Distance, radiation exposure

The presence of radiation in the workplace - which is an inevitable consequence of the radioactivity of uranium - requires that additional safety precautions be taken over and above those observed in other similar workplaces. There are generally three sources from which radiation exposure may occur (i) radiation emitted from uranium ore in-situ and/or during handling (ii) airborne radiation resulting from the decay of radon gas released from the ore and uranium dust and (iii) contamination by ore dust or concentrate. Radiation levels around uranium mining and milling facilities are quite low - for the most part only a few times the natural background levels - and they decrease rapidly as the distance from... 

Suppose the amount of radiation that could be received from a microwave oven varies inversely as the square of the distance from it. How many feet away must you stand to reduce your potential radiation exposure to the amount you could receive standing 1 foot... 

Distance Rule 2 Direct contact is not required to receive radiation exposure — increased distance equates to decreased exposure to radiation. 

How does the radiation exposure change as the distance doubles from 0.1 meter to 0.2 meter As the distance quadruples from 0.1 meter to 0.4 meter ... 

As results vary with species (strains), lamps, detectors, doses, distances, time (exposure chemical to exposure light) chemical routes, endpoint (biological, erythema, edema, ear thickness) a somewhat structured method has been proposed to limit variation. To apply this method, at four skin sites apply 0.05 ml test chemical alone, under radiation, opaque cover, vehicle alone, and positive control at intervals of 5 min to 24 h. Irradiate all skin sites simultaneously for up to 40 min at a distance of up to 15 cm from the source. Adjust the exposure time so that 10Jcm UVA and 0.1 JemUVB using ... 

In addition to radiation exposure, and depending on the distance from the detonation, a nuclear explosion can expose people to two other types of energy, heat and blast. Heat accounts for approximately 35% of the energy released in a nuclear detonation. The bomb blast, or shock, accounts for approximately another 50%. Radiation energy accounts for only 15% of the energy from the detonation (2). 

The radiation exposure varies inversely with the square of the distance from the source. Each radionuclide has an exposure rate constant, r, which is given in units of R-cm2/mCi-h at 1 cm or in SI units, pGy-m2/GBq-h at 1 m, and these values for UC, 13N, 150, 18F, and 82Rb are given in Table 9.3. The exposure X per hour at distance d(cm) from an n mCi source is given by... 

Three basic principles are recommended for keeping radiation exposure to a minimum shielding, control, and distance. If a radiochemical laboratory is designed properly and the work performed in such a manner that the g eral background contamination is suffici tly low to do valid low level tracer experiments, then the health aspects of radiation control are satisfied. We indicate the main principles for work with radioactive substances, but in each notion, special rules may apply. 

Interpret Graphs Determine the distance from the source at which the radiation decreased to 0.69 mrem/ s-m. This intensity is the maximum radiation exposure intensity considered safe. Hint Use the equation... 

Figure 24.33 shows a simplified graph of radiation intensity versus distance from the source. Explain this graph and what itimphes about a method of reducing the effects of radiation exposure. 

There are three basic principles to avoid unnecessary radiation exposure to others. Since the patient is a source of radiation to others keep distance, limit the time spent close to the patient and avoid contamination, i.e., apply meticulous hygiene to reduce the possibility of contamination. 

Routes of entry for radioactive materials are much the same as for poisons. However, the radioactive source or material does not have to be directly contacted for radiation exposure to occur. Exposure occurs from the radiation being emitted from the radioactive source. Once a particulate radioactive material enters the body, it is dangerous because the source now becomes an internal source rather than an external one. You cannot protect yourself by time, distance, or shielding from a source that is inside your body. Contact with or ingestion of a radioactive material does not make you radioactive. Contamination occurs with radioactive particles, but with proper decontamination, these can be successfully removed. After they are removed, they cannot cause any further damage to the body. 

Radiation exposure is defined as the energy deposited by radiation per unit mass. For a gamma ray emitted by a point source, the radiation exposure rate i is related to the gamma-ray decay fraction /, the gamma-ray energy E (in MeV), the activity of the radionuclide a(in Bq), the linear energy absorption coefficient /u-a, the density of air p, and the distance x ... 

Increasing one s distance from a radioactive source is a very effective way to reduce one s radiation exposure. Moving 1 to 2 feet away decreases the dose to one-fourth. Moving to 4 feet away decreases the dose to one-sixteenth. 

Radiation levels decrease with the square of distance from the source. This is the inverse square law for radiant energy sources and materials. As shown in Figure 22-1, a person at one unit of distance from a source has some level of radiation exposure. At double the distance, the amount of radiation will be one fourth that of the first location. 

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