Short-term intense radiation

Long-term exposure to low-level radiation is more likely to cause the problems just described than are short exposures to intense radiation. Short-term intense radiation tends to destroy tissue rapidly in the area exposed and can cause symptoms of so-called acute radiation syndrome. Some of these symptoms are given in I Table 10.3. It is this rapid destruction of tissue that makes relatively intense radiation a useful tool in the treatment of some cancers. 

Radiation generates free radicals in tissue as it passes through. Radiation is hazardous even at low intensity if there is long-term exposure. Radiation sickness is caused by short-term intense radiation. Those working around radioactive sources can minimize exposure by using shielding or distance as a protection. 

The measurement of vibrational optical activity requires the optimization of signal quality, since the experimental intensities are between three and six orders of magnitude smaller than the parent IR absorption or Raman scattering intensities. To date all successful measurements have employed the principles of modulation spectroscopy so as to overcome short-term instabilities and noise and thereby to measure VOA intensities accurately. In this approach, the polarization of the incident radiation is modulated between left and tight circular states and the difference intensity, averaged over many modulation cycles, is retained. In spite of this common basis, there are major differences in measurement technique and instrumentation between VCD and ROA consequently, the basic experimental methodology of these two techniques will be described separately. 

The light sources used for CD measurements must be intense and should possess good short-term stability. Synchrotron radiation promises to be an excellent source of radiation for CD measurements in the wavelength range from vacuum ultraviolet to infrared 247, 248). 

A single-beam system is cheaper and less expensive than a double-beam system, but cannot compensate for instrumental variations during analysis. In a double-beam system, part of the light from the radiation source is diverted around the sample cell (flame or furnace atomizer) to create a reference beam, as shown in Figure 6.14. The reference beam monitors the intensity of the radiation source and electronic variations (noise, drift) in the source. The signal monitored by the detector is the ratio of the sample and reference beams. This makes it possible to correct for any variations that affect both beams, such as short-term changes in lamp intensity due to voltage... 

Compare and contrast the general health effects of long-term exposure to low-level radiation and short-term exposure to intense radiation. 

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