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Joined 9 months ago
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Cake day: March 31st, 2025

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  • the talk about water content in soil was bad but the topic itself was interesting

    things that fella got wrong: TDM moisture meter works by measuring what effectively is electrical length of waveguide formed by 2 electrodes and soil around it. more water = higher dielectric constant = longer delay for reflection, this only measures as deep as probe goes and the rest is fitted from model

    neutron detector works just like geiger tube except gas has large cross-section for reaction with neutrons, that gives charged products that begin a spark which is counted. in train, steel doesn’t interfere but diesel fuel will. the trick is that cosmic neutrons are counted separately from reflected neutrons, because cosmic neutrons are hot and reflected neutrons are thermal and how much of reflected ones is there depends on water content in the soil. helium does not run out. the more helium you have the faster counts go and you can move faster while measuring with decent precision. the lead shield in train is for getting rid of radiation from granite aggregate under rails, because it contains tiny amounts of uranium and gammas from decay chain would add to noise - lead does not interfere