Search results for " Medical imaging"
showing 10 items of 1067 documents
Recent progress with microchannel-plate PMTs
2020
Abstract Microchannel-plate (MCP) PMTs were identified as the only suitable photon sensors for the two DIRC detectors of the PANDA experiment at FAIR. As the long-standing aging problem of MCP-PMTs was recently overcome by coating the MCP pores with an atomic layer deposition (ALD) technique, further improved 2 ″ MCP-PMTs were investigated. The best PHOTONIS device has reached a lifetime of > 20 C/cm2 integrated anode charge without any sign of aging. Also the newly developed 2 ″ MCP-PMTs of Hamamatsu are maturing and are usable in high rate environments. The status of our long-term lifetime measurements and the performance parameters of the currently most advanced ALD-coated MCP-PMTs from …
Irradiation study of a fully monolithic HV-CMOS pixel sensor design in AMS 180 nm
2018
Abstract High-Voltage Monolithic Active Pixel Sensors (HV-MAPS) based on a 180 nm HV-CMOS process have been proposed to realize thin, fast and highly integrated pixel sensors. The MuPix7 prototype, fabricated in the commercial AMS H18 process, features a fully integrated on-chip readout, i.e. hit-digitization, zero suppression and data serialization. MuPix7 is the first fully monolithic HV-CMOS pixel sensor that has been tested for the use in high irradiation environments like HL-LHC. We present results from laboratory and test beam measurements of MuPix7 prototypes irradiated with neutrons (up to 5.0 × 1015 neq/cm2) and 24 GeV protons (up to 7.8 × 1015 protons/cm2) and compare the performa…
High Voltage Monolithic Active Pixel Sensors
2018
Ever higher demands on resolution and rate capability drive the development of particle tracking detectors. Especially at low momenta, multiple Coulomb scattering in the material of the detector is also strongly affecting the resolution of momentum measurements. While gas-based detectors such as drift chambers and time projection chambers can be built with very small amounts of material, their rate capability is limited by ageing and space charge effects. Hybrid semiconductor detectors on the other hand combine a depleted (silicon) sensor with a custom amplifier and readout chip. Pixelated devices especially can operate efficiently in very harsh rate and radiation environments such as the i…
Performance of the cost-effective Planacon ® MCP-PMTs in strong magnetic fields
2020
Abstract We present the behavior of the cost-effective Planacon MCP-PMTs with 25 μ m pore diameter in the presence of axial magnetic fields up to 0.5 T. Having a batch of 62 devices of the same type, two MCP-PMTs were selected and their gain variation measured in different magnetic fields. These two otherwise identical devices satisfied the selection criteria by requiring the lowest (1.15 kV) and one of the highest (1.4 kV) bias voltage values to achieve a given gain. Both MCP-PMTs have a nearly identical tolerance of the strong magnetic field despite the significant difference in the bias voltage. This clarifies the mechanism of the B-field influence on the MCP-PMT gain, emphasizing the im…
A position sensitive β−γ coincidence technique for sample analysis with the upgraded PANDA device
2020
Abstract PANDA (Particles And Non-Destructive Analysis) is measuring system developed for non-destructive analysis of samples for safety, security and safeguards. The capabilities of the PANDA device were expanded by the addition of a thick silicon detector for β particle detection. The upgraded device can now be used for position-sensitive α − γ and β − γ coincidence measurements of various kinds of radioactive samples. The capability of the PANDA device in using the β − γ coincidence technique was tested using a mixed source of 134Cs and 226Ra. In addition, the ability of PANDA to locate nuclides emitting β particles from samples was tested using a combined sample containing a mixed 134Cs…
Resolution changes of MCP-PMTs in magnetic fields
2016
Micro-channel plate photomultiplier tubes (MCP-PMTs) are chosen in many applications that have to cope with strong magnetic fields. The DIRC detectors of the PANDA experiment plan to employ them as they show excellent timing characteristics, radiation hardness, relatively low dark count rates and sufficient lifetime. This article mainly focuses on the performance of the position reconstruction of detected photons. Two different MCP-PMTs with segmented anode geometries have been tested in magnetic fields of different strengths. The variation of their performance has been studied. The measurements show improved position resolution and image shifts with increasing magnetic field strength.
Monte Carlo calculation of beam quality correction factors for PTW cylindrical ionization chambers in photon beams.
2020
The beam quality correction factor k Q for megavoltage photon beams has been calculated for eight PTW (Freiburg, Germany) ionization chambers (Farmer chambers PTW30010, PTW30011, PTW30012, and PTW30013, Semiflex 3D chambers PTW31021, PTW31010, and PTW31013, and the PinPoint 3D chamber PTW31016). Simulations performed on the widely used NE-2571 ionization chamber have been used to benchmark the results. The Monte Carlo code PENELOPE/penEasy was used to calculate the absorbed dose to a point in water and the absorbed dose to the active air volume of the chambers for photon beams in the range 4 to 24 MV. Of the nine ionization chambers analysed, only five are included in the current version of…
First Compton imaging tests with i-TED
2019
The objective of this work is to demonstrate the Compton imaging capabilities of a novel gamma-ray Total-Energy Detector called i-TED. The latter is intended for neutron-capture cross-sections measurements of astrophysical interest, thereby enhancing detection sensitivity by means of the simultaneous combination of Time-of-Flight with Compton-imaging techniques. The developed i-TED demonstrator comprises five position-sensitive radiation detection modules of high energy resolution, which feature an overall position-sensitive field-of-view of 125 cm2, and thus a high efficiency. Each detector module is based on 50x50 mm2 large LaCl 3 (Ce) monolithic crystals optically coupled to 8x8 pixels s…
Application of the small-tip-angle approximation in the toggling frame for the design of analytic robust pulses in quantum control
2021
We apply the Small Tip-Angle Approximation in the Toggling Frame in order to analytically design robust pulses against resonance offsets for state to state transfer in two-level quantum systems. We show that a broadband or a local robustness up to an arbitrary order can be achieved. We provide different control parameterizations to satisfy experimental constraints and limitations on the amplitude or energy of the pulse. A comparison with numerical optimal solutions is made.
Measurements of neutron radiation and induced radioactivity for the new medical linear accelerator, the Varian TrueBeam
2016
Abstract Contemporary linear accelerators applied in radiotherapy generate X-ray and electron beams with energies up to 20 MeV. Such high-energy therapeutic beams induce undesirable photonuclear (γ,n) and electronuclear (e,e'n) reactions in which neutrons and radioisotopes are produced. The originated neutron can also induce reactions such as simple capture, (n,γ), reactions that produce radioisotopes. In this work measurements of the non-therapeutic neutrons and the induced gamma radiation were carried out in the vicinity of a new medical accelerator, namely the Varian TrueBeam. The TrueBeam is a new generation Varian medical linac making it possible to generate the X-ray beams with a dose…