1. Slow Neutron Physics and Neutron Scattering

概要

CO1-1

Improvement of multilayer mirrors for neutron interferometer

M. Kitaguchi, T. Fujiie1, and M. Hino2
KMI, Nagoya University
1
Graduate School of Science, Nagoya University
2
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
INTRODUCTION: Neutron interferometry is a powerful technique for studying fundamental physics. Numerous interesting experiments [1] have been performed
since the first successful test of a single-crystal neutron
interferometer [2]. However, the single-crystal interferometer is inherently not able to deal with a neutron that
has a wavelength longer than twice its lattice constant. In
order to investigate problems of fundamental physics,
including tests of quantum measurement theories and
searches for non-Newtonian effects of gravitation, the
interferometry of cold neutrons is extremely important,
since the sensitivity of interferometer for small interaction increases with the neutron wavelength. A large scale
of interferometer also has the advantage to increase the
sensitivity to small interactions.
One of the solutions is an interferometer using neutron
multilayer mirrors [3]. We succeeded in developing a
multilayer interferometer for cold neutrons in which two
paths are completely separated for the first time using
wide-gap etalons [4]. We can easily control parameters
such as Bragg angle, reflectivity, and Bragg peak width
by selecting the deposited material and tuning the bilayer
thickness and the number of layers.
We have started the development of multilayer interferometer at the beamline 05 NOP in MLF. From 2019, we
are continuing the experiments with etalons with monochromatic mirrors in order to demonstrate the performance of the interferometer. Figure 1 shows the interference fringes with etalons according to time-of-flight. The
phase of interferogram depends on the wavelength of
neutrons. We are testing the practical application of the
interferometer. Neutron coherence scattering length of the
material can be measured by inserting the sample into a
path of the interferometer. The results of the trial measurements were consistent with the literature values.
Because the mirrors have narrow bandwidth of the neutron reflectivity, the number of neutrons contributing to
the interference is limited. When the neutron supermirrors whose lattice constants vary gradually are utilized in
the interferometer, the effective range of neutron wavelength can be broadened to be applicable to a pulsed
source. In addition, the wavelength dependence of the
interactions can be measured simultaneously by using
pulsed neutrons.
EXPERIMENTS AND RESULTS: We are continuing
to fabricate the neutron mirrors with wide band for the
interferometer by using Ion Beam Sputtering facility in
KURNS. The mirrors should have the wide and smooth
top of the reflectivity with the range of momentum trans-

fer from 0.4 nm-1 to 1.0 nm-1. Especially, half mirrors
with the wide range of neutron wavelength are needed for
the interferometer. In 2022, we have been able to fabricate multilayer mirrors with stable performance. We also
measured the reflectivity at MINE2 in JRR3. Figure 2
shows the reflectivity of the half mirrors on the fused
silica substrates. Neutron wavelength was 0.88 nm and
the bandwidth of the beam was 2.7% of the wavelength.
We will try to create an interferometer with the mirrors
shortly.

Fig. 1. Normalized interference fringes with multiplayer mirrors for pulsed neutrons.

Fig. 2. Reflectivity of the half mirror with wide band
of neutron wavelength. Colors represent the sample
ID.
REFERENCES:
[1] H. Rauch and S. Werner, Neutron Interferometry Oxford University Press, Oxford, 2000;
J. Byrne, Neutron, Nuclei and Matter Institute of Physics
Publishing, London, 1994, Chap. 7;
Mater Wave Interferometry, edited by G. Badurek, H.
Rauch, and A. Zeilinger North-Holland, Amsterdam,
1988.
[2] H. Rauch et al., Phys. Lett., 47A (1974) 369 .
[3] M. Kitaguchi et.al., Phys. Rev. A, 67 (2003) 033609.
[4] Y. Seki et. al., J. Phys. Soc. Jpn., 79 (2010)124201.

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CO1-2

Development of a Spin Analyzer for Ultra-Cold Neutron

S. Kawasaki, T. Higuchi1, S. Imajo1, H. Akatsuka 2, K.
Mishima3, M. Kitaguchi2, and M. Hino4
Institute of Particle and Nuclear Study, KEK
1
Resarch Center for Nuclear Physics, Osaka University
2
Graduate School of Science, Nagoya University
3
Institute of Material Structure Science, KEK
4
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
INTRODUCTION: Existence of non-zero permanent
electric dipole moments (EDM) of the fundamental particles violates time reversal symmetry. Under CPT conservation, T violation implies CP violation. Thus, a precise
measurement of an EDM may reveal the origin of the matter dominant universe. The TUCAN (TRIUMF Ultra-Cold
Advanced Neutron source) collaboration aims to measure
a neutron EDM with a sensitivity of 10-27 ecm, which is
one order better sensitivity than the current best measurement.
The neutron EDM is measured by precise measurements
of spin precession frequency of neutrons. Ultracold neutrons (UCNs) , whose kinetic energies are less than a few
100 neV, are used for the measurement. One of the key
components of the measurement is a spin analyzer of
UCNs. The kinetic energy of an UCN is so low that magnetic potential can be used as a spin filter. When iron,
which has a large saturation magnetization of 2.2 T, is used
for the spin filter, the effective potential 𝑉𝑒𝑓𝑓 is
𝑉𝑒𝑓𝑓 = 𝑉𝐹𝑒 ∓ |𝜇| ∙ |𝐵| = 90 neV, or 330 neV
Where 𝑉𝐹𝑒 = 210 neV is the Fermi potential of the iron,
μ = 60 neV/T is the magnetic moment of the neutron,
and B = 2.2 T. Only one spin state of UCNs with kinetic
energies between 90 neV to 330 neV can transmit the iron
magnetic potential. Therefore, magnetized iron film functions as an UCN spin filter. In order to reduce UCN absorption, the iron layer should be as thin as an order of 100
nm.
EXPERIMENTS: The thin iron films were prepared by
an ion beam sputtering facility at the Institute for Integrated Radiation and Nuclear Science, Kyoto University
(KURNS). We produced thin iron on Si substrates and Al
foils similar to the actual UCN spin analyzer size of 83 mm
in diameter. Figure 1 shows the way of iron film fabrication by the sputtering.
We conducted experiments to evaluate the spin-analyzing
power of the ion films at Beamline 05 of the Material Life
Science Experimental Facility at J-PARC, where pulsed
UCNs were available. Figure 2
shows the setup
of the experiments. Two sets
of electromagnets
are used to magnetize iron films.
One is used as a
Fig. 1. Thin iron film

Fig. 2. Experimental Setup
spin polarizer and the other is used as a spin analyzer. Two
spin flippers are installed between the spin polarizer/analyzer. A UCN detector is used to measure the UCNs transmitted through those components. The spin polarizer/analyzer performance is evaluated from the UCN counts with
the spin flippers on and off. Using the time-of-flight information, we can evaluate the performance according to the
energy of the UCNs.
The iron films on the Si substrates and on the Al foils
were tested. As we reported last year and [1], the iron
films on the Si substrates have much smaller coercivity
than that on Al foil. In order to evaluate the dependence of
polarizer/analyzer performance on the applied magnetic
field, several measurements with different magnetic fields
were conducted.
RESULTS:
Figure 3 presents the preliminary results of the measurements. The polarization/analysis power shows as a function of UCN wavelength. In figure 3(a), a comparison between the iron films on the Si substrates and that on the Al
foils in the same magnetic field on 120 Oe. The iron film
on Si substrates has slightly higher performance. Figure
3(b) shows a comparison of different magnetic fields. We
can observe a significant increase between 60 Oe and 120
Oe, On the other hand, it looks saturates higher magnetic
fields. However, further analysis is required to finalize
the analysis.

Fig.3. Preliminary Results. The solid lines indicate a fit to a model. (a) The energy dependent
polarization of UCNs of iron films on Si substrates
and on Al foils. (b) The magnetic field strength dependence on the UCN polarization.
REFERENCES:
[1] H. Akatsuka et al., JPS Conf. Proc., 37, (2022)

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020801.

CO1-3 Development of High-resolution Cold/Ultracold Neutron Detectors Using Nuclear Emulsion
N. Naganawa, M. Hino1, H. Kawahara2, M. Kimura3, 4,
M. Kitaguchi2, 5, K. Mishima6, 7, A. Muneem8, N. Muto2,
J. Yoshida8

and the emulsion layer were checked of their stability
during the development. Finally, the emulsion layer was
observed by epi-illumination microscope.

Institute of Materials and Systems for Sustainability,
Nagoya University,
1
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
2
Graduate School of Science, Nagoya University
3
Nagoya Proton Therapy Center, Nagoya City University
West Medical Center
4
Graduate School of Medical Sciences, Nagoya City
University
5
Kobayashi-Maskawa Institute for Origin of Particles
and the Universe (KMI), Nagoya University
6
High Energy Accelerator Research Organization (KEK)
7
J-PARC Center
8
High Energy Nuclear Physics Laboratory, Cluster for
Pioneering Research, RIKEN

RESULTS:
The both layers were stable during the development.
Tracks of -particles were clearly observed without decrease of grain densities. There was no fog increase. It
was confirmed that the mechanical and chemical stability
of the converter layer was sufficient for experiments.

INTRODUCTION:
Experiments measuring spatial distributions of ultracold
neutrons in the Earth’s gravitational field have been conducted [1-3]. Quantum behaviors of neutrons in the gravitational field have been studied and unknown
short-range forces have been searched by them. ...