Alpha Meter Problems

[atomicarcheologist]

 I am working with an Eberline ESP2 (no laughing allowed) hooked up to a 43-68 and set up for alpha survey purposes.  On these alpha meters, usual range in a scan mode is from the highest measured value down to below 0.1 cpm (actually the lower end of the range is like down to 1E-6 cpm), as long as the survey is performed in a clean and fixed free area.  There is also a method of clearing out the last value so that when you start another scan, the meter will be in an expected range.  Today I got into a situation where I could not clear the display to get down into the expected range which should be <0.1cpm - 40 cpm.   I could eventually get the highest measured value in the range down to the expected, but the lower end of the ranging would not drop to the expected.   Now this wouldn't have bothered me quite so much for the surface measurement range, but if I was free airing the probe, the same problem was present.  It even had me going about getting a radon build up for a bit, until I realized that my ESP2/43-48 set up for beta was not reading alike.
Source checks showed it to be right where it should be.  BKG wasn't bad.  I took the probe apart and cleaned it as best as I could after visually verifying the Mylar was intact.  Air sample results had no activity outside of normal activity.
Do you have any idea what could be causing a problem like this?  Non-ionizing interactions?   Excessive personal magnetism?
Thanks for your attention.

[alphadude]

check the mylar, if you can see through it you have the wrong mylar.  the double coated mylar must be used on these instruments to prevent light response

[atomicarcheologist]

It's not the mylar.  We're using factory specific mylar and frames.  This happened to an instrument after it hs been used for the duration of the job.  It has been through source response cycles without a hitch.  Other instruments set up the same are not experiencing this.  I&C reports no problem with the set up. 
Obviously this is not an instrument response problem, i.e. the free air scenario.

[moke]

Have you performed a Chi-Squared Test?

There is an obvious problem with your system and the meter should be placed out of service. Can it!

You will put too much energy into the topic and waste your time.

Have a Great Week,

Moke

[alphadude]

Yea Moke is right, but i gave it the benefit of doubt.  time for rebuild or trash. just for grins-check to see if the mylar is transparent-you may have the right density but not the double coated.  seen it before-

[atomicarcheologist]

Thank you for the generic replies. 
I am looking for instrument specific knowledge, does anyone have any regarding this type of scenario?

[alphadude]

those probes do respond to light-especially quartz halogen- (could be the IP of the UHP gas is around the energy of quartz halogen energy) First change out the probe. if your problem clears then its the probe-  have seen lots of problems with light on those detectors-we had a discussion about it a while back-   when you have the problem isolated to the probe you have several options- gas purity problem, moisture build up in the probe,  mylar not opaque, discharge corona point, carbonization of the anode,-(someone touched it and left body oils on it ) cold soldier joint, debris in detector, wrong type coax , damaged connector.  those probes are pretty simple, also they dont do well in cold.  thats about as instrument specific as anyone can get.  the voltage plateau should be checked for that specific instrument package.

[atomicarcheologist]

It is not the probe.  That was determined via probe change out.  It is not the cable.  That was determined via cable change out.  It is not the environment.  That was determined by; 1) assessing no radon problem present, 2) same situation in other areas.  Ergo, it must be the instrument.  Help!

[alphadude]

time to tag it out. 

[atomicarcheologist]

OK.  Now that we are done with the elementary generic answerment, has anyone had this experience with an ESP2 before?  Is this a correctable condition in the field, field being outside of a calibration/repair lab, without  tearing everything apart?  When you are doing this type of work, there is not a lot of meters in the inventory, which makes it a challenge when they start going down on you.
I did run this meter past an I&C tech.  He said there was nothing wrong with the meter electronically and did a source and a pulse on it.  However, under further questioning, he did admit to cleaning the button controls.  But he didn't think that would have created the problem.
Help!

[radtype]

What you are seeing is the alpha meter response based on the instrument response time.  If you change the reponse time from slow to fast you will aget different variation on the reading (slow response will not record as high a value but requires a longer time to reach zero while the fast response shows a higher value and drops to zero faster). 

Typical alpha surveys are based on the probability of hearing the "pop" and then a static count.

If you have an instrument shop available, have them connect a pulser and send a count rate < 5 cpm and watch the meter movement.

[atomicarcheologist]

If you change the reponse time from slow to fast you will aget different variation on the reading

How do I do this on the ESP2?

[radtype]

I just looked through the ESP-2 manual and the setup is through the keypad and the default settings are normal with slow as a second option.  The ESP-2 was programmed to be smart in that it adjusts its response time due to the count rate (both normal and slow).  For the ESP-2, you will not probably see much of a difference between the normal and slow settings.

If you are using a meter with the traditional 4/22 second response time circuit - the meter deflection is pronounced on a 0-100 cpm scale (you are not going to see the deflection on a 0-1000 cpm scale)

[atomicarcheologist]

The ESP2 that I am using is digital, there is no scale, either 0-100 or 0-1000.  The electronics have been blessed off by the I&C tech.  I am still trying to figure out why it wouldn't easily clear the captured high value obtained during scan.

[alphadude]

call the vendor 

[atomicarcheologist]

Thanks for all the input.  When I find out what the problem was/corrective action for it, I'll be back to post.