Radiation exposure modes

Both patients and medical staff are understandably concerned about the health effects of exposure to radiation and radioactive contamination. There are two distinct types of radiation exposure, acute and chronic, and two primary exposure modes, radiation and radioactive contamination. Each exposure type and mode is slightly different and must be treated differently by medical staff (see Table 27.2). In addition, there are concerns about the reproductive effects of radiation exposure. In this section, these concerns will be discussed. 

Introduction. The word "LASER" is an acronym for "Light Amplification by Stimulated Emission of Radiation. A laser is a device that produces an intense, narrow, and monochromatic beam of light. Several key laser parameters are the wavelength, the power density, and the divergence of the radiation. The effects produced by laser radiation are dependent on the laser radiation exposure dose. The higher the exposure dose, the more severe the effects. Lasers emit radiant energy in several modes... 

These values together with simple, robust modelling have been used for a number of years to derive segregation tables for different modes of transport. Assessments of radiation exposures arising indicate that continued use of these values is acceptable. In particular, surveys of exposure occurring in air and sea... 

The increase in effective detector width is associated with a proportionate increase in the effect of over ranging in the helical scan mode, and therefore, increased proportion of the overall radiation exposure from the first and last half rotation that does not contribute to image reconstruction. This effect is more significant when smaller volumes are imaged, e.g., when examining children, where this effect may account for up to 50% of the overall dose. The only effective means to reduce this excess radiation is the use of an active colh-mator in front of the X-ray tube, which is commercially available. 

Radiation damage failure occurs when the changes in material properties induced by exposure to a nuclear radiation field are of such a type and magnitude that tlie part is no longer able to perform its intended function, usually as a result of the triggering of some other failure mode, and often related to loss in ductility associated with radiation exposure. 

Applications of industrial photopolymer technology can be divided into two general classifications based on the exposure mode of the applied radiation. 

The ICRP (1994b, 1995) developed a Human Respiratory Tract Model for Radiological Protection, which contains respiratory tract deposition and clearance compartmental models for inhalation exposure that may be applied to particulate aerosols of americium compounds. The ICRP (1986, 1989) has a biokinetic model for human oral exposure that applies to americium. The National Council on Radiation Protection and Measurement (NCRP) has also developed a respiratory tract model for inhaled radionuclides (NCRP 1997). At this time, the NCRP recommends the use of the ICRP model for calculating exposures for radiation workers and the general public. Readers interested in this topic are referred to NCRP Report No. 125 Deposition, Retention and Dosimetry of Inhaled Radioactive Substances (NCRP 1997). In the appendix to the report, NCRP provides the animal testing clearance data and equations fitting the data that supported the development of the human mode for americium. 

Figure 7. Deep UV sensitivity curves of SPP positive node (A) compared with that of SPP negative mode (B). In positive mode, a 0.4 izm thick SPP layer was exposed to deep UV and then dip-developed in a 1.6 wt% TMAH solution for 60 s at 25 °C. In negative mode, SPP was exposed to deep UV followed by a flood exposure using near UV radiation and then dip-developed in a 0.7 wt% TMAH solution for 60 s at 25 C.

Structural information of LB films has also been obtained from FTIR studies. In the carboxylate form of the fatty acid, the relative intensities of the vs(C02-) and va(C02-) signals are dependent on the orientation of the chain axis. The dipole moments of the vs(C02-) and va(C02 ) stretches are parallel to and perpendicular to the chain axis, respectively. In transmission mode the electric vector of the IR radiation interacts strongly with dipole moments parallel to the substrate. This means that in transmission mode the vs(C02-) will be most intense, and the va(C02-) the weakest, for films with the chain axis perpendicular to the substrate. The opposite is true for the FTIR-RA mode. There is general consensus that in M-FA films the chain axis is approximately perpendicular to the substrate while the protonated form of the acid after exposure to H2S has a tilt relative to the substrate. Further discussion of FTIR as an investigative tool into the reaction of M2+-FA films with dihydrogen chalcogenides is given in later sections. 

The dual modes of uranium chemical and radiological toxicity are not usually separately identifiable by end point. The renal and respiratory effects from exposure of humans and animals to uranium are usually attributed to the chemical properties of uranium, while the theoretically potential excess cancers are usually attributed to the radiation properties of this substance. Although the net effects on the lungs and kidneys have been suggested to be a cooperative action of the chemical and radiation properties, with a complementary mechanism of action, this relationship has not been demonstrated experimentally (Ballou... 

In the flash mode, the sample is exposed to more intense radiation than conventional Xenon-arc lamp exposure for only a few milli-second full spectrum energy at a time and with a cooling period between pulses. This results in complete UV-VIS exposure in a matter of fractions of a second without any large heating of the sample, common in other techniques. 

The effects of using polarised radiation on the spectra measured after exposure of the crystal to ethene at 373K are shown in Figure 16. Polarisation parallel to the crystal c axis enhances the contribution of the CH3 symmetric and asymmetric modes to the spectrum relative to the unpolarised spectrum or that obtained with polarisation perpendicular to the c axis. Similar polarisation effects were found for crystals exposed to ethene at room temperature or 473K, regardless of which crystal face the infrared beam was incident upon. After heating... 

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