# Information on X-rays and Gamma Rays

1. Dec 2, 2004

### Staff: Mentor

X-ray energies increase with atomic number, Z. X-rays originate from photon emissions as electrons drop back into the K and L shells of atoms. Thus they have characteristic wavelengths.

Hydrogen has the lowest energy X-rays (Ek=13.6 eV) which is the first ionzation potential. It has one electron in the K-shell.

The highest energy is about 142 keV, which corresponds to Z=100 (Fermium).

See the following resources:

http://www.wsu.edu/~collins/Phys415/writeups/Moseley.htm

http://dental.senzoku.showa-u.ac.jp...el_1970/S&I_Tables_II-VIII/S&I_Table_III.html

http://online.nucleartraining.co.uk/resources/xrayenergies.htm

Gamma-rays originate from the nucleus of atoms upon the absorption of a neutron (n, $\gamma$) reaction, in decay of many radionuclides following beta decay, and from the decay of some subatomic particles.

The lowest energy gamma (from Er-169) has an energy of 8 kev (0.008 MeV). About 58 radionuclides have gamma-energies in the X-ray region (8-145 keV).

For some information on gamma-rays (sources, energies, yields) of selected radionuclides - see http://ie.lbl.gov/toipdf/eandi.pdf

Gamma-rays from neutron capture.

Tables of Thermal Neutron Capture Gammas by Target

Tables of Thermal Neutron Capture Gammas by Energy

Last edited: Jul 29, 2011
2. Dec 3, 2004

### Morbius

Yes - I would only add that gamma rays have characteristic wavelengths
too. Just as there are K and L shells [ quantized energy states ] for the
electrons surrounding atoms - the energy levels of the nucleons [ protons
and neutrons ] in the nucleus of an atom are also quantized. The gamma
rays are the result of a nucleon transitioning between these levels.
[However, because the strong nuclear force which binds nucleons is so
much stronger than the Coulomb force which binds electrons to atoms,
the energies of gamma rays are much greater than the energies of
X-rays].

Because of this - the gamma ray spectrum is indicative of the radioisotope
that emitted it. This allows us to identify materials based on their

This effect is being put to good use in portable radiation analyzers:

http://www.ortec-online.com/psis.htm

Dr. Gregory Greenman
Physicist

3. Jul 28, 2011

### bgc

"... because the strong nuclear force which binds nucleons is so
much stronger than the Coulomb force which binds electrons to atoms,
the energies of gamma rays are much greater than the energies of
X-rays]."

I beg to differ slightly:

Similarly to the atomic shell model the nuclear admits of low energy transitions at the "top". A rather famous example is the Fe 14.4 keV Moessbauer line.

bc