Mike - That is actually not that bad for a detector that was primarily designed for counting anyway, especially considering the age. I also suspect the well lining may be made of a material other than stainless steel... (perhaps copper?). Can you discern what material the well might be made of if different than stainless steel?
Signal on the low energy end (including noise) will always increase as voltage is increased, much more than the high end. This is not the ideal detector for LEG use anyway, you should have something else for that use.
Does your detector have the 2-1/2" well, like this one: [broken link removed - steven]
Or does it have the 1-3/4" well, like this one: [broken link removed - steven]
In either case, the very large well in that detector is great for large samples that would not fit in a smaller well.
Is this Detector Too Big, Too Old, or Just Normal?
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iRad
- Posts: 217
- Joined: 01 May 2015, 12:27
Re: Is this Detector Too Big, Too Old, or Just Normal?
Last edited by iRad on 04 Jul 2020, 05:07, edited 1 time in total.
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luuk
- Posts: 313
- Joined: 01 May 2015, 21:00
Re: Is this Detector Too Big, Too Old, or Just Normal?
Hi Mike,
I must agree with Tom the spectrum looks not so bad at all.
cannot see the resolution but I see a clear acceptable peak a useful detector for sure.
Easy to see that the lower energies are attenuated the 30 KeV from Cs-137 is almost not there, but that is as I said before the thick stainless steel housing.
I expect you can use it for energies as low as 100-150KeV.
luuk
I must agree with Tom the spectrum looks not so bad at all.
cannot see the resolution but I see a clear acceptable peak a useful detector for sure.
Easy to see that the lower energies are attenuated the 30 KeV from Cs-137 is almost not there, but that is as I said before the thick stainless steel housing.
I expect you can use it for energies as low as 100-150KeV.
luuk
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Mike S
- Posts: 95
- Joined: 25 Apr 2020, 10:24
Re: Is this Detector Too Big, Too Old, or Just Normal?
Thanks for the help guys!
I'm surprised you both don't think the milkiness, cracking, or separation are major issues; it makes me wonder what "bad" looks like.
The well appears to be aluminum, it is definitely different than the rest of the housing.
It is the smaller diameter (1-3/4") well, which is still quite large. like you said, my thought was that for samples that don't go into a marinelli beaker (like rocks), I should get improved sensitivity using the well. I'm also thinking I could rig up an air sampling system with the actual filter in the well.
One of the examples linked by Tom shows a setup where a Beta detector was inserted in the well, presumably to get both readings at once. My 1.5x2.25" (gamma) detector will fit into the well. I thought it could be a cool way to take data with both detectors at once. I did try putting a sample and the smaller detector in the well. I'm not sure if it was because the shielding was not good in that configuration, or if there's a lot of scatter coming off the big NaI crystal, but the background was pretty high. I'll do some more testing at some point.
I was hoping that it would work for some of the lower activity Trinitite samples I have. The Cs peak is easy to get, but there's some interesting stuff at the low end (Am-241, Eu-152). Since most of the activity on Trinitite tends to be on one side of the specimen, using a normal detector configuration doesn't reduce sensitivity much. I do have two other detectors that work fine at the low end (example spectra from them are seen in some of the plots).
The large crystal size certainly is luxurious if the source has a little activity, I get usable spectra much faster than my other detectors. This thing is awesome at picking up the mid and higher end peaks (Cs-137 and K-40 peaks are huge compared to my other detectors). I think it will be really good at detecting low levels of environmental Cs-137, which is something I want attempt. The lack of low end response has the benefit of not requiring a graded shield.
The big push for me was to determine if I should send it back before my return window closed. I'll keep it: it wasn't that expensive for what it is, I'd end up paying shipping, I've taken it apart, and I'm not sure I'd feel good about saying it "doesn't work" since it's surplus and it works, just not like I'd hoped. I ordered some optical coupling compound and once that's here I'll reassemble as-is and just run it.
Originally I thought I would design my shield to accommodate this beast, but since it doesn't need the copper and pewter layers, I think it will get its own basic shielding. I may make it so that the cylindrical portion of the shield for this detector can easily come off and be used as an additional outer layer for my main shield.
Thanks again for the help. I'll update once I get it reassembled.
Mike S
I'm surprised you both don't think the milkiness, cracking, or separation are major issues; it makes me wonder what "bad" looks like.
The well appears to be aluminum, it is definitely different than the rest of the housing.
It is the smaller diameter (1-3/4") well, which is still quite large. like you said, my thought was that for samples that don't go into a marinelli beaker (like rocks), I should get improved sensitivity using the well. I'm also thinking I could rig up an air sampling system with the actual filter in the well.
One of the examples linked by Tom shows a setup where a Beta detector was inserted in the well, presumably to get both readings at once. My 1.5x2.25" (gamma) detector will fit into the well. I thought it could be a cool way to take data with both detectors at once. I did try putting a sample and the smaller detector in the well. I'm not sure if it was because the shielding was not good in that configuration, or if there's a lot of scatter coming off the big NaI crystal, but the background was pretty high. I'll do some more testing at some point.
I was hoping that it would work for some of the lower activity Trinitite samples I have. The Cs peak is easy to get, but there's some interesting stuff at the low end (Am-241, Eu-152). Since most of the activity on Trinitite tends to be on one side of the specimen, using a normal detector configuration doesn't reduce sensitivity much. I do have two other detectors that work fine at the low end (example spectra from them are seen in some of the plots).
The large crystal size certainly is luxurious if the source has a little activity, I get usable spectra much faster than my other detectors. This thing is awesome at picking up the mid and higher end peaks (Cs-137 and K-40 peaks are huge compared to my other detectors). I think it will be really good at detecting low levels of environmental Cs-137, which is something I want attempt. The lack of low end response has the benefit of not requiring a graded shield.
The big push for me was to determine if I should send it back before my return window closed. I'll keep it: it wasn't that expensive for what it is, I'd end up paying shipping, I've taken it apart, and I'm not sure I'd feel good about saying it "doesn't work" since it's surplus and it works, just not like I'd hoped. I ordered some optical coupling compound and once that's here I'll reassemble as-is and just run it.
Originally I thought I would design my shield to accommodate this beast, but since it doesn't need the copper and pewter layers, I think it will get its own basic shielding. I may make it so that the cylindrical portion of the shield for this detector can easily come off and be used as an additional outer layer for my main shield.
Thanks again for the help. I'll update once I get it reassembled.
Mike S
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luuk
- Posts: 313
- Joined: 01 May 2015, 21:00
Re: Is this Detector Too Big, Too Old, or Just Normal?
Hi Mike,
You have to consider a few things; even though your crystals is not perfect it is still usable in spite of all faults.
To refurbish a detector of that size and construction is out of hobby range price, because the housing is almost for sure lost during that process and that alone cost maybe 1000-1400$ (just the housing) so that is not an option I would say.
So if you did not paid too much for the detector you have a nice big detector it is not a bad deal I guess.
I have seen many detectors in a terrible condition that still work so I would say use the detector as is, and you can still do some nice measurements with it maybe not the ideal and perfect detector but it works and the results you showed are not so bad.
If you want to see a detector that is(was) in a bad condition look here:
viewtopic.php?f=5&t=99
Now that is a detector in with lots of cracks! You might find that interesting to see and read.
Luuk
You have to consider a few things; even though your crystals is not perfect it is still usable in spite of all faults.
To refurbish a detector of that size and construction is out of hobby range price, because the housing is almost for sure lost during that process and that alone cost maybe 1000-1400$ (just the housing) so that is not an option I would say.
So if you did not paid too much for the detector you have a nice big detector it is not a bad deal I guess.
I have seen many detectors in a terrible condition that still work so I would say use the detector as is, and you can still do some nice measurements with it maybe not the ideal and perfect detector but it works and the results you showed are not so bad.
If you want to see a detector that is(was) in a bad condition look here:
viewtopic.php?f=5&t=99
Now that is a detector in with lots of cracks! You might find that interesting to see and read.
Luuk
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Mike S
- Posts: 95
- Joined: 25 Apr 2020, 10:24
Re: Is this Detector Too Big, Too Old, or Just Normal?
Luuk,luuk wrote: ↑04 Jul 2020, 19:51
If you want to see a detector that is(was) in a bad condition look here:
viewtopic.php?f=5&t=99
Now that is a detector in with lots of cracks! You might find that interesting to see and read.
Luuk
That's an amazing restoration. I'm sure that took a lot of time, skill, and resources, but the results are wonderful.
Do you have any idea what a detector like mine would cost new? I have no plans to buy one, but I'm just curious.
***
Update on my detector: I'm waiting for the optical coupling compound to arrive and hopefully will have a chance to reassemble the detector this weekend. I don't expect any improvement, but I now know what to expect, and I think I'll get some good use out of the big old thing.
--Mike
