Neutron Detection Pager

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Post Reply
User avatar
Frank Sanns
Site Admin
Posts: 1552
Joined: Fri Jun 14, 2002 6:26 pm
Real name: Frank Sanns
Location: Pittsburgh, PA USA

Neutron Detection Pager

Post by Frank Sanns » Mon Dec 10, 2007 7:04 am

At HEAS this past year (2007), I brought a radiation detector made by NeutronRAE. The (CsI) detector is incredibly sensitive to gammas above around 60 KeV and a second detector using a Li6I crystal is sensitive to neutrons from thermal to about 14 MeV.

I have run this unit with my fusor and get counts of between 1 and 2 uSv/hr. Being the proud owner of such a compact unit I took it to Richard's to show it off. Unfortunately when Richard fired up his fusor, my NeutronRAE did not count any neutrons. It did "ping" a few times in the lab but even when Carl held it against the shell of Richards fusor, it was silent. There were some comments that the detector would not count fast neutrons and even though I thought otherwise, I was in favor of a test within a moderator in contact with Richard's fusor. Still nothing. My bubble was burst or at least wounded but I was not yet convinced of a problem with my pager detector.

Armed with the data from my personal fusor and the suspicion that my counts MIGHT be from noise, I decided on a high altitude test. On my recent East Coast to West Coast flight, I took my detector and my GPS. What I found was that the gammas were at a minum at around 3,000 ft ASL and increased rapidly above 20K feet. I attributed this to decreasing ground radiation at higher elevations but more cosmic radiation. This would only be true in air travel since on a mountain, the ground would still be there to contribute to background.

The neutron counts were <1 uSv/hr below 25,000 ft. At 35,000 ft the NeutronRAE read approximately 2.5 uSv/hr and at 40,000 ft was indicating 3.5 uSv/hr. These numbers were very consistant throughout the flight and were similar a week later on the return flight.

During my visit at Jon Rosenstiel's, we positioned the neutron detector on Jon's fusor and also behind a lead plate around 0.3 meters away to eliminate the possibility that high levels of gammas may be causing a false positive neutron reading.

On a run correlated with Jon's instrumentation and a bubble detector, the pager neutron detector agreed with Jon's. Attached is a photo of the pager behind the lead shield on a run of 3.5 E 5 neutrons/second. It is reading 4 uSv.

My three major conclusions from these experiments are:

1. The NeutronRAE is a good neutron detector for thermal and high energy neutrons.

2. RF noise in fusors can fool even the best detectors and can contribute to counts on electronic insturmentation.

3. High altitude flights have ~300 times the the gamma flux and even greater neutron flux than at sea level.

The neutron flux at 40,000 ft. is sufficient enough to activate metals such as silver. In a future flight I am going try a beta only detector and a piece of silver to try activation at altitude. In the mean time, I do not think I will travel with any coins in my pockets when I fly. The human body is a good moderator and activated silver is a fairly hot emitter.

Frank S.
Attachments
FrankSNeutronRAE.jpg
FrankSNeutronRAE.jpg (21.21 KiB) Viewed 1350 times

DaveC
Posts: 2346
Joined: Sat Jun 30, 2001 5:13 am
Real name:

Re: Neutron Detection Pager

Post by DaveC » Mon Dec 10, 2007 9:13 am

Very interesting, Frank. I was wondering if, at Richard's your detector might have been saturated.

Not sure I was around when you were out here. Sorry to have missed your visit.

Dave Cooper

User avatar
Frank Sanns
Site Admin
Posts: 1552
Joined: Fri Jun 14, 2002 6:26 pm
Real name: Frank Sanns
Location: Pittsburgh, PA USA

Re: Neutron Detection Pager

Post by Frank Sanns » Mon Dec 10, 2007 3:21 pm

Hi Dave,

We did think it might have been saturated with the occasional ping and the high gammas in Richard's lab. This still might be a consideration at that particular location. Richard IS making neutrons as evidence by the bubble detectors but I can't remember his neutron flux based on the bubble detector. Jon. and I thought the He3 electronic reading was in the 1.6 E 5 n/s range hence our experiment to try to duplicate the flux.

Sorry I missed you and the others on the West Coast but my time was very limited and it was complicated by our visit being during the day while many of you were at work. I should be out there again in the not too distant future and I will try for a weekend day next time.

Frank S.

User avatar
Richard Hull
Site Admin
Posts: 10871
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Neutron Detection Pager

Post by Richard Hull » Mon Dec 10, 2007 5:59 pm

Based on bubble detector readings at my fusor, I was producing about 2X10e5 neuts/sec isotropic at HEAS. This is represented now by about 11,000 CPM on my He3 counter. I plan on moving it, yet again to about double the current distance now to further down the counts. Naturally, an all new calibration run group will be demand referenced against the bubble detector.

I was able to activate silver at HEAS, but to a very low level. I did not leave the fusor in operation longer than 12 minutes at full power. I felt that my neutron oven was not advantageously placed.

Due to the press of other projects, I haven't fired the fusor up since late October when I did a null test. (ran the fusor with air). The He3 count was on the order of about 15cpm at 30kv over a 5 minute run. Zero bubs in the BTI detector. The normal, power off, background count is about 6-8 CPM. So there is no statistically significant electronic noise in my He3 counter system considering when using D2 I get about 10,000 cpm. at 30 kv. My current supply will not hit 40KV without saturating the transformer.

As currently configured, I figure Fusor IV is pretty much limited to about 250,000 neuts/sec @ 35kv and maybe pushed to about 300K/s if I allow a bit of saturation on the xfrmr.

Why Frank's neutron detector would not function at HEAS remains a mystery. I do not think if would even record the massive, hot, 13 lb. U boulder of gamma radiation I had at the event. That registers about 40 mrem/hr on my cutie pie.

That boulder has been consigned to a tight gasketed, 20mm ammo tin in my outshed now as the radon level in the lab trippled in a week due to its presence on the bench. God only knows what a mine shaft with walls of that stuff did to the 50's Marlboro men who mucked out tonnage each workday.

Richard Hull

Note the original figures for the He3 counts from Fusor IV given here were in error, (low by one order of magnitude), and have now been corrected. 12/11/07 (see subsequent posting admitting to the error) RH
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

User avatar
Frank Sanns
Site Admin
Posts: 1552
Joined: Fri Jun 14, 2002 6:26 pm
Real name: Frank Sanns
Location: Pittsburgh, PA USA

Re: Neutron Detection Pager

Post by Frank Sanns » Mon Dec 10, 2007 8:53 pm

Richard,

Jon and I were trying to remember your BTI count. His was ~40 bubbles (38 bubbles/mrem) in 5 minutes at the 1.5 E 5 neutron flux (30 kv, 10 ma).

His 5 minute activated silver disk gave >500 cpm on a pancake probe. After around a minute, the rate started to fall in the sub 500 cpm range.

Frank S.

User avatar
Richard Hull
Site Admin
Posts: 10871
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Neutron Detection Pager

Post by Richard Hull » Tue Dec 11, 2007 8:57 pm

I had 63 bubbles in mine after 12 minutes. (counted and averaged by three people (Jon, Carl and Kevin Dunn). I was running mine at about 32kv and 7ma. My calcs averaged 200,000 n/sec out of this.

My count on the silver was about double background (260 cpm) but we had a time lag getting it out of the neutron oven and over to the GM counter. Gotta' work on that.

I was in error in my last post! I should not work from memory alone! I was off by one order of magnitude on the HE3 counts in my previous posting, (now corrected), as I later checked my recorded data log for that day as well as the report given on the HEAS 2007 report in image du jour...... I was getting 11,000 to 12,000 cpm on my He3 at HEAS during that last super run with a total during the 10 minute run of 110,334 counts. I definitely gotta' move that HE3 back a bit.....it is still way too close! Of course the statistics of an 8 cpm background against a 11,000 cpm detection count makes for a grossly reduced background adjustment, assuring that the count ....is the count.

Let's see.... 96 background counts over twelve minutes subtracted from 110,000 is............Everyone gets the idea.

The null, air noise tests I did on October 27th did show the count about tripling my background count at 30kv ,but even that was insignificant and might be the result of desorbing deuterons from walls. Still, even if the counts were noise, 20 counts per minute is nothing agianst a recorded 11,000-12,000 cpm detection rate during fusion runs.

I am quite confident in my electronic counter now.....I just gotta shove it over in a corner to reduce the count by hopefully, over an order of magnitude. Never thought I would be "count rich" in this biz.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

User avatar
Frank Sanns
Site Admin
Posts: 1552
Joined: Fri Jun 14, 2002 6:26 pm
Real name: Frank Sanns
Location: Pittsburgh, PA USA

Re: Neutron Detection Pager

Post by Frank Sanns » Fri Feb 29, 2008 3:40 am

George,

I use NiMH batteries and it runs for 2-3 weeks on a charge if left on. When switched off it only runs for 2 days before consuming the battery.

I thought that it might be just my unit but sounds like you experience the same? For the most part I just leave my on since it never seems to false alarm and it is a good detector for neutrons. Around once or twice a week it picks up something on the neutron side as evidence by the distictive neutron alert tone.

This past week I was in a hostipal waiting room with my mom and my detector started screaming at thousands of counts per minute. It gave me a start at the rate of increase of the radiation and its high intensity. Just as I was getting alarmed it started to fall as quickly as it rose. The interesting thing was nobody was around. Unknowing to me I was near the back side of an elevator shaft. I figure I picked up somebody who had just had a nuclear medical test going down the elevator on the other side of the wall. It sure got my attention!

Really sensitive and Interesting unit but it does have the bug of sucking down the battery when off.

Frank S.

Post Reply