Lifetime Setup Research Articles

A Pixel Analog-Counting Single-Photon Imager With Time-Gating and Self-Referenced Column-Parallel A/D Conversion for Fluorescence Lifetime Imaging

A single-photon, time-gated, $160 \times 120 $ pixel imager is presented for its application in fluorescence lifetime imaging microscopy. Exploiting single-photon avalanche diodes and an extremely compact pixel circuitry—only seven MOSFETs and one MOSCAP—the imager is capable of gathering information about photon position, number, and time distribution, enabling cost-effective devices for scientific imaging applications. This is achieved thanks to the photon counting and time-gating capabilities implemented in the analog domain, which in turn enable a $15\;{\upmu}{\text{m}}$ pixel with a 21% fill-factor. A reconfigurable column circuitry supports both the analog conventional readout and a self-referenced analog-to-digital conversion, able to cancel out the pixel-to-pixel nonuniformities, and speeding up the framerate to 486 fps. The imager, featuring also a delay locked loop to stabilize the internal waveform generation for reliable timing performance, has been implemented in a standard high-voltage $0.35\;{\upmu}{\text{m}}$ CMOS technology. Measurements in a fluorescent lifetime setup have been performed, comparing the results with single-point acquisitions made with commercial time-correlated equipment.

Positron lifetime setup based on DRS4 evaluation board

A digital positron lifetime setup based on DRS4 evaluation board designed at the Paul Scherrer Institute has been constructed and tested in the Positron annihilation laboratory Slovak University of Technology Bratislava. The high bandwidth, low power consumption and short readout time make DRS4 chip attractive for positron annihilation lifetime (PALS) setup, replacing traditional ADCs and TDCs. A software for PALS setup online and offline pulse analysis was developed with Qt,Qwt and ALGLIB libraries.

Acceptors in undoped GaSb; the role of vacancy defects

The conventional lifetime setup was used to study Czochralski grown unintentionally p- and n- type ([n] ≈ 6 × 1017cm−3) GaSb bulk samples. Several approaches were used to analyze the data. However, it was not possible to successfully analyze the obtained spectrums with the conventional trapping model. From the analyzed data it was derived that the reason for p-type behavior of GaSb was not VGa. Additionally, the role of gallium vacancy was studied and it's effect to lifetime values are shortly discussed.

Studies of radiation embrittlement of model alloys by thermoelectric measurements and Positron Annihilation Spectroscopy

One of the basic mechanisms of radiation embrittlement of steels is due to matrix damage. Embrittlement results in a raise in the ductile-to-brittle transition temperature, which is used as indicator of the degradation status of the material. Further to mechanical tests, other methods, based on non-destructive measurements, can be also used to follow embrittlement. At JRC-IE measurement of thermoelectric voltage using a specially developed method is regularly performed. The positron annihilation spectroscopy in lifetime set-up is used for study the microstructural changes of matrix due to embrittlement. Both techniques were applied to test several model alloys irradiated at different conditions. Obtained results prove that both techniques are good indicators of the change in material properties.

A three-detector positron lifetime setup suited for measurements on irradiated steels

Abstract An advanced positron lifetime setup is described, particularly suited to perform measurements on irradiated nuclear reactor pressure vessel steel. The equipment exists of three BaF2-detectors operated in triple coincidence mode to avoid the very disturbing 60Co-contribution in the lifetime spectra. The use of BaF2 scintillators gives rise to an acceptable efficiency and a time resolution well below 300 ps.

Positron Annihilation Measurements on Nuclear Reactor Pressure Vessel Steels

Positron Annihilation Spectroscopy is a valuable microscopic method to study radiation damage in nuclear reactor pressure vessel steels. At SCK.CEN, a new positron lifetime setup, suited to measure positron lifetimes in irradiated steel, is being constructed. The particularity of this setup is that the prompt count rate originating from the induced 60 Co-activity in the steel is highly reduced. Some preliminary results obtained for unirradiatd SA-508 steel are discussed