FW: Dosimeters

["Clement, Christopher" <clementc@aecl.ca>]

Radsafers:

Yesterday I asked for some information on dosimeters.  I guess I didn't
give quite enough information...
>
>> - will you be monitoring only photons?
Essentially yes.  The workers wearing the dosimeters will be handling
Ra-226 (plus progeny), natural U and natural Th, so essentially all of
the external dose is due to photons.
>
>> - any need to monitor beta or neutron?
No.
>
>> - what is the energy range for the photons?
The energy range is approximately 0.1 to 2.5 MeV.
>
The dosimeters will be worn indoors and out, and in temperatures from as
low as -30C to +30C.  As I mentioned before, I need to measure
incremental doses down to 10 uSv (or lower) over a period of one day to
several weeks.  I don't think that standard TLDs are quite this
sensitive.  I'd also much prefer direct reading in order to avoid the
expense and inconvenience of a reader.  It is often the case that work
is being done at remote sites, so a single reader would not be
convenient if more than one job is going on at once.

>>If you need to monitor only photons and don't want TLDs because of the
>>reader, take a look at electronic dosimeters. Some use GM tubes, but most
>>use silicon diodes as detectors, with internal software that contains a
>>dose conversion factor to convert from counts to dose. Some of these may
>>get down to the level you want to measure.

Our office owns a few KATA DGM-1500 dosimeters which make use of GM
tubes.
>
>>Beware of energy dependence on silicon diode detectors if you have low
>>energy photons - response can go to essentially zero at lower energies.

Can anyone tell me a little more about the energy dependence of silicon
diode detectors?
>
>>There may be some cadmium telluride electronic dosimeters around, but my
>>experience with these (early 1980's) found a bad temperature dependence
>>problem. When the dosimeter's temperature dropped below a certain temp
>>(about 50 degree F for the unit I tested), the unit under-responded badly.
>>If used indoors where such low temps aren't a problem, CdTe units work
>>really well.

It sounds like this won't meet my requirements for -30C to +30C
temperatures.
>