1. By using the formula of Clause 10.4.9.2 if all of the following conditions are met:
(a) the sensitive volume of the sensor and surrounding material producing background in the sensor are so small that the incident particle spectrum changes by less than 10% in either intensity of energy after passing through the volume;
(b) the pathlength distribution in the sensitive volume and surrounding material changes by less than 10% as a result of multiple scattering;
(c) the probability of secondary nuclear interactions is 10 times lower than the primary interaction rate.
2. By a radiation transport simulation agreed with the customer.
NOTE For guidelines, see ECSS-E-HB-10-12 Section 5.7.
b. If method specified in requirement 10.4.4a.1 is used, the following shall be performed:
1. An estimation of the combined effects of the maximum change in energy, intensity and pathlength, and the influence of secondaries on the energy deposition, and
2. A demonstration that the error produced is within the accepted margins defined for the project.
c. The nuclear interaction rate shall be convolved with relevant response function spectra to radioactive decay in the sensitive volume and surrounding materials, to determine the background count rate in the sensor.