Gamma Spectrometry Forum

By using moderators such as borated paraffin or water or barium sulfate, is it possible to indirectly detect neutrons using a NaI (Tl) detector?

Hi Geoff,

Never tried it but I expect that there will be some effect to see when the Neutrons are thermalized and enter the NaI(Tl) main problem is, how do you separate the Neutrons from the Gamma's/ Beta's etc. e.g. background?
I would expect that they will be all over the spectrum, so you cannot recognize them as Neutrons.
But If I have some time I shall do a simple test it at work next week, only problem is that our Neutron source(CF-252) also gives gamma's so I have to block them first to test it.
But now that I think of it, maybe can put the NaI(Tl)detector in the lead castle and the source with moderator on the outside that could work .

Luuk

Geoff,

If you have enough neutrons and enough boron you should be able to see a peak at 477 keV.
I have never tried this, but can't see why it wouldn't work. Maybe you could make a borated paraffin block with a hole for the detector, so it has 3π surround.

Steven

Ok, cool. I'll set up an experiment tonight to run for a day or so. I don't have a known neutron source, so this might not work at all any way. I'm trying to find out if I've successfully made beryllium hydroxide, and if when pressed with a .9uCi 241Am source neutrons are produced.

I don't have much borated paraffin wax, but I do have a few hundred pounds of sodium tetraborate decahydrate and a Marinelli beaker!

Alright, initial experiment is set up and running. I used my potential source, followed by a 1mm sheet of lead, a 2mm sheet of pewter, a 1mm sheet of copper and finally a 20mm thick disk of borated paraffin wax.

Geoff,

Don't be too disappointed if you don't get a big peak, I can't recall the exact number, but I think the AmBe reaction is something like 10,000:1 so with 0.9 µCi the neutrons might be far and few between.

Steven

I have it set up to run for 48 hours. At the end I'm going to replace the current source with one that is just 241Am in the same configuration and subtract that spectrum from the first. I have no expectations of actually seeing anything, but it might surprise me.

RESULTS!
After runs that weren't 48 hours because I forgot to change a parameter in the PRA settings, I have results!

I took the data from the possible neutron source, subtracted the data from the regular americium source, and found....

Nothing.

I guess I have to buy one of your neutron detectors Steve.

Geoff,

Check out Carl Willis video about neutron detection here. https://youtu.be/skP3SWWR9Kw

and this https://youtu.be/uQ8vwevCq8Q

Obviously Carl is doing it the old school way, but it gives some indication.

Steven

I was digging around in my electronics spare parts bin and found 2 Scionix LiI(Eu) detectors! I took one apart and mounted the crystal to a PMT. Now, what should I be looking for in terms of PRA? I verified that it works by cranking up the voltage to 1000 and seeing the gamma spectrum for Americium 241. After lowering the voltage down until no gamma rays were detected I introduced the possible neutron source, with moderator, and started seeing 1 count every 2 or 3 seconds.