Is there radiation from an accelerator when the machine is switched off?

When an accelerator is switched off, there is generally no radiation being produced. This is because accelerators work by utilizing electromagnetic fields to accelerate charged particles, typically electrons or protons, to high speeds. During operation, these particles can indeed produce radiation, such as bremsstrahlung radiation when they interact with matter. However, when the machine is powered down and the particle beam is no longer being produced, the conditions necessary for radiation generation are also removed.

While there may be some residual radiation effects from the materials used in the accelerator, such as activation of components by previously produced radiation, these effects are usually minimal and do not occur during the standard operation mode of the machine. Therefore, the conclusion is that when an accelerator is turned off, it does not emit radiation in the same way it does when functioning.