Re: Discrpancies among different dosimeters

["Robert Gunter" <rjgunter@icnpharm.com>]

M. Jo,

The other consideration would be the E spectrum of the beam.  Dosimeters which
exhibit energy dependance will tend to over-respond to photons with E less than
100-200 keV (PEE range).  The effect of this is dependent on the spectrum.  The
more energy dependant, the more response would be expected from low photon
energies.  The data supplied implies this.

You provided the range of energy but not the relative spectrum.  As with any
non-tissue equivalent dosimeter; to the extent that the source has not been
characterized (with expected response programed into a dose calculation
methodology), or filters are bypassed (due to high angles of incidence), you are
left to interpret the results based on knowledge of the energy dependence of the
detection media.

Rob Gunter


----------------------------------------------------------------------------------------------------------

Robert J. Gunter         Tel: (714) 545-0100

Sr. Technical Specialist      Tel: (800) 548-5100 Ext. 2414

ICN Biomedicals, Inc.         Fax: (714) 668-3149

Dosimetry Division       Email: rjgunter@icnpharm.com

3300 Hyland Avenue

Costa Mesa, CA  92626




I am trying to characterize radiation field from 100 ns x-ray pulse. The
expected x-ray energy is between 0-2.8 MeV. X-rays below ~60 keV do not
escape the chamber based on my calculation. I used pocket dosimeters (0-200
mR and 0-5 R range), TLD, and Aluminum Oxide dosimeter in a group and placed
them in four directions about one foot from the x-ray chamber (anode).

Here are the readings and the numbers represent locations (TLD (1), Pocket
dosimeter (1), and Al Oxide (1) are from the same location).
    Pocket dosimeters: (1) 0.7 R (2) 0.8 R (3) 0.7 R (4) 0.8
    TLD: (1) 600 mrem (2) 400 mrem (3) 180 mrem (4) 780 mrem
    Al Oxide: (1) 1804 mrem (2) 2098 mrem (3) 2210 mrem (4) 1060 mrem

The TLDs and Al Oxide dosimeters were provided and processed by NVLAP
accredited vendors.

I did not pay attention to whether the dosimeters were facing the beam or
facing away from the beam. Variances in distance should not be significant
as they were placed in a zip lock bag and the bag was taped to the chamber.

I am confused about the results. I welcome any suggestions to explain what
could have happened. Thank you. M. Jo
========================================================
Myung Chul Jo, MS, CHP
EH&S, Mail Stop 328
University of Nevada, Reno
Reno, Nevada 89557
(702)784-4540
(702)784-4553 fax
mjo@scs.unr.edu


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