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Lichtenbergstr.1
85748 Garching

NEPOMUC

Neutron induced positron source munich

NEPOMUC scheme NEPOMUC scheme

NEPOMUC provides a high-intensity low-energy positron beam for applications in solid state and surface physics as well as for fundamental research in nuclear and atomic physics. The intensity amounts to > 109 moderated positrons per second at a beam energy of E = 1 keV.

At NEPOMUC, the positrons are generated by pair production from absorption of high-energy prompt gamma-rays after thermal neutron capture in cadmium (Cd) [1]. A cadmium cap is mounted inside the tip of the inclined beam tube SR11. The released high-energy gamma-radiation is converted into positron – electron pairs in a structure of platinum foils which is mounted inside the cadmium cap. Positive high voltage is applied in order to extract the moderated positrons. The positron beam is magnetically guided in a solenoid field of typically 7 mT.

After upgrading NEPOMUC, 80 % 113Cd enriched cadmium is used as neutron-gamma-converter which has a projected lifetime of 25 years of reactor operation [2] and an intensity of > 109 moderated positrons per second has been achieved [3].

The positron beam facility

The remoderation device of NEPOMUC [4] enhances the brightness of the positron beam and hence enables positron experiments which are highly resolved in space or/and in the time domain. The remoderator is based on the stochastic positron cooling in a W(110) single crystal and reemission of thermalised positrons into the vacuum with discrete energy. For most of the measurements the brightness enhanced positron beam is used. However, there are also experiments which do not depend on a high phase space density but need the full intensity of the primary beam. Therefore, the primary beam can also be used unaltered via two beam switches e.g. for experiments at the open beam port.

By the central, fivefold beam switch the positron beam is delivered to one of the five experiment beam lines. Currently, at these beam lines four instruments are permanently installed:

  • Pulsed low-energy positron system (PLEPS)
  • Coincident Doppler-broadening spectrometer (CDBS)
  • Positron annihilation induced Auger-electron spectrometer (PAES)
  • Scanning Positron Microscope Interface (SPM Interface)

The fifth beam line is for the multi-purpose open beam port (OP) which is used for transportable shortterm experimental set-ups.

[1] Hugenschmidt, C. et al., Nucl. Inst. Meth. A, 593(3), 616-618 (2008).
[2] Hugenschmidt, C. et al., New J. Phys., 14(5), 055027 (2012).
[3] Hugenschmidt, C. et al., J. Phys.: Conf. Ser., 505(1), 012029 (2014).
[4] Piochacz, C. et al., Appl. Surf. Sci., 255(1), 98-100 (2008).

Technical Data

Key values of the primary positron beam

  • E = 1 keV
  • Intensity:
    • > 109 moderated positrons per second
  • Diameter of beam spot:
    • ≈ 9 mm (FWHM) in 7 mT beam guiding field.

Key values of the remoderated positron beam

  • E = 10 … 200 eV
  • Intensity:
    • 5 · 107 remoderated positrons per second
  • Diameter of beam spot:
    • 1.85 mm (FWHM) in ≈ 4 mT beam guiding field

Typical Applications

Some examples and typical applications are listed on the TUM physics department's webpage of Positron Physics.

The Ps ion – A leptonic three body system
The negative positronium ion Ps is a bound system consisting of two electrons and a positron.

The positron – an ideal microprobe for defects
A positron implanted into a solid thermalizes rapidly and then diffuses in the bulk until it annihilates with valence or core electrons. In a defect free lattice, this diffusion process lasts around 100 ps, during this period the positron typically covers a distance of 100 nm in a random walk.

Monoenergetic positrons and thin layers
Positrons have numerously proven their enormous sensitivity for the non-destructive detection of defects. By experiments performed at NEPOMUC it could be shown that also metallic agglomerations can be characterized with highest sensitivity.

Positron annihilation induced Auger electron spectroscopy

Instrument Scientist

Dr. Christoph Hugenschmidt
Phone: +49.(0)89.289.14609
E-Mail:

Marcel Dickmann
Phone: +49.(0)89.289.11770
E-Mail:

NEPOMUC
Phone: +49.(0)89.289.14774

Operated by

TUM
UniBW

Publications

Find the latest publications regarding NEPOMUC in our publication database iMPULSE:

impulse.mlz-garching.de

Citation of the instrument

Heinz Maier-Leibnitz Zentrum. (2015). NEPOMUC: Neutron induced positron source Munich. Journal of large-scale research facilities, 1, A22. http://dx.doi.org/10.17815/jlsrf-1-49

For citation please always include the DOI.

Gallery

NEPOMUC
NEPOMUC

Positron beam facility and instrumentation at NEPOMUC

MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich