Minimum Ionising Particles Research Articles

The effect of fast neutron irradiation on the performance of synthetic single crystal diamond particle detectors

Diamond is known for its extreme hardness which may allow it to operate as a particle detector in high fluence environments even after absorption of large radiation doses. We present a study of the deterioration of the charge collection efficiency ( CCE) due to neutrons produced by 235U fission, with irradiation fluences up to 1 × 10 16 n cm − 2. The planar devices were fabricated by thermal evaporation of Au onto approx. 300 μm thick high purity chemical vapour deposited diamond produced by Element Six Ltd., UK. The detector performance was investigated as a function of bias voltage at room temperature using 241Am α-particles and minimum ionising particles (MIPs) of a 90Sr source. At low fluences up to 2 × 10 13 n cm − 2 , the detectors reach the initial saturated signal amplitude after irradiation. However, the signal is less stable and deteriorates due to polarisation. This effect can be reduced by initial priming with X-rays. No peak could be distinguished in the detector response in the unprimed state after 10 16 n cm − 2 with bias voltages up to 1000 V (equivalent to 32 kV cm − 1). However, a peak at about 18% CCE could be recovered after priming.

Device Simulation of Monolithic Active Pixel Sensors: Radiation Damage Effects

Vertexing for the future International Linear Collider represents a challenging goal because of the high spatial resolution required with low material budget and high ionizing radiation tolerance. CMOS Monolithic Active Pixel Sensors (MAPS) represent a good potential solution for this purpose. Up to now many MAPS sensors have been developed. They are based on various architectures and manufactured in different processes. However, up so far, the sensor diode has not been the subject of extensive modelization and simulation. Published simulation studies of sensor-signal formation have been less numerous than measurements on real sensors. This is a cause for concern because such sensor is physically based on the partially depleted diode, in the vicinity of which the electric field collects the minority carriers generated by an incident MIP (minimum ionizing particle). Although the microscopic mechanisms are well known and modelized, the global physical mechanisms for signal formation are not very rigorously established. This is partly due to the presence of a predominant diffusion component in the charge transport. We present here simulations mainly based on the S-PISCES code, in which physical mechanisms affecting transport are taken into account. Diffusion, influence of residual carrier concentration due to the doping level in the sensitive volume, and more importantly charge trapping due to deep levels in the active (detecting) layer are studied together with geometric aspects. The effect of neutron irradiation is studied to assess the effects of deep traps. A comparison with available experimental data, obtained on processed MAPS before or after neutron irradiation will be introduced. Simulated reconstruction of the Minimum Ionizing Particle (MIP) point of impact in two dimensions is also investigated. For further steps, guidelines for process choices of next Monolithic Active Pixel Sensors are introduced.

Very high momentum particle identification in ALICE at the LHC

We propose to construct and install a limited acceptance detector to identify hadrons (pions, K, p) up to 30 GeV/ c on a track-by-track basis in space available in ALICE. Details and PID performance simulation results will be presented for two possible options, including a high transverse momentum ( p T ) trigger for this detector. The first option is a RICH design with a C 4 F 10 gas UV-photon radiator, UV-mirror, quartz window and pad-readout. This design requires additional tracking detectors to enable high p T triggering. A second option is a combination of three detectors: a RICH with CF 4 gas both as a UV-photon radiator and as a gas amplification medium (a windowless approach); and a threshold Cherenkov detector ( C 4 F 10 ) with a quartz window and pad readout. The response for minimum ionizing particles (MIP) and UV-photons in these detectors can be well separated. With an additional tracking detector this design will also provide high p T triggering. The simulation includes UV-photon production due to CF 4 scintillation.

Signal height in silicon pixel detectors irradiated with pions and protons

Pixel detectors are used in the innermost part of multi-purpose experiments at the Large Hadron Collider (LHC) and are therefore exposed to the highest fluences of ionising radiation, which in this part of the detectors consists mainly of charged pions. The radiation hardness of the detectors has been tested thoroughly up to the fluences expected at the LHC. In case of an LHC upgrade the fluence will be much higher and it is not yet clear up to which radii the present pixel technology can be used. To establish such a limit, pixel sensors of the size of one CMS pixel readout chip (PSI46V2.1) have been bump bonded and irradiated with positive pions up to 6 × 10 14 n eq / cm 2 at PSI and with protons up to 5 × 10 15 n eq / cm 2 . The sensors were taken from production wafers of the CMS barrel pixel detector. They use n-type DOFZ material with a resistance of about 3.7 k Ω cm and an n-side read out. As the performance of silicon sensors is limited by trapping, the response to a Sr-90 source was investigated. The highly energetic beta-particles represent a good approximation to minimum ionising particles. The bias dependence of the signal for a wide range of fluences will be presented.

Silicon Carbide for High Signal to Noise Ratio MIPs Detection From Room Temperature to 80$^{\circ}$C

The relatively low value of the number of electron-hole (e-h) pairs per micron for Minimum Ionizing Particles (MIPs) in SiC against the value for Si, imposes severe constrains on the crystallographic quality, the thickness and the doping concentration of the SiC epitaxial layer used as detection medium. In this work, a 85 mu m thick 4H-SiC epitaxial layer with a low doping concentration, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> les 1 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , was used in order to have a high number ( ap 4700) of e-h pairs generated by a MIP in the active region. We present experimental data on the charge spectrum for beta MIPs from a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> Sr source, collected in a temperature range from room temperature up to 81degC.

Correction of SiPM temperature dependencies

The performance of a high granular analogue hadronic calorimeter (AHCAL) using scintillator tiles with built-in Silicon Photomultiplier (SiPM) readout is reported. A muon beam is used for the minimum ionizing particle (MIP) based calibration of the single cells. The calibration chain including corrections for the non-linearity of the SiPM is presented. The voltage and temperature dependencies of the SiPM signal have been investigated using the versatile LED system of the AHCAL. Monitoring and correction methods are discussed. Measurements from the operation 2006 and 2007 at the CERN SPS test beam and data provided by the Institute for Theoretical and Experimental Physics (ITEP) in Moscow are compared.

Silicon microstrip detectors in 3D technology for the sLHC

The projected luminosity upgrade of the large hadron collider (LHC), the sLHC, will constitute a challenging radiation environment for tracking detectors. Massive improvements in radiation hardness are required with respect to the LHC. In the layout for the new ATLAS tracker, silicon strip detectors (SSDs) with short strips cover the region from 28 to 60 cm distance to the beam. These SSDs will be exposed to fluences up to 10 15 N eq / cm 2 , hence radiation resistance is the major concern. It is advantageous to fuse the superior radiation hardness of the 3D design originally conceived for pixel-style applications with the benefits of the well-known planar technology for strip detectors. This is achieved by ganging rows of 3D columns together to form strips. Several prototype sLHC detector modules using 3D SSD with short strips, processed on p-type silicon, and LHC-speed front-end electronics from the present ATLAS semi-conductor tracker (SCT) were built. The modules were tested before and after irradiation to fluences of 10 15 N eq / cm 2 . The tests were performed with three systems: a highly focused IR-laser with 5 μ m spot size to make position-resolved scans of the charge collection efficiency (CCE), a Sr 90 β -source set-up to measure the signal levels for a minimum ionizing particles (MIPs), and a beam test with 180 GeV pions at CERN. This article gives a brief overview of the performance of these 3D modules, and draws conclusions about options for using 3D strip sensors as tracking detectors at the sLHC.

A fast electronic system of the T0 start trigger detector for the ALICE experiment

A fast electronic system of the T0 start trigger detector for the ALICE experiment has been developed, assembled, and adjusted using a pulsed laser. The system is composed of 24 independent detection channels for secondary particles (this number corresponds to the number of individual Cherenkov counters in the detector); common modules, which generate the signal of the event detection time with an error of <50 ps, the trigger of the interaction vertex position with an error of ∼2 cm, and triggers of two independent levels of the event multiplicity in the range of 1–150 minimum ionizing particles (MIP); and several auxiliary modules. A total of 109 channels are used in the time-to-digital converters to record time, amplitude, and auxiliary data. The time resolution of the detector for single MIP is 38 ps.

Development of Binary Readout CMOS Monolithic Sensors for MIP Tracking

Recently, CMOS Monolithic Active Pixels Sensors (MAPS) have become strong candidates for pixel detectors used in high energy physics experiments. A very good spatial resolution lower than 5 mum can be obtained with these detectors. A recent fast MAPS chip, designed in AMS CMOS 0.35 mum Opto process and called MIMOSA16 (HiMAPS2), was submitted to foundry in June 2006. The chip is a 128times32 pixels array where 8 columns have analog test outputs and 24 columns have their outputs connected to offset compensated discriminator stages. The pixel array is addressed row-wise. The array is divided in four blocks of pixels with different charge-to-voltage conversion factors and is controlled by a serially programmable sequencer. The sequencer operates as a pattern generator which delivers control signals both to the pixels and to the column-level discriminators. Discriminators have a common adjustable threshold. This chip is the basis of the final sensor of the EUDET-JRA1 beam telescope which will be installed at DESY in 2009. In this paper, laboratory tests results using a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">55</sup> Fe source together with beam tests results obtained at CERN using Minimum Ionizing Particles (MIPs) are presented.

3D silicon strip detectors

While the Large Hadron Collider (LHC) at CERN has started operation in autumn 2008, plans for a luminosity upgrade to the Super-LHC (sLHC) have already been developed for several years. This projected luminosity increase by an order of magnitude gives rise to a challenging radiation environment for tracking detectors at the LHC experiments. Significant improvements in radiation hardness are required with respect to the LHC. Using a strawman layout for the new tracker of the ATLAS experiment as an example, silicon strip detectors (SSDs) with short strips of 2–3 cm length are foreseen to cover the region from 28 to 60 cm distance to the beam. These SSD will be exposed to radiation levels up to 10 15 N eq / cm 2 , which makes radiation resistance a major concern for the upgraded ATLAS tracker. Several approaches to increasing the radiation hardness of silicon detectors exist. In this article, it is proposed to combine the radiation hard 3D-design originally conceived for pixel-style applications with the benefits of the established planar technology for strip detectors by using SSDs that have regularly spaced doped columns extending into the silicon bulk under the detector strips. The first 3D SSDs to become available for testing were made in the Single Type Column (STC) design, a technological simplification of the original 3D design. With such 3D SSDs, a small number of prototype sLHC detector modules with LHC-speed front-end electronics as used in the semiconductor tracking systems of present LHC experiments were built. Modules were tested before and after irradiation to fluences of 10 15 N eq / cm 2 . The tests were performed with three systems: a highly focused IR-laser with 5 μ m spot size to make position-resolved scans of the charge collection efficiency, an Sr 90 β -source set-up to measure the signal levels for a minimum ionizing particle (MIP), and a beam test with 180 GeV pions at CERN. This article gives a brief overview of the results obtained with 3D-STC-modules.

Development of a High Dynamic Range Read-Out System using Multiple Photodiodes for the Total Absorption Calorimeter of the CALorimetric Electron Telescope

Read-out systems using Si-PIN photodiodes and front-end circuits (FEC) were studied to measure the energy deposit with a dynamic range from 1MIP(Minimum Ionization Particle) to 10 6 MIPs in a BGO bar of the total absorption calorimeter (TASC) of the CALET (CALorimetric Electron Telescope) instrument. Three types of FEC were tested for the photodiode read out. Two were A225 (AMP-TEK), which consists of a hybrid charge sensitive preamplifier and a shaping amplifier, and MPX-08 (NOVA), which is a charge-integrating chip. It was confirmed that the A225 has a resolution of about 0.31 fC and a maximum range of about 2 pC. It was found that the use of the A225 makes a wide range measurement with six orders of magnitude possible using three photodiodes. A new hybrid integrated circuit is being developed to measure a BGO signal with a dynamic range of seven orders using two photodiodes. This FEC consists of two preamplifiers, one for a smaller photodiode and one for a larger one. A high-gain preamplifier was devel...

Study of the response to minimum ionising particles of microstrip detectors made with float zone and magnetic Czochralski silicon after neutron irradiation

The use of various silicon substrates to improve the radiation hardness of tracker detectors for high energy physics experiments has been investigated for several years. Single crystal silicon grown with different methods has different concentrations of impurities (mainly O and C). It has been found that relatively high concentrations of particular impurities in the silicon crystal can affect the degradation of some of the detector electrical properties as a function of the radiation dose. When high resistivity Czochralski (Cz) silicon became available after refinement of the Cz method for growing single crystal silicon ingots, the new material (magnetic Cz, MCz) was tested for radiation hardness with promising results obtained with simple pad diodes. A crucial measurement for evaluating the radiation tolerance of the detectors is though the response to minimum ionising particles (MIPs) of finely segmented devices. To this purpose, miniature microstrip sensors made on n and p-type MCz substrates have been produced and compared to identical ones made on n and p-type standard floating zone (FZ) detector grade silicon. The study has been performed evaluating the signal induced by beta electrons from a 90Sr source and measured with an LHC speed (40 MHz clock) analogue electronics readout. The comparison of MCz and FZ n and p-type detectors has been carried out after several doses of neutron irradiation (up to 1×10 15 n cm −2).

Fast polycrystalline CdTe detectors for bunch-by-bunch luminosity monitoring in the LHC

The luminosity at the four interaction points of the Large Hadron Collider (LHC) must be continuously monitored in order to provide an adequate tool for the control and optimisation of beam parameters. Polycrystalline cadmium telluride (CdTe) detectors have previously been tested, showing their high potential to fulfil the requirements of luminosity measurement in the severe environment of the LHC interaction regions. Further, the large signal yield and the fast response time should allow bunch-by-bunch measurement of the luminosity at 40 MHz with high accuracy. Four luminosity monitors with two rows of five polycrystalline CdTe detectors each have been fabricated and will be installed at both sides of the low-luminosity interaction points ALICE and LHC-b. A detector housing was specially designed to meet the mechanical constraints in the LHC. A series of elementary CdTe detectors were fabricated and tested, of which 40 were selected for the luminosity monitors. A sensitivity of 10 4 electrons per minimum ionizing particle (MIP) and a pulse width better than 5 ns FWHM have been currently achieved.

The ATLAS Beam Conditions Monitor

Beam conditions and the potential detector damage resulting from their anomalieshave pushed the LHC experiments to build their own beam monitoring devices. The ATLASBeam Conditions Monitor (BCM) consists of two stations (forward and backward) of detectorseach with four modules. The sensors are required to tolerate doses up to 500 kGy and in excessof 1015 charged particles per cm2 over the lifetime of the experiment. Each module includes twodiamond sensors read out in parallel. The stations are located symmetrically around theinteraction point, positioning the diamond sensors at z = ±184 cm and r = 55 mm (a pseudo-rapidity of about 4.2). Equipped with fast electronics (2 ns rise time) these stations measuretime-of-flight and pulse height to distinguish events resulting from lost beam particles fromthose normally occurring in proton-proton interactions. The BCM also provides a measurementof bunch-by-bunch luminosities in ATLAS by counting in-time and out-of-time collisions.Eleven detector modules have been fully assembled and tested. Tests performed range fromcharacterisation of diamond sensors to full module tests with electron sources and in protontestbeams. Testbeam results from the CERN SPS show a module median-signal to noise of 11:1for minimum ionising particles incident at a 45-degree angle. The best eight modules wereinstalled on the ATLAS pixel support frame that was inserted into ATLAS in the summer of2007. This paper describes the full BCM detector system along with simulation studies beingused to develop the logic in the back-end FPGA coincidence hardware.

Neutron irradiation test of an ATLAS Thin Gap Chamber

Thin Gap Chambers (TGCs) will be used as a muon trigger device in the end-cap regions of the ATLAS detector. The detector will be placed in an experimental cavern approximately 100 m below the ground surface. A large amount of neutron background is expected in the cavern. Recoiled nuclei, mostly protons, emerging from the neutron interaction provide a much larger energy deposit in the gas volume than that of the minimum ionizing particle (MIP). This might cause aging and improper operation of the TGC. In order to investigate such influences, we performed a test on the operation stability of a real-use TGC under a much higher neutron flux environment than that expected in the ATLAS cavern. This paper describes the experimental results of the irradiation test using 14-MeV neutrons. The maximum flux was 3.2 × 10 5 Hz / cm 2 , which was effectively approximately nine times higher than that at the worst TGC location. It was proved that the TGC was immune to such a flux and instantaneous large signals originating from the neutrons. The mean output charge from the recoil proton at the nominal operation voltage was found to be approximately 30 times larger than that of MIP. The total fluence was 1.4 × 10 10 neutrons / cm 2 , up to which the TGC operated stably and no detector deterioration was observed. This corresponds to approximately nine months of ATLAS operation at the nominal luminosity of 10 34 cm 2 / s .

Response to minimum ionising particles of p-type substrate silicon microstrip detectors irradiated with neutrons to LHC upgrade doses

Silicon sensors will probably be the choice for the inner tracker detectors of the experiments in the anticipated LHC luminosity upgrade (Super LHC, SLHC). These sensors will have to survive a radiation environment almost an order of magnitude higher than within the already challenging LHC trackers. The final cumulated fluence will depend on the integrated luminosity targeted by the experiments, but an increase of a factor of 5–10 is expected. A significant contribution to the radiation damage of the sensors in the tracker volume is due to backscattered neutrons. Simulations show that the neutron flux equals the charged particle flux emerging from the interactions at a radial distance of about 25 cm from the beam axis. Irradiation with neutrons are therefore a necessary test for proving the ability of prototype silicon detectors to survive the SLHC fluences. Short strip microstrip detectors made on p-type silicon substrate for optimised radiation hardness have been irradiated with fast neutrons to various fluences up to 3 × 10 15 cm - 2 . They have been characterised in term of charge collection efficiency with LHC speed electronics (40 MHz). The results are here presented in the light of a possible upgrade scenario of the ATLAS tracker.

Validation of Synthetic Diamond for a Beam Condition Monitor for the Compact Muon Solenoid Experiment

The CERN Large Hadron Collider (LHC) will collide two counter rotating proton beams. The energy stored in each beam is about 350 MJ. If there is a failure in an element of the accelerator, the resulting beam losses could cause damage not only to the accelerator itself, but also to the physics experiments installed. Within the Compact Muon Solenoid experiment (CMS), the use of a Beam Condition Monitor (BCM) is planned to monitor a possible fast increase of the particle flux near the interaction point. The system will flag the onset of adverse beam conditions within the CMS experiment, and, if necessary, input into the beam abort system of the LHC requesting a fast beam dump. Constraints on BCM design from radiation hardness, a minimal material and services budget, and the need for fast signals from sensors with high sensitivity and a large dynamic range, have led to the investigation of synthetic chemical vapor deposited (CVD) diamond for the BCM sensor. In a 5 GeV hadron beam the response of CVD diamonds was tested in fluxes ranging from single minimum ionizing particles (MIPs) to 108 MIPs per cm2, delivered over 40 ns. The signal response, linearity, and stability of both un-irradiated and irradiated sensors were tested over this flux range, and will be presented herein. The results confirm the applicability of CVD diamond for this beam monitoring application

ATLAS diamond Beam Condition Monitor

The ATLAS experiment has chosen to use diamond for its Beam Condition Monitor (BCM) given its radiation hardness, low capacitance and short charge collection time. In addition, due to low leakage current diamonds do not require cooling. The ATLAS Beam Condition Monitoring system is based on single beam bunch crossing measurements rather than integrating the accumulated particle flux. Its fast electronics will allow separation of LHC collisions from background events such as beam gas interactions or beam accidents. There will be two stations placed symmetrically about the interaction point along the beam axis at z = ± 183.8 cm . Timing of signals from the two stations will provide almost ideal separation of beam–beam interactions and background events. The ATLAS BCM module consists of diamond pad detectors of 1 cm 2 area and 500 μ m thickness coupled to a two-stage RF current amplifier. The production of the final detector modules is almost done. A S / N ratio of 10:1 has been achieved with minimum ionizing particles (MIPs) in the test beam setup at KEK. Results from the test beams and bench measurements are presented.

Minimum Ionizing Particle Detector Based on p&lt;sup&gt;+&lt;/sup&gt;n Junction SiC Diode

In this work ion-implanted p+/n diodes have been used as minimum ionizing particle (MIP) detectors. The diode structure is based on a 0.45 $m deep, NA = 4×1019 cm-3 doped p+ anode, ion implanted in an n-type epilayer with thickness equal to 55 $m and nominal donor doping ND = 2×1014 cm-3. The diode breakdown voltages were above 1000V. At 1000V reverse bias the diode leakage current was of the order of 1 nA. The punch through depletion voltage was nearing the range 220-250 V. The charge collection efficiency to minimum ionizing particle was investigated by a 90Sr β source. The pulse height spectrum was measured as a function of the reverse voltage in the range 0-605 V. At each bias point the signal was stable and reproducible, showing the absence of polarization effects. At 220 V the collected charge was 2970 e- and saturated at 3150 e- near 350 V. At the moment, this is the highest collected charge for SiC detectors. At bias voltages over 100V the spectrum was found to consist of two peaks clearly separated. Around 250 V the signal saturates, in agreement with CV results.

Radiation hardness after very high neutron irradiation of minimum ionizing particle detectors based on 4H-SiC p/sup +/n junctions

In this work we analyzed the radiation hardness of SiC p/sup +/ n diodes used as minimum ionizing particle (MIP) detectors after very high 1 MeV neutron fluences. The diode structure is based on ion implanted p/sup +/ emitter in an n-type epilayer with thickness equal to 55 /spl mu/m and donor doping N/sub D/=2/spl times/ 10/sup 14/cm/sup -3/. The diode breakdown voltages were above 1000 V. At 1000 V the leakage currents are of the order of 1 nA for all the measured diodes. The full depletion voltage is near 220-250 V. The charge collection efficiency to minimum ionizing particle has been investigated by a /sup 90/Sr /spl beta/ source. At 250 V the collected charge of the unirradiated diodes saturates near 3000 e/sup -/. At bias voltages over 100 V the energy spectrum of the collected charge was found to consist of a signal peak well separated from the noise. At around 250 V the signal saturates, in agreement with CV results. These devices have been irradiated at 6 different fluences, logarithmically distributed in the range 10/sup 14/-10/sup 16/ (1 MeV) neutrons/cm/sup 2/. The leakage current after irradiation decreases. The collected charges decrease for increasing fluences, remaining very high only until some 10/sup 14/ n/cm/sup 2/.