Lithium Fluoride detectors?

[johnp]

I came across references to LiF dosimeters recently; that it's used to monitor neutrons. When the crystal is heated after being irradiated, it emits light in proportion to the radiation. I searched the forums here and saw only one brief mention of this kind of detection. Would this be suitable to validate fusor work?

[Wilfried Heil]

Probably not sensitive enough and not a real time detector. The total emitted neutron doses here are very small, fortunately. What would work is a (Li-6)F:Eu scintillator with a moderating sphere. I've seen some appear used occasionally, but they are quite expensive, about twice the cost of a 20" He-3 detector.

[Frank Sanns]

I have one of these:

http://www.raesystems.com/~raedocs/Data ... 051507.pdf

It has worked with my fusor and also at Jon Rs with good agreement with an He3 tube.

Frank Sanns

[ertic]

Hello! Look for such detectors at https://ecotestgroup.com I have ordered some detectors for my needs from that website, and they work very nice. Maybe you will find something for you there too

[Rex Allers]

Frank,
That pdf link didn't work for me. I browsed down from the top level and found this:
NeutronRAE II
http://www.raesystems.com/products/neutronrae-ii
(there's a data sheet link on that page, but different file name)

Is that the same device you have? Datasheet says the neutron detector is a LiI(Eu), 1cc in size. Does that type of crystal detect fast neutrons directly? Just 1cc seems like it would be very small for seeing the kind of flux coming out of a typical fusor.

[Rex Allers]

Jonathan (ertic),

You seem to be a brand new member. You didn't use your full name as forum rules require.

On the link you gave, Firefox won't let me connect. Says the security is invalid for the connection and could be dangerous.

Not sure if there is anything bad there but I'm not going to risk trying to go there to test it. Seems a bit odd that a brand new member would immediately post a link that looks sketchy.

[Rich Feldman]

Rex, thanks for shining a skeptical light on the ertic post and suspicious link.

Too bad Frank's NeutronRAE_ii experience, with the lithium iodide scintillator, didn't come up a year or two ago.
We know the LiI(Eu) crystals do respond to fast neutrons. Whether they respond much more readily to thermal neutrons was a point of gentle argument here.

Bern Bareis used data from a NeutronRAE_ii in a fusor neutron claim, made in his introductory post to fusor.net.
A few skeptics suggested that he add a moderator and see if his (small) count numbers went up.
Bern dismissed that multiple times, citing an RAE spec-sheet table which gives a 2:1 range for neutron sensitivity.
In same table, a different row says the neutron energy range is thermal to 14 MeV.
At least one reader concluded that the spectral sensitivity variation is less than 2:1 over the whole detectable energy range!

Someone wrote to RAE, and got a vague response that a neutron moderator would increase the count. Someone cited spec sheets from Polimaster brand, whose gamma/neutron dosimeter line includes units with a whole 2cc of LiI(Eu). Polimaster gives a sensitivity for Pu-Be neutrons, and a sensitivity value 20x greater for thermals. Someone suggested that the funny units in RAE sensitivity value, counts per 2.5 n/cm^2, hinted at some particular source in the RAE test lab. Bern went and got a BTI detector and a fusor.net neutron trophy. Said if people didn't trust RAE counts by themselves, why would they trust counts from RAE with moderator? We've never yet seen the two side by side. Maybe Frank can help here.

[Frank Sanns]

I am a little late back to this thread as it is an old one but a good one to revive.

The NeutronRAE has come out with the version II. I have version one. I also have their PM 1401GN that is both gamma and neutron. It has a He3 tube as the neutron detector.

A word about both. They both do better with a moderator present. They are made to be worn or carried in close proximity to the body (a good moderator) to work best. For their size, they work well with the larger He3 product doing a little better. This speaks highly of the much smaller and less expensive Neutron RAE. The tiny crystal does a good job at detecting neutrons.

There is a downside to the detectors though and that is the gamma rejection. I have seen that a high gamma field can also show up as some neutron counts. This is most prevalent when there are at least a very small number of neutrons present. It is an inconsistent reaction to gammas that makes it difficult for me to quantify it. Sometimes gamma alone will show neutrons present and other times it does not. It does not seem to have anything to do with the energy of the gammas but maybe more of the self calibration that it does on start up. There are some parameters that can be adjusted but I have not really experimented much with them.

The NeutronRAE is super sensitive to gammas (>~50kev) so it is a great hand sized prospecting instrument. All of the examples of Mauch Chunk minerals that I have found were with this detector alone.

My only complaint about the first generation of the device is that it will drain a battery when it is turned off. On is super for weeks but if you turn it off, the battery is dead overnight. You have to remove the battery after each use or you will be replacing it.