Scintillation detectors


General research interest

  Understanding the lower limit on the energy resolution of a SiPM based scintillation detector

  The limited number of active pixels in a SiPM results not only in a non-linearity but also in an additional fluctuation of its response. Both these effects are taken into account to calculate the amplitude resolution of an ideal SiPM, which is shown to be finite. As one of the consequences, the energy resolution of a scintillation detector based on a SiPM is shown to be limited to some minimum value defined by the number of pixels in the SiPM.

A. Stoykov et al., “On the limited amplitude resolution of multipixel Geiger-mode APDs”, Journal of Instrumentation 2 (2007) P06005


  Understanding the time resolution with a plastic scintillator readout by a SiPM

  We establish the current lower limit on the time resolution of such detector as about 20 ps per 1 MeV detected energy scaling inversely proportional to the square root of the energy. The result allows accurate predictions on the performance of eventual practical detectors as shown by the MEG collaboration.

A. Stoykov et al., “A time resolution study with a plastic scintillator read out by a Geiger-mode Avalanche Photodiode”, Nucl. Instr. and Meth. A 695 (2012) 202
K. Sedlak et al., “A GEANT4 study on the time resolution of a fast plastic scintillator read out by a G-APD”, Nucl. Instr. and Meth. A 696 (2012) 40

Current project

  A SiPM based ZnS(Ag):6LiF scintillation neutron detector for neutron scattering instrumentation

  Helium-3 has been for several decades the most widely used converting material in detectors for neutron scattering experiments. The world-wide shortage of its supply increased significance and stimulated further development of alternative detector technologies. One of these alternatives is the scintillation technology based on ZnS:6LiF scintillators read out by wavelength-shifting (WLS) fibers. Currently all detectors of this kind utilize photomultiplier tubes (PMTs) as photosensors.
  The application of SiPMs in such detectors has been hindered by their orders of magnitude higher dark count rate at room temperature. We solve this problem by substantially improving the light collection from the scintillator and by using an efficient algorithm for separating the signals from the dark counts. The developed prototype detector shows performance parameters comparable or exceeding those of the current PMT based detectors.
  The use of SiPMs in ZnS:6LiF scintillation detectors for application in the neutron scattering experimental technique opens new possibilities in designing this kind of detection systems and thus will serve for further progress in this field.

J.-B. Mosset et al., “Trigger Efficiency of a ZnS:6LiF Scintillation Neutron Detector Readout with a SiPM”, IEEE Transactions on Nuclear Science, Vol. 63, No. 4, 2016
J.-B. Mosset et al., “A 16-ch module for thermal neutron detection using ZnS:6LiF scintillator with embedded WLS fibers coupled to SiPMs and its dedicated readout electronics”, Nucl. Instr. and Meth. A, article in press
J.-B. Mosset et al., “Digital signal processing for a thermal neutron detector using ZnS(Ag):6LiF scintillating layers read out with WLS fibers and SiPMs”, Nucl. Instr. and Meth. A 824 (2016) 319
M. Hildebrandt et al., “Detection of thermal neutrons using ZnS(Ag):6LiF neutron scintillator read out with WLS fibers and SiPMs”, Nucl. Instr. and Meth. A 824 (2016) 204
A. Stoykov et al., “A SiPM-based ZnS:6LiF scintillation neutron detector”, Nucl. Instr. and Meth. A 787 (2015) 361
J.-B. Mosset et al., “Evaluation of two thermal neutron detection units consisting of ZnS/6LiF scintillating layers with embedded WLS fibers read out with a SiPM”, Nucl. Instr. and Meth. A 764 (2014) 299
A. Stoykov et al., “Use of Silicon Photomultipliers in ZnS:6LiF scintillation neutron detectors: signal extraction in presence of high dark count rates”, Journal of Instrumentation 9 (2014) P06015
J.-B. Mosset et al., “Upgrade of the POLDI diffractometer with a ZnS(Ag)/6LiF scintillation detector read out with WLS fibers coupled to SiPMs”, Journal of Physics: Conference Series 528 (2014) 012041

Recent projects

  Upgrade of the μSR instrument GPS at PSI

  We developed and brought into operation detector systems for muon-spin rotation (μSR) experiments performed at the Laboratory for Muon Spin Spectroscopy.
  Bulky detector system of the GPS instrument representing a set of scintillation detectors consisting of plastic scintillators, long and bended light guides, and PMTs was replaced by a more compact and lightweight version in which the light guides are excluded and PMTs are replaced by SiPM arrays. The geometry of the detector and accordingly its acceptance are preserved, while the time resolution is substantially improved due to the exclusion of the light guides and reading out the scintillators from their two opposite sides. The GPS instrument is already the third (out of six) μSR instruments in operation at the Laboratory for Muon Spin Spectroscopy equipped with SiPMs.

  High-time resolution detector for the 9.5 Tesla μSR instrument at PSI

  Detector system for the HAL-9500 instrument was developed. The detector satisfies strict requirements on the time resolution and compactness. Muon-spin precession signals with frequencies up to 1.3 GHz in magnetic fields up to 9.5 T are easily detected, the reduction of the signal amplitude does not exceed 20 %. The accuracy in measuring the muon-positron time correlations is about 80 ps (sigma) – the time resolution unprecedented for such high fields. The small radial dimension of the detector ring allows detecting the decay positrons with the spiral radius down to 1 cm. To preserve the 10 ppm uniformity of the magnetic field at the sample position all detector components located in the vicinity of the sample are non-magnetic.

A. Stoykov et al., “High field muSR instrument at PSI: detector solutions”, Physics Procedia 30 (2012) 7

  A lens-coupled scintillation counter in cryogenic environment

  An elegant approach for integrating a scintillation counter into a cryogenic system is developed. Its distinguishing feature is the absence of a continuous light guide coupling the scintillation and the photodetector parts, operating at cryogenic and room temperatures respectively. The detector consists of a plastic scintillator with glued-in wavelength-shifting fiber located inside a cryostat, a SiPM outside the cryostat, and a lens system guiding the scintillation light re-emitted by the fiber to the SiPM through optical windows in the cryostat shields.
  This approach is used to incorporate a set of scintillation counters serving as a Veto detector into a dilution refrigerator used by the HAL-9500 instrument. The scintillation part of the detector is operated at the temperature of 1 K. Any other solution would require modifications to the cryostat design with enormously increased cost of the system.

A. Stoykov et al., “A lens-coupled scintillation counter in cryogenic environment”, Journal of Instrumentation 6 (2011) P02003

Older projects

  ALC μSR instrument at PSI

  Bulky detector system of the ALC μSR instrument representing a set of scintillation detectors consisting of plastic scintillators, long and bended light guides, and PMTs was replaced by a more compact and lightweight version in which the basic element is a tile-fiber detector readout with a SiPM. The ALC instrument went into operation in 2007 and was the first μSR instrument worldwide equipped with SiPMs. Currently it is replaced by the HAL-9500 instrument.

A. Stoykov et al., “A new detector system for the ALC spectrometer – first experience with G-APDs in muSR instrumentation”, Physica B 404 (2009) 986

  A scintillating fiber detector for muon-beam profile measurements

  A position sensitive scintillating fiber detector with readout of the fibers by SiPMs was developed and used for the measurement of the 29MeV/c muon beam profiles in magnetic fields up to 5 Tesla. Comparing the results with simulations helped us to understand the effect of high magnetic fields on the particle trajectories in the muon-spin rotation experiment. This was an important step towards development of the 9.5 Tesla μSR instrument at PSI. The discussed detector was one of the first developments worldwide where SiPMs found their application.

A. Stoykov et al., “A scintillating fiber detector for muon beam profile measurements in high magnetic fields”, Nucl. Instr. and Meth. A 550 (2005) 212
T. Lancaster et al., “Magnetic field effects on particle trajectories in the muon-spin relaxation experiment: Towards a high-field spectrometer”, Nucl. Instr. and Meth. A 580 (2007) 1578