Radioactivity Lectures and Seminars PDF

Radioactivity 4th December 2023 Lectures and R a d seminars ioactivity 2 Module Learning Objectives  Become familiar Understand Understand the with different...

Radioactivity 4th December 2023 Lectures and R a d seminars ioactivity 2 Module Learning Objectives  Become familiar Understand Understand the with different measures of term radioactivity types of radioactivity and radioactive decay decay Introduction to practical applications in imaging 4th December 2023 Radioactivity 4 Song of the week! Rate the song ⓘ Start presenting to display the poll results on this slide. Radioactivity Two types of radiation sources HUMAN MADE N AT U R A L LY O C C U R R I N G What makes a material radioactive? Radioactivity is the property of some unstable atoms (radionuclides) to spontaneously emit nuclear radiation, usually alpha particles or beta particles often accompanied by gamma-rays. Key point here is that these atomic nuclei are unstable The forces disrupting the nucleus are stronger than the forces which hold it together https://energyeducation.ca/wiki/images/thumb/c/c6/Nuclear_force.png/350px-Nuclear_force.png The planetary model of the atom www.britannica.com/nobel/micro/514_59.html How does an atom become unstable? An atom is stable if the forces among the particles that makeup the nucleus are balanced. An atom is unstable (radioactive) if these forces are unbalanced; if the nucleus has an excess of internal energy. Instability can result from excess of neutrons or protons Nucleus tries to reach stability by emitting protons, neutrons, energy or other particles https://www.arpansa.gov.au/sites/default/files/legacy/images/basics/nuc_stab.gif Radioactive disintegration Each time a nucleus changes Physical phenomenon called to a stable form by emitting a radioactivity, and the particle or energy, this is a radioactive atoms are called radioactive disintegration nuclei Also called a nuclear Hence the terms transformation or radioactive radionuclides, or decay radioisotopes https://www.snexplores.org/wp-content/uploads/2023/01/680_explainer_radioactivity_decay_atom.jpg Types of radioactive decay  Most well known Others Alpha (α) Positron (β+) Beta (β) Electron capture Gamma (γ) Internal conversion* 4th December 2023 Radioactivity 16 Refresher: Atomic nucleus Number of protons and neutrons determines mass and charge of nucleus A – atomic mass number = number protons and neutrons https://cdn1.byjus.com/wp-content/uploads/2018/07/Notation-of-Atom-700x268.png Z – atomic number = number of protons  Alpha decay https://www.arpansa.gov.au/sites/default/files/alpha.jpg Electrostatic force (between Nuclide must have A >150 Produces daughter nuclide & protons) dominates → the AND insufficient neutrons alpha particle nucleus divides Deposit their energy over a Radiation weighting factor Alphas are slow and heavy short distance → highly (WR) = 20 damaging Alpha decay 212 208 4 83 Bi Tl + 81 2 Bismuth Thallium Alpha (parent nuclei) (daughter nuclei) particle  Alpha decay Easily stopped in air or within few mm tissue Can easily damage cornea Particular concern if ingested or gets into a wound https://www.arpansa.gov.au/sites/default/files/alpha_pen.jpg  Beta decay Beta particles (β) are high energy, high speed electrons (β-) or positrons (β+) that are ejected from the nucleus by some radionuclides during a form of radioactive decay called beta-decay. Light mass means they lose energy quickly through interaction with matter Much less ionising than α – range of a few cm in air / few mm in Al WR = 1 Beta decay β- particles emitted from nuclei which Can think of a neutron as consisting of a have too many neutrons for stability proton and a ‘negatron’ 𝑁 −→ 𝑃 + + 𝛽 − Isolated neutron can decay into proton Proton rejoins nucleus – ‘negatron’ and ‘negatron’ ejected 14 14 6𝐶 −→ 7𝑁 + 𝛽− Beta decay β+ particles emitted from nuclei which Can think of a proton as consisting of a have too many protons for stability neutron and a positron 𝑃 + −→ 𝑁 + 𝛽 + Isolated proton can decay into neutron Neutron rejoins nucleus – positron and positron ejected 11 11 6𝐶 −→ 5𝐵 + 𝛽+  Beta decay May penetrate few cm tissue Can cause skin erythema Particular concern if ingested https://cornellprostatecancer.files.wordpress.com/2017/04/alpha-vs-beta-radiation.png Electron capture If a nucleus of low mass number has too many protons for stability (but has insufficient excess energy to eject a positron) it can lose energy by electron capture (usually from the K or L shells). Proton converted to a neutron and a neutrino 𝑃 + + 𝑒 − −→ 𝑁 + 𝑣 Neutrino No charge Zero rest mass Emitted during β decay – accounts for β having range of energies Hardly ever interacts with anything Half value thickness of many miles in lead  Gamma decay A gamma ray is a packet of electromagnetic energy (photon) emitted by the nucleus of some radionuclides following radioactive decay. Gamma photons are the most energetic photons in the electromagnetic spectrum. Highest energy in EM spectrum – generally >100keV Can pass through many materials (inc. tissue) WR = 1 https://www.arpansa.gov.au/sites/default/files/legacy/images/basics/all_pen.jpg  Gamma decay Both alpha and beta decay can leave daughter nucleus in an excited state Energy stability achieved by emission of gamma rays (γ) Does not affects mass number or atomic https://energyeducation.ca/wiki/images/4/4d/Gamma.png number → isomeric transition  Gamma decay Emission of gamma not always 99 𝑚 99 43𝑇𝑐 −→ 43𝑇𝑐 + 𝛾 immediately following alpha and beta decay Can leave daughter nucleus in excited Half life = 6 hours state for measurable period of time Emits gamma ray of 140keV Example – Technetium-99m – commonly used in nuclear medicine examinations Radioactive decay can be very complex! For info only ☺ https://nuclearsafety.gc.ca/images/fact-sheet-images/halflife_e.gif Measures of radioactivity and decay Activity Activity of a radionuclide is: Number of disintegrations per unit time SI unit is Becquerel (Bq) 1 Bq = 1 disintegration per second Specific activity of a radionuclide: Activity per unit mass Bq/kg Half life H a l f l i f e ( t 1 / 2 ) i s t i m e t a ke n f o r a c t i v i t y t o f a l l t o h a l f A c t i v i t y o f r a d i o n u c l i d e d e c r e a s e s o ve r t i m e a s p a r e n t its initial value nuclide becomes depleted Radionuclide t1/2 15O 2 minutes 99Tcm 6 hours 3H 12 years 234U 244,5000 years https://pages.uoregon.edu/soper/Earth/halfli fe.gif Radioactive decay curve Decay constant Decay constant is the probability that a nucleus will undergo a transition in a given time period 0.693 Decay constant used to calculate 𝜆= decay factors and → dosage in 𝑡1/2 nuclear medicine The probability is lower for nuclides with longer half lives Nuclear medicine imaging Nuclear Medicine Radioactive substance injected is called a radiopharmaceutical Uses radioactive substances to image anatomy and analyse physiological disease processes Radioactive substance injected. Gamma camera used to measure uptake in anatomic structures Many radio-isotopes used – Tc99-m used commonly – 6 hour half life https://www.hcahealthcare.co.uk/-/media/images/c004-editorial/spect-ct-scanner.jpg?cx=0&cy=0&cw=850&ch=400&hash=F2C372E77A2837A34EC6B2CF183CFFA5 Bone scan Often fused with CT scan Effective half-life Physical half-life Biological half life Effective half life Time for the Time for a When both activity of a biological system radioactive decay radioactive to eliminate by and elimination material to natural processes are present, reduce to half its half of the effective half life initial value substance that always less than entered it physical half life Calculating activities Activity at any time calculated based on initial activity and 𝐴0 A0 = initial activity A = activity at given time number of half-lives 𝐴= 𝑛 N = number of half-lives 2 If the radiopharmaceutical preparation of Tc 99-m for a bone scan has a specific activity of 672 MBq per ml at 8:30am, what will be its specific activity at 12:30pm? Calculating volumes What volume of radiopharmaceutical should be injected if the patient arrives at 12:30pm? Summary Thank You