How about reading the engineering bulletin below, pity the poor customers that had a detector blow up when out in the field.
PS NO RECALL...................
Under certain conditions (fully charged LiIon battery, unit switched off and back on in less than 30 seconds), as the internal voltages ramp up, the FET Q108 can be turned on for a few milliseconds and get destructed by the remaining charge in C145. The investigation done as part of the GD project has lead to a solution which can be also applied to the GPX4500 and GPX4000 products. It should be noted that the problem is not due to the FET itself, but to the circuitry. Therefore, replacing the FET alone will not solve the problem and the circuit modification described below must be implemented.