Photon Factory Activity Report 2004 #22 Part B (2005)
Instrumentation and Technique

NE1A1/2002G025/2004G022

Development of X-eX spectrometer
Hidefumi UCHIYAMA1, Syunji KISHIMOTO2, Masayoshi ITOU3, Hiroshi SAKURAI4,Hiroshi KAWATA2
1
Graduate University for Advanced Studies, Tsukuba, Ibaraki 305-0801, Japan
2
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan
3
Spring-8, Kouto, Mikazuki-cho, Sayo-gun,Hyogo 679-5198 Japan
4
Gunma Univ., Kiryu, Gunma 376-8515, Japan
Introduction
An ordinary Compton scattering experiment yields theso-called Compton profile J(pz), pz being taken along thephoton scattering vector. J(pz) is electron momentum
density ρ (p) integrated over px and py. The method has
been used to investigate electronic and magnetic propertyof materials. To do so in greater detail, however, it is best
to obtain ρ (p) directly from experiment. The energy andmomentum conservation for the Compton scattering
process tells that when the momentum (and thus energy)of the incident photons is fixed, ρ (p) can be directly
observed by measuring the energy and momentum of therecoiled electrons (or the scattered photons) and themomentum of the Compton scattered photons (therecoiled electrons) in coincidence mode. This method iscalled (X-eX) spectroscopy. In previous works theanalyses of the energy of the recoiled electrons or thescattered photons were carried out by a solid state
detector, thus the resulting momentum resolution waslimited to about 0.4 atomic units (a.u.)[1]. Sometime ago
it was noted that the single bunch operation of the KEKPF-AR allows us to use a time-of-flight (TOF) method toimprove the resolution for the energy analysis of therecoiled electrons [2].
In this report we describe our recently developed (XeX) spectrometer which is equipped with a TOF energy
analyzer to record the flight direction and the kinetic
energies of the recoiled electrons and a two-dimensional
position sensitive photon detector (2D-PSD) to record thedirection of the Compton scattered photons. Installationof the 2D-PSD makes it possible to obtain ρ (p) over thewhole momentum space in one measurement.

Spectrometer
Figure 1 shows a schematic view of the spectrometer.
The incident photons of 115.6 keV impinge on a sample.
The scattered photons are detected by the 2D-PSD. The
recoiled electrons go through a drift path and are detectedby a microchannel plate (MCP). To improve a time
resolution a retarded potential of –23 kV is applied in thedrift path to slow down the recoiled electrons. An angle
between the path of the incident photons and the line
which connects the sample and the center of the 2D-PSD
is 152.9 degrees. The angle between the path of theincident photons and the recoiled electron path is 11.1
degrees. The recoiled electron path is set along the photon
scattering vector.
Figure 2 illustrates the 2D-PSD which consists of anarray of Bi4Ge3O12 (BGO) scintillator and a position
sensitive photomultiplier (Hamamatsu R3941). The sizeof each BGO crystal is 2.2 mm × 2.2 mm × 15 mm. They
are arrayed in 25 × 21 with 0.2 mm spacing. The position
information is given by outputs of X and Y crossed –wireanodes of the photomultiplier each of which is connected
to a resister chain. The measured position resolutions ∆xand ∆y are 2.8 mm and 3.2 mm, respectively. In thepresent setup these position resolutions correspond to a
momentum resolution of 0.19 a.u. and 0.21 a.u.,
respectively. The momentum resolution of the electron
branch is measured to be 0.30 a.u. by observing a TOF
spectrum of the 1s photoelectrons of Au the kinetic
energy of which is 34.6 keV in the present experimental
conditions and very close to the average kinetic energy of
the recoiled electrons. The signals from the recoiledelectron branch and those from the scattered photon
branch are processed in coincidence mode. The observedρ (p) in Si is shown in the following report.
References[1] Th. Tschentscher et al., Phys. Rev. B48, 16965 (1993).
[2] M. Itou et al., J. Synchrotron Rad. 5, 676 (1998).

Fig. 1 Schematic view of the (X- eX) spectrometer.

Fig. 2 Illustration of the two-dimensional position
sensitive photon detector.

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