a. For detailed sector shielding calculations, the following shall be done:
1. Assume that the influence of material type is negligible, and the different materials can be approximated to the equivalent mass of a single material type (such as aluminium) by a proportional change in density.
2. Agree with the customer the specific sector shielding calculation method to use.
NOTE A summary of possible methods to use is presented in ECSS-E-HB-10-12 Section 5.
3. If sectoring calculation is applied, assess if one of the following cases is present:
(a) Performance of graded shields, dose enhancement in a semiconductor die close to materials with high-Z elements, or high-Z packaging materials, or X-ray bremsstrahlung dose in a location shielded by tantalum.
NOTE 1 Examples of these elements are gold, hafnium, tungsten.
NOTE 2 The reason is that sector shielding approach does not consider the physics involved in these phenomena. For graded shields see ECSS-E-HB-10-12 Section 5.
(b) The calculation includes assessment of secondary hadron levels from materials with significantly different (atomic) mass number from the original target material.
NOTE 1 For example: Neutrons generated by high-energy proton interactions in lead.
NOTE 2 This is particularly important for neutron fluxes or cosmic-ray fragments in heavily shielded manned missions or in sensitive scientific instruments.
4. If the assessment specified in requirement 6.2.3a.3 is positive then either:
(a) analyse the case ensuring conservatism in the sector shielding evaluation, or
(b) perform the shielding calculation based on a radiation transport model in accordance with clause 6.2.4, which use the characteristics of the actual materials employed.
5. Use one of the following approaches for the calculation:
(a) Agree with the customer the method for the particular sector shielding evaluation, or
(b) use the “SLANT” approach for calculating the amount of material along a path, and the solid sphere geometry for production of the dose-depth or fluence-versus-depth curve, or
(c) use the “NORM” technique for estimating the amount of material along a path, and the spherical shell geometry for production of the dose-depth or fluence-versus-depth curve.
NOTE
The transport model specified
in clause 6.2.4 considers the actual materials employed. Such
calculations can be performed using, for example, a finite-difference coupled
electron-photon simulation or a
6. Provide to the customer a description of the calculation techniques used, including the:
(a) description of the sector shielding simulation method used.
(b) number of directional rays sampled
(c) dose-depth geometry type.
(d) results of the calculations
7. For protons and heavier ions, use the projected particle range for the calculation of the attenuation of the particle flux.
NOTE In ground based mono-energetic irradiation, particle straggling can result in an underestimation of particle effects. Extrapolated ranged can be more appropriate.
8. For sector shielding calculations, use a minimum of 1800 rays evenly distributed over 4p steradians.
NOTE Sector shielding can be used to compute a shield distribution, rather than direct computation of radiation effects parameters. This can be a useful way of using shielding information for a number of subsequent analyses. Therefore it is important to ensure sufficient resolution of the shielding distribution (which is dependent upon the geometry and the specified precision). In such a situation, the considerations outlined above apply also for the subsequent analyses.