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µ - SR IN NUCLEI WITH SPIN

( NOT “ µ S SR ” ! ). µ - SR IN NUCLEI WITH SPIN. Jess H. Brewer. Canadian Institute for Advanced Research and Dept. of Physics & Astronomy, Univ. of British Columbia Vancouver, BC, Canada. Huh? Wuzzat?. Visit http://musr.org. Transverse Field (TF) µ + SR.

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µ - SR IN NUCLEI WITH SPIN

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  1. (NOT “µSSR ”!) µ-SRIN NUCLEI WITH SPIN Jess H. Brewer Canadian Institute for Advanced Research and Dept. of Physics & Astronomy, Univ. of British Columbia Vancouver, BC, Canada

  2. Huh? Wuzzat? Visit http://musr.org

  3. Transverse Field (TF) µ+SR Typical time spectrum (histogram)

  4. Brewer's List of µSR Acronyms Longitudinal Field Transverse Field Zero Field Avoided Level Crossing Resonance Fourier Transform µSR Muon Spin Resonance Muon Spin Echo

  5. µ+SR vs. µ-SR Typical time spectrum (histogram) Single lifetime τμ = 2.197 μs Multiple lifetimes (some very short!) Asymmetry spectrum Large amplitudes Small amplitudes

  6. Ne Suzuki, 1980 Na Nuclearµ-Capture Mg µ-p n µ in a nucleus: Rate exceeds that of µ-e-µefor Z 11

  7. µ+SR vs. µ-SR Typical time spectrum (histogram) Single lifetime τμ = 2.197 μs Multiple lifetimes (some very short!) Asymmetry spectrum Large amplitudes Small amplitudes

  8. Atomic Capture & LSDepolarization of µ- Large impact parameters are more probable initial orbits tend to be circular. View along µ- momentum LScouplings depolarizeµ-spinunlessfast Auger!

  9. µ+SR vs. µ-SR Typical time spectrum (histogram) Single lifetime τμ = 2.197 μs Multiple lifetimes (some very short!) Asymmetry spectrum Large amplitudes Small amplitudes

  10. Characteristic precession frequencies of F± hyperfine states in selected low-Z muonic atoms ΔEHF F+ F- µ -Z µ -Z

  11. JHB 1982

  12. µ-SR in Teflon [(CF2)n]: High frequency signal: μ-C Low frequency signal: F+ (triplet) state of 19Fμ- HF transition rate F- (singlet) state RHF = 5.2(5) μs-1 fF •f+•P+(0) = 0.08(1)

  13. µ-SRin Melamine (C3H6N6): Low frequency signal: F+ state of 14Nμ- High frequency signal: μ-C fN•f+•P+(0) = 0.050(3)

  14. µ-SR in Melamine (C3H6N6) fN•f+•P+(0) decreases withB ΛNdecreases withB and is much too large to be caused by either RHF or neighbouring nuclear dipoles. ΛCis also anomalously fast.

  15. “Coulomb Explosion” Leftovers free electrons R. paramagnetic ion or radical e- e- γ Auger Depolarization! µ- µ-Z muonic atom ONLY in NONMETALS! (later) (t ≈ 0)

  16. First observation of µ-SR in Sodium Metal fNa•f+•P+(0) = 0.025(4) ΛNa = 13(3) µs-1

  17. Finis LinuxandOpenOfficeRULE!

  18. “Themes” inµ±SR μ+ only (?) μ+ or μ- Muonium as light Hydrogen (Mu = µ+e-)(H = p+e-) • Mu vs. H atom Chemistry: - gases, liquids & solids - Best test of reaction rate theories. - Study “unobservable” H atom rxns. - Discover new radical species. • Mu vs. H in Semiconductors: - Until recently, µ +SR→only data on metastable H states in semiconductors! The Muon as a Probe • Probing Magnetism: unequalled sensitivity - Local fields: electronic structure; ordering - Dynamics: electronic, nuclear spins • Probing Superconductivity: (esp. HTcSC) - Coexistence of SC & Magnetism - Magnetic Penetration Depth λ - Coherence Length ξ • Quantum Diffusion:µ + in metals (compare H+); Mu in nonmetals (compare H). • Ultra-Heavy Hydrogen: neutral muonic helium (α++μ-e-) has m ≈ 4.11 mH

  19. µ-SR : It is easy to get the impression that only positive muons are employed in µSR. Although mostµSRisµ+SR, it is often desirable to use negative muons in the same way, albeit with more difficulty. DRAWBACKS ofµ-SR PROPOSED MITIGATIONS LS Depolarization in the atomic cascade Nuclear Muon Capture: short lifetimes, few decay e- Giant Hyperfine Interaction with nonzero-spin nuclei "Tag" events with specific muonic X-rays Look for neutron asymmetries in heavier elements Observe characteristic F precession signals

  20. Nuclear µ-Capture Suzuki, 1980 PROBLEM µ-p n µin a nucleus: rate comparable to that of µ-e-µefor Z  Possible Help: Many times a fast neutron is emitted from nuclear µ- capture. Very few measurements have been made of the correlation of that neutron with the muon's spin direction. If cases are found where this neutron asymmetry is sizeable, we may be able to do neutron-triggered µ-SR, for which the event rate can be higher than in µ+SR.

  21. µ-SR in 27Al: Residual F- polarization after initial precession in F+ HF state followed by spin-flip transition to F- state RHF due to Auger of core electrons: measured value is consistent with the calculation of Winston (1963): RHF ≈ 41 μs-1.

  22. Relativistic Shift of µ- Frequency Al Taken at 7 kG C,N,O (ωμ-Z - ωμ+) / ωμ+ Cd Pb Atomic Number

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