The physics of radiation damage in particle detectors

Intense high-energy particle beams cause damage to semiconductor detectors and signal-conditioning electronics by displacement and long-term ionization effects. While first-principles prediction of effects are not practical, the magnitude of each effect can be scaled approximately between particle energy and type by using an appropriate scaling parameter.     

Development of radiation hard edgeless detectors with current terminating structure on p-type silicon

The development of edgeless Si detectors was stimulated by the tasks of the total pp cross-section study in the TOTEM experiment at the Large Hadron Collider at CERN. For this, the dead region at the detector diced side should be reduced below 50 μm. This requirement is successfully realized in edgeless Si detectors with current terminating structure (CTS), which are now operating at LHC. The development of the experiment and future LHC upgrade need the elaboration of radiation hard version of edgeless Si detectors. The current investigation represents an extension in understanding on edgeless detectors operation and development of a new issue - edgeless detectors with CTS on p-type Si.     

Further results from the CDMS experiment

The Cryogenic Dark Matter Search experiment utilizes discriminating detectors where both the recoil energy and ionization produced by each particle event are simultaneously measured. Here we present our latest results from operating 4 Ge (4×250 g) and 2 Si (2×100 g) detectors at the shallow Stanford site. Our new WIMP exclusion limit excludes new parameter space for low-mass WIMPS.     

Investigation of Ni/4H-SiC diodes as radiation detectors with low doped n-type 4H-SiC epilayers

The development of SiC minimum ionising particle (MIP) detectors imposes severe constrains in the electronic quality and the thickness of the material due to the relatively high value of the energy required to produce an electron–hole pair in this material by MIP against the value for Si. In this work, particle detectors were made using semiconductor epitaxial undoped n-type 4H-SiC as the detection medium. The thickness of the epilayer is on the order of 40 μm and the detectors are realised by the formation of a nickel silicide on the silicon surface of the epitaxial layer (Schottky contact) and of the ohmic contact on the back side of 4H-SiC substrate. The low doping concentration (6×10¹³ cm⁻³) of the epilayer allows the detector to be totally depleted at relatively low reverse voltages (100 V). We present experimental data on the charge collection properties by using 5.486 MeV -particles impinging on the Schottky contact. A 100% charge collection efficiency (CCE) is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the -particle extrapolated range in SiC. The diffusion contribution of the minority change carriers to CCE is pointed out. By comparing measured CCE values to the outcomes of drift–diffusion simulation, values are inferred for the hole lifetime within the neutral region of the charge carrier generation layer.     

Concept of Double Peak electric field distribution in the development of radiation hard silicon detectors

The concept of Double Peak (DP) electric field distribution is considered for the analysis of operational characteristics of irradiated silicon detectors. The key point of the model is trapping of equilibrium carriers to the midgap energy levels of radiation-induced defects, which leads to a non-uniform distribution of space charge concentration with positively and negatively charged regions adjacent to the p⁺ and n⁺ contacts, respectively. In our new development of the DP model we consider a non-depleted base region in between the space charge regions as a high resistivity bulk, which operates as a drift region with a non-negligible electric field. Electric field characteristics of detectors processed from n-type MCZ Si wafers using various technological procedures, and irradiated by 1 MeV neutrons and 24 GeV/c protons, have been compared. Electric field profiles have been reconstructed from DP pulse response of heavily irradiated detectors and calculated by the simulation of DP electric field distribution caused by carrier trapping. It is shown that detectors from n-type MCZ Si irradiated by 24 GeV/c protons do not show typical space charge sign inversion up to the irradiation fluence of about 2.2×10¹⁵ p/cm² and the region with a positive charge dominates over a negatively charged region.     

New BNL 3D-Trench electrode Si detectors for radiation hard detectors for sLHC and for X-ray applications

A new international-patent-pending (PCT/US2010/52887) detector type, named here as 3D-Trench electrode Si detectors, is proposed in this work. In this new 3D electrode configuration, one or both types of electrodes are etched as trenches deep into the Si (fully penetrating with SOI or supporting wafer, or non-fully penetrating into 50-90% of the thickness), instead of columns as in the conventional (“standard”) 3D electrode Si detectors. With trench etched electrodes, the electric field in the new 3D electrode detectors are well defined without low or zero field regions. Except near both surfaces of the detector, the electric field in the concentric type 3D-Trench electrode Si detectors is nearly radial with little or no angular dependence in the circular and hexangular (concentric-type) pixel cell geometries. In the case of parallel plate 3D trench pixels, the field is nearly linear (like the planar 2D electrode detectors), with simple and well-defined boundary conditions. Since each pixel cell in a 3D-Trench electrode detector is isolated from others by highly doped trenches, it is an electrically independent cell. Therefore, an alternative name “Independent Coaxial Detector Array”, or ICDA, is assigned to an array of 3D-Trench electrode detectors. The electric field in the detector can be reduced by a factor of nearly 10 with an optimal 3D-Trench configuration where the junction is on the surrounding trench side. The full depletion voltage in this optimal configuration can be up to 7 times less than that of a conventional 3D detector, and even a factor of two less than that of a 2D planar detector with a thickness the same as the electrode spacing in the 3D-Trench electrode detector. In the case of non-fully penetrating trench electrodes, the processing is true one-sided with backside being unprocessed. The charge loss due to the dead space associated with the trenches is insignificant as compared to that due to radiation-induced trapping in sLHC environment. Since the large electrode spacing (up to 500 μm) can be realized in the 3D-Trench electrode detector due to their advantage of greatly reduced full depletion voltage, detectors with large pixel cells (therefore small dead volume) can be made for applications in photon science (e.g. X-ray).     

Developing Si(Li) nuclear radiation detectors by pulsed electric field treatment

Fabrication of Si(Li) nuclear radiation detectors using lithium ion drift under the action of a pulsed electric field is considered. Optimum treatment regime parameters are determined, including the pulse amplitude, duration, and repetition rate. Experimental data are presented, which show that the ion drift in a pulsed electric field decreases the semiconductor bulk compensation time by a factor of two to four and significantly increases the efficiency of detectors.

     

Superconductive granule for radiation detectors: Transition time from the normal state

A simple thermodynamic model is developed for the evaluation of the transition time from the normal state of a superconducting sphere in which superconductivity has been quenched by the energy release of an ionizing radiation. This represents a determining step in the recovery time process of granule array systems employed as radiation detectors.     

Water equivalent plastic scintillation detectors in radiation therapy

A review of the dosimetric characteristics and properties of plastic scintillation detectors for use in radiation therapy is presented. The detectors show many desirable qualities when exposed to megavoltage photon and electron beams, including water equivalence, energy independence, reproducibility, dose linearity, resistance to radiation damage and near temperature independence. These detectors do not require the usual conversion and/or correction factors used to convert the readings from common dosemeters to absorbed dose. Due to their small detecting volume, plastic scintillation detectors exhibit excellent spatial resolution. Detector performance, in certain specific cases, can be affected by radiation-induced light arising in the optical fibres that carry the scintillator signal to a photodetector. While this effect is negligible for photon beams, it may not be ignored for electron beams and needs to be accounted for.     

Low radiation level detection with room temperature InAs detector

Recently, room temperature or near room temperature InAs detectors are widely used in laser warning receivers, process control monitors, temperature sensors, etc. requiring linear operation over many decades of the sensitivity range. The linearity of zero biased Si, InGaAs and Ge detectors is thoroughly discussed in the literature, contrary to InAs detectors. In an earlier work of the authors it has been demonstrated that applying a bootstrap circuit to a Ge detector – depending on the frequency of the operation – will virtually increase the shunt resistance of the detector by 3–6 decades compared to the detector alone. In the present work, a similar circuitry was applied to a room temperature InAs detector, the differences between the bootstrapped Ge and bootstrapped InAs detector are underlined. It is shown, how the bootstrap circuit channels the photogenerated current to the feedback impedance decreasing with many decades the detectable low level limit of the detector – I/V converter unit. The linearity improvement results are discussed as a function of the chopping frequency, calculated and measured values are compared, the noise sources are analyzed and noise measurement results are presented.     

Magnetic coupling properties of multiple metal wear particles for high-precision electromagnetic debris detection applications

The electromagnetic wear particle detector is one of effective method to monitor wear debris in lubricating oil for assessing the wear condition of mechanical equipment. However, the motion of wear particles, especially the aggregation behavior in both fluid field and magnetic field, may make the particle detector generate false wear signals. Therefore, to estimate the impact on the detection accuracy of wear debris by the particle aggregation effect, the magnetic coupling model of multiple wear particles is established for studying the magnetic coupling effect between adjacent metal particles. The research results show that the effect changes the total magnetic energy variation induced by the particles and then affects the amplitude of particle signal. Meanwhile, the variation degree is closely associated with the frequency of magnetic field of particle detectors. Overall, the aggregation of wear particles with the same magnetic properties (both ferromagnetic or non-ferromagnetic) leads to false alarms of particle detectors; and the aggregation of wear particles with different magnetic properties causes missing alarms of particle detectors. Meanwhile, increasing the field frequency may increases the probability of missing alarm failure of particle detectors.     

400～1700 nm绝对光谱响应度校准和量值传递

介绍了高准确度光辐射功率校准原理和方法,利用低温辐射计作为主标准器,以陷阱探测器作为传递标准,激光器作为光源,通过激光功率稳定装置,校准了硅陷阱探测器和铟镓砷陷阱探测器的绝对光谱响应度。选取476.1, 488, 514.7, 521, 568, 632.8, 647.1, 785, 852, 980, 1064, 1550,nm共12条谱线完成了校准实验,绝对光谱响应度测量不确定度均优于0.05%。通过量子效率模型得出了硅陷阱探测器的绝对光谱响应曲线。利用InGaAs陷阱探测器分立波长点的绝对光谱响应度与相对光谱响应曲线进行了验证分析。结果表明,2种陷阱探测器均可用作传递标准进行高准确度的可见光和近红外光辐射功率校准和量值传递。     

Tensile damage stages in cast A356-T6 aluminium alloy

Abstract

This paper reports an investigation of the damage stages during straining of A356-T6 alloy by means of quantitative metallography, tensile tests, in situ tensile tests, and in situ micro-extensometry experiments with a SEM. Quantitative analysis of the microstructure and the damage mechanisms have identified the eutectic spatial arrangement as the crucial feature in fracture; interdendrite fine eutectics (eutectic channels) and extended eutectic zones (eutectic clusters) play different roles, so that the Si particle breaking rate varies from one region to another. The current models of Si particle breaking were then checked and their predictions compared with the local cracking rates. None of them were consistent with the experimental results. Next, cavity growth was investigated and the experimental results compared with data reported in literature and with predictions obtained by the Rice and Tracey law. It was shown that the initial porosity generated by Si particle breaking was very low and that void growth calculations completely underestimate void growth rate; once more, the specific role of Si particles spatial arrangement was decisive. Lastly, the analysis of the fracture stage revealed that cracks mostly propagate along the interdendritic channels, and this indicates the localisation of the damage, thus invalidating the ductility predictions of current fracture models.     

Damage observed in silicon diodes after low energy pion irradiation

We present results of irradiation tests performed in the pion beam of the Paul Scherrer Institute. Our results confirm the prediction, that the Δ-resonance is reflected as an enhancement of the damage caused by low energy pions. At the peak of the Δ-resonance we measure a damage constant 1.5 times higher than generally adopted for neutrons and high energy protons. This result means that the lifetime of silicon detectors close to the vertex at LHC experiments will be limited by the pion background. We predict type inversion of high resistivity detectors to occur after two months of full luminosity and the depletion voltage to reach 200 V within the first four years, even if the detectors are operated at 0°C.     

Silicon strip detectors with capacitive charge division

Measurements of the behaviour of various high-resolution silicon strip detectors with capacitive charge division have been made in a high-energy particle beam. The results are compared with an electrostatic model which calculates the charges deposited on the strips after the passage of a minimum ionizing particle. Good agreement is found and the model is used to propose a method of improving the charge-division properties of such detectors.     

High-performance silicon photonics technology for telecommunications applications

By way of a brief review of Si photonics technology, we show that significant improvements in device performance are necessary for practical telecommunications applications. In order to improve device performance in Si photonics, we have developed a Si-Ge-silica monolithic integration platform, on which compact Si-Ge–based modulators/detectors and silica-based high-performance wavelength filters are monolithically integrated. The platform features low-temperature silica film deposition, which cannot damage Si-Ge–based active devices. Using this platform, we have developed various integrated photonic devices for broadband telecommunications applications.     

Variations observed in environmental radiation at ground level

To investigate and monitor environmental radiation at ground level, Physikalisch-Technische Bundesanstalt (PTB) has installed several dosemeters and particle detectors at the new Ambient Radiation Dosimetry Site. The separation of the total ambient dose equivalent rate H*10(env) of environmental radiation into the different contributions is achieved by comparing the data of different detectors: the muon detector MUDOS, a modified neutron dosemeter, proportional counters and ionisation chambers. The response of the latter two dosemeter systems to cosmic radiation was determined at the Cosmic Radiation Dosimetry Site on a lake near PTB. Besides the increase of the ambient dose equivalent rate during rainfall, variations owing to air pressure, solar activity and temperature changes in the upper atmosphere are observed. Without rain and solar effects, smooth variations of the cosmic component at ground level of +/-6.9 nSv h(-1) should be treated as naturally occurring variations during an entire year.     

Silicon detectors in electromagnetic and hadronic calorimetry

A review of investigations performed by SICAPO collaboration at CERN and Si/W and Si/U sandwich calorimeters employing silicon detectors as active medium is presented. Experimental results, such as the response of sensed energy versus incoming electron energy and depleted layer width, of the longitudinal and lateral development of electromagnetic showers and of the energy resolution, are described. Mosaic modules of silicon detectors, which enable the construction of silicon sampling hadronic calorimeters, are also given. A comparison of results from SICAPO, Hamburg (Si/Pb) and from Tokyo (Si/Pb and Si/W) calorimeters is shown.     

Applications of silicon detectors in high energy physics and astrophysics

Silicon detectors are being increasingly used in high energy physics and in astronomy. In the former case they are used for precisely locating the trajectories of particles which traverse the detectors, while in the latter case they are used for very low level light imaging. In both applications, the use of silicon is preferred because of the low energy needed to liberate an electron-hole pair in the medium and because of the highly developed planar technology which allows sophisticated devices with excellent spatial precision to be fabricated.The specific devices discussed are microstrip detectors and 2-dimensional imaging CCDs, including a summary of radiation damage since this is of importance in both the astronomical and particle physics applications.     

In-situ Observation of Tensile Fracture in A357 Casting Alloys

The mechanism of damage evolution and fracture in A357 casting alloys was investigated by in-situ scanning electron microscopy （SEM） tensile testing. Different microstructures of A357 casting alloys were produced by eutectic Si modification and T6 heat treatment. It is shown that microcracks in these alloys are predominantly formed in eutectic Si particles. Large and elongated eutectic Si particles in unmodified alloy show the greater tendency to cracking, whereas cracking of small and round eutectic Si particles in Sr modified and T6 heat treated alloys is relatively lag. The crack mainly propagates along the broken eutectic Si particles in unmodified and Sr modified alloys or along the deepened shear bands in T6 heat treated alloy with accumulating the applied strain. The results were discussed in terms of Weibull statistics and the fracture models were established.