Latest Version of the Munich Pulsed Low Energy Positron System

Bauer-Kugelmann, W.; Sperr, P.; Kögel, G.; Triftshäuser, W.

doi:10.4028/www.scientific.net/msf.363-365.529

Cited by 57 publications

(37 citation statements)

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“…To avoid overheating of the irradiated targets the ion flux density was maintained below 2 Â 10 8 cm À2 s À1 . In situ positron annihilation Doppler broadening measurements as a function of energy were carried out at room temperature with a magnetically guided slow positron beam in Coimbra [4], whereas the in situ positron lifetime measurements were performed at the pulsed positron beam facility in Munich [5] at 16 keV positron beam energy. These two set-ups were used to characterize the damaged region from the surface up to $3 mm depth.…”

Section: Methodsmentioning

confidence: 99%

On the defect pattern evolution in sapphire irradiated by swift ions in a broad fluence range

Gordo

Liszkay

Kajcsos

et al. 2008

Applied Surface Science

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Section: Methodsmentioning

confidence: 99%

On the defect pattern evolution in sapphire irradiated by swift ions in a broad fluence range

Gordo

Liszkay

Kajcsos

et al. 2008

Applied Surface Science

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“…The essential design characteristics of PLEPS as described in [3] have been maintained. Figure 1 shows the layout of PLEPS after installation at the FRM II.…”

Section: Technical Detailsmentioning

confidence: 99%

“…In its original version there were two deflection plates [3], both coupled to a 50 MHz sine wave superimposed on a dc-voltage. The first deflection plate D1 (see Fig.…”

Section: The Chopper Sectionmentioning

confidence: 99%

“…This led to the development of a pulsed low energy positron beam system (PLEPS) for lifetime measurements at our institute over the past two decades. The latest version of this instrument, which was in use over the last few years, is described in detail in [3]. Many successful investigations on metals and alloys [1,2], polymers [4] and semiconductors [5] have been completed with this instrument, often in cooperation with external users.…”

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Pulsed low energy positron system (PLEPS) at the Munich research reactor FRM II

Egger

Sperr

Kögel

et al. 2007

Phys. Status Solidi (c)

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PACS 41.75.Fr, 78.70.Bj Currently, the Munich pulsed low energy positron beam-system (PLEPS) is transferred to the highintensity positron source (NEPOMUC) at the Munich research Reactor FRM II. We expect count-rates up to 10 6 cps. Several improvements to enhance the performance of the system have been implemented. Until now, PLEPS was employed exclusively for lifetime measurements. To enable also Doppler-broadening, coincident Doppler-broadening and AMOC experiments, two additional detector ports have been installed. An additional chopper allows to suppress pulses and, therefore, to extend the standard time window of 20 ns for precise measurements of longer lifetimes. The high event-rate supports the use of smaller scintillators. Consequently an improvement in time resolution is expected. Also envisaged is the use of new detector materials. Various measures to further reduce background from back-scattered positrons and a reduction of the beam diameter down to 1 mm will improve the overall performance of the system.1 Introduction Conventional positron annihilation spectroscopy applied to problems in materials science is limited by the spatial resolution of the order of mm. The measured signals are therefore spatial averages, which blur all finer details on the micrometer and nanometer scale. It is well established that these problems may be overcome by the use of low energy positron beams of variable energy for depth profiling of defects from nanometer to micrometer resolution [1, 2]. To perform positron lifetime studies with monoenergetic positron beams, the implantation time of each positron has to be known. This led to the development of a pulsed low energy positron beam system (PLEPS) for lifetime measurements at our institute over the past two decades. The latest version of this instrument, which was in use over the last few years, is described in detail in [3]. Many successful investigations on metals and alloys [1,2], polymers [4] and semiconductors [5] have been completed with this instrument, often in cooperation with external users. Nevertheless the full potentiality of the instrument has never been exploited. The main reason was the insufficient beam intensity obtainable with a conventional laboratory source. Registration of a lifetime spectrum took about an hour, of a full depth-profile (20 lifetime spectra) about a day. The quality of the spectra usually allowed to deconvolute up to three lifetimes. Higher beam intensity would allow to further reduce the peak-to-background ratio, increase statistics and more lifetimes would be resolvable at reduced acquisition times without drastic changes in the general characteristics of the system. Therefore it was decided to transfer PLEPS to the best currently available positron source, the positron beam facility NEPOMUC at the Munich research reactor FRM II [6]. There, after remoderation, a monoenergetic positron beam with a few millimeter diameter and 10 8 positrons per second will be available.

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“…[15,16]. The Munich group uses a pulsing scheme with two bunchers [17]. A saw-tooth shape pulse is used in a pre-buncher to produce 2 ns pulses from the initial pulse of 13 ns.…”

Section: Introductionmentioning

confidence: 99%

Development of a high-efficiency pulsed slow positron beam for measurements with orthopositronium in vacuum

Albérola

Anthonioz

Badertscher

et al. 2006

Nuclear Instruments and Methods in Physics Research Section A:

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We have developed a high-efficiency pulsed slow positron beam for experiments with orthopositronium in vacuum. The new pulsing scheme is based on a double-gap coaxial buncher powered by an RF pulse of appropriate shape. The modulation of the positron velocity in the two gaps is used to adjust their time-of-flight to a target. This pulsing scheme allows to minimize non-linear aberrations in the bunching process and to efficiently compress positron pulses with an initial pulse duration ranging from ∼ 300 to 50 ns into bunches of 2.3 to 0.4 ns width, respectively, with a repetition period of 1 µs. The compression ratio achieved is ≃ 100, which is a factor 5 better than has been previously obtained with slow positron beams based on a single buncher. Requirements on the degree, to which the moderated positrons should be mono-energetic and on the precision of the waveform generation are presented. Possible applications of the new pulsed positron beam for measurements of thin films are discussed.

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Latest Version of the Munich Pulsed Low Energy Positron System

Cited by 57 publications

References 0 publications

On the defect pattern evolution in sapphire irradiated by swift ions in a broad fluence range

On the defect pattern evolution in sapphire irradiated by swift ions in a broad fluence range

Pulsed low energy positron system (PLEPS) at the Munich research reactor FRM II

Development of a high-efficiency pulsed slow positron beam for measurements with orthopositronium in vacuum

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