# The Naked Scientists Forum

### Author Topic: How radioactive are people?  (Read 1736 times)

#### Atomic-S

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##### How radioactive are people?
« on: 06/12/2015 02:03:51 »
How many particles of ionizing radiation are emitted by the human body per second, due to natural radioactivity?

#### chiralSPO

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##### Re: How radioactive are people?
« Reply #1 on: 06/12/2015 02:14:47 »
My guess would be that most of it would be from potassium. According to wikipedia, 0.012% is 40K, which has a half life of 1.25x109 years. Also from wikipedia, a typical adult has approximately 140 grams of potassium in their body. That works out to about 2.6x1020 atoms of 40K. You do the math :-)

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#### Atomic-S

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##### Re: How radioactive are people?
« Reply #2 on: 06/12/2015 03:09:41 »
Well, if we have a disintegration once every 0.3 milliseconds, then after 1.3 x 1020 atoms have thus disintegrated (which is half the number in the body), we would end up, I calculate, with a total elapsed time of 3.9 x 1016 seconds, i.e. 1.25 x 109 years. That is "hotter" than I would have expected, indicating we are all surrounded by an aura of our own radioactivity. I am somewhat surprised we are still living.

#### Atomic-S

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##### Re: How radioactive are people?
« Reply #3 on: 06/12/2015 03:25:58 »
A detector such as a Geiger counter, near someone, would intersect the radiation at much less than 100% of it because it occupies only a small solid angle with respect to any one part of the body. Taking that into account, the rate of detected radiation using such an instrument would be much less.

#### evan_au

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##### Re: How radioactive are people?
« Reply #4 on: 06/12/2015 06:18:27 »
Quote
we are all surrounded by an aura of our own radioactivity. I am somewhat surprised we are still living.
Each of our cells suffers about 10,000 instances of DNA damage per day
Fortunately, our cells have some efficient mechanisms for repairing DNA.
And, as a safety net, our cells have a mechanism called apoptosis, where if the DNA repair fails, the cell commits suicide.

Cells which accumulate sufficient unrepaired damage are likely to turn cancerous. And a considerable fraction of humans do suffer some form of cancer at some point in their lifetime.

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#### chris

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##### Re: How radioactive are people?
« Reply #5 on: 06/12/2015 09:30:47 »
Thought-provoking question and some really nice answers! The irony of the username of the person who posed the question wasn't lost on me either!

#### alancalverd

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##### Re: How radioactive are people?
« Reply #6 on: 06/12/2015 16:54:40 »
For what it's worth, a fetus receives about 1 millisievert of radiation dose from maternal potassium. This is equal to the annual dose limit for a member of the public from radiation arising from "work practices", and the dose limit to a fetus from its mother's work.

Just for fun, I use a package of "Lo-Salt" (other brands are available) salt substitute to demonstrate radioactivity to my lecture classes. It sends my contamination monitor into "alarm" condition every time. So much for government health warnings.
« Last Edit: 06/12/2015 16:57:30 by alancalverd »

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#### chris

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##### Re: How radioactive are people?
« Reply #7 on: 06/12/2015 23:47:34 »
Sounds like a fun demo. I'd  like to see that!

#### Atomic-S

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##### Re: How radioactive are people?
« Reply #8 on: 14/12/2015 06:38:22 »
Wow; I had no idea.

#### Atomic-S

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##### Re: How radioactive are people?
« Reply #9 on: 14/12/2015 06:47:47 »
I wonder if there is any reliable estimate of what fraction of cancers arise from natural radiation.

#### alancalverd

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##### Re: How radioactive are people?
« Reply #10 on: 14/12/2015 09:07:54 »
Each hour human cells undergo 100 times more spontaneous DNA damaging events than would result from  natural background radiation. So as a first estimate, about 1%.

There is an interesting confounding factor. Within the range of UK background radiation, from about 2 to 10 millisievert per year, there is no detectable correlation with life expectancy. A survey in the USA, comparing life expectancy in Colorado (up to 30 mSv/yr) with matched cases in the Appalachian range (around 4 mSv/yr) found that the Colorado population actually lived longer. This may be an extreme example of "hormesis", a mechanism by which background radiation actually "weeds out" mutant cells that are replicating too quickly: it supports the suggestion that evolution is aided by a low level of background radiation.

#### vhfpmr

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##### Re: How radioactive are people?
« Reply #11 on: 14/12/2015 22:51:53 »
Three years ago I was injected with technetium for a perfusion scan, they tell you to keep away from pregnant women and children for a day or two after that.

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##### Re: How radioactive are people?
« Reply #11 on: 14/12/2015 22:51:53 »

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