Sub-nanosecond Timing Research Articles

Ballistic Acceleration of a Supercurrent in a Superconductor

One of the most primitive but elusive current-voltage (I-V) responses of a superconductor is when its supercurrent grows steadily after a voltage is first applied. The present work employed a measurement system that could simultaneously track and correlate I(t) and V(t) with subnanosecond timing accuracy, resulting in the first clear time-domain measurement of this transient phase where the quantum system displays a Newtonian like response. The technique opens doors for the controlled investigation of other time-dependent transport phenomena in condensed-matter systems.

Direct time-of-flight for quantitative, real-time in-beam PET: a concept and feasibility study

We extrapolate the impact of recent detector and scintillator developments, enabling sub-nanosecond coincidence timing resolution (τ), onto in-beam positron emission tomography (in-beam PET) for monitoring charged-hadron radiation therapy. For τ ⩽ 200 ps full width at half maximum, the information given by the time-of-flight (TOF) difference between the two opposing γ-rays enables shift-variant, artefact-free in-beam tomographic imaging by means of limited-angle, dual-head detectors. We present the corresponding fast, TOF-based and backprojection-free, 3D reconstruction algorithm that, coupled with a real-time data acquisition and a fast detector encoding scheme, allows the sampled β+-activity to be visualized in the object during the course of the irradiation. Despite the very low statistics scenario typical of in-beam PET, real-treatment simulations show that in-beam TOF-PET enables high-precision images to be obtained in real-time, either with closed-ring or with fixed, dual-head in-beam TOF-PET systems. The latter greatly alleviates the installation of in-beam PET at radiotherapeutic sites.

Clinical count rate performance of an LSO PET/CT scanner utilizing a new front-end electronics architecture with sub-nanosecond intrinsic timing resolution

A new front-end electronics architecture with sub-nanosecond intrinsic timing resolution has recently been incorporated into a 16 slice LSO PET/CT scanner for imaging applications in oncology. The new electronics are designed to work optimally with the lutetium orthosilicate (LSO) scintillator. Clinical performance of the LSO PET/CT is examined before and after upgrading to the new PICO 3D electronics, and compared with results using the NEMA NU 2 standard for evaluating scanner performance. Improved noise-equivalent count rates are seen in clinical studies, and reduced scatter fractions are observed, consistent with the increased lower-level energy threshold used to reject scatter events in the upgraded configuration.

A pipelined front-end, timing, and amplitude digitizing system

A front-end digitizing system is needed for the straw tracking-detector of the MECO experiment. This detector has 24 000 channels of time and amplitude readout. The system operates in a high singles count-rate environment, and continuously digitizes the incoming pulses of every channel, using a latency buffer to temporarily hold this information. For each event, channel occupancy signals are sent to a local logic analyzer. Thus, the system can be self-triggered or triggered by a coincidence of the internally generated occupancy signal with an external gate. Upon presentation of a valid trigger, all data stored in the latency buffer are then read with zero-suppression to local RAM. The readout can provide sub-nanosecond timing and 6-9-bit amplitude resolution. This digitizer design will be implemented in an ASIC due to the large number of readout channels, the requirement that the data initially flow in parallel because of high single rates, and the large number of memory buffers. The digitizer is controlled by an FPGA, and the system clock can be varied between 15-60 MHz. This paper presents the conceptual design for the MECO readout system, but we anticipate that it can be used for many other applications requiring the acquisition of time and waveform signals in high counting rate environments.

Subnanosecond optical gating using coax cable input microchannel plate image intensifier

Proximity focused microchannel plate image intensifies (MCPIIs) with a mesh underlay photocathode are analyzed for their iris- ing time, which is found to be of the order of 650 ps. This is much longer than previously reported but is finally explained by the mesh thickness. The reduction of this effect requires further investigation. A newly introduced impedance match has real broadband characteristics, and the irising is fully caused by other effects. The minimum gate time observable was clearly below 1 ns. The mesh underlay MCPII did not open to its full diameter at the shortest applied times. The long laser diode pulse and a too flat voltage slope of the driving generator prevented exact results for subnanosecond timing. Continued development of the system is underway.

The design and performance of the ZEUS Central Tracking Detector z-by-timing system

The ZEUS Central Tracking Detector utilizes a time difference measurement to provide a fast determination of the z coordinate of each hit. The z-by-timing measurement is achieved by using a Time-to-Amplitude Converter which has an intrinsic timing resolution of 36 ps, has pipelined readout, and has a multihit capability of 48 ns. In order to maintain the required sub-nanosecond timing accuracy, the technique incorporates an automated self-calibration system. The readout of the z-by-timing data utilizes a fully customized timing control system which runs synchronously with the HERA beam-crossing clock, and a data acquisition system implemented on a network of Transputers. Three dimensional space-points provided by the z-by-timing system are used as input to all three levels of the ZEUS trigger and for offline track reconstruction. The average z resolution is determined to be 4.4 cm for multi-track events from positron-proton collisions in the ZEUS detector.

Subnanosecond timing with large area avalanche photodiodes and LSO scintillator

The detection properties of 10 mm and 16 mm diameter bevelled-edge avalanche photodiodes fitted with LSO crystal were measured using /spl psi/-sources. Among the properties measured were the electron-hole pair yield, time resolution and energy resolution. These detectors provide excellent time resolution of 570/spl plusmn/17 ps for /sup 60/Co /spl gamma/-rays with the energy threshold set at 1 MeV. The energy resolution of the 662 keV /spl gamma/-peak from a /sup 137/Cs source was measured to be 11% FWHM with a shaping time constant of 0.1 /spl mu/s. A comparative discussion of the observed time resolution of these large area APDs emphasizes that APD gain, its quantum efficiency, and capacitance are important in timing applications.

First demonstration of sub-nanosecond photon timing with a Germanium photodiode

We demonstrate for the first time the capability of commercially available Ge-APDs to achieve single photon sensitivity and sub-nanosecond time resolution at 77K. The selection procedure of the samples both with a curve tracer and in pulsed operation is described in detail. Further improvements of the timing performance can be obtained by a suitable design of the devices.

Subnanosecond timing with ion-implanted detectors

The energy resolution of ion-implanted charged particle detectors may be improved by decreasing the thickness of the implanted detector window to minimize energy straggling. Because of the resistance of this layer, however, the timing depends on the position of entry. Two solutions to this conflict between energy resolution and time resolution are studied: evaporating a very thin aluminum layer on the detector window and fabricating a rectangular detector. Both solutions are shown to be successful with a total time resolution in the low subnanosecond region (< 200 ps).

Subnanosecond timing with semiconductor position sensitive detectors

The timing properties of semiconductor resistive dividing position sensitive detectors (PSD) are studied. It is shown that high quality timing (FWHM < 1 ns) is possible for any selected area of about 10% of the total length of the SPD. The timing signal is generated by the charge signal taken from the nonresistive electrode. If the relation between timing and position of irradiation is known off-line corrections to the timing using position information may improve the time resolution to 350 ps for the full length of the PSD. An attempt is made to explain the time resolution and the empiric position-timing relation for several PSDs.

The electronics readout system for the OPAL vertex drift chamber

The Vertex Drift Chamber for the OPAL experiment at LEP provides high quality track coordinates using multihit subnanosecond timing to detect the drifted electrons. This paper explains the electronic techniques that have been devised and implemented for the detector. The overall performance of the system is demonstrated with measurements from the final OPAL chamber.

A position-sensitive detector system with subnanosecond timing and its utilization in the measurement of pion absorption

A complex position-sensitive, time-of-flight detector was designed at the SIN to be used in the kinematically complete measurements of pion absorption in light nuclei, for the detection of both neutrons and charged particles. Design parameters and TOF properties resulting from the computer calculations and suitable test measurements are given for the system consisting of 200 × 10 × 5 cm 3 NE 102A scintillator bars, XP 2230 photomultipliers and discriminator. Position dependence of the timing parameters of the 2 m long NE 102A bar viewed from the ends by photomultipliers has been clearly revealed in our model and experimentally verified.

A multi-input fast coincidence system with sub-nanosecond timing

A novel configuration of ECL memory devices is used to provide sub-nanosecond coincidence and timing of pulses from at least eight separate inputs.

Simultaneous subnanosecond timing information and 2D spatial information from imaging photomultiplier tubes

We have incorporated a resistive anode, microchannel-plate based photon-counting 2D optical imaging detector with standard time-correlated single photon counting circuitry. The result is a very powerful spectroscopic system which combines the very low dark count and parallel collection capabilities typical of this type of detector with simultaneous time resolution of the individual photon counts. The required timing signal can be generated with a very simple addition to the biasing network of the standard detector, and results in temporal resolution of 500-ps FWHM, equivalent to that typically obtainable with moderately fast single channel photomultiplier tubes.

An inexpensive subnanosecond timing system

ECL circuitry with microstrip techniques is used to provide an inexpensive method of measuring subnanosecond time intervals arising in coincidence measurements. An accuracy of better than 0.2 ns is achieved for time intervals in the range 0.5–80 ns.

Recent results of high-resolution (e,e'p) reactions at NIKHEF-K

A survey is given of the ongoing program of (e, e'x) coincidence experiments at NIKHEF-K. The reaction can be studied at a missing energy resolution of 100 keV and at subnanosecond timing resolution. Results are presented for 3He, 12C, 90Zr and 208Pb.

Time Resolved Fluorescence Spectroscopy With Synchrotron Radiation

ABSTRACT The pulsed properties of synchrotron radiation are being applied extensively for subnanosecond timing studies. Measurements in the time domain take advantage of the well defined time structure, unique tunability, wavelength registration, and polarisation characteristics of synchrotron radiation. A description of the time modulation of synchrotron radiation is followed by a comparison between several subnanosecond timing techniques which have been used at the Synchrotron Radiation Source (SRS) at Daresbury. The present limitations of time-resolved fluorescence measurements and the broad range of possible applications of these methods, are illustrated by some selected examples. In the near future time-domain measurements will be improved to give a resolution of a few picoseconds and will be extended to include excitation over a range of wavelengths in the x-ray, vacuum ultraviolet and infra-red regions.

Timing properties of a R1294Z microchannel plate photomultiplier

The timing properties of a scintillation counter consisting of an NE111 plastic scintillator coupled to a three-stage R1294Z MCP photomultiplier have been studied. The time jitter of the R1294Z photomultiplier, its photoelectron yield for the NE111 scintillator and the time resolution for 511 keV annihilation quanta from a 68Ge 68Ga source were measured. This shows that at present the application of MCP photomultipliers in scintillation counters for subnanosecond timing is limited by the low photoelectron yield. A much longer life for the three-stage R1294Z photomultiplier was observed than that of two-stage photomultipliers. An application of the R1294Z photomultiplier for studying light pulse shapes from scintillators by means of the single photon method was tested.

Time resolved spectroscopy using synchrotron radiation

Measurements have been carried out in the time domain by groups in Orsay, Stanford and Hamburg and the scientific significance of such experiments using synchrotron radiation has been considered in recent review articles [1–7]. At present, time resolved excitation and emission studies can be carried out routinely with a resolution of at least 1 ns, and measurements have been made on the fluorescence decay of individual vibronic levels of small molecules, on emission from low quantum yield vapours (∼10 −4) at low pressure (∼1 Torr) and on quenching mechanisms in rigid matrices. Pure rare gas solids and mixtures have been studied extensively in an attempt to understand the kinetic processes associated with exciton formation. Also, for the first time, quantum coherence effects have been seen in rare gases. Using polarised light for excitation, orientated atomic states can be produced by photoselection and periodic fluorescence modulation can then be seen in the presence of an external applied field. The data give information about lifetimes, spins, multipolarities and “ g” factors — even when the substates are unresolved in energy. Photoselection of an individual residue within a protein with pulsed, polarised light can, and has, led to an understanding of the microenvironment within the large molecule and has enabled initial estimates to be made of the flexibility of such large structures as well as of their overall size and shape. The best time resolution obtained so far using standard photon counting techniques is about ±50 ps and has been limited by the time response of the photodetector used. The narrow pulse width and the associated broad frequency spectrum (extending beyond 1 GHz) from storage ring sources has led to the study of phase shift and modulation techniques at a number of different frequencies. Preliminary results have revealed that in the frequency domain times of the order of a few ps can be measured. It is highly probable that, in the future, time domain measurements will be improved to give a resolution of about 1 ps and will be extended to include excitation over an extensive range of wavelengths in the VUV and X-ray regions. In this paper, a description of the actual time modulation of synchrotron radiation is followed by a comparison between several subnanosecond timing techniques which have been used at synchrotron radiation sources. The broad range of possible applications of these methods is illustrated by some slected examples. Finally a discussion is included on the prospects for reducing the bunch length into the picosecond region in future storage rings.

Barium fluoride — Inorganic scintillator for subnanosecond timing

The discovery of an intense, fast component of the light pulse from a BaF 2 crystal coupled to a XP 2020 Q photomultiplier with quartz window prompted this detailed study of its properties as a scintillator. Light pulse shape investigations performed by means of the single photon method showed that the fast component is characterised by a decay time constant equal to 600 ps and by a fwhm equal to 550 ps. The intensity of it expressed by the number of photoelectrons released at the photocathode of the XP 2020 Q photomultiplier was equal to about 400 phe/MeV when the total light yield was measured to be equivalent to about 2000 phe/MeV. The time-resolved measurement of the emission spectrum showed that the fast component is due to the emission at 220 nm wavelength, the slow component is associated with 310 nm wavelength band. The energy resolution and time resolution studies performed with a number of crystals 24 mm in diameter and 1 to 4 cm thick showed that BaF 2 combines a lot of advantages: • - a high time resolution equal to 112 ps for γ-rays from 60Co source; • - a good energy resolution equal to 10% for 662 keV γ-rays from 137Cs source; • - a very good efficiency for γ-rays detection due to a high density equal to 4.88 g/cm 3.