Topic 2 - Basic Information of Ionising Radiation JAN 2023 ver1 RPO Course.pptx

Basic Information on Ionising Radiation CONTENTS ¨Introduction ¨Atomic Structure ¨Radioactivity ¨Types of Ionising Radiation ¨Radiation Quantities & Units ¨Sources of Radiation AWAS MESIN SINAR-X Introduction 1890s – X-rays and radioactivity were discovered and spurred the development of atomi...

Basic Information on Ionising Radiation CONTENTS ¨Introduction ¨Atomic Structure ¨Radioactivity ¨Types of Ionising Radiation ¨Radiation Quantities & Units ¨Sources of Radiation AWAS MESIN SINAR-X Introduction 1890s – X-rays and radioactivity were discovered and spurred the development of atomic and nuclear radiation applications. • W.C. Röntgen reported the discovery of X-rays in 1895 • The radioactivity of uranium was discovered in 1896 by Henri Becquerel • In 1898, two new radioactive elements, polonium and radium, were discovered by Pierre and Marie Curie 1900s – the theory of atomic structure was discovered which eventually led to the theory of the relationship between mass and energy in 1907 by A. Einstein. In Malaysia 1897 - Two years after discovery of ionizing radiation (X-ray), Malaysia received its first X-ray machine in Taiping Hospital, Perak 1972- Centre of Research and Application in Nuclear Energy (CRANE) established under PM Dept. 1973- CRANE was changed to PUSPATI which later underwent various administration changes prior to be renamed as UTN. Introduction  Radiation is a general term use to describe emission and transmission of energy through space in the form of waves, including charged and uncharged particles as well as electromagnetic radiation.  Radiation consists of two types: ionizing and non-ionizing radiation.  Ionizing radiation causes ionization whereas non-ionizing radiation does not cause ionization when it interacts with matter. Atomic Structure Matter, Elements, and Atoms • Matter - Anything that occupies space & has mass [e.g. water, diamond] • Elements - A substance that can’t be separated into simpler substance by ordinary chemical means - forms of matter that contain only one type of atom - there are 118 known elements - periodic table [e.g. water is made up of 2 elements: H and O] • Atom - Smallest unit of an element that has all the properties of that element • the basic structure of any element • 12 g of carbon element - contain 6.022 x 1023 carbon atoms - Cannot be broken down into smaller particles by ordinary processes - Determines structure; arrangement and types give matter its properties - Atom is the smallest particle of an element that is capable of entering into a chemical reaction and can take part in chemical combinations Atomic Structure Atoms basically consist of :Nucleus – constituted of proton and neutrons known as nucleons Orbital Electron – the nucleus is surrounded by electrons, orbiting the nucleus in their respective orbits Bohr Model of the Atom Summary of the Atom Particle Symbo l Proton p Neutro n Electro n n Charge +1 (positive) 0 (neural) Mass (kg) Mass (amu) 1.672 x 10- 1.00727 Energy (MeV) 938.2 27 1.675 x 10- 1.00866 939.2 27 e -1 (negative) 0.911x 10- 0.000548 30 0.511 Atomic Mass Unit (amu) Where 1 amu is approximately equal to 1.6605 x 10-24 grams Atomic Mass Unit (amu) The atomic mass of the electron is approximately: Electron = 9.1094 x 10-28 grams = 0.00055 amu Thus, the electron has a much smaller mass than either the proton or the neutron, 1837 times smaller or about 2000 times smaller respectively Nucleus Protons and neutrons together form the nucleus of the atom The nucleus determines the identity of the element and its atomic mass Proton and neutrons have essentially the same mass but only the proton is charged while the neutron has no charge Proton s Protons are positively charged particles found inside the nucleus of an atom. Each element has a unique atomic number (a unique number of protons) Proton number never change for any given element. For example, oxygen has an atomic number of 8 indicating that oxygen atom always has 8 protons Neutron s Neutrons are the other particle found in the nucleus of an atom. Unlike protons and electrons, however, neutrons carry no electrical charge and are thus "neutral" Atoms of a given element do not always contain the same number of neutrons Electron s Electrons are negatively charged particles that surround the nucleus in “orbits” similar to moons orbiting a planet The sharing or exchange of electrons between atoms forms chemical bonds which is how new molecules and compounds are formed Atomic Structure Nuclide - a specific species of an element with a specific no. of neutrons & protons X = chemical symbol of element (e.g: Li, O, Cs, Co, U, Th) A = Mass No. (number of Protons + number of Neutrons) Z = Atomic No. (number Representation of nuclide X: of Protons) A 7 3 Z X or X-A [e.g. 7 3 Li or lithium-7] Li has 3 protons (p) and 3 electrons (e), 4 neutrons (n) Elements The number of protons in an atom dictate the element For an uncharged atom, the number of electrons equals the number of protons Periodic Table System for classifying elements Atomic Structure of Elements Nuclides Hydrogen Z 1 A 1 Helium Lithium-6 Lithium-7 2 3 3 4 6 7 Beryllium Oxygen Sodium 4 9 8 16 11 23 10 Most Abundant Elements Earth's Crust Element Symbol Protons Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium O Si Al Fe Ca Na K Mg 8 14 13 26 20 11 19 12 Relative % of Earth’s Mass 46.6 27.7 8.1 5.0 3.6 2.8 2.6 2.1 Titanium Hydrogen Ti H 22 1 0.4 0.1 Isotopes Isotopes are • Atoms of the same atomic no. (Z) with different mass no. (A) • Isotopes refer to the same element • Isotopes of any element may also be called nuclides Isotope notation typically written as: A X Z X = element symbol A = atomic mass (neutron + protons) Z = atomic number (protons) Isotopes The number of protons and electrons remain the same But the number of neutrons varies Radioactivity Stable Nuclear stability : neutron-proton ratio (n/p) is crucial for the stability Stable nuclide : correct balance in the number of neutrons and protons in the nucleus Stable elements in the low atomic number range have an almost equal number of neutrons, n and protons, Z Stable Nuclides long range electrostatic forces p Line of stability p n short range nuclear forces Note: Stable elements in the low atomic number range have an almost equal number of neutrons, n and protons, Z Radioactivity Unstable Nuclides The nucleus is unstable – “incorrect” balance in the number of neutrons (n) and protons (p) in the nucleus – it will eventually re-arrange itself into more stable configuration So, If ratio too low or too high:  Nucleus become unstable  Rearrange itself into a more stable configuration through transformation or spontaneous decays and the emission of radiation  Nucleus become radioactive Radioactivity Unstable Nuclides Example:• Beta radiation (emission of energetic electrons) occurs when an n/p ratio is too high for stability • Positron emission (Beta positive decay, or β+) or electron capture occurs when n/p ratio is too low for stability Stable and Unstable Nuclides Too many neutrons for stability Too many protons for stability Line of stability Definition and Unit of definition : theRadioactivity property of certain nuclides of spontaneously Radioactivity emitting ionising radiation Transformation is termed as radioactive decay Term ‘Nuclide’ known as; radionuclide or radioisotope for the same element Radionuclide activity - a measure of the number of nuclear transformations taking place every second Unit - Becquerel (Bq) = one nuclear transformation per second Radioactivity Spontaneous disintegration of nuclides – which have “incorrect” number of n and p Emit ionising radiation (alpha, beta, gamma, etc.) e.g. 140 Ba ®140 La ®140 Ce (T1/2 = 12.8 d, 40.3 h, emit beta & gamma) Activity - Disintegration rate S.I. Units: Becquerel (Bq), 1 Bq = 1 dps (s-1) Old units: Curie (Ci), 1 Ci=3.7 x 1010 Bq Specific activity - activity per unit mass (Bq/g) Half life and Decay Law Half life (T1/2): time for activity of radionuclide to reduce by half Decay law: Where: A = activity at time t Ao = the initial activity l = decay constant = 0.693/ T1/2 Half Life - Time for activity to reduce by half No. Of T1/2 Fraction of Activity Left A(t)/A0 1 0 1 1/21 2 1/22 3 1/23 (23 = 2x2x2 = n 1/2n 8) A(t) = A0/2n n = t/T1/2 n = no. of half-lives Half life and Decay Law A(t) = A0 e-t l = ln(2)/T1/2 0.6931/T1/2 A(t) = A0/2n n = t/T1/2 ; n = No. of half-lives Radioactivity – Half Lives Radionuclides Half life (T1/2) Strontium-90 (90Sr) 28.5 yrs Caesium-137 (137Cs) 30.1 yrs Radium-226 (226Ra) 1600 yrs Carbon-14 (14C) 5736 yrs Potassium-40 (40K) 1.28 x 108 yrs What is the activity of Co-60 (100 kCi) after 5 years? Note: T1/2 = 5.27 years λ = 0.693/T1/2 Answer:Aο = 100kCi T1/2 = 5.27 years, t = 5 years, A(t) = ? λt = [0.693/5.27] x 5 = 0.6576 e-λt = 0.5181 A(t) = Aο e-λt = 100 x 0.5181 = 51.81 kCi Chart of Radionuclides (A portion of nuclide chart) Absorption p D ec - ay Emission n E on i s is  m n it o rp o s  b A Original Absorption n Nucleus El ec De tr ca on y Emission Ca + p pt ur e Chart of Radionuclides Decay mode, energy of radiation Cs-137 Cs137 30.07 a Thermal neutron capture cross section Β- 0.514, … g 661.7D _ σ 0.25, 0.4 E 1.1756 Chemical symbol & mass number Half life, annum Fission product Beta decay energy (MeV) Artificially Produced Radioactive Nuclide O 16 Natural abundance 99.76 (atom %) Thermal neutron capture cross section ^  γ 0.19 mb, 0.4 mb 15.994914622 Mass of nuclide based on C-12 Stable Isotope Chemical symbol & mass number Chemical symbol & mass number K 40 Natural abundance (atom %) a Decay mode and energies 0.0117 1.28E9 Half life, annum Β- 1.33, ε γ 1460.8 β+ vw σγ 30 σp 4.4 σα .42 E- 1.3111 1.5049 E+ Naturally Occurring Radionuclide Beta decay energy (MeV) Properties Properties of of Ionizing Ionizing Radiation Radiation cosmic X-rays  2 4 He neutron  - (negatro n) Electron + (positron) -rays Ionisation Removal of e- from atom (normally outer e-) Atom becomes positive ion + free eNumber of +ve charge of ion = number of e removed Ionising radiation : radiation that causes ionisation when passing through matter (  ,  ,  , n, p, ....) Atom becomes -ve ion if it captures electron one eionising radiation Properties Properties of of Ionizing Ionizing Radiation Radiation Alpha Particle •Helium nucleus: 2 protons and 2 neutrons tightly bound together •Emitted from naturally occurring radio nuclides such as uranium and thorium •Lose energy by collisions with atomic electrons - cause ionizations to occur •Directly ionizing particles - cause ionization of an atom without any intermediate interaction taking place •Cause large specific ionization (number of ion pairs formed per unit energy) because of their double positive charge and large mass •Lose their energy in short distance hence range in media is short (less of external hazard but present an internal hazard) Alpha (a ) Particles Helium nucleus (He2+), high E (> 4 MeV), discrete E e.g. 210 84 Po ® 4 2 He + 206 82 Pb Short range (high mass and charge) - few cm in air Not an external hazard but an important internal hazard a emitters: 226Ra, 241Am, 239Pu 238 U 234Th + 4He Beta Particles High speed electrons emitted by a radionuclide. Either be positive (positron) or negative (electrons). Not emitted with discrete energies but show a continuous energy spectrum (unlike alphas). Lose energy more frequently through ionization and excitation. Directly ionizing particles - cause ionization of an atom without any intermediate interaction taking place. Beta Particles For high speed electron (more than 1 MeV) more energy may be lost in the form of X-rays due to interaction with the nuclear field in dense material (bremsstrahlung). Produce less ionization per unit length than alpha particles because of its smaller mass and charge. Have greater range than alpha hence, depending on its energy constitute an external hazard. Not as great an internal hazard as alpha particles. Beta (b -) Particles and Positrons (b +) b- (negatron, e-), positron (e+, b+ ), emitted when nuclides decay, continuous energy distribution, avg. E = (1/3) Emax e.g. 32 15 P ® 0 -1 b + 32 16 S + anti neutrino Cause ionisations and excitations in matter, accompanied by X-rays (bremsstrahlung - increasing with Z), greater range than a , use low-Z materials (Z<13) as shields An external hazard if E > 70 keV (penetrates dead skin layer). An internal hazard although not as harmful as alpha Pure b emitters: 3H, 14C, 90Sr, 90Y, 32P X and Gamma (g ) Rays E.M. radiation (photons) g from excited nucleus; normally g rays have higher E than Xrays X-rays originate from orbits, Characteristic X-rays - de-excitation or transition of electrons in orbits of atoms Bremsstrahlung X-rays - braking radiation, increase with Z Long range, an external hazard but not a great internal hazard Use high-Z materials to shield against photons Photon interactions: Photoelectric, Compton, and Pair production, all three interactions increase with Z Production of characteristic X-rays Production of bremsstrahlung X-rays: (1) Interaction at large distance from the nucleus produces low energy X-rays, (2) interaction at intermediate distance from the nucleus produces intermediate energy X-rays, and (3) direct collision with nucleus produces maximum energy X-ray. Interactions of X- and Gamma-rays with matter •Photoelectric effect •Compton scattering •Pair production Pusat Latihan Nuklear Malaysia / Nuclear Malaysia Training Centre Photoelectric Effect Interaction of photon has a particle-particle collision with an atomic electron Photon transfers all of its energy to the electron If the energy is sufficient to release the electron from its atomic orbit, the atom is ionized Compton Scatter  Happens when a photon collides with an atomic electron and transfers only part of its energy to the electron  Rest of the original photon’s energy is radiated as a lower energy photon  Secondary photon travels in a different direction from the one creating it Pair Production Happens when photon, in the presence of a nuclear field, disappears, changing all its energy into matter in the form of an electron and a positive electron (positron) Incoming photon must have energy greater than 1.02 MeV PHOTON INTERACTION Atomic number (Z) 100 90 80 70 60 Photoelectric effect Pair production 50 40 Compton process 30 20 10 0 0,01 0,1 1 Photon energy (MeV) 10 100 Neutrons Produced by (a,n), (g,n), (n,f), spontaneous fission reactions, and other nuclear reactions Classify according to energy: Slow or thermal (E £ 0.025 eV) Resonance or intermediate (0.5 eV to about 100 keV) Fast (100 keV to 10 MeV) Relativistic (E > 10 MeV) Produce recoil nucleus that causes ionisations (indirect) Neutral - long range, external hazard, much more damaging than g Source of Neutron ( , n) [ Po-Be, Am-Be] Penetrating power of ionising radiation Radiation Quantities And Units Exposure (in Air) Radiation Quantities And Units Exposure (X) = dQ/dM dQ = sum of electrical charges of all ions of the same sign produced by photons in air when all the e- and e+ released in air of mass dM are completely stopped in air Only applicable to photons, S.I. units: 1 C kg-1 Old units: Roentgen (R) 1 R = 2.58x10-4 C kg-1 ; 87.8 ergs/g (air); » 96 ergs/g (tissue) Air Photon dQ dM Radiation Quantities And Units Absorbed Dose (D) = dE/dM dE = mean energy imparted by the ionising radiation to matter of mass dM S.I. units: Gray (Gy); 1 Gy = 1 J kg-1 ; Should specify the medium. Old units: rad 1 Gy = 100 rad; 1 rad = 100 ergs/g Approx. for photon: 1 R »1 rad (for tissue) Ionising radiation dE dM Absorbed Dose (D) Radiation Quantities And Units Radiation Quantities And Units Equivalent Dose [at a Point in Tissue] H = D x WR Put all ionising radiation on an equal basis with regard to potential harm to tissue D = absorbed dose, WR = radiation weighting factor S.I. units: Sievert (Sv) 1 Sv = 1 J kg-1 Old units: rem ; 1 Sv = 100 rem Radiation Weighting Factors (WR) Type and Energy of Radiation Photons (all energies) WR 1 Electrons (all energies) Neutron < 10 keV 10 keV to 100 keV > 100 keV to 2 MeV > 2 MeV to 20 MeV > 20 MeV 1 5 10 20 10 5 Proton with energies > 2 MeV 5 Apha particles, heavy nucleus 20 if WR = Photon = 1 H = D x WR H = 1 gray × 1 (WR) = 1 Sv if WR = Alpha = 20 H = D x WR H = 1 gray × 20 (WR) = 20 Sv Effective Dose HE H E  wT H T T WT = Tissue/risk weighting factor HT = Dose equivalent for tissue or organ Values of WT Tissue or organ Weighting factor Gonads 0.20 Bone marrow (red) 0.12 Colon 0.12 Lung 0.12 Stomach 0.12 Bladder 0.05 Breast 0.05 Liver 0.05 Oesophagus 0.05 Thyroid 0.01 Bone surface 0.01 Remainder (adrenals, kidney, muscle, 0.05 upper large intestine, small intestine, pancreas, spleen, thymus, uterus, brain) Effective Dose HE Radiation Quantities And Units Radiation Quantities And Units Radiation Quantities And Units COLLECTIVE DOSE The total equivalent dose or effective dose to a certain population, such as all patients in a nuclear medicine department, all staff in the department, the whole population in a country, etc. The unit is man.Sv e.g.: 100 people x 0.1Sv = 10 man.Sv SOURCES OF IONIZING RADIATION Natural • Cosmic - from outer space - Be-7, C-14, n, 3H • Terrestrial - from the ground - Uranium series - Thorium series - K-40 Man-made • • • • Medical - diagnostic X-ray, particle accelerator, etc. Fall out of nuclear test - food chain Consumer Goods – colour TV, gas lantern, smoke detectors Occupational Exposure - X-ray machine, radioactive source Natural Radiation Natural Radiation - Cosmic Extraterrestrial - Primary cosmic rays (outer space), secondary cosmic rays (interactions between primary cosmic rays and atmosphere) Produce cosmogenic radioisotopes : 14C, 3T Cosmic ray dose increases with latitude (influence of magnetic field, strongest at the poles) Also increases with altitude (less shielding by atmosphere), Dose approx. doubled for every 1500 m up to a few km above the earth. Global yearly avg. » 0.4 mSv (Radiation Safety, 96-00725 IAEA/PI/A47E, 1996) Natural Radiation Terrestrial Terrestrial - from radionuclides in soil, rocks, atmosphere, food chain, etc. U-238, U-235, Th-232, K-40, rubidium-87 Three main natural decay chains: Th-232, U-235, and U238 Each of the 3 decay chains produces a radioactive gas (e.g. Rn-222 from U-238 decay chain) External and internal exposure Natural Radioactivity in Building Materials (mBq/g) Material Granite Sandstone Concrete Wallboard Gypsum Clay Brick Uranium Thorium Potassium 63 6 31 14 186 111 8 7 8.5 12 66 44 1184 414 89 89 5.9 666 Natural Radiation World average 2.7 mSv/yr, whole body, from all sources Areas with high background radiation: Kerala and Madras states in India, coastal areas of Brazil, Niue Island in the Pacific Certain areas in India and Brazil 13 mSv/y and even 50 mSv/y No significant higher rates of cancer and genetic disorder are observed even at places with much higher than normal background Man-Made Radiation Medical X-ray (0.1 mSv per chest X-ray), nuclear medicine (diagnostic and therapeutic) [0.3 mSv/y] Nuclear weapon test - radioactive fall-out (0.006 mSv/y) Nuclear power (0.008 mSv/y to the public), industries (process control, QC) Consumer products: smoke detectors, luminous watches, gas mantles, TV. [very low] Average Yearly Global Radiation Dose 88.5% of annual dose is attributed to natural radiation (cosmic rays, gamma rays from rock and soil, radon, and internal dose from food and drink). 11% of annual dose is attributed to medical purposes Avg. Yearly Global Radiation Dose (Source: UNSCEAR, 2.7 mSv total) 17.1% 14.5% Radon Internal Medical Others Gamma Cosmic 0.3% 11.2% 8.6% 48.3% 48.3 % 8.6 % 11.2 % 0.3 % 17.1 % 14.5 % Summary Atomic structure – protons, neutrons, electrons Elements – periodic table, isotopes Radioactivity – half life & decay law Ionisation Properties of ionising radiation – α, β, X and γ-rays and neutrons Radiation quantities and units – exposure (R), absorbed dose (Gy), dose equivalent (Sv) and effective dose (Sv) Sources of ionising radiation – natural and manmade A(t) = A0/2n n = t/T1/2 n = no. of half-lives Thank you “All the best in your examination”