Exposure, radiation limiting

Various MAA compounds have different responses to partitioned radiation exposures. In whole water samples of Antarctic phytoplankton monitored over a 2-week period, shinorine and porphyra-334 increased in concentration with exposure to either total sunlight or visible light alone.173 In contrast, mycosporine-glycine and palythine concentrations increased only under total sunlight treatments and not when exposure was limited to the visible band. MAA-specific increases also occur in unicellular freshwater Chlorophyta species.131... 

Regulations for the general public are based on an annual TEDE of 0.1 rem/year, with provisions for a limit of 0.5 rem/year under special circumstances (USNRC 1997b). Considering the lower limit for members of the public and their potential continuous exposure, the limits on air concentrations of radionuclides for the public are two orders of magnitude lower than the DACs for radiation workers. Regulations for specific applications limit the dose to the public to values <0.1 rem/year. Under its... 

This is the intensity of the exposure radiation in the plane of the wafer. The extended source method, or Hopkins method,is often used to predict the aerial image of a partially coherent, diffraction-limited, low-numerical-aperture-aherrated projection system based on scalar diffraction theory. For very high NA, vector calculations involving the complete solution of Maxwell s equation are used. The illumination may be of a single wavelength or it may be broadband. The illumination source may be a conventional disk shape or other more complicated shapes as in off-axis illumination. ... 

HOP personnel exposure is limited in accordance with the SNL RPPM. Administrative Control Levels (ACL s), trigger levels, and an established dosimetry program are used at SNL to monitor and limit the dose to radiation workers. Dose to workers in excess of 100 mrem per year must be specifically approved In accordance with the RPPM at levels as shown in Table 7.6-1. These limits are monitored and enforced through the use of dosimetry records, approved individual ACL s, and technical work documents. 

A class 1 laser is safe under all conditions of normal use. Never exceed the maximum permissible exposure (MPE) limit. This class includes high-power lasers within an enclosure that prevents exposure to the radiation and that cannot be opened without shutting down the laser. For example, a continuous laser at 600 nm can emit up to 0.39 mW, but for shorter wavelengths, the maximum emission is lower because of the potential of those wavelengths to generate photochemical damage. The maximum emission is also related to the pulse duration in the case of pulsed lasers and the degree of spatial coherence. 

NRC requires a variety of records and reports." Records include radiation protection programs, surveys, individual monitoring results, waste disposal, and other records. Some reports range from theft or loss of licensed material, notification of incidents, to reports of exposures, radiation levels, and concentrations exceeding limits. 

Regulatory dose limits are set by international, federal, and state agencies for the general public and occupational exposure to limit cancer risk (Table 4.7). Other radiation dose limits are applied to potential specific biological effects with workers skin and lens of the eye that will not be elaborated here. 

Above background. Suggests caution and investigation of source of radiation. Total exposure is limited to 1-5 remannually. 0.02-0.2... 

A patient may be given radioactive tracers such as technetium-99m, iodine-131, gallium-67, and thallium-201 that emit gamma radiation, which is detected and used to develop an image of the kidneys or thyroid or to follow the blood flow in the heart muscle. Radiologists must be knowledgeable about radiation exposure to limit the amount of radiation to which patients are exposed. 

In setting radiation limits, it is customary to assume that, for exposure of the whole body to radiation, the effect produced is proportional to the absorbed dose. Since this assumption ignores the possibility of damaged tissue repairing itself during long-term exposure to low radiation doses, it is believed to represent a conservative approach to the estimation of possible damage. Somatic effects where the probability of injury (e.g., the initiation of cancer) is proportional to the dose are known as stochastic effects. In contrast to these, an effect such as cataract of the eye is nonstochastic in this case, a threshold dose exists such that no cataract will be induced if the absorbed dose is below this amount. 

In order to minimize the radiation dose, the inspection time is limited to 30 seconds of exposure (programmable) after which the X-ray on/off shutter will shutter off the X-rays and the block must be unloaded. A timer will keep the operator informed of the time that has elapsed. 

The resist must have suitable radiation sensitivity. Today s exposure tools are so costiy that tool throughput is a key measure of performance. The overall time to expose a resist film is the sum of the times to load and position the substrate in the exposure tool, to align the substrate and the mask, to irradiate the film, and to unload the complete part. In the optimum case the resist exhibits sufficient radiation sensitivity so that the fraction of the overall cycle apportioned to irradiate the film does not limit the number of substrates exposed in a given period of time. 

Radiation protection, ie, the limits on radiation dose to workers and the pubHc are specified. Exposure is maintained as low as reasonably achievable... 

Radiation dose limits at a disposal site boundary are specified by the NRC as 25 x 10 Sv/yr (25 mrem/yr), a small fraction of the average radiation exposure of a person in the United States of 360 x 10 /Sv/yr (360 mrem/yr). Protection against nuclear radiation is fully described elsewhere... 

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