Gamma discrimination check

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Richard Hull
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Gamma discrimination check

Post by Richard Hull »

The last time I made a gamma discrimination adjustment on my 3He neutron detection system was around 2009. I thought it might be time to test to see if it was still good or needed tweaking.
I ran a background test for ten minutes and got a total of 70 counts..... 7CPM which is right in the middle of my normal 6-8 CPM background. All the current blast of testing those new Ludlum neutron counters drove my decision to practice what I preach...

I went to my out building and got my WWII turn and bank indicator with the glass removed. I brought it to the lab and using my calibrated Victoreen ion chamber with the alpha beta shield in place to see the gamma only does rate. It turned out to be 150mR/hr!! I slapped it face down on the moderator and ran another test for ten minutes and got 74 counts. Naturally, no adjustment is needed. It is to be remembered that the fusor mainly shoots out x-rays of no more than 45KeV energy here and that the Ra dial has a blast of low end gammas of 200KeV all the way up to over 1MeV! The 3He never saw them.
I put the lead glass face back on the meter and took it back to safe storage in the shed.

It is good to check on your electronic neutron counters from time to time. I ran the fusor V system up to a TIER of 193,000 n/s and activated Rhodium to 8 times background. 31kv, 10ma, 7.6 microns of D2.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Matt_Gibson
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Re: Gamma discrimination check

Post by Matt_Gibson »

Gonnna need some pictures of that thing, Richard!
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Richard Hull
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Joined: Fri Jun 15, 2001 9:44 am
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Re: Gamma discrimination check

Post by Richard Hull »

What thing? the turn and bank indicator? This is a common thing from 80% of all WWII aircraft. I found it at a hamfest about 10 years ago. I detected it 20 feet away from the table it sat on with my TSA portable gamma detector! (These are hyper-sensitive to a mere whiff of Gamma.) the T&B has radium paint on the dial plate as all WWII aircraft meters did, but it is also slathered all over the rear of the glass bow shaped ball bubble bank indicator. I have yet to see anything like it! I found another T&B from a modern Beechcraft. It is far less radioactive and illuminated. It is absolutely identical to the WWII instrument. As near as I can tell they removed virtually all of the radium and painted it solid black painting the back of the glass bow snow white. Apparently, their clean up was not well done as it is about 1/40th the radiation of the original. I have seen not one single WWII radioactive meter of any type at hamfests for the past 5 years!! Most old meters found at hamfests in the past were never cockpit instruments but from electronic gear in the belly of the plane. They were from radio transmitters, receivers, antenna tuners, and flight engineer, radio operator and navigator electronics. As such they were not heavily doped with Ra and rarely read 1mR/hr.

These are all gamma only emitters as the leaded glass stops the alphas, betas and lower energy K shell x-rays. Oddly, the Radium emits no gammas it is the massive daughter build up of many hot, short half-life gamma emitters that this puppy puts out. It is only the never seen or penetrating alpha particles from Ra and its daughters that burn the hell out of the phosphor over time.

During long bomber raids in WWII all aircraft had radium dials that would glow the dull green that was just bright enough for the pilots to see. A brilliantly lit up instrument panel of 30 or more dial indicators on a night raid would direct any intercepting fighter right to the cockpit, creating a great point to aim and kill the pilot and his co-pilot. Thus the heavy Ra loading on all meters.

No! I will not sell or loan this out as it is a perfect gamma rejection tester for calibrating and discriminating a neutron counting system. If any are still there, you'll have to get your own.

Photos attached.

It is absolutely important that such aircraft meters never be taken apart or dismantled for internal items. (against general license regs for the NRC). Use such a meter "as found" and store them out of doors in a shed and never in a dwelling. While these are usually hermetically sealed, play it say to avoid the build up of Radon in an enclosed area where people are. Thus, store out of doors.

Richard Hull
Attachments
This is the beastie!  So old and so hot that all the white zinc sulfide phosphor is burned up!  the black ball in the center rolled about based on turn or back angle.  Gravity powered.
This is the beastie! So old and so hot that all the white zinc sulfide phosphor is burned up! the black ball in the center rolled about based on turn or back angle. Gravity powered.
Turn and bank reading.jpg
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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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