8.5.2 Calculation of the DD dose

8.5.2.1 Calculation of the DDEF

a. DDEF shall be calculated from the environmental proton, electron or neutron spectra and the conversion factors for the device type being assessed as follows:

1. Divide the TNID from clause 8.5.2.2 by the NIEL value for the considered material and particle species at the energy required.

NOTE The reason is that the level of displacement damage observed per unit fluence is highly dependent upon the material and the particle energy and species.

2. Calculate the DDEF as a function of equivalent shielding thickness and for each particle (trapped protons and electrons, and solar protons) spectrum estimated for a specified mission.

3. Predict the decrease in performance of a component from tests performed on the component at those mono-energetic energies.

NOTE Typically 10 MeV proton fluences or 1 MeV electron equivalent fluence is used, these are defined based on NIEL values for the considered material and radiation environment specification. If no valid NIEL values are available in the open literature, they are determined following methodologies presented in [4] or [5].

b. The decrease in the component performance shall be calculated from experimental performance test data collected on the component at these mono-energetic energies.

8.5.2.2 Calculation of the TNID

a. TNID shall be calculated by one of the following procedures:

1. If the NIEL as a function of energy, particle type and target material is known, calculate the TNID through the integration over energy of the NIEL function (multiplied by fluence) for each particle species on the target material.

2. Otherwise, calculate the NIEL as a function of energy for the material and particle type following a methodology agreed with the customer and calculate the TNID through the integration over energy of the NIEL function (multiplied by fluence) for each particle species on the target material.

NOTE Methodologies described by Jun et al or Messenger et al [4] [5] can be used for this purpose.

b. Conversion from TNID to component parameter degradation shall be obtained by testing the component to different TNID levels.

c. The same NIEL function shall be used in converting the test particle fluence to the test TNID in requirements 8.5.2.2a and 8.5.2.2b, and the calculation and approach shall be specified.