Radionuclide emitting photons

Because of the unique operational and safety requirements of radiopharmaceutical synthesis, the motivation for the development of automated systems is clear. These unique constraints include short synthesis times and control from behind bulky shielding structures that make both access to and visibility of radiochemical processes and equipment difficult. The need for automated systems is particularly expressed for PET radiopharmaceutical synthesis, with the short-lived radionuclides emitting high-energy y photons at 511 keV. Automated synthesis systems require no direct human participation. The short half-lives of the PET radionuclides may require repeated synthesis during the day, thus being a potential radiation burden for the operator when not using automated systems. 

Radiation dose is created by the energy of ionizing radiation being absorbed by some substance, such as biological tissue. The basic unit of dose is the gray (Gy), and dose rates are expressed per unit time (e.g., Gy hr ). A Gy is defined as 1 J of energy absorbed in 1 kg of material. Each radionuclide emits radiation (photon, electron, alpha... 

When interpreting spectra, it is worth remembering that a 511 keV photon can also be expected whenever a radionuclide emits positrons as part of its decay process. Common examples of such nuclides are Na, Zn and " Cu. The interpretation of the presence of a 511 keV peak is not, therefore, as obvious as it might appear. There are three possible explanations, which are not mutually exclusive ... 

Gamma (y) rays are photons deriving from isomeric transitions. Isomeric transitions occur when a nucleus remains in an excited state after a particle emission or a decay by electron capture. These intermediate levels are referred to as isomeric states (or metastable states), and each decays to a lower state (either the ground state or another intermediate state) with lifetimes from picoseconds to years. Gamma ray emissions are characteristic of the radionuclide, and the energies of the emitted photons depend on the energy differences between the initial excited state and the next one. 

Rh is a ft emitting radionuclide suitable for therapeutic applications. It has a 35.4-h half-life and emits 0.566 MeV and 0.248 MeV ft particles and a 319 keV gamma photon. It is a reactor-produced radionuclide that is also potentially available from the separation of fission products in... 

Photons with detectable energy differences that are emitted by various radionuclides can be quantified simultaneously, but independently from each other. This allows the use of dual-labeling approaches (4). These experiments will reveal information regarding both the liposomal carrier—labeled with one radionuclide—and the encapsulated compound—labeled with a different radionuclide—after a single injection in the same animal. However,... 

Scatter occurs when the gamma ray photons emitted from the radionuclide in the lung encounter the thorax tissues and change the travelling direction from their origi-... 

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