Coherent coulomb excitation of nuclei and atoms moving through a crystal: The review of main results
- PDF / 659,835 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 203 Views
CLEI Experiment
Coherent Coulomb Excitation of Nuclei and Atoms Moving through a Crystal: The Review of Main Results V. V. Okorokov Institute for Theoretical and Experimental Physics, Bol’shaya Cheremushkinskaya ul. 25, Moscow, 117218 Russia Received November 20, 2006
Abstract—The basic characteristics and features of the coherent excitation of particles moving through a crystal—a new physical phenomenon predicted and experimentally discovered at ITEP—are discussed. PACS numbers: 04.80.Cc, 23.20.-g, 61.85.+p DOI: 10.1134/S1063778807070058
INTRODUCTION A new physical phenomenon—coherent Coulomb excitation of nuclei [1] and atoms [2] moving through a crystal—was predicted at ITEP in 1965. The first experimental evidence of existence of the coherent excitation of He+ ions moving through a single-crystal silver film was also obtained at ITEP [3].
The Fourier spectrum of the perturbation of this particle interacting with n atoms is related to the singleinteraction spectrum S0 (ω) as |S0n (ω)|2 = |S0 (ω)|2
sin2 (ωT n/2) , sin2 (ωT /2)
(2)
where T = a0 /V0 . The resulting spectrum |S0n (ω)|2 U(t) T = a0 /v0
PHYSICS OF THE PHENOMENON The conditions of the motion of a particle (nucleus or atom) having a level with the excitation energy ΔE = Eexc − Egr through a crystal can be chosen so that the frequency of collisions of the particle with the atoms of the crystal, ν0 = V0 /a0 (V0 is the particle velocity and a0 is the distance between the atoms of the crystal), is equal to the transition frequency (or is lower by an integer m): νtr = (Eexc − Egr )/h = ν0 m.
(a)
t
S0 ( ω ) T2 > T1
(b)
(1) n
2
ω
In this case, the velocity dependence of the probability of the Coulomb excitation must obviously be of resonant character, because the dependence of the interaction energy U (t) between the moving particle and the atoms of the crystal has the form of a periodic sequence of single peaks (Fig. 1a), each associated with the interaction of the particle with an atom of the crystal.
S0 ( ω )
The Fourier frequency spectrum of a single interaction S0 (ω) is shown in Fig. 1b for two different velocities of the particle moving through the crystal.
Fig. 1. Formation of the Fourier spectrum of multiple interaction of the moving particle with the atoms of the crystal (see the main text).
1174
(c)
2π/T
ω
COHERENT COULOMB EXCITATION OF NUCLEI AND ATOMS
for large n values is shown Fig. 1c for two velocities of the moving particle. According to Eq. (1) and Figs. 1b and 1c, the spectral density S0n (ω) at the frequencies ωm = m2π/T (m = 0, 1, 2, ...) increases proportionally to the interaction number n and the frequency band near each frequency ωn is narrowed in inverse proportion to n (Δωn ∼ π/(nT )). Such a change in the spectrum S0n (ω) (sequence of narrow intense lines at the frequencies ωm = 2πm/T ) with an increase in the interaction number n is associated with coherence (this fact explains the term coherent excitation) of the spectral components of single interactions S0 (ω) (Fig. 1a) periodically following each other (see
Data Loading...
