Particle interactions with matter A. Lechner (CERN) based on slides by A. Ferrari and F. Cerutti Calculations based on the FLUKA Monte Carlo code CAS, Erice, Italy March 11th, 2017 A. Lechner (CAS, Erice, Italy) March 11th, 2017 1 / 37 Contents Introduction and basic definitions Atomic interactions (photons, charged particles) Nuclear interactions (hadrons) Energy deposition and particle showers A. Lechner (CAS, Erice, Italy) March 11th, 2017 2 / 37 Contents Introduction and basic definitions Atomic interactions (photons, charged particles) Nuclear interactions (hadrons) Energy deposition and particle showers A. Lechner (CAS, Erice, Italy) March 11th, 2017 3 / 37 Why do particle-matter interactions matter? Eventually all beam particles and/or their secondary products will interact with surrounding media ... SPS dump • Beam disposal on a dump/stopper • Particle impact on protection or beam manipulation devices Collimators, absorbers, scrapers ◦ (105-450 GeV/c protons) ) halo cleaning ) radioprotection ) background reduction machine protection (in caseto of extract equipment the beam malfunctions) ) , crystals Jaw s: 4.18 ◦ Stripping foils 5 m • Beam directed on targets • Sources of secondary particles: ◦ Collisions in interaction points (luminosity) th , 2017 4 / 37 March 11 ◦ Synchrotron radiation ◦ Interactions with residual gas molecules 2 (18 .826 m hBN b Interactions with macroparticles locks a ◦ 15.7c m) 0.6 m LHC injection (1 0.7 Al blo m ... ck) (1 ◦ CuBe protection absorber block) A. Lechner (CAS, Erice, Italy) Why do particle-matter interactions matter? Eventually all beam particles and/or their secondary products will interact with surrounding media ... SPS dump • Beam disposal on a dump/stopper • Particle impact on protection or beam manipulation devices Collimators, absorbers, scrapers ◦ (105-450 GeV/c protons) ) halo cleaning ) radioprotection ) background reduction machine protection (in caseto of extract equipment the beam malfunctions) ) , crystals Jaw s: 4.18 ◦ Stripping foils 5 m • Beam directed on targets • Sources of secondary particles: ◦ Collisions in interaction points (luminosity) th , 2017 4 / 37 March 11 ◦ Synchrotron radiation ◦ Interactions with residual gas molecules 2 (18 .826 m hBN b Interactions with macroparticles locks a ◦ 15.7c m) 0.6 m LHC injection (1 0.7 Al blo m ... ck) (1 ◦ CuBe protection absorber block) A. Lechner (CAS, Erice, Italy) Why do particle-matter interactions matter? Eventually all beam particles and/or their secondary products will interact with surrounding media ... SPS dump • Beam disposal on a dump/stopper • Particle impact on protection or beam manipulation devices Collimators, absorbers, scrapers ◦ (105-450 GeV/c protons) ) halo cleaning ) radioprotection ) background reduction machine protection (in caseto of extract equipment the beam malfunctions) ) , crystals Jaw s: 4.18 ◦ Stripping foils 5 m • Beam directed on targets • Sources of secondary particles: ◦ Collisions in interaction points (luminosity) th , 2017 4 / 37 March 11 ◦ Synchrotron radiation ◦ Interactions with residual gas molecules 2 (18 .826 m hBN b Interactions with macroparticles locks a ◦ 15.7c m) 0.6 m LHC injection (1 0.7 Al blo m ... ck) (1 ◦ CuBe protection absorber block) A. Lechner (CAS, Erice, Italy) Why do particle-matter interactions matter? Eventually all beam particles and/or their secondary products will interact with surrounding media ... SPS dump • Beam disposal on a dump/stopper • Particle impact on protection or beam manipulation devices Collimators, absorbers, scrapers ◦ (105-450 GeV/c protons) ) halo cleaning ) radioprotection ) background reduction machine protection (in caseto of extract equipment the beam malfunctions) ) , crystals Jaw s: 4.18 ◦ Stripping foils 5 m • Beam directed on targets • Sources of secondary particles: ◦ Collisions in interaction points (luminosity) th , 2017 4 / 37 March 11 ◦ Synchrotron radiation ◦ Interactions with residual gas molecules 2 (18 .826 m hBN b Interactions with macroparticles locks a ◦ 15.7c m) 0.6 m LHC injection (1 0.7 Al blo m ... ck) (1 ◦ CuBe protection absorber block) A. Lechner (CAS, Erice, Italy) Why do particle-matter interactions matter? Eventually all beam particles and/or their secondary products will interact with surrounding media ... SPS dump • Beam disposal on a dump/stopper • Particle impact on protection or beam manipulation devices Collimators, absorbers, scrapers ◦ (105-450 GeV/c protons) ) halo cleaning ) radioprotection ) background reduction machine protection (in caseto of extract equipment the beam malfunctions) ) , crystals Jaw s: 4.18 ◦ Stripping foils 5 m • Beam directed on targets • Sources of secondary particles: ◦ Collisions in interaction points (luminosity) th , 2017 4 / 37 March 11 ◦ Synchrotron radiation ◦ Interactions with residual gas molecules 2 (18 .826 m hBN b Interactions with macroparticles locks a ◦ 15.7c m) 0.6 m LHC injection (1 0.7 Al blo m ... ck) (1 ◦ CuBe protection absorber block) A. Lechner (CAS, Erice, Italy) Consequences & relevant macroscopic quantities A non-exhaustive list Quench of superconducting magnets: - Energy density (transient losses) - Power density (steady state losses) Activation of equipment: - Residual dose rate Gas production: - Induced radioactivity - Residual nuclei production Figure courtesy of A. Bertarelli Oxidation, radiolysis: - Energy Instantaneous damage deposition of equipment because of thermal shock: - Energy density Radiation effects in electronics: Fig. courtesy of TE/EPC - High-energy hadron fluence (single event effects) Long-term radiation - Total ionizing dose damage of equipment: (cumulative effects) - Displacement per Atom - Si 1 MeV neutron equivalent fluence (non-organic materials) (cumulative effects) - Dose (insulators) Fig. courtesy of P. Fessia A. Lechner (CAS, Erice, Italy) March 11th, 2017 5 / 37 The particle zoo Some properties: • Hadrons: ◦ Proton (p) 938 MeV/c2 stable ◦ Neutron (n) 940 MeV/c2 τ=886 s + − 2 −8 ◦ Charged pions (π ; π ) 140 MeV/c τ=2.6×10 s [mainly π ! µνµ] (cτ=780 cm) ◦ Neutral pions (π0) 135 MeV/c2 τ=8.4×10−17 s [mainly π ! γγ] (cτ=25 nm) ◦ Charged and neutral kaons, (anti)hyperons, antiprotons, antineutrons ... • Photons (γ), stable, m=0 • Leptons: ◦ Electron, positron (e−; e+) 511 keV/c2 stable − + 2 −6 ◦ Muons (µ ; µ ) 106 MeV/c τ=2.2×10 s [mainly µ ! eνeνµ] (cτ=687 m) A. Lechner (CAS, Erice, Italy) March 11th, 2017 6 / 37 Cross section and mean free path • Cross section per atom/nucleus σ (microscopic cross section) [area] For a given particle with energy E, -24 2 on an atom with atomic/mass number Z/A (common unit: 1 barn (b) = 10 cm ) σ = σ(E; Z; A) • Mean free path λ [length] 1 M Molar mass [mass/mol] λ = = Nσ ρNAσ Avogadro’s constant [6.022 x 1023 mol-1] Atom density [1/volume] Material density [mass/volume] Microscopic cross section [area] = average distance travelled by a particle between two successive collisions • Macroscopic cross section Σ [inverse length] 1 Σ = = Nσ λ • Remark: ◦ The amount of material traversed by a particle is often expressed as surface density ) length × density ρ [ cm × g=cm3 = g=cm2] A. Lechner (CAS, Erice, Italy) March 11th, 2017 7 / 37 Cross section and mean free path • Cross section per atom/nucleus σ (microscopic cross section) [area] For a given particle with energy E, -24 2 on an atom with atomic/mass number Z/A (common unit: 1 barn (b) = 10 cm ) σ = σ(E; Z; A) • Mean free path λ [length] 1 M Molar mass [mass/mol] λ = = Nσ ρNAσ Avogadro’s constant [6.022 x 1023 mol-1] Atom density [1/volume] Material density [mass/volume] Microscopic cross section [area] = average distance travelled by a particle between two successive collisions • Macroscopic cross section Σ [inverse length] 1 Σ = = Nσ λ • Remark: ◦ The amount of material traversed by a particle is often expressed as surface density ) length × density ρ [ cm × g=cm3 = g=cm2] A. Lechner (CAS, Erice, Italy) March 11th, 2017 7 / 37 Cross section and mean free path • Cross section per atom/nucleus σ (microscopic cross section) [area] For a given particle with energy E, -24 2 on an atom with atomic/mass number Z/A (common unit: 1 barn (b) = 10 cm ) σ = σ(E; Z; A) • Mean free path λ [length] 1 M Molar mass [mass/mol] λ = = Nσ ρNAσ Avogadro’s constant [6.022 x 1023 mol-1] Atom density [1/volume] Material density [mass/volume] Microscopic cross section [area] = average distance travelled by a particle between two successive collisions • Macroscopic cross section Σ [inverse length] 1 Σ = = Nσ λ • Remark: ◦ The amount of material traversed by a particle is often expressed as surface density ) length × density ρ [ cm × g=cm3 = g=cm2] A. Lechner (CAS, Erice, Italy) March 11th, 2017 7 / 37 Cross section and mean free path • Cross section per atom/nucleus σ (microscopic cross section) [area] For a given particle with energy E, -24 2 on an atom with atomic/mass number Z/A (common unit: 1 barn (b) = 10 cm ) σ = σ(E; Z; A) • Mean free path λ [length] 1 M Molar mass [mass/mol] λ = = Nσ ρNAσ Avogadro’s constant [6.022 x 1023 mol-1] Atom density [1/volume] Material density [mass/volume] Microscopic cross section [area] = average distance travelled by a particle between two successive collisions • Macroscopic cross section Σ [inverse length] 1 Σ = = Nσ λ • Remark: ◦ The amount of material traversed by a particle is often expressed as surface density ) length × density ρ [ cm × g=cm3 = g=cm2] A. Lechner (CAS, Erice, Italy) March 11th, 2017 7 / 37 Interaction probability Assume that particles are normally incident on a homogeneous material and that they are subject to a process with a mean free path λ between collisions: • Path length distribution dl Z 1 l 0 0 1 l Note : p(l )dl = 1 p(l)dl = exp − dl 0 λ λ p(l)dl = probability that a particle has an interaction between l and l + dl • Cumulative interaction probability P(λ) = 63.2% Survival probability: Z l P(2λ) = 86.5% 0 0 l Ps (l) = 1 − P(l) P(3λ) = 95.0% P(l) = p(l )dl = 1 − exp − = exp(−l/λ) P(4λ) = 98.2% 0 λ P(l) = probability that a particle interacts before reaching a path length l • In case of a thin target (thickness d λ) d P = P(d) ≈ target λ A.