Strong Reduction of the Effective Radiation Length in an Axially Oriented Scintillator Crystal

Abstract

We measured a considerable increase of the emitted radiation by 120 GeV/c electrons in an axially oriented lead tungstate scintillator crystal, if compared to the case in which the sample was not aligned with the beam direction. This enhancement resulted from the interaction of particles with the strong crystalline electromagnetic field. The data collected at the external lines of the CERN Super Proton Synchrotron were critically compared to Monte Carlo simulations based on the Baier-Katkov quasiclassical method, highlighting a reduction of the scintillator radiation length by a factor of 5 in the case of beam alignment with the [001] crystal axes. The observed effect opens the way to the realization of compact electromagnetic calorimeters or detectors based on oriented scintillator crystals in which the amount of material can be strongly reduced with respect to the state of the art. These devices could have relevant applications in fixed-target experiments, as well as in satellite-borne γ telescopes.

Radiation by an electron in an electromagnetic plane wave: The quasiclassical formula and other domains of applications

“…This was done in [5][6][7][8], where incoherent scatterings were generated at the differential rate ðd 2 σ el =d 2 qÞ × ðDebye-Waller factorÞ × ρðrÞ, where ρðrÞ is the local density of scattering centers. The simulation results obtained with the above methods in [5,6,18,19] are in good enough agreement with experiments.…”

“…p ⊥ instead of p T is the component perpendicular to k, not to a z axis related to F in . To summarize, the BK formula is obtained from (18a), (19), (23) and (24) by parametrizing the trajectory with t instead of ζ and making the replacementsp T ⇒ p ⊥ and…”

“…the 4-vectors p i and k are nearly collinear and we still have (19) and dζ=p þ i ≃ dt=ϵ i for Eq. (23).…”

Quantum features of high energy particle incoherent scattering in crystals

“…High energy particle interaction with oriented crystals makes it possible to both observe many remarkable phenomena and apply them to develop diverse sources of x and gamma radiation [1][2][3], to efficiently deflect high energy particle beams [4][5][6], to measure and even to modify elementary particle properties, such as magnetic momenta [1], and to reduce the thickness of particle detectors as well as to make the latter sensitive to both the direction and polarization [7][8][9][10]. All the pronounced effects, induced by the coherent particle interaction with an oriented crystal lattice, are described by the averaged (continuum) potential of atomic strings or planes [11,12] introduced by Lindhard, who also proved that the particle motion in the averaged potential can be treated classically at a high enough energy.…”

“…This problem is readily solved by the quantum treatment of transverse particle motion [25,26], being, however, both really necessary and practically feasible only at the electron and positron energies of a few dozen MeV and less. However, most of the current investigations are conducted at GeV [13,14,27] and higher [1][2][3][4][5][6][7][8][9][10][15][16][17][28][29][30][31][32][33][34] energies, at which the quantum description of particle motion in the averaged crystal field becomes both redundant and cumbersome, revealing the necessity for the introduction of classical particle motion features into the treatment of their incoherent scattering by the inhomogeneously distributed nuclei. Till now, a redefinition of the scattering impact parameter upper limit R → u 1 [28][29][30][31]35] has been used, which did not take into consideration any incoherent scattering dependence on the transverse particle coordinate, giving, thus, a qualitative estimate only.…”