Results of theoretical and experimental research on capture of negative muons in hydrogen are reported with an emphasis on the accompanying phenomenon of muon catalysis in hydrogen and subtleties of the experimental method. A conclusion is drawn that precise determination of the capture rate is important for refining the standard model.

The mechanism for the muon catalyzed fusion reaction t + t → 4He + 2n + 11.33 MeV is investigated. The model of the cascade reaction with 5He as an intermediate state is considered, both the ground and the first exited states being taken into account. The neutron energy spectrum measured in the recent experiment is compared with the Monte-Carlo-simulated one. Varying reaction parameters, we obtain optimum values for the relative weights of the 5He ground and excited states and for the excitation energy and width of the excited state.

A search for the muon-catalyzed fusion reaction d + d -> He-4 + gamma in the dd mu muonic molecule was performed using the experimental installation TRITON with BGO detectors for gamma-quanta. A high-pressure target filled with deuterium was exposed to the negative muon beam of the JINR Phasotron to detect gamma-quanta with the energy 23.8 MeV. An experimental estimation for the yield of radiative deuteron capture from the dd mu state J = 1 was obtained at the level of eta(gamma) <= 8 x 10(-7) per fusion.

A search for the muon-catalyzed fusion reaction d + d → 4He + γ in the ddμ muonic molecule was performed using the experimental installation TRITON with BGO detectors for γ-quanta. A high-pressure target filled with deuterium was exposed to the negative muon beam of the JINR Phasotron to detect γ-quanta with the energy 23.8 MeV. An experimental estimation for the yield of radiative deuteron capture from the ddμ state J = 1 was obtained at the level of η γ ≤ 8 × 10−7 per fusion.

The muon-catalyzed fusion ( µ CF) process in tritium was studied by the µ CF collaboration on the muon beam of the JINR Phasotron. The measurements were carried out with a liquid tritium target at the tem- perature 22 K and density approximately 1.25 of the liquid hydrogen density (LHD). Parameters of the µ CF cycle were determined: the tt µ muonic molecule formation rate λ tt µ = 2.84(0.32) µ s -1 , the tt µ fusion reaction rate λf = 15.6(2.0) µs -1 , and the probability of muon sticking to helium ωtt= 13.9(1.5)%. The results agree with those obtained earlier by other groups, but better accuracy was achieved due to our unique experimental method.

This work is devoted to the correct interpretation of the steady state parameters of the muon catalyzed fusion (MCF) process in a D/T mixture. Previously the influence of the epithermal effects dtμ-molecule formation by ‘hot,’ non-thermalyzed tμ-atoms) on the steady state parameters was studied only for measurements with a low-density target (density φ = 0.01 relative to the liquid hydrogen density). We suggest a new method allowing direct determination of the necessary corrections to the MCF cycling rate for high-density data (φ ≥ 0.4).

A vast program of the experimental investigation of muon-catalyzed dt fusion was performed on the Joint Institute for Nuclear Research phasotron. Parameters of the dt cycle were obtained in a wide range of the D/T mixture conditions: temperatures of 20–800 K, densities of 0.2–1.2 of the liquid hydrogen density (LHD), and tritium concentrations of 15–86%. In this paper, the results obtained are summarized.

The article is devoted to the problem of the determination of the MCF parameters without essential loss in statistics. A new analysis method is suggested for this. This makes it possible to increase the statistics by a factor of 4–5 as compared with the previous analysis.

Muon catalyzed fusion (MCF) in deuterium was studied by the MCF collaboration on the Joint Institute for Nuclear Research Phasotron. The measurements were carried out with a high-pressure deuterium target in the temperature range 85–790 K at densities of about 0.5 and 0.8 of the liquid hydrogen density. The first experimental results for the dd μ molecule formation rate λ dd μ in the temperature range 400–790 K with a deuterium density of about 0.5 of the liquid hydrogen density are presented.

A search for the muon-catalyzed fusion (MCF) reaction d+d → 4He+γ in the ddμ muonic molecule was performed using the experimental MCF installation TRITON and NaI(Tl) detectors for γ quanta. A high-pressure target filled with deuterium was exposed to the negative muon beam of the JINR phasotron to detect γ quanta with an energy of 23.8 MeV. The first experimental estimation for the yield of radiative deuteron capture from the ddμ state J=1 was obtained at a level of ηγ≤2×10−5 per one fusion.

A rigorous expression for the neutron multiplicity distribution in the muon catalyzed fusion reaction is obtained. Some problems of its use in the experimental data analysis are considered.

Muon catalyzed fusion in deuterium was studied by the MCF collaboration at JINR phasotron. The measurements were carried out with a high-pressure deuterium target at the JINR phasotron in the temperature range 300–800 K at densities ≃0.5 LHD. The first experimental results for ddμ-molecule formation rate λ ddμ in the temperature range 400–800 K with deuterium density 0.5 LHD are presented.

Considerable efforts in μCF studies (since [1]) were aimed at observation of various fusion processes. The impact of these studies on the understanding of properties of the lightest nuclei, the dynamics of low-energy fusion reactions and the Coulomb three-body system structure are reviewed. Unsolved theoretical and experimental problems are summarized.

Experimental study on muon catalyzed dt fusion in a triple mixture of hydrogen isotopes (H/D/T) was carried out at the JINR phasotron. The measurements have been performed at various temperatures and densities with liquid and gaseous H/D/T mixtures. Results are presented for the main characteristics of the dt μ cycle. A reduction of the number of dt fusions is observed when hydrogen is added to the D/T mixture, This is mainly due to muon loss to the pt and pd cycles, which have a high sticking probability. We also observe an increase of the cycle rate when the temperature of the H/D/T mixture rises. This confirms the theoretical prediction.

Experiments on the study of the muon catalyzed fusion (μCF) process in a double D/T mixture of hydrogen isotopes in the temperature range 300–800 K at densities 0.3–0.5 LHD are performed at the JINR phasotron. The values of the effective μCF parameters (cycling rate λ c , neutron yield Y n , muon losses w) are obtained. Tentative dtμ-molecule formation rates on D2 and DT molecules (λ dtμ−d and λ dtμ−t ) are obtained for different mixture temperatures and densities. The results obtained show that λ dtμ−t increases with temperature, but its value is smaller than theoretical predictions.

The effective muon losses w measured in the last experiment of the JINR group with D/T mixture are analyzed. They are considered as a function of the tritium concentration C t taken for different temperatures. The obtained results indicate different muon transfer rates from deuterium and tritium to impurities with Z>1 (λ dZ and λ tZ ) and show that the ratio λ tZ /λ dZ increases with temperature.

Muon catalyzed dt fusion in dense D/T and H/D/T gas mixtures of hydrogen isotopes is studied by the MCF collaboration at JINR. The measurements were carried out with a high pressure target at the JINR phasotron in the temperature range 300-800 K at mixture densities \( \simeq 0.4{\text{ and }} \simeq {\text{0}}{\text{.8 LHD}}\). Tentative experimental results obtained by several analysis methods are presented.