Review or Introduction to Atomic and Nuclear Physics Atoms are composed of a dense nucleus of positively charged protons and neutral neutrons and negatively charged electrons in discrete energy levels or orbitals.

Review or Introduction to Atomic and Nuclear Physics Nuclear stability depends on the ratio of neutrons to protons or the N/P ratio. At low atomic numbers the N/P ratio for stability is 1:1. At High atomic numbers the N/P ratio for stability is 1:1.5. Above atomic number 83, Bismuth there are no stable isotopes.

Review or Introduction to Atomic and Nuclear Physics Atomic Number = the number of protons in the nucleus of an atom, this defines the element or Z Number. Mass Number = the number of total particles in the nucleus, this defines the isotope or A Number. Neutron Number = Number of neutrons in the nucleus, or N Number.

Review or Introduction to Atomic and Nuclear Physics Isotope = species with the same atomic (Z) number and therefore chemical properties but differing numbers of neutrons (N number) and therefore different mass or A number. Isomer = Nuclides that have the same atomic (Z), and mass (A) and neutron (N) numbers but differing nuclear energy states. These are important concepts.

Review or Introduction to Atomic and Nuclear Physics Isotone – Nuclides that have the same number of neutrons (N) but different number of protons. Isobar – Nuclides that have the same mass number (A) but different number of Protons (Z number). These are not important concepts.

Review or Introduction to Atomic and Nuclear Physics Chemistry is the result of rearranging of the electrons in the orbits of atoms. Radiation is the result of the decay of unstable nuclei. There are three + kinds of ionizing radiation Alpha particles Beta particles Gamma rays

Review or Introduction to Atomic and Nuclear Physics ALPHA PARTICLES – Helium-4 Nuclei Elemental symbols are one or two letters. The first letter is upper case and the second if any is always lower case. At the lower left is the atomic number or Z number.

Review or Introduction to Atomic and Nuclear Physics Elemental Symbols At the upper left hand corner is the mass number A At the upper right is the charge In chemical equations the lower right is for the number of the species. This depicts an alpha particle also designated by a Greek letter alpha

Review or Introduction to Atomic and Nuclear Physics Types of Radiation Alpha particles - 4He2+ or a Beta particles – High Speed Electron b- Gamma Rays – Electromagnetic radiation originating in the nucleus. g

Review or Introduction to Atomic and Nuclear Physics X-rays are the same electromagnetic waves as gamma rays only they result from movements of electrons outside of the nucleus. Generally x-rays are less energetic than gamma rays but the energies actually overlap.

Review or Introduction to Atomic and Nuclear Physics Alpha Particle Emissions – Large Nuclei getting smaller. This decay is one of the probable reasons that cigarette and other tobacco products increase risk of lung cancer. Polonium 210 is in tobacco smoke. It is a member of the uranium decay chain. Uranium and other decay products do not volatilize and stay in the ash but the polonium volatilizes and is in the smoke.

Review or Introduction to Atomic and Nuclear Physics Beta particle emissions are the result of the neutron rich nuclei transforming a neutron into a proton and an electron or beta particle. Cs-137  Ba-137 + b-

Review or Introduction to Atomic and Nuclear Physics Gamma Decay – Involves the more stable arrangement of nuclear particles without a particle being emitted. Nuclear stability appears to depend on magic numbers. Even numbers of protons and neutrons are more stable than odd numbers. The numbers 2, 8, 20, and 50 appear to be more stable. There are apparently energy levels within the nucleus also.

Review or Introduction to Atomic and Nuclear Physics Gamma Decay

Review or Introduction to Atomic and Nuclear Physics Positron emission is where neutron deficient nuclei splits a proton into a positron and a neutron. The positron is ejected from the nucleus.

Review or Introduction to Atomic and Nuclear Physics Type of Decay Emissions Alpha – 4He 2+ Beta – b- Gamma – g Positron - b+

Review or Introduction to Atomic and Nuclear Physics Another decay mechanism does not involve a nuclear emission but rather a capture of an electron. Electron capture involves the capture of an inner shell electron by the nucleus which then neutralizes a proton turning it into a neutron. This is a competing process with positron emission for neutron deficient nuclei.

Review or Introduction to Atomic and Nuclear Physics While there is no nuclear emission there is emission of an x-ray due to the movement of an outer shell electron into the vacant orbital of an inner shell. Electrons exist in discrete energy levels called orbitals and there must be the emission of energy to go to a lower orbital.

Review or Introduction to Atomic and Nuclear Physics Radiation Interactions Alpha particles interact with the electrons since alpha particles are about 7300 times as massive as an electron the large alpha particles scatter very many electrons removing them from the atoms that comprise the matter they are passing through in a very short space. They create very many ion pairs.

Review or Introduction to Atomic and Nuclear Physics Radiation Interactions Beta Particles will also cause ionizations by interacting with the orbital electrons of the matter it passes through but an electron has the same mass as a beta particle, in fact is a slowed down beta particle so the interactions are less concentrated and the penetration of beta particles relatively farther than that of alpha particles.

Review or Introduction to Atomic and Nuclear Physics Radiation Interactions Beta particles passing near a nucleus will be deflected and slowed by that nucleus. In doing that they must give up some energy. That energy is electromagnetic energy, because it comes from electron interaction it is called X-Rays instead of Gamma Rays that originate in the nucleus. Unlike characteristic x-rays resulting from a change from one discrete energy level [orbital] to another discrete energy level this Bremsstrahlung or braking radiation is a spectrum of energy.

Review or Introduction to Atomic and Nuclear Physics Radiation Interactions

Review or Introduction to Atomic and Nuclear Physics Radiation Interactions

Review or Introduction to Atomic and Nuclear Physics Radiation Interactions Gamma and X-Rays are the same electromagnetic phenomenon and behave the same way, depending on energy.

Review or Introduction to Atomic and Nuclear Physics X and Gamma Radiation Interactions Coherent Scattering Coherent scattering is also sometimes called excitation. Energy from an x or gamma ray is absorbed and moves an electron to a higher unfilled shell. The left over energy continues on. Eventually in most cases the atom will de-excite and emit an x-ray. This reduces the energy of the x-rays until eventually it is expressed as vibrational energy or heat. Coherent scattering is the lowest energy process of energy absorption of x-rays.

Review or Introduction to Atomic and Nuclear Physics X and Gamma Radiation Interactions Photoelectric Effect – All energy absorbed in ionizing the atom. Photoelectric effect is the next higher energy interaction.

Review or Introduction to Atomic and Nuclear Physics X and Gamma Radiation Interactions Compton Scattering – Similar to photo electric effect but energy is left over. It should be somewhat obvious that Compton Scattering is a higher energy process than the photoelectric effect.

Review or Introduction to Atomic and Nuclear Physics X and Gamma Radiation Interactions Pair Production In the vicinity of a nucleus an x or gamma ray of energy greater than 1.02 million electron volts may become an electron positron pair. A positron is a positively charged electron and will be attracted to the first negatively charged electron it encounters and they will annihilate and form two x-rays of 0.511 MeV energy. This effectively reduces the energy intensity of the incident [usually] gamma ray.

Review or Introduction to Atomic and Nuclear Physics Radiation Interactions Annihilation is the fate of positrons emitted from the nucleus also and the annihilation, producing two orthogonal x-rays is the basis of positron emission tomography or PET scanning.

Review or Introduction to Atomic and Nuclear Physics Decay processes are Alpha Emission Beta Emission Positron Emission Electron Capture and Gamma Ray Emission X-rays are often emitted as secondary interactions occur with electrons outside of the nucleus.

Review or Introduction to Atomic and Nuclear Physics Interactions are Particulate Scattering Alpha lots of scattering over short distance Beta low amount of scattering over longer distance Coherent Scattering Photoelectric Effect Compton Effect Pair production / Annihilation Annihilation also occurs with positron emission.