[ExI] Fish in space

John Clark johnkclark at gmail.com
Mon Mar 20 00:53:32 UTC 2017

On Sun, Mar 19, 2017 at 5:53 PM, Adrian Tymes <atymes at gmail.com> wrote:

​>> ​
> On the surface of the Earth you get
>> about 2.4
>> mSv
>> per *year*
>> from normal
> ​​
> background radiation
> ​> ​
> Is that 100 mSv over a certain duration?

Over a lifetime. ​The survivors of Hiroshima and Nagasaki who received more
than 100 mSv were more likely to develop solid cancers than the general
population of Japanese, but those who were under 100 mSv were not. Those
who received a massive dose of 2000 mSv were 7.9 times as likely to get
Leukemia as the general population of Japanese; If things were linear then
those who received half that amount, 1000 mSv, should be be 3.95 times as
likely to get that disease but instead they were only 2.1 times as
likely. Strangely if they got 200 mSv they were 4% *LESS* likely and with
100 mSv they were 17% *LESS l*ikely to get Leukemia.

For obvious reasons large human studies on this are rare but there are a
few others. A study was done on 71,000 people who were shipyard workers
between 1957 and 1981, they were divided into 3 categories, a high dose
group received more than 500 mSv, a low dose group that received less than
200, and a control group of shipyard workers that didn’t work on nuclear
ships and so received no excess radiation. Actuarial studies show that the
high radiation group had a 25% *LOWER *death rate than the control no
radiation group; the low radiation group had a bigger death rate than the
high radiation group but it was still lower than the zero radiation control
group of shipyard workers.

In 1983 steel bars used in the construction of 180 apartment buildings in
Taiwan were accidentally contaminated with Cobalt 60, it took about a
decade for this to be discovered and in the meantime 10,000 people were
exposed and some residents received as much as 500 mSv each year, the
average was 50. In a group of people that large you’d expect that 232 would
die from cancer by now if there was no Cobalt 60 in the steel,  but the
astonishing thing is that only 7 people died of cancer. In addition you'd
expect 46 birth defects, but the actual number was 3.

Also, radiologists spend their lives exposed to X rays, but they have less
cancer and a lower death rate than other physicians. People who became
radiologists between 1955 and 1970 had a 29% lower cancer rate and a 32%
lower death rate than non-radiologist physicians.

The major difference between these studies is that the Hiroshima and
Nagasaki people received their millisieverts
in a fraction of a second while the shipyard
, Taiwan apartment dwellers, and radiologists received their
over a period of years or decades. A spaceman's exposure would be somewhere
in the middle of that range. My hunch is that very short very intense
exposure is more dangerous than much less intense exposure over a much
longer time even if the number of millisieverts
is the same, but it's only a hunch.
​ What's clear is the radiation harm-function is far from linear. ​

> ​> ​
> Otherwise, at 2.4 per year, you'd reach your lifetime cap in about 42
> years - and many, many people live to well past double that.

​Yes, and maybe that's one reason old people are more likely to die than
young people, or maybe not.

John K Clark  ​
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