Testing of a Modified GS-STANDUP

How to build the perfect shield for your measurements? Discuss it here!
Post Reply
User avatar
isoenzyme
Posts: 33
Joined: 20 Feb 2019, 17:36
Location: Utah (USA)
Contact:

Testing of a Modified GS-STANDUP

Post by isoenzyme » 27 Mar 2019, 16:44

The following describes the modifications I made to my GS-STANDUP and the results from the initial testing. I'd be interested in comments from anyone who knows about shielding as to whether there are other tests I should run or other modifications that should be made.

The GS-STANDUP is a fantastic product. I added a shielded door that incorporated a sample holder (for 1" sealed sources) that can be used to hold a variety of other samples simply by rotating it 180 degrees. Photographs of said door are shown below.
GS-STANDUP-Shielded Sample Holder.png
The door (which is filled with lead shot) and plexiglass sample holder in the GS-STANDUP.
GS-STANDUP-Shielded Sample Holder.png (380.99 KiB) Viewed 1361 times
The interior of the door is filled with lead shot (about 1 1/2" thick) and has an integrated sample holder that places 1" sealed source disks directly below the center of the 2" detector.

Modifications were made to the well that holds the detector. It was first lined with a layer of >99% tin (0.03125") and then pure >99.999% copper (0.02"). This shielding is about 6 inches tall from the bottom of the well. The padding at the bottom was reinstalled to protect the detector. The interior of the STANDUP was filled with lead (Pb) shot (about 90% full until I ran out of shot). The added tin (Sn) and copper (Cu) shielding is shown in the photographs below.
GS-STANDUP-Sn-Cu Shielding.png
Tin (Sn) and copper (Cu) shielding added to the bottom and sides of the well that holds a 2" detector.
GS-STANDUP-Sn-Cu Shielding.png (288.51 KiB) Viewed 1361 times
The efficacy of the modified GS-STANDUP was tested using a 1000 nCi Na-22 source taped to the outside of the shielding (location highlighted with the red arrow in the photograph below). The CsI(Tl) detector was held vertically in the same position it would occupy inside the shielding and the same distance away from the outside of the shield as it would be when installed inside the shield. The counts/second were recorded for a little over 200 seconds then the detector was relocated inside the shield and counting continued.
GS-STANDUP-Na22 Testing.png
The experimental setup used to test the efficacy of the modified GS-STANDUP shielding.
The results of this trial were:
Lead Shielding Na-22 Results.png
Recorded counts/second before and after the detector was placed in the modified GS-STANDUP.
Lead Shielding Na-22 Results.png (45.55 KiB) Viewed 1361 times
Background spectra (10 minutes) were collected before and after the shielding were added:
Background Pb vs noPb.png
Background spectra of the empty GS-STANDUP with installed door-sample holder before and after the shielding was added.
Background Pb vs noPb.png (54.92 KiB) Viewed 1361 times
What surprised me is how little Sn and Cu was needed to cut out the x-rays:
Cs-137 ZnSnCu Shielded.png
Spectra of a 1000 nCi Cs-137 source before and after the Sn and Cu shielding was installed. (No x-rays from the Pb shot are detected that I can see.)
Cs-137 ZnSnCu Shielded.png (53.85 KiB) Viewed 1361 times
I'm still trying to get the hang of how to adjust the volume on the GS-USB-PRO and using the PRA software so things might not be optimized as well as they could be. Are there other or better-designed experiments that I could be using to test the modified shielding? (I'd ultimately like to detect MUCH smaller amounts of radium (Ra) and uranium (U) and hope that good shielding will make that possible.)
Christopher Lloyd
Salt Lake City, Utah (US)


Setup: Modified GS-STANDUP-20 with GS-USB-PRO
Primary Detector: GS 2" x 2" CsI(Tl)

User avatar
Steven Sesselmann
Posts: 693
Joined: 27 Apr 2015, 11:40
Location: Sydney
Contact:

Re: Testing of a Modified GS-STANDUP

Post by Steven Sesselmann » 28 Mar 2019, 17:13

Christopher,

Wow, that's a very nice report, you have really dressed up the STANDUP :D

I am also amazed at how you managed to attenuate the Pb x-rays with only 0.8 mm Sn, this is a good improvement, I have thought about it, but haven't found a good source of Sn.

The cap is also very neat, nice work, I shall create a link to this post from the GS-Standup page.

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

User avatar
isoenzyme
Posts: 33
Joined: 20 Feb 2019, 17:36
Location: Utah (USA)
Contact:

Re: Testing of a Modified GS-STANDUP

Post by isoenzyme » 29 Mar 2019, 05:41

Steven,

Thanks so much for the kind words. I'm pretty sure that the Pb shot-filled "door" was your idea from the original post on your initial STANDUP construction many moons ago (viewtopic.php?f=10&t=177), but it sure worked nicely as a good solid way of integrating a replaceable sample holder to keep geometric variability at a minimum. You are also right about difficulties finding a good source of tin (Sn). I found MANY places on the internet that tried to pass off "tinned sheet metal" as Sn and didn't seem to know the difference between iron (Fe) and Sn. If you or others are interested I finally got some good Sn from https://www.mcmaster.com/ - though their tin isn't free their copper was of exceedingly good quality and relatively inexpensive. I originally expected that multiple layers of 1/32" Sn would be required so I've got quite a bit left over if anyone could use some.

The only other thing that I should have mentioned in the modifications to the GS-STANDUP was that it originally came with a foam weather strip pad around the top of the well that holds the detector. This was a nice touch as it kept my very expensive detector from bouncing around the pipe, but said foam had to be removed to get the Sn and Cu shielding in the well. After the shielding installation it was replaced with a strip of thicker 1/4" foam weather stripping that now holds the 2" detector centered in position with what I refer to as a "honeymoon tight" hold (i.e., the detector is held in exactly the same place each time it is inserted into the well).

Christopher
Christopher Lloyd
Salt Lake City, Utah (US)


Setup: Modified GS-STANDUP-20 with GS-USB-PRO
Primary Detector: GS 2" x 2" CsI(Tl)

User avatar
Steven Sesselmann
Posts: 693
Joined: 27 Apr 2015, 11:40
Location: Sydney
Contact:

Re: Testing of a Modified GS-STANDUP

Post by Steven Sesselmann » 29 Mar 2019, 09:35

Christopher,

The only problem I see is that you have lined the bottom of the detector well, which filters out low energy gamma.

Ideally you should use the surplus tin and copper to line the inside of the sample chamber, and remove the layer between the detector and the sample chamber.

Hope that makes sense.

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

Sebastien_billard
Posts: 25
Joined: 28 Jan 2019, 04:28
Location: Marcq en Baroeul
Contact:

Re: Testing of a Modified GS-STANDUP

Post by Sebastien_billard » 29 Mar 2019, 23:48

This seller has affordable 0.2mm tin (Sn) foil : https://www.ebay.fr/itm/Feuille-de-meta ... Swx6pYrWJn the only downside is that only one size is proposed.
Sébastien Billard, north of France
http://www.sebastien-billard.fr/tacticool/

25*25mm NaI detector

cicastol
Posts: 65
Joined: 19 Jul 2017, 21:39
Contact:

Re: Testing of a Modified GS-STANDUP

Post by cicastol » 30 Mar 2019, 00:03

Hi,
i can't understand the 137Cs spectra with shield, Ba X rays (32keV) are gone ,it looks like the source is placed outside the shield !
Ciro

User avatar
isoenzyme
Posts: 33
Joined: 20 Feb 2019, 17:36
Location: Utah (USA)
Contact:

Re: Testing of a Modified GS-STANDUP

Post by isoenzyme » 08 Apr 2019, 12:34

Ciro,
Sorry it wasn't clearer. The Cs-137 source (1 uCi) was tested on different days - once before any lead shot or Sn/Cu shielding was added and one after all the shielding was in place. In both these spectra the source was INSIDE the GS-STANDUP. The source that was used outside the GS-STANDUP was a 1 uCi Na-22 (to compare how many counts the detector found per second when outside then inside the shielding. I think that the Cs-137 graph looks a bit 'wonky' because I'm still learning how to use my system (and especially the software) - it could be understood that using slightly different calibration methods would shift the energies of the detected peaks but I still have yet to figure out why the intensity of the peak at 661.7 keV would be lower with the shielding in place. Hope that helps clear it up.
Christopher Lloyd
Salt Lake City, Utah (US)


Setup: Modified GS-STANDUP-20 with GS-USB-PRO
Primary Detector: GS 2" x 2" CsI(Tl)

cicastol
Posts: 65
Joined: 19 Jul 2017, 21:39
Contact:

Re: Testing of a Modified GS-STANDUP

Post by cicastol » 08 Apr 2019, 19:25

Hi Christipher,
i readed later that you lined the bottom of the detector, as Steven said you need to use Cu/Sn to line the shield,not the detector, otherwise the x-rays lines disappear.

Remember that lininig the shield reduce Pb Xrf but add a lot of scatter in the lower end of the spectrum.
Steven Sesselmann wrote:
29 Mar 2019, 09:35
Christopher,

The only problem I see is that you have lined the bottom of the detector well, which filters out low energy gamma.

Ideally you should use the surplus tin and copper to line the inside of the sample chamber, and remove the layer between the detector and the sample chamber.

Hope that makes sense.

Steven
Ciro

Steve C
Posts: 5
Joined: 29 Nov 2018, 00:57
Location: USA
Contact:

Re: Testing of a Modified GS-STANDUP

Post by Steve C » 02 May 2019, 04:56

I like your modifications to the GS-STANDUP very much. I had intended to build something similar for mine from lead shot-filled PVC pipe which would either slip over the specimen well opening or be inserted into it. However, I could not find any PVC fittings that would work, due to what I am guessing are metric-measurement Australian PVC fittings. Instead I used the few parts I had cobbled together to make a lead shot-filled cover to go over the detector well. I have the feeling it has only a marginal effect on background reaching the detector from above, but I had the parts and the shot, so why not?
Steve Conway
San Angelo, Texas, USA

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest