tailieunhanh - Lesson: Gas-filled detectors

Gas-filled detectors display content Structure of gas-filled detectors, onization and excitation of counting gas, Recombination processes, Recombination processes, charge collection and DC ion chambers,. invite you to refer | HUVINETT 2012 Gas-filled detectors Gaseous or gas-ionization: Gas-filled detectors ionization chamber proportional counter Nuclear measuring methods Geiger-Müller (GM) tube Lecture 2 First electronic sensor measuring ionization radiation Dr. Imre Szalóki Simple structure, low cost associate professor Head of Department of Nuclear Energetics Suitable to measure any kind of ionizing radiation (α, β, γ) Development: first half of the 20th. century Budapest University of Technology and Economics Institute of Nuclear Techniques (BME NTI) Nuclear measuring methods Lecture 2 1 Dr. Imre Szalóki., BME NTI Nuclear measuring methods Lecture 2 2 Dr. Imre Szalóki., BME NTI Ionization and excitation of counting gas Structure of gas-filled detectors Ionization, atomic/molecular excitation processes Electronic signal Average number of pairs + statistical fluctuation + 2 Molecule ions He + He → He + e Characteristic: Uanode-output current/pulse ~ 20 - 40 eV/ion − eEntrance window Anode wire Nuclear measuring methods Lecture 2 eGas eα e- e Output signal Cathode Dr. Imre Szalóki., BME NTI 3 Nuclear measuring methods Lecture 2 Dr. Imre Szalóki., BME NTI 4 Recombination processes, charge collection Recombination processes Mobility of charges µ = Electron capture dn + dn − = = −α n + n − dt dt E=0 3 [α ] = 10 − 10 cm s −6 −8 Pressure Interaction between positive ions and negative ions Electron capture : O2 , H2O. ; He, Ne, Ar. (Hgmm·103) − m Drift-velocity of ions ≈ 1 m/s (1bar, 104 V/m) Drift-velocity of electrons ≈ 104 m/s Vdrift 105 [m/s] diffusion, drift, Avalanche effect Gain effect secondary, tertiary ionization gas multiplication M= n = e λx n0 5 Variation of number of generated ion-electron pair in gaseous ionization detectors Nuclear measuring methods Lecture 2 Dr. Imre Szalóki., BME NTI E/p٠105 [Vm/bar] 6 DC ion chambers Time constant of the integration Geometry: cylinder, wire system Radiation: constant .