2/2/2024 RADIOACTIVE DECAY MODES AND RATES Flashcards
Can the identity of atoms change?
Yes: Nuclear reactions change the identity of atoms because their nuclei change.
What determines whether a substance is radioactive or not?
The ratio of neutrons to protons in the nucleus
What is the “belt of stability”?
The region on a graph of number of neutrons vs. number of protons that includes all stable nuclei (usually green)
What does the orange represent on a graph of number of neutrons vs. number of protons?
Radionuclides: neutron rich or neutron poor nuclei that are unstable and undergo “radioactive decay” (the spontaneous disintegration of unstable particles AND the release of ELECTROMAGNETIC RADIATION)
What is “Radiation”?
The emission of energy as ELECTROMAGNETIC WAVES or as moving subatomic particles, especially high-energy particles which cause ionization.
What is Beta Decay?
Radionuclides ABOVE the belt of stability are neutron rich and tend to undergo decay reactions that reduce their neutron-to-proton ratio.
ATOMIC MASS STAYS THE SAME (increase of 1 proton at the expense of 1 neutron)
- near massless electron (-b particle) is shot off as radiation
What is Alpha Decay? What causes it?
Alpha decay produces a nuclide with two fewer protons and two fewer neutrons when an unstable nuclide spontaneously emits a 4/2He atom (or a 4/2alpha particle)
ATOMIC # DECREASES BY 2 AND ATOMIC MASS DECREASES BY 4
- Result of an unstable nucleus (almost always with the heaviest nucleotides of mass more than 100)
- Often creates a chain reaction called a “radioactive decay series”
What occurs if the nuclides fall below the belt of stability?
Positron Emission or Electron Capture (increasing neutron-proton ratio)
ATOMIC # INCREASES BY 1 BUT THE MASS STAYS THE SAME
What happens during Positron Emission?
The radioactive NEUTRON-POOR nucleus emits a fast-moving, positively charged particle with the same mass as an electron (0/1b POSITRON)
- Produces a nucleus with one fewer proton and one more neutron
What happens during Electron Capture?
The radioactive NEUTRON-POOR draws in a surrounding electron, turning a proton into a neutron
What is “antimatter”?
Subatomic particles that have the opposite charge but the same mass as particles typically found in atoms (positrons and 1/-1p antiprotons)
What is Mass Defect?
The tiny difference between the mass of a stable nucleus and the masses of its individual nucleons. It represents the Binding Energy (BE) of the nucleus because mass turns into energy through radiation!
What is Binding Energy?
The energy that would be released if free nucleons were to fuse to form the nucleus. It is also the energy needed to split the nucleus into free nucleons.
- We can calculate it using E = mc^2 !!
What makes a nucleus stable or unstable?
The stability of a nucleus is directly proportional to its BINDING ENERGY per nucleon.
(An atom is stable if the forces among the particles that makeup the nucleus are balanced. An atom is unstable (radioactive) if these forces are unbalanced; if the nucleus has an excess of internal energy. Instability of an atom’s nucleus may result from an excess of either neutrons or protons.)
What is the “Nuclear Strong Force”?
The fundamental force of nature that keeps quarks together in subatomic particles and nucleons together in atomic nuclei.
- ONLY OPERATES OVER VERY SMALL DISTANCES!
- 100 TIMES STRONGER THAN THE REPULSIONS THAT PROTONS & NEUTRONS EXPERIENCE
