Question

Electrons cannot be accelerated by cyclotron.Why?

Answer 1

Cyclotrons can be used for heavy particles only, because heavy particles, at the same energy will increase their mass due to relativistic effects much less then light particles like electron. Cyclotrons can only be used for acceleration to non-relativistic speed, however proton with non-relativistic speed has much more energy then electron with non-relativistic speed. So they use it for protons.