11. Nuclear radiation [COMPLETE] Flashcards
What is the difference in mass when the total mass of a nucleus is less than the sum of its constituent nucleons also known as?
Mass defect or mass deficit
What is mass defect or mass deficit defined as?
The difference between the measured mass of a nucleus and the sum total of the masses of its constituents
What is mass-energy equivalence?
E=mc^2
Mass can be converted into energy
Energy can be converted into mass
What does a mass defect imply?
The mass lost if released as energy.
What is binding energy defined as?
The energy required to break a nucleus into its constituent protons and neutrons
Is the formation of a nucleus from its constituent nucleons an exothermic or endothermic reaction?
The reaction releases energy hence exothermic reaction
What is one unified atomic mass unit or 1u defined as?
The mass of exactly 1/12th of a carbon-12
What is 1u equivalent to in MeV?
1u = 931.5 MeV
What do you look at when comparing stability of different nuclei?
The binding energy per nucleon
What is the binding energy per nucleon defined as?
The binding energy of a nucleus divided by the number of nucleons in the nucleus
What does a high binding energy per nucleon indicate?
A higher stability since it requires more energy to pull the nucleus apart
What is the most stable element?
Iron with a mass number of 56 and the highest binding energy per nucleon
Give the sketch of the graph of the binding energy per nucleon against nucleon number
- Anomaly at He-4
- Don’t start at 0, no such nuclei exist
- Axes and units (MeV)
- Peak at Fe-56
What are the trends and anomalies of the binding energy per nucleon against nucleon number graph?
- At low mass numbers: lower binding energy per nucleon, hence, they are generally less stable.
- At high mass numbers: general binding energy per nucleon is high and gradually decreases as mass number increases, hence, more unstable.
- Helium-4, Carbon-12 and Oxygen-16 do not fit into the trends: He-4 is v. stable as it has a high binding energy per nucleon. C-12 & O-16 can be considered as 3 and 4 He-4 bound together.
What element are likely to undergo FUSION and why?
The lightest elements (before iron) as their nuclei tend to have a lower binding energy per nucleon, hence, they are generally less stable and have weaker electrostatic forces.
What element are likely to undergo FISSION and why?
The heaviest elements (after iron) as they are the most unstable.
What is fusion defined as?
When small nuclides that combine together to make larger nuclei, releasing energy
What are the conditions for fusion?
- Both nuclei must have high K.E. to over come electrostatic repulsion between protons.
- achieved in a star’s core
Outline the process of hydrogen burning
1: 2 protons fuse → 1 proton, 1 neutron + 1 positron, 1 neutrino
2: a proton and the deuterium nucleus join to make He-3
3: 2 He-3 fuse → He-4 + 2 protons ejected
What is background radiation is defined as?
Low levels of radiation from environmental sources, which are always present around us
What is radiation measured in?
Counts per second in a unit called Becquerel (Bq)
What are the two types of background radiation?
- Natural sources (rocks, cosmic rays)
- Man-made sources (radon gas, building materials)
What is the corrected count rate?
When we account for the background radiation and subtract it from the readings we taken.
How does a radiation detector detect radiation?
- When alpha or beta radiation pass close to an atom, they can deliver enough energy to remove electrons, ionising the atom
- Radiation detectors work by detecting the presence of either these ions, or the chemical changes that they produce
What are radioactive nuclei?
When unstable nuclei emit particles and/or EM radiation to become stable
What are alpha particles?
Alpha (α) particles are high energy particles made up of 2 protons and 2 neutrons
4
α
2
What emits alpha particles?
Usually emitted from nuclei that ar very large.
What are beta(-) particles?
Beta (β−) particles are high energy electrons emitted from the nucleus
0
β
-1
What emits beta(-) particles?
Nuclei that have too many neutrons
How ionising are beta particles?
They are moderately ionising due it having a charge of +1e, meaning it can do some slight damge to cells.
How penetrating are beta particles?
They are moderately penetrating, having a range of around 20 cm - 3 m in air, depending on their energy and can be stopped by a few millimetres of aluminium foil
What are gamma rays?
Gamma (γ) rays are high energy electromagnetic waves (less than 10^-10)
0
γ
0
What emits gamma rays?
Nuclei that needs to lose some energy
How ionising are gamma rays?
Very ionising, can knock out electrons, cause chemical changes in materials, can damage or kill living cells
What is a beta(+) particle?
A high energy positron
Give the general equation for alpha decay
A A-2 4
X → Y + α
Z Z-2 2
Give the general equation for beta minus decay
A A 0
X → Y + β
Z Z+1 -1
OR
A A
X → Y + e- + antineutrino
Z Z+1
Give the general equation for beta plus decay
A A 0
X → Y + β
Z Z-1 +1
OR
A A
X → Y + e+ + neutrino
Z Z-1
Give the general equation for gamma decay
A A 0
X → Y + γ
Z Z 0
What is radioactive decay is defined as?
The random spontaneous decay of a unstable nucleus to form a more stable nucleus, resulting in the emission of an alpha, beta or gamma particle
What is a spontaneous process is defined as?
A process which cannot be influenced by environmental factors
What is a random process is defined as?
A process in which the exact time of decay of a nucleus cannot be predicted
Is it possible to predict how many nuclei decay in a given time?
Yes as the chance to decay is a constant probabality
What s the average decay time?
The average number of nuclei which are expected to decay per unit time
What is the decay constant (λ) is defined as
The probability, per second, that a given nucleus will decay
What is activity?
The number of decays per unit time
What is activity measured in?
Becquerels (Bq) = one decay per second, or 1 s-1
What is half-life is defined as?
The time taken for half the number of nuclei in a sample to decay
