Showing papers in "Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment in 2011"

GEMS: Underwater spectrometer for long-term radioactivity measurements

Abstract: GEMS (Gamma Energy Marine Spectrometer) is a prototype of an autonomous radioactivity sensor for underwater measurements, developed in the framework for a development of a submarine telescope for neutrino detection (KM3NeT Design Study Project). The spectrometer is highly sensitive to gamma rays produced by 40 K decays but it can detect other natural (e.g., 238 U, 232 Th) and anthropogenic radio-nuclides (e.g., 137 Cs). GEMS was firstly tested and calibrated in the laboratory using known sources and it was successfully deployed for a long-term (6 months) monitoring at a depth of 3200 m in the Ionian Sea (Capo Passero, offshore Eastern Sicily). The instrument recorded data for the whole deployment period within the expected specifications. This monitoring provided, for the first time, a continuous time-series of radioactivity in deep-sea.

The T2K Experiment

Abstract: The T2K experiment is a long-baseline neutrino oscillation experiment Its main goal is to measure the last unknown lepton sector mixing angle {\theta}_{13} by observing { u}_e appearance in a { u}_{\mu} beam It also aims to make a precision measurement of the known oscillation parameters, {\Delta}m^{2}_{23} and sin^{2} 2{\theta}_{23}, via { u}_{\mu} disappearance studies Other goals of the experiment include various neutrino cross section measurements and sterile neutrino searches The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem

ANTARES: the first undersea neutrino telescope

Abstract: The ANTARES Neutrino Telescope was completed in May 2008 and is the first operational Neutrino Telescope in the Mediterranean Sea. The main purpose of the detector is to perform neutrino astronomy and the apparatus also offers facilities for marine and Earth sciences. This paper describes the design, the construction and the installation of the telescope in the deep sea, offshore from Toulon in France. An illustration of the detector performance is given.

Fundamental Limits of Spatial Resolution in PET.

Abstract: The fundamental limits of spatial resolution in positron emission tomography (PET) have been understood for many years. The physical size of the detector element usually plays the dominant role in determining resolution, but the combined contributions from acollinearity, positron range, penetration into the detector ring, and decoding errors in the detector modules often combine to be of similar size. In addition, the sampling geometry and statistical noise further degrade the effective resolution. This paper quantitatively describes these effects, discusses potential methods for reducing the magnitude of these effects, and computes the ultimately achievable spatial resolution for clinical and pre-clinical PET cameras.

The FE-I4 pixel readout integrated circuit

Abstract: A new pixel readout integrated circuit denominated FE-I4 is being designed to meet the requirements of ATLAS experiment upgrades. It will be the largest readout IC produced to date for particle physics applications, filling the maximum allowed reticle area. This will significantly reduce the cost of future hybrid pixel detectors. In addition, FE-I4 will have smaller pixels and higher rate capability than the present generation of LHC pixel detectors. Design features are described along with simulation and test results, including low power and high rate readout architecture, mixed signal design strategy, and yield hardening.

Medipix3: A 64 k pixel detector readout chip working in single photon counting mode with improved spectrometric performance

Abstract: Hybrid pixel detectors have been demonstrated to provide excellent quality detection of ionising photon radiation, particularly in X-ray imaging. Recently, there has been interest in developing a hybrid pixel detector specifically for photon dosimetry. This thesis is on the design, implementation, and preliminary characterisation of the Dosepix readout chip.Dosepix has 256 square pixels of 220 mm side-length, constituting 12.4 mm2 of photo-sensitive area per detector. The combination of multiple pixels provides many parallel processors with limited input flux, resulting in a radiation dose monitor which can continuously record data and provide a real-time report on personal dose equivalent. Energy measurements are obtained by measuring the time over threshold of each photon and a state machine in the pixel sorts the detected photon event into appropriate energy bins. Each pixel contains 16 digital thresholds with 16 registers to store the associated energy bins. Preliminary measurements of Dosepix chips bump bonded to silicon sensors show very promising results. The pixel has a frontend noise of 120 e-. In low power mode, each chip consumes 15 mW, permitting its use in a portable, battery-powered system. Direct time over threshold output from the hybrid pixel detector assembly reveal distinctive photo-peaks correctly identifying the nature of incident photons, and verification measurements indicate that the pixel binning state machines accurately categorise charge spectra. Personal dose equivalent reconstruction using this data has a flat response for a large range of photon energies and personal dose equivalent rates.

Precise energy calibration of pixel detector working in time-over-threshold mode

Abstract: The semiconductor pixel detector Timepix (256×256 pixels with pitch of 55 μm) is a successor of the Medipix2 device. Each Timepix pixel can be independently operated in one of three possible modes: (1) counting of the detected particles; (2) measurement of the particle energy; and (3) measurement of the time of interaction. The energy measurement in the second mode is performed via the determination of the “time-over-threshold” (TOT). The energy measurement with the Timepix detector in TOT mode requires knowledge of the energy calibration of each pixel of the matrix. Such calibration is very nonlinear in the low energy range and can be described by a surrogate function depending on four parameters. The determination of all these parameters can be performed by measurement and evaluation of the response of each pixel in at least four calibration points. The procedure is extremely demanding: it requires the analysis of at least 250 thousand spectra and the performance of 330 thousand least-squares fits. In this article, it is demonstrated that even better result can be achieved with only two or three calibration points halving the number of least-squares fits needed. The method is based on precise analysis of the shape of spectral peaks. The article also discusses the performance of energy calibrated device for spectrometry of heavy charged particles.

The ICON beamline – A facility for cold neutron imaging at SINQ

Abstract: The beamline for Imaging with COld Neutrons (ICON) at Swiss spallation neutron source (SINQ) at Paul Scherrer Institut has a flexible design to meet the requests from a wide user community. The current status of the beamline and its characteristics are described. The instrumentation includes three experimental positions from which two are equipped with digital camera based imaging detectors. Tomographic imaging is among the standard methods available at the beamline. Advanced methods such as energy-selective imaging and grating interferometry are available as instrument add-ons which are easily installed.

A spark-resistant bulk-micromegas chamber for high-rate applications

Abstract: We report on the design and performance of a spark-resistant bulk-micromegas chamber. The principle of this design lends itself to the construction of large-area muon chambers for the upgrade of the detectors at the Large Hadron Collider at CERN for luminosities in excess of 1034 cm−2 s−1 or other high-rate applications.

A new mass reconstruction technique for resonances decaying to ττ

Abstract: Accurate reconstruction of the mass of a resonance decaying to a pair of τ leptons is challenging because of the presence of multiple neutrinos from τ decays. The existing methods rely on either a partially reconstructed mass, which has a broad spectrum that reduces sensitivity, or the collinear approximation, which is applicable only to the relatively small fraction of events. We describe a new technique, which provides an accurate mass reconstruction of the original resonance and does not suffer from the limitations of the collinear approximation. The major improvement comes from replacing assumptions of the collinear approximation by a requirement that mutual orientations of the neutrinos and other decay products are consistent with the mass and decay kinematics of a τ lepton. This is achieved by maximizing a probability defined in the kinematically allowed phase space region. In this paper we describe the technique and illustrate its performance using Z / γ ⁎ → τ τ and H → τ τ events simulated with the realistic detector resolution. The method is also tested on a clean sample of data Z / γ ⁎ → τ τ events collected by the CDF experiment at the Tevatron. We expect that this new technique will allow for a major improvement in searches for the Higgs boson at both the LHC and the Tevatron.

Time Projection Chambers for the T2K Near Detectors

Abstract: The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector located 295 km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator–bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker are used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/NOMAD dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system.

The adaptive gain integrating pixel detector AGIPD a detector for the European XFEL

Abstract: The European X-ray free electron laser is a new research facility currently under construction in Hamburg, Germany. Typical for XFEL machines is the high peak brilliance several orders of magnitudes above existing synchrotron facilities. With a pulse length below 100 fs and an extremely high luminosity of 30,000 flashes per second the European XFEL will have a worldwide unique time structure that enables researchers to record movies of ultrafast processes. This demands the development of new detectors tailored to the requirements imposed by the experiments while complying with the machine specific operation parameters. The adaptive gain integrating pixel detector (AGIPD) is one response to the need for large 2D detectors, able to cope with the 5 MHz repetition rate, as well as with the high dynamic range needed by XFEL experiments (from single photons to 104 12 keV photons per pixel per pulse). In addition, doses up to 1 GGy over three years are expected.

Development of SOI pixel process technology

Abstract: A silicon-on-insulator (SOI) process for pixelated radiation detectors is developed. It is based on a 0.2 μm CMOS fully depleted (FD-)SOI technology. The SOI wafer is composed of a thick, high-resistivity substrate for the sensing part and a thin Si layer for CMOS circuits. Two types of pixel detectors, one integration-type and the other counting-type, are developed and tested. We confirmed good sensitivity for light, charged particles and X-rays for these detectors. For further improvement on the performance of the pixel detector, we have introduced a new process technique called buried p-well (BPW) to suppress back gate effect. We are also developing vertical (3D) integration technology to achieve much higher density.

LET, a cold neutron multi-disk chopper spectrometer at ISIS

Abstract: LET is a new multi-chopper direct geometry cold neutron spectrometer, recently installed on target station 2 (TS2) at the ISIS spallation neutron source. The characteristics of the primary spectrometer are a 25 m straight super-mirror guide viewing the new highly efficient coupled solid methane moderator system. This combination yields a high incident flux of neutrons with a wide dynamic range of 0.6–80 meV. LET employs a novel flux compression guide design which in combination with two 300 Hz counter rotating choppers produces fine energy resolutions of ≥ 0.8 % δ E / Ei , to be realised with very little flux sacrifice compared to conventional methods. The multi-chopper system is designed to make full use of the long 100 ms time frames of TS2, allowing the user to make multiple measurements within a single frame. The secondary spectrometer is characterised by a wide area position sensitive 3He multidetector with π steradians of nearly gapless coverage over the angular range from −40° to +140° in the horizontal plane and ±30° in the vertical plane. The multidetector utilises the worlds first 4 m position sensitive 3He neutron detector tubes. LET has been designed specifically to allow the use of polarised neutrons allowing the user to exploit full XYZ neutron polarisation analysis. In addition a new 9 T magnet has been designed for LET allowing the use of large samples of 25 mm×25 mm with a 30° vertical opening to make use of the large multidetector.

EIGER: Next generation single photon counting detector for X-ray applications

Abstract: EIGER is an advanced family of single photon counting hybrid pixel detectors, primarily aimed at diffraction experiments at synchrotrons. Optimization of maximal functionality and minimal pixel size (using a 0.25 μ m process and conserving the radiation tolerant design) has resulted in 75 × 75 μ m 2 pixels. Every pixel comprises a preamplifier, shaper, discriminator (with a 6 bit DAC for threshold trimming), a configurable 4/8/12 bit counter with double buffering, as well as readout, control and test circuitry. A novel feature of this chip is its double buffered counter, meaning a next frame can be acquired while the previous one is being readout. An array of 256×256 pixels fits on a ∼ 2 × 2 cm 2 chip and a sensor of ∼ 8 × 4 cm 2 will be equipped with eight readout chips to form a module containing 0.5 Mpixel. Several modules can then be tiled to form larger area detectors. Detectors up to 4×8 modules (16 Mpixel) are planned. To achieve frame rates of up to 24 kHz the readout architecture is highly parallel, and the chip readout happens in parallel on 32 readout lines with a 100 MHz Double Data Rate clock. Several chips and singles (i.e. a single chip bump-bonded to a single chip silicon sensor) were tested both with a lab X-ray source and at Swiss Light Source (SLS) beamlines. These tests demonstrate the full functionality of the chip and provide a first assessment of its performance. High resolution X-ray images and “high speed movies” were produced, even without threshold trimming, at the target system frame rates (up to ∼ 24 kHz in 4 bit mode). In parallel, dedicated hardware, firmware and software had to be developed to comply with the enormous data rate the chip is capable of delivering. Details of the chip design and tests will be given, as well as highlights of both test and final readout systems.

Performance test of Si PIN photodiode line scanner for thermal neutron detection

Abstract: Thermal neutron imaging using Si PIN photodiode line scanner and Eu-doped LiCaAlF6 crystal scintillator has been developed. The pixel dimensions of photodiode are 1.18 mm (width)×3.8 mm (length) with 0.4 mm gap and the module has 192 channels in linear array. The emission peaks of Eu-doped LiCaAlF6 after thermal neutron excitation are placed at 370 and 590 nm, and the corresponding photon sensitivities of photodiode are 0.04 and 0.34 A/W, respectively. Polished scintillator blocks with a size of 1.18 mm (width)×3.8 mm (length)×5.0 mm (thickness) were wrapped by several layers of Teflon tapes as a reflector and optically coupled to the photodiodes by silicone grease. JRR-3 MUSASI beam line emitting 13.5 meV thermal neutrons with the flux of 8×105 n/cm2 s was used for the imaging test. As a subject for imaging, a Cd plate was moved at the speed of 50 mm/s perpendicular to the thermal neutron beam. Analog integration time was set to be 416.6 μs, then signals were converted by a delta–sigma A/D converter. After the image processing, we successfully obtained moving Cd plate image under thermal neutron irradiation using PIN photodiode line scanner coupled with Eu-doped LiCaAlF6 scintillator.

The multipurpose time-of-flight neutron reflectometer “Platypus” at Australia's OPAL reactor

Abstract: In this manuscript we describe the major components of the Platypus time-of-flight neutron reflectometer at the 20 MW OPAL reactor in Sydney, Australia. Platypus is a multipurpose spectrometer for the characterisation of solid thin films, materials adsorbed at the solid–liquid interface and free-liquid surfaces. It also has the capacity to study magnetic thin films using spin-polarised neutrons. Platypus utilises a white neutron beam (λ=2–20 A) that is pulsed using boron-coated disc chopper pairs; thus providing the capacity to tailor the wavelength resolution of the pulses to suit the system under investigation. Supermirror optical components are used to focus, deflect or spin-polarise the broad bandwidth neutron beams, and typical incident spectra are presented for each configuration. A series of neutron reflectivity datasets are presented, indicating the quality and flexibility of this spectrometer. Minimum reflectivity values of <10−7 are observed; while maximum thickness values of 325 nm have been measured for single-component films and 483 nm for a multilayer system. Off-specular measurements have also been made to investigate in-plane features as opposed to those normal to the sample surface. Finally, the first published studies conducted using the Platypus time-of-flight neutron reflectometer are presented.

Characterization and Simulation of the Response of Multi Pixel Photon Counters to Low Light Levels

Abstract: The calorimeter, range detector and active target elements of the T2K near detectors rely on the Hamamatsu Photonics Multi-Pixel Photon Counters (MPPCs) to detect scintillation light produced by charged particles. Detailed measurements of the MPPC gain, afterpulsing, crosstalk, dark noise, and photon detection efficiency for low light levels are reported. In order to account for the impact of the MPPC behavior on T2K physics observables, a simulation program has been developed based on these measurements. The simulation is used to predict the energy resolution of the detector.

A new pnCCD-based color X-ray camera for fast spatial and energy-resolved measurements

Abstract: We present a new high resolution X-ray imager based on a pnCCD detector and a polycapillary optics. The properties of the pnCCD like high quantum efficiency, high energy resolution and radiation hardness are maintained, while color corrected polycapillary lenses are used to direct the fluorescence photons from every spot on a sample to a corresponding pixel on the detector. The camera is sensitive to photons from 3 to 40 keV with still 30% quantum efficiency at 20 keV. The pnCCD is operated in split frame mode allowing a high frame rate of 400 Hz with an energy resolution of 152 eV for Mn K α (5.9 keV) at 450 kcps. In single-photon counting mode (SPC), the time, energy and position of every fluorescence photon is recorded for every frame. A dedicated software enables the visualization of the elements distribution in real time without the need of post-processing the data. A description of the key components including detector, X-ray optics and camera is given. First experiments show the capability of the camera to perform fast full-field X-Ray Fluorescence (FF-XRF) for element analysis. The imaging performance with a magnifying optics (3×) has also been successfully tested.

The Nuclear Science References (NSR) database and Web Retrieval System

Abstract: The Nuclear Science References (NSR) database together with its associated Web interface is the world's only comprehensive source of easily accessible low- and intermediate-energy nuclear physics bibliographic information for more than 200,000 articles since the beginning of nuclear science. The weekly updated NSR database provides essential support for nuclear data evaluation, compilation and research activities. The principles of the database and Web application development and maintenance are described. Examples of nuclear structure, reaction and decay applications are specifically included. The complete NSR database is freely available at the websites of the National Nuclear Data Center http://www.nndc.bnl.gov/nsr and the International Atomic Energy Agency http://www-nds.iaea.org/nsr .

Fluorescence Efficiency and Visible Re-emission Spectrum of Tetraphenyl Butadiene Films at Extreme Ultraviolet Wavelengths

Abstract: A large number of current and future experiments in neutrino and dark matter detection use the scintillation light from noble elements as a mechanism for measuring energy deposition. The scintillation light from these elements is produced in the extreme ultraviolet (EUV) range, from 60{200 nm. Currently, the most practical technique for observing light at these wavelengths is to surround the scintillation volume with a thin lm of Tetraphenyl Butadiene (TPB) to act as a uor. The TPB lm absorbs EUV photons and reemits visible photons,

Performance of the improved larger acceptance spectrometer: VAMOS++

Abstract: Measurements and ion optic calculations showed that the large momentum acceptance of the VAMOS spectrometer at GANIL could be further increased from ∼ 11 % to ∼ 30 % by suitably enlarging the dimensions of the detectors used at the focal plane. Such a new detection system built for the focal plane of VAMOS is described. It consists of larger area detectors (1000 mm×150 mm) namely, a Multi-Wire Parallel Plate Avalanche Counter (MWPPAC), two drift chambers, a segmented ionization chamber and an array of Si detectors. Compared to the earlier existing system (VAMOS), we show that the new system (VAMOS++) has a dispersion-independent momentum acceptance. Additionally, a start detector (MWPPAC) has been introduced near the target to further improve the mass resolution to ∼ 1 / 220 . The performance of the VAMOS++ spectrometer is demonstrated using measurements of residues formed in the collisions of 129Xe at 967 MeV on 197Au.

Hexagonal boron nitride epitaxial layers as neutron detector materials

Abstract: Micro-strip metal–semiconductor–metal detectors for thermal neutron sensing were fabricated from hexagonal boron nitride (hBN) epilayers synthesized by metal organic chemical vapor deposition. Experimental measurements indicated that the thermal neutron absorption coefficient and length of natural hBN epilayers are about 0.00361 μm−1 and 277 μm, respectively. A continuous irradiation with a thermal neutron beam generated an appreciable current response in hBN detectors, corresponding to an effective conversion efficiency approaching ∼80% for absorbed neutrons. Our results indicate that hBN semiconductors would enable the development of essentially ideal solid-state thermal neutron detectors in which both neutron capture and carrier collection are accomplished in the same hBN semiconductor. These solid-state detectors have the potential to replace 3He gas detectors, which faces the very serious issue of 3He gas shortage.

Pixel array detector for X-ray free electron laser experiments

Abstract: X-ray free electron lasers (XFELs) promise to revolutionize X-ray science with extremely high peak brilliances and femtosecond X-ray pulses. This will require novel detectors to fully realize the potential of these new sources. There are many current detector development projects aimed at the many challenges of meeting the XFEL requirements [1] , [2] . This paper describes a pixel array detector (PAD) that has been developed for the Coherent X-ray Imaging experiment at the Linac Coherent Light Source (LCLS) at the SLAC National Laboratory [3] . The detector features 14-bit in-pixel digitization; a 2-level in-pixel gain setting that can be used to make an arbitrary 2-D gain pattern that is adaptable to a particular experiment; the ability to handle instantaneous X-ray flux rates of 1017 photons per second; and continuous frames rates in excess of 120 Hz. The detector uses direct detection of X-rays in a silicon diode. The charge produced by the diode is integrated in a pixilated application specific integrated circuit (ASIC) which digitizes collected holes with single X-ray photon capability. Each ASIC is 194×185 pixels, each pixel is 110 μ m × 110 μ m on a side. Each pixel can detect up to 2500 X-rays per frame in low-gain mode, yet easily detects single photons at high-gain. Cooled, single-chip detectors have been built and meet all the required specifications. SLAC National Laboratory is engaged in constructing a tiled, multi-chip 1516×1516 pixel detector.

Release of internal curing water from lightweight aggregates in cement paste investigated by neutron and X-ray tomography

Abstract: A sealed sample of cement paste containing a pre-wetted and a dry lightweight aggregate (LWA) particle was investigated in the period between 0.5 and 20.3 h after mixing. Changes in the local water distribution in the sample during hydration were evaluated using the subtraction of 3D images obtained by subsequent neutron tomographies (NT). As both water retention in the LWA and its release to the cement paste are influenced by the pore structure of the aggregate, a high-resolution image of the sample was subsequently captured by X-ray tomography. The internal curing water released from the LWA traveled at least 3 mm from the LWA into the cement paste in the first day. Hardly any gradient in the water content of the cement paste against the distance from the LWA was observed. This suggests that the release of water for internal curing (IC) is relatively fast and the water is distributed fairly homogeneously from the LWA for at least 3 mm within the hydrating cement paste.

CASCADE, neutron detectors for highest count rates in combination with ASIC/FPGA based readout electronics

Abstract: The CASCADE detector system described herein is designed for high intensity neutron applications with high demands on the dynamical range, contrast as well as background The detector front-end is a hybrid, solid converter gas detector using several gas electron multiplier (GEM) foils as charge transparent substrates to carry solid 10B layers These coated GEMs are then stacked (“cascaded”) one behind the other to cumulate the detection efficiency of every layer without loosing position information The use of GEM foils allows high count rates up to 107 n/cm2 s The well-defined neutron absorption locus inside the thin boron layer provides sub-microsecond absolute time resolution, which opens the door towards new TOF applications Because 96% isotopically enriched boron is available in large quantities in contrast to 3He, 10B-converter based neutron detector technology is one of the very few technological alternatives to 3He in view of the imminent crisis in world-wide supply of 3He Using GEM foils, the neutron detection bottleneck shifts to data read-out electronics and its bandwidth The CASCADE detector uses an ASIC electronic front-end paired with an adaptable integrated FPGA data processing unit to provide high rate capacity and realtime event reconstruction

Design, construction, operation and performance of a Hadron Blind Detector for the PHENIX experiment

Abstract: A Hadron Blind Detector (HBD) has been developed, constructed and successfully operated within the PHENIX detector at RHIC. The HBD is a Cherenkov detector operated with pure CF 4 . It has a 50 cm long radiator directly coupled in a windowless configuration to a readout element consisting of a triple GEM stack, with a CsI photocathode evaporated on the top surface of the top GEM and pad readout at the bottom of the stack. This paper gives a comprehensive account of the construction, operation and in-beam performance of the detector.

Charge sharing in common-grid pixelated CdZnTe detectors

Abstract: The charge sharing effect in pixelated CdZnTe (CZT) detectors with a common anode steering grid has been studied. The impact on energy resolution of weighting potential cross-talk and ballistic deficit due to cathode signal shaping has been investigated. A detailed system modeling package considering charge induction, electronic noise, pulse shaping, and ASIC triggering procedures has been developed to study the characteristics of common-grid CZT detectors coupled to the VAS_UM/TAT4 ASIC. Besides an actual common-grid CZT detector coupled to VAS_UM/TAT4 ASIC, a prototype digital read-out system has been developed to better understand the nature of the charge sharing effect.

On active disturbance rejection based control design for superconducting RF cavities

Abstract: Superconducting RF (SRF) cavities are key components of modern linear particle accelerators. The National Superconducting Cyclotron Laboratory (NSCL) is building a 3 MeV/u re-accelerator (ReA3) using SRF cavities. Lightly loaded SRF cavities have very small bandwidths (high Q) making them very sensitive to mechanical perturbations whether external or self-induced. Additionally, some cavity types exhibit mechanical responses to perturbations that lead to high-order non-stationary transfer functions resulting in very complex control problems. A control system that can adapt to the changing perturbing conditions and transfer functions of these systems would be ideal. This paper describes the application of a control technique known as “Active Disturbance Rejection Control” (ARDC) to this problem.

Design of a Compton camera for 3D prompt-γ imaging during ion beam therapy

Abstract: We investigate, by means of Geant4 simulations, a real-time method to control the position of the Bragg peak during ion therapy, based on a Compton camera in combination with a beam tagging device (hodoscope) in order to detect the prompt gamma emitted during nuclear fragmentation The proposed set-up consists of a stack of 2 mm thick silicon strip detectors and a LYSO absorber detector The γ emission points are reconstructed analytically by intersecting the ion trajectories given by the beam hodoscope and the Compton cones given by the camera The camera response to a polychromatic point source in air is analyzed with regard to both spatial resolution and detection efficiency Various geometrical configurations of the camera have been tested In the proposed configuration, for a typical polychromatic photon point source, the spatial resolution of the camera is about 83 mm FWHM and the detection efficiency 25×10−4 (reconstructable photons/emitted photons in 4 π ) Finally, the clinical applicability of our system is considered and possible starting points for further developments of a prototype are discussed