I-125 thyroid detector

[cast@epcaba.bologna.enea.it]

I would like to know if someone can give me some indication about direct 
measurement of iodine radioisotopes in thyroid by means of a thin window NaI(Tl) 
crystal.
We are looking forward putting a 0.2 window NaI(Tl) 3"x3" in our WBC cell to 
make simultaneously measurements to the whole body (with a 9"x4" crystal) and 
thyroid. We are looking forward the detection of I-125 (this is the reason of 
the thin window) and I-131 and I-123. 

Can someone help me in design the shelding of the 3"x3" crystal?

I would like to kwow, if someome has experience :

1)	crystal lateral shielding thickness
2) materials used in shielding (e.g. Pb, Cu, Al etc ) and relative thickness
3)	shape and geometry of collimator (cylindric, truncate conical with major base 
to the neck of the patient,truncate conical with major base to the detector, 
etc.)
4) calibration methodologies and phantoms 
5) minimum detectable activities achievable for I-131, I-125, I-123.

Can you also give me some references related to this issue.

I thank you in advance.

Carlo-Maria Castellani
ENEA Institute for Radiation Protection
Italy
Carlo-Maria CASTELLANI
ENEA Rad. Prot. Institute
BOLOGNA - Italy