Positron Production in Tungsten Crystals by 1.2-GeV Channeling Electrons

Abstract

The efficiency of positron production by a 1.2-GeV electron beam incident on a tungsten single crystal oriented in an axially channeling condition has been experimentally studied. Positron yields from a 1.2-mm-thick crystal have been measured to be ϳ2.5 3.0 times larger than those from amorphous targets with the same thickness. A simple model simulation of the positron production process shows that coherent bremsstrahlung, as well as channeling radiation, contributes to the enhancement of the positron yields. [S0031-9007 (98)05357-5]

On the Theory of Coherent Pair Production in Crystals in the Presence of Acoustic Waves

“…In this paper we have investigated the electron-positron coherent pair creation by highenergy photons in a single crystal in the presence of a hypersonic wave. If the displacements of the atoms in the crystal under the influence of hypersound have the form (4), the coherent part of the corresponding cross-section per single atom, averaged on thermal fluctuations, is given by formula (15). To compared with the cross-section in an undeformed crystal this formula contains an additional summation over the reciprocal lattice vector mk s of the one dimensional superlattice induced by the hypersonic wave.…”

“…In formula (15) for the pair creation cross-section the main contribution comes from the terms with g m ∼ δ. It follows from here that the external excitation with a wave vector k s will influence on the process of pair creation if mk s δ.…”

“…Due to the coherent bremsstrahlung this gives more intense radiation of photons, and as a result higher positron intensity. To further improve the positron yield the channeling radiation can be used, which is more intense than coherent bremsstrahlung and gives more electron-positron pairs [11,12,13,14,15,16,17,18,19]. An additional increase in the yield of positrons can be reached by using acoustic waves excited in crystals [20].…”

Development of an intense positron source using a crystal-amorphous hybrid target for linear colliders

“…Chehab and his colleagues at LAL d'Orsay [5], and experimental studies has been carried out with the 1.3-GeV synchrotron in Institute for Nuclear Study, the University of Tokyo [6], at CERN with the experiment WA 103 [7,8] and the KEKB linac at KEK [9]. Simulations have shown [10] that a crystal converter presents the advantage of less energy deposition than the equivalent amorphous converter (giving the same positron yield).…”

Advantages of axially aligned crystals used in positron production at future linear colliders

“…In further experiments (see [8][9][10][11][12][13]) using 1.2-10 GeV electrons aligned to the < 111 >-axis of tungsten crystals, measurements of some shower characteristics were already aimed to the development of a crystal-assisted positron source. Theoretical estimations performed in [14] display a rather good agreement with results of recent experiments [10][11][12][13].…”