Harshaw 16X16MKS12/3.5 B-X scintillation probe

Scintillation crystals, PMTs, voltage dividers etc...
Post Reply
drovak
Posts: 4
Joined: 06 Oct 2019, 14:09
Contact:

Harshaw 16X16MKS12/3.5 B-X scintillation probe

Post by drovak » 07 Oct 2019, 11:53

I got this Harshaw 64 cubic inch scintillator off of eBay, where all good things come from. I tested it with an Eberline ASP-1 at 1000V, but haven't gotten the proportional background rate I expected for its volume. With its 64 cubic inch NaI(Tl) crystal, I read a background of 21,000 CPM. In comparison, my brother's Exploranium GR-130 with a 4.5 cubic inch crystal yielded 3200 CPM. I expected the Harshaw to show about 14 times the rate that the Exploranium showed based on the difference in crystal volume. Does this seem about right, or is the crystal likely showing signs of aging? In the coming months I plan to get a Gamma Spectacular USB spectrometer to start characterizing this and other scintillators I have access to.

Does anyone know if this type of scintillator is able to be disassembled further with relative ease? It appears it may be epoxied, but I didn't attempt to mess with it further.

Thanks in advance!
Kyle
Huntsville, AL
USA

User avatar
iRad
Posts: 93
Joined: 01 May 2015, 12:27
Location: Stuart, FL USA
Contact:

Re: Harshaw 16X16MKS12/3.5 B-X scintillation probe

Post by iRad » 08 Oct 2019, 00:14

Hi Kyle - Could be a number of issues with either the crystal or PMT (or the VD value is too low for the meter to drive efficiently). Most detectors that size I have seen are easily disassembled, however it would be nice to see some pictures and more descriptions of your testing to offer better opinions. Tom
Please check out my eBay Store: http://stores.ebay.com/The-Rad-Lab
Cheers, Tom Hall

luuk
Posts: 209
Joined: 01 May 2015, 21:00
Location: the Netherlands
Contact:

Re: Harshaw 16X16MKS12/3.5 B-X scintillation probe

Post by luuk » 08 Oct 2019, 05:39

Hello Kyle,
Even if a crystal is old or wet it still will give you more or less the same amount of counts as a new detector, only thing that will happen is that the resolution is decreasing and peak(s) will be broadened, only if the crystal is very wet you will lose some low energy counts in the wet surface.

I think you made a mistake with your expected background between the small 4.5 inch³ and the large 64inch³ crystal.
Most background will be found in the low end of the energy scale somewhere between 0 and 1.4Mev, easy to see if you look at your background spectrum.
So a lot of the background signal will be stopped in the first 1-2 cm of the crystal, it means that the surface off a crystal is actually more important than the volume, and surface of your large crystal is not 16 times your small crystal.

Example: 1x1 (cylinder)crystal has a volume of 0.79 and a surface of 4.6
2x2 (cylinder)crystal has a volume of 6.68 and a surface of 18.9
So the ratio volume is 6.68/0.79 =8.5
Ans the ratio surface is 18.9/4.6=4.1

So you may expect a background of 8.5 times according to the higher volume but your surface that is important for the low background counts is only 4.1 times.
Of course that the larger crystal will show more higher energies but they have only a small contribution to your background counts.
I could be wrong but I think it is a logical explanation.
Luuk

drovak
Posts: 4
Joined: 06 Oct 2019, 14:09
Contact:

Re: Harshaw 16X16MKS12/3.5 B-X scintillation probe

Post by drovak » 08 Oct 2019, 11:57

Tom: I put photos up here. https://imgur.com/a/wsNrAeN Are there other photos you would like to see?

My brother can chime in more on the testing, but suffice it to say, it was connected up to the Eberline (and my Ludlum, which is not calibrated in CPM) and was compared directly to the Exploranium. The voltage divider is comprised of 10 MEG resistors, so I assume the Eberline will have no trouble with that. Does that sound reasonable with the VD?

Luuk: thank you for the information. I had not thought about how the crystal thickness plays into detection. That gives me better hope of this crystal being relatively healthy.
Kyle
Huntsville, AL
USA

drovak
Posts: 4
Joined: 06 Oct 2019, 14:09
Contact:

Re: Harshaw 16X16MKS12/3.5 B-X scintillation probe

Post by drovak » 08 Oct 2019, 13:46

Also, does anyone have a clue as to the nomenclature of this probe? Can't really make much sense of it...
Kyle
Huntsville, AL
USA

luuk
Posts: 209
Joined: 01 May 2015, 21:00
Location: the Netherlands
Contact:

Re: Harshaw 16X16MKS12/3.5 B-X scintillation probe

Post by luuk » 08 Oct 2019, 15:24

Harshaw used to multyiply the the size by 4 so this detector 16x16 is actual a 4"x4", it is has a mu metal shield (M) for the (KS) I have to look not certain, the pmt(B) is 3.5" and the (X) stands for special. (not standard)
Luuk

Post Reply

Who is online

Users browsing this forum: No registered users and 0 guests