3. Radioactivity Flashcards
1
Q
Radioactivity facts
A
- 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
2
Q
Alphas
Betas
Gamma rays
A
- Are positive (curve path of travel field)
- Are negative (curved path in opposite direction)
- Have no charge (not affected by field)
3
Q
Stable nucleons
Unstable nucleons
A
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
4
Q
Decay constant
A
- 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
5
Q
Half life
A
Time required for activity of number of radioactive atoms to decay to 1/2 initial value
6
Q
Radioactive series
A
- 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
7
Q
What are the naturally occurring radioactive elements?
A
- uranium series
- actinium series
- thorium series
8
Q
Alpha decay
A
- 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
9
Q
Beta and article decay
A
- 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
10
Q
Electron capture
A
- electron capture is alternative process to beta plus decay
- orbital electron captures by nucleus. Transforming proton into neutron
11
Q
Internal conversion
A
- ‘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)
12
Q
The alpha, p reaction
A
- first nuclear reaction was observed by Rutherford
- bombarded nitrogen gas with alpha particles(radioactive source)
13
Q
The alpha, n reaction
A
-bombardment of nucleus by alpha particles with subsequent emission neutrons
14
Q
Proton bombardment
A
-proton captured by nucleus with emission of gammas
15
Q
Neutron bombardment
A
- 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