In my last physics exam, I asked how many bananas would it take to deliver a fatal dose of radiation. This question came up when we were discussing different types of radiation and looking at this graph. One banana gives you about 0.1 microSieverts, while the usually fatal dosage is about 4 Sieverts. That means 4 million bananas. Michael Blastland uses the instantly fatal dosage of 8 Sieverts to make his estimate of eight million.
My students were insistent, “Would eating four million bananas really kill you with radiation?”
My answer was, “Yes. But other problems might arise if you try to eat four million bananas.”
I believe your math is off.
It’s .1uSv (78nSv actually). In any case .1uSv == .1e-06Sv == 100e-09 == 4/100e-06 == 40e06 or 40M (million). With the more accurate 78nSv figure it’s more like 51.28M.
Likely a result of the typo of your initial graphic. The xkcd image snippet has the acceptable .1uSv but you have 1uSv in the caption. Seems like you used 1 instead of .1 for the calculation.