Neutron beam manipulation utilizing spin magnetic dipole moment

Fuwa, Yasuhiro   ; Iwashita, Yoshihisa*; Kuriyama, Yasutoshi*; Yamada, Masako*; Hirota, Katsuya*; Kitaguchi, Masaaki*; Shimizu, Hirohiko*

Since neutrons have a spin magnetic moment, they are subject to a force due to their interaction with the magnetic field gradient. The direction of this force coincides with the direction of the magnetic field gradient vector, and the force acts in the opposite direction depending on the direction of the spin. By utilizing this force, the neutron beam can be manipulated. If the magnetic field gradient is transverse to the beam axis, the beam is deflected. Therefore, if a sextupole magnet is used to generate a magnetic field, the magnetic field gradient changes in proportion to the distance from the center of the beam axis, which causes the same effect as a lens, and the neutron beam can be focused. In addition, by arranging permanent magnets in a Halbach array on a plane and generating a uniform magnetic field gradient in the direction normal to the plane, a neutron beam reflecting wall can be formed, which can be combined in a duct-like configuration to form a guide tube. The magnetic field gradient in the longitudinal direction relative to the beam axis can change the energy of the neutrons. The integral value of this energy change is zero if the neutrons just pass through, but if the spins are flipped in the magnetic field gradient, the neutron beam can be accelerated or decelerated with the energy corresponding to the magnetic flux density at the flipped location. By applying this technique, spatial focusing and energy modulation of neutron beams are possible. In this presentation, the principle and configuration of the instruments we are developing for neutron beam manipulation and the planned experiments are described, and their potential applications are discussed.