Ionising Radiation and Nuclear Reactions Flashcards
What is the nuclear model
Extremely small nucleus, contains 99.9% of atoms mass (Specific type of atom/nuclei) = Nuclide
- Contains positively charged protons & uncharged neutrons (Nucleons)
Surrounded by negatively charged electrons
What is nuclear stability (Forces holding nuclei together)
Electric repulsion of protons, as positively charged protons repel
- Strains nucleus
Strong nuclear force between nucleons, overcomes electrostatic repulsion of protons
- Balance of two forces keeps nucleus stable
What is the notation for different nuclides
Atomic Number = n(Protons) in nucleus
Atomic Mass = n(Protons + Neutrons) in nucleus
AZX Notation
What are isotopes
Atoms that have same n(Protons), different n(Neutrons)
Same chemical properties
Different physical properties because of different mass number
What is atomic mass unit
Unit for relative atomic mass
1 amu = 1/12 mass of Carbon-12 atom
What are radioisotopes
Unstable isotopes
Randomly decay by emitting radiation from nucleus to be more stable (electron-Volts)
What are uses of radioisotopes as diagnostic tools
Scans of heart, lung, kidneys, gullbladder, thyroid
Diagnoses Heart disease, Alzheimer’s disease, Brain disordes
What are uses of radioisotopes as tumour treatment
Targets harmful organ / tissue, stops growth of its cells by damaging it
What is radioactive decay
Radioisotopes break down to become stable
- During process, radiation is released
- 3 forms; Alpha, Beta, Gamma
What is alpha decay
2 protons, 2 neutrons (Helium nucleus)
Posiively charged (+2)
What is properties of alpha decay
Low penetrating ability
Range few cm
High ionising ability
10% speed of light
What is beta decay
Beta Negative:
- 1 electron, 1 antineutrino
- Negatively charged (-1)
Beta Positive;
- 1 positron, 1 neutrino
- Positively charged
What is properties of beta decay
Medium penetrating ability
Medium ionisation ability
Range few m
90% speed of light
What is gamma decay
No particle, only high-energy electromagnetic radiation (High frequency light)
No charge
What is properties of gamma decay
High penetrating ability
Low ionisation ability
Range unlimited
Speed of light
What are the combinations of radiation
Atoms can emit more than one type of radiation at same time
Gamma radiation usually emitted with alpha / beta radiation
How to write nuclear equations
Mass, charge conserved
Use chemical symbols for elements
What are spontaneous transmutation reactions
Unstable nucleus becomes more stable by spontaneously emitting particle
- Changes into different element / isotope
Alpha & Beta decay
What are artificial transmutation reactions
Managed process, changes 1 nuclide into another
What is decay series
Radionuclide decays, daughter nucleus not completely stable, undergoes further decay
- Eventually stable isotope reached, sequence ends = Decay series
What is radioactive half-life
Time it takes for half the atoms in radionuclide sample to decay
- Unaffected by physical & chemical conditions (Eg. Pressure, Temperature)
What is activity
n(Atoms) in sample that decay per second
- Decreases over time, over one-life, activity halves
Can be measured using geiger counter
What is absorbed dose
Amount of energy that can be absorbed by 1kg mass of tissue
What does effect of radiation on body depend on
Quantiy & type of radiation absorbed
Nature of organs, cells, tissues exposed to radiation
Time exposed to radiation (How large)
What is ionising radiation
Radiation that can ionise cells (Removes / Adds electrons to become charged, ion)
- Can cause unwanted reactions, damaging / killing cells, or affecting cell division
What is dose equivalence
Measuring absorbed radiation dose, taking into account type of radiation involved (Measured in Sieverts / Sv)
What is quality factor
Weighting of damage caused by different types of radiation
What does sources of radiation outside the body do
Beta & Gamma most dangerous, can reach & be absorbed by cells of organs
Alpha radiation unlikely to reach living cells
What does source of radiation inside the body do
Alpha radiation most dangerous, strongly absorbed by cells, high ionisation ability
Beta & Gamma radiation unlikely to be absorbed by cells
How to monitor radiation at work
People working around radiation monitor exposure to radiation for safety
Radiation invisible, cannot be felt, radiation workers wear radiation monitoring badge
- 3 filters for each type of radiation
- After worn, film devleoped to determine amount & type of radiation exposed to
What is mass defect
Difference between mass of nucleus and sum of masses of nucleons
- Mass of stable nucleus < Sum of masses of protons & neutrons
- “Missing mass” = Binding energy (Mass-Energy equivalence)
What is binding energy
Energy required to separate components from nucleus
- Released when nucleus forms / separates (Hence mass missing)
What does the binding energy graph tell us
Smaller nuclei undergo fusion
Bigger nuclei undergo fission
More energy per nucleon in fusion released, as greater % mass transformed into energy
How to calculate binding energy if mass defect in amu
D(Energy) = 931m eV
How to calculate binding energy if mass defect in kg
D(E) = mc^2
What is nuclear fission
Atomic nucleus splits into 2 or more pieces
- Triggered by absorption of neutron
When split: Daughter nuclei
What are fissile nuclides
Capable of undergoing fission by slow-moving neutrons
- Only high atomic number elements, very few exist naturally
What are fissionable & non-fissile nuclides
Capable of undergoing fission, by only high-energy neutrons
How does fission occur
Fissile nuclide absorbs slow / high energy electron
- Unstable, spontaneously undergoes fission
How to calculate fission reactions
Use mass defect and binding energy
How do chain reactions happen in nuclear fission
U-235 undergoes fission (Absorbs neutron), releases two or three neutrons
- Neutrons absrbed by another U-235 nuclide, triggers another reaction
Mass release of energy in short time
What are nuclear fuel
Many naturally occuring radioisotopes, like U-238, U-235
Proportion of U-235 too low for chain reaction, is enriched to be nuclear fuel
What is critical mass
Minimum amount of enriched fissile material in sphere shape required to sustain chain reaction
Shape of nuclear fuel affects capacity to start chain reaction
- Sphere U-355 > Sheet U-235
What are the elements of nuclear reactors
Fuel Rods
Moderator
Control Rod
Radiation Shield
What are fuel rods
Long, thin rods containing pellets of enriched uranium
What are moderators
Material that slows neutrons
So fissile nuclei can absorb neutron
What are control rods
Material that absorbs neutrons
To control energy release
What are radiation shields
Thick concrete wall
Prevents neutrons from escaping reactor
How to manage low-level nuclear waste
From hospitals, industry, laboratories
Tools, clothing, wrapping material
Compacted / Incinerated, buried in sea / land
How to manage medium-level nuclear waste
Reactor components, chemical sludges, contaminated materials
Solidified in bitumen / concrete, then buried
How to manage high-level nuclear waste
Contaminated reactor parts
Requires special shielding, stored permanently
What is nuclear fusion
Two light nucli fuse to form larger nucleus, with release of energy
Mass of reactants > Mass of products
How to achieve nuclear fussion
Difficult to achieve, as both nuclei positively charged
- Electrostatic force of repulsion
2 nuclei slowly approaches, electrostatic force makes them repel
- Can’t get close enough for strong nuclear force to take affect
2 nuclei approach at high speeds, overcomes electrostatic force
- Close enough for strong nuclear force to take effect
= Fusion Reaction
How to calculate fusion reactions
Calculate using mass defect and binding energy
What is needed in nuclear fusion reactors, and why are they better than nuclear fission reactors
Energy per nucleon far greater than fission reactions, as greater % mass transformed to energy
High temperature needed for fusion
