nuclear processes
DESCRIPTION
Nuclear Processes. In chemical reactions, electrons in atoms are responsible for bonds forming and being destroyed. The identity of the atoms involved does not change. This is not true for nuclear processes. . - PowerPoint PPT PresentationTRANSCRIPT
NUCLEAR PROCESSES
In chemical reactions, electrons in atoms are
responsible for bonds forming and being destroyed.
The identity of the atoms involved does not change
This is not true for nuclear processes.
These reactions involve the protons and neutrons in the nucleus – too large or too small of a ratio between
protons and neutrons
There are two types of nuclear reaction
Fission and Fusion Reactions
Fission Reactions Usually involve atoms with large nucleii
such as the Lathanides and Actinides They produce , and emissions. Involve a nucleus collapsing to form a
smaller nucleus
Fusion Reactions These involve nuclei joining together to
make larger ones. These type of reactions are what go on
inside stars and provide the energy that causes them to shine.
The particle Is emitted from a
nucleus during radio active decay due to too many protons
Consists of 2 protons and 2 neutrons (a helium nucleus)
Decreases mass by 4 and atomic # by 2
241Am95 237Np93 + 4He2 4.0 cm of air Low penetration -protected by skin Is the most destructive radiation
because it ionizes atoms it bumps into Relative danger is low unless
ingested Used in smoke detectors
An decay reaction
The Uranium atom U23892 decays by particle emission
U238
92 He 42 + ?
234
90
What is represented by ?
An decay reaction
The Uranium atom U23892 decays by particle emission
U238
92 He 42 + Th
234
90
Th is thorium – we can work it out by using the periodic table and looking up the atom with atomic number 90. The mass number does not matter – it is simply an isotope of Th.
More decay reactions
The Thorium atom Th22790 decays by particle emission
Th227
90Complete the equation
More decay reactions
Th227
90 He 42 + Ra
223
88
More decay reactions
The Actinium atom Ac22589 decays by 3 particle emissions
Ac225
89Complete the equation
More decay reactions
Ac225
89 3He 42 + Bi
213
83
Particle emissions
Particles are electrons but they do not come from the electron shells which surround the nucleus – they come from the nucleus itself. Due to neutron to proton ratio being too great.The electron is emitted when a neutron sheds its negative chargeand becomes a proton. (Bet you didn’t know it could do that!)
10N 1
1 p 0-1
Tritium decay (beta)
Particle emissions
The effect of Particle emission is to increase the proton count by 1 while leaving the overall mass unchanged.
Th231
90 0
-1 + PaNotice how particle emission raises the atomic number by 1
231
91
Particle emissions Can penetrate 6-300 cm of air Blocked by clothing and paper Moderate danger Excessive exposure can be harmful Used in many medical diagnostic tests
and treatments
Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma radiation.
Gamma Ray Emission
Gamma rays have no mass and no charge – may accompany and/or emissions
High energy and very penetrating May be stopped with very thick (6 ft. or so
of concrete) or 3-5 cm of lead (think about the dentist)
γ00 or 0
0γ Used for medical tests and treatments Sterilization of equipment & foods
Electron Capture Sometimes a nucleus will capture an
electron and a proton converts to a neutron.
This decreases the atomic number but does not change the mass
201Hg80 + 0-1e 201Au79 + γ0
0
Positron Emission A positron has the mass of an electron
and the charge of a proton – it’s kind of like a “positive electron”
It may be emitted when a proton turns into a neutron
Atomic number decreases and mass stays the same.
22Na11 0+1e + 22Ne10
Decay Series
When a radioactive nucleus such as 238U92 decays it often produces another radioactive isotope which goes on to decay further.
You are going to construct a decay series on graph paper for the element 238U92 to show how it eventually forms a stable isotope of lead 206Pb82
GET A PIECE OF GRAPH PAPER Draw a vertical axis representing atomic
mass. It will need to run from 200 to 240
Draw a horizontal axis representing atomic number. It will need to run from 78 to 93.
Position the isotope U23892 on your graph
and mark it clearly.
240
20078 93
Mass
Atomic Number
* 238U92
Plotting an decay The nucleus gives off an alpha particle
first to form a new nucleus Work out what the new nucleus is Find the nucleus on your graph and add
it in Join the points with an arrow
240
20078 93
Mass
Atomic Number
* 238U92
234Th90 *
Plotting a beta emission The Thorium next loses a Beta particle Work out what would be formed Add the nucleus onto your chart
240
20078 93
Mass
Atomic Number
* U23892
Th23490 * * Pa234
91
Building up the decay series
Continue to build up the series using the following emissions. Each alpha emission is shown as a diagonal to the left and each beta emission is a horizontal line to the right.
If you are successful you should end up with Pb20682
Good Luck !
Emission sequence (including the first two example emissions)
1. 2. 3. 4. 5. 6. 7.
8. 9. 10. 11. 12. 13. 14.