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Re: Spiking of iodine cartridges for calibration
This answer presupposes a cartidge similar in shape to the cartridge in a
respirator rather than a tubular shape.
When we calibrated our cartridges for I-125, we simply introduced the
spike as a solution. However, because of the low energies of the gamma
and x-rays from I-125, we do not count the cartridge on the Ge(Li)
detector. There is a significant difference in the apparent activity
depending upon which side of the cartridge would be in contact with the
detector. This difference would depend upon the depth of penetration and
it would be very difficult to correct for the self-shielding. Instead, we
count the cartridge with the edge in contact with the detector, but the
bulk of the cartridge perpendicular to the detector. We have constructed
a simple jig so we can reproduce the counting geometry. Even then, we
count the cartidge with one side facing up, and then repeat the count
with the cartidge flipped, and then average the results. This accounts
for less than perfect positioning.
Even if you were counting I-131 or the rare gases, you may want to
consider this geometry rather than the more obvious one. It compensates
for different pentration depths and self-shielding somewhat better.
=======================================================================
John Harvey | McMaster University
Senior Health Physicist | NRB-110
(905) 525-9140 ext 24226 | 1280 Main St. W.
harveyj@mcmail.cis.mcmaster.ca | Hamilton, Ont Canada L8S 4K1
On Wed, 15 Nov 1995, Andrew Welsh wrote:
> Hi everyone
>
> I would appreciate obtaining information on the best way to spike
> activated-charcoal iodine cartridges with mixed-gamma source for
> gamma-spectrometry calibration.
>
> Particularly for geometries where the cartridge is placed directly on
> the germanium detector, the volume distribution of the source is
> critical.
>
> Thanks
> Andrew Welsh
>