# How is a cathode ray tube different from beta minus radiation?

In beta minus the result is one neutron in the nucleus changing to a proton, plus an electron and an anti-neutrino being sent off.

The antineutrino is indifferent to our health. So I guess what makes a beta source dangerous compared to a cathode ray tube must be a difference in the kinetic energy of the emitted electrons?

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FYI: Electron beams are being used for radiation therapy, but I don't know to what extent. See Electron therapy or the famous Therac 25 that killed a few people because of faulty programming. –  Lucy Brennan Jul 28 '12 at 20:12

Modest energy electrons (such as those found in CRT televisions and monitors) range out (i.e. dump all their energy and stop) very quickly in dense materials like glass, so these tubes are not emitting significant numbers of electrons and those that penetrate are even lower in energy.

In fact they do emits small quantities of soft x-rays do to electron interactions with the material, but again the rate is low and the energy is minimal so there is little penetration.

You probably don't want to sleep on an operating CRT, but watching television subjects you to a infinitesimal dose. (And the allowed dose is regulated throughout the industrialized world.)

We can use the online interface to PSTAR to quantify the range TVs runs at a few tens of thousands of volts, meaning the electrons get, say 30,000 eV = 30 keV = 0.03 MeV, so the penetration is around $10^{-4}\text{ g/cm^2}$, which given that the density of glass is about 2.5ish we get a range of $4\times 10^{-5}\text{ cm}$.

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What is the maximum energy that an electron can carry when being the result of Beta decay? –  Lucy Brennan Jul 28 '12 at 20:16
Your go-to page for that kind of question is ie.lbl.gov/toi/radSearch.asp. I see that Boron-14 has a 20 MeV line, but that is a very short-lived extremely neutron rich isotope. For things that last a while Clorine-40 has a 7.5 MeV line and a 90 second half-life and Antimony-124 has a 2.3 MeV line and a 2 month half-life. The common, day-to-day beta radiation is mostly under 1 MeV. –  dmckee Jul 28 '12 at 20:48
Great answer, thank you very much :) –  Lucy Brennan Jul 29 '12 at 7:39