Radiation enteritis

For a grey body, the emissivity and the absorptivity are, by definition, independent of temperature and hence equation 9.115 may be applied more generally showing that, where one radiation property (a, r or e) is specified for an opaque body, the other two may be obtained from equations 9.115 and 9.124. KirchofPs Law explains why a cavity with a small aperture approximates to a black body in that radiation entering is subjected to repeated internal absorption and reflection so that only a negligible amount of the incident radiation escapes through the aperture. In this way, a - e = 1 and, at T K, the emissive power of the aperture is aT4. 

Baughan, C.A., Canney, P.A., Buchanan, R.B. and Pickering, R.M. (1993). A randomised trial to assess the efficacy of 5-aminosalicylic acid for the prevention of radiation enteritis. Clin. Oncol. Roy. Coll. Radiol. 5, 19-24. 

Diarrhea Drug related Antibiotic-induced bacterial overgrowth Hyperosmolar medications administered via feeding tubes Antacids containing magnesium Malabsorption Hypoalbuminemia/gut mucosal atrophy Pancreatic insufficiency Inadequate GIT surface area Rapid GIT transit Radiation enteritis Tube feeding related Rapid formula administration Formula hyperosmolalty Low residue (fiber) content Lactose intolerance Bacterial contamination... 

When radiation enters a proportional counter, the detector gas, at the point of incident radiation, becomes ionized. 

Recently, polyethylene and Teflon mesh sample holders have been used. A drop of sample is placed on the mesh and spread to a relatively uniform thickness for analysis. These holders can often be rinsed and reused. A very convenient alternative to liquid sample holders is the technique called attenuated total reflection or ATR. The ATR cell is a crystal of gallium arsenide, GaAs and the infrared radiation enters one end of the trapezoidal crystal. With the angles adjusted to obtain total internal reflection, all of the IR radiation passes through the crystal and exits the other end as shown in Fig. 5.14. 

Figure 4.5 Schematic diagram of a Fourier transform infrared (FTIR) spectrometer. Infrared radiation enters from the left and strikes a beam-splitting mirror (BS) angled such that half of the beam is directed towards a fixed mirror (Mi) and half towards a moveable mirror (M2). On reflection the beam is recombined and directed through the sample towards the detector. M2 is moved in and out by fractions of a wavelength creating a phase difference between the two beam paths. This type of device is called a Michelson interferometer.

The instrument described by Adamson and colleagues is shown in figure 10.1. The latest reported version consisted of a 10 cm3 glass reaction vessel that contained a bar for magnetic stirring and was separated from a thermostated jacket by an evacuated shell. The jacket temperature could be maintained at 25.000 0.001°C. Monochromatic radiation entered the reaction vessel through... 

Figure 3 is the absorbance spectrum of a sample of the ambient laboratory air drawn into the cell. Here, in accord with the usual procedure, the initially determined spectrum was first corrected for radiation that had reached the detector without having passed through the sample (room temperature background radiation entering the optical path via imperfect optical components and nonoverlap of the source and detector pupils and fields), ratioed against a zero-sample spectrum, and converted to absorbance. Trace (A) shows the spectrum from 3600-600 cm l. The massive absorbances seen here truncated at 1% transmission are due to water vapor and to carbon dioxide. 

Attenuated total reflectance infrared (ATR-IR) is used to study films, coatings, threads, powders, interfaces, and solutions. (It also serves as the basis for much of the communication systems based on fiber optics.) ATR occurs when radiation enters from a more-dense material (i.e., a material with a higher refractive index) into a material that is less dense (i.e., with a lower refractive index). The fraction of the incident radiation reflected increases when the angle of incidence increases. The incident radiation is reflected at the interface when the angle of incidence is greater than the critical angle. The radiation penetrates a short depth into the interface before complete reflection occurs. This penetration is called the evanescent wave. Its intensity is reduced by the sample which absorbs. 

Ruggedized detectors are available in which the radiation enters the silicon through the thicker and fight-tight aluminum contact. The bulk of the material is p-type silicon and a negative bias is applied to the gold contact so that the entry... 

Equations (34) and (35) show that the result of any actual measurement will strongly depend of the direction of propagation G, that is, of the surface through which the electromagnetic radiation enters the detector. As a first approximation, let us concentrate on the average direction of propagation (G) ... 

For accurate work a pair of matched cells should be used and each should be placed in the instrument so that the incident radiation enters via the same optical face every time. 

Reaction (6) as an allowed transition means that absorption of the 1849 A line by mercury vapor is extraordinarily high, and with mercury vapor in equilibrium with liquid mercury at room temperature nearly all of the radiation will be absorbed in a distance of less than one millimeter from the window through which radiation enters the vessel. 

The radiation enters the imaging spectrograph (B) through a line slit aperture (b) and is projected by optics (c) onto the dispersive PGP element (d). The spectrally... 

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