Reply to Bubble Dosimetry question

["Morris, Robert" <Robert.Morris@rfets.gov>]

Tim Kirkham of Calvert Cliffs NPS posed this question:

Question 2 -
Regarding Neutron Bubble Detectors -=20
    1.    Whom among you use bubble detectors?
    2.    Who uses them for neutron record dose?
    3.    Do you have a technical basis for using them instead of your =
normal TLD?

Answer:

Safe Sites of Colorado, a major subcontractor at the U.S. DOE's Rocky Flats
Environmental Technology Site, is using approximately 100 Bubble Technology
Industries BDPND bubble dosimeters each quarter for daily neutron dose
equivalent tracking in operating plutonium facilities.  The data from BDPND
do not become part of the dose of record except in the unlikely event that a
dose reconstruction is performed.  

We prepared a technical basis document with special emphasis on an
evaluating the match between the neutron spectra found in our workplace and
the portion of the neutron spectrum detected by the BDPND (every thing with
energy > 0.2 MeV).  We found good agreement.  In the worst case, the BDPND
might miss up to 10% of the neutron dose equivalent in our workplace; in
most cases the match was better.  We also prepared procedures on issuance,
readout, and re-zeroing the bubble dosimeter.

In my opinion, the bubble dosimeter is an excellent device.  One problem -
dynamic range - keeps it from being a general purpose neutron dosimetry
device.  Assuming the automatic reader can accurately count up to 350
bubbles in a dosimeter tube, the high sensitivity BDPND we normally use has
a dynamic range of approximately  0.3 to 40 mrem.  (Low sensitivity BDPNDs
go from about 3 to 450 mrem).  Any dose in excess of this level cannot be
determined.

Bubble Technology Industries can be contacted at PO Box 100, Chalk River,
Ontario, Canada.  (613) 589-2456



Bob Morris, CHP CIH
Safe Sites of Colorado
(303) 966-6468
Robert.Morris@RFETS.gov

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