Contents Marcel MiGLiERiNi Nuclear Medicine, Radiology and Their Metrological Aspects. Radiation in Medicine. Dosimetry 4. Diagnostics & Therapy 5. Accelerators in Medicine 6. Therapy Planning 7. Nuclear Medicine 8. Radiology 9. MRI 0. Combined Techniques Principles of detection of ionizing radiation interaction of radiation with matter charged particles photons neutrons detection of radiation Detectors of ionizing radiation gas filled detectors detectors of neutrons scintillation detectors semiconductor detectors dosimeters Pulse counting system signal chain basic blocks of a counting system Marcel MiGLiERiNi MMiiii Charged Particles Coulomb Interactions Elastic Scattering heavy particles: p +, d, α, ions light particles: e -, e + interaction with nuclei and/or electrons no energy transfer Coulomb interactions elastic scattering inelastic scattering excitation ionization bremsstrahlung nuclear reactions Cerenkov radiation Marcel MiGLiERiNi MMiiii 3 Marcel MiGLiERiNi MMiiii 4 Coulomb Interactions - Inelastic Scattering Bremsstrahlung excitation ionization high for heavy particles (α) at the end of their trajectory mean linear losses: de NZ dx v ( ze) E kinetic energy N number of nuclei inabsorber Z atomic number of absorber ze electric charge of particle v velocity of particle Marcel MiGLiERiNi MMiiii 5 observed for electrons change in acceleration scattering of moving electrons (e - ) in the electric field of nuclei acceleration ofelectrons (e - ) along a non straight path (synchrotron) radiation losses r ionization losses -i de dx r t = de dx i Eβ.Z = 800 E β maximum energy of β-spectrum in MeV Z atomic number of absorber Marcel MiGLiERiNi MMiiii 6
Nuclear Reactions Cerenkov Radiation direct excitation of a nucleus by (heavy) charged particles (p +, d, α) originates when the velocity of particle in a given medium (water) is higher than the velocity of light blue fluorescence (in a nuclear reactor) electron-positron annihilation ( x 0.5 MeV) 0.5 MeV 0.5 MeV Marcel MiGLiERiNi MMiiii 7 Marcel MiGLiERiNi MMiiii 8 Interactions of Photons Photons Photoelectric Effect electromagnetic interactions but other mechanisms no Coulomb forces (interactions) velocity of photons does not change => absorption, scattering no definition of range (loss of energy per unit length) decrease in beam intensity bound e - E k = h.ν I A ν. + + h A + e h. ν > I h.ν E k I X-rays three independent processes: photoelectric effect (photoeffect) Compton scattering (Compton effect) electron-positron pair production E k kinetic energy of electron h Planck constant ν frequency I binding energy nuclear photoeffect Marcel MiGLiERiNi MMiiii 9 Marcel MiGLiERiNi MMiiii 0 Photons Compton Scattering Photons Pair Production free e - λ = λ - λ = Λ.sin (θ/) Λ = h/m.c A ν. + + h A + e h.ν h.ν h.ν min =.0 MeV = x0.5 MeV pair production e - -e + only at the vicinity of heavy nuclei consecutive e - -e + annihilation 0.5 MeV h. ν >> I 0.5 MeV λ wave length Λ Compton wave length θ angle between original and scattered photon m mass of electron h Planck constant c velocity of light h.ν A ν. + + + h A + e + e h. ν >. m c 0. Marcel MiGLiERiNi MMiiii Marcel MiGLiERiNi MMiiii
Photons Neutrons probability of interaction via: photoelectric effect Compton scattering 00 pair production decrease in photon beam intensity I t ( t) = I e 0. µ. t thickness µ linear attenuation coefficient I 0 intensityof incoming radiation Z - atomic number 0 0.0 0. 0 00 E γ - energy of photons (MeV) Marcel MiGLiERiNi MMiiii 3 80 60 40 0 photoeffect 53 I 6 C Compton scattering pair production interactions via strong forces (~0-3 m) scattering inelastic elastic absorption Marcel MiGLiERiNi MMiiii 4 Neutrons -Absorption Measurement of Radiation absorption radiation capture ofn 0 fission absorption with consequent emission hadron shower All types of radiation, whether directly or indirectly ionizing, interact with the atoms or molecules of the medium through which they traverse and produce: ionization in gaseous media scintillations in certain materials (scintillators) exposure of photographic emulsions decomposition of chemical media heating of a medium in calorimeters damage in crystals (tracks in vapours, gasses) These properties are used in the design and development of various devices for the detection as well as measurement of radiation. Marcel MiGLiERiNi MMiiii 5 Marcel MiGLiERiNi MMiiii 6 Principles of Detection Gas Filled Detectors formation of electron ion pair gas amplification regions: interaction mechanisms: charged particles: e -, e +, p, d, α, heavy ions (A>4) photons: γ, X-rays neutrons secondary ionization (Townsend avalanche) α β I. recombination II. ionization ionisation chambers III. proportional proportional counters IV. limited proportionality V. Geiger-Müller GM counters VI. continuous discharge Marcel MiGLiERiNi MMiiii 7 Marcel MiGLiERiNi MMiiii 8 3
Type of Detectors Ionisation Chamber Ionization chamber type of particle and its energy only strong ionizing particles: α, p, fission fragments, heavy ions detection of neutrons Proportional counters any type of particle (α, β, γ, neutrons) and its energy detection of low energy possible Geiger-Müller counters only number of particles can be detected detection of low-level radiation quenching gas Marcel MiGLiERiNi MMiiii 9 chamber filled with gas (air) small noise current without radiation (gas is insulator) ionization of gas by passing ionizing radiation charge carriers produce a current flow current is proportional to the intensity of radiation Marcel MiGLiERiNi MMiiii 0 Proportional Counter Geiger-Müller Counter much higher electric field than in ionization chamber acceleration of electrons towards the central electrode gain of sufficient energy further ionization by collision gas amplification Marcel MiGLiERiNi MMiiii lower pressure of gas (Ar+CH 4 ) than in ionization chamber high voltage (~ kv) strong gas amplification single particle of radiation gives a pulse Marcel MiGLiERiNi MMiiii Fission chamber slow neutrons 33 U, 35 U, 39 Pu Boron-lined counter Detection of Neutrons working chamber boron lined gamma + neutrons compensated chamber uncoated gamma only net signal proportional to neutrons Compensated Ionization Chamber BF 3 counter He counter 0 5 3 B 5 7 +++ 4 ++ + 0n 3Li + He + e He + n 0 T + 3 Marcel MiGLiERiNi MMiiii 3 p Marcel MiGLiERiNi MMiiii 4 4
Scintillations Scintillators scintillation = emission of visible light principle excitation of electrons from valence to conduction band by incoming radiation without activator states emission of the same photon reabsorption presence of activator non-radiative transition emission of a scintillation photon emission of a photon with lower energy no absorption occurs energy states of electrons in crystal Scintillators inorganic: NaI(Tl), CsI(Tl), CaI(Na), LiI(Eu), CaF (Eu), ZnS high efficiency for gamma, ms organic: stilbene, anthracene detection of beta, 0 ns plastic: chemicals in plastic matrix detection of fast neutrons possible (contain H ), - ns gaseous: noble gasses Photomultiplier tube ~5 dynodes 80 0 V amplification >0 6 scintillator photocathode dynode anode Marcel MiGLiERiNi MMiiii 5 Marcel MiGLiERiNi MMiiii 6 Scintillation Detectors Semiconductor Detectors Principle: electron hole pair Types of detectors surface barrier detector oxidized high purity Si Ł p-type surface layer diffused junction detector high purity Si wafer with n-type layer (P) Ł p-n junction silicon-lithium drifted detector SiLi formation of n-p junction by Li diffusion germanuim-lithium drifted detector GeLi operated at low temperature hyper pure germanium detector HPGe impurity concentration less than 0 6 atoms/m 3 Marcel MiGLiERiNi MMiiii 7 Marcel MiGLiERiNi MMiiii 8 Standard Cryostat Configuration NaI(Tl) Gamma Spectroscopy We can use energy of detected gamma radiation to determine radionuclides and their activities. 60 Co 37 Cs Some types of silicon and all types of germanium detectors must be operated at low temperatures. GeLi Marcel MiGLiERiNi MMiiii 9 Marcel MiGLiERiNi MMiiii 30 5
Thermoluminescence Detectors TLD personal dosimeter Personal Dosimeters thermoluminescence -some materials, such as LiF and CaF, when exposed to radiation can store energy which can be released by heating to a certain temperature in a form of visible light scintillation is prompt luminescence thermoluminescence is delayed luminescence initiated by heating neutron personal TLD dosimeter 6 Li, 7 Li: beta + gamma 6 Li: neutrons 6 Li(n, α) 3 H Marcel MiGLiERiNi MMiiii 3 Marcel MiGLiERiNi MMiiii 3 Photographic Dosimeter Film Badge Dosimeters blackening evaluation It is well known that the effect of ionizing radiation on photographic emulsion is similar to that of visible light. The degree of blackening is a measure of the dose. Historical Hanford film badge dosimeter (970) Marcel MiGLiERiNi MMiiii 33 Marcel MiGLiERiNi MMiiii 34 Electronic Personal Dosimeter Energy Spectrum energy compensated silicon pin diode detector dose equivalent: µsv 0 Sv dose equivalent rate: µsv/h Sv/h alarm thresholds: current dose and dose rate day dose month/quarter cumulative doses interface bidirectional infrared RS-3 link pulses from a detector energy spectrum Marcel MiGLiERiNi MMiiii 35 Marcel MiGLiERiNi MMiiii 36 6
Signal Chain Signal Chain (cont.) detector preamplifier amplifier discriminator counter detector identification of ionizing radiation electronic output signal preamplifier amplification of a weak signal from detector (mv) impedance matching amplifier linear amplification to 0 V signal shaping (pile-up) optimization of signal-to-noise ratio timer discriminator analog-to-digital converter single-channel analyzer (SCA) sorts incoming signals according to their height LLD, ULD window modes of operation normal (or differential) window: ULD = LLD + E integral counter accumulation of pulses from SCA multichannel analyzer (MCA) different memory locations for different amplitudes of pulses Marcel MiGLiERiNi MMiiii 37 Marcel MiGLiERiNi MMiiii 38 7