Unit 5 Nuclear Decay
- Created by: megan
- Created on: 21-03-13 16:01
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- Nuclear Decay
- Background Radiation
- The natural environment exposes us the low levels or radiation from both natural and man made source.
- Radiation levels are recorded in counts per second. unit - becquerel. Bq
- On earth half the radiation is from naturally radioactive gases in the atmosphere, particluarly radon
- radon is produced in the decay of uranium, and is present in certain rocks.
- Types of Nuclear Radiation
- Many nuclei are slightly unstable and there is a probability that they will decay
- a nucleon may change from one type to another
- The composition or energy state of the nucleus may change
- When nuclear decay occurs the radiation particle emitted will leave the nucleus with kinetic energy
- The particle released will ionise particles in its path, losing kinetic energy.
- When all kinetic energy is transferred the radiation particle stops and is absorbed by the substance.
- Many nuclei are slightly unstable and there is a probability that they will decay
- a nucleon may change from one type to another
- The composition or energy state of the nucleus may change
- The particle released will ionise particles in its path, losing kinetic energy.
- Alpha= 2 protons + 2 neutrons. large in size. +2 charge. Highly ionising
- As it is ionises so quickly, it is easily absorbed by paper/skin
- Beta = an electron. Emitted at high speed from the nucleus when a neutron decays into a proton. Smaller in size and charge it is less ionising
- can penetrate much further than alpha, but blocked by aluminium
- Gamma= High energy, high frequency electromagnetic radiation. photons with no max or charge so will rarely interact with particles= least ionising.
- Gamma is never completely absorbed although their energy can be reduced by thick lead
- Many nuclei are slightly unstable and there is a probability that they will decay
- Probability and Decay
- For each second that it exists, there is a certain probability that the nucleus will decay. = Decay constant.
- Each nucleus acts entirely independently
- The likely hood that a particular nucleus will decay is not affected by factors outside the nucleus such as temp/pressure
- A= - ?N
- A= activity (number decaying per second) N= the number of nuclei in the example.
- N=N0 E^- ?t
- Half life
- The activity of a radio active sample decreases over time as the radioactive nuclei decays.
- The rate at which the activity decreases depends on the particular isotope
- A measure of this rate is the half life t 1/2
- The time taken for half of the atoms of that nuclide within a sample to decay
- ?=Ln2/ t(1/2)
- Half life graphs
- An experiment to determine half life of a substance will usually measure activity over time
- The shape of a graph of activity against time shows exponential decay.
- we can use the graph of activity against time to determine the half life of the substance by finding the time taken for the activity to halve.
- Background Radiation
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