[time-nuts] How dangerous if a Rb lamp broken?

Chuck Harris cfharris at erols.com
Wed Jul 10 12:48:06 EDT 2013


In brief,

Gamma rays are just another form of light... that is to say photons.  What makes
them special is they are much higher energy than visible light.  What makes them
potentially dangerous is they have enough energy to knock electrons off of many
atoms, turning them into ions that could combine chemically in your body in ways
that wouldn't normally happen.  If it happens to the right molecule... say a DNA
strand... it could cause a mutation that could result in cancer.  Most such
mutations result in premature cell death, and are harmless... unless there
happens to be millions of them all at once.

Your body is mostly water.  Somewhere around 45 to 60% by weight.  The rest of
your weight are minerals and things like bone.

The molecules in your body are mostly free space... that is to say vacuum... a high
energy gamma photon is more likely to pass right on through your body than to
hit anything. And if it does hit something, it is most likely going to be water,
or bone.  Think back to the last time you had an X-Ray.  What showed up?

When you look at a normal light source, say a candle, what you are seeing is a spray
of photons radiating out in all directions from the source.  There are so many
photons that the light source appears to your eye to be continuous.  When a light
source gets small enough, it appears dim, and if it is dim enough, it starts to
appear grainy.  The grains you see are individual photons.  Your eye doesn't see
all of the visible photons that strike it, perhaps only 50%...

Eyes are amazing!

One of the earliest ways of measuring radioactivity was the geiger-muller tube.  It
can count individual gamma photons that strike the tube.  Even still, some of the
gamma photons will pass right through, and not be counted.  It catches about 30%, as
I recall.

A source like a radium dial watch will make a geiger counter clatter pretty good,
but you can still hear the clicks caused by individual photons.

If the radioactive source was emitting photons at the same rate as a candle, the
geiger counter tube would be completely overwhelmed, and you would not be able to
count the deluge of photons hitting it.

The moral of this story is that the probability of any given gamma photon, that
irradiates a human body, even hitting something is small.  The probability of
anything it hits being more interesting than water is even smaller, and the
probability of it doing dangerous damage is terribly small.

It is only when the flux of gamma photons becomes quite large that these
probabilities start to tip into the direction of likely damage, or cancer.

A tiny, low flux source of radiation, like a radium dial watch, is highly
unlikely to cause you any harm... it could happen, but the odds of it doing so
make winning the lottery look like a sure thing.  The odds drop very quickly
the farther the watch is from your body... its one of those radius squared
things.

-Chuck Harris


Lee Mushel wrote:
> I just tried calling your cell because you seem to be the "legitimate" person to
> ask.   I don't read all the time-nuts postings but has anyone ever brought up the
> most logical aspect of ionizing radiation for the group: the radium dial wrist watch?
> or are they all too young to have experienced that? I think I got one for Christmas
> when I was 12 or 13.   I'm still here at 74! I do think that all reflector's are at
> their best when they are entertaining---maybe not exactly on topic!
>


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