NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/sci/chem/5970

Text File | 1993-01-25 | 5.3 KB | 113 lines

Newsgroups: sci.chem
Path: sparky!uunet!zaphod.mps.ohio-state.edu!howland.reston.ans.net!usc!rpi!batcomputer!munnari.oz.au!mel.dit.csiro.au!dmp.csiro.au!lachlan
From: [e-mail] (Lachlan Cranswick)
Subject: Re: Brehmstrehhlung X-rays  - Safety
Message-ID: <[e-mail]>
Organization: CSIRO Division of Mineral Products, Melbourne, AUSTRALIA
References: <[e-mail]>
Date: Mon, 25 Jan 1993 10:05:19 GMT
Lines: 102

[e-mail] (Brian Baker) writes:



>Anyway, a couple of the guys in the lab are doing dot blots in attempts to
>detect CMV virus and do HLA typing.  They started with 5 millicuries of
>32-p (now they're up to 10 or 15).  They're working behind 1/2" plexiglass,
>which is sufficient to
>block all betas coming from the source.  However, one guy took the geiger
>counter in front of the screen and noticed a few thousand counts.  I
>told him it was somthing along the lines of X-rays coming from the plexi-
>glass.  This person has since talked with a couple of people (a state of
>Colorado Radiation Safety officer and some guy at Amersham I believe) and
>now is convinced (and has others in the lab convinced) that working with
>32-p behind plexiglass is very dangerous because of the X-rays coming
>off.  They have scavanged some lead bricks from an old scintillation
>counter and won't work without stacking the lead in front of the shields
>(this lead is about three inches thick and VERY heavy).  I do my work
>with a max of 0.5 mCi (usually .25 tho) and they call me crazy when I
>don't put the lead in front of me.  A guy who sits at a desk about
>twenty feet away from the 32-p room is worried about X-rays bombardidng
>him while he's at his desk.  The way I understand this is:

>    1)  The X-rays are caused by betas being deflected by lead
>        in the plexiglass, which causes a rapid change in velocity
>        and a subsequent X-ray

>    2)  These X-rays are of low energy (compared to X-rays you get
>        at the hospital) and the extinction coefficient is only
>        a few feet or so

>    3)  5 millicuries, which is a large amount of 32-p, will not
>        generate enuff X-rays from plexiglass to be concerned about,
>        certainly .5 mCi behind 1/2" plexiglass is safe

>Oh yeah...this same person claims X-rays to be 'ionizing radiation'
>Now I  had a pretty good Nuclear/Radiochemistry class and I certainly
>don't remember X-rays being classified as ionizing radiation.  This person
>also claims X-rays and Gamma rays to be "almost" the same.

[STUFF DELETED]

If I could just put in my 2 cents worth:-

I think a lot of the above depends on the attitude to safety.
(NB:- Low energy X-rays are ionizing radiation!!! but not in the same
league as gamma rays)

If your company has a "safety first" attitude, then I think you
should be trying your best to setup the equipment that nothing
above background is measured by the counts detector. (i.e., nothing
above 2 counts per second)  This brings up the point on what
type of plexiglass are you using.  A single crystal diffractometer
in the next lab uses Molybdinum X-ray Tube (relative high-energy
radiation) and has a zinc doped perspex enclosure and no radiation
gets through.  I am told you can go one further and get lead doped
plexiglass or even lead glass enclosures.  It takes very little
to stop low evergy X-rays - the chlorine in PVC has decent
stopping power.

Also, it can be argued that low energy X-rays can be more dangerous
than high energy X-rays as the high energy X-rays go through
you - while the low energy X-rays are stopped by the body and
can cause nasty burns - in high enough doses.

With using radiation detectors, you have to distinguish between
count detectors and biological damage detectors.  With low-energy
X-rays, you can have thousands of counts per second on a "counter"
but hardly a needle moving on a biological damage detector (I think
is measured in micro severts(sp?)?)

As our company has a safety first policy, anything above background
counts coming from our Powder X-ray diffractometers is considered
a leak even if they have negligable biological damage value.
While it can be argued that there is no health risk, it is definitely
a good feeling when your superiors imply they care about your heath
enough to spend money on your safety rather than their company cars, etc.
We have had over $16,000 authorized for a full radiation enclosure
because of a small leak (3 times background counts -
CuK X-rays) that was only detectable
1cm from the source.  This gives two complete levels of safety on our
diffractometers which some people would argue is total overkill.


However, given safety can have a large psychological component,
I would try to design something that makes your other colleages
happy about the radiation levels - yet doesn't get in your way.
If well thought out, safety is not a synonym(sp?) for
inconvenience.  Lack of radiation won't
hurt anyone, but the reverse cannot be stated as forcefully.

Does anyone disagree with the statement that "It is very hard
to be officially kicked up the arse by superiors for being too
safe."


Hope this helps?  Lachlan.
--
  Lachlan Cranswick  -  CSIRO             _--_|\  [e-mail]
  Division of Mineral Products           /      \ tel [phone]
  PO Box 124, Port Melbourne 3207        \_.--._/ fax [phone]
  AUSTRALIA                                    v