Re: Release Criteria - Fe55

[Yann Donjoux <Yann.Donjoux@cern.ch>]

"Hall, Donald C. Jr" wrote:

> 

> We would like information on how other nuclear plant radiological protection

> programs address "hard-to-detect" isotopes such as Fe-55 with regard to

> release of personnel and materials from Radiologically Controlled Areas

> (RCAs).



Dear Sir,



I would be very interested if you have any reports concerning your

question, if you could forward any answers.

I have been involved, in the past into Fe-55 measurement. The only non

destructive method that we tested was X-Ray spectrometry using a Si PIN

detector (called XR-100T, Amptek) to detect Fe-55 X-Ray (5.9 keV).

Unfortunately, such kind of detector are not stable and can not be

efficiency calibrated. We then used a comparative method, since most of

the sample also have Mn-54 in it. We then make a comparison between area

of Mn-54 X-Ray peak (5.4 keV) and Fe-55 X-Ray peak (5.9 keV). By a

"standard" gamma spectrometry we determine the amount of Mn-54 and by

calculation can obtain the quantity of Fe-55 (taking into account auto

absorption, difference of efficiency of the XR-100T between Fe-55 &

Mn-54 and so on...). We then tried to evaluate the success of this

method, by intercomparison with a chemical process, but the chemical

process has never been conducted to its final state and we now have more

important things to carry on. Consequently, I cannot tell you if it's a

good method or not. Anyway, in accelerator, the activation is not

uniform, and you generally measure with this non-destructive method only

the first micrometer (depth) of the material, which maybe not

representative.



PS: interesting article: Applied radiation Isotopes, Vol 43, No 11, pp

1355-1362 (1992)

[Int. J. Radiat. Appl. Instrum. Part A]



For information, France has no release criteria, and switzerland takes

30 Bq/g (free release) or 5 MBq.



Regards,

-- 

 _____________________________________________________________

| Yann Donjoux   Division TIS / Radioprotection (RP) - E07900 |

| CERN, Organisation européenne pour la Recherche Nucléaire   |

| CH-1211 Geneve 23, Switzerland.                             |

| Electronic mail      Yann.Donjoux@cern.ch                   |

|_____________________________________________________________|

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