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Re: Dumb Question of the Month
Date sent: Wed, 8 Jul 1998 08:43:47 -0500 (CDT)
Send reply to: radsafe@romulus.ehs.uiuc.edu
From: "Mike Malaxos" <<rss@arach.net.au>
To: Multiple recipients of list <<radsafe@romulus.ehs.uiuc.edu>
Subject: Re:
<color><param>7F00,0000,0000</param>> Hullo Radsafers,
> Dumb question of the month,
>
<bold></color>Here is a dumb answer of the month!
</bold><color><param>7F00,0000,0000</param>> I would welcome your comments on the following;
>
> Potential for pressure build-up of Radon in double encapsulated special
> form sources
</color> <bold> It does exist. It is a real problem. (at least in the older </bold>
<bold>form of single encapsulated sources)</bold>
<color><param>7F00,0000,0000</param>> Method of calculating this build-up if it exists.<bold>
</color>Speculative: Each</bold> <bold>disintegration of Ra-226 produces one helium atom
(nucleus is an alpha particle) and one Radon atom. Since these are
both "Nobel Gases", there should be a chemist somewhere who could
use the dpm of the source, the internal volume of the capsule, and
relate this creation of the two nobel gaes to the internal pressure.
</bold>> Details of any experience with incidents arising from pressure build-up.
sources).
<bold>Oh Boy! I responded to a request for assistance from a bank. A doctor
who died 30 years previously had a set of radium needles (used in his
practice in the 1920's ,1930's) stored in his safety deposit box. (Radium
was considered quite valuable in those days!) His estate maintained
this same box for deeds, etc until one of the new board members asked
,"what is that ?" The radiation level on contact with the polished wood
container was 300 mR/hr. An alpha probe detected contamination on
all painted metal surfaces of the box that were not covered by the
contents. An air path existed between all the boxes in this vault. Alpha
contamination was found in all the safety deposit boxes - higher levels
closer to the sources, lesser levels farther from the sources). Later
analysis of the wipe samples taken, showed NO Radium, only radon and
it's daughter products</bold>. <bold>Thus this was a real case of a leaking source
due to gas pressure building up until it cracked the capsule, leaking
only the nobel gas components of the decay chain, He-4 is stable, but
the Radon then decayed more outside the capsule. (409 cleanser did
great in removing the contamination from the box surfaces. With the
chain primary source of Ra-226 removed, time did a great job of
decaying the problem.) I spent a week at the bank decontaminating
each box. The boxes could only be opened by the boxholder's key and
the bank's key used together. The bank president arranged for all the
box holders to come in, one at a time. The contents of each box was
checked for contamination, if none were found, the contents were
placed in a new safety deposit box located in a separate group of boxes
. Almost everything in the boxes were in envelopes. Contamination
was found on many envelopes, but none on the contents!
Contamination Items were removed to a RAM waste storage area. A
certificate of deposit with contamination was easy. The bank declared
it lost and issued a replacement! Contaminated deeds of trust was also
easy...they were all on file at the court house and replacements were
easily obtained! The things I worried most about were the easiest
solved.</bold>
<color><param>7F00,0000,0000</param>>
> Has any one experience in calculating a pressure equalibrium which takes
> into account the migration of gas through the metal walls of any source
> capsules.
<bold></color> Good question, Helium as small atom will posibly migrate through</bold>
<bold>the walls. Radon as a large atom...does the phrase "a snowball's
chance in hell" apply? (that is, if the walls are not cracked!) Also, the
identification of the metal used in the walls will be important. One
example comes to mind - Hydrogen 3 easily passes through paladium,
(or is it platinum?)
</bold><color><param>7F00,0000,0000</param>>
> Is there any pressure build-up due to Helium formed from Alpha /beta
> combination.
</color> <bold>I'm not sure what you mean by combination of Alpha/Beta, but</bold>
<bold> by its self, an alpha particle is the nucleus of a stable helium atom,
which will easily acquire the orbital electrons, and will indeed build up
a pressure. (Since beta particles are electrons, maybe you meant the
capture of the orbital electrons by the helium nucleas thus becomming
a complete helium atom?)</bold>
<color><param>7F00,0000,0000</param>> Do all alpha emitters have an internal pressure problem
</color>.<bold>..oh yes, see above.
</bold><color><param>7F00,0000,0000</param>> Does the migration of gas through the capsule wall cause pressure
> equilibrium.
</color>. <bold> ?Production of Radon minus the decay to a non-gaseous daughter,
and minus the migration through the wall (If real), could cause a
pressure equilibrium inside the capsule. But for He-4 there is no decay,
therefore the production of He-4 keeps raising the internal pressure. ( I
am not famaliar with gas penetration through metal walls)</bold>
<color><param>7F00,0000,0000</param>> Do Ra 266 sources have an internal Helium and Radon gas pressure build-up.
><bold>
</color>YES, see above.
</bold><color><param>7F00,0000,0000</param>> Thanks for your advice.
>
> Best Regards
> M.Malaxos
> Radiation Safety Services
> 69-71 Robinson Avenue Belmont
> Western Australia. 6104
> Fax 61 89 475 0165
> P 61 89 475 0099 a/h 089 255 1214
> email rss@arach.net.au
>
>
> ----------
> >
</color>I don't have a disclaimer on the signature portion of my E-mail, so I better put
one here. These are all my own opinions and not those of my employeer.
<nofill>
Clarence W. Dittman, Health Physicist
Radiation Control Program Manager
Texas Department of Health
Public Health Region 7
2408 South 37th Street
Temple, Texas 76504-7168
(254) 778-6744
Fax (254) 778-4066
Clarence.Dittman@tdh.state.tx.us
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- From: "Mike Malaxos" <rss@arach.net.au>