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The very cold and ultracold neutron facility

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Instruments & Support : Instruments & groups > PF2 > How it works

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Principle of the ILL neutron turbine

The neutron turbine of PF2 is a mechanical device which slows down (cools) neutrons the same way a tennis player can slow down a tennis ball (Doppler effect).The reactor generates neutrons whose speeds (energies, temperatures) are very diverse.

  • The curved guide directed upwards selects neutrons with an average speed of 50 m/s. Faster neutrons are unable to negotiate the bends, while slower neutrons are unable to overcome gravity to reach the top of the guide.
  • These neutrons, already very slow, arrive on a turbine. In bouncing off the blades turning at 25 m/s, they are greatly slowed down.
  • Neutrons with an average speed of 5 m/s (ultra-cold neutrons or UCN) come out of the turbine via a series of guides that direct them to experiment sites.