Nuclear Physics Flashcards
rutherford scattering
originally plum pudding model
studied scattering of alpha particles from a radioactive source producing a tiny flash of light when they pass the fluorescent screen
conclusions from Rutherford scattering
atom must be mostly empty space as alpha particles pass directly through it
the nucleus must be positively charged as some positive alpha particles deflected
the nucleus muscles be very tiny as few deflected at an angle larger than 90 degrees
most of the mass is within the nucleus as the fast alpha particles are deflected
properties of alpha beta and gamma rays
alpha- 2 protons & 2 neutrons, +2 charge, few cm in range, stopped by paper, high ionisation
beta- free electron, -1 charge, 10s cm in range, stopped by aluminium, medium ionisation
gamma ray- electromagnetic ray, 0 charge, infinite range, reduced by lead, low ionisation
ionisation
the process in which an electron is given enough energy to break away from an atom is called ionisation
background radiation
there is always low levels of background radiation
decay constant
the constant of proportionality- the probability of a specific nucleus decaying per unit of time
nuclear fission and fusion
fission- large nuclei that can randomly split into two smaller nuclei, energy is released
fusion- when 2 nuclei combine to create one larger nuclei, energy released due to heavier nuclei created
Changes in Atomic models
Thought particles where indivisible
Positive bodies with negative electrons in them
Rutherford then discovered that they were mostly empty space with electrons orbitting them
The Plum Pudding Model
Atoms were a ball of postive charge with negative electrons evenly distributed throughout them
Rutherford scattering
Alpha particles fired at thin gold foil- with plum pudding model, particles were expected to pass through
Actually …
Most passed through- suggesting atoms mostly empty space
Some were deflected at large angles sugessting that there is a positively charged nucleus that repels alpha particles
Few were deflected less than 90° suggesting that the nucleus was very dense
Alpha Radiation
2 protons
2 neutrons
Helium nucleus
Strongly ionising
Slow moving
Stopped by paper
Deflected in magnetic field
Beta Radiation
Electron
Positron
Mildly ionising
Fast moving
Stopped by aluminium
Negative charged
Deflected in magnetic field
Gamma Radiation
Electromagnetic radiation
High frequency
Weak ionising
Travels at speed of light
Stopped by lead
Chargeless
Uneffected by fields
How to safely handle radiation
Never directly handle source
Long- armed tongs
Sinage and warning lables
Minimum time handling
Store in lead box
Background Radiation
Radon gas
Rocks
Cosmic Radiation
Nuclear weapon testing
Nuclear disasters
Radioactive decay
Random process
Nucleus decays in an unpredictable manor
Activity
The number of nuclei decaying per second, Becquerels- Bq
Half-Life
The time it takes for radiosvyive nuclei to decay to half, for given isotope
Decay Constant
The probability of decay occuring in a given time
Distance of closest Approach
The first method to calculate the approximation for nuclear radius
Kinetic energy to potential energy
Always over estimate
Electron Diffraction
More accurate way to measure nuclear radius
High speed electrons fired at thin material
The diffraction pattern forms on a screen
Nuclear radius can be calculated using the pattern
Nuclear Fission
splitting of large nuclei into two smaller nuclei, two/three neutrons and energy
Uranium - 235
A slow moving neutron will induce fission- commonly fissle isotope is U-235
Critical mass
the minimum amount of substance to maintain a steady flow of fission reactions
Control rods
Absorb neutrons to prevent further fission- the more absorbed the few number of fission reactions
Moderator
Responsible for slowing down neutrons that are released so that they are at the speed of a thermal neutron and can induce fission
Fuel rods
cossist of fissle material, contains less than the critical mass so reactions remain control
Coolant
carries away thermal energy produced by fission
Nuclear Fusion
Where two unstable smaller nuclei combine and form a larger one with a lot of energy
Common = deuterium and tritium
Mass defect
the difference between the mass of the nucleus and its induvidual constituents
Binding Energy
Energy required to split up the nucleus into its induvidual constituents
The greater the binding energy, the more stable the nucleus
Atomic mass unit
the average mass of nucleon
