Atoms and Astrophysics Flashcards
What three particles is an atom made up of?
Proton (+1), neutron (no charge) and electron (-1)
Atomic number symbol
Z
What is the atomic number?
The total number of protons in the nucleus of an atom. It tells us what element the atom is from.
Mass number symbol
A
What is the mass number?
The total number of protons and neutrons in the nucleus of an atom.
What are particles in the nucleus called?
Nucleons
What is an isotope?
Nuclei with the same number of protons but a different number of neutrons.
What are the forces in the nucleus?
Strong nuclear force between all nucleons and repulsive force between protons.
For a nucleus to be stable, what must happen?
The strong nuclear force between the nucleons must balance the repulsive force between the protons.
What happens to the repulsion force as the number of protons increases?
It increases. Larger nuclei have a larger amount of neutrons to balance the repulsive force.
What is radioactive decay?
Radioactive decay is when an unstable nucleus does not have the ‘right’ number of protons and neutrons and becomes more stable by emitting particles.
What are the three types of particles that a nucleus can emit?
Alpha particles, beta negative particles and beta positive particles
What is an alpha particle made up of?
Two protons and two neutrons joined together ( a helium nucleus)
What is a beta negative particle made up of?
Electrons from the nucleus
What is a beta positive particle made up of?
Positive electrons (positrons)
What is gamma radiation?
Gamma radiation usually accompanies alpha or beta particles. It is part of the electromagnetic spectrum and carries energy away from the nucleus. As it is just energy it doesn’t change the number of protons/neutrons.
What happens in alpha radiation?
The mass number decreases by four and the atomic number decreases by two, meaning a new element is formed.
What happens in beta-negative radiation?
A neutron in the original nucleus turns into a proton. This means the mass number stays the same but the atomic number increases by one.
What happens in beta-positive radiation?
A proton in the nucleus turns into a neutron. The mass number doesn’t change but the atomic number decreases by one, meaning a new element is formed.
What is half-life?
The time that is taken for half of the nuclei in a radioactive sample to decay.
As a radioactive substance emits radioactivity and decays into a more stable form, what happens to the number of particles that are given off per second?
It decreases
What are protons and neutrons made up of?
Quarks
What are the six flavours of quarks?
Up, down, top, bottom, strange and charm
What is the charge of an up quark?
+2/3
What is the charge of a down quark?
-1/3
How many quarks are protons made of?
2 up quarks and 1 down quark
How many quarks are neutrons made of?
1 up quark and 2 down quarks
How does a neutron turn into a proton in beta-negative decay?
A down quark (-1/3) turns into an up quark (+2/3), changing the charge to +1
How does a proton turn into a neutron in beta-positive decay?
A up quark (+2/3) turns into a down quark (-1/3), changing the charge into 0
What is ionisation?
The removal of an electron from an atom or molecule. It is dangerous to living things as the ionised atoms/molecules will react differently, damaging or even killing a cell
What type of radiation is the most ionising?
Alpha radiation, because of it’s greater charge from two protons
What is the speed and range in air of an alpha particle?
10% of the speed of light and about 5cm range in air
What is the speed and range in air of a beta particle?
90% of the speed of light and about 30cm.
What is the speed and range in air of a gamma particle?
The speed of light and hundreds of metres
What is the penetration of each particle?
Alpha can be stopped by paper, beta can be stopped by a few mm of aluminium and gamma is stopped by 10cm of lead.
Why aren’t alpha particles very dangerous even though they are the most ionising?
They cannot penetrate the outer layer of our skin.
How dangerous is beta radiation?
It can partially penetrate our skin and it’s ionising ability can cause beta burns on our skin cells.
Why is gamma radiation the most dangerous?
While gamma radiation is the least ionising particle, it can easily penetrate the human body and so is the most harmful to us.
How is radioactivity used in cancer treatment - external beam therapy?`
The radioactive source is outside the body and directed towards the tumour to kill cancer cells. Gamma is used as it can penetrate the body. A number of low-intensity rays are used and overlap the tumour to receive a high dosage.
How is radioactivity used to treat cancer in brachytherapy?
A radioactive source is placed inside the body in or near the tumour. It’s radiation penetrates the tumour. Gamma or beta is usually used as it can penetrate the cancer tumour. The type of radiation/half life/type of cancer/where the cancer is will decide how long it stays in place.
How is radiation used in smoke detectors?
Smoke detectors contain a small amount of a radioactive source which emits a stream of alpha particles, being sensed by a detector which creates a current. When the smoke comes between the source and the detector, the current is decreased and sets off the alarm. Alpha particles are used as they can’t penetrate through the alarm.
How is radioactivity used in checking for leaks in water pipes?
Water supplies are contaminated with a gamma source. The contaminated water seeps into the ground where the leak is, causing a build-up of gamma. This can be detected by gamma rays. It needs to be gamma so it can penetrates the ground and road but needs a half-life of only a few days so it allows it to build up but isn’t long enough to be harmful.
How is radioactivity used to control thickness of a piece of paper?
An emitter is placed on either side of a piece of paper with a detector on the other. If the thickness remains constant, the activity won’t change. If there is a change in thickness, the rollers will be triggered to squeeze harder/softer. A beta source is used as it can penetrate paper or thin aluminium. It will need a long half life.
What is nuclear fission?
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei.
How does nuclear fission work?
A neutron is fired at a larger unstable atom, which sticks to the nucleus and makes the atom even more unstable so it breaks apart into smaller nuclei.
What is the chain reaction in nuclear fission?
The neutrons that are formed after the fission go on to hit other atoms, causing the chain reaction.
What happens to the energy in nuclear fission?
It is used to produce electricity.
What is nuclear fusion?
When smaller nuclei are joined together to make one larger nucleus.
Give an example of nuclear fusion
Hydrogen nuceli in stars are joint to create a helium nucleus
What conditions are needed for nuclear fusion?
High heat and pressure to push the nuclei together
Why does nuclear fusion need high heat and temperature?
The positively charged nuclei repel each other. There needs to be enough energy to overcome the repulsion, and once they are close enough to each other the strong nuclear force will overcome the repulsion.
If a electron shell is further from the nucleus, will it have more energy or less?
More - the further away, the more energy
How can electrons be given energy?
Heat or electricity
What is an AU?
An astronomical unit - the average distance between the Earth and the Sun. It is used to measure distances between planets.
What is a light year?
The distance light travels in a year. Used to measure distances between stars or sizes of galaxies
What is a parsec?
A larger unit than the light year. Used to describe distances to other galaxies. 1 Mpc = 1 x 10^6 pc.
What is a star?
A luminous ball of heated gas held together by gravity
What is a stellar nebula?
A star forms from a cloud of gas (hydrogen and helium). Gravity pulls the particles close until the gas is hot enough for a protostar to be formed. This keeps contracting due to gravity until pressure and temperature gets hot enough for fusion of hydrogen to helium to occur.
Why is a main sequence star have a stable period?
Inwards gravitational force = outwards force due to fusion
What happens when there isn’t enough hydrogen in the star to continue fusion?
The core contracts and temperature and pressure become high enough for helium to be fused. Layers expand to create a red giant, and continue expanding to create a super red giant.
What happens after fusion stops in a star?
It dies. (Death of a star)
Death of a star (up to 8M)
A planetary nebula occurs, where the stars lose their outer layers. It leaves a white dwarf behind, which cools to become a black dwarf.
What is a white dwarf?
A stage after a planetary nebula where atoms are forced together by gravitational forces until repulsion between electrons stops further contraction.
Death of a star (over 8M)
A supernova (short-lived explosion) occurs, once iron fusion stops. The core collapses before nuclei repel each other, blowing away outer layers. Core contracts again to form a neutron star (packed protons and electrons together to form neutrons) or black hole (gravity is so strong light cannot escape)
What is a galaxy?
Groups of billions of stars held together by gravity.
What are the three shapes of galaxies?
Spiral, elliptical and irregular
Constellation
Stars that make patterns in the sky. The stars aren’t always close together, they just appear that way when we see them.
What are the eight planets?
Mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
Rocky planets -
Mercury, venus, earth, mars
Gas planets
Jupiter Saturn Uranus Neptune
Mercury info -
Closest to sun, smallest planet, no moons or atmosphere, rotates slowly so one side is hot, other is cold
Venus info -
Hottest planet, because of thick atmosphere made of sulfuric acid that traps heat. No moons but has volcanoes.
Earth info -
Only known life, has water/oxygen, one moon
Mars info -
Red planet due to iron oxide on surface, has largest volcano, two moons
Jupiter info -
Gas planet, biggest planet, fastest spinning, has a red spot of a storm, faint rings and 60+ moons
Saturn info -
Has rings made of ice and dust, over 50 moons
Uranus info -
Tilted on its side, has rings, almost 30 moons
Neptune info -
Faint rings, coldest planet, over 10 moons
What is a dwarf planet?
Made of rock/ice. It is big enough for gravity to cause them to be round but haven’t cleared the orbit of smaller bodies.
What is an astroid?
Lump of rock, found mostly in Astroid belt between mars and jupiter
What is a comet?
Ice/dust substance. Takes 100s of years to orbit the Sun. starts to melt as they come close to earth, makes a tail that points away from the sun
What is an exo planet?
A planet orbiting a star outside of our solar system. Difficult to see.
What are the two methods of detecting an exoplanet?
Look for wobbly stars - when a planet orbits a star, the planet and star orbit their common centre of mass, making the star wobble.
Transit method = planet passes in front of the star, blocking light so the star appears less bright. Can work out the size of planet and distance from star
What is the difference between a planet’s day and planet’s year?
The year is the time taken to orbit the planetary body eg sun. The day is the time taken for it to rotate fully on its axis
