[AndyJackson]

What does the Xray_7 denote?

Sounds like the field call sign of an operational military unit, e.g. Extortion 17. Air Force helicopter squadron in DC [for ferrying around Generals and Civilian VIPs] use e.g. Muscle_13.

[No_Doll_i]

Thanks very much!

[Diogenesis]

It could also mean a manmade radioactive event at level 7 (log scale):