Re: Measuring pulsed fields

[Ted de Castro <tdc@XRAYTED.COM>]

But if it is a pulse train of significant duration then under very

specific conditions a GM can be used (its a matter of playing the

statistics).  It most certainly is not the best choice - its just that

in some circumstances it can be used to derive some information - in a

pinch.  The question as posed does not contain enough information to

answer.



As for the IC - you do need to be very concerned about the peak exposure

rate to be sure that saturation is maintained - 200 mR pencil dosimeters

do seem to go out of saturation somewhere around 10^4 r/hr.



The best choice is the HPI 1030 - its is made for this purpose!  As with

any instrument we use for specific purposes - there are tradeoffs and

that is certainly the case here - but no other portable survey

instrument even comes close for the very low duty cycle or even single

pulse.  Its even better if ordered with an output jack so that the pulse

may be observed and/or recorded on a scope.



It gets even more interesting when you consider very very short pulses

like 50 femto seconds!  Then to think about saturation peak exposure

rate is not so important as considering the actual number of photons

involved - you very quickly see that the ion density is more like a much

lower rate and cannot lead to significant recombination.  After all - an

exposure to a single photon would be extremely short and a very high

peak rate - but still only the ions from the reaction with a single

photon in the chamber.



John Andrews wrote:

> 

> Kim, you cannot measure short duration pulses with a GM detector.  The

> instrument responds with one count regardless of the size of the

> radiation event.  You can use dosimeters (quartz fiber ion chambers, not

> GM electronic) to measure the integrated dose.  Be sure the wall

> thickness is sufficient to ensure electronic equilibrium for the energy

> of the incident radiation.

> 

> You didn't say what you wanted to measure.  I assume you want to measure

> the total dose over some period of time.   My experince with flash x-ray

> equipment is that the total doses are pretty small per flash because of

> the very short duration.  Given that you may find that you need to

> integrate over a number of events to get a reasonable reading.  Good luck.

> 

> John Andrews

> Knoxville, Tennessee

> 

> Kim D. Merritt wrote:

> 

> > Is the Bicron 2000 w/ HP270 or the RO2 adequate for measuring pulsed

> > x-ray fields with microsecond pulsewidths?  I don't have the manuals

> > for these instruments.  Alternately, can anyone recommend an

> > instrument that is good for measuring these kinds of fields.

> >

> > Kim Merritt

> > Radiation/Laser Safety Officer

> > HazMed, Inc.

> > NASA Langley Research Center

> 

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