Slowing-down times and stopping powers for {approx}2-MeV {mu}{sup +} in low-pressure gases

Journal Article · Sun Oct 15 04:00:00 EDT 2006 · Physical Review. A

DOI:https://doi.org/10.1103/PHYSREVA.74.042708· OSTI ID:20857885

Senba, Masayoshi; Arseneau, Donald J; Pan, James J; Fleming, Donald G ^[1]

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1. Department of Physics, Dalhousie University, Halifax, Nova Scotia, B3H 3J5 (Canada)

The times taken by positive muons ({mu}{sup +}) to slow down from initial energies in the range {approx}3 to 1 MeV, to the energy of the last muonium formation, {approx_equal}10 eV, at the end of cyclic charge exchange, have been measured in the pure gases H{sub 2}, N{sub 2}, Ar, and in the gas mixtures Ar-He, Ar-Ne, Ar-CF{sub 4}, H{sub 2}-He, and H{sub 2}-SF{sub 6}, by the muon spin rotation ({mu}SR) technique. At 1 atm pressure, these slowing-down times, {tau}{sub SD}, in Ar and N{sub 2}, vary from {approx}14 ns at the highest initial energies of 2.8 MeV to 6.5 ns at 1.6 MeV, with much longer times, {approx}34 ns, seen at this energy in H{sub 2}. Similar variations are seen in the gas mixtures, depending also on the total charge and nature of the mixture and consistent with well-established (Bragg) additivity rules. The times {tau}{sub SD} could also be used to determine the stopping powers, dE/dx, of the positive muon in N{sub 2}, Ar, and H{sub 2}, at kinetic energies near 2 MeV. The results demonstrate that the {mu}{sup +} and proton have the same stopping power at the same projectile velocity, as expected from the historic Bethe-Bloch formula, but not previously shown experimentally to our knowledge for the muon in gases at these energies. The energy of the first neutralization collision forming muonium (hydrogen), which initiates a series of charge-exchanging collisions, is also calculated for He, Ne, and Ar. The formalism necessary to describe the stopping power and moderation times, for either muon or proton, in three energy regimes - the Bethe-Bloch, cyclic charge exchange, and thermalization regimes - is developed and discussed in comparison with the experimental measurements reported here, and elsewhere. The slowing-down times through the first two regimes are controlled by the relevant ionization and charge-exchange cross sections, whereas the final thermalization regime is most sensitive to the forwardness of the elastic scattering cross sections. In this regime the slowing-down times (to kT) at nominal pressures are expected to be (less-or-similar sign)100 ns.

• OSTI ID: 20857885
• Journal Information: Physical Review. A, Journal Name: Physical Review. A Journal Issue: 4 Vol. 74; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ARGON
CARBON TETRAFLUORIDE
CATIONS
CHARGE EXCHANGE
COLLISIONS
COMPARATIVE EVALUATIONS
CROSS SECTIONS
ELASTIC SCATTERING
EV RANGE
HYDROGEN
IONIZATION
KINETIC ENERGY
MEV RANGE
MIXTURES
MUON SPIN RELAXATION
MUONIC ATOMS
MUONIUM
MUONS PLUS
NITROGEN
PROTONS
STOPPING POWER
SULFUR FLUORIDES
THERMALIZATION