Absorption of Ionizing Radiation PDF

Absorption of ionising radiation Medical Biophysics – practical training d o c. R N D r. Mg r. K a t a r í n a K o zl í k o v á , C S c. d o c. RNDr. S ilv ia Du lan ská, P h D. Mg r. J á n P...

Absorption of ionising radiation Medical Biophysics – practical training d o c. R N D r. Mg r. K a t a r í n a K o zl í k o v á , C S c. d o c. RNDr. S ilv ia Du lan ská, P h D. Mg r. J á n P á n i k , P h D. I n g Dan iel Ko sn áč I MP BI T F M C U i n Br a t i s l a v a Th e p r e s e n t a t i o n i s p a r t o f t h e p r o j e c t s K E G A 0 4 0 U K - 4 / 2 0 2 2 a n d K E G A 0 1 5 U K - 4 / 2 0 2 0  Disclaimer This material is intended exclusively for the educational purposes of the subject Medical Biophysics in the 1 st year of General Medicine and Dentistry of the Medical Faculty of Comenius University in Bratislava in the academic year 2022/23. Resources are provided for materials used to better visualize the topic. The individual educational use of this material does not authorize its further distribution as a whole or in parts. Citing of this presentation is possible according the norm ISO 690 (STN 01 0197). Contact: doc. RNDr. Mgr. Katarína Kozlíková, CSc. Mail: [email protected] Workplace of FM CU in Bratislava: Institute of Medical Physics, Biophysics, Informatics and Telemedicine Web: https://www.fmed.uniba.sk/en/ (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 2 Contents ◦ Ionising radiation ◦ Ionising radiation distribution ◦ Radioactivity ◦ Activity ◦ Half-life T1/2 ◦ Types of radioactive decay ◦ Absorption law ◦ Penetrating power of individual types of radiation ◦ Radiation protection ◦ Background radiation ◦ Natural background radiation ◦ Detectors of ionising radiation ◦ Geiger-Müller detector ◦ References (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 3  Ionising radiation Ionising radiation ◦ an energy-carrying radiation in the form of particles or electromagnetic waves ◦ wavelength less than 100 nm ◦ frequency greater than 3 · 1015 Hz ◦ has the ability to directly or indirectly ionize the surrounding environment - to create ions. ◦ has enough energy to strip electrons from atoms, thus leaving the atoms electrically charged Irradiation is exposure to ionising radiation (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 4  Types of ionising radiation (1) (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 5  Types of ionising radiation (2) (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 6  Radioactivity Radioactivity ◦ is a spontaneous transformation of unstable isotopes accompanied by the emission of ionising radiation ◦ division from the point of view of origin ◦ natural radioactivity ◦ artificial radioactivity Radioactive decay ◦ the parent nuclei are spontaneously transformed into daughter nuclei ◦ is accompanied by the emission of energy in the form of ionising radiation (e.g.: a, b, g radiation,...) (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 7  Activity (1) Activity A ◦ represents the main quantity characterizing a radionuclide in terms of the number of radioactive decays that occur in it per unit of time ◦ defined as the average number of spontaneous nuclear decays dN per time interval dt d𝑁 𝐴 = − d𝑡 Bq ◦ the minus sign indicates a decrease in the undecayed number of radioactive nuclei. ◦ SI unit: 1 becquerel (Bq) = 1 s-1 (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 8  Activity (2) Activity expressed according to the number of undecayed nuclei N 𝐴 = 𝜆 · 𝑁 [Bq] ◦ : decay constant Decay constant (𝝀) ◦ characterizes the given isotope ◦ is defined as the probability of the decay of an atomic nucleus in an infinitesimally small time interval ◦ SI unit: s-1 (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 9  Activity (3) The activity of the radioisotope is a function of time ◦ 𝐴0 is the initial activity at time t0 ◦ 𝐴𝑡 is the activity at time t Analogously, for the decrease in the number of undecayed radioactive nuclei applies ◦ 𝑁0 is the initial number of untransformed nuclei at time t0 ◦ 𝑁𝑡 is the number of untransformed radioactive nuclei at time t (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 10  Half-life (1) Half-life T1/2 ◦ average time interval during which the original activity/number of undecayed radioactive nuclei decreases to one half of the initial value For activity A at time T1/2 applies ◦ 𝐴0 is the initial radioactivity of the radioactive nucleus From the given relationship, the half-life T1/2 can be derived (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 11  Half-life (2) 1.0 1 The graph shows: 0.9 Activity with multiples 0.8 T1/2 decreases as 2n, 0.7 where n is a multiple of 0.6 T1/2 N/N0 A decrease in the relative number of nuclei of the parent nuclide (T1/2(P) = 1) 0.5 0.5 An increase in the relative number of nuclei of the daughter nuclide A(0) = A0 0.4 A(1 · T1/2) = (1/2) · A0 0.3 0.25 0.2 A(2 · T1/2) = (1/4) · A0 0.125 0.1 0.0625 A(3 · T1/2) = (1/8) · A0 0.0 A(n · T1/2) = (1/2n) · A0 0 1 2 3 4 5 6 7 8 9 10 11 Multiples of T1/2 (graph: Ján Pánik) (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 12  Types of radioactive decay 1. α decay: A A−4 ZX → Y−2 Y + 42He 226 88 Ra → 222 4 86 Rn + 2 He 2. β decay: A A ∗ a) Negative beta decay (β- decay): ZX → Z+1X + e− + ν෥e 1n 0 → 11p + e− + ν෥e A A ∗ b) Positive beta decay (β+ decay): ZX → Z−1X + e+ + νe 1p 1 → 10n + e+ + νe A − A ∗ 81Kr + e− 81 c) Electron capture (e.g. K-capture): ZX + e → Z−1X + νe 36 → 35Kr + νe 3. γ decay: A ∗ ZX → AZX + 𝛾 238 ∗ 92 U → 238 92 U +γ (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 13  Radiation absorption Absorption of a monoenergetic beam of radiation ◦ described by the exponential absorption law ◦ I is the intensity of the radiation after passing through an absorbing medium of thickness x ◦ I 0 is the intensity of the incident radiation ◦ µ is the linear absorption coefficient ◦ indicates the decrease of the number of particles in a unit thickness of the absorbing layer (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 14  Half-value thickness Half-value thickness (half-layer) d1/2 ◦ The thickness of the absorbing medium, which reduces the intensity of the incident radiation by half Linear absorption coefficient 𝝁 ◦ characterises the attenuation of the beam intensity ◦ N0 the number of particles incident on the medium ◦ N is the number of particles that have left the medium (attenuated beam) ◦ x is the thickness of the medium Absorption of radiation in a medium of thickness x (figure: Ján Pánik) (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 15  Absorption law Exponential attenuation of γ beam for water and concrete. 1.0 Intensity of γ radiation Relative intensity of g radiation 0.9 Exponential decrease Concrete with an energy of 364 keV (131I) 0.8 Water is attenuated to 50 % 0.7 of the original value 0.6 0.5 2.9 6.2 after passing 0.4 through a thickness of 0.3 12.5 2.9 cm in concrete 5.9 0.2 or 18.8 8.8 0.1 6.2 cm in water 0.0 0 5 10 15 20 25 30 35 40 45 50 Penetration depth [cm] (graph: Ján Pánik) (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 16  Penetrating power of individual types of radiation Modified after: https://openclipart.org/detail/274074/penetrating-power-of-different-types-of-radiation-alpha-beta-gamma-and-neutrons (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 17  Radiation protection The role of radiation protection ◦ to reduce the absorbed dose in the human body to the lowest possible extent ◦ ALARA principle: „As Low As Reasonably Achievable" Time: When working with RA emitters, it is necessary to limit the time to the smallest possible level, so as not to expose yourself to unnecessary radiation 𝐷 = 𝐷ሶ ∙ 𝑡 [Gy] Distance: Stay away from sources of RA radiation as far as possible 𝐷ሶ = 𝐷ሶ 0 /𝑟 2 [Gy/s] Shielding: When working with RA sources, use appropriate shielding depending on the type of radiation W 𝐼 = 𝐼0 ∙ 𝑒 −𝜇∙𝑥 m2·sr (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 18  Background radiation Background radiation consists of ionising 0.48 mSv/year 15.84% 0.6 mSv/year radiation originating from: 0.39 mSv/year 12.87% 19.8% 1. Cosmic and cosmogenic sources 0.29 mSv/year 9.57% (cosmic radiation,...) 0.01 mSv/year 1.26 mSv/year 0.33% 2. Terrestrial sources 41.58% Radon (radon, soil, atmosphere, hydrosphere,...) Cosmic radiation Natural radiation Medical applications 3. Anthropogenic sources released as a result Ingestion Nuclear weapons tests, Chernobyl accident, nuclear energy of human activities (medical applications nuclear weapons tests,...) Average annual doses and contributions from individual radiation sources according to UNSCEAR, 2008 (Pie chart: Ján Pánik). (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 19  Detectors of ionising radiation The principle of detection of each type of radiation ◦ its interaction with the detector material, which must be constructed in such a way that a sufficient number of registrable secondary phenomena arise in it due to the effect of radiation Detectors ◦ devices that transform the result of the interaction of ionising radiation with a suitable material environment into a registerable form (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 20  Detectors of ionising radiation Mechanism Usage Type of device Detector type ionisation chambers gaseous proportional computers gaseous Ionization radiation monitoring GM computers gaseous semiconductor detectors solid substance crystal or liquid scintillation radiation monitoring scintillation detectors scintillating substance thermoluminiscence personal dosimetry TLD dosimeter Crystal chemical reactions personal dosimetry fotographic film phtoemulsion calibration of heating measurement devices calorimeter liquid or solid and standards biological changes emergency situations biological tissue biological tissue (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 21  Geiger-Müller detector The G-M detector ◦ is an electronic detector ◦ electrodes are connected to high voltage (600-1000 V). ◦ filled with gas (Ne, Ar) with lower pressure than atmospheric one Process of detection ◦ After the IR enters the detector, ionization occurs in the gas ◦ the process is avalanche-like ◦ up to 1010 secondary electrons are generated from 1 primary electron ◦ a strong current pulse is generated Usage Working principle of the G-M detector. (howstuffworks.co ◦ contamination meters, infestation detectors, monitoring systems… (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 22  References BISWAS, R., H. SAHADATH, A. S. MOLLAH a Md. F. HUQ, 2016. Calculation of gamma-ray attenuation parameters for locally developed shielding material: Polyboron. Journal of Radiation Research and Applied Sciences [online]. B.m.: Elsevier Ltd, 9(1), 26–34. ISSN 1687-8507. Available at: doi:10.1016/j.jrras.2015.08.005 HRAZDIRA, I., MORNSTEIN, V., BOUREK, A., ŠKORPÍKOVÁ, J. Fundamentals of Biophysics and Medical Technology. 2nd revised edition. Brno : Masaryk University, Faculty of Medicine, 2012. 325 p. ISBN 978-80-210-5758-6.​ JIRÁK, D., VÍTEK, F. Basics of Medical Physics. Praha : Charles University, Karolinum Press, 2017. 223 p. ISBN 978-80-246-3810-2. KOZLÍKOVÁ, K., MARTINKA, J. Theory And Tasks For Practicals On Medical Biophysics. Brno : Librix, 2010. 248 p. ISBN 978-80-7399-881-3 ZÁKON Č. 87/2018, Z.z., 2018. Zákon č. 87/2018 Z. z. o radiačnej ochrane a o zmene a doplnení niektorých zákonov [online]. 2018. Available at: http://www.slov-lex.sk/static/pdf/2018/87/ ZZ_2018_87_20200406.pdf (c) K. Kozlíková et al., 2022 Absorption of ionising radiation 23