M. Tanase

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.

Muon catalyzed fusion and muon to 3He transfer in solid T2 studied by X-ray and neutron detection

X-ray and neutron measurements were carried out for muon catalyzed fusion and related phenomena in solid T2. The X-ray originated from the μ- to α sticking in muon catalyzed fusion; t + t + μ-→ (μ-α) + 2n was measured for the first time, yielding Kα X-ray intensity of (μα) atom and the intensity ratio of Kβ to Kα. Utilizing the phenomena of 3He accumulation in solid T2, the X-ray in the μ- transfer process from (tμ) to 3He was detected, providing a formation rate and radiative decay branching-ratio of (t3Heμ) molecule. From fusion neutron measurements, estimated values were obtained for (ttμ) molecular formation rate as well as sticking probability ωt in ttμ fusion. A possible new insight in t + t fusion reaction process at a low energy limit is also obtained.

MEASUREMENTS OF 3HE ACCUMULATION EFFECT ON MUON CATALYZED FUSION IN THE SOLID/LIQUID DT MIXTURES

Abstract An effect on the muon catalyzed fusion (μCF) of the 3He originating from the tritium decay was studied by measuring the time-dependent change of the fusion-neutron disappearance rate (λn) in the deuterium and tritium (DT) mixtures with various tritium concentrations, C t =0.1, 0.2, …, 0.7 . A clear difference between the solid and the liquid DT mixtures due to the 3He accumulation effect was observed: in solid λn increased with the time after solidification, whereas in liquid λn did not change. This indicates that 3He produced in the solid DT mixtures is trapped. Admitting that all the 3He remain in solid, the muon transfer rate from tμ to 3He is determined to be about 4×109 s−1, consistent with the theoretical prediction.

Measurement of X-rays from muon to alpha sticking and fusion neutrons in solid/liquid D-T mixtures of high tritium concentration

We measured the yields of K-series X-rays from (αμ)+ ion formed by muon to alpha sticking as well as the yields and the disappearance rates of fusion neutrons in 3He-free solid and liquid D-T mixtures. The effective sticking probability ωs obtained by neutron measurement is much smaller than any theoretical values so far published, while the discrepancy in αμ X-ray yield seems less significant.

Preparation of pure tritium for a liquid D2/T2 target of muon-catalyzed fusion experiments

Abstract To prepare a pure liquid D 2 /T 2 target for muon-catalyzed fusion (μCF) experiments, 50 TBq of tritium gas was purified with gas chromatography for isotopic enrichment and with the tritide formation reaction of uranium for chemical purification. The isotopic purity of the processed tritium was as high as 99.9% and the chemical purity 99.7%. The 3 He content was 0.02% or less immediately after the preparation. A 300 mL (30 TBq) portion of pure T 2 gas was mixed with 700 mL of pure D 2 gas to be loaded into a target chamber made of stainless steel. The D 2 /T 2 mixed gas was liquefied in the target chamber by cooling with liquid helium and irradiated with pulsed μ − beams for more than 200 h. No characteristic muonic x-rays arising from impurities in the D 2 /T 2 target were observed.

The first observation of muon-to-alpha sticking Kβ X-rays in muon catalyzed D-T fusion

Abstract At the RIKEN-RAL Muon Facility, we have observed K β (3 p →1 s ) μα sticking X-rays from muon catalyzed D-T fusion with various tritium concentrations ( C t =0.1−0.7) and high density solid and liquid phases. Statistics of K β X-rays were not enough to determine the peak shape, but the intensity was obtained with an adequate constraint to the K β shape using the theoretically calculated peak shape. No significant dependence of the K β /K α ratio on these target conditions was found, and our results ( Y ( K β )/ Y ( K α )∼7%) gave smaller values than the existing theoretical calculations. It suggests an existence of unexplained atomic process in the collision processes between ( αμ ) + and condensed media.

He accumulation effect in solid and liquid D-T mixture

This article reports the accumulation effect of the 3He originating from tritium β decay; 3He created in solid remains in it, while one in liquid diffuses and goes out to the vapor gas. We observed this effect through the neutron detection from muon catalyzed fusion phenomenon (μCF), and gave it qualitative understanding, by which the muon transfer rate from (dμ) and (tμ) to helium was derived.

Strong n-α Correlations Observed in Muon Catalyzed t-t Fusion Reactions

We conducted X-ray and neutron measurements associated with muon catalyzed t-t fusion process using high-purity tritium solid and liquid targets. We observed K α X-rays originating from muonic helium atoms (μα) formed in the muon sticking process: t + t + μ → μα + n + n + Q (11.33 MeV), and determined the Doppler shift broadening width which gave the average value of kinetic energy distribution of μα atoms in the target. We estimated then the maximum kinetic energy of μα atoms, which agreed well with the calculated kinetic energies assuming strong n-α correlations (sequential neutron decay through intermediate 5 He resonances) in the three-particle decay at the exit channel of t+t reactions. In the neutron measurement, the t-t fusion neutrons showed a continuous energy distribution with the maximum energy at 9 MeV. The obtained shape of neutron-energy distribution was analyzed and reproduced well by a simple model of two neutron-energy components, where we also assumed strong n-α correlations in the three-particle decay. Both the average kinetic energy of recoiling μα atoms and the characteristic feature of the observed neutron-energy spectrum supported a possibility of strong n-α correlations at the exit channel of t+t reactions.

Review of Measurements of Fusion Neutrons and X-Rays in Muon Catalyzed d–t Fusion at RIKEN-RAL – Details of the Detection System

Precise measurements of the absolute yields and the disappearance rates were carried out for both the X-rays from the (αμ)+ ion formed by muon to alpha sticking after the muon catalyzed fusion and for the fusion neutrons from 3He-free liquid and solid D/T mixtures. While the αμ X-ray yield does not contradict the values predicted by the atomic-process theories, the effective sticking probability (ωs) obtained by neutron measurement is much smaller than that from any of the calculations published so far, suggesting, e.g., enhanced reactivation.

The First Observation of the Temperature-Dependent Phenomenon of Muon Catalyzed Fusion in Solid D-T Mixtures

A systematic study on muon catalyzed fusion (μCF) was conducted in solid deuterium and tritium (D–T) mixture. A variety of experimental conditions were investigated, i.e., tritium concentrations from 20 to 70%, temperatures from 5 to 16 K. A preliminary analysis result suggests a steep decrease in the dtμ-molecule formation rate with decreasing temperature, and also an increase in the probability for a muon reactivation after an α-sticking phenomenon.