NucMed

• All matter in the universe has its origin in an event called the "big bang", a huge cosmic explosion
• Since the planet Earth was formed, most of the atomic nuclei have undergone transformation to more stable(non-radioactive)combinations
• Naturally occurring isotopes that remain


  • 40K
  • 204Pb
  • 232Th
  • Uranium isotopes
• First steps in the history of radioactivity


  1. Discovery of spontaneous radioactivity

  2. Separation of radioisotopes and elucidation of its properties

  3. Demonstration of practical uses of the radioactive elements
• Henry Becquerel


  French physicist considered one of pioneers in the history of radioactivity
• Henry Becquerel shared the Nobel prize of Physics with Marie Sklodowska Curie and Pierre Curie, for the discovery of radioactivity


  1903
• Marie Sklodowska Curie


  Conducted pioneering research on radioactivity, isolating the first radioisotopes
• Marie Sklodowska Curie was the discoverer of polonium and radium, and became the first woman to win a Nobel Prize, and the only person to win in multiple sciences (Physics and Chemistry)
• Georg Hevesy


  Hungarian radiochemist, became a Nobel laureate in 1943 for his key role in the development of radioactive tracers to study chemical processes such as in the metabolism of animals
• Hermann L. Blumgart


  Chair of the Department of Medicine at Beth Israel Hospital in Boston from 1928 To 1962, measured the arm-to-arm circulation time with a modified cloud chamber detector
• Irène Joliot-Curie


  Daughter of Maria and Pierre Curie, jointly with her husband Frederic Joliot, was awarded the Nobel Prize for chemistry in 1935 for their discovery of artificial radioactivity
• Irradiating stable isotopes with charged particles resulted into unstable isotopes, leading the way to the production of artificial radioactive materials
• Ernest Orlando Lawrence


  Built a cyclotron capable of accelerating deuterons up to about 3 MeV, and used it to produce several biologically important radionuclides
• Enrico Fermi


  Realized the neutron was advantageous for radionuclide production, made a strong neutron source, irradiated 60 elements and induced radioactivity in 40 of them, later supervised the design and operation of the world's first artificial nuclear reactor
• Nuclide chart


  Plot with the number of neutrons in the nucleus on the x axis and the number of protons on the y axis

  
• Line of stability


  Divides the nuclides in neutron deficient and neutron excess nuclides, each decaying in a different way

  
• Periodic system


  Organized according to the number of protons (atom number) in the nucleus

  
• Isotopes


  Elements occupying the 'same place' in the periodic system, introduced by Soddy in 1913
• Neutron


  Discovered by Chadwick in 1932
• Nuclide chart


  • Darkened fields represent stable elements, nuclides to the left are deficient in neutrons and those to the right are rich in neutrons

  
• Stability line


  Best stability is achieved when the number of protons and neutrons in the nucleus is about the same, for light elements it follows a straight line, for heavier elements there is a neutron excess

  
• Nuclear stability


  • Determined by the 'strong force' that binds the nucleons together, and the Coulomb force that repulses particles of like charge
• Proton-neutron system


  The nuclear force amounts to 2.225 MeV, forming a stable combination called Deuterium

  
• Proton-proton system


  The nuclear force is equally strong but the repulsive Coulomb forces are stronger, so this system cannot exist
• Neutron-neutron system


  The nuclear force is equally strong and there is no Coulomb force, but this system cannot exist due to other repulsive forces
• 1. value


  Energy gained or lost in a nuclear reaction, calculated from the mass difference of particles before and after the reaction
• Radioactive elements have positive Q-values and decay spontaneously, particle induced reactions usually have negative Q-values except for thermal neutrons</b>
• Positively charged particles have to overcome the repulsive Coulomb force of the nucleus leading to higher threshold values than Q-values
• Scheme of target irradiation


  • The incident beam irradiates the target, is scattered and absorbed, energy can be transferred totally or partly to the target, interaction can be with parts or the whole of the target nucleus, target should be thick enough to ensure high activity of the product
• Proton reactions


  Have to overcome the Coulomb barrier, having a threshold energy
• Neutron reactions


  Have no threshold energy, very low energy neutrons can penetrate into the nucleus to cause a nuclear reaction

  
• General equation for a nuclear reaction


  1. incoming particle, A: target nucleus in ground state, b: outgoing particle(s), B: rest of the nucleus, Q: reaction energy
• Reaction characteristics


  • Energy threshold, probability (cross section) varying with the incoming particle energy
• Reaction mechanisms


  Formation of a compound nucleus, direct reactions
• Compound nucleus formation


  • Large probability to be formed in a central hit, preferable at low energies, close to the threshold energy
• Direct reactions


  • Occur at the edge of the nucleus, at high energies, associated with the geometry of the nucleus, small cross-section, fairly constant with energy
• There are two major ways to produce radionuclides: using reactors (neutrons) or particle accelerators (protons,deuterons, a particles or heavy ions)
• Reactor produced radionuclides are generally neutron-rich, accelerator produced are neutron deficient
• Nuclear reactor


  • Facility where a fissile atomic nucleus undergoes fission after irradiation with low energy neutrons, produces fast neutrons with energies up to about 10 MeV
• Reactor regulation


  • Neutrons are slowed down in a moderator, the slowed down neutrons start new fissions, by regulating this nuclear chain reaction there will be a steady state production of thermal neutron with a typical neutron flux in the order of 1014 neutrons • cm-2. S1