P. Baumann

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 kinetics of muon-catalyzed dt fusion

A main source of information about the muon-catalyzed fusion cycle in D-T mixtures are the cycling rates λc, which are characteristic for the kinetic equilibrium of states attained rapidly in dense targets. The measurement, analysis and interpretation of these rates will be discussed, concentrating on the extensive set of rates observed at PSI over the last decade in gaseous, liquid and solid targets.

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.

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.

Absolute probabilities of fission induced by stopped antiprotons

Abstract Absolute probabilities for the fission induced by stopped antiprotons have been determined for U, Th, Au, Ho by measuring the fission fragments in coincidence. The numbers of antiprotons stopped in the targets were obtained from an activation analysis. The fission probabilities are 77(4)%, 70(4)% and 3.1(3)% for 238 U, 232 Th and 197 Au. For 165 Ho an upper limit of 1.1% was determined. The results are compared with intranuclear cascade calculations.

Spectra and multiplicities of n, p, d, t, K±, π± from antiproton annihilation in Cu and U

Abstract Inclusive energy spectra of neutrons, protons, deuterons, tritons, charged kaons and pions following antiproton annihilation at rest in copper and uranium have been measured. The determined multiplicity charged kaons is compared to recent measurements and indicates an enhancement of strangeness production. Ratios of directly emitted neutrons and protons have been determined for copper and uranium to 3.0±0.6 and 3.2±0.5, respectively.

The ptμ cycle in muon catalyzed fusion

A detailed theoretical description of the ptμ muon catalyzed fusion cycle in H/D/T mixtures at low deuterium and tritium concentrations is presented. The experimental data on the γ-ray time spectra from the reaction p+t » γ+4He in the mesic molecule ptμ obtained by the μCF collaboration at SIN/PSI have been analyzed. The radiative pt fusion rate in the ptμ mesic molecule is found to be λγ=0.067 ± 0.002−0.002+0.005 μs−1. This corresponds to a reaction constant for the pt radiative capture ofK0=1.0 × 10−22 cm3 s−1.

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.