Laboratory for High Energy Physics |
Novel Detectors for particles and radiation
Development of novel detectors for particles and radiation
Members of the Bern group have large experience in the field of particle
detectors. This includes knowledge on tracking devices, on calorimetry,
on cryogenic detectors, on high-resolution emulsion films, on imaging
detectors, etc. Synergy of different known detector technologies leads
to the development of novel detectors with improved and often
unprecedented characteristics. This motivates our interest in continuing
along this line of research aiming at proposing, designing, realizing
and operating powerful tools for future particle physics experiments.
Among present activities of the group are:
- Development of the cryogenic TPC on the mixture of liquid Argon and Nitrogen for security applications
- Development of test gamma source facility based on 2 MeV proton RFQ LINAC
- Characterization of Multi-pixel Avalanche Photo Diodes (MAPD or Silicon Photomultipliers) for the cryogenic use and developing readout electronics for them
- Development of Hybrid Field-Induced Emission sensor for low-threshold charge readout from the TPC on liquid Argon
- Development of portable devices for Alpha-Beta selective radiometry with the use of MAPD.
The increasing concern of the terrorism in the modern world triggers
more and more developments of the instrumentation capable of effective
early detection of objects that potentially constitute danger to public
security. Detection of explosive materials on the public transport is
one of the important tasks. Our group is contributing to this matter by
developing the explosive detection system, based on the principle of
Gamma-Resonant Nuclear Absorption (GRNA) radiography of large aviation
cargo containers.
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Fig.1: Illustration to the principle of the GRNA radiography of the Nitrogen-rich materials with the detector, also containing Nitrogen. |
The detector we develop combines principles of GRNA on the nitrogen nuclei and the excellent particle identification capability of Time Projection Chambers (TPC) filled with the liquefied noble gases. We have demonstrated that such TPC is capable to work on the mixtures of liquid Argon and Nitrogen with the content of Nitrogen up to 15%. The reaction between gamma-rays in the resonant band with the Nitrogen nuclei produces proton with the energy of about 1.5 MeV, while out-of-resonance gammas produce electrons with the wide energy spectrum. Separating one from the other we gain the selective sensitivity in the resonant absorption band on Nitrogen. This allows detecting objects with high density and high atomic content of Nitrogen, which is a characteristic feature of most of commercially used explosives. We continue to work on improving of the electron-proton separation capability by detecting scintillating light from the liquid Argon, which results from the charge recombination, and brings information, important for electron-proton identification.
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Fig.2: Photographs of the Liquid Argon-Nitrogen TPC. Left: 1-dewar, 2-TPC wires, 3-resonance density meter, 4-level meter. Right: 6-Dewar, 7-Low-pass for the high voltage, 8-TPC. |
In order to bring the above development to the working prototype of the object screener we work on the source of the gamma-rays of energies, suitable for GRNA, namely around 9.17 MeV. This radiation presently can only be obtained by employing the nuclear reaction, inverse to resonant absorption. Bombarding the solid target made of Carbon-13 isotope by 1.8 MeV protons we obtain Nitrogen-14 in the excited state, which relaxes then with the emission of 9.17 MeV gamma quant. Protons with required energy will be produced by the Linear Radio Frequency Quadruple accelerator (RFQ LINAC), which we installed at LHEP and currently setting up.
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Fig.3: Photograph of the 2MeV proton RFQ LINAC, installed at LHEP. |
The solid state photomultipliers (or MAPD - Multi Pixel Avalanche Photodiodes) appeared on the photo-sensor market relatively recently. They employ the matrix of cells, each of them operating in Geiger mode (full discharge). This allows this devices to have high sensitivity and high gain in the single photon counting mode, which are comparable to those of conventional vacuum Photo Multiplier tubes. However, unlike vacuum PMTs, MAPDs are not subjected to the influence of the magnetic field, mechanically much more stable and robust, compact and consume much less power. The revolutionary invention made by Z. Sadygov (JINR, Dubna), so-called Deep Microwell MAPD (often referred to as MAPD-3), allows to reach pixel density up to 40000 pix/mm2. These devices, unlike previous designs, are capable of operation in cryogenic liquids, like liquefied Argon or Nitrogen. This makes them an attractive solution for reading out the scintillation light from these liquids. Out group is presently studying this possibility in view of the further use of them in the Hibrid Field-Induced Emission sensor for the amplified readout of the charge in LAr TPC.
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Fig.4: Photograph of the Deep Microwell Multipixel Avalanche Photodiodes (MAPD-3 or SiPM). |
Hibrid Field-Induced Emission (HFIE) sensor uses the scintillation light, which is emitted by electrons, which drift in a strong electric field through the liquefied Argon. The ionization charge to be read is drifting towards the readout plane, containing electrode arrangement, similar to those of GEM (Gas Electron Multiplier). In each whole of this plate charge enters the high electric field region, where it emits scintillating light, with the amount proportional to the amount of the initial ionization. This light is then registered by the MAPD sensor. Such arrangement allows reaching charge amplification of the order of 100. Our group is presently working on the systematic optimization of this technology for future use in Long-Drift TPC (Argontube), also being developed at LHEP.
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Fig.5: Illustration to the operation principle of Hybrid Field-Induced Emission (HFIE) sensor for amplified readout of the ionization charge in TPC on liquid Argon. |
The compactness of MAPD and their high sensitivity allows their use for measuring of the radioactive isotope content by the means of the detection light from the liquid scintillators. This technique is well developed on the basis of the conventional vacuum PMT, using the Pulse Shape Discrimination to separately count Alpha and Beta emitting isotopes. The use of MAPD for this application will allow much more compact, even hand-held instruments for Alpha-Beta selective dosimetry and radiometry.