Geometric attenuation

Radiation Shielding and Dose 8.3.3.1 Geometric Attenuation of Radiation... 

Figure 2. Geometric attenuation of an image from a point source.

This discussion of geometric effects ignored the attenuation of radiation by material through which the radiation must travel to reach the receptor. The number of particles, dN, penetrating material, equals the number of particles incident N times a small penetration distance, dx, divided by the mean free path length of the type of particle in the type of material (equation 8.3-8). Integrating gives the transmission coefficient for the radiation (equation 8.3-9). 

These coefficients must be multiplied by the density of air and tissue, respectively. Figure 15.7.2-1 depicts a radiation fallout field. Let C be the curie activity/m. The radiation into a unit area receptor at z = 1 m above the ground. The area is emitting C r dr d0 gammas/s. These are attenuated in the air as exp(-p, R) and geometrically as l/(4 7t R). The radiation received by the receptor is given by equation 15.7.2-1 which becomes 15.7.2-2 by a change of... 

The factor (q/a ) may be obtained from independent optical and geometrical measurements, since q is the transmittance of the attenuator used for the incident beam, a is the solid angle of detection of scattered light and is the thickness of sample. 

In most high-resolution lenses, Ft % 1 so that z0, and hence —zmin and zmax, are of the order of Ao. With the further notation that the wavenumber and attenuation in the coupling fluid are k and ( o, respectively, and that the response of the transducer to a uniform field of unit amplitude would be V0> the response to the geometrically reflected field is... 

The geometrical models allow the prediction of a room s early reverberant response, which will consist of a set of delayed and attenuated impulses. More accurate modeling of absorption and diffusion will tend to fill in the gaps with energy. Linear filters can be used to model absorption, and to a lesser extent diffusion, and allow reproduction of the directional properties of the early response. 

The efficiency of the detection system is based on both detector and sample parameters. Detector parameters include the intrinsic detector efficiency, the geometric relation of detector to sample, scattering by the sample support and nearby material, and attenuation between the sample and the detector. Sample parameters include material stopping power based on composition, mass, diameter and thickness type and amount of sample cover and backing and radiation type, energy, decay fraction, and decay rate. 

The main difference between photochemical and thermal reaction is the presence of a radiation-activated step. The rate of reaction of this step is proportional to the local volumetric rate of energy absorption (LVREA). For any emission model, the LVREA is a function of the spatial variables, of the physical properties and geometrical characteristics of the lamp-reactor system, and some physicochemical properties of the reacting mixture. The most important design parameter that is pertinent in photochemical and photocatalytic reactions is the effective attenuation coefficient. 

Sound attenuation is defined as the decrease in intensity of the sound signal as it propagates from the source to the receiver. This definition does not, however, include the change in intensity due to geometrical spreading of the sound wave (such as, for example, the spherical spreading of the sound in the far field of a finite... 

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