Hello, I'm Greg in California

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Greg
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Hello, I'm Greg in California

Post by Greg » 01 May 2015, 15:04

Little of my background. I'm 55 and disabled. My first job was with the USAF working on Doppler, Inertial Nav. Sys. Nav computers. I worked on U2's SR-71, B-52's , AWACS, KC-135. The next ten years were spent in a sugar mill on instrumentation. Then after a back injury I went in to Antropology and worked as an Archaeologist Studing prehistoric peoples of California and the Great Basin. In the U.S. an Archaeological study is require part of any large construction project. So it has been privatized and is now done by the lowest bidder. We were required to dig more like dich diggers than scientist and joked about minding artifacts. This didn't do well on my back and I was tring to work my way trough Grad school, but!

I live near one of the detectors that stopped working just after 3/11/11. So I have little trust left that our Gov. will give us good numbers. I've had a Gieger for over a year but I've become frustrated with not being able to tell what I'm looking at.
I'm new to scintillation and trying to learn the Physics of radiation so go easy on me.
I'm working on getting a side well up and running right now. Bicor 1.5x1.5 The first one I bought the PMT didn't start conducting till I was at 1090v. I have a GS 1000 PRO so I was at my limit on voltage. So I asked for a replacement detector and I'm waiting on it. I want to see if I can see the Cs137-134 from Fukashima and much more.
I live 3.5 hrs from one of the undergound test sites in Nevada that is on open land and hope to go visit it this summer and grab some soil.

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brehwens
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Re: Hello, I'm Greg in California

Post by brehwens » 01 May 2015, 20:58

Hi Greg!

Interesting background! I am myself quite "into" quantifying Cs137 in soil, as some parts of Sweden got quite alot of fallout. I have focused my efforts on an area where my wife's grandparents happen to live. We go there occasionally, and I bring back soil samples.

I have until now been doing quantification with an 1" well crystal (see thread in old forum), but will in time trade up to a bigger crystal that will be better at seeing the 662 keV photons.

http://www.gammaspectacular.com/index.p ... &path=1283


If you are interested, I could send you some soil in test tubes with Swedish soil, which I have measured and quantified the Cs137 content in. As a standard, I have used soil measured at the Swedish Radiation Safety Authority, so as far as a standard goes, it is quite accurate. Still, there are other sources of error, but at least one gets a feel for what kind of response one gets from a certain activity level. The soil I have now is between 1-2 kBq/kg. In my analysis, I analyse a few grams of it in the well crystal. I have plenty of these test tubes and would be happy to send you a few tubes of it, and a few empty tubes for your other samples if you are interested.

It sounds very interesting that you could collect samples from a test site. I for one would be quite keen to get my hands on such samples!
Karl Brehwens
Eskilstuna, Sweden.

Setup: 5 cm lead castle, 2mm copper lining. Gamma Spectacular Pro 2002, Sound Blaster Live! 5.1,
Primary detector: Scionix refurbished 2x2" NaI(Tl) well detector, 7.5% @ 662 keV

Greg
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Re: Hello, I'm Greg in California

Post by Greg » 09 May 2015, 06:59

Thank you very much Karl.
I've read many of your post and am honored by your response. I would love to swap samples. Not sure of the customs issues? How does Pacific Ocean water samples sound? The test site that I was speaking of is a below ground shot that apparently had some venting. There is a second site that is a few hours from this one that created a huge subterranean cavity a large sink and swallowed up much of its monitoring equipment. I would like to also check that one out, however right now I would be happy to get this side well up and running.
The savager that I bought the side well from sent me two others to choose from, a Bicor and a Saint-Gobain. From my research it looks as if Saint-Gobain makes both detectors. The Saint-Gobain will not conduct until around 1000v then it seams to short, my voltage indicator on my GS flashes, gives random voltage readings and even a neg 1 volt. The other Bicor much like the first Bicor just starts conducting at my voltage limit and I can only get a strong enough signal for the software by turning the mic volume up, adding 20 Db boost and increasing the gain on the GS.
One of my big issues is removing the back plate off of the detector to inspect the PMT on the side wells. I was hoping you or someone else might have some insight and/or knowledge to share with me on these detectors voltages and access.
I bought a 1x3 Square Bicor to make sure that I wasn't having problems with my laptop or sound card and it is giving me two beautiful peaks for Cs-137 at 700v. I hope to compleat setting it up today.
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Bicor sidewell
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Bicor sidewell
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Steven Sesselmann
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Re: Hello, I'm Greg in California

Post by Steven Sesselmann » 09 May 2015, 10:02

Greg wrote: The Saint-Gobain will not conduct until around 1000v then it seams to short, my voltage indicator on my GS flashes, gives random voltage readings and even a neg 1 volt. The other Bicor much like the first Bicor just starts conducting at my voltage limit and I can only get a strong enough signal for the software by turning the mic volume up, adding 20 Db boost and increasing the gain on the GS.
I am a little bit concerned about what you write here.. Does your GS work with any other detector? Is the voltage nice and stable below 1000V? You need to get to the bottom of where the arc is taking place, is it in the detector, the cable or in the GS?

Your detector has three cables coming out, ground, HV and signal. It's not always obvious which is which, unless you can see the divider. It's likely that the thin wire is ground.

Large voltage spikes can damage the opamp (LM358) in the GS-PRO which regulates voltage, if this happens you will see random voltage drift. The part is easily replaced without soldering and costs about a dollar.

Steven
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | beejewel.com.au |

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iRad
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Re: Hello, I'm Greg in California

Post by iRad » 10 May 2015, 07:48

The large coax is more than likely the signal wire, but like Steven said, the other two wires might not be the obvious ground and HV positive the colors would seem to indicate, as the voltage divider could be setup for negative bias.

A simple way to determine otherwise, is to see if any of the wires are grounded to the housing. Most likely (for many reasons other than just the obvious shock hazard) if the housing is grounded, then it is not negative bias. BUT, if it is not grounded at all, I would suspect the VD of being wired for negative bias.

It looks like the wiring is potted inside of the rear housing, is that correct? If not, you could probably knock off the back cap by taking a sharp tool (chisel) to the seem and gently seeing if you can persuade it to come loose. Don't try heat, as it could damage the VD, wiring and/or PMT permanently. Chemicals that work on epoxy (like chloroform) have proven helpful to me before.

If you can get the cap off, even if it is potted you may still be able to use small tools to remove the potting if soft enough.

Cheers, Tom
Cheers, Tom Hall / IRAD INC / Stuart, FL USA
Please check out my eBay Store: http://stores.ebay.com/The-Rad-Lab

Greg
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Re: Hello, I'm Greg in California

Post by Greg » 10 May 2015, 17:24

Thank you Steven and Irad,
Ya, Steve I do have a plastic detector(Irad special)and I got a cheap 1" NaI(TI) square Bicor to check my computer and software.
"I bought a 1x3 Square Bicor to make sure that I wasn't having problems with my laptop or sound card and it is giving me two beautiful peaks for Cs-137 at 700v. I hope to compleat setting it up today."
It was advertised as a 1x1x3 however it reads 1.25x1.25m3/1.25L. It gives me two nice peaks for Cs 137 with a 5 u and with a .1 u Ci. source. However, that's all I can see with it, I'm getting a lot of scatter. I'm still working on my castle and need copper to complete it. It is a paint can type (peanut can) with 4.5 cm lead(retired dive whts.) This is stacked onto a second can to make a Marinelli beaker like arrangement with 100 mm to sample.

One side well detector is obviously bad and the other two start conducting just below my voltage limit. So I was hoping I would be able to pull the back and with Steven's help make adjustments to the voltage divider. But at this point the one I mark is the one I buy. So I'm a little reluctant to start hammering on the back.

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Steven Sesselmann
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Re: Hello, I'm Greg in California

Post by Steven Sesselmann » 10 May 2015, 20:04

Greg,

You should be able to turn up your GS-1102-PRO higher than 1100V, the only limitation is the BNC connector which might fail somewhere around 1400V. If you are unable to turn the voltage up over 1000V, then the problem is the voltage divider in the detector, and the GS can't supply the current. The solution would then be to change the voltage divider to something with higher resistance. 12 M Ohm to 18 M Ohm is good.

If those detectors need over 1000V to give a pulse, the chances are they might be old and, 1000's of hours use has depleted the inside coating on the cathode.

Steven
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | beejewel.com.au |

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