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We just received back 3 pieces of equipment that may have been inadvertently put through a Gamma radiation sterilisation process. The equipment is a low-power embedded device consisting of a 16 bit microcontroller with peripheral FLASH memory and SRAM backed up by a lithium battery. The equipment appears completely dead.

What possible effects would Gamma radiation have on embedded devices? FLASH memory corruption? Circuit degradation? Component failure?

More info:

The equipment is three nephelometer instruments that we make, which use a quite expensive COTS logger as the brains. The instruments were sent back to us from overseas along with some sediment samples. Customs / quarantine decided that they wanted to sterilise the sediment samples, and I think they must have put the instruments through as well.

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I can't see gamma radiation being good for flash at all... –  Ignacio Vazquez-Abrams Aug 7 at 1:42
    
Yea its looks that way. Arrgh overzealous Australian customs. –  geometrikal Aug 7 at 1:45
    
I guess that'll teach you to stick to FRAM ;) –  Ignacio Vazquez-Abrams Aug 7 at 1:46
    
Wow, that series just keep getting better and better. –  geometrikal Aug 7 at 1:57
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I guess they were trying to get the bugs out of the code! –  Enemy Of the State Machine Aug 7 at 5:54

1 Answer 1

up vote 7 down vote accepted

The prognosis is probably not too flash [groan].

Depending on energy of radiation, device death ranges from possible to essentially certain.

You can potentially expect all the effects you described.
Even if apparently still operating you may get increased leakage currents and 'general unhappiness'.

What was the gamma source? what energy?, what distance? Why?


Radiation Damage in Electronic Memory Devices PDF
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Says:

... Obtained results show that gamma radiation causes decrease in threshold voltage, being proportional to the absorbed dose of radiation.

EPROM & EEPROM: ... Gamma radiation causes generation of electron-hole pairs in SiO2 insulator of the gate. The number of generated pairs is directly proportional to the energy deposited in material, depending on the total absorbed dose of radiation [8, 14]. ...

Conclusion

... Based on analysis of data gathered from performed experiments, the exposure of semiconductor memories to gamma radiation causes three effects: holes being captured in trapping sites of an oxide, injection of holes from oxide into FG, and emission of electrons through FG-oxide interface.

The generation of electron-hole pairs leads to trapping of positive-charged carriers (holes) in insulator, causing negative shift in characteristics. Namely, positive-charged carriers induced by gamma radiation require the increase of negative gate voltage to compensate the positive charge. It means that gamma radiation causes decrease in threshold voltage, being proportional to the absorbed dose of radiation.

NASA - Chips in space

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If the board only got medium rad and recovers after reload, if "decrease in threshold voltage" may lead to still work but reduced temperature, supply tolerance then still it could 'still be used' in lab, good temperature, education purposes. Not reliable enough if the board controls heavy motor, or similar dangerous stuff. –  EE developer Aug 7 at 3:28
    
See update to the question for more info on what happened. In Australia strict quarantine often results in things getting sterilised. Don't bring in any cuban cigars! –  geometrikal Aug 7 at 3:54
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I don't know the protocols involved in sterilization, but to be honest, I would be surprised if a standard customs sterilization process will have enough gamma intensity to reach the kill level of radiation for semiconductors. That sort of sterilization would likely needs it's own heavy lead containers and so forth to protect the customs folk. Most likely, the levels are those needed to kill bacteria and such, which is much, much lower than what silicon can tolerate. Reprogram all flash and EEPROM, and you should be fine. If you have EPROM in there, then you're out of luck if that got hit. –  Chintalagiri Shashank Aug 7 at 9:03

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