Thorium decay series in a soil sample from Oranienburg, Germany

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Svilen
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Thorium decay series in a soil sample from Oranienburg, Germany

Post by Svilen » 28 Jul 2019, 07:11

Here is the spectrum I got from a contaminated soil sample from Oranienburg, Germany. It is quite weak, since the activity of the sample is low, but it could be interesting for the German members of the forum at least, so I decided to show it. Maybe someone living near Berlin will be interested to take his own samples and measure them himself. Since there is also an interesting WWII military history behind this contamination, I'll write a short description too, so let it be a bit more historical post.

Oranienburg is a town in Germany, located 35 km north of the capital - Berlin. It is considered to be the most important case of industrial radioactive contamination in Germany outside the uranium ore mining areas (BMU – 2007-697). The source of this contamination is the operation of the factory "Auer-Werke" AG (and its predecessors) from the late 19th century till the end of the WWII, when it was almost completely destroyed after a heavy bombing from the Allied forces. The contamination is mostly from residues of raw materials (especially Monazite) and processed products (mainly chemically separated thorium, but also uranium and radium), which were scattered around in the vicinity of the factory.
"Auer-Werke" AG used to produce radium luminous paint, radium sources for medical use, thorium doped lantern mantles, the radioactive toothpaste "Doramad" and other products. Importantly, the company also participated in the German nuclear weapons project("Uranprojekt" in German), which was a scientific effort led by Germany to develop and produce nuclear weapons during World War II. From 1940 "Auer-Werke" was delivering one ton of uranium oxide per month to Degussa Corporation for further processing. The raw material was coming from "Union Miniers" through the "Reges" company from occupied France. The Oranienburg plant provided the uranium sheets and cubes for the "Uranmaschine" experiments conducted at the "Kaiser Wilhelm Institute for Physics" and the Versuchsstelle (testing station) of the Heereswaffenamt (Army Ordnance Office) in Gottow.
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In November 1944, The American Operation "ALSOS" teams uncovered leads which took them to the company in Paris that handled rare earths and had been taken over by the Auergesellschaft. This, combined with information gathered in the same month through an "ALSOS" team in Strasbourg, confirmed that the Oranienburg plant was involved in the production of uranium and thorium metals. Since the plant was to be in the future Soviet zone of occupation and the Red Army's troops would get there before the Allies, General Leslie Groves, commander of the Manhattan Project, recommended to General George Marshall the plant to be destroyed by aerial bombardment, in order to prevent the Soviets of getting its uranium production equipment. On 15 March 1945, 612 B-17 Flying Fortress bombers dropped 1,506 tons of high-explosive and 178 tons of incendiary bombs on the plant. Later, the head of the scientific headquarters of Auergesellschaft, Nicolaus Riehl, visited the site with the Soviets and said that the facility was mostly destroyed. When the Russians entered Berlin near the end of World War II, he was invited to the Soviet Union, where he stayed for 10 years. For his work on the Soviet atomic bomb project, he was awarded a Stalin Prize, Lenin Prize, and Order of the Red Banner of Labor. Riehl also recalled long after the war that the Soviets knew precisely why the Americans had bombed the Auer-Werke — the attack had been directed at them rather than the Germans.
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On the image below with 1 and 2 are marked respectively The Auer-Werk I and Auer-Werk II:
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4.png (257.38 KiB) Viewed 2879 times
Immediately after the war, the already processed uranium and thorium stocks were confiscated by the Soviet army. The Monazit sand and other raw materials, however, remained in Oranienburg. They were either scattered by the bombing or were used for filling bomb craters. The amount of radioactively contaminated soil in the city of Oranienburg is currently not exactly known. The radioactive contaminants are mainly characterized by the nuclides of the thorium decay series. A survey with aero-gamma spectrometry, done by the Federal Office for Radiation Protection in 1997, showed three areas with greatly increased Tl-208 activity and several smaller spots with lower activity (Tl-208 is used as an indicator of the Th decay series):
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Today, the areas with elevated gamma signals are located at the crossing "Oranienburger Kanal"/"Walter Bothe Strasse", the former facility grounds of Auer-Werke I, now "Lindenring", the industrial area "Südliche Lehnitzstraße", the periphery of these core areas, and in several other places due to filling of bomb craters (BMU – 2007-697).

With a red dot here is marked the place where I took the sample (the former grounds of Auer-Werke I, near "Lindenring"). On a GQ GMC-320+ geiger counter, a meter above ground, it was showing 6 times higher activity than the background measured at the Central Train Station. I was in a hurry and didn't look for a hot spot in the ground, otherwise a more active sample can be easily found in this area.
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And the spectrum I got (Sample: ~300g of soil; Shielding: 3mm Cu/25mm Pb; Detector: Thermo Scientific SPA-3 2x2" NaI(Tl); Driver: GS-1100A2; Time: 4h):
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7.png (85.27 KiB) Viewed 2879 times
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8.png (62.67 KiB) Viewed 2879 times
Below is the calibration of the detector with Lu-176, Cs-137 and K-40:
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9.png (57.74 KiB) Viewed 2879 times
Last edited by Svilen on 13 Sep 2019, 18:59, edited 1 time in total.
Svilen

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Re: Thorium decay series in a soil sample from Oranienburg, Germany

Post by gwgw » 28 Jul 2019, 08:57

Sorry for the offtopic...but where does your nickname come from? It is a common name in my country, I'd say endemic, because you rarely find people named like that in other Slavic-speaking countries...
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Milen Rangelov

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Svilen
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Re: Thorium decay series in a soil sample from Oranienburg, Germany

Post by Svilen » 28 Jul 2019, 14:25

Well, not that common I would say :) Zdravei Milene, It's my real name and I come from the same country as you do, but I live in Germany. I was anyway going to say "Hi" under your introductory post, so off-topic is not that bad. You can write me a PM if you wish.
Pozdravi.
Svilen

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Re: Thorium decay series in a soil sample from Oranienburg, Germany

Post by Go-Figure » 28 Jul 2019, 19:26

Hi there.
You probably have something in the 900 region as well (911 and 968 from Ac228). You can see there's a little bump, and I would also take a look at 2.6 MeV in order to see of Tl208 showed up, which probably did.

Thank you for the post, I didn't know about Oranienburg!

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Re: Thorium decay series in a soil sample from Oranienburg, Germany

Post by gwgw » 28 Jul 2019, 19:47

Nice :)

Glad to see I am not the only one here born on that tiny piece of land :)
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Milen Rangelov

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Svilen
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Re: Thorium decay series in a soil sample from Oranienburg, Germany

Post by Svilen » 28 Jul 2019, 20:59

Thank you for your reply Massimo. And thanks for all your other posts - very neat job and very well presented! The activity in the 900keV region is too low to say unfortunately. And for the 208-Tl at 2615keV - there is nothing after 2keV, but so is the technical specification of this detector also (~60-2000keV range of detection).
Svilen

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Re: Thorium decay series in a soil sample from Oranienburg, Germany

Post by Go-Figure » 29 Jul 2019, 21:47

Svilen wrote:
28 Jul 2019, 20:59
Thank you for your reply Massimo. And thanks for all your other posts - very neat job and very well presented!
We are all here to learn from each other I think :)

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