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Metrology

Positron Annihilation Lifetime Spectroscopy (PALS)

Measurement of atomic defects

Positron annihilation lifetime spectroscopy (PALS) is a non-destructive spectroscopy technique that allows studying a variety of phenomena and material properties on an atomic scale. PALS measures the elapsed time between the implantation of the positron into the material and the emission of annihilation radiation. Once the positron is implanted into a material, it quickly thermalises (~10 ps) and then either annihilates through interaction with electrons or forms a positronium atom. The positronium atom seeks out pores within the material where they are confined to bounce off of the walls and each time they collide with the walls there is a probability of the atom being annihilated releasing γ-rays that can be deteced with suited detectors. The lifetime of the positron can thus be used to determine the pore size of the sample. Typical examples are smallest atomic defects in crystals, metals, semiconductors and polymers or chemical structures in fluids and biological systems.

Typical setup for a PALS spectrometerThe typical setup of a PALS spectrometer includes a radioactive positron source (often 22Na) and two or more scintillator detectors. One of the detectors generates the „start“ signal for a TCSPC module using the gamma rays emitted simultaneously with the positron from the positron source. The other detectors are arranged to detect the gamma rays emitted by the annihilation process at the sample. The resulting histogram can then be analysed to extract the average positron or positronium lifetimes.

PicoQuant offers several TCSPC instruments that can be used for PALS:

TCSPC and time-tagging units

HydraHarp 400 - multichannel time tagging moduleHydraHarp 400

Multichannel Picosecond Event Timer & TCSPC Module

  • Up to 8 independent input channels and common synch channel (up to 150 MHz)
  • Time channel width of 1 ps
  • Time tagging with sustained count rates up to 40 Mcps
  • USB 3.0 connection

PicoHarp300 - time tagging unitPicoHarp 300

Stand-alone TCSPC Module with USB Interface

  • Two identical synchronized but independent input channels
  • Time channel width of 4 ps
  • Time tagging with sustained count rates up to 5 Mcps
  • USB 2.0 connection

TimeHarp260 - time tagging moduleTimeHarp 260

TCSPC and MCS board with PCIe interface

  • One or two independent input channels and common synch channel (up to 84 MHz)
  • Two models with either 25 ps (PICO model) or 1 ns (NANO model) base resolution
  • Ultra short dead time (<25 ns for PICO model, <1 ns for NANO model)
  • PCIe interface