OK, I stand corrected on the alpha/gamma ray front. I was trying to work
out whether the REEs would emit gamma rays, but as an astronomer I've long
since forgotten the physics I learnt about small, insignificant things like
atoms...
But with all this talk about gamma rays, X-rays and other film-fogging rays,
I was just wondering if anyone had ever noticed any effect from airport
X-ray machines? I read a lot about in photo literature, but I've never had
a problem with it (took ISO1600 film in the main luggage to Australia and
back and it looked just fine), and I've never heard of anyone else having a
problem. Is it all a big fuss about nothing?
-----Original Message-----
From: Mark Marr-Lyon <markml@xxxxxxx>
To: olympus@xxxxxxxxxxxxxxx <olympus@xxxxxxxxxxxxxxx>
Date: 07 April 2001 20:43
Subject: Re: [OM] Another radioactive Zuiko!
>As far as I know, Geiger counters are not sensitive to alpha particles
>(helium nuclei), since they don't make it into the tube. They are
sensitive
>to beta particles (electrons or positrons) and gamma rays (high-energy
>photons). Putting a thin piece of metal in between the radioactive element
>and the tube cuts the detected radioactivity about in half. Since the
>electrons shouldn't make it through the metal, this suggests that about
half
>of the radiation is gamma rays. A thin lead sheet has about the same
effect
>as the thin piece of metal, and a thick lead brick stops all the detected
>radiation.
>
>I would guess that the electrons would have no effect on the film, but the
>gamma rays could fog film, similar to x-rays. I would also guess that the
>rate of gamma rays coming out of the lens is many orders of magnitude less
>than a typical airport x-ray machine, so it would take much much longer for
>the lens to fog the film than the airport x-ray machine.
>
>Incidentally, if alpha particles can hit you, they cause more damage than
>beta particles or gamma rays, since they're big and heavy (well, compared
to
>electrons and photons they are). So, eating alpha emitters is definitely a
>Bad Thing, since the emitter would be close to tissue and the alphas could
>then hit it before being stopped. This is why plutonium is so dangerous.
>
>Mark Marr-Lyon.
>
>You wrote:
>> Just been thinking about this. They're radioactive due to Rare Earth
>> Elements in the glass, am I right? These elements emit alpha particles,
>> which do not travel very far or fast. A few centimetres of air is plenty
>> enough to stop an alpha particle, so if the shutter's closed the film is
>> absolutely safe, and even if you were to leave it on B for a month, the
air
>> between the lens and the film would absorb pretty much all the radiation.
>> The alpha particles are also not going to have any effect on the
>> photographer - unless you eat the lens, the particles can't get anywhere
>> where they can do any damage.
>>
>> Of course, if you find that you're sprouting an extra thumb a few years
>> down the line, I'll stand entirely corrected.
>>
>> Roger
>
>
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