K. Kudo

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.

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.

Evidence for strong n–α correlations in the t+t reaction proved by the neutron energy distribution of muon catalyzed t–t fusion

Abstract We conducted a neutron measurement associated with muon catalyzed t–t fusion reactions, t+t+μ − →α+n+n+μ − + Q (11.33xa0MeV), in a solid T 2 target formed by a high-purity tritium gas (98.9%) with a deuterium component of less than 100 ppm. The observed fusion neutrons showed a continuous energy distribution with a shoulder at 6 MeV and the maximum energy at 9 MeV. This feature is inconsistent with the reaction Q -value and three-particle decay with no particle correlations at the exit channel. The obtained neutron-energy distribution was well reproduced by a simple model with two neutron-energy components. The result suggests strong n–α correlations in the three-particle decay at the exit channel of the t+t reactions which proceed at an extremely low energy through ttμ mesomolecule formation.

Neutron detection system for a muon catalyzed fusion experiment with an intense pulsed muon beam

Abstract We have developed a neutron detection system for muon catalyzed fusion (μCF) experiments at the RIKEN-RAL Muon Facility (Nagamine et al., Hyperfine Interactions 85 (1994) 343; 101/102 (1996) 521), where the worlds strongest pulsed muon beam is available. This system has been used in μCF experiments (separately reported (Ishida et al., Hyperfine Interactions 118 (1999) 203; Kawamura et al., Hyperfine Interactions 118 (1999) 213; Kawamura et al., Phys. Lett. B 465 (1999) 74; Matsuzaki et al., Hyperfine Interactions 118 (1999) 229; Nakamura et al., Hyperfine Interactions 118 (1999) 209; Nakamura et al., Phys. Lett. B 473 (2000) 226)) in order to detect a 14.1 MeV neutron emitted through a muon catalyzed dt-fusion process, and to determine the neutron yield ( Y n ) and the neutron disappearance rate ( λ n ), which are the most fundamental observable quantities in the μCF study. Although the utilization of an intense pulsed muon beam is essential for X-ray detection against a huge bremsstrahlung background from tritium β-decay (Nagamine et al., Hyperfine Interactions 85 (1994) 343; 101/102 (1996) 521), a large number of emitted neutrons cause a pileup event in the detection system. We developed the neutron detection system, which had sufficient performance to determine Y n and λ n even in such a condition.

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.

First observation of radiative photons associated with the μ− transfer process from (tμ−) to 3He through an intermediate (t3Heμ−) mesomolecule

Abstract For the first time, we have observed the 6.76 keV radiative transition photons associated with the μ− transfer process from (tμ−) atoms to 3He nuclei through intermediate (txa03He μ − ) mesomolecule formation in a solid T2 target. The radiative decay branching ratio of the (txa03He μ − ) mesomolecule and the muon transfer rate were determined and compared with theoretical values. We also studied an accumulation process of 3He atoms in a solid T2 target by observing the neutron decay rates originating from t–t muon-catalyzed fusions. Their time dependence indicates a sudden 3He bubble formation in the solid T2 at an atomic concentration of 130 ppm.