From: knapp@ucsu.Colorado.EDU (David Knapp)
Subject: Re: P32 b-emmissions -> gammas?
Organization: University of Colorado, Boulder
Date: Fri, 24 Jul 1992 05:57:11 GMT

In article <1992Jul23.131714.22226@nmsu.edu> tbaker@nmsu.edu (Trevor Baker) writes:
>I'm putting this to sci.chem for my brother who doesn't have net
>access.
>
>He is working at a lab which is using P-32 in common doses of 5 mC, but
>they would like to use 15 mC.  They are working behind a plastic
>shield, I guess its just thick plexiglass.  One of his co-workers
>suggests that the b-emission from the P-32 is causing gamma particles
>to be emitted from the shield.

*highly* unlikely. Shoot, ok, I'll say it... he's wrong. Now watch,
I'll have missed something ;-/

Do you mean 15 milliCuries or 15 microCuries?  15 milliCuries is a goodly
amount of material.

>The X-ray emission from the plastic is
>high enough to be picked up with a survey meter, but the co-worker
>holds that not all that is being picked up is X-ray.  Comments on any
>of this ?

The xrays are coming from something else. It'd be good to find out, if
it is higher than background noise from cosmic radiation, where it's
coming from .

I would be *very* surprised if betas coming several or many inches from a 
source to a shield would have enough energy for x-ray production let alone
gammas.

What was the distance?
 
Gammas are a photon, not a classical particle like a proton or electron. 
Better not to call them 'particles'.

I find it hard to believe that there is a high enough cross section in 
plexiglass to creat bremsstrahlung xrays. Brehmsstrahlung radiation
is typically produced (terrestrially) by interactions with rather dense
materials like lead or other metals. In the hospital xrays, it is (or
was)  beta impacts with Aluminum that gave the xrays.


>He wanted me to look up Brehmstallung (sp?) X-rays from P-32 b's in my
>old nuclear chem book, but I don't have it anymore.  I would go to the
>campus library to look it up, but all the books are being split
>between 2 buildings now and its a big mess.  I've seen that we have a
>few nuclear/radio chemists (.sig) and was hoping someone could fill me
>in.  Any comments would be appreciated :)

Brehmsstrahlung is how xrays can be produced, but I doubt there is enough energy
after traveling through several inches of air, to allow xray production.
P32 has a decay energy of ~1.7 MeV which is nothing to sneeze at but which 
cannot travel far through air without getting slowed.

Gammas are generally a result of nuclear processes and not due to accelerating
charges, save exotic phenomena like black holes.  I would be interested to
hear a mechanism whereby betas impact plexiglas yielding gammas.

Seeing as how the radiation count will drop off with the square of the distance,
it would make sense, if this is a concern, to move the source away from 
the shield or other objects.  5uC is not a heck of a lot of material,
that's on the order of what you'd find if you cracked open a smoke detector
but that would be Am241 which is an alpha emitter. That is ~5 MeV and only goes
several inches in air; I demonstrated that to myself in a cloud chamber.

I was just injected with 15 uC of Tc99 the other day for a medical test. 
Tc99 emits gammas (143 keV) all by itself, and I survived! It was spooky
walking into the nuclear medicine lab and seeing the gamma camera go
bonkers, though.