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Registered Member #311
Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253
I just acquired an old EG&G Linescan baggage X-ray machine. What sort of detector/counter would be suitable to check for safe leakage levels - tube is 145kv.
How necessary would it be to have something that is calibrated ? i.e what sort of difference is there between levels of "detecting nothing, so safe", "Detecting a little but but still safe", "Detecting unsafe levels", and "extreme levels due to detector placed in beam path to check that it's working"
I have a pre-delivery inspection sheet showing a test level of 0.7uSv/h
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
I'd ensure the counter works before even thinking about powering the machine, X-ray leakage is likely if the machine's shielding is damaged in any way.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
mikeselectricstuff wrote ...
I have a pre-delivery inspection sheet showing a test level of 0.7uSv/h
That figure will be the background radiation in the place where the equipment was tested.
Baggage and mail X-ray machines should have no detectable X-ray leakage*, as operators will be exposed continuously throughout their working period, and annual permitted dose rates must not be exceeded.
* with ordinary X-ray survey instruments, at least.
Registered Member #311
Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253
Proud Mary wrote ...
mikeselectricstuff wrote ...
I have a pre-delivery inspection sheet showing a test level of 0.7uSv/h
That figure will be the background radiation in the place where the equipment was tested.
Baggage and mail X-ray machines should have no detectable X-ray leakage*, as operators will be exposed continuously throughout their working period, and annual permitted dose rates must not be exceeded.
* with ordinary X-ray survey instruments, at least.
The sheet shows a background level of "<0.2uSv/h", presumably the limit of the equipment used.
What I'm concerned about is whether a normal gieger counter is sufficent to check that I'm not going to nuke myself during a few hours of x-raying anything I can get my hands on, before I get bored, strip the thing down, do a teardown video, weigh in the lead at the local scrappie, put the tube on the mantelpiece as a cool ornament and see how long the 160kv PSU can pull an arc before self-destructing...!
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The Mini Instruments 900D is specified as follows:
"Type D:
Uses partially compensated G-M tube to obtain an extended low energy response Scaled over the range of 0.5 to 1000µSvh-1 (0.05 to 100mR/h) Useful energy range: 30keV to 1.5MeV but response is maintained down to at least 17keV Suitable for measuring radiation from X-ray apparatus operating at or above 45kVp"
The test engineer seems to have interpolated his figures by eye right at the bottom of the scale. How he determined that the background count was 0.2μSv/hr with this single range instrument is unclear.
A survey meter with a 0 - 3 μSv/hr FSD range would have been far more suitable for measuring the low dose rates likely to be encountered in a leakage survey of professionally designed equipment.
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What sort of detector to check safety of baggage X-ray machine?
