[cnvogel]

In my day-job, I (help) design electronics that is subjected to (much less) radiation, and we also irradiate our devices to check for long-term effects (and this is done with a comparable doserate in a facility for this purpose).

Damage to your electronics in practice is almost exclusively caused by Photons (convention is to call this γ-Radiation when caused by radioactive decay in the nucleus, X-Rays when created in an accelerator). β-radiation (fast electrons) is easily shielded by thin layers of metal, and α (He nuclei) can't penetrate sheets of paper.

Individual photons can't really deposit much energy at a single location in your semiconductor, so they aren't able to generate enough charge to "flip bits" instantly. Flash still uses a lot of charge/bit, so it's relatively stable, DRAM is constantly refreshed and SRAM would need a jolt of high current to flip, so that does not really happen, either.

What radiation does, however, is to slowly damage the Silicon and change its crystal structure (introducing defects) which increases leakage and moves the analog threshold voltages of circuits around in a funny way. So, what we often see is flash becoming un-programmable on a more global scale (rather than individual stuck bits), and most importantly the analog aspects (voltage references, brownout-protection circuits, voltage regulators) cease to function.

This is all very variable, but we normally observe effects starting at "a few 100 Gy" when testing more complicated modules. We don't research individual components, though.

One especially nasty type or radiation are neutrons, though. When being "moderated" (slowly decelerated by successive interactions with material) they tend to have a high likelihood of merging with some other nucleus (being captured), and the energy resulting from this capture effect can be huge and concentrated on a single spot. This can be enough to flip bits, and this indeed may be an issue near the funny isotope mixture present in Fokushima at various places. Having a strong neutron emitter is very uncommon, though.

Unfortunately these damages are not specific to digital electronics, and especially optical components (parent refers to long fibre cables) tend to be rather sensitive due to their large structures, so "keeping the computers out" may not help much overall.

[Pica_soO]

I dimly remember reading about a chemical treatment to the material, that would react with the ionized silicon until the reaction was depleted. I do not remember the substance- and it was ridiculous expensive (in addition to the ridiculous expenses of custom made chips)

https://en.wikipedia.org/wiki/Radiation_hardening#Physical

[ethbro]

So, simple question: why isn't everything electronic shielded inside big lead blocks?

I get why this isn't the prevailing approach in aerospace applications: weight. But for a ground based robot with an external power source, why not heavy shielding cubes with minimal connections to the necessary exposed bits?

And why not just load it down with 5x CotS sacrificial cameras, then expose them as needed when the previous one dies?

[cnvogel]

For typical Gamma radiation of about 1MeV photon energy or higher, you need about 1cm thickness of lead to reduce the radiation to about a third (by a factor of 1/ℯ). One order of magnitude of radiation hardness (reduce radiation to 1/10th) needs two centimeters of lead. That's getting heavy pretty fast.

Radiation intensity inside your box depends on the thickness t: I(t) = I₀·exp(-tρμ)

t: thickness, say 1 cm ρ: density of the material, for Lead 11 g/cm³ μ: absorption coeffcient 0.1 cm²/g [see ref 1] I₀: intensity outside of the box

    ...import numpy as np...
    In [5]: np.exp(-0.1 * 11.34)
    Out[5]: 0.32174370422037013

I(1cm) = 32,2%, I(2cm) = 10,4%

[1] http://www.eichrom.com/PDF/gamma-ray-attenuation-white-paper...

[choonway]

Everything had to fit into a 100mm diameter pipe leading into the containment vessel.

https://youtu.be/rQVT9beES08?t=27s

[Retric]

In this case there is zero need for electronics on the robot. You can have a pure mechanical system with a fiber optic camera etc like a endoscope. Power as torc through a plumbers snake. It can then either carry a box with some sensor package, or take remote samples. For extreme radiation, you can put a Film badge dosimeter in a water tub to work out the radiation levels indirectly.