Nuclear + Space physics

Household fire alarms - uses of radiation

• alpha particles are used in smoke detectors

• alpha radiation ionises the air within the detector creating a current

• Alpha emitter is blocked when smoke enters the detector

• Alarm is triggered by microchip when the sensor no longer detects the particles

sterilization of equipment - uses of radiation

• gamma radiation

• kills bacteria by breaking down bacterial DNA, inhibiting bacterial division

Irradiating food to kill bacteria - uses of radiation

• gamma rays can irradiate food to kill any microorganisms that are present on it

• this makes food last longer + reduces risk of food-borne infections

Measuring the thickness of materials - uses of radiation

• Beta radiation is most commonly used

• 1 - material moves across radiation source and the particles that go through it are monitored using a detector above

• 2 - the thickness of the material is monitored. ( thicker → less particles are detected by detector due to them being absorbed by the material)

• the machine makes adjustments to keep the thickness of the material constant

diagnosis of cancer

• tracer - a radioactive isotope that can be used to track the movement of substances like blood around the body

• PET scan can detect the emissions from a tracer to diagnose cancer and determine the location of a tumor

treatment of cancer - uses of radiation

• radiotherapy (chemotherapy is with chemicals)

• beams of gamma rays are directed on to the cancerous tumor (gamma rays can go through the body)

• beams are moved around to minimize harm to healthy tissue whilst being aimed at tumor

Atomic/proton number (Z)

• determines what element it is

• = number of protons

• = number of electrons

Nucleon number (A)

• total number of particles in the nucleus of an atom

• = protons + neutrons

Nuclear charge

• = relative charge of nucleus

• determined by the proton number of the atom

• nuclear charge = number of protons in nucleus x relative charge of a proton

ionisation definition

when an atom becomes negatively or positively charged (by gaining or losing electrons)

Nuclear radiation ionizing an atom

• Nuclear radiation can ionise the atoms that it hits

• this is mostly done by removing an electron so the atom looses a negative charge → left with an overall positive charge

Background radiation

• the radiation that exists around us all the time

• 2 types :

  • Natural sources - from radioactive elements that have always existed on earth + outer space

  • Man-made sources - from human activity

sources of background radiation

• radon gas

• rocks and buildings

• food and drinks

• cosmic rays

detecting radiation

• Ionising nuclear radiation can be measured using a detector connected to a counter

• the detector uses count rate measured in counts/s or counts/minute

• count rate = number of decays per second

Geiger–Müller tube

• Each time it absorbs radiation, it transmits an electrical pulse to a counting machine

  • This makes a clicking sound and it displays the count rate on a screen

• Higher count rate = tube is absorbing more radiation

• tube higher away from source = lower count rate

alpha decay (α)

• alpha particle = helium nucleus = 2 neutrons + 2 protons

• unstable isotope → helium nucleus + stable isotope

• Range in air = few cm

• High ionising ability

• can be stopped by a sheet of paper (low penetrating power)

• affected by an electric field as it has a 2+ charge

• looses 2 atomic numbers + 4 mass numbers

beta decay (β)

• neutron in nucleus spontaneously decomposes into an electron and a proton

• can be affected by electrical field due to having a charge of -1

• Beta particle = high energy electron

• Range in air → a few 10s of cm

• moderate penetrating power → stopped by a few mm of aluminum/perspex

• moderate ionising ability

gamma decay (γ)

• no charge

• electromagnetic wave

• infinite range in air

• high penetrating power (reduced by few cm of lead)

• low ionising ability

radioactive decay definition

a change in an unstable nucleus that can result in the emission of α-particles or β-particles and/or γ-radiation. (changes are spontaneous + random)

half-life definition

the time taken for half the nuclei of that isotope in any sample to decay

dangers of ionising nuclear radiation

• cell deaths

• mutations

• cancer

safe storage of radioactive materials

• reducing exposure time

• increasing distance between source and living tissue (e.g using tongs, building power plants in remote places)

• using shielding to absorb radiation (e.g made out of lead, water or concrete)

what is a light year

the distance travelled in (the vacuum of) space by light in one year

order of planets

mercury, venus, earth, mars, jupiter, saturn, uranus, neptune

minor planets

• dwarf planets - object similar to planet but much smaller - pluto

• asteroids of asteroid belt

moons

• natural satellite

• orbit planets

Light

• electromagnetic wave

• 3×10 to the power of 8

how to calculate the time it takes for light to travel a distance

time = distance / speed of light

orbital motion

• a result of the gravitational force of attraction acting between two bodies

• always acts towards the centre of the larger body

• causes the orbiting body to move in a circular path

gravitational attraction of the sun

• sun contains most of the mass of the solar system

• objects orbiting the sun stay in orbit due to the gravitational attraction of the sun

• the force is directed from the orbiting object to the center of the sun

The Sun

• a medium sized star

• consists mostly of hydrogen and helium

• radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum

orbital speed equation (π)

• v = 2πr/T

• T = orbital period

• r = radius of the orbit

what happens when the distance from the sun increases

• Sun’s gravitational field strength decreases

• orbital speed of planets decreases

what are stars powered by

• nuclear reactions that release energy

• in stable stars nuclear reactions involve the fusion of hydrogen into helium

first stages of a stars life cycle that every star experiences

stellar nebula → protostar → stable star

how is a stable star formed

formed as prostars from interstellar clouds of gas and dust(stellar nebula) due to gravitational attraction

life cycle of a small mass star

• about the same mass as the sun

• red giant → white dwarf + planetary nebula

what is a Red giant

• Formed when a small mass star reaches the end of its life

• The outer layers of the star expand and cool

planetary + supernova nebula

• planetary nebula - Formed when the outer layers of the star are pushed away

• supernova nebula - may form new stars with orbiting planets

what is a white dwarf

• Formed when the core of the star collapses

• Found at the centre of a planetary nebula

life cycle of a large mass star

red supergiant → supernova → neutron star

what is a red supergiant

• when a star reaches the end of its life

• the outer layers of the star expand and cool

what is a supernova

an exploding red supergiant

what is a neutron star

• formed when the core of a large super star collapses

• very dense (not as much as dark holes)

life cycle of a very large mass star

red supergiant → supernova → black hole

black hole

• Formed when the core of a very large star collapses

• Extremely dense

galaxies + milky way

• galaxies are made up of billions of stars

• Sun is a star in the milky way(a galaxy)

• other stars that make up the Milky Way

  are much further away from the Earth

  than the Sun is from the Earth

• diameter of milky way = approximately 100000 light-years

Big Bang theory

• theory is supported by many astronomical observations

• 13.8 billion years ago a giant explosion caused the universe to expand from one single point of high density and temperature

• The Universe is still expanding ( causes galaxies to be further apart from each other)