Particle Physics Reference Library

Others are in the form of an original contribution supplemented by a detailed appendix relating to recent developments in the field. Great progress has been made over the past three decades in understanding the microcosm.

The Interaction of Radiation with Matter

Introduction

The integrated cross-section (zero moment), multiplied by the atomic density N, corresponds to the charged particle's inverse mean free path λ−1 or, in other words, the average number of collisions per track length unit. Due to the stochastic nature of the interaction process, the number of collisions and the sum of energy losses along a particle track are subject to fluctuations.

Photon Interactions

Photoabsorption
Compton Scattering
Pair Production

The energy transfer from the incident particle to the electrons of the medium typically leads to excitation and ionization of the target atoms. The kinetic energy T =E−E that is transferred to the electron is the largest for a head-on collision (θ =π) and the energy spectrum of the recoil electrons consequently shows a cut-off point (Compton edge) at.

Fig. 2.2 Photoabsorption cross sections of argon (solid curve) and neon (dashed curve) as a function of the photon energy E [25, 26]

Interaction of Heavy Charged Particles with Matter

Dielectric Theory
Bethe-Fano Method
Fermi Virtual-Photon (FVP) Method
Integral Quantities

Stopping Power

In the intermediate range, Q1< Q < Q2, numerical calculations of the general oscillator power density are used. Due to the more detailed (and more realistic) modeling of the general oscillator strength density at intermediate Q, the Bethe-Fano algorithm can be expected to be more accurate than the FVP method.

Fig. 2.5 Generalized oscillator strength density for Si for an energy transfer E = 48 Ry to the 2p-shell electrons [41–44], as function of ka 0 (where k 2 a 2 0 = Q/Ry)

Electron Collisions and Bremsstrahlung

Bremsstrahlung

In addition to M0, M1, Table 2.2 also includes the most probable value of the power loss spectrum in an 8μm thick silicon layer. Due to the asymmetric shape of the differential cross section dσ/dE, the most probable value of the energy loss distribution is usually significantly smaller than the average energy loss = M1x.

Table 2.2 Integral properties of collision cross sections for Si calculated with Bethe-Fano (B-F) and FVP algorithms

Energy Losses Along Tracks: Multiple Collisions and Spectra

Monte Carlo Method
Convolutions
Laplace Transforms
Examples
Methods for Thick Absorbers

The collision energy loss is then sampled by drawing another uniform random variable u∈[0,1] and determining the corresponding energy loss E from the inverse cumulative distribution. As can be seen in Figures 2.11 and 2.12, the characteristics of the differential cross section dσ/dE are clearly visible in the stretching functions f (, x).

Fig. 2.9 Distributions f (n) of the energy loss in n collisions (n-fold convolution of the single- single-collision energy loss spectrum) for Ar/CH 4 (90:10)

Energy Deposition

Atomic Relaxation
Ionisation Statistics
Range

Measurements of W for electrons in gases as a function of the initial kinetic energy of the electron are reported in Refs. In the literature, there are a number of different definitions of "range", two of which - the fractional ionization range Rx and the practical range Rp - are illustrated in Fig.2.17.

Fig. 2.15 After the ejection of an inner-shell electron, the resulting vacancy is filled by an electron from a higher shell

67. Stopping power for electrons and positrons, International Commission on Radiation Units and Measurements, Washington, DC, 1979, ICRU Report 37. 101. Average energy required to produce an ion pair, International Commission on Radiation Units and Measurements, Washington, DC, 1979, ICRU Report 31.

Scintillation Detectors for Charged Particles and Photons

Lecoq

Basic Detector Principles and Scintillator Requirements

Interaction of Ionizing Radiation with Scintillator Material
Important Scintillator Properties
Scintillator Requirements for Various Applications
Organic Material, Glass and Condensed Gases

Scintillation and Quenching Mechanisms in Inorganic Scintillators

The Five Steps in Scintillation Process
Scintillation Efficiency
Response Linearity and Energy Resolution
Scintillation Kinetics and Ultrafast Emission Mechanisms

Role of Defects on Scintillation Properties

It is related to the rate of decrease of the population of excited luminescent centers. The radiation strength of the scintillation mechanism is related to the strong electrostatic field of the crystal. Most scintillation materials can be used depending on the energy range of the detected γ-radiation.

One contribution to the energy resolution is the statistical variation of the number of photoelectrons, npe, produced in the photodetector. Another important loss is related to the transfer of excitations to the luminescent centers. In the opposite case, a reduction of the scintillation yield can be expected when the temperature increases (temperature quenching).

However, the light response may differ due to the non-linear response of the scintillator.

Fig. 3.1 Energy dependence of photon total cross sections in Lead (from Particle Data Group)

Point Size Defects
Impurities
Impact of Defects on Optical Properties

Charge Carrier Traps

Radiation Damage
Crystal Engineering. Impact of New Technologies
Table of Commonly Used Scintillators

This energy trapped in the Pr or Tb sites decays non-radiatively in the presence of the Eu3+ ion. Defects generally have energy levels in the forbidden band, which reduce the optical transparency of the crystal. There is almost a continuum of such levels, reducing the optical transparency window of the crystal.

Figure 3.17 shows the radiation-induced absorption coefficient spectrum for PWO crystals as a function of accumulated 60Co dose. For most known scintillators, the concentration of such defects at the ppm level can result in a radiation-induced absorption coefficient limited to about 1 m−1. The induced absorption coefficient μ resulting from irradiation is proportional to the concentration of absorption centers N via μ=σN, where σ is the cross section of the absorption center.

3 Scintillation Detectors for Charged Particles and Photons 83 related to structural defects, impurities, and anion or cation vacancies caused by differential evaporation of chemical components during crystal growth.

Table 3.1 Calculated optical absorption band of H s , O s –

Gaseous Detectors

Introduction

In the second half of the 1940s, however, the demand for faster counters with a longer lifetime and higher sensitivity started a move towards scintillation techniques, which experienced rapid development, especially after the introduction of the photomultiplier, which soon provided fast response and time resolutions below 10−8s. The following decades saw a rapid development of the techniques, especially in high-energy physics but also for nuclear physics and other fields. Most of the detector developments have only been made possible by the extremely rapid progress in the field of electronics, with regard to miniaturization, integration density, cost and radiation hardness.

Powerful simulation programs have been developed in recent decades and have been widely used in the development and optimization of gas detectors. The development of recent years can be well followed in the Proceedings of the Vienna Conference on Instrumentation which was initiated in 1977 as Wire Chamber Conference on a triennial basis [18] and of the annual IEEE Nuclear Science Symposia. The following sections will begin with a description of the basic processes in gas detectors: ionization of the gas by charged particles (Sect.4.2.1), transport of electrons and ions in electric and magnetic fields (Sect. 4.2.2), avalanche amplification in high electric fields (Sect.4.2.3), formation of the.4.4 signals (Sect.4 readout) and '. diation (Sec.4.2.6).

4 Gaseous Detectors 93 of the main directions of detector design and performance follow in Section 4.3: Single-Wire Tubes (Sec. 4.3.1), Multi-Wire Proportional Chamber (Sec.

Basic Processes

Gas Ionization by Charged Particles

Primary Clusters
Total Number of Ion Pairs
Dependence of Energy Deposit on Particle Velocity

Transport of Electrons and Ions

Drift Velocities
Electron Attachment

Avalanche Amplification

Operation Modes
Gas Gain
Dependence of Amplification on Various Factors
Statistical Fluctuations of the Amplification

Signal Formation
Limits to Space Resolution

Drift Time Measurement

Ageing of Wire Chambers

Due to the random nature of the collisions, the individual drift velocity of an electron or ion deviates from the average. In each direction from the cloud center is the mean squared deviation of the electrons. In addition, the effects of space charge will depend on the track angle relative to the wire and on the density of the primary ionization.

In the narrow transition zone one finds a rapid change in the ratio of transmission/proportional signal speeds. The increase in ionization is obviously proportional to the gas density p and depends on the ionization cross sections, which are a function of the instantaneous energy ε of the electrons. The eminence is equal to the ionization energy of the gas molecules divided by the mean free path between collisions.

The rms width of the induced charge distribution is comparable to the anode-cathode gap.

Table 4.1 Properties of gases at 20 ◦ C, 1 atm

Detector Designs and Performance .1 Single Wire Proportional Tubes

Multiwire Proportional Chambers (MWPC)
Drift Chambers

Planar Geometries
Cylindrical Geometries
Time Projection Chambers (TPC)

Parallel Plate Geometries, Resistive Plate Chambers (RPCs)
Micropattern Devices
Gas Electron Multiplier (GEM)
Micromegas

The change of the electron drive in a magnetic field in a similar cell is indicated on the right. Sometimes relative timing with readout from both ends of the wire is used, again providing a resolution of about 1% of the wire length. The avalanche position along the wires is obtained from measuring the center of gravity of pulse heights from pads of the segmented cathode below.

A charge deposited locally on this resistive layer takes time τ ≈ρε to be removed, where ε is the permittivity of the resistive plate. By reducing the size of the gas gap to 0.1 mm and operating the detector at a pressure of 12 bar, a time resolution of 27 ps was achieved with this detector [67]. Figure 4.28b shows the geometry used for the ALICE time-of-flight system.

The rate limit of the RPC is reached at the point where the effective voltage across the gas gap moves beyond the efficiency plateau.

Fig. 4.16 ATLAS MDT drift tubes: space resolution as function of impact radius and background rates

Outlook

To increase the resistance to discharges for these very large surfaces, resistive strips are placed over the read strips at a distance of 64μm. Charpak et al., Using multiwire proportional counters to select and localize charged particles, Nucl. Aielli et al., Layout and performance of the RPCs used in the Argo-YBJ experiment, Nucl.

Kuger et al., Performance Studies of the Resistive Micromegas Detectors for the Upgrade of the ATLAS Muon Spectrometer, NIMA. Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link for Creative Commons licenses, and indicate. The images or other third-party materials in this chapter are included in the chapter's Creative Commons license, unless otherwise indicated in a credit line for the material.

If material is not included in the chapter's Creative Commons license and your intended use is not permitted by law or exceeds the permitted use, you must obtain permission directly from the copyright holder.

Solid State Detectors

Lutz and R. Klanner

Introduction
Basic Detection Process of Single Photons in Semiconductors
Basics of Semiconductor Physics
Radiation Damage
Semiconductor Detector Principles

Reverse Biased Diode (as Used in Strip and 3-D Detectors)
Semiconductor Drift Chamber
DEPFET Detector-Amplification Structure

Silicon Strip Detectors (Used in Tracking)

Strip Detector Readout
Strip Detectors with Double-Sided Readout
Strip Detectors with Integrated Capacitive Readout Coupling and Strip Biasing

Detector Front-End Electronics

Operating Principles of Transistors
The Measurement of Charge
Integrated Circuits for Strip Detectors

Silicon Drift Detectors

Linear Drift Devices
Radial and Single Side Structured Drift Devices

Charge Coupled Devices

MOS CCDs
Fully Depleted pn-CCDs
CCD Applications

Active Pixel Detectors

Hybrid Pixel Detectors
Monolithic Active Pixel Sensors (MAPS)
DEPFET Active Pixel Sensors

Detectors with Intrinsic Amplification

Avalanche Diode
Low Intensity Light Detection
Solid-State Photo Multipliers: SiPMs

In intrinsic (unoccupied) semiconductors only a small fraction of the electrons in the valence band are thermally excited into the conduction band. Active electrical defects have three main consequences for detectors: (1) increasing the dark current, (2) blocking signal charges thereby reducing charge collection, and (3) changing the electric field in the space charge region from which the signal charge is collected. As the signal charge arrives at the then+anode, the amount of charge and time of arrival can be measured.

As shown in Fig.5.8, it is possible to segment the electrodes on both sides of the wafer. Disruption of the electron layer by a suitable biased (negative with respect to then strips) MOS structure (Fig.5.9d). Readout in most cases uses large-scale integrated (LSI) electronics tailored to the needs of the special application.

Note that the serial noise is generated in the amplifier, the influence of the detector is only due to the capacitive load at the input of the amplifier. It is advisable to match the pixel size to the properties of the rest of the system. Electrons produced below the n+p junction (and holes produced above the junction) will pass through the high field region of the junction as they float in the electric.