3. Radioactivity Flashcards
Radioactivity facts
- discovered by Becquerel in 1896
- radiation given off by nucleus of unstable elements
- radiation in form of particles or electromagnetic radiation
- separates using magnetic field
Alphas
Betas
Gamma rays
- Are positive (curve path of travel field)
- Are negative (curved path in opposite direction)
- Have no charge (not affected by field)
Stable nucleons
Unstable nucleons
Potential barrier prevents nucleons entering/escaping nucleus
Nucleons posses kinetic energy
- Energy not sufficient to escape
- Nucleus has excess energy
Constantly redistributed among nucleons
Eventually one particle gains enough energy to escape
Decay constant
- radioactive decay is statistical phenomenon
- can not predict when a single atom will disintegrate
- predict proportion of large collection that will decay in time t
Half life
Time required for activity of number of radioactive atoms to decay to 1/2 initial value
Radioactive series
- first 92 elements in periodic table occur naturally
- Z>92 elements produced artificially
- elements with low Z tend to be stable, high Z is radioactive
- as number of nucleons increases, nuclear forces become less effective
- all elements with Z>82(lead) is radioactive
What are the naturally occurring radioactive elements?
- uranium series
- actinium series
- thorium series
Alpha decay
- typical of radioactive nuclides with very high Z (>82)
- for Z >82, repulsion between protons overcomes nuclear forces
- transformation characterized by emission of alpha particle
- unstable nucleus emits particle of two protons and two neutrons
Beta and article decay
- radioactive decay accompanied by ejection of positively or negatively charged electron ( positron or negatron)
- neither particle exists in nucleus
- creates at instant of decay process
Electron capture
- electron capture is alternative process to beta plus decay
- orbital electron captures by nucleus. Transforming proton into neutron
Internal conversion
- ‘emission gamma’ is one mode by which an excited nucleus gets rid of excess energy
- internal conversions is an alternative mode
- excess nuclear energy passed to orbital electron (ejected)
The alpha, p reaction
- first nuclear reaction was observed by Rutherford
- bombarded nitrogen gas with alpha particles(radioactive source)
The alpha, n reaction
-bombardment of nucleus by alpha particles with subsequent emission neutrons
Proton bombardment
-proton captured by nucleus with emission of gammas
Neutron bombardment
- neutrons posses no electric charge
- effective in penetrating nucleus and producing nuclear reactions
- they do not have to posses high KE in order to penetrate nucleus
- thermal neutrons extremely effective at producing transformations
Photodisintegration
- nuclear reaction produced by interaction of high energy photon with nucleus
- results in emission of neutrons
- occurs for higher Z
Fission
- produced by bombarding high Z nuclei by neutrons
- after absorbing n. Nucleus splits into two nuclei of lower Z (plus extra neutrons)
Nuclear reactors produce
Power
- heat generated by absorbing gammas and neutrons
- concerted to electric power
Radioisotopes
- reactors provide large and continuous supple neutrons
- necessary since probability of collusion low
- used in medicine and research
Fusion
- reverse of nuclear fission
- low mass nuclei combined to form one nucleus
- total mass of products is less than the reactants
- energy is released in the process
