Re: Radioactive Material Thresholds

["David W. Lee" <lee_david_w@lanl.gov>]

Greg:

	While in the U.S., IAEA recommendations are not necessarily "legal"
limits, you may want to review IAEA Safety Series No. 115, (1996),
"International Basic Safety Standards for Protection Against Ionizing
Radiation and for the Safety of Radiation Sources," pages 81-88.  These
pages contain "exemption" limits in Bq/g for various nuclides.  Some might
conclude that the listed values are basically "de minimus" values below
which one would not need a license or any radiation safety surveillance,
and below which one might treat the substance without regard to its
radioactivity.

REGARDS  David  

At 03:43 AM 05-08-97 -0500, you wrote:
>     Greetings Radsafers
>     
>     I've just joined this discussion group and already have a question to 
>     ask. It's one of those straight forward questions that never seems to 
>     get a straight forward answer I'm afraid - at least not if based on 
>     the UK legislation anyway.
>     
>     The problem I have is this: In the current Radioactive Substances Act 
>     (RSA93) there is a schedule (Schedule 1) listing certain elements 
>     associated with certain values (in Bq/g) above which the elements (or 
>     at least the radioactive isotopes of the element) are considered to be 
>     radioactive. This is fine for the elements listed (Ac, Pb, Po, Pa, Ra, 
>     Rn, Th, U), but its not very useful for radioactive materials 
>     consisitng of any other elements. According to RSA93 all other 
>     elements (or rather their relevant radioactive isotopes) are deemed to 
>     be radioactive if they have been produced artificially. With this 
>     definition there is no threshold value below which the elements can be 
>     considered non-active.
>     
>     In the Approved Code of Practice 'The Protection of Persons against 
>     Ionising Radiation arising from any Work Activity' the definition of 
>     radioactive material is anything above 100Bq/g with the exception of 
>     certain elements (such as Th and U).
>     
>     This creates a problem when trying to decide legally and safely 
>     whether an item is considered to be a radioactive or not. Here at 
>     Harwell Laboratories in the UK a certain amount of interpretation and 
>     extrapolation of the RSA93 values has been implemented to create 
>     threshold values for two groups of radionuclides: Those which emit 
>     alpha particles (0.4Bq/g) and those which do not (4.0Bq/g).
>     
>     This broad classification may seem strange for some as the 
>     radiotoxicity of some radionuclides is far greater than others (e.g. 
>     Alpha emitter Pu-239 is 100 times more radiotoxic than alpha emitter 
>     Po-210 according to ICRP 30). However, I believe the threshold values 
>     used at Harwell (and at other sites around the UK) are conservative 
>     ones.
>     
>     My question is this:
>     Is there a definitive legal threshold activity per mass value defining 
>     the limit below which material can be considered non-active (either 
>     generically or individually)? i.e. have I missed something?
>     
>     (This question relates mainly to the UK legislation but information 
>     with regard to other country's laws will be useful and appreciated. 
>     Perhaps the IAEA has some guidance on threshold values?)
>     
>     Apologies if this subject has been brought up before. I'm having 
>     trouble accessing the Radsafe archive. What's the current address by 
>     the way?
>     
>     Greg Wells
>     
>     P.S. I've got an even more tricky question to follow!!!
>
>
David W. Lee
Los Alamos National Laboratory
Radiation Protection Services Group (ESH-12)
PO Box 1663, MS K483
Los Alamos, NM  87545
PH:   (505) 667-8085
FAX:  (505) 667-9726
lee_david_w@lanl.gov