Physics and Engineering of Radiation Detection
176 Chapter 3. Gas Filled Detectors r 0 −+ Cathode a Anode Figure 3.4.7: Production of an electron ion pair in a cylindrical ion ...
3.4. Ionization Chambers 177 To determine the total change in potential we must addV−andV+together. V = V−+V+ = − Q 2 πl ln [ a ...
178 Chapter 3. Gas Filled Detectors 3.4.D SpecialTypesofIonChambers................. Ionization chambers are perhaps the most wi ...
3.4. Ionization Chambers 179 charge pairs are always produced near the cathode (which in this case is actually the grid). Hence ...
180 Chapter 3. Gas Filled Detectors filled with some conventional gas. In commercially available chambers the boron is enriched ...
3.4. Ionization Chambers 181 i 1 iout=i 1 −i 2 i 2 +− +− HV HV − −+ α+−+−+ + − − + + − − + + − Boron + − Neutron γ Li Figure 3.4 ...
182 Chapter 3. Gas Filled Detectors affect their performance. This is true for at least the low resolution systems working in mo ...
3.5. Proportional Counters 183 Vout + − Eb Ea a r b E (a) a b Cathode Anode (b) (c) Figure 3.5.1: (a) Schematic of a cylindrical ...
184 Chapter 3. Gas Filled Detectors whereMis the multiplication factor, which for typical chambers lies between 10^3 - 104. Sinc ...
3.5. Proportional Counters 185 Ec rc Ea Eb a r b Electric Field Intensity Cathode Anode Avalanche Region Figure 3.5.2: Depiction ...
186 Chapter 3. Gas Filled Detectors Also, if we substituter=rc in equation 3.5.1, we will get an expression for the critical fie ...
3.5. Proportional Counters 187 For argonDα=1. 81 × 10 −^17 cm^2 /V(see Table 3.3.1) and its molecular number density can be calc ...
188 Chapter 3. Gas Filled Detectors 3.5.B ChoiceofGas........................... As with ionization chambers, virtually any gas ...
3.5. Proportional Counters 189 used noble gas in proportional counters is argon mainly because of its lower cost as compared to ...
190 Chapter 3. Gas Filled Detectors charge of positive ions gets accumulated near the cathode. These ions attract free electrons ...
3.6. Geiger-Mueller Counters 191 possible energies (2.31MeVand 2.79MeV). n+B^105 →Li^73 +α Theα-particle thus produced has a ver ...
192 Chapter 3. Gas Filled Detectors 2.31MeV 2.79MeV 2.31MeV 2.79MeV Energy Bins Noise + Background Events per Energy Bin Energy ...
3.6. Geiger-Mueller Counters 193 γuv γuv γuv γuv γuv γuv γuv e e e Incident Localized Avalanche Radiation e HV Signal Anode Cath ...
194 Chapter 3. Gas Filled Detectors 3.6.B DeadTime The physical process of a Geiger breakdown takes some time to subside in a GM ...
3.6. Geiger-Mueller Counters 195 Example: A GM detector having an efficiency of 67% is placed in a radiation field. On the avera ...
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