How much higher is the radiation around Jupiter than at Chernobyl, after the explosion?

Question

I suppose the radiation levels are higher at Jupiter, but how much? Would the Juno probe have been able to "operate" on the Chernobyl roof in $12\,000\, {\rm Roentgen/hr}$?

After watching the short series Chernobyl, I was curious how the radiation levels compare with that around Jupiter (generally), and what the Juno probe in particular have to withstand, but I couldn't directly compare the numbers I found.

In the Chernobyl accident, the reactor explosion causes pieces of graphite to fall on the roofs of the reactor building, and they describe that they can't push them off with remote-control machines because the radiation damages the circuits.

In the series, the value given for the most dangerous roof is $12\,000\, {\rm Roentgen/hour}$.

The Juno probe's radiation vault is a titanium box with ${\rm 1.75cm}$ thick walls, and the article says

But this orbit would still expose an unprotected probe to a radiation dose of more than 20 million rads [...] over the course of its mission.

The mission was planned for 14 Earth months but the probe only spends short periods of time around Jupiter.

Perhaps someone has an idea how to fill in the gaps and help to make a comparison.

Answer 1

Let's first quickly estimate whether the numbers by HBO's TV series make sense: According to gesundheit.ch/strahlung the liquidiators were exposed to $2 \ldots 20 {\rm Sv}$ which compares to a life dose of $\approx 100 {\rm mSv}$ for usual people. I remember from my education that each worker was supposed to spent only ${\rm 40s}$ on the roof of the reactor. Assuming a dose of ${2 \rm Sv}$ in ${\rm 40s}$ corresponds to ${\rm 180Sv/h}$, so the value of ${\rm 12\,000R/h=120Sv/h}$ makes sense.

On the other hand, you give an absorbed dose of $20 \cdot 10^6 {\rm rad}=2 \cdot 10^5{\rm Gy}$ which is a physical quantity. However, the dose equivalent in Sievert quantifies the biological effect (of the deposit of a joule of radiation energy in a kilogram of human tissue), see https://www.ncbi.nlm.nih.gov/books/NBK230653/

${\rm 1 Sv}$ is the amount of radiation necessary to produce the same effect on living tissue as ${\rm 1Gy}$ of high-penetration ${\rm 200 keV}$ x-ray

Only if we incorrectly assume that the composition of the radiation on the roof Chernobyl in April 1986 and on Juno's flight path are comparable, we could proceed with cross-multiplication by setting ${\rm 1 Sv= 1 Gy}$.

But this (wrong) assumption is not enough, we also need a time frame for your Gedankenexperiment: If we assume that the radiation dose would remain constant (aka reactor core being exposed) at the lower bound of ${\rm 120 Sv/h}$, the maths gives $2 \cdot 10^5 \frac{\rm J}{\rm kg}/ (120 \frac{\rm J}{\rm kg \cdot h}) = 1\,666.7 {\rm h}$ which is a bit more than 69 days of survival for the Juno probe on the roof of a burning nuclear reactor. Realistically, I assume the probe would stop working much earlier.

Further reading

You might also find the presentation Charged Particle Fluxes and Radiation Doses in Earth-Jupiter-Europa Spacecraft’s Trajectory by M. V. Podzolko et al. interesting which gives quite a few estimates on radiation dose around Jupiter.