J. L. Beveridge

A windowless frozen hydrogen target system

Abstract A cryogenic target system has been constructed in which gaseous mixtures of all three hydrogen isotopes have been frozen onto a thin, 65 mm diameter gold foil. The foil is cooled to 3 K while inside a 70 K radiation shield, all of which is mounted in a vacuum system maintained at 10−9 Torr. Stable multi-layer hydrogen targets of known uniformity and thickness have been maintained for required measurement times of up to several days. To date, hundreds of targets have been successfully used in muon-catalyzed fusion experiments at TRIUMF.

Experiments with energetic [mu]d and [mu]t emitted from solid hydrogen

A set of experiments is reviewed which makes use of the emission of muonic deuterium from the surface of a layer of solid hydrogen. The behaviour of muons in a solid target system has been studied via detection of muon decay electrons, muonic X-rays, and fusion products (neutrons and charged particles). The emission of muonic deuterium is understood to result from the Ramsauer-Townsend scattering minimum. The energy distribution of the emitted atoms ranges from tenths of eV to about 10 eV, and can be controlled to some extent. A proposal is described to use muonic tritium emission to measure the energy dependence of muonic molecular formation.

Muon catalyzed fusion in 3-K solid deuterium

Muon catalyzed fusion in deuterium traditionally has been studied in gaseous and liquid targets. The TRIUMF solid-hydrogen-layer target system has been used to study the fusion reaction rates in the solid phase of D{sub 2} at a target temperature of 3 K. Products of two distinct branches of the reaction were observed: neutrons by a liquid organic scintillator and protons by a silicon detector located inside the target system. The effective molecular formation rate from the upper hyperfine state of {mu}d and the hyperfine transition rate have been measured: {tilde {lambda}}{sub (3)/(2)}=2.71(7){sub stat}(32){sub syst}{mu}s{sup {minus}1} and {tilde {lambda}}{sub (3)/(2)(1)/(2)}=34.2(8){sub stat}(1){sub syst}{mu}s{sup {minus}1}. The molecular formation rate is consistent with other recent measurements, but not with the theory for isolated molecules. The discrepancy may be due to incomplete thermalization, an effect that was investigated by Monte Carlo calculations. Information on branching ratio parameters for the s and p wave d+d nuclear interaction has been extracted. {copyright} {ital 1997} {ital The American Physical Society}

Muon-catalyzed fusion in deuterium at 3 K

Muon-catalyzed fusion in deuterium has traditionally been studied in gaseous and liquid targets. The TRIUMF solid hydrogen layer target system has been used to study the fusion reaction rates in the solid phase at a target temperature of 3 K. Both branches of the cycle were observed; neutrons by a liquid organic scintillator, and protons by a silicon detector located inside the target system. The effective molecular formation rate from the upper hyperfine state and the spin exchange rate have been measured, and information on the branching ratio parameters has been extracted.

Production of slow muonic hydrogen isotopes in vacuum

Muonic hydrogen isotopes (μ− p, μ− d, and μ−t) are simple quantum mechanical systems ideally suited for studies of numerous fundamental phenomena in electroweak and strong interactions as well as in applied areas such as muon chemistry or muon catalyzed fusion.Emission of muonic hydrogen isotopes into vacuum helps to overcome the limitations which are normally imposed on conventional investigations with gaseous and liquid targets. A proof of principle experiment for this new technique was performed at TRIUMF last year. Negative muons with 30 MeV/c momentum were stopped in a thin film of solid hydrogen and produced very low energy μ−d in vacuum. The distribution center of the normal velocity components of emitted μ−d atoms was measured to be ∼1 cm/μs. The yield of μ−d in vacuum is an increasing function of H2 film thickness δ up to a value of δ≥1 mm.

Muon molecular formation and transfer rate in solid hydrogen-deuterium mixtures

In an experiment at TRIUMF to study muon-catalyzed fusion and associated atomic and molecular effects, negative muons were stopped in a solid protium hydrogen layer containing a small amount of deuterium. Most of the resulting µp atoms disappeared by formation of ppµ molecules or by muon transfer to a deuteron. The µd can drift almost freely through the hydrogen layer due to the Ramsauer-Townsend effect and may even leave the layer. If a thin neon layer is frozen atop the hydrogen, the exiting muonic atoms will very rapidly release their muon to a neon atom. The analysis of the time structure of the neon X-rays is used to determine the rates of the slower processes involved in the evolution of the µp. This analysis has been performed with the help of Monte Carlo calculations, which simulate the kinetics of both µp and µd atoms in the hydrogen mixtures.

Producing μ−d and μ−t in vacuum

After the feasibility of vacuum isolated μ−d production was demonstrated at TRIUMF in 1989, development was begun on a target system that would take advantage of the process to aid in the understanding of the muon catalyzed fusion cycle. Minimal neutron backgrounds, the ability to use silicon detectors, and compatibility with tritium were considered important for a very versatile target system. The advantages which the target gives in isolating μCF process will be outlined.

Characterization of solidified gas thin film targets via alpha particle energy loss

Abstract A method is reported for measuring the thickness and uniformity of thin films of solidified gas targets. The energy of α particles traversing the film is measured and the energy loss is converted to thickness using the range. The uniformity is determined by measuring the thickness at different positions with an array of sources. Monte Carlo simulations have been performed to study the film deposition mechanism. Thickness calibrations for a TRIUMF solid hydrogen target system are presented.

Muon transfer from hot muonic hydrogen atoms to neon

A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of μ−p atoms in each target. The rates λppμ and λpd can be extracted

Muon facilities at TRIUMF

TRIUMF provides its user community with a wide variety of muon beams for use in μSR and fundamental particle studies. The existing muon channels and their characteristics are described along with a proposed superconducting solenoid to be constructed in 1987.