Start Detector Research Articles

Record high counting rate of a non-beam-based positron annihilation age–momentum correlation (AMOC) spectrometer achieved by geometrical optimization of detectors

Positron annihilation age–momentum correlation (AMOC) spectroscopy is not only a critical approach to investigate positronium formation and annihilation, but also a powerful technique for materials science to characterize the chemical environment of pores. However, due to the long measurement time (several days to collect 10 million counts for one sample, at a low coincidence counting rate of approximately 20–40 cps) of a conventional non-beam-based AMOC spectrometer, AMOC technique has been rarely applied. In this work, based on the geometrical simulations of detectors using Geant4 program, we developed a new semi-digital AMOC spectrometer with two start detectors. After systematic optimizations of geometrical configurations of detectors, timebase of digital oscilloscope, and the energy windows of start and stop detectors, this instrument achieved the highest coincidence counting rate for a non-beam-based AMOC spectrometer (∼ 180 cps for a narrow stop energy window of 469–589 keV and the shaping time of HPGe detector at THPGeshaping = 6μs, and ∼ 500 cps for a wide stop energy window of 104–589 keV and THPGeshaping = 2μs). The drastic rise of coincidence counting rate will broaden the applications of AMOC spectrometers in positronium physics and materials characterization in future.

New measurement of the235U(nth,f) fission yields and development of a Time of Flight line at the LOHENGRIN spectrometer

The study of nuclear fission yields has a major impact on the characterization and understanding of the fission process and is mandatory for reactor applications. In the framework of a collaboration between the CEA, the LPSC and the ILL, a program of actinide fission yield measurements has been ongoing for several years at the LOHENGRIN spectrometer. However, the measurement of very low fission yields in the symmetry region and the heavy wing of the distributions is difficult to achieve due to the strong contamination by other masses with much higher yields and requires the development of a new experimental setup.This paper will first present the results of a new absolute measurement of the235U(nth,f) mass yields using an ionization chamber placed at the exit of the spectrometer. Although very well documented in the literature, these yields show uncertainties lying from 3% to 10% with large discrepancies between libraries and a lack of correlation matrices. New experimental data obtained at the LOHENGRIN spectrometer will be detailed, along with the measurement method and the production of the experimental covariance matrix.The second part will show the development of a Time of Flight (ToF) line in order to improve the background rejection in the mass yield measurements. In the symmetry region, the precision of the measurement is limited by the background estimation due to the charge exchanges with the residual gas of the separator. We plan to analyze the events using a triple coincidence (∆E x E) x ToF, whereas today only (∆E x E) selection is available. The new ToF line is built using Si3N4foils and secondary electron detectors (SED) for the start and stop detectors. We will present the choices made for the SED technology along with the progress achieved on the ToF line characterization.

Development of a time of flight spectrometer based on position sensitive multi-wire proportional counters for fission fragment mass distribution studies.

Characteristics and performance of a time of flight (TOF) spectrometer developed for performing fission mass distribution studies are presented. The spectrometer contains two TOF arms based on multi-wire proportional counters (MWPCs). Each arm has two MWPCs to form a start-stop detection system for TOF measurements. The start detector has an active area of 4 × 4cm2. The stop detector is a two-dimensional position sensitive MWPC with an active area of 16 × 11cm2. Salient features of the MWPCs are the use of reduced sub-millimeter wire pitches of 0.635 and 0.317mm in the electrodes along with the use of gold plated tungsten wires of diameters 10 and 20 µm. A delay line for position electrodes is prepared using chip inductors and capacitors. Ten different configurations of MWPC were investigated for the start detector, which involved the use of three and four electrode geometries, use of different wire pitches, and use of aluminized mylar for timing electrodes. Performance results close to micro-channel plate detectors have been observed with some designs of MWPC, displaying rise times better than 2ns with an estimated inherent time resolution of ∼100ps FWHM. A position resolution of ∼1mm (FWHM) has been observed. Design features of the MWPCs and their test performance results are described in this article.

Time Performance Study of Plastic Scintillator Detector with SiPM Readouts

In this paper the time performance of a plastic scintillator detector with an area of 10 cm×10 cm and read out by multiple silicon photomultipliers (SiPMs) at both ends was studied. The results tested with a 239Pu source are shown as: (1) the time resolutions became better gradually with the increase of the quantities of SiPMs connected in series; (2) when the number of 12 SiPMs was fixed, the time resolutions got worse as the number of parallel branches were increased; (3) the detector time resolutions can be effectively improved by using a fast-time plastic scintillator and adding its thickness; (4) to improve the positional uniformity of the time resolution, the scintillator with larger dimensions than beam spots should be used; (5) a resolution less than 131 ps was achieved with a 0.1 cm thickness EJ232 scintillator detector read out on each side by 12 SiPMs conncted in series. This study has importance significance for the upgrading of the start detector at RIBLL2.

Diamond Detectors for Timing Measurements in High Energy Physics

Timing detectors are a well established part of High Energy Physics experimental instrumentation. The choice of sensors with fast (less than 10 ns) and precise (better than 100 ps) signals is an essential part of the design of a timing detector, together with radiation resistance considerations. Single crystal diamond sensors are one of the most promising technologies in this field. In this paper, the main characteristics that make single diamond crystal sensors ideal for timing applications will be described and an introduction to the design of fast front-end electronics will be given. Finally, two examples of diamond timing detectors used in High Energy Physics, the START detector of HADES and the TOTEM/CMS timing detector, will be discussed.

Measurement of the Time of Flight of Charged Particles by a Time Detector Based on the MCP for the MAVR Facility

Within the study of the time-of-flight method, an appropriate system has been created and the first test data have been obtained that fully demonstrate the efficient operation of the equipment. An MCP detector is used as the start detector. During the experiment at this facility, the time resolution, depending on parameters of the reaction products (mass, charge, and energy), has been measured. The characteristics of the detector operating at the IC-100 accelerator (FLNR, JINR) have been measured. The results demonstrate a high time resolution for charged particles in a wide mass range.

Charge identification performance of a [formula omitted]E-TOF detector prototype for the FOOT experiment

FOOT (FragmentatiOn On Target) is an applied nuclear physics experiment aimed at measuring the production cross sections of fragments for energies, beams and targets relevant in particle therapy and radioprotection in space. The ΔE-TOF detector will measure the energy deposited by the fragments in a wall of plastic scintillators and the time of flight with respect to a start detector. These two quantities allow to determine the charge Z of the fragment. In this work, we summarize the charge identification procedure of a detector prototype with two scintillator modules.

Development of trigger and start detectors for experiments with high-energy heavy ions at the Joint Institute for Nuclear Research

Fast Cherenkov and scintillation detectors based on microchannel-plate photomultiplier tubes and silicon photomultipliers are being developed for application in the multi-purpose detector and baryonic matter at the Nuclotron experiments with the heavy ion beams at the Joint Institute for Nuclear Research. The aim of the detectors is the fast triggering of nucleus–nucleus collisions with high efficiency and to generate the start signal with picosecond time resolution for time-of-flight measurements. The detectors provide a time resolution better than 50 ps and can operate in the strong magnetic field of the experimental facilities.

Experimental verification of a method to create a variable energy neutron beam from a monoenergetic, isotropic source using neutron elastic scatter and time of flight

An experiment was performed to determine the neutron energy of near-monoergetic deuterium–deuterium (D–D) neutrons that elastically scatter in a hydrogenous target. The experiment used two liquid scintillators to perform time of flight (TOF) measurements to determine neutron energy, with the start detector also serving as the scatter target. The stop detector was placed 1.0m away and at scatter angles of π/6, π/4, and π/3rad, and 1.5m at a scatter angle of π/4rad. When discrete 1ns increments were implemented, the TOF peaks had estimated errors between −21.2 and 3.6% relative to their expected locations. Full widths at half-maximum (FWHM) ranged between 9.6 and 20.9ns, or approximately 0.56–0.66MeV. Monte Carlo simulations were also conducted that approximated the experimental setup and had both D–D and deuterium–tritium (DT) neutrons. The simulated results had errors between −17.2 and 0.0% relative to their expected TOF peaks when 1ns increments were applied. The largest D–D and D–T FWHMs were 26.7 and 13.7ns, or approximately 0.85 and 4.98MeV, respectively. These values, however, can be reduced through manipulation of the dimensions of the system components. The results encourage further study of the neutron elastic scatter TOF system with particular interest in application to active neutron interrogation to search for conventional explosives.

First results from the new double velocity–double energy spectrometer VERDI

The VERDI spectrometer (VElocity foR Direct mass Identification) is a two arm time-of-flight spectrometer built at the European Commission Joint Research Centre IRMM. It determines fragment masses and kinetic energy distributions produced in nuclear fission by means of the double velocity and double energy (2v–2E) method. The simultaneous measurement of pre- and post neutron fragment characteristics allows studying the share of excitation energy between the two fragments. In particular, the evolution of fission modes and neutron multiplicity may be studied as a function of the available excitation energy. Both topics are of great importance for the development of models used in the evaluation of nuclear data, and also have important implications for the fundamental understanding of the fission process. The development of VERDI focus on maximum geometrical efficiency while striving for highest possible mass resolution. An innovative transmission start detector, using electrons ejected from the target itself, was developed. Stop signal and kinetic energy of both fragments are provided by two arrays of silicon detectors. The present design provides about 200 times higher geometrical efficiency than that of the famous COSI FAN TUTTE spectrometer [Nuclear Instruments and Methods in Physics Research 219 (1984) 569]. We report about a commissioning experiment of the VERDI spectrometer, present first results from a 2v-2E measurement of 252Cf spontaneous fission and discuss the potential of this instrument to contribute to the investigation prompt fission neutron characteristics as a function of fission fragment properties.

Geant4 simulation of the PSI LEM beam line: energy loss and muonium formation in thin foils and the impact of unmoderated muons on the μSR spectrometer

The PSI low-energy μSR spectrometer is an instrument dedicated to muon spin rotation and relaxation measurements. Knowledge of the muon beam parameters such as spatial, kinetic energy and arrival-time distributions at the sample position are important ingredients to analyze the μSR spectra. We present here the measured energy losses in the thin carbon foil of the muon start detector deduced from time-of-flight measurements. Muonium formation in the thin carbon foil (10 nm thickness) of the muon start detector also affect the measurable decay asymmetry and therefore need to be accounted for. Muonium formation and energy losses in the start detector, whose relevance increase with decreasing muon implantation energy (<10 keV), have been implemented in Geant4 Monte Carlo simulation to reproduce the measured time-of-flight spectra. Simulated and measured time-of-flight and beam spot agrees only if a small fraction of so called ``unmoderated'' muons which contaminate the mono-energetic muon beam of the μSR spectrometer is introduced. Moreover the sensitivity of the beam size and related upstream-downstream asymmetry for a specially shaped ``nose'' sample plate has been studied for various beam line settings, which is of relevance for the study of thermal muonium emission into vacuum from mesoporous silica at cryogenic temperatures.

Background reduction in 236U/238U measurements

The measurements of actinide isotopic ratios, in particular 236U/238U, in environmental samples requires high sensitivity. In particular, special effort must be devoted to the suppression of interfering nuclides, such as 235,238U, when measuring 236U. At the AMS facility of CIRCE, isotopic ratios down to ∼10−10 are currently measured using a gas E−ΔE detector. In order to push this limit lower towards natural levels, a time-of-flight system is used, featuring a micro-channel plate start detector and a Si stop detector. As the mass resolution of the latter is limited by the layout, an attempt to reduce the abundant isotope interference by other means has been undertaken.In this study, we report preliminary results on the characterization of the presence of molecular interferences when using UO−, UC− and UC2− as injected molecular ions. In particular the possibility to stabilize the current yield from carbide cathodes has been investigated: it was found that the best cathode preparation procedure is obtained pressing U salts baked at 800°C mixed with graphite and Al powder. Moreover, the 238U background in 236U measurements is strongly reduced injecting UC− ions, as verified using a time-of-flight detection system. On the other hand, 235U interference is larger with respect to UO− injection, but this increase is smaller than expected on the basis of abundances of 13C and 17O in UC and UC2 molecules on one side and UO, on the other.

Development and study of picosecond start and trigger detector for high-energy heavy ion experiments

Two modular Cherenkov detectors based on MCP-PMTs XP85012 are developed for study Au+Au collisions in future experiments with beams of Nuclotron and collider NICA at JINR, Dubna. The detector arrays register high-energy photons and relativistic charged particles with aim of fast triggering the collisions and generation of start signal with time resolution better then 50ps for TOF detector. The MC simulation showed the trigger efficiency of 100% for impact parameter range b<10fm. The best time resolution for single detector channel σt≈21ps was obtained with DRS4 digitizer in TOF measurements with a deuteron beam.

A method to enhance coincidence time resolution with applications for medical imaging systems (TOF/PET)

A coincidence timing spectrometer was assembled using NaI(Tl) inorganic and BC418 type organic (plastic) scintillation detectors. The constant fraction timing method was used. Coincidence time resolution values of the detectors, which have great importance in TOF/PET measurements, were obtained separately. The resolutions were enhanced using a different method in a start-stop coincidence spectrometer: the signals from the start detectors were delayed. The results from the FLUKA Monte Carlo simulation code agreed well with the experimental results.

The VERDI fission fragment spectrometer

The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF) technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This configuration, where the stop detector will provide us simultaneously with the kinetic energy of the fragment and timing information, significantly limits energy straggling in comparison to legacy experimental setup where a thin foil was usually used as a stop detector. In order to improve timing resolution, neutron transmutation doped silicon will be used. The high resistivity homogeneity of this material should significantly improve resolution in comparison to standard silicon detectors. Post-neutron fission fragment masses are obtained form the time-of-flight and the energy signal in the silicon detector. As an intermediary step a diamond detector will also be used as start detector located very close to the target. Previous tests have shown that poly-crystalline chemical vapour deposition (pCVD) diamonds provides a coincidence time resolution of 150 ps not allowing complete separation between very low-energy fission fragments, alpha particles and noise. New results from using artificial single-crystal diamonds (sCVD) show similar time resolution as from pCVD diamonds but also sufficiently good energy resolution.

SOME CHARACTERISTICS AND APPLICATIONS OF PARALLEL PLATE AVALANCHE DETECTORS (A REVIEW)

Parallel plate avalanche detectors (PPADs) are new gas detectors and are being extensively used to detect heavy ions, fission fragments and minimum ionizing particles. Due to their excellent timing characteristics and low cost, they are being widely used in different areas of science and technology, particularly as start and stop detectors in different experiments. These detectors are ideal for coincidence measurements and for photofission studies. Different characteristics; construction operation, performance, time resolution, energy resolution and experimental techniques based on PPADs are reviewed in this paper.

In-Beam Diamond Start Detectors

This paper describes operation principles and the in-beam performance of Start Detector (SD) assemblies consisting of Diamond Detectors (DDs) grown by Chemical Vapour Deposition (CVD) and Front End Electronics (FEE) which have been designed for and used in various nuclear physics experiments at GSI Helmholtz Center for Heavy Ion Research in Darmstadt.

New Technologies for Submillimeter Laser Ranging

We are presenting the work progress and recent results in a development and construction of new technologies for submillimeter laser ranging and picosecond accuracy laser time transfer. The key hardware components: the Start detector and discriminator, the echo signal detector, the timing device and signal cablings were studied in detail. The new devices have been designed, built and tested in our lab. To minimize the systematic errors the photon counting approach has been selected. The ranging chain has been designed and optimized with a goal of single shot resolution of several millimeters and sub-millimeter normal points and overall system stability. The Start detector and discriminator are constructed as a single device to optimize their matching and maintain stability. The NPET timing system based on surface acoustic wave interpolator has a resolution of 800 fs and 4 fs long term stability. The echo detector is based on innovated SPAD detector optimized for high repetition Gate rate and minimal dark count rate. Both the detectors output signals have ultrafast slew rates &lt; 200 ps / 1 V. In connection to the 6 GHz bandwidth of the timing system inputs these fast slew rates improves the timing and temperature stability along with the RF interference immunity. The new low temperature drift signal cables have been selected, tested and used. The new hardware was tested in indoor calibration experiments. We have achieved the single shot resolution of 3 mm rms. The temperature and temporal stability of the individual components is excellent. The drift is typically below 200 fs/K for each contributor. The overall temperature drift of the entire laser ranging chain is below 500 fs/ K. The long term stability of the ground target calibration is better than ± 800 fs within 3 days. During this period the environment temperature changed by more than 4°C. In the sense of time deviation Tdev the stability of 300 fs was achieved. The presented components will enable to carry out laser ranging with submillimeter normal points stability and reproducibility. The accuracy of the “ranging machine” based on these devices will reach sub-mm values, as well. The concept and construction will be presented along with the achieved devices parameters.

Performance of the improved larger acceptance spectrometer: VAMOS++

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.

A module for shaping control signals of the T0 detector of the ALICE experiment

An algorithm for synchronizing operation of the T0 start detector (ALICE experiment on the Large Hadron Collider) with an accelerator, a data reading system, and a laser detector testing system is described. The main functions and arrangement of the GRPG electronic module inserted additionally into the electronic support structure of the detector for shaping control signals are considered in detail.