Search Results (9 total)

Epithermal effects in muonic molecular formation were observed during experiments in a low-density deuterium-tritium gas target carried out at the Paul Scherrer Institute. The high molecular formation rate of ‘‘epithermal’’ (not yet thermalized) muonic tritium atoms was reflected by a strong fast component in the fusion neutron time spectra followed by a smaller ‘‘steady-state’’ component where molecular formation occurs mostly from thermalized (‘‘cold’’) tμ atoms. Further experimental evidence for high epithermal dtμ molecular formation rates has been derived from measurements in triple H-D-T mixtures. First, theoretical calculations predicted strong resonances at high tμ kinetic energies and showed qualitative agreement with the observed experimental data, but yielded molecular formation rates that differed substantially from the observed values. At present, refined calculations are being carried out which may improve the agreement with experiment. Further experiments are being planned to clarify open questions.

Large discrepancies have existed, factor of ∼2.5 (∼5σ), between a variety of cascade-type theoretical models and published experimental results for the inclusive protonlike production corss sections at the 20° polar laboratory angle for relativistic La + La collisions. In view of this discrepancy the present work was undertaken to check the experimental cross sections for 0.76 GeV/nucleon La + La collisions using a small-acceptance magnetic spectrometer. The 20° cross sections were determined by measuring the appropriate range of polar laboratory angles and momenta which, when transformed into the projectile frame, produce the cross sections at 20°. Cross sections have been determined from 30° to 75° for protons and light nuclei with rigidities from 0.5 to 2.0 GeV/c in the laboratory frame. Cross sections were also deduced at 15° and 20° in the projectile frame for nucleon momenta from 0.9 to 1.5GeV/c. The original experimental results for the larger polar laboratory angles (40° and 60°) were confirmed; however, the 20° cross sections disagree by a factor of about 1.5 (∼2σ). At large polar laboratory angles (40°-70°) the model calculations disagrees in the low-momentum range with the present data by a factor of 1.5 (∼3σ). The discrepancy at small polar angles (15° and 20°) has been significantly reduced from the original factor of 2.5 down to a value of 1.2 (∼3σ).

Gamma rays and, for the first time, conversion muons of pt fusion have been measured from liquid mixtures of protium, deuterium, and tritium. The rate λ₁₀ for spin flip from the triplet to the singlet state of tμ(1s) was found to be λ₁₀=(1.06±0.13)×10³μs^-1, the rate for muon-catalyzed pt fusion from the (I=1) nuclear-spin state to be λ_pt^f(I=1) =0.067±0.002_-0.002^+0.005μs^-1, and the and the molecular formation rate to be λ_pt^m=(7.5±0.3_-0.3^+1.0)μs^-1 (all rates normalized to liquid hydrogen density).

Bose-Einstein correlations of negative pions in heavy ion collisions have been investigated for the reaction ¹³⁹La+^natLa→2π^-X at 12.6 GeV/nucleon at two acceptances, centered at laboratory observation angles of approximately 0° and 45° with respect to the beam axis. A scintillation counter array downstream of the target was used to sample the charged particle multiplicity of each event and hence give some information on the impact parameter of the collision. Including results from previous experiments, space-time dimensions of the pion source are now available for mass-symmetric collisions in the mass range of A=40 to 139. The sources are oblate for nearly all systems, except for La+La central collisions viewed near 45° in the laboratory (90° in the center of mass) where the source is spherical. The perpendicular radius R_⊥ is never less than 4 fm, regardless of the centrality of the La+La collision. Furthermore, R_⊥ seems independent of the mass of the collision system.

The method of two-pion interferometry was used to obtain source-size and lifetime parameters for the pions produced in heavy ion collisions. Two acceptances (centered at approximately 0° and approximately 90°, in the center of mass) were used for each of three systems, 1.70 GeV/nucleon ⁵⁶Fe+Fe, 1.82 GeV/nucleon ⁴⁰Ar+KCl, and 1.54 GeV/nucleon ⁹³Nb+Nb, allowing a search for dependences on nuclear mass and viewing angle. The correlation functions were calculated by comparing data samples to event-mixed reference samples. The effect of the particle correlations on the reference samples was corrected by weighting the events appropriately to remove the residual correlation effect. The source parameters, in the nucleus-nucleus center-of-mass frame, show an oblate source (i.e., R_⊥>R_∥) for the lighter systems and an approximately spherical source for the heaviest system. The dependence on nuclear mass shows that R_⊥ is essentially constant (under both viewing angles), whereas R_∥ for the 90° (c.m.) data increases with the nuclear mass. No evidence was found for a dependence of the source size on the pion momentum.

X-ray yields of the muonic helium (2-1) transition from μ-catalyzed fusion have been measured for the first time in various mixtures of hydrogen isotopes. They were determined to be 0.032(4), 0.016(2), and 0.0019(5) for pd, dd, and dt fusion, respectively.

Muon-catalyzed deuterium-tritium fusion was investigated within a wide range of mixtures in liquid and gas (23–35 K) by detection of fusion neutrons. Our improved analysis includes hyperfine effects and allows a clear separation of intrinsic dt sticking ω_s from kinetic effects. Strongly density-dependent cycle rates with values up to 1.45×10⁸ s^-1, yields of 113 fusions per muon, and ω_s=(0.45±0.05)% are found. In comparison with previous experiments we confirm that ω_s in liquid is lower than theoretically predicted, but do not find a strong dependence on either c_t or density.

Muonic x-ray spectra of μ³He from dμd and pμd fusion have been measured for the first time. Intensity ratios μ³He(3→1) / μ³He(2→1) were found to be 0.13±0.02 and 0.053±0.007 in the cases of dμd and pμd fusion, respectively. The population of excited μ³He states from pμd→μ³He+γ was measured with the help of the γ rays.

High rates for mesomolecular processes were found in a study of neutron spectra from muon-catalyzed dt fusion in low-density D/T mixtures. An interpretation is given in terms of a reaction-kinetics model which includes hyperfine effects. The hyperfine components of the d μt formation rates, first separated in this experiment, are large from 30 to 300 K. An unexpected temperature dependence for the transition rate between μt hyperfine states is found.