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)