Presentation on theme: "NE Introduction to Nuclear Science Spring 2012"— Presentation transcript:
1 NE 301 - Introduction to Nuclear Science Spring 2012 Classroom Session 8:Radiation Interaction with MatterNon-Charged RadiationMass Attenuation Tables and UseAbsorbed Dose (D), Kerma (K)Gray (Gy) = 100 radDose CalculationsAnalysis of Gamma Information (NAA)Chemical Effects of Nuclear Reactions
2 Reminder Load TurningPoint Reset slides Load List Homework #2 due February 9Next Tuesday February 14 – 1st Demo SessionMCAGamma Spectroscopy identification of isotopesNAA of samples
3 Ionizing Radiation: Electromagnetic Spectrum Each radiation have a characteristic , i.e.:Infrared: Chemical bond vibrations (Raman, IR spectroscopy)Visible: external electron orbitals, plasmas, surface interactionsUV: chemical bonds, fluorecense, organic compounds (conjugated bonds)X-rays: internal electron transitions (K-shell)Gamma-rays: nuclear transitionsNeutrons mK, can be used to test metal lattices for example)Ionizing
4 Radiation Interaction with Matter Five Basic Ways:IonizationKinetic energy transferMolecular and atomic excitationNuclear reactionsRadiative processes
5 Radiation from Decay Processes ChargedDirectly ionizing (interaction with e-’s)β’s, α’s, p+’s, fission fragments, etc.Coulomb interaction – short range of travelFast moving charged particlesIt can be completely stoppedUnchargedIndirectly ionizing (low prob. of interaction – more penetrating), X-Rays, UV, neutronsNo coulomb interaction – long range of travelExponential shielding, it cannot be completely stoppedR
6 Stochastic (Probabilistic) With an electron or a nucleus Neutral InteractionsStochastic (Probabilistic)With an electron or a nucleusCan be scattering – elastic or inelasticCan be absorptiveIt is still a collision:Flux of particles is important
7 Flux or Intensity Flux is usually for neutrons (n) Intensity is usually for photons (’s)TargetBeamDensity of particles in the beamVelocity of beam particles
8 Attenuation of Uncollided Radiation How do we calculate the change in the flux of (uncollided) particles as it moves through the slab?Uncollided radiation is a simplification. In reality not every collided photon/neutron is lost and there are buildup factors (Bi)
9 Attenuation of Uncollided Radiation Beam with intensity I, interacting with shield (1-D)
10 Microscopic and Macroscopic Cross Sections Sigma-N =Linear Attenuation Coefficient or Macroscopic Cross Section ( or )Notice Different Units: is measured in cm-1 is measured in barns1 barn = cm2Constant of Proportionality or Microscopic Cross-Section
11 A beam of neutrons is normally incident on a slab 20 cm thick A beam of neutrons is normally incident on a slab 20 cm thick. The intensity of neutrons transmitted through the slab without interactions is found to be 13% of the incident intensity. What is the total interaction coefficient t for the slab material?0.01 cm-10.1 cm-11 cm-110 cm-1
13 Attenuation of Uncollided Radiation Beams of particles: with intensity I0, interacting with shield (1-D)Point sources: Isotropic source emitting Sp particles per unit time
14 Related Concepts Mean Free Path (mfp or ): Average distance a particle travels before an interactionHalf-thickness (x1/2) of the slab?Thickness of slab that will decrease uncollided flux by halfSimilar concepts to mean-life and half-life
15 10 and 6.9 cm 20 and 13.8 cm 116 and 80 cm 1000 and 693 cm It is found that 35% of a beam of neutrons undergo collisions as they travel across a 50 cm slab. What is the mfp and x1/2 for the slab?10 and 6.9 cm20 and 13.8 cm116 and 80 cm1000 and 693 cm
30 For homogeneous mixes of any type Valid for any cross section type (fission, total, etc)Valid for chemical compounds as wellDO NOT add microscopic cross-sections
31 In natural uranium (=19. 21 g/cm3), 0. 720% of the atoms are 235U, 0 In natural uranium (=19.21 g/cm3), 0.720% of the atoms are 235U, % are 234U, and the remainder 238U. From the data in Table C.1.What is the total linear interaction coefficient (macroscopic cross section) for a thermal neutron in natural uranium?0.24 cm-1cm-1238U: 0.59 cm-1Who dominates?
32 Absorbed Dose, D (Gray, rad) Energy absorbed per kilogram of matter (J/kg)Gray: 1 Gy = 1 J/kgThe traditional unit:Rad: rad = 1 Gyrad = Radiation Absorbed ManDose rate = dose/time
33 Kerma (Approx. dose for neutrons) Kinetic Energy of Radiation absorbed per unit MAssFor uncharged radiationKerma is easier to calculate than dose for neutronsKerma and Dose: same for low energyKerma over-estimates dose at high energyNo account for “Bremsstrahlung” radiation loses.
34 Calculating Dose Rate and Kerma Rate en(E)/ =mass interaction coefficient (table C3)E = particle energy [MeV] = flux [particles/cm2 s]Notice Differencetr(E)/ =mass interaction coefficient (table C3)E = particle energy [MeV] = flux [particles/cm2 s]Engineering Equations – PLEASE Watch out for units!