5 Nuclear physics Flashcards
Atom
The smallest unit of an element, made from neutrons, protons and electrons.
Summary of the constituent parts of an atom
proton p 1 +1
neutron n 1 0
electron e 0(12000) −1
Nuclide
An atom or nucleus is characterised by a specific number of protons and neutrons.
Nuclide notation
A notation using symbols for elements along with the atomic number and nucleon number to describe the composition of an element’s nucleus
X
is the symbol for an element.
Z (SMALLER NUMBER)
is the proton number but is also called the atomic number. This is the number of protons found in the nucleus. Since atoms are neutral, this is also the number of electrons orbiting the nucleus.
A (LARGER NUMBER)
is the nucleon number (also known as mass number). This is the total number of protons and neutrons that are found in the nucleus.
Proton number
The number of protons in a nucleus.
Atomic number
The number of protons in a nucleus.
Mass number
The total number of protons and neutrons in the nucleus, also the total relative mass of the nucleus.
Radioactivity
Atoms that are radioactive have unstable nuclei that spontaneously break down. Usually, leads onwards but an exception of technetium.
Reasons for instability of an atom
Too many neutrons
Too few neutrons
Too much energy
Types of radiation
Alpha
Beta
Gamma
Alpha ( α ) Radiation
The nucleus of a helium atom( 2 protons and 2 neutrons)
CHARGE: +3.2x10^-19 / 2
Travel at 10% speed of light
Can only travel 10cm in the air before ionising to helium gas
Blocked by paper
Formula:
X,A,Z –> Y,A-4,Z-2 + α 4,2
Beta radiation β
Beta particles(β) are high-speed electrons
When a neutron spontaneously decays into a proton, it also emits beta particles from the nucleus
CHARGE: -1.6x10^-18 / -1
Travel 2.9x10^8 m/s
Can travel through paper but is blocked by thin aluminium
Formula:
X,A,Z–> Y,A,Z+1 + e,0,-1
Gamma radiation γ
High-energy electromagnetic waves with a very small wavelength Gamma rays have no mass or charge and are represented by γ
Lowest ionising ability
Highest penetrative ability, block by several centimetres of lead
Formula:
X,A,Z–> Y,A,Z + γ,0,0
Penetration and ionising abilities of different radiation
Radiation Ionising effect Penetrating ability
alpha (α) particles strong weak
beta (β) particles mild mild
gamma (γ) emissions weak high
Radiation deflection in an electric field
Radiation is deflected within an electric field. Opposite charges attract, so negative Beta particles move towards the positive side.
Positive Alpha particles are attracted to the negative side.
Gamma rays are unaffected since they have no charge
(This only occurs when they travel perpendicular to the field)
Radiation deflection in a Magnetic field
Dot: Magnetic field coming out of the page
Dot: Alpha particles go left, Beta particles go right and Gamma is unaffected
Cross: Magnetic field going into the page
Cross: Alpha particles go right, Beta particles go left and Gamma is unaffected
Right hang slap rule
Thinger tips are the direction of the magnetic field
Force on positive charge is the palm/negative charge is knuckles
Thumb of direction of moving charge
Background radiation
There is a natural supply of background radiation all around us (Radiation we experience without measuring a specific object)
This can be found from: Food, Building materials and rocks, Radon gas, Cosmic rays, medical procedures
Formula: Radiation measured-background = Object radiation
Radon gas
Radon gas is naturally found in the atmosphere due to uranium decay in the ground
Cosmic rays
Cosmic ray is a generic term used to describe particles and waves that come from space.
The high energy radiation comes from outside of our solar system with its exact origins unknown
Half-life
The time taken for half of the nucleus in a sample of radioactive material, to decay.
All decay is random and spontaneous. You can not predict when it will decay
A half-life measurement is a probability of when half a sample has decayed
On a graph, the y-axis could be the Nuclei number, count rate, mass
without graph: Number of nuclei remaining= Original amount÷ 2^n(n=the number of half-lives that have happened)
Uses for half lives
Smoke detector
Thickness measurements and Quality control
Fault detection
Food irradiation
Cancer treatment
Organ function and blood flow testing
The effects of ionising radiation
Radioactive materials are dangerous because ionising radiation can damage cells. In humans, exposure to radiation can result in cancer, radiation burns, mutations, and ultimately death.
Rutherfords Gold foil
- The majority of the alpha particles pass through the gold sheet undeflected and are detected on the far side. The majority of the atom is empty (nucleus is small)
- A small number of alpha particles are deflected as they pass through the gold sheet. There must be a concentrated positive charge (nucleus)
- A very small number of alpha particles are deflected through very large angles or return back the way they came. The nucleus is most of the mass of the atom and is dense and it hits it straight on.
Exposure to radiation may cause the following
Cell death
Genetic mutation
Cancer
Contamination
The unwanted presence of materials containing radioactive atoms on other materials
Irradiation
Irradiation is the process of exposing an object to nuclear radiation
How can Alpha radiation be stored
Alpha can be stored in a thin package
However, protective clothing must still be worn when handling sources of alpha particles as they are very dangerous if they get inside the body
How can Beta radiation be stored
Beta must be stored in a lead or similarly dense metal container
How can Gamma radiation be stored
Only stopped by thick lead or concrete, so radioactive waste emitting gamma radiation is typically buried deep underground
Time exposed to radiation to be safe
Less time spent near source - less radiation recieved
Distance to be safe from radiation
Greater distance from the source - less radiation received
Shielding to be safe from radiation
Behind shielding from the source - less radiation received
Nuclear Fission
The splitting of large nuclei into smaller nuclei, releasing energy in the process
n,1,0 + U,235,92 –> Ba,144,56 + Kr,89,36 + n,3,0
Nuclear Fusion
The joining of smaller nuclei into larger nuclei, releasing energy in the process
H,2,1 + H,3,1 –> He,4,2 + n,1,0
Energy
E=mc2
Speed of Light= 3x108
Reaxtants–>Products–>Mass lost x c*2= energy released
The products have slightly Less mass than the reactants
what is the source of the sun’s energy
Nuclear fusion in the sun’s core
