Radioactivity and Nuclear Energy Flashcards
How was the nucleus discovered?
Rutherford’s Scattering
Alpha source directed through thin gold foil
Observe the path of the alpha source
Explain the observation of Rutherford’s Scattering
Majority α particles went through without scattering -> atom is mostly empty space
Small amount of α particles deflected by large angle –> centre of the atom is positively charged
Few particles deflected by more than 90° –> centre of atom is very dense
Properties of different types of radiation
alpha radiation:
highly ionising so not v penetrating
2-10 cm range in air
deflected by magnetic fields
absorbed by paper
beta radiation:
less ionising but more penetrating
1m range in air
deflected by magnetic fields
absorbed by aluminium foil
gamma radiation
least ionising but most penetrating
infinite range in air
NOT deflected by magnetic fields
absorbed by concrete or lead
Uses of alpha and beta radiation
Quality control for thickness of materials
Signal of radiation goes through if thickness is too thin
Signal stops if thickness too thick
Uses of gamma radiation
Kill cancerous cells
Sterilise equipment
Detector for radioactive source with short half life
Safety precautions for radioactive source
Handle with tongs and at arms length
Store in lead lined container
Limit exposure
Never point source towards other people
What are the sources of background radiation?
Radon gas from rocks
Nuclear testing and weapons
Cosmic rays from space
Rocks with naturally occuring radioactive isotopes
Describe the nature of radioactive decay?
Random –> can’t predict when the next decay
Spontaneous –> Can’t cause or influence the decay
Definition of half life
The average time taken for a radioactive source’s activity to halve
Equation for nuclear Activity
A = Initial activity x e^-λt
When can the decay constant be used?
Can model the decay of nuclei when there is a large number of nuclei in the sample
Uses of half life
C-14 dating –> date organic objects according to half life of C-14
Medical diagnosis –> Short half life isotopes can be used as medical tracers
What causes nuclear instability and the type of decay?
Too many neutrons –> Beta minus decay
Too many protons –> Beta plus, electron capture, alpha emission
Too many nucleons –> Alpha emission
Too much energy –> Gamma emission to de-excite the nucleus
Strong nuclear force is not strong enough to overcome the electrostatic repulsion of the protons
More neutrons = stronger nuclear force
How to estimate the radius of a nucleus?
Calculate the distance of closest approach which is the distance where there’s no kinetic energy as particle has stopped
Will always be an overestimate
The larger the number of nucleons = larger radius
Why is electron diffraction a better estimate of the radius?
Because e- are leptons which don’t react with nucleons unlike alpha particles
electrons are accelerated so de broglie wavelength is similar to diameter of nucleus
Graph of intensity against diffraction angle
sinΦ = 0.61λ/R
Definition of Binding energy
Work that must be done to separate a nucleus from its constituent nucleons
Iron has the highest binding energy per nucleon
Definition of mass defect and its three conditions
Difference between mass of the atom and mass of its constituent nucleons
Mass defect is small compared to total rest mass of the atom
Energy released is E = mc^2
Mass is in kg, E is in J
Describe Induced Nuclear Fission
A thermal neutron is fired at a U-235 nucleus
The U-236 nucleus splits into two daughter nuclei and 2/3 fast moving neutrons
Energy is released because daughter nuclei has higher binding energy per nucleon
Definition of critical mass
The minimum mass of fuel required to maintain a steady chain reaction
Purpose of Nuclear Reactors’ Features
Moderator: Slows down fast moving neutrons into thermal neutrons through elastic collisions between nuclei/water/ graphite molecules and neutrons
Control Rods: Absorbs neutrons in reactor to control chain reactions using boron or cadmium
Coolant: Absorbs heat released during fission in the core. Heat used to make steam to power electricity-generating turbines. Use water, molten salt or gas
Fuel Rods: U-235 rods that can move up and down, deteriorate overtime and become more radioactive
Describe Nuclear Fusion
When two smaller nuclei join to form one larger nucleus
Energy is released due to large binding energy per nucleon of larger nucleus
Can only occur at very high temperature or very high pressures
Safety aspects of Nuclear Reactors
Thick concrete shielding around reactor
Fuel rods inserted into reactor remotely to limit worker’s exposure
Emergency: Control rods dropped in completely to stop reaction
Spent fuel rods are most dangerous nuclear waste –> disposed underground with concrete and steel in geologically stable locations
