7) Radioactivity & particles Flashcards
Units: frequency of decay, distance, time
frequency of decay : becquerel (Bq), 1 (Bq) for 1 decay / sec
distance : centimetres (cm), normally (m)
time : hour (h), minute (min), normally (s)
Isotope
Atoms of the same element with the same number of protons but different numbers of neutrons
-emit radiation as the atoms are unstable and undergo radioactive decay
–unstable due to large size, or because they have too many or too few neutrons
Atomic/ proton number
The number of protons in an atom
Mass/ nucleon number
The total number of particles in the nucleus of an atom is called its mass number
-number of protons and neutrons in the atom
Radiation
-Unstable nuclei can emit radiation to become more stable
-Radiation can be in the form of a high energy particle or wave
-as it moves away from the nucleus, takes some energy with it - reduces overall energy of the nucleus/ makes the nucleus more stable
-emitting radiation: radioactive decay - a random process
Types of radiation that can be emitted
When an unstable nucleus decays, it emits radiation
-Alpha (α)
-Beta (β-)
-Gamma (γ)
Alpha particle - nature, charge, electric field, mass, speed, ionizing, most dangerous, penetration
-two neutrons and two protons - same as a helium nucleus
+2 charge
-can be affected by an electric field
-relatively large mass
-slow speed
-strong ionizing effect
-most dangerous inside the body
-low penetration - can be stopped by a piece of paper or skin
Beta Particles - nature, charge, electric field, mass, speed, ionizing, most dangerous, penetration
-fast moving electrons
-produced in nucleu when a neutron changes into a proton and an electron
-1 charge
-can be affected by an electric field
-very small mass
-fast speed
-weak ionizing effect
-most dangerous outside the body
-medium penetration - can be stopped by 2-3mm of aluminium
Gamma rays - nature, charge, electric field, mass, speed, ionizing, most dangerous, penetration
-electromagnetic waves
-highest energy
-no charge
-not affected by an electric field
-no mass
-speed of light
-very weak ionizing effect
-most dangerous outside the body
-high penetration - partially stopped by thick lead/ concrete
Investigating radiation
- use Geiger-Müller tube to measure background radiation over a one minute period
- Repeat this three times, and take an average
- Place a radioactive source a fixed distance (3 cm) away from the tube and take another reading over a one minute interval
- Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
- One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
- Repeat the above experiment for other radioactive sources
Investigating radiation - safety conditions
-when not using a source - keep in a lead lined container
-when in use: keep a metre between you and the source
-when handling: use tweezers/ tongs and point the source away from you
Alpha decay equation
The mass number decreases by 4
The atomic number decreases by 2
Charge on the nucleus decreases by 2
Beta decay equation
The mass number remains the same
Atomic number increases by 1
Gamma decay equation
Mass number and atomic number remain the same
Detecting radiation
-photographic film
-geiger-muller tube
Detecting radiation - photographic film
Photographic films detect radiation by becoming darker when it absorbs radiation, just like it does when it absorbs visible light
-The more radiation the film absorbs, the darker it is when it is developed
Detecting radiation - geiger-muller tube
-Each time it absorbs radiation, it transmits an electrical pulse to a counting machine
-This makes a clicking sound or displays the count rate
-measured in becquerels (bq)
Background radiation
-rocks
-cosmic rays
-food and drink (bananas, brazil nuts)
-nuclear weapons testing
-nuclear accidents
-medical equipment
Radioactivity
Rate at which the unstable nuclei from a source of radiation decays
-measured in becquerels (Bq)
-1 Bq = 1 nucleus in the source decaying in 1 second
-activity of a source decreases with time
Half life definition
The time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half
Uses of radioactivity
-monitoring thickness of aluminum foil/ paper in factories
-detecting leaks in underground pipes
-smoke alarms
-sterilizing food/ medical equipment
-medical tracers
-gamma radiography
Use of radioactivity - smoke detector
- Household smoke alarms measure the movement of alpha particles across a small gap
- if smoke enters a detector, it will absorb the alpha particles and the detector will measure a drop in the number of particles across the gap
- This will trigger an alarm
Use of radioactivity - detecting leaks in underground pipes
- Water supplies can be contaminated with a gamma-emitting isotope
- When there is a leak, contaminated water seeps the ground
- Build up of gamma emissions in that area can be detected with a Gieger Muller tube
Use of radioactivity - monitoring thickness of aluminum foil/ paper in factories
- Rollers roll out sheets of aluminum foil and beta particles are passed through the foil and detected
- The detector monitors width of foil and expects particle activity to remain the same
- If it changes, the detector sends signals to the roller to change the width accordingly
Use of radioactivity - sterilising food/ medical equipment
Gamma radiation kills microbes and bacteria on fruits and vegetables
Use of radioactivity - medical tracers
- Radioactive isotopes (gamma) gets injected into the body.
- Certain chemicals concentrate on different parts of the body, and radiation concentrates with it
Use of radioactivity - gamma radiography
-X-rays and gamma rays can travel through different materials -makes it useful in inspecting materials without having to move or damage the material itself
Contamination
The unwanted presence of materials containing radioactive atoms on other materials
Irradiation
The process of exposing a material to alpha, beta or gamma radiation
-does not make material radioactive but can kill living cells
-method of sterilisation
Dangers of radiation
-ionising radiation can damage human cells and tissues
-Atoms in a DNA strand can be ionised and become damaged
-DNA may be mutated
-If a mutated cell is able to replicate itself then a tumour may form - cancer
Problems with disposal of radioactive waste
-If an isotope has a long half-life then a sample of it will decay slowly - remain radioactive for a very long time
-transportation - possible for leaks
-stored deep in the ground - might leak and contaminate the soil
Nuclear energy
-The nucleus of the atom contains a huge amount of energy
-nuclear reactions have the potential to produce large amounts of energy
-This energy can be released nuclear reactions -fusion, fission, radioactive decay
Fission
A large unstable nucleus splitting into two smaller daughter nuclei, releasing enormous amounts of energy
Fission of Uranium-235
-commonly used as fuel in nuclear reactor
1. neutron is shot into it to make uranium-236
2. this is very unstable and splits by nuclear fission almost immediately
3. Produces two smaller daughter nuclei - barium and kryton
4. Also produces 2 or 3 neutrons
5. New neutrons can start another fission reaction, which again creates further excess neutrons
6. Chain reaction starts
Elements of a nuclear reactor
-control rods
-fuel rods
-moderator
-coolant
-shielding
Nuclear reactor - control rods
Keeps the fission chain reaction active and prevents it from accelerating out of control by absorbing neutrons
-boron is typically used
-lowering rods: decreases rate, more neutrons absorbed
-raising rods: increases rate, fewer neutrons absorbed
Nuclear reactor - moderator
Reduces speed of neutrons so that they are more likely to be absorbed into a fuel rod
-material that surrounds the fuel rods and control rods inside the reactor core
Nuclear reactor - fuel rods
Contains fission products (U-235)
Nuclear reactor - coolant
Heated up by energy released and is used to boil water to drive turbines
Nuclear reactor - shielding
Absorb hazardous radiation
-surrounds reactor with steel and concrete wall that is nearly 2 metres thick
-absorbs emissions from the reactions
Fusion
Two smaller nuclei fuse together to form a single large nucleus, releasing energy
-energy produced comes from a very small amount of the particle’s mass being converted into energy
Fusion in stars
-stars use nuclear fusion to produce energy
-hydrogen atoms fuse together to form helium and produce lots of energy
-deuterium and tritium combine to form helium, a neutron, and energy
Conditions for fusion
-protons have a positive charge, they repel each other
-in order to overcome this, protons must have very high kinetic energy in order to be travelling towards each other at high speeds
-in order to make them travel at such speeds, gas has to be heated to millions of degrees celsius
-in order to increase number of collisions between nuclei, high densities and pressures also needed
-therefore, fusion is not currently used as a source of power on Earth
