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Physical of Nuclear Medicine The radioactive element :It is unstable nuclei that disintegrate to emit various rays and particles, such as :1- The Alph (α) particles : Are positively charged, helium nucleus, 24 He have range of energy stop in a few cm of air. 2- Beta particles (β) : Are two kind : a- β- are negatively charged are called negatron, are more penetrating but can be stooped in a few meters of air or few millimeters of tissue, they are high – speed electrons. b- β+ positive beta or positron are produced by cyclotrons. β+ is physically identical to an electron except that it has a positive charge. 3- γ – rays Electromagnetic radiation, identical to χ – ray but γ – rays have much higher energies and they are very penetrating than α and beta, α and γ rays from a given source have fixed energies, but β have a continuous of energies up to a maximum characteristic of the source (fixed energies). Isotopes: Nuclei of a given element with different numbers of neutron : Stable isotopes Isotopes Unstable isotopes - Stable isotopes : They are not radioactive like 12C , 13C ) - Unstable isotopes : They are radio active nuclei like [11C , 14C and 13C) most elements do not have naturally occurring radioisotopes but all produced artificially. Nuclear reactor and nuclear medicine : - The production of many artificial radio nuclides. - In medicine used for: Research , diagnostic and therapy from the cancer , tumor , ………… - γ – ray in medicine : γ – rays are very penetrating, γ emitting radioactive element inside the body can be detected outside the body. - Use less 1g of radio nuclides element in medicine purpose. The Radioactive decay and units of radioactivity : A The symbol of radioactive element is Z X where the : X is the element A atomic mass [total number of nucleons) A=p+n p = proton n = neutron Z atomic number Z=e=p n=A–Z number of neutron If n < normal unstable radioactive nucleic γ , α , β rays stable. Radioactive decay : Decay the nuclei of unstable isotopes to its daughter, which is also radioactive, is formed each daughter decays until the final daughter (stable isotope) after emitting the radioactive rays (α , β and γ) A Z ــ decay X 24He ZA ــy A = ــA – 4 Z = ــZ – 2 Ex : 27 When 13 Al is bombarded by deuterons, α – particles are emitted. How many protons and neutrons does its nucleus contain. Solution : A deuteron is the nucleus of the isotopes of H2of mass 2, the equation of the reaction is : 27 2 4 A Al H He 13 1 2 ZX A + 4 = 29 Z + 2 = 14 A = 25 , Z = 12 25 the atom of 12 X is 1225 Mg Ex : α γ ,β β,γ α 234 234 U 234 90Th 91 Pa 90 U Th 234 92 206Pb( stabe) Each radio nuclide decays at a fixed rate indicate by the half life T1/2. T1/2 : the time needed for half of the radioactive nuclei to decay. The basic equation describing radioactive decay is: A = A0 e-λt A = the activity in disintegration per second A0 = the initial activity λ = decay constant t = is the time of decay A=λN N = the number of radioactive atoms N = N0 e-λt T1/2 = 0.693 / λ λ = 0.693 / T1/2 (a) activity % A0 A0/2 Time (hr) 0 T1/2 The unit of radioactivity : The Curie (ci) = 3.7 × 1010 disintegration / s mci = 10-3 ci , ci = 10-6 ci , nci = 10-9 ci 1CRU = international SI unit is Becquerel (Bq) Bq = disintegration / sec 1 ci = 3.7 × 1010 Bq KBq = 103 disintegration / sec MBq = 106 disi / sec Ex : 1g of K40 (40K) to emit 105 B/sec what is and T1/2 of 40 K. Solution : 40g and 40K contains 6.02 × 1023 Avogardo's number Potassium atoms. 1g contains 6.02 10 atom 23 40 A 10 3 6.7 10 18 Sec N 1.5 10 23 T1 / 2 0.693 1017 Sec 1 18 6.7 10 Year = 3.15 × 107 Sec Ex : What is the decay constant of 131I in the Thyroid if T1/2 = 1s days. Ex : If a radio nuclide has a decay constant of 0.001 days-1 a- T1/2 b- How much do have left after 24hr if you have 10MBq at t = 0