Part B Radiation sources Radiation Safety JUAS 2014
Part B. Radiation sources Radiation Safety - JUAS 2014, X. Queralt 1. Interaction of electrons with matter 2. Interaction of photons with matter 3. Interaction of neutrons with matter 4. Interaction of protons with matter / 34
1. Interaction of electrons with matter Radiation Safety - JUAS 2014, X. Queralt The physical processes: 1. Ionization losses inelastic collisions with orbital electrons 2. Bremsstrahlung losses inelastic collisions with atomic nuclei 3. Rutherford scattering elastic collisions with atomic nuclei Positrons at nearly rest energy: annihilation emission of two 511 ke. V photons / 34
1. Interaction of electrons with matter Radiation Safety - JUAS 2014, X. Queralt Electrons – stopping power Copper – Z = 29 Graphite – Z = 6 Lead – Z = 82 / 34
1. Interaction of electrons with matter Radiation Safety - JUAS 2014, X. Queralt Continuous Slowing Down Approximation range: Radiation yield: Fraction of the initial kinetic energy that is converted to Bremsstrahlung energy as the electron slows down to rest. / 34
1. Interaction of electrons with matter Radiation Safety - JUAS 2014, X. Queralt Differential Bremsstrahlung cross section: mbarn lead – Z = 82 k/T k: photon energy T: electron kinetic energy carbon – Z = 6 k/T / 34
1. Interaction of electrons with matter Radiation Safety - JUAS 2014, X. Queralt Multiple scattering mean scattering angle mass scattering power Ssc Es = 21. 2 Me. V X 0: radiation length β: v/c p: momentum / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt The physical processes: 1. Photo-electric effect removal of an orbital electron of the inner shells (K, L, M) 2. Compton scattering inelastic scattering on loosely bound electrons 3. Pair production of e-/e+ pair essentially with nuclei 4. Rayleigh (coherent) scattering elastic scattering not important for radiation physics / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Photon cross sections Graphite - Z = 6 / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Photon cross sections Lead - Z = 82 / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Photo-electric effect: photo-electron ΔE = E – E 0 ΔE = E 0 – E 1 = Ka E 2 E 1 E 0 E ΔE = E 0 – E 2 = Kb E 0 K L M N incoming X-ray The K lines ΔE = E 1 – E 2 = La E 2 ΔE = E 1 – E 3 = Lb Auger-electron E 1 ΔE = E 1 – E 2 – E 3 E 2 K L M N E 3 The L lines Auger electron / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Compton scattering: θ primary photon energy E 0 Ec (Me. V) Compton electron energy = E 0 - Ec scattered photon energy Ec dσ/d. W (re 2 x cm 2 / electron) / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Pair production: σnucleus Z 2 threshold: 1. 022 Me. V σelectron Z threshold: 2. 044 Me. V / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Interaction of photons with matter Macroscopic description - Attenuation factors The mass attenuation coefficient μ/ρ: N units: cm 2. g-1 The linear attenuation coefficient μ: units: cm-1 The conversion factor from σ (barns. atom-1) to μ/r (cm 2. g-1): d (cm) d (g. cm-2) / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt • Particles involved: – Electrons / Positrons – Photons – Neutrons / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Electromagnetic cascade cm one 500 Me. V electron interacting with lead target / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Electromagnetic cascade cm one 6 Ge. V electron interacting with lead target / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt photonuclear reactions Photonuclear reactions: Neutron production Photo-pion γ(d, p)n Quasi-deuteron m Giant resonance 55 Mn(γ, n)54 Mn e-60/E sγ(d, p)n / 34
2. Interaction of photons with matter Radiation Safety - JUAS 2014, X. Queralt Photonuclear reactions: Neutron production Giant resonance Quasi-deuteron Photo-pion Example: neutron spectrum produced by 600 Me. V electrons on Cu target / 34
3. Interaction of neutrons with matter Radiation Safety - JUAS 2014, X. Queralt The physical processes: 1. Elastic scattering • compound elastic scattering • potential scattering 2. Inelastic scattering (n, n’) 3. Other inelastic reactions: (n, p), (n, a), … 4. Absorption reactions • radioactive capture • charged particle reactions 5. Direct reactions: spallation / 34
3. Interaction of neutrons with matter Radiation Safety - JUAS 2014, X. Queralt Compound nucleus formation target nucleus ZA neutron energy = EC / 34
3. Interaction of neutrons with matter Radiation Safety - JUAS 2014, X. Queralt Neutron cross sections Example 1: iron / 34
3. Interaction of neutrons with matter Radiation Safety - JUAS 2014, X. Queralt Neutron cross sections Example 2: cadmium / 34
3. Interaction of neutrons with matter Radiation Safety - JUAS 2014, X. Queralt Neutron cross sections Example 3: hydrogen / 34
3. Interaction of neutrons with matter Radiation Safety - JUAS 2014, X. Queralt Neutron cross sections Example 4: boron / 34
3. Interaction of neutrons with matter Radiation Safety - JUAS 2014, X. Queralt Neutron cross sections inelastic cross section (barn) Example: iron neutron energy (Ge. V) / 34
3. Interaction of neutrons with matter Radiation Safety - JUAS 2014, X. Queralt Elastic scattering scattered neutron energy = E 1 target nucleus initial neutron energy = E 0 recoiling nucleus Minimum energy of scattered neutron: Average energy loss per collision: target E 1, minimum Hydrogen (A=1) 0 0. 5 E 0 Iron (A=56) 0. 93 E 0 0. 034 E 0 Lead (A=207) 0. 98 E 0 0. 0096 E 0 / 34
4. Interaction of protons with matter Radiation Safety - JUAS 2014, X. Queralt The physical processes: 1. ionization 2. inelastic proton-nucleus scattering spallation / 34
4. Interaction of protons with matter Radiation Safety - JUAS 2014, X. Queralt Proton ionization loss – Stopping power stopping power (Me. V. g-1. cm 2) minimum ionizing particle proton energy (Me. V) / 34
4. Interaction of protons with matter Radiation Safety - JUAS 2014, X. Queralt Comparison CSDA range of protons and electrons in iron / 34
4. Interaction of protons with matter Radiation Safety - JUAS 2014, X. Queralt Inelastic proton – nucleus scattering: Spallation reaction n n p incident proton (Ge. V range) π Δ π n p intra-nuclear cascade α d n γ evaporation / 34
4. Interaction of protons with matter Radiation Safety - JUAS 2014, X. Queralt Inelastic proton – nucleus scattering Spallation reaction Inelastic cross section E > 1 Ge. V / 34
4. Interaction of protons with matter Radiation Safety - JUAS 2014, X. Queralt Inelastic proton – nucleus scattering Comparison ionization energy loss and inelastic scattering E > 1 Ge. V: 100 % probability for spallation reaction / 34
4. Interactionn of protons with matter Radiation Safety - JUAS 2014, X. Queralt inter-nuclear cascades Spallation n p π Δ incident proton (Ge. V range) π n p e. V intra-nuclear cascade l evaporation α fast induced fission p d α on eutr γ rt be spo tran N spallation product α, β, γ decay n γ n fission n n fission products 0 M ow 2 γ fission products (n, n’), (n, xn), γ (n, γ) , … reactions / 34
4. Interaction of protons with matter Radiation Safety - JUAS 2014, X. Queralt Spallation / 34
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