For folks who might be interested in more details on this: The _cross section_ allows you to quantify the frequency of a specific event occurring in your chip when bombarded by a specific particle (or class of particles). For example, in a case of an SRAM, you might want to calculate the cross-section for bit flips due to 24-GeV protons. The result that you get will be in units of cm^2; you can also interpret it as the physical surface area of the chip, multiplied by the probability (0..1) that any 1 particle passing through will trigger an event. Let's say you measure a cross section of 0.01 mm^2. Then if you expose that component to a flux of 10^3 particles/cm^2/sec, you will get an average of 1 event every 10 seconds.
The cross-section is only valid for one combination of the (event type, particle, energy) tuple. But often in dosimetry, errors on the order of 20% are acceptable, so we can "abuse" the results a bit. Within one manufacturing lot of chips, the cross-sections should be reasonably consistent. Typically you would estimate the mean and variance by measuring a few samples from the lot.
Then, to accurately measure a radiation field using these findings, you would generally need to measure the flux of every particle-energy combination separately. This is impractical, and for SEE* concerns we generally get away with distinguishing thermal neutrons and high-energy hadrons (which are separated by several orders of magnitude in energy). For this, it is sufficient to have 2 types of SRAM where each has a dominant cross-section for one of the particle classes of interest.
To measure the type of radiation that causes long-term gradual damage (TID) such as X-ray and gamma rays, you would use a different principle of measurement altogether (RadFET, P-i-N diode, floating-gate dosimeter...)
Radiation measurement can be fun!
[*] single-event effects, including bit flips and latch-ups
For folks who might be interested in more details on this: The _cross section_ allows you to quantify the frequency of a specific event occurring in your chip when bombarded by a specific particle (or class of particles). For example, in a case of an SRAM, you might want to calculate the cross-section for bit flips due to 24-GeV protons. The result that you get will be in units of cm^2; you can also interpret it as the physical surface area of the chip, multiplied by the probability (0..1) that any 1 particle passing through will trigger an event. Let's say you measure a cross section of 0.01 mm^2. Then if you expose that component to a flux of 10^3 particles/cm^2/sec, you will get an average of 1 event every 10 seconds.
The cross-section is only valid for one combination of the (event type, particle, energy) tuple. But often in dosimetry, errors on the order of 20% are acceptable, so we can "abuse" the results a bit. Within one manufacturing lot of chips, the cross-sections should be reasonably consistent. Typically you would estimate the mean and variance by measuring a few samples from the lot.
Then, to accurately measure a radiation field using these findings, you would generally need to measure the flux of every particle-energy combination separately. This is impractical, and for SEE* concerns we generally get away with distinguishing thermal neutrons and high-energy hadrons (which are separated by several orders of magnitude in energy). For this, it is sufficient to have 2 types of SRAM where each has a dominant cross-section for one of the particle classes of interest.
To measure the type of radiation that causes long-term gradual damage (TID) such as X-ray and gamma rays, you would use a different principle of measurement altogether (RadFET, P-i-N diode, floating-gate dosimeter...)
Radiation measurement can be fun!
[*] single-event effects, including bit flips and latch-ups