Slow Positron Facility |
High Energy Accelerator Research Organization (KEK) Institute of Materials Structure Science |
The slow positron beam of this Facility is created at the target (converter/moderator) of the dedicated linac placed at the north end of the Test Hall on the basement floor of the Electron Linac Control Building, magnetically transferred along the beam line, and led into the experiment stations on the same hall. The beam line is also branched in midstream upward into the Klystron Gallery Experiment Hall upstairs and the beam is led into the stations there. The present arrangement of the stations is the result of a major rearrangement made in winter 2012. The beam line branches and the stations connected are listed below.
Test Hall
Klystron Gallery Experiment Hall
A positron may be bound with an electron to form a positronium atom, a boud state like an hydrogen
atom. It is also possible to form a positronium negative ion (Ps-) by binding one more electron. Ps- ions are emitted from a tungsten surface when it is bombarded with a slow positron beam. Its
formation efficiency increases drastically when alkali metals such as Na and Cs is deposited on the
surface. This station is for the formation of pulse Ps- by bombarding such a
surface with a slow positron pulse and the applications. Recently an experiment of photodetachment of Ps- (dissociation into Ps and an
electron by an irradiation of a laser beam) was successfully conducted (2011). Then an energy tunable neutral Ps beam was created by using this
technique (2012).
(This station is connected to a general purpose beam line branch.)
This station is for the analysis of the atomic configuration of a crystal surface by using the reflection high-energy positron diffraction (RHEPD). In this method, a positron beam is incident on a sample surface with a small glancing angle. When the angle is smaller than a certain critical angle, the beam is totally reflected, making it possible to determine the surface structure accurately. The experiment started with a beam with a collimator in 2011. A brightness enhancement unit using a transmission-type positron remoderator was installed in 2012.
This station is for the measurement of the energy of positronium emitted from a solid surface. The incident positrons hit the sample target and the ortho-Ps atoms emitted from the surface annihilate in flight. The annihilation γ-rays are viewed by detector through lead slits and the time of the detection with reference to the positron injection time is recorded. The width and the frequency of the incident positron pulse are 1ns-10ns (variable) and 50 Hz, respectively.
under construction