China
Africa
Explore chapters and articles related to this topic
Radiation Sterilization
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Barry P. Fairand, Dusan Razem, Karl Hemmerich
At equivalent output powers, gamma irradiators have the lowest dose rates, X-ray irradiators higher dose rates, and electron beam irradiators the highest dose rates. By way of comparison, if the dose rate in a gamma irradiator were normalized to 1, dose rate in an X-ray irradiator would be approximately 10 or more, and dose rate in an electron beam irradiator would be greater than 100. For a given modality of irradiation, various methods are available for controlling the dose rates that are delivered to a product. For example, decreasing the output power of the irradiator offers one method for reducing the dose rate. In the case of a gamma irradiator, this would entail loading less isotope in the source plane(s), and for electron beam and X-ray irradiators, it could be accomplished by simply dialing down the current of the accelerator. Placement of a shield between the source and the target is another method for reducing the dose rate. In a gamma irradiator, one can take advantage of the isotropic nature of the radiation field and simply move the product further from the source, which will reduce the power density incident on the target. If dose rate is considered an important parameter in the irradiation of a specific pharmaceutical/medical product, selection of the modality of radiation that best meets the dose rate requirements should be taken into account at an early point in the sterilization project.
Chapter 5 Ionizing Radiation: Dose and Exposure—Measurements, Standards and Protection
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
If a person is being exposed to radiation, we do not want to have to wait a year before knowing whether they have exceeded the maximum permitted dose equivalent. We need to know the dose rate, so that we can calculate the accumulated dose and give a warning if the dose rate is very high. Monitoring equipment will often be calibrated in terms of mrad h−1 or µGy h−1. It is easy to calculate that the maximum dose of 20 mSv in a year corresponds to an x-ray dose rate of about 10 µSv h−1 over a 40 h week. Spread over the whole year it represents a dose rate of about 2 µSv h−1, which we can compare with normal background of about 0.1 µSv h−1. These levels of dose rate can easily be measured using Geiger-Müller (G-M) tubes or scintillation counters. Dose rate can also be measured using an ionization chamber, which is more accurate and less affected by the energy of the radiation than either the G-M tube or scintillation counter monitors. Ionization chamber systems also have the advantage that they can measure high dose rates which would saturate the other monitors.
The work and leisure environments
Published in Stephen Battersby, Clay's Handbook of Environmental Health, 2016
Jonathan Hayes, Stuart Wiggans
Sieverts are the units that relate to an amount of energy that is received without reference to any time period. Radiation hazards may be assessed or controls applied either in terms of a simple dose, or in terms of a dose rate. The dose rate is expressed in sieverts per hour. The standards that must be applied may be derived, for example, from standards such as those contained in the Ionising Radiation Regulations 199978 made under the Health and Safety at Work etc. Act 1974. Also the associated Approved Code of Practice [22] is made under the provisions of the Health and Safety at Work etc. Act 1974 to implement the basic requirements of various European Directives. They lay down basic standards for the protection of workers and the general public against the dangers arising from the use of ionising radiation in work activities. The European Commission has brought forward a formal proposal for a new Basic Safety Standards Directive as at 2015, seeking to bring together and consolidate five existing EURATOM Directives. This is under negotiation at the time of writing.
Relationship between viability and genotoxic effect of gamma rays delivered at different dose rates in somatic cells of Drosophila melanogaster
Published in Journal of Toxicology and Environmental Health, Part A, 2019
Elizabeth Jiménez, Emilio Pimentel, Martha P. Cruces, Araceli Amaya-Chavez
The growing use of nuclear power increases occupational exposures and risk of industrial accidents. It is well known that ionizing radiation produces lesions in DNA, diminished reproductive capacity, reduced somatic growth, inhibition of bone marrow stromal cells and genotoxic effects correlated with an increasing dose rate (DR) (Lecomte-Pradines et al. 2017; Zhang et al. 2010; Zuo et al. 2012). Based upon these observations there is a growing interest examining the role of different factors such as DR in the biological consequences attributed to ionizing radiation, particularly when delivery of a low-DR occurs, a situation which is environmentally relevant (Brenner et al. 2003). As with other organisms such as Caenorhabditis elegans or mouse (Lecomte-Pradines et al. 2017; Zhang et al. 2010), radiation may exert either acute or lethal and sublethal effects on Drosophila induced by high or low doses of radiation, respectively (Hall and Giaccia 2012).
Dose Rate Evaluation for the ES-3100 Package with HEU Content Using MCNP, ADVANTG, Monaco, and MAVRIC
Published in Nuclear Technology, 2018
Photon and neutron dose rate contours are generated by the Java application, Mesh File Viewer for MCNP, ADVANTG/MCNP, Monaco, and MAVRIC cases. The grid geometry used to generate dose rate contours is 2 cm apart in the x-direction, y-direction, and z-direction for each source configuration in the MCNP calculations. The same grid geometry is used in ADVANTG/MCNP to calculate weight windows and biased source distributions by Denovo for MCNP. The photon and neutron dose rate contours for the cylindrical hemishell configuration are presented in this paper. The units for dose rate contours are shown in millirems per hour (100 mrem/h = 1 mSv/h). Figure 8 shows the MCNP photon dose rate contours near the source center for the cylindrical hemishell (x-y plane) along with the geometry grids. Figures 9 and 10 show the MCNP photon and neutron dose rate contours (x-z plane). The ADVANTG/MCNP-generated photon and neutron dose rate contours (x-z plane) are presented in Figs. 11 and 12. The following grid geometry is used to generate mesh tally dose rate contours for Monaco and MAVRIC for each source configuration, and the grids are shown in Figs. 13 and 14; also, the same grid geometry is used to generate importance maps for each source configuration in MAVRIC:
Everything you wanted to know about space radiation but were afraid to ask
Published in Journal of Environmental Science and Health, Part C, 2021
Jeffery Chancellor, Craig Nowadly, Jacqueline Williams, Serena Aunon-Chancellor, Megan Chesal, Jayme Looper, Wayne Newhauser
The biological effect of the radiation dose depends on physical and biological factors, e.g., multiple particle and energy-specific factors, dose rate per exposure and the frequency of multiple exposures. The (physical) absorbed dose is the energy absorbed per mass (J/Kg, Gy). For a dose-based system of radiation protection and for the determination of occupational dose limits, it is necessary to attempt summing the total risk of radiation from multiple sources (e.g., SPE protons, GCR, etc.).33 At a given ion velocity, LET increases with atomic number. Thus, for ground-based research, it is key to have the correct abundances and energy distributions of each ion present in the space radiation environment. As charged particles lose energy successively through material interactions, each energy loss event can result in damage to the biological tissue. In addition, as charged particles near the end of their track (i.e., as they slow down and are nearly stopped) the LET rises sharply, creating the so-called “Bragg peak”.34 This is demonstrated in Figure 3. The phenomenon of the Bragg peak is exploited in cancer therapy in order to concentrate the dose at the target tumor while minimizing impact to the surrounding tissue. This is demonstrated in Figure 3 where the relative dose deposition in tissue for various radiation types utilized in space radiobiology studies is plotted versus depth in tissue. The gray shaded area is the average width of a mouse model. Also shown are the average diameters of Yucatan mini-pigs and humans. Gamma and X-ray radiations deposit most of the energy at or near the surface, while in contrast, charged particles such as protons, carbon, iron, etc., have distinct Bragg peaks. In each example, the Bragg peak is located outside the body mass of the mouse, indicating the difficulty in replicating the relative organ dose distribution of a GCR exposure incurred by humans during spaceflight.