Ionizing Radiation PDF

IONIZING RADIATION Dr. Reda Čerapaitė-Trušinskienė  Ionizing radiation Ionizing radiation consists of subatomic particles or electromagnetic wav...

IONIZING RADIATION Dr. Reda Čerapaitė-Trušinskienė  Ionizing radiation Ionizing radiation consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from https://byjus.com/physics/ionizing-radiation/ them. LSMU/Ionizing Radiation Types of Ionizing Radiation https://polimaster.com/eu/articles/radiation-safety-basics/types-of-ionizing-radiation/ LSMU/Ionizing Radiation NATURAL IONIZING RADIATION. RADIOACTIVITY Radioactivity is a spontaneous disintegration of nuclei with simultaneous emission of elementary particles or electromagnetic waves. LSMU/Ionizing Radiation  NUCLEAR COMPOSITION P PROTON + N NEUTRON 0 Mass of proton mp = 1,672⋅10−27 kg; it is 1840 times bigger than mass of electron (me = 9,11⋅10−31 kg). Mass of Neutron is little bit smaller than mass of This Photo by Unknown Author is licensed under CC BY-SA-NC proton: mn = 1,675⋅10−27 kg. LSMU/Ionizing Radiation  NUCLEAR COMPOSITION NUCLIDE 12 A 6 C ZX LSMU/Ionizing Radiation NUCLEAR COMPOSITION ISOTOPE 12 14 6C C 6 LSMU/Ionizing Radiation  Radioactivity Stable nuclei: N/Z≈1; Have so-called Magic number of protons, neutrons or the sum of protons and neutrons is equal to Magic number (2, 8, 20, 50, 82) Unstable nuclei: N/Z>1. LSMU/Ionizing Radiation  Radioactivity Decay must be "energetically beneficial" > + Erest (initial) Erest (after decay) Erest (initial) - Erest (after decay) = Ekinetic LSMU/Ionizing Radiation  Radioactivity Unstable nuclei can spontaneously transform into nuclei of other elements, radiating: lighter nuclei (alpha particle, fission fragments); elementary particles (electrons, positrons, protons, neutrons, neutrinos); electromagnetic waves (gamma quanta). LSMU/Ionizing Radiation Radioactivity. Types of Decay Beta particle Alpha particle Gamma ray LSMU/Ionizing Radiation Radioactivity. Alpha decay Main features of α decay: α decay is observed only for nuclei with Z > 82 (isotopes that lie behind Pb in the periodic table of elements); The kinetic energies of α particles emitted by α radioactive isotopes belong to a relatively narrow range E = (4 ÷ 8.7) MeV; According to the definition of kinetic energy (mv2/2, where m is the mass of the particle and v is A Z X→ AZ−−42Y+ 42 He its speed), this corresponds to a speed of tens of thousands of km/s; LSMU/Ionizing Radiation  Radioactivity. Beta decay Types of Beta decay: Beta negative; Beta positive; Electron capture. LSMU/Ionizing Radiation Radioactivity. Beta negative decay Specific to isotopes with a relatively high number of neutrons. A Z X→ Y + e + v~ A Z +1 − LSMU/Ionizing Radiation Radioactivity. Beta positive decay A Z X→Z −A1Y + e+ + LSMU/Ionizing Radiation Radioactivity. Electron capture + + - e − + ZA X→ Z −A1Y + v LSMU/Ionizing Radiation  Radioactivity. Beta decay The energy of β particles emitted by unstable nuclei varies from hundreds of keV to tens of MeV, and the speed is close to the speed of light. β particles are significantly lighter than α particles (an electron is about 7000 times lighter than a 4He nucleus). The electrons ejected during the decay have a different amount of energy. dN/dE is the number of particles per unit energy interval. The kinetic energy of β particles can take all values ​from 0 to a certain maximum energy Emax. LSMU/Ionizing Radiation  Radioactivity. Gamma radiation Nuclear γ-radiation is electromagnetic radiation that occurs during quantum jumps of an excited nucleus to lower energy levels. During this process, the composition of the nucleus (mass number A and charge number Z) does not change; only his energy has changed. The energies of emitted photons usually belong to the range 0.01 ÷ 5 MeV. LSMU/Ionizing Radiation  Radioactivity. Gamma radiation Isomeric transformation Accompanies α and β decays Anihilation Isomeric transformation is the transformation of the nucleus from the excited state to the ground state: mBr → 80Br + γ. 80 LSMU/Ionizing Radiation  Law of Radioactive Decay The law that describes the change in the number of atoms, in 1902 discovered by English physicists Ernest Rutherford and Frederick Sodis: dN = −N dt where N is the number of nuclei of the radioactive isotope, and λ is the DECAY CONSTANT of the radioactive isotope, indicating which fraction of nuclei decays in 1 s. The solution of the differential equation is an exponential function of time: N (t ) = N e 0 − t where N0 is the number of nuclei of the radioactive isotope at the initial time t = 0. This equality expresses the MAIN LAW OF RADIOACTIVE DECAY. LSMU/Ionizing Radiation  Law of Radioactive decay This law can also be written as follows: t − N (t ) = N 0  2 T1 / 2 where T1/2 is the physical HALF-LIFE of the radioactive isotope: ln 2 T1 / 2 =  The Half-life for a given radioisotope is a measure of the tendency of the nucleus to “decay” and is the time required for a quantity to reduce to half of its initial value. This Photo by Unknown Author is licensed under CC BY-SA LSMU/Ionizing Radiation  Law of Radioactive decay Average number of nuclei decay per second: dN A− dt is called the activity of the radioactive source. Activity is usually expressed as the average number of decays per second (decays/s). In the SI system, the unit of activity is called becquerel (Bq): 1 Bq = 1 skil./s. LSMU/Ionizing Radiation X-rays LSMU/Ionizing Radiation Wilhelm Conrad Roentgen 1845-1923 First X-ray Image LSMU/Ionizing Radiation X-ray TUBE LSMU/Ionizing Radiation Rentgeno vamzdis Supaprastinta Rentgeno vamzdžio schema: Įprastuose Rentgeno vamzdžiuose spinduliuotę sužadinančių elektronų energija yra 104 ÷ 105 eV. LSMU/Ionizing Radiation Types of X-rays When electrons strike the atoms of the anode material, two types of X- rays are excited: ❑ bremsstrahlung (when the electron energy does not exceed the ionization energy of the material), ❑ and characteristic (when the electron energy exceeds the ionization energy of the substance. LSMU/Ionizing Radiation Bremsstrahlung How does bremsstrahlung X-ray "appear"? The electron accelerated by the voltage U interacts with the atoms of the anode material. The electron in the anode material is stopped due to the Coulomb interaction with the electric particles of the anode material - atomic nuclei and electrons. As a result of this interaction, the electron is decelerated (it moves with negative acceleration), and the "loss" of the electron's energy is partly transferred to the atoms of the material, the other part turns into bremsstrahlung. LSMU/Ionizing Radiation Bremsstrahlung Source of electrons Acceleration Stopping LSMU/Ionizing Radiation  1 Scattering close to Accelerated electron the nucleus Average photon 1 energy 2 3 3 Scattering far away from the nucleus 2 Photon energy is Collision with the nucleus low Maximum photon energy LSMU/Ionizing Radiation Bramsstrahlung The energy of the photon, which is emitted during the interaction of the electron with the nucleus, is the highest when the photon receives the entire kinetic energy of the electron (A1 = 0), i.e. eU = h LSMU/Ionizing Radiation Bremsstrahlung The wavelength λmax The critical wavelength λc is corresponding to the the short-wave limit of the maximum of the continuous braking stopping spectrum is spectrum and depends on related to the critical the acceleration voltage U. wavelength λc: 3 𝜆𝑐 = 12,345 𝑈 max = k 2 The critical wavelength does not depend on the anode material, but depends only on the accelerating voltage. LSMU/Ionizing Radiation  𝐸𝑀 Accelerated electron 1 𝐸𝐿 𝐸𝐾 2 When an electron jumps from an orbit K that is further from the nucleus to an orbit N that 𝐸𝑀 is closer to the nucleus, a photon is emitted with an energy equal to ℎ𝜈 = 𝐸𝐾 − 𝐸𝑁 LSMU/Ionizing Radiation  𝐸𝑀 Accelerated electron 1 𝐸𝐿 𝐸𝐾 2 When an electron jumps from an orbit K that is further from the nucleus to an orbit N that 𝐸𝑀 is closer to the nucleus, a photon is emitted with an energy equal to ℎ𝜈 = 𝐸𝑘 − 𝐸𝑛 LSMU/Ionizing Radiation Characteristic X-ray The transformation of the energy of the primary electron into a quantum of characteristic X-ray radiation takes place in two stages: 1) initially, the primary electron ionizes the atom, i.e. part of the energy of the primary electron is used up to break the electron bond in the atom, and the remaining part of the energy is transformed into the kinetic energy of the knocked-out free electron (secondary electron); 2) since the resulting positive ion is in an unstable excited state, the electrons of the atom redistribute between the states, emitting a photon at the same time, i.e., the excitation energy is transformed into photon energy (a quantum of characteristic X-ray energy). LSMU/Ionizing Radiation Characteristic X-rays The spectrum of characteristic X-ray radiation is linear. The spectrum is made up of individual lines. The wavelength corresponding to each line depends only on the nature of the material and is independent of the accelerating voltage. LSMU/Ionizing Radiation Quality of X-ray radiation X-rays are often described by the following three terms: Radiation hardness (or just “quality”), The number of photons of radiation ("quantity" of radiation), Exposure dose of radiation. LSMU/Ionizing Radiation Quality of X-ray radiation Factors that determine the exposure dose, hardness and amount of X-ray radiation: 1) X-ray tube target material (Z), 2) Acceleration voltage (U), 3) Anode current (I), Φ=kU2IZ 4) Time of exposure (t), k – proportionality factor 5) Flux filtering. LSMU/Ionizing Radiation X-ray radiation “hardening” LSMU/Ionizing Radiation  Quality of X-ray radiation Φ=kU2IZ Target material Anode current Accelaration Voltage = = = Z Φ mA Φ kVp Φ mA s Φ The spectral composition changes LSMU/Ionizing Radiation Interaction of Ionizing Radiation with Matter LSMU/Ionizing Radiation Interaction of Ionizing Radiation with Matter Ionizing Radiation is divided into: ▪ directly ionizing (alpha, beta particles); ▪ indirectly ionizing (gamma radiation, neutrons) LSMU/Ionizing Radiation  Interaction of Ionizing Radiation with Matter In medicine, the most important characteristics are: Linear stopping power or Energy loss (therapy), Ionizing capacity (therapy), Bragg’s peak (therapy) Linear range or penetration (diagnostic). LSMU/Ionizing Radiation  Interaction of Ionizing Radiation with Matter Linear range is the path a particle travels in a material before losing all of its kinetic energy. It depends on: particles of energy, particle mass, particle charge and material properties. For gamma and X-rays, the range depends on scattering and absorption processes LSMU/Ionizing Radiation Interaction of Ionizing Radiation with Matter Linear range This Photo by Unknown Author is licensed under CC BY-SA-NC LSMU/Ionizing Radiation  Interaction of Ionizing Radiation with Matter Interaction of alpha particles Alpha particles in any absorbing environment (air, water, metal or biological tissue) can interact with: ▪ Nucleus: - Scattering without energy change (Rutherford scattering); - Scattering with a small change in energy; - Alpha particle absorption. ▪ Electrons: - Ionization; - Excitation. LSMU/Ionizing Radiation Interaction of Ionizing Radiation with Matter Interaction of Electrons o Electrons that are stopped emit X-rays. o When interacting with the electrons of atoms, impact ionization occurs. o When encountering atomic nuclei, nuclear excitation and nuclear decay may occur. LSMU/Ionizing Radiation  Interaction of Ionizing Radiation with Matter Interaction of positrons A positron, even after losing all of its kinetic energy, cannot exist in a state of rest. When the positron slows down sufficiently, it is attracted to an electron with a negative charge. They undergo annihilation, and the energy of both particles is released in the form of two photons. LSMU/Ionizing Radiation  Interaction of Ionizing Radiation with Matter Interaction of Photons The nature of the interaction of photons with atoms of matter depends on the energy of photons. Coherent scattering; Photoelectric effect; Compton scattering; Pair production; Photonuclear reactions. LSMU/Ionizing Radiation  Interaction of Ionizing Radiation with Matter Interaction of Photons Coherent scattering This process is typical of low-energy X-rays and gamma radiation. It occurs when the photon energy, hν, is lower than the hν ionization energy of the atoms of the material, AI: hν