Interactions of Particles/Radiation with Matter ESIPAP : European School in Instrumentation for Particle and Astroparticle Physics Lucia Di Ciaccio - ESIPAP IPM - January 2018 1 Non-exhaustive list of « Particles/Radiation » and « Matter » PARTICLES RADIATION 4 • 2He α radiation MATTER • e ± β± radiation • γ e.m, X, γ radiation • μ, γ, e±, π, ν ,p … cosmic radiation PARTICLES <--> RADIATION 2 aspects of the same « entity » De Broglie relation λ = h/p ( h = Planck constant) MATTER PET • detectors ( research, medical app.,..) • humain tissus/body ( medical app.) • electronic circuits • Louvre paintings • beauty cream, potatos, … Lucia Di Ciaccio - ESIPAP IPM - January 2018 2 Motivation § The interaction between particles & matter is at the base of several human activities § Plenty of applications not only in research and not only in Particle & Astroparticle Very important for particle detection ! § In order to detect a particle, the latter must interact with the material of the detector, and produce ‘a (detectable) signal’ Charged particle electrical signal + - + - + - gas Charged particle photodetector The understanding of particle detection requires the knowledge of the Interactions of particles & matter 3 Lucia Di Ciaccio - ESIPAP IPM - January 2018 Brief outline and bibliography Two lectures + two tutorials § Interaction of charged particles « heavy » (mPa >>me ) « light » (mPa ~ me ) § Interaction of neutral particles Photons Neutral Hadrons: n, π0, … § Radiation detection and measurement, G.F. Knoll, J. Wiley & Sons § Experimental Techniques in High Energy Nuclear and Particle Physics, T. Ferbel, World Scientific § Introduction to experimental particle physics, R. Fernow, Cambridge University Press § Techniques for Nuclear and Particle Physics Experiments , W.R. Leo, Springer-Verlag § Detectors for Particle radiation, K. Kleinknecht, Cambridge University Press § Particle detectors, C. Grupen, Cambridge monographs on particle physics § Principles of Radiation Interaction in Matter and Detection, C. Leroy, P.G. Rancoita, World Scientific § Nuclei and particles, Emilio Segré, W.A. Benjamin “The classic “ § High-Energy Particles, Bruno Rossi, Prentice-Hall Lucia Di Ciaccio - ESIPAP IPM - January 2018 4 Also: Particle Data Group http://pdg.lbl.gov/2017/reviews/rpp2017-rev-passage-particles-matter.pdf For ‘professionals’(*) : GEANT4 (for GEometry ANd Tracking) (Platform for the simulation of the passage of the particles through the matter Using Monte Carlo simulation) My slides have been inspired by : Hans Christian Schultz-Coulon’s lectures Johann Collot @ ESIPAP 2014 (*) more exists: Fluka Garfield (simulation gas detector) 5 Lucia Di Ciaccio - ESIPAP IPM - January 2018 Interaction Cross Section (σ) definition Target parameters: σ characterises the probability of a given interaction process n ≡ number of target particles M = target mass S0 N have interacted Amol = molar mass ρ = target density N0 particles X N0- N on area S0 23 -1 (thin) target NA= 6.022 10 mol (Avogadro number) Number of interactions per number of target particles in unit time σ ≡ Incident flux Number of interactions per number of target particles in unit time = (1/n) * dN/dt Incident flux = (1/S0) * dN0 /dt Interaction probability σ ≡ [(1/n) * dN/dt] / [1/S0 * dN0 /dt ] = (dN/ dN0 * (S0 / n ) where n = (M/Amol) NA = (ρ V) (NA/Amol) = ρ (S0 X) (NA/Amol) σ doesn’t depend from S0 6 Lucia Di Ciaccio - ESIPAP IPM - January 2018 Cross section (σ) σ ≡ ( interaction probability) * (S0 /n) n ≡ number of target particles . σ ≡ area of a small disk . around a target particle X target S0 1 barn = 10-28 m2 = 10-24 cm2 [ σ ] = [ l ]2 --> σ is measured in m2 or barn 1 mbarn = 10-27 cm Oder of magnitude of cross sections : ‘strong interaction’ 48 -22 2 Neutron of ~ 1 eV on 113Cd σ = 100 barn = 10 cm ‘weak interaction’ See also Neutrino of ~ 1 GeV on p σ= 10-38 cm2 Marco Delmastro lectures Lucia Di Ciaccio - ESIPAP IPM - January 2018 7 Mean free path λ (*) λ = Average distance traveled between two consecutive interactions in matter 1 Another way of expressing the λ ≡ probability of a given process σ nv σ total interaction cross-section nv number of scattering centers per unit volume nv = (ρ NA)/Amol Order of magnitudes: Electromagnetic interaction : λ < ~ 1 μm N0 N(X) = number of Strong interaction : λ > ~ 1 cm surviving particles at thickness X Weak interaction : λ > ~ 1015 m N(X) A practical signal ( > 100 interactions or ‘hits’ ) results from the electromagnetic interaction -x/λ N(X) = N0e N0/e Particle detection proceeds in two steps : 1) primary interaction 2) charged particle interaction producing the signals X= λ X (*) Also: λ = absorption length, interaction length, attenuation length, …then σ is the cross-section for the corresponding process (see later) Lucia Di Ciaccio - ESIPAP IPM - January 2018 8 Examples: detection of photons(γ), π0(2γ), neutrons(n), neutrinos (ν) Signals are induced by e.m. interactions of charged particles in detectors Detector Detector γ τ (π0) ~ 10-16 s Compton γ e+ scattering γ 0 e- π e- e- Pair γ e+ γ production e+ e- _ ν e Detector _ νe _ νe Nuclear reactor _ + νe p à n e Lucia Di Ciaccio - ESIPAP IPM - January 2018 9 Useful relations of relativistic Kinematics and HEP units 1 m0 ≡ rest mass • p = m 0 γ v γ ≡ β ≡ v/c γ ≡ Lorentz boost √1- β2 m ≡ m0 γ 2 • Kinetic energy Ek = (γ-1) m0 c 2 2 2 • Total energy E = √ (pc) + (m0 c ) 2 2 2 2 • Total energy E = Ek + m0 c = m0 γ c = m c γ =E/(m0 c ) E = m c2 « equivalence mass & energy » Units : [E] = eV [m] = eV/c2 [p] = eV/c See Marco Delmastro [l] [c] = [l] = [t] lectures « Natural units » h =1 [t] c = 1 [E] = [p] = [m] = [ν] = [t]-1 Lucia Di Ciaccio - ESIPAP IPM - January 2018 10 Outline: main interaction processes § Charged particle interactions • 1) Ionization: inelastic collision with electrons of the atoms lecture • 2) Bremsstrahlung: photon radiation emission by an accelerated charge e.m. interactions 2nd • 3) Multiple Scattering: elastic collision with nucleus • 4) Cerenkov & transition radiation effects: photon emission ( • 5) Nuclear interactions (p, π, Κ): processes mediated by strong interactions ) lecture § Neutral particle interactions • Photons : e.m. + - 1rst • photoelectric and Compton effects, e e pair production interactions • High energy neutral hadrons with > τ ~ 10-10 s ( n, K0, ..) : • nuclear interactions • Moderate/low energy neutrons : • scattering (moderation), absorption, fission • Neutrinos : • processes mediated by weak interactions not treated here After the interaction the particles loose their energy and/or change direction or ‘disappear’ Lucia Di Ciaccio - ESIPAP IPM - January 2018 11 Neutral particle interactions • Photons • High energy neutral hadrons with > τ ~ 10-10 s ( n, K0, ..) : • Moderate/low energy neutrons Lucia Di Ciaccio - ESIPAP IPM - January 2018 12 Interactions of photons (γ) PC - - γ : particles with mγ = 0, qγ = 0, J (γ) = 1 Since qγ = 0 , the photons are indirectly detected : in their interactions they produce electrons and/or positrons which subsequently interact (e.m.) with matter. Main processes : 1. Photoelectric effect 2. Compton scattering 3. e+ e- pairs production Eγ Photons may be absorbed (photoelectric effect or e+e- pair creation) or scattered (Compton scattering) through large deflection angles. à difficult to define a mean range à an attenuation law is introduced : −µx µ absorption coefficient I0 I(x) I(x)= I 0e N atoms/m3 A masse molaire NA 1 NA nombre Avogadro µ = N σ = ρ σ ≡ ρ density A λ σ Photon cross section € See also slide 8 λ Mean free path or x absorption lenght Lucia Di Ciaccio - ESIPAP IPM - January 2018 13 γ Absorption lenght (λ’ ≡ 1/µ’) , , -2 −µx −µx x’ ≡ x ρ [ x’ ] = [m] [ l ] I(x)= I 0e I(x)= I 0e [ µ’ ] = [m]-1 [ l ]2 µ’ ≡ µ/ρ [ λ ] = [ m ] [ l ]-2 λ’ ≡ 1/µ’ € € Lucia Di Ciaccio - ESIPAP IPM - January 2018 14 1.Photoelectric effect § The energy of the γ is transferred to the σphotoe electron and the γ disappeares Absorption edges § Energy of the final electron: Ee = Eγ - Eelectron binding energy = hν - Eb Eb = EK or EL or EM etc… 5 ~Z /Eγ This effect can take place only on bounded electrons since the process (on ‘free’ electrons) γ e --> e Eγ photon energy cannot conserve the momentum and energy Lucia Di Ciaccio - ESIPAP IPM - January 2018 15 1.Photoelectric effect 2 I = ionisation potential § At « low » energy ( I 0<< Eγ << mec ): 0 α fine structure constant 2 re = α/(mec )= classical electron 2 radius § At « high » energy ( Eγ >> mec ): σphotoe Example: -10 aB = 0.53 10 m I0 = 13.6 eV For Eγ = 100 KeV σ (Fe) = 29 barn σ (Pb) = 100 barn Rayleigh scattering § At low energy (E γ <100 keV) , the photoelectric effect dominates the total photon cross section Eγ ~Z5/E 3.5 5 γ ~Z /Eγ 2 mec Lucia Di Ciaccio - ESIPAP IPM - January 2018 16 Atom de-excitation (after photoelectric effect) Following the emission of a “photoelectron”, the atom is in an excited state De-excitation occurs via two effects (time scale: ~10-16 s) § Fluorescence: Atom*+ à Atom *+ + γ à X rays Observed § Auger effect Atom*+ à Atom *++ + e- ! Auger electron first by Lisa Meitner Auger electrons deposit energy locally (small energy < ~ 10 KeV) wk Fluorescence yield : Prob (fluorescence) wk= Prob (florescence) + Prob (Auger) Lucia Di Ciaccio - ESIPAP IPM - January 2018 17 General definition of fluorescence Emission of light by a substance that has absorbed light or other electromagnetic radiation. Energy levels in a molecule : Important for scintillators ! Lucia Di Ciaccio - ESIPAP IPM - January 2018 18 2. Compton scattering Scattering of γ on