Victoreen 450B question

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Jon_Iverson
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Victoreen 450B question

Post by Jon_Iverson »

I have a Victoreen 450B that had been in storage more or less for a decade and was brought out recently for some testing. One thing I noticed right away were that the background levels were higher than they should be, anywhere from .10-.15 mR/hr. So, a quick look at the desiccant, all pink, so baked it and also placed the unit at 50 C after reinstalling the recharged desiccant for 12 hours. However, some days I am getting normal background levels (around 0.01 mR/hr or 10 uR cumulative), but other days it's acting as before, averaging at least .10 mR/hr. I've checked background with other instruments I have here and it has not changed. Nothing comes up on the meter at start and everything checks out normal. Any ideas what might be going on would be welcome and how to remedy. Thank you in advance.

Jon
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Richard Hull
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Re: Victoreen 450B question

Post by Richard Hull »

There are a couple videos on goggle/you tube that show a working 450B and in a room it was reading .10 to .14 mr/hr right beside a GM counter that was indicating only 60-70 cpm and .01mr/hr. Ion chambers are funny beasts and most have a pot to zero the device relative to a neutral back ground to take up for drift or bias in the electronics, battery condition, etc. I did not see this on the 450. Sometimes on my Victoreen model with a zero pot, I just don't bother to zero it for quick use. I just record what its reading and then place the suspect near it, take another reading and let the differential be my reading. These are not very low end precise systems in simple hand held meters. If you adjust the pot for zero the reading will bobble about zero on a 0-1mr/hr range.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Rex Allers
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Re: Victoreen 450B question

Post by Rex Allers »

Jon, when you registered you agreed to some site rules. One was:

The Rules: #2
New members are required to introduce themselves in the "Please Introduce Yourself" forum prior to posting elsewhere on the site.

Please now make that introductory post.
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Jon_Iverson
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Re: Victoreen 450B question

Post by Jon_Iverson »

Rex Allers wrote: Fri Mar 05, 2021 5:28 am Jon, when you registered you agreed to some site rules. One was:

The Rules: #2
New members are required to introduce themselves in the "Please Introduce Yourself" forum prior to posting elsewhere on the site.

Please now make that introductory post.
done!
Jon_Iverson
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Re: Victoreen 450B question

Post by Jon_Iverson »

Thanks, Richard. I'll have to try and track down those videos to see a comparison. In the meantime, I think I've ruled out any possible moisture issues as I've had the entire chamber inside a sealed desiccant container for the past day.

If they vary that much on background, looks like I better stick with probe based instruments to measure the low levels.

Thanks for your help.
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Re: Victoreen 450B question

Post by Rex Allers »

Thanks for the intro post.

As Richard is fond of advising...

Please don't use that quote of whole messages when replying here.

Maybe a few words for context, but we are capable of following a thread without block quotes of the message being replied to.

Just a suggestion of posting norms here.
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Richard Hull
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Re: Victoreen 450B question

Post by Richard Hull »

Low levels of radiation, certainly those that are just a hair above background are best done statistically with 10,000 count runs on a GM counter. statitically that runs you out to a +/- 1% error. assuming a fixed 60 cpm for background, just an accurate background count would take 2.8 hours of counting. Now all of this would demand a digital counter recording the counts from the GM counters (scaler). So very much depends on just how accurate you need to be when measuring low levels.

So often, you do not know your background, especially with a portable instrument. A simple analog reading GM counter is fine to determine very small levels above background, but never precisely. Your ear is your statistician in such remote location cases.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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