Comments by "Dr Gamma D" (@DrDeuteron) on "Most Radioactive Men Ever" video.

no. Cherenkov threshold in air for electrons is 21 MeV, way too high for any beta decay. For an alpha, it's thousands of times higher: far out of range for any nuclear reaction. It's prompt radiation (gamma, beta, neutrons scattering charged nuclear) which ionizes the air, which causes scintillation as the electrons fall back to the ground state. Basically, a mini Aurora.
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@HappyBeezerStudios Cherenkov in water is beta ray, they are easy to stop. These ppl were dealing with neutrons, so they had no chance.
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@nsbse2287 particles can go faster than light in a medium, because light goes slower than the speed-of-light, in a medium.
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OK, ppl. this is getting out of hand. Yes, the speed of light is constant, and nothing (including information) can go faster, and anything with mass must go slower. The speed of light can measure w/o light, all you need to do is measure the permittivity (epsilon_0) and permeability (mu_0) of free space, and find c = 1 /sqrt(e0*u0). The permittivity measure the strength of the coupling of the electric field to charge (mu does the magnetic part). So...in a medium like air or water or glass, the electric field of the lightwave polarizes the atoms/molecules, thereby creating little dipoles of charge, thereby increasing the local coupling of the field to charge (epsilon > epsilon0) This makes light travel slower in a medium. Nevertheless, it is still dispersion less for constant "n(f)" (though it usually does disperse, hence: rainbows). So it's not "ionized particles" that cause Cherenkov, it's "ionizing particles", which are energetic charge particles. As they pass through the medium, their electric field is strong enough to ionize the nearby molecules/atoms in the medium. The point of ionization follows the particle, which is faster than the speed of light in the medium, which is c/n, where n is the index of refraction. Hence the similarity to sonic booms, where the air pressure disturbance position is moving faster than sound, so at a forward point, you hear (see) all the sound (light) from everywhere at once...that's just trigonometry. In air, n = 1.000278 (see: The Particle Data Group). that c/n is totally out of reach for nuclear fission; however, in water n ~ 1.5: so you can Cherenkov in water and not in air with fission/beta-decay. (Beta decay is a few MeV, while the threshold for electrons in air is 21 MeV, which is a number I used in 1989 and have not since recalculated). Air glow is caused by scintillation: ionized air recombines with free electrons and emits blue light in random directions. In these accident cases, its neutrons knock protons out, which then ionize. Very deadly. 1 neutron can blast a lot of atoms before tossing energy. Think: golf ball bouncing of bowling ball, golf ball keeps moving. Cherenkov is focused in a forward cone with opening angle arc-cos(1/n). Moreover, the spectral power depends on n (bigger=better) and the photon energy, so it is strongly weight to blue (and even more in the ultraviolet). It is cut-off at the point where the Cherenkov photon energy can ionize the atom...otherwise it would extend to X-ray like synchrotron radiation. An even whackier effect is called "Transition Radiation", which requires ultra-relativistic particles traversing a boundary between 2 media. Finally: the comment about space expanding faster than light is not relevant. The speed of light is constant for all observers in flat spacetime locally. No matter how fast you go, the speed of light always moves a "c" in all directions...so which way do you go to reach "c"? It's a hyperbolic geometry. In curved / expanding space time. There is no unique way to even define the relative speed of distance objects. Nevertheless, if two particles/people/galaxies are moving apart fast then "c", then they are separated by a horizon: either a black hole's event horizon, or the cosmological horizon. Source: Me. I did get the highest degree (PhD) in the hardest subject (Nuclear Physics) from the worlds toughest school, and I built Cherenkov detectors for several projects in high background environments (read: scintillation). So it's hella studied. Re: general relativity, I am not an expert, but both my teacher and one of my fellow students won Nobel Prizes for black holes, so: osmosis of genius?
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@agailham8476 it's not Cherenkov, it's scintillation. The index of refraction of air is c=1.000273, so the particle needs to go v > c/n to radiate. The Lorentz factor is g=1/sqrt(1-(v/c)^2 ~ 1/sqrt(2*(n-1)) ~ 43, which is ultrarelativistic...way out of range for fission.
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@jedaaa that makes no sense, if it bounced around randomly, optics would not work
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@eadld blue in the water is lot different from blue in the air.
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@charlesnathansmith if it's coherently remitted in random directions such that only the forward amplitude is non-zero: that's not really random emission. I've heard that explanation many times, but why not just note the polarization of the atoms increases the permittivity, leading to slower propagation. But the light isn't Cherenkov light anyway. It's scintillation
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@charlesnathansmith OP says it's Cherenkov, that's the whole point of this misguided thread.
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@curbyourshi1056 and if you freeze the frame on the exact start: it is blinding (prompt betas from fission), but then is immediately decaying secondaries (from nuclear waste) as the reactor stops in milliseconds.
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@IR0Navt I doubt. I don't need to read wiki, I have Cherenkov and Tamm's book. Cherenkov in gas is a high energy physics thing, and not associated with fission. (air's index of refraction is 1.000273). Chernekov in water works at low energies associated, which is why you see those amazing yt videos of pulse nuclear reactors--scary bright for a few milliseconds, and then decay).
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@AngryMillennial yes that's it. Light travels at c/n where n is the index of refraction. For water/glass/plastic it's around 1.5, so you can get there. In air, it's 1.000278. No charged particle from a fission reaction is going c/1.000278, ever. So we are seeing prompt neutrons striking protons, and the protons are then ionizing the air, or gammas kick out electrons. The air atoms glow blue as electrons fall to the ground state: if you can see it, you're in trouble,
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@charlesnathansmith if the phases are coherent, then it is not random scattering.
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@krzysztof_jablonski You're welcome. I built a Cherenkov detector in grad school--a long time ago, but I had the original book by Tamm and Frank...very detailed. Nobel prize worthy detailed (not a 1st edition, tho, now worth $1500.,..). I also learned about accidentally inhaling freon gas, but that's a different story.
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@jagmarc in the biz, the speed of light means c. The speed of light in a medium is not a precise concept, as green light may go 200k km/s in leaded glass, a 400 GeV gamma goes c. The speed of light in a medium is frequency dependent. When workin with cherenkov light, ppl care about violet and near UV, since the cherenkov spectrum is proportional to frequency. There are very few red or IR photons, and PMTs aren’t very sensitive to these. Deeper in the UV the atoms are just ionized, and there is no radiation.
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@jagmarc I it’s been a long time since I looked at an is oscilloscope …maybe it’s less. Photon hits photocathode, knock electron out into pmt …which is an inverse lightbulb at 2kV. Electron accelerates into GaAs film, knock out 10 electrons, another 100V to the next one, repeat 10 times, pulse comes out the base…into coax cable, into oscilloscope, or NIM logic boxes…forgot what they were called. In air you get about 30 Cherenkov photons per meter (poission distribution from exponentially distributed emission), 20 % quantum efficiency (binomial dist) cuts that to 6 photoelectrons. Still poission dist. Then each mulitplier is poison, leading to a Polya Distributed signal .
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first time I head of a FOE was from Hans Bethe, who figured out how stars work, among other things. It's "ten to the Fifty One Ergs". That's a lot of energy. If a supernova occurred where the sun is, the radiant energy would be around 3kT TNT per square meter, per second, for a few days, and would hold at 0.3 kT for 100 days...per square meter/s, and then start to decay. Depending on type. A gamma ray burster is way more.
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@SteveBrownRocks2023 cos theta = c/(nv) is the angle of the dangle, which is used in Ring Imaging CHerenkov (RICH) detectors.
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@walturowhite69 not in air.
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@tedarcher9120 no. www says 2.3% of the sun's output is in neutrinos, so that's 30 Watts/m^2 24/7/365 for your whole life. If that were gamma rays at the same energy you'd get a lethal dose in ten seconds. I think only supernova are dangerous, only because there are so many, like 10^58, a flux of 10^29 per atom (!) carrying 99% of the SN energy (and the 1% electromagnetic energy kills planets out to 100 light years). The number are insane.
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@ no, the blue flash in these accidents is in air.
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@AngryMillennial Cherenkov is not FTL and this is not Cherenkov
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@jagmarc photomultiplier tube, like in the water cherenkov neutrino observatories. Turns one photon into a few volts for 30 ns. I turned on in the sunlight once. Whoops.
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@kensurrency2564 quantum entanglement is a phenomenon from quantum mechanics, which is inherently non-relativistic.
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@koenth2359 you mean E_tot, b/c E_kin = E_tot - m (m is E_0, c=1). If you work with gasses, ppl use eta = (n-1) x 1e6 for indexes near 1 (source pdg dot lbl dot gov) so: gamma = 1000 / sqrt(2 x eta)
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@koenth2359 also, I went by memory. I built an e/pi separating Cherenkov for TJNAF in the 90s (it was a POS, I hope its been replaced!). The point is, nuclei don't make 21 MeV electrons (nor gamma's which can give their energy to electrons)...the max is 5-ish (iirc). Nuclear weapons are consider "low energy", but extraordinarly high power.
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the highest doses were near ground zero in Nagasaki, around 6000 Sv, but there were other hazards such as 5 digit temps and 4 digit wind speeds.
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