Samarium-153
Decay Mode
(Above) Depiction of negatron emission.
Radiation Energies
The maximum beta minus energies for Samarium-153 are: 810 keV (20%), 710 keV (30%), 640 keV (50%); with a 103 keV (28%) gamma photon. While it's evident that the negatron energies are far to high for detection by a scintillation camera, the 103 keV gamma photon is appropriate for imaging use.
In comparison to massive alpha particles, beta particles are smaller and have less mass. Consequently, negatrons are therefore much more penetrating. An alpha particle is easily stopped by a sheet of paper; whereas wood, aluminum and plastic are needed for beta particle shielding. Gamma photons have no mass, as they are electromagnetic waves that only act as particles. Thus, they are the most penetrating form of radiation and materials such as lead and concrete are required for adequate shielding.
Negatron decay
Samarium-153 decays by Beta minus, or negatron, decay; which occurs in nuclei containing too many neutrons relative to the number of protons. During negatron decay; a neutron transforms into a proton, a negatron, and an antineutrino. A negatron is a negative electron from the nucleus with the same mass and -1 charge as an electron; and an antineutrino is a particle with no mass, no charge, and is primarily detected by the amount of energy it carries away from the nucleus. The proton is retained in the nucleus, while the negatron and antineutrino are emitted. This results in the parent and daughter nuclei having the same mass number, but the daughter having an atomic number that is one less than that of the parent.
(Below) Shields required to stop specific types of radiation.