Gamma Rays are produced but absorbed by the copper reactor walls
These Coherant Gamma Ray Interference Patterns are detected inside of the Reactors.
Relationships between Isotope Half Life times and Reactor Cycle Times are extremely restrictive of what Isotopes can slip through the timing window to produce gamma ray or hard x-ray interference patterns.
Below: Showing spectral lines of Tungsten isotopes that have a half life of about 5 milliseconds and could be the gamma radiators that produce these gamma ray or hard x-ray interference patterns.
Gamma Rays are located in the continuous electromagnetic spectrum defined as frequencies above 10 to the plus 17th Hertz.
Below: Gamma ray interference patterns that have frquencies of about ten to the plus 17th Hertz, at the lower end of the gamma ray determining frequencies.