Radioactivity Flashcards
What are isotopes
Atoms with the same number of protons but different number of neutrons
What is radioactive decay
In a radioactive atom, the nucleus is unstable and so emits particles or waves (radiation) to form a more stable atom
Can we predict or influence radioactive decay
No radioactive decay is random- we cannot predict or influence when it will happen
What does it mean if a substance is classed as radioactive
They are unstable and continuously emit radiation
What did jj thompson discover in 1897
He discovered tiny particles with a negative charge, he had discovered the electron which is a sub atomic particle
What did the plum pudding model look like
It is a positively charged sphere with negative electrons distributed throughout it
Who was the first to discover the atom and who rejected this idea
Democritus - first to describe an atom (440 bc ) Vs Aristotle - rejected the atom
Describe geiger and marsdens gold foil experiment and what conclusions were made
A thin gold sheet was placed in front of the opening of a lead box containing an alpha source. This apparatus and an alpha detector were placed in a dark vacuum chamber.
Most of the alpha particles went straight through the gold foil without any deflection - atoms are mostly empty space
Some alpha particles were slightly deflected by the gold foil - a repulsive electrostatic force is caused by a small nucleus which has the same charge as the alpha particles
A few alpha particles bounced back from the gold foil - most of the mass of the atom is in the nucleus which is more massive than the aloha particle
What is an alpha particle
-nucleus of helium atom (2 protons and 2 neutrons)
-most ionising type of radiation
-charge : +2
-speed : less than 10% of the speed of light
What is a beta particle
-consists of one electron
-less ionising than alpha particles
-charge: -1
-speed: up to 50% speed of light
What are gamma rays
-high frequency electromagnetic wave
-least ionising type of radiation
-no charge
-fastest speed: speed of light
Describe alpha radiation
An atom decays into a new atom and emits an alpha particles (2 protons and 2 neutrons- the nucleus of a helium atom )
Describe beta radiation
An atom decays into a new atom by changing a neutron into a proton which stays in the nucleus and electron. The fast moving, high energy electron is called a beta particle and it is emitted
Describe gamma radiation
After alpha or beta decay surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The atom is not changed
What is ionisation
Atoms are ionised when electrons are removed, turning them into an ion which is more likely to take part in chemical reactions
How many protons and neutrons are released in alpha decay
The atom looses 2 protons and 2 neutrons. This causes the mass number to decrease by 4 and the atomic number decrease by 2
How does mass and atomic number change due to beta decay
Mass number stays the same atomic number increases by 1
What is activity
The number of atoms that decay per second OR the rate at which radioactive nuclides decay
What happens to reactivity over time
- as time goes on, fewer and fewer radioactive atoms remain
-this means that the number of atoms decaying in a given time decreases - so the amount of radiation detected (or count rate) also decreases
What is half life
The half life of a radioactive isotope is the average time it takes for half the nuclei in a sample to decay
What is alpha radiation stopped by and what is its range in air
Stopped by : skin or paper range in air : 5cm
What is beta radiation stopped by and what is its range in air
Stopped by : thin sheet of aluminium range in air : 1m
What is gamma radiation stopped by and what is its range in air
Stopped by : thick lead or thick concrete range in air : unlimited
Compare the penetration power of alpha beta and gamma radiation
Alpha has the least penetration power
Beta has medium penetration power
Gamma has the most penetration power
What is nuclear radiation used for in medicine
The exploration of internal organs
Control or destruction of unwanted tissue
What is the most common tracer used and why
Technetium -99 because it
Only emits gamma rays - it can be detected outside the body by a gamma camera, doesnt cause much ionisation
Short half life
Describe how cancer can be treated using radiotherapy
Gamma rays are sent through the body at various different angles. This happens inside a large circular machine. On its own each beam has too little energy to harm the body or the cancer. However the beams are aimed so they cross at the point where the cancer need to be killed
Sterilizing
Gamma rays can be used to kill bacteria mould and insect in foods, even after the food has been packaged. They are also used sterilise hospital equipment
Describe how smoke detectors use radiation
Smoke detectors contain a weak source of alpha radiation. The alpha particles ionize the air, which leads to the creation of an electrical current. It smoke is present it interacts with the ions produced by the alpha particles. This means that current is flowing through the air which causes the alarm to sound
How is radiation used safely in medicine
-when radiation is used in medicine patients are given as small a dose as possible and split into a number of treatments
- this radiation is targeted at the area of the body being imaged or treated other areas are protected using a lead shield
- tracers should contain isotopes that have half lives that are as short as possible, so that the patient is not exposed to radiation in the body for longer than possible
What should you do when dealing with radiation
- limit time of exposure
-avoid direct contact by using tongs
-always wear protective clothing
-keep the source in shielded labelled, lead lined storage
Explain why gamma emission does not change the atomic number of an element
Gamma radiation is an electromagnetic wave not a particle so it doesn’t affect the number of protons or neutrons in the nucleus since the proton number stays the same the atomic number does not change
Describe how irradiated food is different to radioactive food
Irradiated food is treated with radiation to kill germs but it does not absorb the radiation or become radioactive
Radioactive food - contains unstable radioactive isotopes that emit harmful radiation
What is contamination and irradiation
Contamination is when you take a radioactive material inside your body or if it is put on your skin
Irradiation is when there is radioactive material outside your body that can reach you as waves
What is nuclear fission
When a large and unstable nucleus absorbs a neutron and splits into two smaller and lighter nuclei releasing a large amount of energy and 2-3 neutrons
Examples of isotopes that undergo fission
Uranium -235 and plutonium -239
What are the 2 major isotopes of uranium
Uranium- 238 more common ; does not undergo nuclear fission
Uranium- 235 less common ; does under go nuclear fission
What has to happen before the uranium 235 can be used as fuel
It needs to be enriched until it has 3% of fissionable uranium
What are the stages in a nuclear power station
Stage 1- in the reactor, nuclear fission in the uranium fuel rods releases heat, which is used to boil water
Stage 2- the boiling water produces high pressure steam. The force of moving steam turns the turbine
Stage 3- the turbine turns the generator and electricity is produced
Stage 4 - the low pressure steam is condensed back into water in the cooling towers. The water is reused
What is a chain reaction
Nuclear fission produces daughter nuclei and neutrons. If these neutrons go on to split other nuclei, this sets up a chain reaction. These released neutrons can cause fission to occur in other nuclei, producinh even more neutrons, which can continue the chain reaction, as each fission occurs more and more neutrons are produced . The rate of fission increases rapidly resulting in a massive release of heat and energy
What are the fuel rods
They contain enriched uranium which has an increased percentage of uranium -235 compared to the uranium ore from which it is extracted. This fuel is for the reactor
What are the control rods
They are made of cadmium or boron, which can absorb neutrons without undergoing fission. Can be lifted in and out of the reactor to control the number of neutrons so that fission happens at a steady rate
What is the coolant
Water flows around the core, transferring heat away from the fuel, to be used to produce steam. The water is usually pressurised to prevent it boiling inside the reactor
What is the moderator
Reactors use graphite or the coolant water to slow down fission neutrons. Slow moving neutrons are more readily absorbed by uranium - 235 nuclei so moderation is needed to keep the reaction going.
What is nuclear fusion
The process of joining 2 smaller nuclei to form a larger one. The process involves bringing two hydrogen atoms close enough to make them fuse to form helium. This process happens in stars and at very high temperatures and pressures . These conditions are necessary to overcome the electrostatic repulsive forces between all the protons in the nuclei and force them together
