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[Jean-Charles ABBE <abbe@in2p3.fr>]

Sorry for my preceeding mails : I did not pay attention to the fact that attached files were not accepted.
Thanks for comments, critiscisms, ....	

The Magnitude of Radiological Risk

Periodically, the media report on some kind of contamination and, consistently, they refer to Becquerels, sometimes to curies. In other circumstances, reference is made to doses and thus to grays or sieverts, seldom to the former units rads and rems. It is clear that the public gets lost and cannot appreciate the real extent of the danger which is, in fact, restricted to a very limited number of specialists.
It would be safe that simple references although of high scientfic merit would be given. The directive 96/29 from the ECC « establishing the basic norms related to the sanitary protection of the public and workers against the dangers of radiations » can be used as a good basis. In this directive, a table gives for any radionuclide both the quantity, in Bq, and the specific activity, in kBq/kg, corresponding to the threshold dose risks for workers, that is 50 mSv/year and less than 100 mSv over 5 consecutive years. Some of these values are given in the table :

Nuclide	quantity (Bq)	Concentration (kBq/kg)
H-3	10**9		10**6
I-129	10**5		10**2
Co-60	10**5		10
Cs-137	10**4		10
Ra-226	10**4		10

By analogy with the INES scale related to nuclear accidents, a scale of Magnitude of Radiological Risk, MRR, could be built up, the coefficient 4 corresponding to the threshold values as indicated in the directive and being related to an « exposure within the accepted limits». An order of magnitude in the activity would correspond to one degree of MRR. Thus for a Co source,  to specific activities of 1, 10 and 100 Bq/g would be associated the coefficients 3, 4 and 5, respectively. For diffuse contamination, reference would be made to the quantities as given in the directive.	Coefficients 3 and 5, would correspond to exposures representing « a fraction of the threshold doses » and « necessitating definite action », respectively. This scale would of course extend from 1 to 7 with the same significances as those associated to the INES scale.
In case of a mixture of radionuclides, the global RRM would be the sum of the individuals.
Using this procedure, a report would appear on the news as : « a radioactive contamination of ashes by Cs 137 has been discovered at So&So. The activity is of about 200 Bq/kg corresponding to a Magnitude of Radiological Risk of 2,2 that is significantly lower than the limiting risk acceptance (which would not mean that procedures should not be started to eliminate this source of pollution ...) ».
Thus, from the present and accepted knowledges of dose effects and of impact calculations, simplified and easily understandable information could be given to the public, with strong relation to what is now well known on the wind forces, on earthquakes intensities, etc...  

***********************************
Jean-Charles ABBE
Laboratoire SUBATECH
Faculte des Sciences et Techniques
Departement de Physique
2, Rue de la Houssinière
BP 92208
44 322 NANTES CEDEX 3

Tel 33 (0)2 51 12 55 10
Fax 33 (0)2 51 85 84 79

ABBE@SUBATECH.IN2P3.FR
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