Dear Researcher

The gamma band (19°) and the 002 reflection (27°) represent two different directions of the crystal structure of carbon fibers. The gamma band represents the amorphous carbon phase and the irregularities. The 002 reflection represents the regular graphite crystal structure. The fact that the gamma band is located to the left of the 002 reflection indicates that the amorphous phase has a lower degree of regularity than the graphite crystal phase and therefore appears at a lower two-theta angle.

I hope the following article will be useful to you.

Article Effect of γ-ray radiation on the polyacrylonitrile based carbon fibers

Kind Regards.

Özgün Ceren Akbay , I am sorry to say but your answer, as it is, leaves much to be desired.

My question about the term "gamma band" still remains. I have not had other answers affirming it as standard nomenclature.

The paper you referred to used gamma radiation to alter the structure of PAN to try to make it more graphitic. However, I don't see them ever use the term gamma band with regard to the XRD results. (Your link only afforded me a partial look at the paper.)

You said that the 19 and 27 degree peaks represent different directions, but then you say that the 19 degree peak represents the amorphous carbon. That would not have a direction, as such. Also, the fact that the 19-degree peak is left of the 27-degree 002 reflection simply means that it comes from a larger spacing. The two peaks have similar widths suggesting that they have similar regularity. Neither one is all that regular.

Other papers have shown peaks at a lower angle for their starting materials and processing has seen them shift to a higher angle due to closer packing. That would happen as the material transitions from something with lots to side groups to aromatic sheets of C atoms which can pack closer together. But so far, there was no reference to "gamma band".

My original question remains.