ENTC 4390 MEDICAL IMAGING. RADIOACTIVE DECAY. Nuclear Particles & Radiation. Only a few of the many different nuclear emanations are used in medicine. In order of importance, the entities are: x-rays Electromagnetic waves of very short wavelength that behave in many ways like particles.
Don’t be confused by this picture!
A single radioactive source does not emit all three types a, b and g.
detector3 Types of Radioactivity
a particles: helium nuclei
b particles: electrons
Stopped by metal
g : photons (more energetic than x-rays) penetrate!
2. Elements/Atomic Number (Z) & Atomic Masses
Key: Chemical Behavior Determined by Z and Ionization
Radium (parent) nucleus equals the sum of the mass numbers of the product (progeny) nucleus and the ejected particle.
Energy of radioactive decay.
a. has a decay constant of 9.49 x 10-3 hr -1. Find the activity in becquerels of a sample containing 1010 atoms.
natural log format
Gamma rays are emitted due to electrons making transitions to nuclear energy levels.
No, gamma rays are high energy photons emitted when nucleons make transitions between their allowed quantum states.
Beta rays are produced when the atom spontaneously repels all its electrons from its orbits.
Beta particles are electrons. However, the atom does not emit its atomic electrons.
Beta electrons are emitted by a nucleus along with a neutral weakly interacting particle called the neutrino when one of the neutrons in the nucleus decays.
Free neutrons are unstable - they decay. Sometimes in atoms with large numbers of neutrons, one of its neutrons may be loosely bound - spontaneous decay!
Beta particles are:
Some radioactive elements emit a positively charged particle which is in all other respects similar to an electron! Anti-matter!! Positrons!!!
Alpha particles are:
Some nuclei have lots of protons and many more protons. Lowest energy bound-states require about equal numbers of protons and neutrons. Those nuclei emit most tightly bound nuclear matter, i.e., Helium nuclei with two protons and two nuclei.