Coefficient, conversion

T = temperature result from the ASTM D 2887 test a, b,c = are conversion coefficients (refer to Table 4.7)... 

Uncertainty in last digit or digits is shown in parentheses. ICC = internal conversion coefficient. 

The iatensity of a conversion fine can be expressed relative to that of the associated y-ray as the internal-conversion coefficient (ICC), denoted as d. For example, is the ratio of the number of electrons emitted from the K atomic shell to the number of photons emitted. For the other atomic levels, the corresponding conversion coefficients are denoted by (X, The total conversion coefficient is a = n, where the sum iacludes all atomic... 

A sample of theoretical conversion coefficients is given ia Table 12, iUustrating the great range of values. The most common case where two multipolarities compete is Ml + E2. For example, the for Ml and E2 are nearly equal at Z = 60 and E = 150 keV. It is, however, relatively easy to determine the fraction of each of these components that is present if the relative iatensity of the three E conversion fines can be measured. For the E2 portion the three fines are almost equal, = 0.035, = 0.050, and = 0.048, whereas for the Ml portion they change by factors of 10, namely,... 

Table 12. Calculated Internal-Conversion Coefficients for y-Rays ...

In addition to the possible multipolarities discussed in the previous sections, internal-conversion electrons can be produced by an EO transition, in which no spin is carried off by the transition. Because the y-rays must carry off at least one unit of angular momentum, or spin, there are no y-rays associated with an EO transition, and the corresponding internal-conversion coefficients are infinite. The most common EO transitions are between levels with J = = where the other multipolarities caimot contribute. However, EO transitions can also occur mixed with other multipolarities whenever... 

An isotope effect seen in Sb03 by Maddock and Sutin was studied by Hall and Sutin , whose results are shown in Table 3. Again, phenyl radicals were cited as the likely means of reforming the bonds. It was pointed out that owing to the occurrence of isomeric transitions in both of these antimony isotopes, differences in the conversion coefficients could lead to the isotopic differences. 

The influence of the decay scheme on the retention (through differences in the percent conversion of y-transitions) was demonstrated by comparison of the -decay products of Pb and Pb in Pb(CgH5)3Cl. The retention of Bi in Bi(CgH5)3Cl2 was 17—19% and of Bi about 50%. According to Nefedov, this isotope effect is directly proportional to the conversion coefficients of the two isotopes. Corresponding to the complement of the conversion coefficient, 1—a, the molecular structure should be preserved to the extent of 80% for the two isotopes. The probability of chemical reaction for change or preservation of molecular structure is the same for the two cases. 

Work on mercury alkyls has been done by Heitz and Adloff (31-33), who studied Hg(CH3)2, Hg(C2Hj)2 and HgPh2. They found no isotope effect between " Hg, Hg, and ° Hg, and no correlation with the respective conversion coefficients. They also noted that the retentions could not be satisfactorily explained by exchange of the respective ligands, and thus concluded that the molecules are reformed by an epithermal not by a thermal process. Parent yields were typically 74, 15, and 8% for the diphenyl-, dimethyl- and diethylmercury, respectively. 

Not all nuclear transitions of this kind produce a detectable y-ray for a certain portion, the energy is dissipated by internal conversion to an electron of the K-shell which is ejected as a so-called conversion electron. For some Mossbauer isotopes, the total internal conversion coefficient ax is rather high, as for the 14.4 keV transition of Fe (ax = 8.17). ax is defined as the ratio of the number of conversion electrons to the number of y-photons. 

Total internal conversion coefficient Recoil energy (in 10 eV)... 

The first Mossbauer measurements involving mercury isotopes were reported by Carlson and Temperley [481], in 1969. They observed the resonance absorption of the 32.2 keV y-transition in (Fig. 7.87). The experiment was performed with zero velocity by comparing the detector counts at 70 K with those registered at 300 K. The short half-life of the excited state (0.2 ns) leads to a natural line width of 43 mm s Furthermore, the internal conversion coefficient is very large (cc = 39) and the oi pj precursor populates the 32 keV Mossbauer level very inefficiently ( 10%). 

In order to compare exposures to radon decay-products with those to other forms of ionising radiation, it is useful to assess the effective dose equivalent expressed in sieverts (Sv). A conversion coefficient of 15 Sv per J h m"3, equivalent to 5.5 mSv per WLM, has been recommended (UNSCEAR, 1982). With this conversion factor, the... 

On the basis of a conversion coefficient of 5.5 mSv WLM"1, occupants of the vast majority of dwellings in the UK receive annual effective dose equivalents less than 2 mSv. Even in the areas surveyed because of their potential for high radon exposures, the annual effective dose equivalents are unlikely to exceed a few tens of mSv. However, in certain areas of Cornwall and Devon, annual effective dose equivalents higher than 25 mSv may be received in a small percentage of dwellings. In some dwellings more than 50 mSv per year may be received. 

It is noted that the ICRP has assumed a higher conversion coefficient between annual effective dose equivalent and radon concentration (ICRP, 1984) in recommending an action level for remedial measures in homes, i.e. 1 mSv y"1 per 10 Bq m"3 of equilibrium equivalent radon gas concentration (9 mSv per WLM). If this conversion coefficient were applied to our regional survey data, we would estimate, from the distribution parameters given in table 3, that about 15% of the residents of certain areas of Devon and... 

All these conflicts can now be resolved because of what appears to be a deflnitive experiment by Bocquet et al. (4), who directly measured the internal conversion coefficients of the transition from the first nuclear level to the ground state. They directly compared the L, M, N, and O conversion electron intensities in two different states—namely, in stannic oxide and white tin. They found that the 5s electron density is 30% smaller in stannic oxide than in white tin, and since the isomer shift of stannic oxide is negative with respect to white tin, AR is clearly positive. From these data, the Brookhaven group has calculated the value for AR/R for tin-119 as +3.3 X 10". ... 

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. 

The performance test standards used in the NVLAP and DOELAP programs list the applicable conversion coefficients. 

The principal data available to determine or E directly from ifpdO) are conversion coefficients which give the quotient of or E and /fp(lO) [i.e., He/[Hp(10)1 or /[ifp(10)]). The unit for each of the three quantities is Sv therefore, these conversion coefficients are dimensionless. Such conversion coefficients have been derived from calculations for a number of idealized conditions for irradiation by monoenergetic photons of mathematically described reference adult anthropomorphic phantoms. The conversion coefficients are a function of photon energy, photon beam direction, surface of the phantom on which the radiation is incident, and location where //p(lO) is being evaluated on the phantom. 

To use these conversion coefficients directly in practice, one would need to be able to characterize the irradiation conditions in the workplace for a particular situation with regard to the following factors ... 

For those irradiation conditions for which the conversion coefficients are close to a value of 1.0, the value of /fp(lO) recorded by an appropriately placed personal monitor is a practical surrogate for He or E. This case is explored in Section 3.1. 

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) ... 

ICRU and ICRP currently have a joint effort underway to review and present similar conversion coefficients for E, but that work is not yet published. When conversion coefficients are published, a... 

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 first or probability factor is essentially a ratio of partition functions, and represents the integrated equilibrium density of phase points on S per phase point in A. The second or trajectory-corrected frequency factor is the number of successful forward trajectories per unit time and per unit equilibrium density on S. The ratio of this to the uncorrected frequency factor 0) >s represents the number of successful forward trajectories per forward crossing. Anderson called this ratio the conversion coefficient to distinguish it from the transmission coefficent of traditional rate theory (1), which was usually defined rather carelessly and given little attention, because it could not be computed without trajectory information. 

Usually one deals with a system whose equations of motion are invariant under time reversal, and the definitions of the dividing surface and reactant and product regions involve only coordinates, not momenta. Under these conditions (which will henceforth be assumed) the factor ux-(ux>0) in eqs. 4 and 5 can be replaced by lu J, and the frequency factor (and conversion coefficient) will be the same in the forward and backward directions, because every successful forward trajectory is the reverse of an equiprobable successful backward trajectory. One can then use a third form of the function, viz. 

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