What high-school taught me:

In beta radiation, beta particles are lone electrons that are emitted from the nucleus at high speeds after a neutron decays into a proton and an electron.

Beta radiation is dangerous when exposed to humans because it can create burns on the skin.

And from one of my previous questions on Physics SE I learnt that the electron can resist the nuclear attraction of the nucleus because it has magnitudes higher kinetic energy than the pull of the nuclear attraction.

So where does this electron go after it leaves the atom if it resists nuclear attraction from atoms it passes? Does it it hit another nucleus out of pure chance, if so what happens to the nucleus it hits? That would explain its interaction with human skin, but it wouldn't explain the burns, because it would theoretically just affect one atom in the skin layer, it wouldn't be a large enough impact to cause burns (unless lots and lots of these atoms experienced beta decay). If the kinetic energy had anything to do with it, the electron would cause the atom affected to rebound inwards in the direction of the electron's trajectory due to conservation of momentum, unless it just absorbed the electron and the kinetic energy converted into some other form of energy (maybe thermal because of the burnt skin?).

  • $\begingroup$ It depends on the environment. Back in the day, in Earth orbit, beta particles emitted by the unshielded nuclear reactors in Soviet RORSATs could be detected streaming along terrestrial magnetic field lines thousands of km from where they were emitted. $\endgroup$
    – John Doty
    Dec 30, 2022 at 18:31
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    $\begingroup$ One term a ctrl-f didn't bring up that you should know: bremsstrahlung. This describes the phenomenon whereby electrons bleed kinetic energy as radiation when they are accelerated by electric fields around nuclei. This explains in part how an electron can lose enough kinetic energy to be captured by another nucleus. $\endgroup$ Dec 31, 2022 at 0:33

2 Answers 2


Since a beta particle is a bare unbound electron, it is highly chemically reactive after it sheds enough of its kinetic energy to interact with atoms and molecules instead of just bouncing violently off them as it zooms through the air.

It is those energetic collisions which convey high energy to the atoms and molecules, breaking them up or ionizing them into chemically reactive states which then react with other molecules or atoms in the neighborhood. Those collisions also can induce the target atom to throw off an energetic photon (x-ray or sometimes gamma ray) which then itself proceeds to wreak further havoc.

(Complicated protein molecules are particularly susceptible to this sort of damage, which is why beta radiation is dangerous for living things. Since the outermost skin cells covering your body are not technically alive, they can withstand the damage- but beta emission inside your body is deadly.)

Anyway... the beta particles ionize those atoms and molecules, turning them into extremely reactive free radicals which then undergo chemical reactions with other atoms and molecules in the surrounding air. At the end of the process, a number of new molecules have been created and one of them along the way winds up with the extra electron- either that, or the extra e- gets sorbed onto the surface of some (insulating) solid in the neighborhood and resides there as a very slight excess of negative charge.

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    $\begingroup$ I do not know exactly how fast the electron is ejected; at lower speeds the incoming electron is scattered electrostatically by the electrons bound to the atom. At higher speeds it is scattered off the innermost electrons and an x-ray photon is shed. at highest speeds it is scattered off the nucleus and a gamma ray is shed. $\endgroup$ Dec 29, 2022 at 23:36
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    $\begingroup$ @AshtonDowling for scattering try understanding this weitzlab.seas.harvard.edu/files/weitzlab/files/… , To answer really your questions a course is needed. $\endgroup$
    – anna v
    Dec 30, 2022 at 4:37
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    $\begingroup$ @AshtonDowling Is it just terminology that has you confused? "Particle A scatters off Particle B" is just physicist speak for "A hits B (and bounces off)" (thinking of the particles just as classical "billiard balls"). The details of how this really happens for quantum particles can be extremely complicated, but the concept is simple. Then it should be clear why we should expect an electron-scattering interaction to also emit photons: (speaking schematically) an electron is charged, and it must "accelerate" when it bounces off another particle, and accelerated charges emit EM radiation. $\endgroup$
    – HTNW
    Dec 30, 2022 at 8:14
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    $\begingroup$ @AshtonDowling I think a source of confusion here is the mixing of classical and quantum concepts. Both are models: one is intuitive and good enough for many things, while the other is both much more complicated and accurate. Classically: EM radiation is just varying electric and magnetic fields. Any charge sources an electric field "centered" on itself, and when a charge accelerates its field adjusts in kind, sending out a ripple. This ripple is the EM radiation. Quantum mechanically: EM radiation is comprised of photons. The various structures of charges are shifting between states of (1/2) $\endgroup$
    – jawheele
    Dec 30, 2022 at 19:20
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    $\begingroup$ different energy/momentum (say, as a free electron wavefunction "passes by"), and the difference is accounted for by photons to balance the energy/momentum deficit. Regarding the internal structure of a nucleus undergoing decay, only the latter picture can really be made sense of. Importantly, in neither of these pictures was there EM radiation always present in the substructure of the electron/nucleus that is "released" during the interaction. You don't need substructure to emit EM radiation; you just need changes in energy/momentum, wherein the deficit manifests as radiation. (2/2) $\endgroup$
    – jawheele
    Dec 30, 2022 at 19:21

unless lots and lots of these atoms experienced beta decay

Exactly this. Macroscopic amounts of even moderately radioactive materials will experience trillions of decays every second.

A single beta particle won't cause burns. A single beta particle has an energy of about 0.5 MeV or 8e-14 Joules.

To cause erythema (redness) Wikipedia gives an estimated dose of 5-15 Joules per kg. So to cause redness to 1g of skin, there would need to be an absorbed dose of 0.005 Joules or about 60 billion beta particles.

This sounds like a lot, but one gram of Strontium-90 (a common beta emitter) has an activity of 5.2 trillion decays per second, so easily emits enough beta particles to do skin damage.

What happens to the beta particles? They collide with atoms, transferring their kinetic energy to the atoms and causing ionization, which results in damage to the cells. Although beta particles are charged, the total amount of charge in 60 billion beta particles is small and the electrons, once they have slowed down enough will conduct through the skin to ground or become trapped in some insulating material, producing a tiny static charge.


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