Planned positron experiments at FRM-II

Kögel, G.; Dollinger, G.

doi:10.1016/j.apsusc.2005.08.048

Cited by 8 publications

(5 citation statements)

References 19 publications

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“…Both facts are caused by the low intensity of the source. It is evident and already remarked in detail in reference [6], that the source size has to be small to obtain a small spot size at the specimen. Due to this and the effect of self absorption the maximal useable intensity of a radioactive positron emitter is limited.…”

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confidence: 90%

“…Now the positrons are extracted from the guiding field by a novel field termination. It is built up from 6 perfectly plan-parallel ferromagnetic strips of 25 µm thickness and 1 mm spacing [6]. This setup ensures minimal perturbation of the beam and minimal loss of intensity.…”

mentioning

confidence: 99%

“…The first remoderation stage will be installed at the NEPOMUC beam system, providing remoderated positrons to all connected experiments [6]. In this remoderation stage the beam will be focused on a W(100) crystal with an expected spot size of about 3 mm.…”

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confidence: 99%

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Implementation of the Munich scanning positron microscope at the positron source NEPOMUC

Piochacz

Egger

Hugenschmidt

et al. 2007

Phys. Status Solidi (c)

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The Munich scanning positron microscope (SPM) permits positron lifetime measurements with a lateral resolution down to 2 µm within an energy range of 1-20 keV. One practical limitation of the SPM is set by the long measurement times of several days per a 2D-scan due to the low intensity positron beam produced by standard 22 Na sources. This disadvantage will be overcome by installing the SPM at the high intense positron beam facility NEPOMUC at the research reactor FRM II in Garching. Thus the time for one measurement will be shortened by a factor of 60. In addition it is expected to reduce the lateral resolution to about 100 nm. Due to the beam characteristics of the NEPOMUC facility an interface is needed, which enhances the phase space density of the beam. The requirements, which have to be fulfilled by the interface, will be described and an overview of the different components such as bunching units, remoderation stages and rf-elevator will be given. 1 Introduction The Munich SPM is an instrument for performing positron lifetime measurements with a lateral resolution down to 2 µm within an energy range from 1 to 20 keV. Thus within an area of at least 600 × 600 µm a three-dimensional lifetime map could be obtained. Because of the high time resolution of about 255 ps (FWHM) it is possible to decompose the lifetime spectra in two components and thus it is possible to identify two different defect types. These features were established in studies on test specimens [1, 2] as well as in research studies [3][4][5]. However, to obtain a two-dimensional spectrum of the size of about 45 × 45 µm and a resolution of 2 µm by using a 30 mCi 22 Na takes typically more than a week. Not only the acquisition time for the image but also the time for adjusting the microscope consume a lot of time. Both facts are caused by the low intensity of the source. It is evident and already remarked in detail in reference [6], that the source size has to be small to obtain a small spot size at the specimen. Due to this and the effect of self absorption the maximal useable intensity of a radioactive positron emitter is limited. Even utilising a 1 Ci 64 Cu source would only lead to an enhancement factor of about 7. Therefore, the Munich SPM is transferred to the research reactor "Heinz Maier-Leibnitz" (FRM II) and connected to the high intense positron source NEPOMUC. Because the beam produced by NEPOMUC not only occupies a much greater phase space volume but also has less energy than the beam produced by the combination of a

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Implementation of the Munich scanning positron microscope at the positron source NEPOMUC

Piochacz

Egger

Hugenschmidt

et al. 2007

Phys. Status Solidi (c)

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“…Experimental data suggest that the moderation of a tungsten foil could reach 0.23 for 1-5keV positrons. [4] In addition, lower energy positrons will deposit less energy in the material and thus reduce radiation damage to single-crystal moderators or decrease thermal load on cryogenic moderators. Another option is that it would be possible to trap and cool positrons in a trap, if the energy of the positrons can be decreased below 100 keV.…”

Section: Introdutionmentioning

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Study on high flux accelerator based positrons source

Long

Chemerisov

Gai

et al. 2007

2007 IEEE Particle Accelerator Conference (PAC)

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Present accelerator-based slow-positron technology impinge the positrons coming out of a conversion target on a thin foil of metal (moderator) where the positrons are thermalized and then ejected from the moderator with the surface work energy of the material. This study represents a new direction in developing accelerator-based highintensity slow-positron sources. We investigate the use of RF fields to decelerate the positrons out of the target. Techniques, such as a Penning trap or moderation can then be used to get the needed thermal positrons with higher yield. Using a relatively simple beam-line scheme, our preliminary simulations showed that it could increase the final thermal positrons yield by more than 20 times. This suggests a promising future for this new method.

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“…The modified sample station (schematic) of the pulsed low energy positron system[11]. The controlled experimental parameters are indicated.…”

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Status of the pulsed low energy positron beam system (PLEPS) at the Munich Research Reactor FRM-II

Sperr

Egger

Kögel

et al. 2008

Applied Surface Science

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Planned positron experiments at FRM-II

Cited by 8 publications

References 19 publications

Implementation of the Munich scanning positron microscope at the positron source NEPOMUC

Implementation of the Munich scanning positron microscope at the positron source NEPOMUC

Study on high flux accelerator based positrons source

Status of the pulsed low energy positron beam system (PLEPS) at the Munich Research Reactor FRM-II

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