Irradiation, geometry

Figure 3.1 reproduces the conversion coefficients provided in ICRU (1988) for FrE/[ 3fp(10)]. For these conversion coefficients, i p(10) was approximated by the dose equivalent at a depth 10 mm along an appropriate radius (i.e., the central axis) in the ICRU sphere (ICRU, 1988). Conversion coefficients are given for personal monitors located on the body at the center of the chest (i.e., the front) or the center of the back (i.e., the back) for the following irradiation geometries ... 

This region encompasses the conversion coefficients for the following irradiation geometries and the indicated locations of the personeil monitor, provided the photon energy is greater than about 40 keV (about 50 keV for the PA irradiation geometry listed) ... 

In practice, if one knows that the actual conditions in the workplace can be reasonably simulated by these idealized irradiation geometries and locations of the personal monitor, and the photon energy is within the indicated range, Hp(lO) can be used directly as a surrogate for He even if the precise conditions are not known. The most frequently encountered condition of AP irradiation with the personal monitor located on the front of the body is well within this region for photon energies above 40 keV, and use of Hp(lO) would not overestimate He by more than a factor of three for photon energies as low as 30 keV. 

For energies less than about 30 keV for all irradiation geometries, and for PA and AP irradiation geometries where the personal monitor is located on the side of the body opposite to the incident photons, Hp(lO) can severely under- or overestimate He as indicated in Figure 3.1. 

In scenarios for which the irradiation geometry in practice is difficult to determine, investigators have recommended the use ofii/pdO) values determined from multiple personal monitors to obtain improved estimates ofi/g (Lakshmanan et al., 1991 Xu, 1994). These investigators have demonstrated that i p(10) values from personal monitors placed on the front (i.e., center of the chest) and back (t.e., center of the back) of individuals can be combined in specific algorithms that yield closer estimates of than the values of 10)... 

These analyses require that the 10) values for normal incidence be modified for irradiation geometries where the field is incident other than perpendicular to the surface of the personal monitor. The methods used in developing these modifications to fl pdO) for nonnormal incidence included extensive Monte Carlo calculations of photon interactions in anthropomorphic phantoms (Xu, 1994) or in PMMA and tissue slabs and the ICRU sphere (Grosswendt, 1991 Grosswendt and Hohlfeld, 1982), and thermoluminescent dosimeter measurements in water cubes (Lakshmanan et al., 1991). Some of these modifications for /fp(lO) are presented in ICRU (1992). 

Xu (1994) explored three photon energies (i.e., 80 keV, 300 keV and 1 MeV) and a number of irradiation geometries, including geometries with a large range of non-normal incidence. In particular, Xu (1994) provided (estimate) values for a variety of point sources at various locations and distances from the body. Xu (1994) computed the/fpdO) values in tissue-equivalent spheres located on the relevant surface of the anthropomorphic phantom. 

In this Report, the NCRP uses the published /fp(lO) modification factors for PMMA slabs (Grosswendt, 1991) and the conversion coefficients tabulated in ICRP (1987) to calculate conversion coefficients for i/g/Lf/pdO)] for a variety of irradiation geometries and a number of photon energies between 30 keV and 1 MeV. This Report also develops two alternative algorithms which weight the //p(10) values for the two personal monitors depending on the desired objective, as follows ... 

The useful criteria introduced earlier for radiation protection purposes are that the estimate of He should (1) not be much less than the actusd He U-C., Htiest mate)/HE between 0.9 and 1.0] to avoid underestimating He by much, and (2) not be much higher than the actual He [i.e., He (estimate)///e not much greater than 2.0 to 3.0] to avoid seriously overestimating He- How the various results in Table 3.1 compare to these criteria for each irradiation geometry and algorithm is summarized in Table 3.2. 

Table 3.1— Ratio of He (estimate) to He for various irradiation geometries and combinations of Hp(10) values from personal monitors... 

An i p(10) value determined with one personal monitor is recommended as a surrogate for for working conditions where the locations of the personal monitor, photon energies and irradiation geometries are consistent with those listed below ... 

For working conditions not listed in Section 4.1 or for scenarios where the irradiation geometry or photon energy is unknown or... 

GROSSWENDT, B. (1991). The angular dependence and irradiation geometry factor for the dose equivalent for photons in slab phantoms of tissue-equivalent material and PMMA, Radiat. Prot. Dosim. 35, 221-235. 

Figure 15. Cross section along the plane perpendicular to the axis of a photochemical reactor using (a) an annular excimer lamp of coaxial (positive) irradiation geometry and (b) of a combination of cylindrical and annular excimer lamps (see also [60],...

Suitability for photochemical investigations, because the actinometric system is easily replaced by the sample of interest without changing the irradiation geometry or other experimental conditions. (This is especially valid for liquid samples.)... 

In a current developing standards document being considered for the international sterilisation community, under a section on Dosimeters , it is specified that each batch of dosimeters to be used must be properly calibrated. This entails either (1) irradiation of a user s dosimeter in a standards or accredited reference (secondary) laboratory, and subsequent appropriate evaluation by the user, (2) irradiation in a suitably designed irradiation geometry in the user s laboratory along with dosimeters issued by a standards or reference laboratory, or (3) use of a radiation field where the calibration is traceable to a standards laboratory, according to an acceptable accreditation procedure. 

Figure 8 Optimal flow system irradiator geometry. Penetration of 2 MeV electrons in water is 1 cm.

The main reactor exposed to microwave irradiation is generally a coiled tube or a low inner volume chamber located inside the micro-wave oven. Winding the coiled tube around the oven output antenna can improve the irradiation geometry [128]. 

Masarik J, Kollar D, Vanya S (2000) Nnmerical simnlation of in situ production of cosmogenic nnchdes Effects of irradiation geometry. Nncl Instr Meth Phys Res B 172 786-789 Masarik J, Reedy RC (1995) Terrestrial cosmogenic-nnchde production systematics calcnlated from nnmerical simnlations. Ea Planet Sci Lett 136 381-395 Masarik J, Reedy RC (1996) Monte Carlo simnlation of in situ produced cosmogenic nnchdes. Radiocarbon 38 163-164... 

Wavelength-dispersive XRF instramentation is almost exclusively used for (highly reliable and routine) bulk-analysis of materials, e. g., in industrial quality control laboratories. In the field of energy-dispersive XRF instrumentation, next to the equipment suitable for bulk analysis, several important variants have evolved in the last 20 years. Both total reflection XRF (TXRF) and micro-XRF are based on the spatial confinement of the primary X-ray beam so that only a Hmited part of the sample (+ support) is irradiated. This is realized in practice by the use of dedicated X-ray sources. X-ray optics, and irradiation geometries. 

Fig. n.l9 Schematic drawings of (a) a direct-excitation XRF instrument, (b) a secondary target XRF instrument, (c) a polarized XRF instrument employing a cartesian (XYZ) irradiation geometry. 

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