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Institut Laue-Langevin

Ultracold neutrons with wavelengths around 1000 Å have several unique features: one of them is that they are totally reflected from the surface of most materials under any angle of incidence. This offers the possibility of storing neutrons in so called neutron bottles (or traps) for the observation of several fundamental characteristics of the neutron itself.

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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.