Nuclear physics Flashcards
Einstein’s mass energy equation
E = mc²
Why do individual nucleons have more energy than the mass of a nucleus
nucleons at high energy state have more mass
A nucleus has a higher mass because of what energy
Binding energy
any extra energy is kinetic
Mass defect
Difference between the total mass of individual nucleons and the mass of the nucleus when infinitely seperated
Binding energy
Minimum energy required to separate nucleons to infinity
How to find binding energy per nucleon
- find mass defect
- use Einstein’s equation to find the energy
- Divide the energy change by the number of nucleons
What is the binding energy of a neutron
Zero because it is a lone nucleon
Radioactive decay
Random and spontaneous disintegration process where a nucleus emits ionising radiation such as alpha, beta and gamma rays
Radioactive decay constant
Probability of the decay of a nucleus per unit time
unit s^-1
Atomic mass unit
1/12 of the mass of a neutral atom of carbon-12
Mass excess
Mass in u minus the nucleon number
Nuclear fission
(3)
A single large nucleus divides to form smaller nuclei
- initiated by neutron bombardment
- binding energy per nucleon increases
Nuclear fusion
(3)
Two light nuclei combine to form a single mroe massive nucleus
- initiated by very high temperatures
- release energy
Decay constant
Probability that an individual nucleus will decay per unit time interval
Activity definition
rate at which the nuclei decay/ disintegrate.
unit is becquerel
Activity formula
A= -λN
A= ∆𝑁/ ∆t
why is radioactive decay random
2 marks
- time at which a nucleus will decay cannot be predicted
- constant probability of a decay of each nucleus in the sample
why is radioactive decay spontaneous
2 marks
- the decay is not influenced by external factors
- the decay of a particular nucleus is not affected by the presence of other nuclei
Half life
Time taken for activity of sample to halve
Number of decayed nuclei, count rate and activity of a sample can be given by:
N, R, A
x = x0^e–λt
Half life formula in terms of decay constant
= ln2/λ
Charge of a beta particle
4e
Charge of an alpha particle
2e
A radioactive element has a half life of 4 hours. Explain why its mass and activity cannot be used to determine its half life
Sample would decay appreciably whilst measurements are being made
