[ RadSafe ] x-ray tube fade

Robert Cherry bobcherry at satx.rr.com
Sat Oct 14 17:24:41 CDT 2006


I think that indicates a gassy tube. As the tube heats up, the "getters" are
releasing the gas they had absorbed (adsorbed?) to help maintain the vacuum.
The lower vacuum impedes the tube current, lowering the output. It should
not affect the peak tube voltage.

If reproducibility is out of specs, the tube should be replaced.


-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
Of cehn at aol.com
Sent: Saturday, October 14, 2006 8:59 AM
To: radsafe at radlab.nl
Subject: [ RadSafe ] x-ray tube fade

Doing QC checks with a dental x-ray unit & RadCal, I'm seeing fading of the
dose with successive exposures.  Did 10; the first 2 were about the same
dose (~40 mrem; 77 kVp, 12 mA; 2.5 sec).  Next 8 dropped by about 0.1% each
time. Final exposure was about 1% less than the first. Steady drop.  But kVp
measurements held steady.  Is this normal, or does it indicate a problem?
Thanks in advance.
Joel Cehn
joelc at alum.wpi.edu
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