K. H. Kaiser

Mass and Γ3π0/Γγγ decay branching ratio of theη-meson from the p(γ, η)p reaction

Near threshold photoproduction ofη-mesons from the proton has been measured at the MAMI accelerator with the TAPS spectrometer. The mass of theη-meson was deduced from the threshold energy forη-photoproduction. The result of mη=(547.12 ± 0.06 ± 0.25) MeV supports the low value of theη-mass reported from a dp →3Heη measurement at SATURNE in 1992. Theη-decay branching ratio Γ3π0/Γγγ was measured to be (0.832±0.005±0.012).

Novel digital K-edge imaging system with transition radiation from an 855-MeV electron beam

A novel K-edge imaging method has been developed at the Mainz Microtron MAMI aiming at a very efficient use of the transition radiation (TR) flux generated by the external 855-MeV electron beam in a foil stack. A fan-like quasi-monochromatic hard X-ray beam is produced from the /spl plusmn/1-mrad-wide TR cone with a highly oriented pyrolytic graphite (HOPG) crystal. The absorption of the object in front of a 30 mm/spl times/10 mm pn charge-coupled device (pn-CCD) photon detector is measured at every pixel by a broad-band energy scan around the K-absorption edge. This is accomplished by a synchronous variation of the lateral crystal position and the electron beam direction which defines also the direction of the TR cone. The system has been checked with a phantom consisting of a 2.5-/spl mu/m thick molybdenum sample embedded in a 136- or 272-/spl mu/m-thick copper bulk foil. A numerical analysis of the energy spectrum for every pixel demonstrates that data as far as /spl plusmn/0.75 keV away from the K edge of molybdenum at 20 keV still improve the signal-to-noise ratio (SNR). Prospects are discussed to investigate the human lungs with xenon as a contrast agent at the available total primary photon flux of 2/spl times/10/sup 10//(s/spl middot/0.1% bandwidth (BW)) only.

Transition radiation in the x-ray region from a low emittance 855 MeV electron beam

The interference of transition radiation coherently produced from a periodic stack of four polyimide foils of 7.2 μm thickness and a separation of 162 μm was investigated. This stack has been brought into the low emittance (3 π nm rad) electron beam of the 855 MeV Mainz Microtron MAMI. Transition radiation was observed in the energy range from 2 to 15 keV with a LN2-cooled pin photodiode. A good energy resolution of 0.8 keV and angular resolution of 0.15 mrad was achieved simultaneously allowing for the first time to quantitatively study the interference pattern. Good agreement with theoretical calculations is found. Prospects to exploit transition radiation in the x-ray region from a low emittance electron beam as a high brilliant radiation source are discussed.

INVESTIGATION OF FAR-INFRARED SMITH-PURCELL RADIATION AT THE 3.41 MEV ELECTRON INJECTOR LINAC OF THE MAINZ MICROTRON MAMI

An experiment has been set up at the injector LINAC of the Mainz Microtron MAMI to investigate far-infrared Smith-Purcell radiation in the THz gap (30 μm ≤ λ ≤ 300μm). The essential components are a superconductive magnet with a magnetic induction of 5 Tesla in which 200 mm long gratings of various periods between 1.4 mm and 14 mm are located, and a composite silicon bolometer as radiation detector. First experiments were performed in the wavelength region between 100 μm and 1 mm with a bunched 1.44 MeV electron beam.

A novel type of x-ray interferometer

Novel types of interferometers have been developed at the Mainz Microtron MAMI with which the complex index of refraction of thin self-supporting foils can be measured. For the vacuum ultraviolet and soft x-ray region the interferometer consists of two collinear undulators, between which a foil can be placed, and a grating spectrometer. For the hard x-ray region, up to an energy of about 40 keV, it consists of two foils in which the electron beam produces transition radiation, and a single crystal spectrometer in Bragg geometry. Taking advantage of the low emittance 855 MeV electron beam distinct intensity oscillations have been observed as a function of the distance between the undulators and foils, respectively. The complex index of refraction has been investigated at the K- and L-absorption edges of carbon and nickel.