K. Lou

Experimental survey of the sticking problem in muon catalyzed dt fusion

The “sticking” process dtμ → αμ + n, which constitutes the most severe limit to the number of fusions which a muon can catalyze, is reviewed. Many attempts were made to determine by calculations and measurements the probability for initial stickingωs0 (immediately after dtμ fusion) and for final stickingωs (after the αμ came to rest). Previous results based on neutron disappearance rates and on the observation of αμ-X-rays were controversial and also in some disagreement with theory. New data are reported from PSI on direct observation of final sticking, using a setup with the St. Petersburg ionization chamber. These data mark a significant improvement in reliability and may clarify questions concerning previous discrepancies. The new results isωs∼(0.56±0.04)%, lower than the theory predictionωs=(0.65±0.03)%, at medium density.

The PSI experiments on muon-catalyzed pt fusion

The experiments on pt fusion performed at Paul Scherrer Institut, Villigen, Switzerland, are described. Liquid triple mixtures of protium, deuterium and tritium with low concentrations on deuterium and tritium were used. Gamma rays, X-rays, neutrons and, for the first time, conversion muons, were measured. Preliminary results are: Rate for spin flip from the triplet to the singlet state of tμ(1s), λ10=(1.0±0.2) × 103μs−1; rate for muon-catalyzed pt fusion from the (I=1) nuclear-spin state, λptf(I=1)=0.07±0.01μs−1; and the molecular formation rate, λptm=(7.5±1.3)μs−1 (all normalized to liquid hydrogen density).

Systematic analysis of the PSI experiment to directly measure the sticking probabilityωs in dt fusion

Starting in 1989 an experiment was run at PSI to directly measure the final sticking probability in muon catalyzed dt fusion. This experiment was based on an “active-target” ionization chamber (IC) built at Gatchina, Russia, and an array of plastic neutron counters. In three runs approximately 5×106 isolated alpha signals were recorded with around one half of these occurring in the inner chamber region where we have more complete understanding of the systematic errors. Particularly from a long run in 1992 we were able to obtain a very clean sticking peak of some 5000 μα events. However, to reach an accurate value of sticking, all systematic effects and several major backgrounds had to be understood in detail. To this end a Monte Carlo code was written to simulate the full electrostatic environment of the IC and to recreate completely each signal type including the actual tritium decay noise from the live experiment. A slightly model dependent value of approx. 0.56±0.04% is obtained for final sticking.

Epithermal effects in muon catalyzed fusion in H / D / T mixtures at low deuterium and tritium concentrations

The results of a Monte Carlo simulation of muon catalyzed fusion in H/D/T mixtures at low deuterium and tritium concentrations are presented, and the kinetics of the dt branch of the μCF cycle is discussed. It is shown that the epithermal effects in the dtμ cycle produce a multicomponent structure in the time spectra of dt fusion, in agreement with the recent experimental results obtained by the μCF collaboration at PSI. The importance of further studies of the μCF reactions in triple mixtures is emphasized.

Final dt sticking? s using the ?survived moun method?

A new direct measurement of the final dt sticking probability ωs using a special data analysis called the “survived muon method” is presented. The data were obtained at PSI using a high pressure ionization chamber with H/D/T gas mixtures. The method can provide information on final sticking dμt → μα+n independent of theoretical models of stripping and initial sticking. It was found:ωs=(0.57±0.07±0.02)%. The experiment and the analysis method are discussed in detail.

Survey of experimental results on μCF including hyperfine effects

Complementary to the investigations of the most efficient dt cycle, also the other muon-induced fusion cycles in mixtures of hydrogen isotopes have been studied. The results of these dedicated experiments provide rich information about muon-induced few-body reactions and contribute significantly to a better overall understanding of μCF. A summary of the recent progress will be presented. Special emphasis will be put on two characteristic examples, namely a new experimental approach to study the muonic cascade in H-D mixtures and the systematic study of hyperfine effects in muon-induced reactions.

Feasibility of an experiment to determine the branching ratio for the emission of a heavy neutrino after muon capture in3He

The triton energy of the muon capture reaction μ3He → t+vμ, where μ3 He is the ground state of muonic3He, has been measured in order to investigate a possible heavy v admixture into the μ flavour with high sensitivity. μ3 He has been formed via the pμd fusion reaction by stopping μ− in an ionization chamber (IC) filled with an H/D gas mixture of 3% D concentration at a pressure of 161 bar. In a first short experiment 650 triton events were observed yielding an upper limit for the μ-heavy v mixing strength of 2.3×10−3 atE0v=60 MeV.

Preliminary Results on Muon-Catalyzed pt Fusion

Muon-catalyzed pt fusion certainly is not interesting for a possible energy production as dt fusion might perhaps be. Nevertheless there have been good reasons to perform a second experiment on the pt fusion process, after it was carried out for the first time a few years ago [1]. Several fusion channels exist for pt fusion [cf. Table 1]. Besides 7 emission muon conversion [Reaction (3)], i. e. the transfer of the fusion energy to the catalyzing muon, and internal pair formation [Reaction (4)] should be possible. From rates and branching ratios of these processes one may draw conclusions about the nuclear structure of the few body system 4He [2] and on spin-flip processes in the μ t atom. This will be described in more detail now.

Direct Measurement of Sticking in Muon Catalyzed DT Fusion and Physics of “Hot” µt Atoms

New results are reported from a recent PSI experiment about the fusion reactions dµt → µ + α + n and dµt → µα (sticking) + n. The apparatus consisted of a high pressure ionization chamber to detect charged particles directly and of an array of neutron counters to measure the fusion neutrons. The principle and performance of the experiment are described as well as a detailed study of its systematics by using a new Monte Carlo code. The preliminary results for the probability ω s of final dt sticking are (0.50 ± 0.06)% from a reanalysis of a 1989-run and (0.47 ± 0.06)% for the recent 1991-run, nearly 3 standard deviations lower than the theoretical calculations. The initial time distributions of the neutrons at various low deuterium and tritium concentrations of the H/D/f mixture are presented providing new insights of the fast non-thermalized transfer of the muon from the μd to the μt atom.

Measurement of the stopping power for μ− and μ+ at energies between 3 keV and 100 keV

An experiment has been performed to measure the stopping power of carbon, gold and magnesium fluoride for μ− and μ+ at energies between 3 and 100 keV. The energy loss of negative and positive muons was determined by measuring their time of flight in front of and behind a target. For these measurements a parallel plate avalanche counter and a microchannel plate were used. The Bragg peak has been observed. The Barkas effect was measured down to two times the Bohr velocity.