4 ms·

I'm just a physics student by incidentally I'm researching tritium right now. Tritium is one of the least toxic radionuclide because the β radiation it emits is

I'm just a physics student by incidentally I'm researching tritium right now. Tritium is one of the least toxic radionuclide because the β radiation it emits is very low energy, also the biological half life is only 10 days (it means it's quickly eliminated by the body): unless you ingest very large quantities of it, you're probably going to be fine. In fact, the range of the electrons is even less than you quote: around 5 mm in air and 6 μm in water, which means it's effectively stopped by the dead skin layer. If I were to decide, I would probably pick dilution in water over vaporisation.

eganist 6y ago
> around 5 mm in air and 6 μm in water Interesting. My source re: beta radiation was (admittedly a nuclear promotion nonprofit) http://nuclearconnect.org/know-nuclear/science/protecting http://nuclearconnect.org/know-nuclear/science/protecting > β BETA – can only be stopped after traveling through about 10 feet of air, less than 2 inches of water, or a thin layer of glass or metal. Additional covering, for example heavy clothing, is necessary to protect against beta-emitters. Some beta particles can penetrate and burn the skin. I won't be surprised if you're right, but if a nonprofit getting government grants to promote the nuclear industry gets it wrong, I'd be pretty worried.
- ascar 6y ago
  The problem is that the source is generalizing, which is fine for saying beta has usually shorter range and is less dangerous than gamma, but is too general to be applicable here. Beta radiation just describes a certain kind of radiation, namely emitting an electron (or positron). However it doesn't directly tell you how much energy that electron has. Wikipedia on Beta particles says that "Beta particles with an energy of 0.5 MeV have a range of about one metre in air; the distance is dependent on the particle energy." [1] Tritium beta decay just has an energy of 0.018590 MeV [2] and I wouldn't be surprised if reach isn't proportional but for example cubic (I don't know the formula) thus the huge difference in reach. [1] https://en.m.wikipedia.org/wiki/Beta_particle#:~:text=Beta%20particles%20with%20an%20energy,less%20ionising%20than%20alpha%20particles https://en.m.wikipedia.org/wiki/Beta_particle#:~:text=Beta%2.... [2] https://en.m.wikipedia.org/wiki/Tritium https://en.m.wikipedia.org/wiki/Tritium
  - eganist 6y ago
    Helpful, thanks!
- perpetualpatzer 6y ago
  My understanding is that penetration depends on the energy associated with the the β particle [0] and tritium decay releases relatively lower-energy β particles [1]. The nonprofit isn't wrong... they're just saying "a .22 bullet can kill you" while parent is saying "tritium is like throwing the bullet instead of firing." [1] https://sciencedemonstrations.fas.harvard.edu/presentations/%CE%B1-%CE%B2-%CE%B3-penetration-and-shielding https://sciencedemonstrations.fas.harvard.edu/presentations/... [1] https://en.wikipedia.org/wiki/Tritium https://en.wikipedia.org/wiki/Tritium
  - rnhmjoj 6y ago
    Exactly, the electron produced by the decay of tritium have an energy that is distributed between 0 and 18.59 keV (the Q value of the reaction), with an average of 5.68 keV (this is pretty low compared to other common radiation sources). The rest of energy is shared between the neutrino (which practically never interacts with matter) and the residual nucleus (which is very massive compared to the electron and thus can't travel far). So, electrons are the only source of concern here. Electrons can deposit energy in two ways: one is by bremsstrahlung, which is basically EM radiation (X rays, usually) emitted during a fast deceleration caused by another ion; or by ionising neutral atoms and breaking bonds. Bremsstrahlung is only significant at much higher energies, so this leaves ionisation. The energy lost per unit length (-dE/dx) depends on the electron energy and can be computed using the Bethe-Bloch formula. Integrating this quantity yields the particle range R = ∫_E₀ ⁰dE (dE/dx)⁻¹. An empirical formula that can be derived from this is the following: R = 1/ρ 0.44cm E^(1.265 - 0.0954 log(E)) where ρ is the medium density (in g/cm³) and E the electron energy (in MeV). In water you get: R = 4 μm for the average energy and 50 μm for the maximum energy, which is extremely rare, by the way. Note that to damage tissues, radiation must reach the radiosensitive layer of the skin at depths greater that 40 μm.

eganist 6y ago

> around 5 mm in air and 6 μm in water Interesting. My source re: beta radiation was (admittedly a nuclear promotion nonprofit) http://nuclearconnect.org/know-nuclear/science/protecting http://nuclearconnect.org/know-nuclear/science/protecting > β BETA – can only be stopped after traveling through about 10 feet of air, less than 2 inches of water, or a thin layer of glass or metal. Additional covering, for example heavy clothing, is necessary to protect against beta-emitters. Some beta particles can penetrate and burn the skin. I won't be surprised if you're right, but if a nonprofit getting government grants to promote the nuclear industry gets it wrong, I'd be pretty worried.

ascar 6y ago
The problem is that the source is generalizing, which is fine for saying beta has usually shorter range and is less dangerous than gamma, but is too general to be applicable here. Beta radiation just describes a certain kind of radiation, namely emitting an electron (or positron). However it doesn't directly tell you how much energy that electron has. Wikipedia on Beta particles says that "Beta particles with an energy of 0.5 MeV have a range of about one metre in air; the distance is dependent on the particle energy." [1] Tritium beta decay just has an energy of 0.018590 MeV [2] and I wouldn't be surprised if reach isn't proportional but for example cubic (I don't know the formula) thus the huge difference in reach. [1] https://en.m.wikipedia.org/wiki/Beta_particle#:~:text=Beta%20particles%20with%20an%20energy,less%20ionising%20than%20alpha%20particles https://en.m.wikipedia.org/wiki/Beta_particle#:~:text=Beta%2.... [2] https://en.m.wikipedia.org/wiki/Tritium https://en.m.wikipedia.org/wiki/Tritium
- eganist 6y ago
  Helpful, thanks!
perpetualpatzer 6y ago
My understanding is that penetration depends on the energy associated with the the β particle [0] and tritium decay releases relatively lower-energy β particles [1]. The nonprofit isn't wrong... they're just saying "a .22 bullet can kill you" while parent is saying "tritium is like throwing the bullet instead of firing." [1] https://sciencedemonstrations.fas.harvard.edu/presentations/%CE%B1-%CE%B2-%CE%B3-penetration-and-shielding https://sciencedemonstrations.fas.harvard.edu/presentations/... [1] https://en.wikipedia.org/wiki/Tritium https://en.wikipedia.org/wiki/Tritium
- rnhmjoj 6y ago
  Exactly, the electron produced by the decay of tritium have an energy that is distributed between 0 and 18.59 keV (the Q value of the reaction), with an average of 5.68 keV (this is pretty low compared to other common radiation sources). The rest of energy is shared between the neutrino (which practically never interacts with matter) and the residual nucleus (which is very massive compared to the electron and thus can't travel far). So, electrons are the only source of concern here. Electrons can deposit energy in two ways: one is by bremsstrahlung, which is basically EM radiation (X rays, usually) emitted during a fast deceleration caused by another ion; or by ionising neutral atoms and breaking bonds. Bremsstrahlung is only significant at much higher energies, so this leaves ionisation. The energy lost per unit length (-dE/dx) depends on the electron energy and can be computed using the Bethe-Bloch formula. Integrating this quantity yields the particle range R = ∫_E₀ ⁰dE (dE/dx)⁻¹. An empirical formula that can be derived from this is the following: R = 1/ρ 0.44cm E^(1.265 - 0.0954 log(E)) where ρ is the medium density (in g/cm³) and E the electron energy (in MeV). In water you get: R = 4 μm for the average energy and 50 μm for the maximum energy, which is extremely rare, by the way. Note that to damage tissues, radiation must reach the radiosensitive layer of the skin at depths greater that 40 μm.