Re: HOT PARTICLE DDE

["DR MW CHARLES" <charlemw@novell1.bham.ac.uk>]

Timothy Martinson wrote:

     According to NUREG/CR 6204, "Questions and  Answers" based on the 
revised 10CFR20, it is a requirement that DDE (Deep Dose Equivilant) 
associated with a hot particle exposure be assessed and added to the 
monitored DDE for demonstrating compliance with the occupational dose limit 
(ref: Question #435). Have any of you had experience with hot particles that 
produced a significant gamma exposure (eg: Cobalt 60), thus requiring a DDE 
assessment and recording in a persons exposure records ?  If so,could you 
please share your methodology for assessment and record keeping ?

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I am not aware of details of US regulations so my comments come from 
a UK perspective.  According to ICRP 60 it is now required to 
evaluate the contribution to the effective dose from skin 
exposure.  The contribution would appear intuitively to be given by the average 
dose (at a depth of 70 microns) to the whole skin multiplied by the tissue 
weighting factor for the skin (0.01).  This does not necessarily 
require that the body will have been subjected to a penetrating 
radiation exposure as implied in the question.  A very significant contribution to the 
effective dose would be made for example if the whole of the body skin was 
exposed at the deterministic limit even from beta radiation.  A practical problem
however which was not directly addressed in ICRP 60 was how do you do this 
evaluation if only part of the skin is exposed, such as when only the hands are 
irradiated, or I guess if the skin exposure was from a hot particle as 
in the question posed by Timothy Martinson.  The problem is mentioned in 
ICRP 59 paragraph 317, where dose averaging appears to be recommended 
- with the proviso that due note should be taken of the fact that potentially 
UV exposed parts of the body have a much greater skin cancer risk than 
UV shielded areas.

I understand that in the USA the hot particle dose limit is 
effectively about 5 Sv averaged over an area of 1 square centimeter.  
If we assume that such an exposure occurs to a UV exposed site, such 
as the face, then it will contribute about 17 micro Sv to the effective 
dose ( 5Sv averaged over the area of UV exposed skin, 3000 
square centimeters, and multiplied by the tissue weighting factor for 
skin).

I don't know of any UK organisation which currently actually does what I have 
just described, but the NRPB in the UK will shortly publish an advisory 
document which will recommend such a procedure.
Dr Monty Charles, Reader in Radiation Physics
School of Physics & Space Research
University of Birmingham
Edgbaston
Birmingham B15 2TT
England
TEL +44  0121 414 3483
FAX +44  0121 414 4725