Depth-dose function

Figure 31 Depth-dose function for electrons in a target of low atomic number. The normalized penetration f = z/Rq.

Another exposure tool is available in gamma radiation. While the correlation is not always perfect, there is a high degree of similarity in the response of polymers to the radiation from 60Co and from 50 keV electrons. Because of the penetrating nature of gamma rays, the exposure is not restricted to thin films or small amounts of polymer. Also, the absorbed dose is not complicated by the depth-dose function which must be used when electron-... 

The present nomograph (Figure 14) has been constructed by conventional methods and is relatively compact. Compromises have been made in the choice of ranges for each variable and in the accuracy with which the depth dose function can be represented. All of the equations are used with the following assumptions ... 

Each of these features provides a safety benefit, however not all of these features are necessary to mitigate dose consequences to acceptable levels. Only those features that are relied upon to function or actuate to prevent or mitigate uncontrolled releases of radioactive materials are so identified. Analyses accomplished to evaluate the consequences of release of radiological materials, described in Section 3.4, identify those SSC s that are part of the primary success path in each scenario. The SSC s so identified are associated with a significant mitigation of radiological releases in abnormal and accident scenarios and therefore perform a defense in depth Safety Function. 

Bragg Peak and Physical Selectivity. The physical selectivity of carbon ions, other heavy ions, and protons is quite similar. Fig. 19 shows the Bragg peak for carbon ions as a function of depth [44]. The Bragg peak has to be spread out, as for protons, to fully cover the planning target volume (PTV). The ratio between the dose at the level of spread-out Bragg peak (SOBP) and of the initial plateau is compared for carbon ions and protons and for different ions in Figs. 20 and 21 [44,45]. 

Figure 23 Variation of RBE as a function of depth in the carbon-ion beam used for clinical applications at HIMAC, Chiba, Japan (carbon-12, 290 MeV/u, SOBP 60 mm). The biological system is the well-codified intestinal crypt regeneration in mice. The selected criterion is 20 regenerating crypts per circumference after a single fraction irradiation. RBE determinations were performed at the beginning, middle, and end of the SOBP and at the level of the initial plateau. The dose-effect relationship for cobalt-60 is indicated for comparison. An estimation of the LET is presented for each depth where biological determinations were made. (From Gueulette, unpublished.)...

Calibration of the intensities of the radiation flelds is traceable to the NIST. The ionization chambers and electrometers used by the service laboratories to quantify the intensity of the radiation fields must be calibrated by the NIST or an accredited secondary standards laboratory. The intensity of the field is assessed in terms of air kerma or exposure (free-in-air), with the field collimated to minimize unwanted scatter. Conversion coefficients relate the air kerma or exposure (free-in-air) to the dose equivalent at a specified depth in a material of specified geometry and composition when the material is placed in the radiation field. The conversion coefficients vary as a function of photon energy, angle of incidence, and size and shape of backscatter mediiun. 

Fig. 3.1. Ratio of He to as a function of photon energy. ffp(lO) is approximated by the dose equivalent at depth 10 mm along the central axis in the ICRU sphere (ICRU, 1988). Five geometries and two locations for the personal monitor are considered in the calculations (see Section 3.1) (adapted from ICRU, 1988 and reproduced with permission).

SIMS and SNMS are versatile analytical techniques for the compositional characterization of solid surfaces and interfaces in materials research.92-94 As one of the most important applications, both surface analytical techniques allow depth profile analysis (concentration profile as a function of the depth analyzed) to be performed in materials science and the semiconductor industry with excellent depth resolution in the low nm range. For depth profiling in materials science, dynamic SIMS and SNMS using high primary ion beam doses are applied. Both techniques permit the analysis of light elements such as H, , C and N, which are difficult to measure with other analytical techniques. 

Figure 6. From figure 11 of Kylling et al. 1998. The ratio between simulated Brewer and Bentham UVB dose rates with and without aerosols as a function of the aerosol optical depth at 355 nm. Ratios of model results with aerosol single scattering albedo of (0.95 solid line), 0.87(dotted line) and 0.80 (dashed line) versus aersosol free model results are shown for solar zenith angle of 10° and an ozone column of 340 DU.

The diffusional displacement of B is a function of implant dose and energy. The energy dependence is illustrated in Figure 24, which shows the diffusion of B at a concentration of 1 X 1017/cm3 versus Rp, the projected range of B implantation. The implants were 1 X 1014-2 X 1014 B atoms per cm2 annealed at 800-850 °C for approximately 0.5 h. The displacement increases with implant depth and then reaches saturation. The calculated curve in Figure 24 is based on the concentration of excess self-interstitials in the tail of the implant that increases directly with range, up to a maximum value. 

Atmospheric effects of large-scale TNT expins have also been studied in depth both practically and theoretically. Factors considered include pressure and impulse effects, decay characteristics and travel and duration times, all as a function of distance, and for both free-field and reflection situations (Refs 3,9,15,16, 17,24,32, 33,34,35,36,44, 53,75,76,115 116). A distinction is made between the blast area dose to the source, comprising air and the products of expln, and that farther away involving air only (Ref 53). Double-burst conditions (fireball and shock wave interaction, and torus formation) have been studied (Ref 149), as have also the dynamics of dust formation and motion (Refs 25,26 117). Performance tests were run on a naval blast valve (Ref 92), and on aircraft wing panels (Ref 4)... 

More in-depth behavioral tests are required if dose-related toxicant effects are noted in screening tests. These tests may also be required as part of more selective toxicological screening, such as for developmental neurotoxicity. Focused tests of neuromotor function and activity, sensory functions, memory, attention, and motivation help to identify sites of toxicant-mediated lesioning, aid in the classification of neurotoxicants, and may suggest mechanisms of action. Some of these tests, like the schedule-controlled operant behavior tests for cognitive function, require animal training and extensive operator interaction with the animals. 

In ordinary doses, meperidine exerts inappreciable effects on respiration and circulation. In large doses, it interferes with the facilitatory function of the pneumotaxic center and the vagal afferent impulses, thereby reducing the rate and depth of respiration. With still higher doses, meperidine produces an irregular respiratory rhythm and ultimately induces apnea. It causes relaxation of the ureter, gall bladder, and bronchi. This action is partly a direct one on the smooth muscle of these structures and, in part, a result of its anticholinergic activity. It does not affect the size of the pupil or alter the tonus of the uterus. 

Whole-animal studies assess the percent of the applied dose absorbed into the body using classic techniques of bioavailability, where absorbed chemical is measured in the blood, urine, feces, and tissues with mass balance techniques. Recently, methods have been developed to assess absorption by measuring the amount of chemical in the stratum comeum because it is the driving force for diffusion. Cellophane tape strips are collected 30 minutes after chemical exposure and the amount of drug assayed in these tape strips correlates to the amount systemically absorbed. If the focus of the research is to determine the amount of chemical that has penetrated into skin, core biopsies may be collected and serially sectioned, and a profile of the chemical as a function of skin depth may be obtained. 

Positronium formation is also sensitive to ion-implanted amorphous Si02. Figure 9.7 shows the intensity of the long-lived component, IL, as a function of the positron incident energy for Xe ion-implanted amorphous Si02 ([22]). The sample was obtained by a vapor-phase axial deposition (VAD) method. Xe ions of 400 keV were implanted into the sample to doses of 1 x 1014 and 5 x 1015 ions/cm2 at room temperature. While there is a small difference between IL of 1 x 1014 and II of 1 x 1015, both have a minimum at around 4-5 keV, corresponding to the mean positron implantation depth of -200 nm at which the ions are implanted. 

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