change significantly before and after irradiation. However, the color of the polyurea changed from light yellow to dark red with decreasing dose rate or increasing cumulative dose, which is related to the radiation oxidation time. Some white fragments appeared after the polyurea was irradiated with γ-rays. The number of white fragments increased with decreasing dose rate or increasing cumulative dose, which may be caused by the soft segment embrittlement of polyurea under radiation oxidation. A comparison of the mechanical properties under different γ-ray irradiation conditions found that the newly synthesized polyurea coatings had good resistance to γ-ray radiation. Moreover, their performance was improved to a certain extent after irradiation. The performance of irradiated polyurea was optimum when the irradiation dose rate was 2 KGy/h, and the cumulative dose was 220 KGy.

Translocation dose-response curve for 137Cs γ-rays: Dose validation at various dose rate and changing dose rate conditions

A Fluorescence In-Situ Hybridization (FISH) based translocation dose-response curve has been constructed for biodosimetry application in our nuclear establishment at Kalpakkam, India. Peripheral blood sample from a healthy male donor (27 years) was exposed to nine different doses (0.1 Gy–5 Gy) of 137Cs γ-rays (100 mGy/min) in an automated calibration facility with a linear distancing system and subjected to FISH assay using chromosome 1, 2 and 4 specific fluorescent probes. Validation of the dose-response curve was done following three different approaches i) by blind test method ii) using blood samples exposed to γ doses (0.5, 1 & 2 Gy) at different dose rates (124, 23 & 10 mGy/min) and iii) with blood samples exposed to 0.5, 1 & 2 Gy γ doses at changing dose rates (increasing and decreasing dose rates). Results showed that a predefined dose-response curve constructed at a particular acute dose rate can be used for dose estimation in exposures involving varying dose rates and changing dose rate scenarios.

Dose rate correction for a silicon diode detector array.

PurposeA signal dependence on dose rate was reported for the ArcCHECK array due to recombination processes within the diodes. The purpose of our work was to quantify the necessary correction and apply them to quality assurance measurements.MethodsStatic 10 × 10 cm2 6‐MV fields delivered by a linear accelerator were applied to the detector array while decreasing the average dose rate, that is, the pulse frequency, from 500 to 30 MU/min. An ion chamber was placed inside the ArcCHECK cavity as a reference. Furthermore, the instantaneous dose rate dependence (DRD) was studied. The position of the detector was adjusted to change the dose‐per‐pulse, varying the distance between the focus and the diode closest to the focus between 69.6 and 359.6 cm. Reference measurements were performed with an ion chamber placed inside a PMMA slab phantom at the same source‐to‐detector distances (SDDs). Exponential saturation functions were fitted to the data, with different parameters to account for two generations of ArcCHECK detectors (types 2 and 3) and both DRDs. Corrections were applied to 12 volumetric modulated arc therapy plans.ResultsThe sensitivity decreased by up to 2.8% with a decrease in average dose rate and by 9% with a decrease in instantaneous dose rate. Correcting the average DRD, the mean gamma pass rates (2%/2‐mm criterion) of the treatment plans were improved by 5 percentage points (PP) for diode type 3 and 0.4 PP for type 2. Correcting the instantaneous DRD, the improvement was 8.4 PP for type 3 and 0.9 PP for type 2.ConclusionsThe instantaneous DRD was identified as the prevailing effect on the diode sensitivity. We developed and validated a method to correct this behavior. The number of falsely not passed treatment plans could be considerably reduced.

English

The herein reported study was conducted to evaluate the parasitic potential of Anisopteromalus calandrae (Howard) against larvae of Callosobruchus maculatus (F.), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) while, adult pests on the food medium treated with two formulations of diatomaceous earth (DE); Marine (Celite) and fresh water (Perma Guard) as grain protectants. The DE was applied at three dose rates i.e., 200, 400 and 600 ppm, at 25°C temperature and 65% relative humidity. Mortality and emergence of adults of tested insects and parasitoid were observed after 14 and 28 days of exposure respectivly. The highest mortality of C. maculatus was 43.37% against higher dose of Perma Guard (600 ppm) while the maximum mortality of S. oryzae was recorded 39.56% on application of Celite (600 ppm). The maximum mortality of A. calandrae parasitoid was observed 66.86% in S. oryzae infested grains treated with higher dose of Perma Guard (600 ppm), while 63.81% mortality of parasitoid was observed in S. oryzae infested grains at higher dose of Celite DE (600 ppm). The Perma Guard effectively controls population of tested insect’s mortality than the Celite. The highest emergence of C maculatus observed was 62.44% at lower dose of 200 ppm of Perma Guard DE while the highest emergence recorded on application of Celite was 60.66% from C. maculatus. The highest emergence of A. calandrae was 65.65% from S. oryzae at lower dose of 200 ppm of Perma Guard DE while the highest emergence of parasitoid recorded on application of Celite was found 60.66% at lower dose of 200 ppm from C maculatus. The emergence of tested insects and parasitoid increased with the decrease in dose rate of DE in most of the tested combinations. Higher dose (600 ppm) of both DE (Celite and Perma Guard) used in experiment showed mortality of tested insects and parasitoid activity of Anisopteromalus calandrae and furthermore release of A. calandrae on host insects would be adversely affected by use of diatomaceous earth product on stored grains. The experiments were carried out in laboratory of Grain Research, Training and Storage Management cell, Department of Entomology, University of Agriculture Faisalabad.

Radiation Dose of LND on the Lunar Surface in Two Years

The radiation dose on the lunar surface is an important parameter affecting the safety of astronauts and the residence time of the lunar surface. The measurement of the particle radiation on the lunar surface can provide an important basis for the radiation safety protection of astronauts. Based on the two-year observation data of lunar neutron and radiation dose detector on ChangE-4 lander, the average total absorbed dose rate of lunar particle radiation in silicon is 12.66±0.45 μGy·h^-1, and the absorbed dose rate of neutral particle is 2.67±0.16 μGy·h^-1. The radiation dose rate decreases slowly with time, but the change of LET spectrum is very small. The decrease of radiation dose rate due to the decrease of fubusch of GCR at the end of solar activity in December 2020 was observed.

The Effect of Cobalt-60 Dose-Rate and Biologically Effective Dose on Local Control for Intracranial Meningiomas Treated with Stereotactic Radiosurgery

To determine whether dose-rate is associated with local tumor failure in patients treated with cobalt-based stereotactic radiosurgery (SRS). Using data from a prospectively maintained research database, we reviewed patients treated with cobalt-based SRS between October 2005 and December 2018 at a single hospital network. Patients treated for more than one condition simultaneously (e.g. meningioma and trigeminal neuralgia) were excluded. Actual dose rates on the day of SRS were calculated from the calibration dose-rate while accounting for the cobalt-60 half-life of 5.2713 years. SRS dose (median 12 Gy, range 10-18 Gy) was prescribed to the 50% isodose line. Biologically effective dose (BED) was calculated using an SRS-specific monoexponential model accounting for treatment time per lesion, assuming α/β = 2.47 Gy. Cumulative incidences of local failure (LF) were reported after accounting for competing risks of death, on a per-lesion basis. Comparisons of actuarial LF were made using Gray’s test. Multivariable analysis of local failure was performed using a proportional hazards model. A total of 336 patients with 414 lesions were included. Median follow-up duration was 41.3 months. The median dose-rate was 2.33 Gy/min (range, 1.32-3.68). A dose-rate cutoff of 2.95 Gy/min was the most predictive of LF; five-year LF was 15.2% and 4.5% in patients who had a dose-rate of <2.95 and ≥2.95 Gy/min, respectively (p = 0.0375). On multivariable analysis, after adjusting for tumor grade, prior surgery, prior therapeutic RT, and tumor volume, each 1 Gy/min decrease in dose-rate had a hazard ratio of 1.89 for LF (95% CI, 1.03-3.46, p = 0.041). Use of prescription doses greater than 12 Gy among those who had a dose-rate of <2.95 Gy/min did not reduce the local failure rate in grade I (p = 0.99) or grade II/III lesions (p = 0.19). Finally, in all grade I tumors, BED of ≥50 Gy2.47 was associated with lower rates of LF (five-year LF 2.7% vs. 12.3%, p = 0.0030); this effect was maintained in the subgroup with dose-rate <2.95 Gy/min (p = 0.0075). Patients with meningiomas treated using cobalt-based SRS with low dose-rates had a higher risk of local failure than those treated with higher dose-rates. Institutions should ensure that their radiation sources for cobalt-based SRS are renewed regularly. The effects of BED, accounting for overall treatment time, should be further studied as a potential method of reducing LF.Abstract 1154; TableVariableHazard ratio for LF (95% CI)p-valueDose rate (per Gy/min)1.89 (1.03-3.46)0.041Meningioma volume (per cc)1.049 (0.983-1.12)0.15Marginal dose >12 Gy (vs ≤12 Gy)1.1 (0.52-2.1)0.89WHO gradeI1.0 (reference)II3.65 (1.55-8.58)0.003III4.42 (1.55-12.6)0.006Prior surgery4.31 (1.51-12.3)0.006Prior therapeutic radiation4.69 (1.87-11.8)0.001 Open table in a new tab

Dose rate effects on shape memory epoxy resin during 1 MeV electron irradiation in air

The effects of 1 MeV electron irradiation in air at a fixed accumulated dose and dose rates of 393.8, 196.9, 78.8, and 39.4 Gy s−1 on a shape memory epoxy (SMEP) resin were studied. Under low-dose-rate irradiation, accelerated degradation of the shape memory performance was observed; specifically, the shape recovery ratio decreased exponentially with increasing irradiation time (that is, with decreasing dose rate). In addition, the glass transition temperature of the SMEP, as measured by dynamic mechanical analysis, decreased overall with decreasing dose rate. The dose rate effects of 1 MeV electron irradiation on the SMEP were confirmed by structural analysis using electron paramagnetic resonance (EPR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The EPR spectra showed that the concentration of free radicals increased exponentially with increasing irradiation time. Moreover, the FTIR spectra showed higher intensities of the peaks at 1660 and 1720 cm-1, which are attributed to stretching vibrations of amide CO and ketone/acid CO, at lower dose rates. The intensities of the IR peaks at 1660 and 1720 cm-1 increased exponentially with increasing irradiation time, and the relative intensity of the IR peak at 2926 cm-1 decreased exponentially with increasing irradiation time. The solid-state 13C nuclear magnetic resonance (NMR) spectra of the SMEP before and after 1 MeV electron irradiation at a dose of 1970 kGy and a dose rate of 78.8 Gy s-1 indicated damage to the CH2–N groups and aliphatic isopropanol segment. This result is consistent with the detection of nitrogenous free radicals, a phenoxy-type free radical, and several types of pyrolytic carbon radicals by EPR. During the subsequent propagation process, the free radicals produced at lower dose rates were more likely to react with oxygen, which was present at higher concentrations, and form the more destructive peroxy free radicals and oxidation products such as acids, amides, and ketones. The increase in peroxy free radicals at lower dose rates was thought to accelerate the degradation of the macroscopic performance of the SMEP.