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Register a new userUsing Thin Film Targets for Muonic Atoms and Muon Catalyzed Fusion Studies
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Studies of muonic atoms and muon catalyzed fusion have been conventionally done in a bulk target of gas, liquid or solid hydrogen isotopes. The use of thin film targets developed at TRIUMF have notable advantages in tackling some of the most important questions in the field, which could be further exploited at future high intensity muon sources. We review the technique of the thin film method with emphasis on recent results and a future proposal.
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This report presents the results of an experiment aimed at observation of the muon catalyzed $^3!He;d$ fusion reaction $^3!He + mu;dto^3!He;mu;dto^4!He(3.66MeV)+p(14.64MeV)+mu$ which might occur after a negative muon stop in the $D_2+^3!He$ gas mixture. The basic element of the experimental setup is a Time Projection Chamber (TPC) which can detect the incoming muons and the products of the fusion reaction. The TPC operated with the $D_2 + ^3~He (5%)$ gas mixture at $31K$ temperature. About $10^8$ $^3!He;mu;d$ molecules were produced with only 2 registered candidates for the muon catalyzed $^3!He;d$ fusion with the expected background $N_{bg}=2.2pm 0.3$ events. This gives an upper limit for the probability of the fusion decay of the $^3!He;mu;d$ molecule $P_{F}(^3!He;mu;d)leq 1.1cdot 10^{-7}$ at 90% C.L. Also presented are the measured formation rate of the $^3!He;mu;d$ molecule $lambda_{d3He}=192(3)cdot 10^6 s^{-1}$ and the probability of the fast muon transfer from the excited to the ground state of the $mu;d$ atom $q_{1S}=0.80(3)$.
Studies of muonic hydrogen atoms and molecules have been performed traditionally in bulk targets of gas, liquid or solid. At TRIUMF, Canadas meson facility, we have developed a new type of target system using multilayer thin films of solid hydrogen, which provides a beam of muonic hydrogen atoms in vacuum. Using the time-of-flight of the muonic atoms, the energy-dependent information of muonic reactions are obtained in direct manner. We discuss some unique measurements enabled by the new technique, with emphasis on processes relevant to muon catalyzed fusion.
Building on the rare pion and muon decay results of the PIBETA experiment, the PEN collaboration has undertaken a precise measurement of B_{pi e2} = R^pi_{e/mu}, the pi^+ -> e^+ u(gamma) decay branching ratio, at the Paul Scherrer Institute, to reduce the present 40times experimental precision lag behind theory to ~ 6-7times. Because of large helicity suppression, R^pi_{e/mu} is uniquely sensitive to contributions from non-(V-A) physics, making this decay a particularly suitable subject of study. Even at current precision, the experimental value of B_{pi e2} provides the most accurate test of lepton universality available. During runs in 2008-10, PEN has accumulated over 2times 10^7 pi_{e2} events; a comprehensive maximum-likelihood analysis is currently under way. The new data will also lead to improved precision of the earlier PIBETA results on radiative pi and mu decays.
A method is reported for measuring the thickness and uniformity of thin films of solidified gas targets. The energy of alpha particles traversing the film is measured and the energy loss is converted to thickness using the stopping power. 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.
The role of the breakup process and one neutron stripping on the near barrier fusion are investigated for the weakly bound projectile $^{9}$Be on $^{28}$Si, $^{89}$Y, $^{124}$Sn, $^{144}$Sm and $^{208}$Pb targets. Continuum-discretized coupled channels (CDCC) calculations for the breakup with a $^{8}$Be + n model of the $^{9}$Be nucleus and coupled reactions channels (CRC) calculations for the one neutron stripping to several single particle states in the target are performed for these systems. A good description of the experimental fusion cross sections above the Coulomb barrier is obtained from the CDCC-CRC calculations for all the systems. The calculated incomplete fusion probabilities for different target systems are found to be consistent with the systematic behaviour of the complete fusion suppression factors as a function of target atomic mass, obtained from the experimental data.
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