Self-shielding factor

The self-shielding factor s corrects for the fact that the target (emitter) is thick, as a result of which the flux in the emitter is depressed. Thus, interior atoms are shielded from exposure to the full flux by the atoms close to the surface. The... 

Figure 14.27 The self-shielding factors for rhodium detectors with 10-mil (0.254-mm) thick MgO insulator (from Ref. 68).

The special features of the unified cross-section are (a) use of the latest JENDL-3.2 library-based cross-section set and corresponding covariance data, (b) application of various integral parameters besides JUPITER data, such as MOZART and FCA critical experiments, JOYO and MONJU reactor data which include bumup and temperature characteristics, and (c) extension of adjusted nuclear data to self-shielding factors and scattering matrix components. 

Doppler reactivity is the other important parameter in FBR cores because it assures the intrinsic safety characteristics of the core. The present cross-section adjustment method cannot treat the Doppler reactivity which is dominated by resonance-peak broadening of cross-sections. We have launched a new study to extend the applicability of the cross-section adjustment and design accuracy evaluation system to the Doppler effect. The basic method to evaluate sensitivity of self-shielding factors has been successfully derived from a generalized perturbation theory, and a prototype system to calculate the Doppler sensitivity is now under verification. 

It is customary to introduce a self-shielding factor, G, which is the ratio of thick target-to-thin target rates. For a thick foil or slah in a collimated heam, this self-shielding factor is... 

For a foil in a diffused isotropic radiation field, the self-shielding factor is given by ... 

Calculations used a two-dimensional model based on the KARE diffusion theory code and WOXX three-group cross sections. Homogenization (self-shielding) factors were determined from fine structure calculations using the Tranvar thermal transport code. Several other cross section schemes and transport codes in common usage were also Investigated, but no significant differences were noted. 

The analysis of the measurements was accomplished using first-order perturbation theory in two dimensions, using ENDF/B-68 cross-secUim data and corrected for resonance self-shielding. The corrections were determined from a of the self-shielding factor vs Op, where Op was calculated for each sample in the cell environment. Further corrections were applied to the B... 

For the cases to which the first-flight transport model is applicable, there is a relation between the transmission coefficient a and the over-all self-shielding factor/o this is... 

J. Dwork, P. L. Hofmann, H. Hurwitz, Jr., and E. F. Clancy, Self-shielding Factors for Infinitely Long, Hollow Cylinders, KAPL-1262, Jan. 10, 1965. 

If a sizable fraction of the neutrons incident upon an absorber are non-isotropic in distribution, the expressions developed in the first part of this section for determining the flux inside the absorber, and therefore also the self-shielding factors, will be invalid. The correct calculation of these quantities, although straightforward, is laborious. 

Ingamm 3, a Code for the Calculation of Self-shielding Factors of Resolved Resonances using Collision Probability Methods. Not published. 

The thermal-neutron self-shielding factor of the foil, a, is computed by diffusion theory. This factor is based upon an isotropic flux it is therefore implied that the foil was irradiated in a medium having good scattering properties for thermal neutrons. The calculation of the self-shielding factor is considered in Appendix C. 

The ratio of actual reactions in the foil to those which would have occurred if the flux had remained constant at 0o throughout the foil is known as the self-shielding factor of the foil, a ... 

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