Nuclear Pharmacy Lecture 2
Several nomenclatures are important: ● Nuclide: is any particular atomic nucleus with a specific atomic number Z and mass number A, it is equivalently an atomic nucleus with a specific number of protons and neutrons.Nuclides may be stable or unstable and unstable nuclides are radioactive. ● Isotopes: is one series of nuclides have the same atomic number, but a different number of neutrons. They exhibit the same chemical properties. Examples : A carbon atom: It has 6 protons and 6 neutrons we call it ʺcarbon-12“ 126C because it has an atomic mass of 12. One useful isotope of carbon is ʺcarbon-14“, 146C which has 6 protons and 8 neutrons. Another example is the oxygen isotopes 158O, 168O, 178O, 188O.
● Isotones: nuclides having the same number of neutrons but different atomic number. Example, 5926Fe, 6027Co, 6229Cu each having 33 neutrons.● Isobars: nuclides with the same mass number, but different number of protons and neutrons, example 6729Cu, 6730Zu are isobars having the same mass number 67.●Isomers: nuclides having the same number of protons and neutrons but differing in energy states. Example 99Tc and 99mTc.The nuclides, both stable and radioactive are arranged in the form of a chart.
Radioisotopes, Radionuclides: unstable isotopes which are distinguishable by radioactive transformation. Radioactivity:the process in which an unstable isotope undergoes changes until a stable state is reached and in the transformation emits energy in the form of radiation (alpha particles, beta particles and gamma rays). Radiation refers to particles or waves coming from the nucleus of the atom (radioisotope or radionuclide) through which the atom attempts to attain a more stable configuration. Electron volt: 1 eV is the energy acquired by an electron when accelerated through a potential difference of 1 V. This amount of energy is very small, so the energies of particles are usually given in terms of: MeV (megaelectron volt) KeV (kiloelectron volt) 1 MeV = 103 KeV = 106 eV
Nuclear stability The stability of the atoms depends (N/Z) ratio in the nucleus. Above the atomic number 82, all elements are radioactive. The nucleons (P or N) are in a state of continual motion (natural isotopes) If additional N or a deficiency of N occurs, the atom attempts to regain its stability by giving off either a photon, such as gamma ray, or particle from the nucleus to attain a more stable (N/Z) ratio and the nucleus is transformed into another. This phenomenon is known as radioactivity or radioactive decay
Radioactive decay Majority of nuclides are unstable and the unstable nuclei decay by spontaneous fission, α-particle, β-particle, or γ-ray emission or electron capture in order to achieve stable. The radio-nuclides decay to achieve the N/Z ratio of the nearest possible stable nuclide. Radioactive decay by particle emission or electron capture changes the atomic number. Radionuclides may decay by any one or a combination of five process α decay, β- decay, β+decay, electron capture or isomeric transition.
Mode of radioactive decay: Radioactive decay Is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, named the daughter nuclide. When an unstable nucleus decays, It may give out:-
1. Alpha particle decay (α-decay):● α-decay occurs in very heavy elements, for example, Uranium (U) and Radium (Ra). ●Alpha particles are made of2 protons and 2 neutrons bound together in the nucleus.We can write them as 42α , or 42He, because they're the same as a helium nucleus.● This means that when a nucleus emits an alpha particle, its atomic number decreases by 2 and its atomic mass decreases by 4. Example: 23592U 23190Th + 42He● Alpha particles are relatively slow and heavy.●Alpha particles emitted from a particular nuclide have the same energy.
They have a low penetrating power - you can stop them with just a sheet of paper. Because they have a large charge, alpha particles ionize other atoms strongly. Since alpha particles cannot penetrate the dead layer of the skin, they do not present a hazard from exposure external to the body. However, due to the very large number of ionizationsthey produce in a very short distance, alpha emitters can present a serious hazard when they are in close proximity to cells and tissues such as the lung. Special precautions are taken to ensure that alpha emitters are not inhaled, ingested or injected.
2- Beta particle decay (β-decay):● Beta particles have a charge of minus 1. This means that beta particles are the same as an electron. We can write them as β- or e-, because they're the same as an electron.A. Negatron (β- ) emission: Nuclei with excess neutrons gain stability by conversion of a neutron into a (proton + β- + v). v is an antineutrino which is needed to conserve energy in the decay. There is no change in the mass number, but the atomic number increases by one unit.Example of β- decay:13153I 13154Xe + β- + v generally: n → p +β-+ v
Negatron (β- ) emission: 4019K 4020Ca + β- + antineutrino
B. Positron or β+ Decay: This process occur with neutron deficient or proton rich nuclei. Conversion of a proton into neutron + positron (β+) + v (neutrino). Positrons are emitted with a continuous energy spectrum. After β+ particle emission, the daughter nuclide has an atomic number that is one less than that of the parent. There is no change in the mass number but the atomic number is reduced by one unit.Examples:6429Cu → 6428Ni + β+ + v158O → 157N + β+ + v generally: p → n + β++ v
● They are fast, and light. ●Beta particles have a medium penetrating power - they are stopped by a sheet of aluminium.●Beta particles ionize atoms that they pass, but not as strongly as alpha particles do. Beta particles are much less massive and less chargedthan alpha particles and interact less intenselywith atoms in the materials they pass through, which gives them a longer range than alpha particles.
3. Gamma-emission (γ rays):● Gamma rays are waves, not particles. ● This means that they have no mass and no charge. ●In Gamma decay: atomic number unchanged, atomic mass unchanged. ● Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead to reduce them.● Gamma rays do not directly ionize other atoms, although they may cause atoms to emit other particles which will then cause ionization.● We don't find pure gamma sources - gamma rays are emitted alongside alpha or beta particles.
Determine whether alpha or beta decay occurs in the reaction in which lead-210 decays to bismuth-210.21082Pb 21083Bi + AZX 21082Pb 21083Bi + 0-1β Negatron decay β- Identify the decay particle emitted and the decay process that occurs when protactinium-231 decays to actinium-227. 23191Pa 22789Ac + AZX 23191Pa 22789Ac + 42He Alpha (α)-decay