T. Matsuzaki

The RIKEN-RAL pulsed Muon Facility

Abstract RIKEN has constructed a pulsed muon facility at Rutherford Appleton Laboratory (RAL) in the UK under an international collaboration between RIKEN and RAL to promote muon science. We have confirmed that the facility produces a pulsed decay muon beam as well as a pulsed surface positive muon beam with the highest instantaneous intensity in the world and initiated the muon science research program, which includes muon catalyzed fusion, since June 1995.

Search for heavy neutrinos in the beta decay of 35S. Evidence against the 17 keV heavy neutrino

Abstract A precise measurement of the beta-ray spectrum of 35S has been carried out using a Si(Li) spectrometer system to look for the signiture of heavy neutrino emission. The results are consistent with no heavy neutrino admixture, and the resulting upper limits for the mixing |UeH|2 ≲0.3% were determined in the mass range 10–50 keV.

New RIKEN-RAL pulsed µCF facility and X-ray studies on DT-µCF

In November 1994, the construction of a new superconducting muon channel of the RIKEN-RAL muon facility at ISIS of Rutherford Appleton Laboratory was completed. Subsequently, important features, such as the highest instantaneous intensity with a single-pulse structure and a high purity have been confirmed. Along with the installation of advanced µCF experimental equipment, including a high-purity D-T mixture target system with an in situ3He removal capability and a 4 T confinement magnet, an advanced µCF experiment, e.g. a precise X-ray measurement on µ-α sticking in dtµ-µCF will be realized. An account of the commissioning experiments, a plan for the earliest phase of the µCF experiment and possible future directions are reported.

X-ray studies on muon transfer reactions from hydrogen to helium

We have experimentally studied the muon transfer reactions from hydrogen to helium in liquid hydrogen with helium impurity concentration around 100–1000 ppm. The X-ray from the decay of (d4Heμ) molecule was clearly observed in the D2-4He system, whereas the corresponding X-ray was very weak in other systems such as D2-3He and H2-4He. This is well explained by the particle decay mode of the muonic molecule.

Construction of Riken-ral muon facility at ISIS and advanced μSR

By utilizing the intense pulsed proton beam available at the ISIS facility of RAL, the new muon facility project of an advanced superconducting muon channel funded by the RIKEN is now under construction. The new facility, by adopting the superconducting solenoid system, will produce the strongest backward decay pulsedμ+ orμ−in the momentum range from 20 MeV/c to 120 MeV/c. Also, by adopting the pulsed magnetic kicker, each one of two muon pulses will be supplied to two extraction channels simultaneously. Various important muon science experiments including advanced pulsedμ−SR andmu+SR experiments will be realized.

Band structures of 76Se and 78Se

Band structures of 76Se and 78Se have been studied with the 74,76Ge(α, 2nγ)76,78Se reactions by using a variety of in-beam γ-techniques : γ-ray singles spectra, γ-ray excitation functions, γ-γ-t coincidences, γ-ray angular distributions and γ-ray linear polarizations. Spins and parities have been assigned uniquely for many new levels in 76Se and 78Se and four bands have been identified in both nuclei: (i) the ground-state band, (ii) a positive-parity ΔJ = 1 band built on the second 2+ state (γ-vibrational band), (iii) a negative-parity Δ J = 2 band built on the 3− state (octupole band) and (iv) a ΔJ = 2 band built on the high-lying J = 4 state. In addition, the second 8 + and 10+ states, which are possibly the lowest members of a band, have been found in both nuclei. Systematics of the band structures obtained are discussed. Level energies of the band members and B(E2) ratios for some of the inter-band transitions between γ- and ground-state bands have been calculated with the proton-neutron interacting boson model IBM-2 and a reasonable agreement with the present data has been obtained.

Proposal for X-ray spectroscopy of muonic atoms formed from implanted ions in solid hydrogen films

A new method is proposed to extend muonic atom X-ray spectroscopy to the study of nuclear beams, including radioactive beams, by stopping both muon and nuclear beams in a solid hydrogen film. The muon transfer reaction to higher Z nuclei is used then to form muonic atoms. This method would allow studies of the nuclear charge distribution of unstable atoms.

Experimental setup for X-ray spectroscopy of muonic atoms formed from implanted ions in solid hydrogen

Abstract An experimental setup comprising of a cryogenic target and an ion implantation system has been constructed to perform muonic X-ray spectroscopy with muonic atoms formed from implanted ions in solid hydrogen films. Gaseous mixtures of hydrogen (H2) and deuterium (D2) have been frozen onto a thin 60-mm diameter silver foil, and then irradiated with charged particles of energies up to 33 keV /q . Already, solid films of H2 and D2 mixtures with implanted helium ions have been successfully used in muon catalyzed fusion related experiments at RIKEN-RAL Muon Facility. This new method allows studies of the nuclear charge distribution of unstable atoms by means of the muonic X-ray method at facilities where both negative muon and radioactive nuclear beams would be available.

Line broadening and Coulomb displacement energies of the hole-state analogs in the A = 111−123 odd-mass Sn isotopes

Abstract Line broadening and orbit dependence of the Coulomb displacement energy have been observed for the 1g 9/2 , 2p 1/2 and 2p 3/2 hole-state analogs in a series of odd- A Sn isotopes. The observed widths are discussed in terms of spreading width with main contributions from mixing with the isovector monopole state as well as the escape width.

Density enhancement of muon beams with tapered glass tubes

We have demonstrated that the beam density of 54 MeV/c muons can be increased almost by a factor of two when a tapered glass tube is inserted coaxially along the muon beam. The observations are compared with a multiple Coulomb scattering calculation, which reproduces the observation reasonably. This technique opens a new and simple way to increase the muon intensity effectively.