FIG. 1: The TRIUMF Meson Hall, where the TUCAN experiment is located. Part of the UCN source is visible at the centre of the photo.

UCNs are neutrons that have been cooled to extremely low energies—on the order of 100 nano-electronvolts. Because of their low energy, they can be confined in material containers for several hundred seconds, allowing high-precision studies of the fundamental properties of the neutron. Although electrically neutral, neutrons may possess a minute separation of electric charge—an electric dipole moment (EDM). The existence of a finite neutron EDM would imply a violation of time-reversal symmetry—one of the fundamental symmetries of the laws of physics. This, in turn, is directly connected to CP (charge-parity) symmetry violation, which is believed to underlie the matter–antimatter asymmetry of the universe. In this context, the neutron EDM has profound implications in particle physics. The TUCAN experiment aims to produce large numbers of UCNs for a high-precision measurement of the neutron EDM, with the ultimate goal of probing time-reversal symmetry violation at unprecedented sensitivity.

In the UCN production scheme of TUCAN, proton beams from a cyclotron accelerator are impinged on a metal target to induce spallation reactions, producing fast neutrons. These neutrons are then cooled in stages, with the final stage utilising inelastic scattering in superfluid helium [1]. In 2017, a prototype UCN source developed in Japan was transported to TRIUMF, enabling the first successful production of UCNs at TRIUMF [2]. Since then, development has continued on a new, advanced UCN source designed to deliver UCNs at world-leading intensity [3].

In the latest experiment conducted in June 2025, the team successfully confirmed UCN production from the TUCAN source. The measured UCN production rates were in good agreement with predictions based on simulations, even though the liquid deuterium moderator—required for efficient deceleration of fast neutrons—had not yet been installed. With its installation planned, the collaboration is now poised to advance towards full-performance operation of the UCN source and the upcoming neutron EDM experiment.

FIG2: Response of the UCN detector recorded during the experiment. The blue line shows the counting rate of the UCN detector. During proton beam irradiation, the detector also responds to gamma rays and fast neutrons produced in the surroundings, causing increased counting rates. After the beam is turned off , opening the valve that extracts UCNs from the production region allows detection of the UCNs.

For further details, please see TRIUMF’s official news release:

https://triumf.ca/2025/06/30/new-ultracold-neutron-source-produces-record-for-canada/

The following researchers from RCNP are participating in this project:

From KURNS, Assistant Professor Takashi Higuchi and Ph.D. student Ryuto Fujitani are part of the TUCAN collaboration. Furthermore, a method for diagnosing cold neutron fluxes from the UCN source was developed at the CN-3 beamline of the Kyoto University Research Reactor (KUR), with support from Professor Masahiro Hino and Assistant Professor Takushi Takata, together with the participation of exchange student Antoine Beaudouin (Grenoble INP – Phelma). A UCN source based on a superfluid helium converter is also proposed at the new research reactor that is planned to be built on the Monju site in Tsuruga, Fukui prefecture. The experience and knowledge gained through TUCAN are expected to contribute to the development of this future facility.

This project is supported by the following funding bodies and programmes:

the Canada Foundation for Innovation; the Canada Research Chairs program; the Natural Sciences and Engineering Research Council of Canada (NSERC) (SAPPJ-2016-00024,

SAPPJ-2019-00031, and SAPPJ-2023-00029); British Columbia Knowledge Development Fund; Research Manitoba; JSPS KAKENHI (Grant Nos. 18H05230, 19K23442, 20KK0069, 20K14487, and 22H01236); JSPS Bilateral Program (Grant No. JSPSBP120239940); JST FOREST Program (Grant No. JPMJFR2237); International Joint Research Promotion Program of Osaka University; RCNP COREnet; the Yamada Science Foundation; the Murata Science Foundation; the Grant for Overseas Research by the Division of Graduate Studies (DoGS) of Kyoto University; Joint Usage/Research of the Institute for Integrated　Radiation and Nuclear Science, Kyoto University (KURNS) (R6055,R6056), and the Universidad Nacional Autonoma de Mexico – DGAPA program PASPA and grant PAPIIT AG102023.

References
［1］ Y. Masuda et al. Phys. Rev. Lett. 108, 134801 (2012).
［2］ S. Ahmed et al. (TUCAN collaboration), Phys. Rev. C 99, 025503 (2019).

［3］ W. Schreyer et al., Nucl. Inst. Meth. A 959, 163525 (2020); R. Mastumiya et al., JPS Conf. Proc. 37, 020701 (2022)

Electrons, protons and other charged particles can be accelerated with electric fields. Neutrons cannot be handled by the same way. We took notice of the character of a neutron as a tiny magnet (called as ‘magnetic dipole moment’). The gradient magnetic field pushes or pulls a magnetic dipole moment. We have already developed neutron lens, which exerts the force for transverse direction by sextupole magnets. Neutron beam can be focused to transverse direction by the lenses to improve the efficiency for the neutron small angle scattering experiments.(Figure 1)

Figure 1 : Accelerator for charged particles enables us to use the beam efficiently (Top). Control of neutrons was difficult because neutrons don’t have electric charge (Bottom).

Although neutrons can be accelerated or decelerated by the force to the longitudinal direction in principle, this technique was not demonstrated before. The velocity does not change because the net force is equal to zero only through the magnetic potential. When the force to the neutron reverses in the middle of the traveling, the net force can be finite value to make the velocity change. Combination of gradient magnetic field and high frequency RF field makes flipping of neutron magnetic moment to change of the direction of the force in the magnetic field.(Figure2)

Figure 2 : Our neutron accelerator system can reshape the neutron packet at the experimental position by using gradient magnetic field and RF field.

Now we have demonstrated this type of neutron accelerator to control the neutron velocity precisely. We have also observed space-time focusing of neutrons by controlling the energy distribution of the neutrons successfully. (Figure3) This technique enables us to improve the neutron density at the experimental area. This will be a powerful technique for measurements which require high density of neutrons, for example, the search of the permanent electric dipole moment of neutrons, which is related to the violation of time-reversal invariance in particle physics.

Figure 3 : The data tells us that the neutron packet was injected and made the peak in the graph.

This results was published in Physical Review A on 23 August 2012.

Paper Information

DOI

10.1103/PhysRevA.86.023843

Title

Demonstration of focusing by a neutron accelerator

Authors

Y. Arimoto, P. Geltenbort, S. Imajo, Y. Iwashita, M. Kitaguchi, Y. Seki, H. M. Shimizu, T. Yoshioka

Journal

Phys. Rev. A 86, 023843 (2012)

• *This work was supported by the Grants-in-Aid for Scientific Research of the Ministry of Education of Japanese Government under the Programs No. 19GS0210 and No. 23244047; the Quantum Beam Fundamentals Development Program of the Ministry of Education, Culture, Sports, Science and Technology; and Yamada Science Foundation.
• *The neutron scattering experiment was approved by the Neutron Scattering Program Advisory Committee of IMSS, KEK (Proposal No. 2009S03).

Rlated Links

Figure 4 : Members of the collaboration. Neutron accelerator can be seen behind the members.