Local geographic gamma counting- how is your soil?

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Richard Hull
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Local geographic gamma counting- how is your soil?

Post by Richard Hull » Fri Sep 13, 2019 10:40 pm

This is a main collection thread in this forum for all such work. The thread that got this kicked off is to be found in the "interesting links forum"

viewtopic.php?f=22&t=12947&p=84201#p84201

Please read through the above link and then realize that all that follows are part of that thread.

Hunter Long and I are not the only ones involved here. Jon Rosenstiel will add to this thread as he finds time from work he has already done.

What do you need? At minimum a very good scintillation counter system that is portable. It is suggested that the scintillation counter have a digital rate meter. If you have no internal logging capability, a pencil and paper and a map of the area to log locations and readings would give special significance to your effort. GM counters are to be mere "tag-alongs" for unusual hot spots. (GM counters are terrible Gamma detectors)

I include some images of what I use. It is a TSA, PRM 470P

Note the manner in which it is used once out of a vehicle searching for local hot spots or for mineral ore collecting.
The image with the low count is in my computer room.
The higher reading is in my bed room which is near my lab's check source safe on the other side of the wall. Don't worry it is all gamma...My homage to Taipei City. I have a Pylon, lucas cell based radon diagnostic system and my home's living space is 2.3pCi/l, so no radon or significant daughters just pure gamma.

Richard Hull
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Re: Local geographic gamma counting- how is your soil?

Post by Hunter Long » Sat Sep 14, 2019 6:33 pm

Frank,

Safecast looks really interesting! It looks like there has already been quite a lot of geographical data collected on it. How do you all handle calibrating all of those devices?

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Re: Local geographic gamma counting- how is your soil?

Post by Richard Hull » Sat Sep 14, 2019 10:27 pm

Locally there is absolutely no need for any form of calibration. I doubt if there is any national calibration on any level!

A portable scintillator is at the mercy of relative detection area and detection volume just like a GM counter. For the scintillator it is a matter of what you establish as your base level. GM counters call it background. In gamma searches where you can set your sigma level over background, you are assured that the alarm level will trigger with that degree of confidence over your trigger setting above background. Due to the hyper sensitivity of scintillators, large or small, all readings are in counts per second. The key item to have is a digital rate meter so that once the alarm goes off you can find variations as the display finds hot spots.

A national survey from the air with a 36" or 50" scintillator will look a lot different from someone walking the ground with a 4 inch scintillator 1" above the soil. The air survey is general, the ground survey very localized and specific to within feet to inches. (Hunter Long's great GPS logger really traces his steps well!).

If I had been at that fence seen in Hunter's video, with the GM counter going nuts, once the scintillator pointed at it, I would have used a small garden hand spade and in short order would have owned the hot rock probably 4" down that was giving my counter's speaker a workout. Scintillators find stuff like this and a contact GM reading gives an idea how deep you might have to go to retrieve your hot rock. In broad land survey work, the GM counter is just not needed unless you have Hunter's good fortune. Sadly, he did not indicate if he dug it up.

Calibration is solely relative to your background set point. You don't care about how many mrem/hr there is or even how many pCi/L is in the air. You want to know what's, warm, hot, and hotter than your normal setting. What is a normal setting? That is the real question!

Big area, large volume scintillation plastics or crystals will have vastly higher counts as the "norm". Go to an area where your GM counter reads a very low background. (ideally using a 2" pancake tube). place your portable scintillator near the soil and allow it to reach a stable count....This is your normal counts per second.

Scintillators tend to sample every second and read out. The TSA Scintillators have a cool feature. When turned on after about 5 seconds, they have a ten second count down. Over this period they average out a "per second rate" this is locked into a "normal background rate" in memory. Based on where you set you alarm trigger over this normal level and the sigma for setting off the alarm, your TSA does all the rest from here.

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
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Re: Local geographic gamma counting- how is your soil?

Post by Jim Kovalchick » Mon Sep 16, 2019 5:16 am

Richard, I have on occasion driven with a large block plastic scintillator from a portal monitor in my back seat connected to a digital rate meter set to alarm at twice the typical reading I see as I drive. With regards to your area, I have seen gamma reading 3 to 4 times my chosen background on 95 south somewhere between Ladysmith to just below Ashland. The first time I saw it I was sure it was coming from a truck that coincidentally pulled along side as my alarm sounded, but it continued as it cleared me. I have since seen these elevated readings two other times passing through. For reference, I get readings of twice normal in downtown RVA, and I always assumed that was from construction material like granite in the buildings.

Jim Kovalchick

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Re: Local geographic gamma counting- how is your soil?

Post by Richard Hull » Mon Sep 16, 2019 8:12 pm

Much of what creates high readings on highways is the composites used in the concrete or blacktop. On our way to Ed Wingate's Teslathon, Bill Kolb and I recorded about a 4X-6X jump for about a mile along I-83 in Pennsylvania just north of the Maryland state line. Cities do tend to read higher due to the streets and concrete buildings creating a "wall effect" warned about in Uranium prospecting.

Bill and I were fooled by this when in Utah prospecting back in 2005. We hit a hot spot and started digging. At 4 inches down, we stopped and the reading went up and so we kept digging thinking we were getting closer. At 1 foot the reading was just slightly higher. We laughed and realized we were just digging in hot dirt. We quickly learned to recognize this wall effect and saved ourselves a lot of digging on the high desert. A good hot rock will blaze away as you dig for it. 2 or 3 inches of digging will tell the tale.

Richard Hull
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Re: Local geographic gamma counting- how is your soil?

Post by Jim Kovalchick » Tue Sep 17, 2019 12:06 am

Richard, I definitely could be convinced that my spot on 95 is the road itself. The only way to be sure is to venture off the road and see.

The spot you spoke about on 83 would have been in York County PA which was my former home for 34 years. I found the whole area full of hot spots. Recall that the area has a reputation for radon. Mike and I measured big variations in background with weather. Lots of rain would displace gas in the ground.

Jim K

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Re: Local geographic gamma counting- how is your soil?

Post by Jim Kovalchick » Tue Sep 17, 2019 12:28 am

Here is a picture of my travel rig. As Richard said before scintillators are high count rate. I usually leave my device on c/s, but the detector block is pretty amazing. In scaler mode I have been able to sense repeatably an old style smoke detector at 20 ft.
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Re: Local geographic gamma counting- how is your soil?

Post by Jon Rosenstiel » Tue Sep 17, 2019 10:27 pm

Gamma radiation Levels in Selected Soil Samples
Soil comparisons.pdf
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With the help of family scattered around the country I’ve been slowly bringing this together over the past couple of years. Instructions to my prospective soil samplers were to remove the top 1.5 to 2-inches of soil before filling a gallon zip-lock. Once the soil was in my possession it was dried and run through a ¼” mesh sieve to remove stones, pieces of wood, roots etc. 600 grams of the dried and sifted soil was then transferred to a 0.5-liter Marinelli beaker for analysis.

Detector is an hpGe Ortec GEM 40P4. (40% efficiency) Shield is also Ortec and consists of 4-inches of lead with a cadmium/copper liner for x-ray suppression. Spectroscopy amplifier is a Canberra 2025, bias supply is an Ortec 459 at +3900 V, pulse height analyzer is a Canberra Series 35+, and spectroscopy software is a demo version of Fitzpeaks. Run times (live times) were 24 to 48-hours. Pb-212’s 238.7 KeV emission was used to represent the thorium series and Pb-214’s 352 Kev emission was used to represent the uranium series. K-40 and Cs-137 are represented by their one and only gamma emission, 1460.8 KeV for K-40 and 661.7 KeV for Cs-137.

Discussion of the Naturally Occurring Radioactive Materials (NORM)…
About the only thing that stands out to me is the similarity of potassium-40 activity values for locations that are geographically close together. (The CA collection sites are 8-miles apart, the WI sites 20-miles apart, and the NY sites 30 miles apart) To me the thorium and uranium series emissions appear random in nature. Maybe someone else will find a pattern there.

Discussion of cesium-137…
Cs-137, (half-life of 30-years) is a fission product from the atmospheric testing of nuclear weapons at the Nevada Test Site (NTS) during the 1950’s. Radioactive debris from these tests was injected into the upper atmosphere and carried eastward by the prevailing winds. The cesium-137 in our California soil is from the Fukushima disaster. Evidence of that is the presence of both 30-year Cs-137 and 2-year Cs-134 in the sample. More evidence is the dewey, early morning, patio table wipe done 12-days after the March 11, 2011 accident. Found were: 8-day I-131, 2.3-hour I-132 (daughter of Te-132), 3.2-day Te-132, 2-year Cs-134, 30-year Cs-137.

Jon Rosenstiel
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Re: Local geographic gamma counting- how is your soil?

Post by Richard Hull » Wed Sep 18, 2019 5:13 am

Jim, The location is indeed in York County, but we had hits all along 83. York was the whopper. Great large area scintillator. Nice!
Jon, fabulous report on the soil samples. Thorium is the big one in my area.

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.

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Re: Local geographic gamma counting- how is your soil?

Post by Jim Kovalchick » Wed Sep 18, 2019 11:36 am

Richard,
Interesting that you find Th in your soil. There are some known Th deposits around southeast PA where I used to do most of my amateur measuring, but the radon source in the area of our former home in York was U. Way back when Mike was in the seventh grade he did a project that proved it by using a muffin fan to pull a piece of filter material to equilibrium. Then he recorded live time equilibrium countrate that he plotted in log form. Over time he saw distinct slopes as different daughters became the most significant. I helped him with the differential equations to derive the half lives. The different Pb, Bi, and Po isotopes in radon and thoron are tell tale.
I haven't been out surveying much in my new digs in GA and SC but now I'm thinking I might.

Jon,
Do you ever survey the dew moisture in your area these days to catch radiological events that aren't as well publicized as the Fukushima accidents? As always, your work is amazing. My compliments.

Jim K

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