7 Energy from the nucleus

Question 1

How is energy released in a nuclear reactor?

Answer 1

nuclear fission

Question 2

How does nuclear fission work?

Answer 2

• the nucleus of an atom of a fissionable substance splits into 2 smaller fragment nuclei (which can produce a chain reaction)
• nucleus releases 2 or 3 neutrons at high speeds and energy in the form of radiation…
• plus kinetic energy of the fission neutrons and fragment nuclei

Question 3

What can a chain reaction be caused by?

Answer 3

the fission neutrons may cause further fission

Question 4

What are the 2 main fissionable isotopes?

Answer 4

• uranium-235 (2-3% proportion)

- plutonium-239 (heavy nuclei from u-235 which is fissionable)

Question 5

What is inside a nuclear reactor (what is does)?

Answer 5

• fuel rods, control rods and water at high pressure
• moderator: fission neutrons are slowed down by collisions with atoms in the water molecules
• control rods: in core absorb surplus electrons which keeps chain reaction under control
• coolant: water-molecules gain kinetic energy from the neutrons and the fuel rods, water pumped through core then goes through sealed pipes to and from exchanger (water transfers energy for heating to the heat exchanger from the core)
• reactor core: made of thick steel to withstand very high temperature and pressure in the core, enclosed by thick concrete walls which absorb radiation that escapes through the walls of the steel vessel

Question 6

What is the process of nuclear fusion?

Answer 6

• 2 small nuclei release energy when they are fused together to form a single larger nucleus
• releases energy only if the relative mass of the nucleus is formed no more about 55 and energy is supplied to create a bigger nuclei

Question 7

How does nuclear fusion work?

Answer 7

• when two protons (hydrogen nuclei) fuse they form “heavy” hydrogen nucleus 2.1 H and other particles are created and emitted at the same time
• two more protons collide separately with two 2.1 H nuclei and turn them into heavier nuclei
• the two heavier nuclei collide to form the helium nucleus 4.2 He
• energy released at each stage is carried away as kinetic energy of the product nucleus and other particles emitted

Question 8

What are the factors required for a fusion reactor?

Answer 8

• plasma of light nuclei must be heated to very high temperatures before nuclei will fuse
• 2 nuclei approaching each other would repel each other due to positive charges but if they are moving fast enough, they can overcome the force of repulsion and fuse together

Question 9

What are the conditions in a fusion reactor?

Answer 9

• the plasma is heated by passing a very large electric current through it
• the plasma is contained by a magnetic field so it doesn’t touch the reactor wall (if it did, it would go cold and the fusion would stop)

Question 10

Why could fusion reactors in the future help our energy needs?

Answer 10

• the fuel for fusion reactors is readily available as heavy hydrogen and is naturally present in sea water
• the reaction product, helium, is a non-radioactive inert gas, so is harmless
• the energy released could be used to generate electricity

Question 11

What is radon gas?

Answer 11

an alpha particle-emitting isotope that seeps into houses in certain areas through the ground

Question 12

What was the Chernobyl disaster?

Answer 12

• 1986, nuclear reactor in Ukraine exploded
• workers struggled to control fire and a cloud of radioactive material from it drifted over parts of Europe
• 100 000+ people were evacuated
• over 30 people died
• many more developed leukaemia or cancer since

Question 13

What safety measures/features have been used in nuclear reactors since Chernobyl?

Answer 13

• different design
• the Chernobyl accident didn’t have a high-speed shut down system like most reactors have
• operators at Chernobyl ignored safety instructions
• hundreds of nuclear reactors worldwide which have always worked safely

Question 14

What does the effect on living cells of radiation from radioactive substances depend on?

Answer 14

• the type and amount of radiation from radioactive substances (the dose)
• whether the source of the radiation is inside or outside the body
• how long the living cells are exposed to the radiation

Question 15

Explain how dangerous the 3 types of radiation are (when inside/outside the body):

Answer 15

Alpha) inside: very dangerous- affects all surrounding tissue
outside: some danger- absorbed by skin; damages cells

Beta and Gamma) inside/outside: dangerous- reaches cells throughout the body

Question 16

How does the dose of radiation affect living organisms?

Answer 16

• the larger the dose of radiation someone gets, the greater the risk of cancer - high doses kill living cells
• the smaller the dose, the less risk - but it’s never 0, due to background radioactivity there is a very low level of risk

Question 17

How do workers at risk from ionising radiation cut down their exposure?

Answer 17

• keep as far as possible from radiation source, using special tools with long handles
• spend as little time as possible in “at risk” areas
• shield themselves from radiation by staying behind thick concrete barriers and/or using thick lead plates

Question 18

What is a galaxy?

Answer 18

a collection of billions of stars held together by their own gravity

Question 19

When were things formed from the big bang- order?

Answer 19

• quarks and electrons form from radiation after 0.1s
• neutrons and protons form after 100s
• hydrogen and helium atoms form after 100 000 years
• first galaxies and stars form after a few billion years

Question 20

How has the universe changed since the Big Bang?

Answer 20

• space, time and radiation were created
• at first the universe was a hot glowing ball of radiation and matter
• as it expanded temperatures fell
• now the universe is cold and dark except for hotspots-stars

Question 21

What happened as the universe expanded?

Answer 21

• became transparent as radiation passed through empty space between its atoms
• background microwave radiation was released
• for the next few billion years the universe was completely dark, patchy, expanding cloud of hydrogen and helium
• then stars and galaxies formed and lit up the universe

Question 22

What force formed the stars and galaxies?

Answer 22

GRAVITY

• uncharged atoms don’t repel each other but they can attract each other
• at first the force of gravitational attraction was at work without any opposition from repulsive forces
• denser parts of universe attracted nearby matter turning them into gigantic clumps
• eventually they formed galaxies and stars

Question 23

What is a protostar?

Answer 23

a gas and dust cloud that can go on to form a star

Question 24

What is a planet?

Answer 24

a large object that moves in an orbit around a star

a planet reflects light from the star and does not produce its own light

Question 25

What is a main sequence star?

Answer 25

the main stage is the life of a star during which it radiates energy because of fusion of hydrogen nuclei in its core

Question 26

What is a red giant?

Answer 26

a star that has expanded and cooled, resulting in it becoming red and much larger and cooler than it was before it expanded

Question 27

What is a white dwarf?

Answer 27

a star that has collapsed from the red giant stage to become much hotter and denser than it was

Question 28

What is a black dwarf?

Answer 28

a star that has faded out and gone cold

Question 29

What is a supergiant?

Answer 29

a massive star that becomes much larger than giant star when fusion of helium nuclei commences

Question 30

What is a supernova?

Answer 30

the explosion of a massive star after fusion in its core ceases and the matter surrounding its core collapses on to the core and rebounds

Question 31

What is a neutron star?

Answer 31

the highly compressed core of a massive star that remains after a supernova explosion

Question 32

What is a black hole?

Answer 32

an object in space that has so much mass that nothing, not even light, can escape from its gravitational field

Question 33

What is the timeline of a low mass star (like our sun)?

Answer 33

protostar –> main sequence star –> red giant –> white dwarf –> black dwarf

Question 34

What is the timeline of a high mass star?

Answer 34

protostar –> main sequence star –> red supergiant –> supernova –> neutron star –> black hole (if sufficient mass)

Question 35

How does the birth of a star work?

Answer 35

• particles in clouds pulled together by gravitational attraction
• clouds merge together
• become more concentrated to form protostar
• becomes denser = hotter (once hot enough, nuclei of hydrogen atoms and other light elements fuse together)
• energy released in fusion = core hotter and brighter till it starts to shine = star
• some objects may form which are too small to form stars e.g. planets which may be attracted

Question 36

What happens during the time when a star is a main sequence star?

Answer 36

• radiate energy because of hydrogen nuclei in the core (main stage of life- can maintain energy output for millions of years until star runs out of nuclei to fuse together)
• energy released in core keeps it hot so fusion processes continue- radiation flows out steadily from the core in all directions
• star stable because forces within it are balanced- force of gravity making a star contract is balanced by the outward force of radiation from core
• forces remain balanced until end of hydrogen fusion

Question 37

How do stars die?

Answer 37

Low mass)

• swell out, cool down and turn red
• red giant- helium and other lighter elements in core fuse to form heavier elements
• when no more light elements are in core, fusion stops and no more radiation is released so star collapses in on itself
• as it collapses turns from red to yellow to white (heats up) which is hot, dense and smaller…eventually fade out to become black dwarfs

High mass)

• end lives more dramatically
• swells to become a red supergiant which then collapses
• during collaps, matter surrounding core compresses increasingly until it reverses into cataclysmic explosion known as supernova

Question 38

What happens after a supernova?

Answer 38

• explosion compresses core of star into a neutron star

- if star is massive enough then it becomes a black hole instead of neutron star

Question 39

How do light elements form?

Answer 39

• from fusion in stars
• stars like sun fuse hydrogen nuclei i.e. protons into helium and other small nuclei e.g. carbon
• when star becomes red giant, it fuses helium and other small nuclei into larger nuclei
• nuclei larger than iron can’t be formed because too much energy is needed

Question 40

How do heavy elements form?

Answer 40

• when a massive star collapses then explodes as a supernova
• enormous force of collapse fuses smaller nuclei into nuclei larger than iron (explosion scatters star into space)
• debris of supernova contains all known elements from lightest to heaviest and eventually new stars form as gravity pulls debris together
• planets form from debris surrounding new star and therefore are composed of all known elements

Question 41

What was the sun and rest of the solar system formed from?

Answer 41

debris of a supernova
(evidence from natural element uranium on planet earth-heaviest with half-life of 4500 million years so evidence was formed from supernova)