Larmor clock and measuring of neutron interaction time with quantum objects

Experimental activity in the field of neutron spin precession optics was started some years ago by the Achiva et al. In 1999 we demonstrated the unique possibility of the IN15 spin-echo instrument of ILL for such kind of investigations. In the present paper we shall report some new results. Larmor precession of neutron spin was used as a clock for the measurement of the delay in neutron time of flight, caused by the difference in neutron velocities in vacuum and in matter. Coherence length density was measured for a number of materials with an accuracy of some percent. It was found that diamagnetic properties of materials may affect the results remarkably. The giant anisotropic diamagnetic acceptability was found for the pyrolytic graphite. The achieved accuracy in the delay time, (3-5) × 10^-10 s, permits us to perform a number of new experiments for the measurement of neutron interaction time with different quantum objects.