Radioactive Decay
The process by which unstable nuclei reach a more stable configuration.
Radioactivity
Process by which unstable nucleus (parent) decays into a new nuclear configuration (daughter) that may be stable or unstable.
What are the 4 main modes of radioactive decay?
- Alpha Decay
- Beta Decay (+, -, EC)
- Gamma Decay (Pure, IC)
- Spontaneous Fission
Explain Alpha Decay
Occurs When: Strong nuclear force cannot hold large nucleus together (Z>83). Alpha Decay reduces mass, high particle stability configuration (2p, 2n) causes Alpha particle clusters in nucleus. More energetically favorable to emit alpha particles.
Process:
- energetic alpha particle is emitted
- atomic number Z of parent decreases by 2, atomic mass A decreases by 4
- causes increased neutron/proton ratio
Describe Alpha Particles
- very stable configuration
- emission is monoenergetic
- heavy
- charged
- high LET
- short range
- densely ionizing, rapid energy loss through collisions with electrons after emission
Explain Beta - Decay
Occurs When: Neutron rich radioactive parent needs more protons and less neutrons to become stable.
Process:
- parent nucleus transforms neutron into a proton
- electron (b- particle) + anti neutrino share available energy and are ejected from nucleus
- atomic number Z of parent nucleus increases by 1, atomic mass A remains the same
- daughter is an isobar of parent
Describe Beta - Particles
- charged, electron (-1)
- light
- low LET
- medium range
- undergo collisions after ejection until all kinetic energy is lost, mostly with electrons but some with nucleus resulting in x-rays
Explain Beta + Decay
Occurs When: Proton rich radioactive parent needs more neutrons and less protons.
Process:
- parent nucleus transofrms a proton into a neutron
- positron (b+ particle) + neutrino share available energy and are ejected from nucleus
- atomic number Z of parent decreases by 1, atomic mass A remains the same
- daughter is an isobar of parent
Describe Beta + Particles
- charged, positron (+1)
- light
- low LET
- medium range
- Positron is annihilated after ejection by a free electron. Masses disappear and 2 photons are emitted travelling in opposite directions.
Explain Electron Capture
Occurs When: Beta + Decay requires energy to create extra mass (mass of neutron and positron is greater than mass of proton), when this energy is not available electron capture occurs.
Process:
- nucleus captures atomic orbital shell electron 9usualy k-shell)
- proton in nucleus transforms into neutron
- neutrino is ejected
- atomic number Z of parent decreases by 1, atomic mass A remains the same
- daughter is an isobar of parent
Describe Electron Capture Particles
- no specific particle is emitted
- a very weakly interacting neutrino particle is ejected
- low energy gamma rays and characteristic x-rays follow process due to k-shell vacancy
Explain Gamma Decay
Occurs When: Nucleus decays from excited state to lower state (commonly after Beta or Alpha Decay)
Process:
- Gamma rays = high energy photons
- emitted when nucleus decays from excited to lower state
- atomic number Z and atomic mass A remain the same
