Demonstration of focusing by a neutron accelerator

Space-time focusing was demonstrated by a neutron accelerator. Test experiments were performed by using very slow neutrons at High-Flux Reactor at Institut Laue-Langevin. Focusing of neutrons at the detector position through the accelerator was observed. Focusing neutrons enables us to transport the neutrons while maintaining density from source to experimental position. This will be a powerful technique for measurement of the permanent electric dipole moment of neutrons, which require a high density of neutrons.

Figure 1

Concept of space-time focusing by using a neutron accelerator. (1) Neutrons are generated as a pulse. (2) Neutrons spread spatially during transport. (3) Neutrons are accelerated or decelerated properly. (4) Some neutrons are focused at the experimental position. This figure illustrates the behavior of polarized neutrons.

Figure 2

Experimental setup. The neutron accelerator is installed in the middle of the guide tube. The rf and data acquisition systems are synchronized with the shutter operation.

Figure 3

Measured velocity distribution of incident neutrons.

Figure 4

Position distribution of the neutrons (top). Shutter and rf operation (middle and bottom). Neutrons that are not affected by the accelerator are omitted in this figure. This figure is not to scale.

Figure 5

Neutron TOF spectra. Top and bottom show the cases of the rf off and on, respectively. Lines show the simulations.

Figure 6

Ratio of these two TOF histograms. Line shows the simulation with focusing.