Toru Ebisawa

An improvement of the detection efficiency of a solid state UCN detector with a 6Li/Ti multilayer neutron converter working at liquid helium temperature

Abstract The detection efficiency of a solid state ultracold neutron (UCN) detector which works at liquid helium temperature has been improved. The neutron converter was a 6Li/Ti multilayer evaporated onto the surface of a commercial silicon-surface-barrier detector for the charged particles. The advantage of a 6Li/Ti multilayer is that the positive optical potential of 6Li is compensated by the negative potential of Ti. UCNs can therefore penetrate into the neutron converter which transforms neutrons to charged particles. The surface of the neutron converter was coated by a 1800 A thick Ti layer which prevents lithium from reacting with oxygen in the atmosphere. Ti easily absorbs oxygen during evaporation so that the effect of the Ti negative potential was diminished in our previous detector due to the positive potential of oxygen. The main improvement now is that the 6Li/Ti multilayer and a protective Ti layer were evaporated in one order of magnitude higher vacuum than in the previous case. As a result, the neutron reflectivity of a 6Li/Ti multilayer mirror, which was made in the same evaporation as the solid state UCN detector, has been decreased at wavelengths longer than 800 A compared with the previous case and is 0.6 at 1500 A. This implies that even UCN of 1500 A can penetrate into the 6Li/Ti multilayer and could be detected with a high detection efficiency by the solid-state UCN detector with a 6Li/Ti multilayer neutron converter.

Multilayer neutron polarizing mirrors working under a low external magnetic field less than 100 gausses

Abstract We have developed multilayer neutron polarizing mirrors which are controlled under an external magnetic field less than 100 gausses. Multilayers of Permalloy-Ge and Fe-Ge have been evaporated on Si wafers in the magnetic field of about 130 gausses parallel to the surface of the wafer. The polarizing efficiencies of Fe-Ge and Permalloy-Ge multilayer mirrors were 95% and 91% respectively under a low external magnetic field of 80 gausses. Under a very low external field of 50 gausses, the polarizing efficiency was 90% in case of Permalloy-Ge. A neutron pulse was obtained by applying a pulsed magnetic field of about 50 gausses parallel to the Permalloy-Ge polarizing mirror. The pulse rise time is the order of 100μs in the present pulsed magnetic devices.

Modified spin-echo method using cold neutron spin interferometry with RF flippers

Abstract We have been developing a modified spin-echo method using a cold neutron spin interferometry with radio frequency flippers, which is similar to “Mieze spectrometer”. The performances of the method are discussed.

Cold neutron spin interferometry and its application to modified spin echo methods

Abstract We propose three kinds of modified neutron spin echo methods using cold neutron spin interferometry, which is based on the coherent superposition principle of the neutron spin. Two kinds of the modified methods are based on a novel quantum precession of neutron spin by multilayer spin splitters and another method on time dependent spin interferometry using RF flippers. The performances of the last type are discussed and the firmer two methods are described in other proceedings.

Neutron optics and neutron forward-scattering using a transverse neutron-spin-echo instrument

Abstract A new principle of neutron-spin-echo (NSE) method is proposed for neutron optics and neutron forward-scattering experiments. The essential of this method is to set a sample in one of the Larmor precession fields. This sample geometry gives new physical information, in particular the refractive index of neutrons for a Si single crystal which was determined to be 1 − (1.85 ± 1.16) × 10 −5 at 5.7 A.

Development of a neutron spin echo spectrometer using four sequential reflection of multilayer spin splitters

Abstract We propose two types of modified neutron spin echo (NSE) spectrometer using the quantum precession caused by multilayer spin splitters. The first spectrometer is constructed by replacing the precession magnet with a pair of two spin splitters. The new NSE spectrometer requires much less volume and magnetic field compared to the conventional NSE spectrometer. The second spectrometer is designed to measure the small angle scattering from a plane sample. The principle and performances of the two types of the modified methods are discussed.

Determination of the hydrogen content in an evaporated Pd film by neutron interferometry

We demonstrate the feasibility of a microneutron interferometer (MINI) to determine the hydrogen content in the evaporated palladium film. MINI consists of a thin palladium film sandwiched by two semitransparent multilayer mirrors of Ni/Ti. The atomic ratio H/Pd as obtained from the shift of the interference fringes, under hydrogen pressures of 1 and 2 atm, was found to be 0.43 and 0.55, respectively. The accuracy of the results is 5.5%. MINI realized a better determination of the atomic ratio H/Pd than that in the case of a single Pd film by obtaining high neutron reflectivity in a relatively high Q range.

Neutron spin echo interferometry through magnetic potentials

Abstract We have established new principles of neutron spin interferometry based on a coherent superposition of (a) two eigen-states of ↑ and ↓ neutron spins or (b) two different energy states with the same ↑ spin state by using non-resonance or resonance neutron spin flippers, respectively. These interferometric states appear as spin precession or time beat, respectively. The phase difference between two spin states can be observed by the neutron spin echo, or by the resonance neutron spin echo. Using these interferometers, we have observed neutron spin precessions through various Fabri–Perot magnetic potentials in the tunneling region. We have also demonstrated that the phase shift of time beat is different depending on whether the magnetic potential is at the upstream of the spin analyzer or at the downstream of it, in the time-beat interferometer. Time-beat neutron interferometry opens new physics on tunneling time and diffraction time problems.

Quantum beat experiments and their applications using cold neutron spin interferometer

Abstract We have carried out quantum beat experiments using cold neutron spin interferometers installed at KURRI and JAERI. Quantum beat profiles (time-dependent interference fringe) with frequencies from 20 μHz to 34 kHz were observed, which correspond to energy difference 8.271 × 10−20and 1.406 × 10−10eV. Delayed choice experiment using quantum beat are proposed as an application.

DEVELOPMENT OF COLD NEUTRON PULSER FOR DELAYED CHOICE EXPERIMENT

Abstract The delayed choice experiment was done using the cold neutron spin interferometer of Jamin type arrangement which is installed at the JRR-3M of JAERI. “A multilayer polarizing cold neutron mirror placed in the pulsed magnetic field” is called a multilayer cold neutron pulser, or, in short, a cold neutron pulser. The switching function of the cold neutron pulser was used for producing the condition of whether or not the magnetic mirror is placed for the polarized neutron. It was shown that the cold neutron pulser is applicable to a cold neutron optical switch for the delayed choice experiment.