As stated above....

How often do nuclei stripped bare emit radiation?

Can nuclei be identified by the wavelengths or amplitudes of gamma rays they emit? How about isotopes?

  • 1
    $\begingroup$ Yes, there are several ways that bare nuclei can potentially be identified by photons emitted. I'd recommend you slightly rewrite this to ask specifically about how this is ever achieved observationally in astronomical contexts so that it doesn't appear to be a general physics question. $\endgroup$
    – uhoh
    Aug 4 at 3:02

It makes very little difference whether there is a bare nucleus, a partially ionized atom, or a neutral atom. Their gamma emission spectra are all the same (with the exception of electron capture, which can't occur for a bare nucleus). For gamma-ray astronomy, it makes no difference in principle whether we're talking about a plasma or a cold gas.

Identifying a nucleus is the same thing as identifying an isotope. The term "gamma ray" usually refers to photons emitted by the nucleus, meaning that the gamma spectrum is a fingerprint of the nucleus, not just of the chemical element. However, there are K-shell x-rays that overlap in energy with the low-energy gamma spectrum, and these are signatures of the element. (In fact, this was one of the first methods used to determine atomic numbers, ca. 1910.)

How often do nuclei stripped bare emit radiation?

The rate of emission is inversely related to the half-life. Every nucleus has a ground state, which can't emit gammas. Almost all nuclei in the universe are in their ground states.

To observe a discrete gamma-ray line spectrum from an astronomical source, you would need all of the following things: (1) you need a detector with high resolution; (2) you need an event that created a whole bunch of nuclei in excited states; (3) the source can't be moving fast enough to smear out the lines due to the Doppler effect; (4) the gammas need to be able to escape from the event that created them without being reabsorbed; (5) the excited state has to have a half-life that is short enough to make the source fairly intense, but long enough for the nuclei to have escaped far out enough so that their gammas are not reabsorbed.

#1 is sometimes but not always the case in gamma-ray astronomy. We can get #2 from supernovae. #3 is not normally the case for most highly energetic gamma-ray sources, which are black holes. #4 is not the case for supernovae.

The first open-access review article I hit by googling was this one, which is from 1982. It basically says that no discrete line source had ever been successfully identified with a gamma-ray emission line of a nucleus, up to that time. (The 511 keV electron-positron annihilation line does show up in some of the spectra they show.) In other words, this is quite difficult to do. However, it looks like nuclear lines have been detected from the Cassiopeia A supernova remnant. This was done recently (2018) and appears to have been at the limits of current technology.


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