0 Introduction. Radiation Physics. Radiation Physics. 1 Radioactive Decay. 1.1 Radioactive Decay Law

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1 Radiation Physics 0 Introduction Introduction Radioactive Decay Decay Types Decay Diagrams Decay Schemes Radioactive Decay Law Radioactive Decay Examples Activity Ionising Radiation Radiation Types Physical Interactions Cross Sections Exercises References Radiation Physics radiation protection, neutron activation, material sciences, nuclear sciences Radiation Biology radiation protection, biological effects of radiation, medical radiation applications Radiation Chemistry research on metabolism, biological effects of radiation, material sciences Radioactive Decay. Radioactive Decay Law A t ½ t activity half life time time A λ t A() t = A e λ = 0 ln τ / Exponential Decay t ½ t A = activity at t τ = λ A 0 = activity at ( t = t 0 ) λ = decay constant τ ½ = half life time τ = mean life = decay time to the e-th part of starting material

2 . Decay Types.3 Radioactive Decay Examples Type Mass Number Daughter Atomic Number Daughter - Decay M 4 Z - β - Decay M Z + γ - Decay M Z Radio Nuclide Occurance Decay Type Half Life τ / T 0,0003 % β -,346 a Ra - 6 / γ, a I - 3 β - / γ 8,04 d Cs - 34 β / γ,06 a,09 h U ,70 %, β, γ, sf * 7, a U ,8 %, β, sf 4, a * sf is spontaneous fission.4 Activity.4. Specific Activity Activity Activity is the number of disintegrations per time unit. Becquerel (Curie) ( Bq = disintegration) ( Ci = 3, Bq). Example: g of the element Radium has an activity of 3, Bq = Ci Activity Mass Bq kg Cs-34 / Cs-37 content in meet (D 990),0 Bq / kg beef, calf 0,3 Bq / kg pig 8,0 Bq / kg sheep Bq / kg deer

3 .4. Surface Activity.4.3 Volume Activity Activity Surface Bq cm Activity Volume Bq 3 cm surface contamination limit in controlled areas StrlSchV average radon load in houses (D): P-3 (β - Source): 500 Bq / cm 50 Bq / m 3 top loads (D): >00 Bq / m 3.5 Ionising Radiation.5. Radiation Types Radiation from radio nuclide decay Radiation, that ionises materials direct ionising radiation charged particles indirect ionising radiation uncharged particles, photons particles n neutrons p protons He + β electrons, positrons electromagnetic waves γ / X gammas, X-rays indirect ionising direct ionising

4 .6 Alpha Decay.6. Alpha Decay Animation alpha particle.6. Alpha Radiation.7 Beta Decay negatron decay positron decay Particles He- 4 particles Radio Nuclides Pu - 39, Ra - 6, Rn -, Am - 4, Po - 0, U - 35 Energy MeV Reach at 5 MeV ca. 3,5 cm (air) Energy Deposition mostly at once Interaction Danger incorporation, beta particle Protection shielding with paper, distance > 0 cm

5 .7. Beta Decay Animation.7. Beta Spectra most probable energy Probability maximum energy Energy [MeV].7.3 Beta - Reach.7.4 Bremsstrahlung Maximum surface density R = x. ρ empirical formula Emax =.85 R radiation from deceleration E max R max (if R > 0,3 g/cm ) maximum beta energy maximum surface density R electron Mass Absorption Coefficent µ empirical formula 5 µ =.5 E max (if E in MeV, if 0, MeV E 3,5 MeV, µ [cm/g]) Claus Grupen, Grundkurs Strahlenschutz, Vieweg Verlag

6 .7.5 Beta Radiation.8 Gamma Decay Particles negatrons, positrons Radio nuclides H - 3, C - 4, Sr - 90, Cs - 37 Tl - 04, Co - 60 Energy kev... MeV Reach at MeV ca. 4 m (air) Energy Deposition continued Interactions ionisation, excitation, Bremsstrahlung Danger scattered radiation, skin exposition, mucous membranes, incorporation Protection shielding with Al, PMMA gamma photon.8. Gamma Decay Animation.8. Decay Diagram Co-60 (I) level energy half life time mother energy in kev daughter

7 .8.3 Decay Diagram Co-60 (II).8.4 Decay Diagram Co-60 (III) Decay Diagram Co-60 (II) Decay Diagram Co-60 (III) transient probability energy Mother decay probability transients energy in kev energy in kev.8.6 Gamma Radiation.8.7 Distance Law Particles photons Sources Am - 4, Co - 60, I - 3, Ba - 33, Ba - 37m, Tc - 99m Energy kev... MeV Reach theoretically Energy Deposition packets Interactions scattering, photo effect, COMPTON effect, pair effect Danger body exposure, incorporation Protection shielding with Pb H dh/dt A r G H A H = Γ H r = Personal dose = Personal dose rate = Activity = Distance Source Detector = Gamma dose rate constant attenuation without scattering!

8 .8.8 Equivalent Dose.9 X Ray equivalent dose H H = D x Q Sievert = Sv = J.kg - = 00 rem Inner electron transitions (not from the nucleus!) intensity characteristic lines proportional to radiation effect on man, Q introduces different radiation types = cell damage from absorbed energy brems spectrum rem ( Sv=00 rem) energy in kev.0 Spontaneous Fission.0. Fissionable Materials Nuclear Fission Uranium + Neutron Fission Products +,3 Neutrons - Sources: Isotopes τ½ Occurrence σf ther [barn] U-34, a 0,005 % U-35 7, a 0,70 % 58 U-38 4, a 99,75 % < 0,0005 Pu-39, a 743 Pu-40 6, a 0,03 Pu-4 4,4 a 009 Pu-4 3, a < 0, Pu-43 4,956 h 96

9 .0. Free Neutrons.0.3 Neutron Sources Generation from Ra-Be sources: Be + 6C + Generation from fusion reactions D + 3 T 4 He + + 7,58 MeV 0 0 n n 600 a Rn γ 9 Be (,n) C γ 6 Ra / Be Sample ~ 3, Bq up to MeV 35 U.0.4 Neutron Radiation. Other Decays free neutrons τ ½ = ca.,5 min thermal neutrons thermal equilibrium with surrounding medium, energy ca.,5 0 - ev, velocity ca.,. 0 3 m/s electron capture isomeric transitions conversion electrons fast neutrons energy > 0, MeV up to ca. MeV, velocity up to ca m/s

10 . Decay Schemes.. Uranium Radium Decay Decay Schemes successive radio nuclide sequences, Uranium-Radium Uranium-Actinium Thorium Plutonium-Neptunium plutonium neptunium decay was restarted by mankind Pb-4 Bi-4 Tl-0 Hg-06 Tl-06 U-38 Th-34 Pa-34 U-34 Th-30 Ra-6 Rn- Po-8 Pb-0 Pb-06 At-8 Rn-8 Po-4 Bi-0 Po-0.. Uranium Actinium Decay..3 Thorium Decay Th-7 Pb- Po- U-35 Th-3 Pa-3 Ac-7 Ra-3 Rn-9 Po-5 Bi- Pb-07 Fr-3 At-9 Bi-5 At-5 Tl-07 Po- Th-3 Ra-8 Ac-8 Th-8 Ra-4 Rn-0 Po-6 Pb- Bi- Pb-08 Tl-08

11 ..4 Plutonium Neptunium Decay Physical Interactions Bi-3 Tl-09 Pu-4 Am-4 U-37 Np-37 Pa-33 U-33 Th-9 Ra-5 Ac-5 Fr- At-7 Rn-7 Po-3 Pb-09 Bi-09 Ionising radiation can interact with materials as follows: Excitation of outer electrons Ionisation of atoms Deceleration of particles and heating Nuclear reactions materialisation von electromagnetic waves activation of atoms. Specific Ionisation. Čzerenkov Radiation Čerenkov radiation occurs if the accelerated charged particles velocity in the surrounding materials is faster than light s velocity in the same materials. Ionisations are caused by all accelerated charged particles of higher energies in the surrounding materials. The particles energy will be deposited in small packages along the particles way in materials. The specific ionisation of an accelerated charged particle of higher energy is the number of produced ion pairs along the particles way per mm track length in the surrounding material.

12 .3 Ionisation Density.3. Absorption of a & b Particles Gamma Radiation (Co-60) 50 kv X Radiation Alpha Particles Dense ionisation Nuclear reactions with high energy alpha particles 0 kv X Radiation Alpha Radiation Beta Particles Less dense ionisation X-ray emission with high energy beta particles Scattering on atoms with large Z.3. Empirical Equation for b Radiation Reach.3.3 Absorption of g Radiation d = E Beta,max ρ Photon Absorption Mechanisms: Photo effect at low photon energies (complete absorption in the electron shells) d E beta,max ρ No physical equation! = β radiation reach = maximum β -energy = density of shielding material COMPTON effect at medium photon energies (incoherent scattering in the electron shells) Pair effect at high photon energies (complete absorption in the nucleus COULOMB field) Depending on the density of materials!

13 .3.4 Photo, COMPTON and Pair Effect.3.5 Photo Effect Atomic number Photon Interactions Incoming photon Photo electron Photon energy.3.6 Photo Effect - animated.3.7 COMPTON Effect Photo Effect Scattered photon Incoming photon COMPTON electron

14 .3.8 COMPTON Effect - animated.3.9 Pair Effect COMPTON Effect Incoming photon Positron Electron.3.0 Pair Effect - animated.3. Neutrons Interactions with Materials Pair Effect Major Interactions: Scattering σ scattering Elastic scattering σ scat, el Inelastic scattering ( neutron moderation) σ scat, inel Absorption σ absorption Capture ( neutron activation) σ capture Fission σ fission

15 .3. Neutron Moderation.3.3 Neutronenstreuung deceleration of fast neutrons down to thermal velocity H, D Als Neutronenstreuung bezeichnet man den Zusammenstoß eines Neutrons mit einem Kern, wenn es zu keiner Absorption kommt. Die vom Neutron an den Kern abgegebene Energie ist am größten, wenn der Kern dieselbe Masse wie ein Neutron hat. Das ist bei Wasserstoff der Fall. Wasserstoffhaltige Materialien, wie H O, PE, etc können deshalb als Neutronenmoderator eingesetzt werden um schnelle Neutronen auf die Geschwindig-keit thermischer Neutronen abzubremsen D O, Graphit und Be haben ebenfalls große Streuquerschnitte.3.4 Neutronenabsorption.3.5 Neutron Absorbers Bei der Absorption verschwindet das einfallende Neutron als freies Teilchen. Es wird entweder von einem Atomkern eingefangen (Aktivierung) mit anschließender Kernreaktion oder es kommt zur Kernspaltung. Bei der Kernspaltung zerfällt der Kern in meist Bruchstücke und einige Neutronen, die bei geeigneter Geschwindigkeit neue Spaltungen und somit eine Kettenreaktion in Gang setzen können. Control Rods Cd In / Ag Hf B 4 C, B O 3 Nucleus Protection Biological Shielding (reactor control) 3 Cd (n,γ) 3 Cd 0 B (n,) 7 Li (nuclear incidents) Na B 0 O 6.0 H O (SUR-00 FHF): H 3 BO 4

16 3 Gamma Radiation Attenuation 3. Attenuation Law Attenuation factor for unscattered photons: S u H 0 Hu H 0 Su = Hu Attenuation factor Dose rate before attenuation Dose rate after attenuation S µ d d n u H 0 Hu / / Attenuation factor Dose rate before attenuation Dose rate after attenuation Mass attenuation coefficient Layer width Half layer width Number of half layer widths µ d u = H 0 e H H 0 µ d = e H u ln µ = d d = n d = S u 3. Attenuation Equations 3. Mass Attenuation Coefficient H 0 d = e µ = S u H u ln µ = d log S n u = n log Su = log log d = n d µ d ρ ρ H = H 0 e µ = linear attenuation coefficient µ = τ + σ + χ Photo effect COMPTON effect Pair effect µ / ρ = mass attenuation coefficient

17 4 Radiation Induced Material Degradation Displacement of atoms in the crystal Frenkel defect Increasing hardness, tensile strength Decreasing viscosity Volume increase, density decrease Formation of foreign atoms Nuclear reactions Structural deformations Increasing brittleness by (n,) reactions Radiolysis H O H + O