Measurement of X-Rays from magnetrons
Measurement of X-Rays from magnetrons
(OP)
Hi folks,
Does anyone have experience of the correct way to accurately measure X-ray emissions from magnetrons?
In one of our small radars we have a need to measure if any x-rays are generated, and if so, is the level "hazardous" to service personnel. The magnetron is running at an anode voltage of about 7kV and p.r.f. of 800Hz, so presumably any X-rays will be soft (7keV max). We have tried using hired-in instruments (all G-M tube based) with variable success: some read nothing at all, others suddenly read once a distance threshold is crossed, but with no expected distance / strength field attenuation. These meters may be responding to stray r.f., as a conventional field strength meter gives a power reading of about 0.2mW/cm2
Thanks in advance
Does anyone have experience of the correct way to accurately measure X-ray emissions from magnetrons?
In one of our small radars we have a need to measure if any x-rays are generated, and if so, is the level "hazardous" to service personnel. The magnetron is running at an anode voltage of about 7kV and p.r.f. of 800Hz, so presumably any X-rays will be soft (7keV max). We have tried using hired-in instruments (all G-M tube based) with variable success: some read nothing at all, others suddenly read once a distance threshold is crossed, but with no expected distance / strength field attenuation. These meters may be responding to stray r.f., as a conventional field strength meter gives a power reading of about 0.2mW/cm2
Thanks in advance
RE: Measurement of X-Rays from magnetrons
RE: Measurement of X-Rays from magnetrons
TTFN
RE: Measurement of X-Rays from magnetrons
From what I remember about film badges, etc. is that they only measure an accumulated dose over a relatively long period via diferent energy level filters. The difficulty is that I'm not sure our x-rays are hard enough to get through some of the filters, then there's the problem of reverse-calibrating any exposed film back to a dose rate.
RE: Measurement of X-Rays from magnetrons
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RE: Measurement of X-Rays from magnetrons
Since I first posted here, other forums have told us that you can't use g-m tube based detectors with magnetrons because of the pulsed nature of the drive voltage. It seems that an ion chamber type instrument may be the best sort for this application, so we will try that.
Thanks to all who replied.
RE: Measurement of X-Rays from magnetrons
RE: Measurement of X-Rays from magnetrons
If there is any possibility you could exceed the limit, perhaps you should re-negotiate your contract to cover the cost of testing at a lab equipped to do so. Such labs could probably be suggested by vendors of the sensors you have had contact with.
RE: Measurement of X-Rays from magnetrons
If your magnetron is emitting x-rays in to the open, your problem will be one of which part of the magnetron they are coming from. -So x-ray cassettes as used in hospital diagnostic imaging departments sound like a good idea here...you could stand them round the magnetron and start it up....then simply put them through a film processor in a hospital diagnostic imaging department. X-ray film is cheap..a 35cm*43cm sheet of film used to cost about £1.10 in 1995...the chemicals used in processing it will be a few pence. (in fact you can wet process in a big bowl as long as you have a dark room preferably with a safelight)..many new hospitals have dry-processors and there is no "wet chemical".....i think this would be an excellent and cheap and quick way to start as it would indicate where to put your dosemeters (when you know which type you want)....
give me a shout if you want details of how to get in touch with a hospital etc....i also used to get inspections from radiation guys so know who to point you to for advice if you want it.
RE: Measurement of X-Rays from magnetrons
RE: Measurement of X-Rays from magnetrons
RE: Measurement of X-Rays from magnetrons
RE: Measurement of X-Rays from magnetrons
Here in the UK with the ever-increasing "health and safety" culture we now have to do a risk assessment - OK - but then we have to quantify this risk with a specific dose rate measurement. Getting a meaningful reading, that's the real problem!
RE: Measurement of X-Rays from magnetrons
You could try emailing someone at http://www.hpa.org.uk/radiation for advice. Or if you do military work you could try the "Defence Radiological Protection Service" -Though I think (after re-arrangement) that this is now under http://www.dstl.gov.uk (or else some division of Qinetiq).
7kV might be relatively low -however, we were often taught that the "lower kV xrays" were potentially more harmful than those from higher kVs, since they would give rise to more (harmful) absorption by human tissue.
Best Regards.