Half-value thickness

Isotope PET/SPECT Decay mode (%) Half-life (min) (max/most abundant) (half-value thickness) reactor (R), generator (G)... 

Figure 6 RBE variation of neutron beams as a function of energy. The p(65) + Be beam of Louvain-la-Neuve is taken as reference (RBE = 1). The closed squares and circles correspond to six different visited neutron facilities. The open squares and circles correspond to beams produced at the variable-energy cyclotron of Louvain-la-Neuve. On the abscissa, the effective energy of the neutron beams is expressed by their half-value thickness (HVT 5/15) measured in specified conditions. Intestinal crypt regeneration in mice, after a single fraction irradiation, is taken as the biological system. The 95% confidence intervals are shown. A straight line is fitted through the points (squares) corresponding to neutron beams produced by the (p + Be) reaction. For comparison, the neutron beams produced by the (d + Be) reaction are represented by circles. (From Ref. 22.)...

The linear attenuation coefficient ji is closely related to the so-called half-value thickness Dj/2, which reduces the intensity of a narrow X-ray beam to one-half of its original value (/i = 0.693/Di/2). 

Shielding effectiveness varies with the shielding material. The unit of measure for the attenuation properties of materials is half-value thickness. One half-value thickness will cut the energy level of radiation arriving at the material to one half as it leaves the material after passing through it. The amount of radiation absorbed, 7 , and the amount transmitted, Rt, are given by... 

Material Radiation Type Half-Value Thickness Attenuation Coefficient... 

What is a half-value thickness and for what means of control is it used ... 

A useful shield thickness to know is the half-value thickness, that is, the thickness of shielding required to reduce the incident radiation intensity to one half of its previous value. If radiation surveys have been performed to determine the dose rate in a given area, quick estimates of the amoimt of shielding needed to reduce the dose rate can be made... 

Because attenuation is exponential, the effect of different shields can be evaluated by use of "half-value thickness" or "tenth-value thickness."... 

Thin membranes have the advantage of low area specific conductivities and more favorable back diffusion of water in comparison with thicker membranes. In the former case, this means that membranes with lower conductivity values could be tolerated. Analysis of voltage loss versus membrane thickness and specific conductivity has revealed that, if a membrane voltage loss of 25 mV at a current density 1 A cm can be tolerated, then existing materials with conductivity values similar to Nation (0.1 S cm i) could be prepared as 20-30 pm thick membranes. However, thinner membranes also typically exhibit lower mechanical strength than their thicker counterparts and can therefore fail earlier. Therefore, future materials might be suitable with just half the specific conductivity if they can be prepared into membranes of half the thickness and still possess sufficient mechanical strength. ... 

Figure 5.8 Log-log plots of the depletion time and time for the surface potential to decay to its half-value fj/2 versus charging voltage Vq for an amorphous Se Te 13 wt% photoreceptor film of thickness 70 pm (from Ref. [8]). The inset shows the dependence of the depletion time on the Te content (from Ref. [9]).

Half-value layer. It is that thickness of a given material (i.e. shielding) required to reduce the exposure rate from a source of gamma or x-rays to one-half of its unshielded value. 

An important quantity in the discussion of photon interaction with matter is the half-value layer (HVL), which is defined as the thickness of the absorber that attenuates an initial photon beam intensity to one-half. The HVL increases with higher energy of the photon and decreases with increasing atomic number of the absorber. Lead is a high atomic number inexpensive metal that has very high absorbing power for 7 radiations providing low HVL values and that is why it is commonly used for radiation protection. The HVL... 

Half-value layer (HVL). The thickness of an absorbing material required to reduce the intensity or exposure of a radiation beam to one-half of the initial value when placed in the path of the beam. 

The dimensionless spatial coordinate rj is measured in the thinnest dimension of rectangular catalysts. For cylindrical and spherical catalysts, r] is measured in the radial direction. The characteristic length L which appears in the intrapellet Damkohler number and is required to make the spatial coordinate dimensionless (i.e., rj = spatial coordinate/L) is one-half the thickness of catalysts with rectangular symmetry, measured in the thinnest dimension the radius of long cylindrical catalysts or the radius of spherical catalysts. q A is the molar density of reactant A divided by its value in the vicinity of the external surface of the catalyst, CAsurf- Hence, by definition, q A = 1 at r = 1. 

Lakshmanan (1992) has fitted a CaSOa.Dy badge for simultaneous measurements of peak voltages, half-value layer thickness and exposure to diagnostic X-rays. This TLD badge is used in India for 3, y and X-ray personnel monitoring. 

Not only does intact or disrupted morphology of the slices correlate with their electrical activity, but also with their ability to synthesize acetylcholine. Rather surprisingly, 300- xm slices maintained at 36°C for 2 hr contain 10 times as much acetylcholine (ACh) as a similar slice in vivo (Weiler et al., 1979). At room temperature, in vitro levels of acetylcholine are reduced to half. In thick slices, ACh levels never attain these higher values, but they are still in excess of those in vivo. 

The half-value layer (HVL) of shielding material is a useful concept and is the thickness of a specified material that will cut down the incident radiation by one-half. For iodine-125 with an energy of 0.033 MeV, the HVL is 0.002 cm of lead for iodine-131 with an energy of 0.364 MeV, the HVL is 0.25 cm of lead. 

Copper thickness is assumed 35.6 pm (0.0014 in.) thick for 1 oz. copper or possibly 34.3 pm (0.00135 in.). Two-ounce copper is considered twice those values and half the thickness for V2 oz. copper. IPC 2221 specifies the minimum acceptable copper thickness for an internal layer as shown in Table 16.4. The minimums are significantly less than what designers may think and should be considered when pushing current limits on small trace widths. For example, 1 oz. is... 

Even though the rigid adherend idealization is reasonable for steel adherends joined by an epoxy adhesive, a noticeable deviation occurs when steel is replaced by aluminum [42]. Table 2 shows that the strength of the stress singularity decreases from —0.32 for rigid adherends to —0.30 for steel adherends to —0.27 for aluminum adherends (for an epoxy with E = 3.5 GPa, v = 0.35). Table 2 also lists A(a,j3) values for these three adherend materials. Once again the characteristic length scale is the half-bond thickness (h in Fig. 2) and the characteristic stress... 

HALF-VALUE LAYER The thickness of a particular material necessary to reduce the intensity of an X-RAY or GAMMA RAY beam to one-half its original intensity. 

The column with i/s6h values demonstrates that only a fraction of the maximum available surface participates in the H2 oxidation. Otherwise the factor of 10 by which i/sQu differs for FC 100 and SM 2 should have a greater effect on the values of the ratio i/(Pt content). While the electrode CAAl has a similar porosity as the electrodes SM 2 and SM 1 and about the same mean hydraulic diameter as SM 1, its thickness is about half the thickness of the other electrodes and the ratio (Pt con-tent)/sQH is the smallest. The same limiting current and the same current-potential curve were obtained [12] when several thicknesses of electrode were compressed and used as one electrode. This result rules out any effect of the thickness on performance and suggests [12] in connection with the small ratio (<0.05) between the double layer capacity of the same electrode under diffusion conditions and in the flooded state for elec-... 

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