Nuclear Physics: Radiation, Interactions, and Detection
Mass number A = N + Z, where N = A – Z. There are three types of nuclides: Isotopes: same number of protons, different number of neutrons. Isobars: same mass number A. Isotones: same number of neutrons, different Z and A. Equivalence between mass and energy: E = mc2. The nucleus mass M is equal to Mp + Me.
Electromagnetic Radiation
Electromagnetic radiation transfers energy via an electric field and a magnetic field. One form of transport is by radiation or waves. The energy carried by a photon is proportional to the frequency of the associated wave. The longer the wave, the less energy and the lower the frequency.
Nuclei
The stable number of protons and neutrons (n) varies with time. Unstable nuclei tend to change their composition by the spontaneous emission of some particles, i.e., radioactivity. The atoms that behave this way are radionuclides. The speed with which they transform is characteristic of each radionuclide and is expressed by the decay constant.
Types of Radiation
- Ionizing Radiation: Consists of charged particles (e–), protons, and alpha particles. These are directly ionizing radiation, and the ionization of the medium is constituted by the subject itself.
- Electromagnetic Radiation (photons) and Neutrons: Consisting of neutral particles (neutrons), they produce ionization indirectly through other ionizing particles.
Collisions
- Elastic: A particle strikes the atom, ceding part of its energy in the form of kinetic energy; there is no alteration.
- Inelastic: The atom is ionized or excited. A radioactive particle is stopped or diverted around the nucleus without modifying the structure of the atom, causing braking radiation.
Photoelectric Effect
At low energies, the photoelectric effect transfers the total energy of a photon to an electron bound to an atom. The electron comes with an energy of the photon that is less constraining.
Compton Effect
At medium energies, the photon gives part of its energy to another photon, becoming less energetic and diverting its trajectory.
Pair Creation
At high energies, a photon approaching an atomic nucleus is embodied in a positron and an electron only when the energy is greater than 1.002 keV.
Detection and Measurement of Radiation
- Detectors: Particle counters.
- Spectrometers: Measures energy and radiation.
- Ionization Chamber: Uses plane or cylindrical electrodes. Low efficiency to detect gamma radiation.
- Proportional Counter: The radiation interacts and produces ionization on its way to the electrodes.
- Geiger Counter: A greater potential difference reaches a particle, producing a flood of electrons. For low radiation levels, it does not provide information on radiation and is slow with a long dead time.
- Scintillation Detectors: A substance formed by a luminescent photomultiplier.
Characteristics of the Glass
The conversion rate should be as high as possible. The glass should be as transparent as possible to adjust the wavelength emitted to this optimal spectral band. The crystals contain glass activators. The thickness equals the maximum range of particles.
Personal Dosimeters
- Operational Dosimeter: Direct reading, personal.
- Thermoluminescent Dosimeters: When the dosimeter is irradiated, it emits light, registering thermoluminescence. It is heated and emits light with a photomultiplier. If not irradiated, it can be used again and cannot be archived.
- Photographic Dosimeters: Can be recorded.
- Operational Dosimeters: Instantaneous reading for configuration.
Monitors
Brentano exposure dose = open beta and gamma, gamma single window closed.