Topic 3 - Radioactivity and Astronomy Flashcards
What is the structure of the atom
A positively charged nucleus surrounded by negatively charged electrons,
Pretty much all mass condensed into nucleus
What are the relative sizes of atoms and small molecules
1 x 10^-10
How has the model of the atom changed over time
-Plum pudding- spheres of positive charge with negatively charged electrons in the “dough”
-Rutherford did Gold foil experiment- fired alpha beam and some went through but others were reflected showing empty space
Bohr model- showed electrons were in fixed orbits from the nucleus called energy levels and only in these orbits
-This model is closest to modern day which says shells are elipse
What is meant by an isotope
Different forms of the same element but has a different number of neutrons
What are the relative charges of the 3 subatomic particles
proton +1
neutron 0
electron -1
What are the relative masses of the 3 subatomic particles
proton 1
neutron 1
electron 0.0005
Why do atoms have no overall charge
because they have the same number of electrons as neutrons so they have an equal and opposite charge
Where are electrons found inside atoms
In shells or energy levels at different distanced from the nucleus
when can electrons change orbit
by moving up an energy level
what is an ion
an atom which has lost or gained an electron to form a
- positively charged ion if it loses an electron
- negatively charged ion if gained
How does ionisation occur
if the outer electron absorbs enough energy it will move so far it leaves the atom and is now a free electron
-the atom is now a positive ion
What is background radiation
low level radiation surrounding us all the time coming from building materials, foods and rocks
Why does background radiation occur
naturally occuring unstable isotopes radioactively decaying
how does a geiger muller tube work
inert gas inside tube becomes conductive of electricity when impacted by a high energy particle
What is exposure to radiation known as?
Irradiation - doesnt make it radioactive
What is radioactive contamination
unwanted radioactive atoms getting in an object
Why is radioactive contamination bad
because radioactive particles could decay inside your body and cause damage to cells
How can we prevent radioactive contamination
By wearing gloves and using tongs
protective suits to stop breathing in particles
What are the 5 types of radiation which can be emitted in random processes by an unstable nucleus
Alpha decay Beta minus Positron emission Neutron Gamma
Describe how Alpha decay effects the charge and mass of the nucleus
mass number decreases by 4
atomic number decreases by 2
Describe how Beta-minus decay effects the charge and mass of the nucleus
mass number doesnt change
atomic number increases by 1
(one more proton)
Describe how Positron emission effects the charge and mass of the nucleus
mass number doesnt change
atomic number decreases by 1
(one less proton)
Describe how Neutron emission effects the charge and mass of the nucleus
mass number decreases by 1
atomic number stays the same
Describe how Gamma decay effects the charge and mass of the nucleus
Mass and atomic numbers stay the same as nucleus gets rid of excess energy as gamma and returns to a more stable state
Describe What an alpha particle is
Helium nuclei (two protons + two neutrons)
dont penetrate far so stopped quickly
absorbed by paper
size makes them strongly ionising as theyre bigger
Describe What an Beta minus particle is
`fast moving electron with charge of -1 relatively no mass
moderately ionising
absorbed by sheet of aluminium
Describe What an Beta plus particle is
fast moving positron with charge of +1 relatively no mass
moderately ionising
absorbed by sheet of aluminium
What happens when a Positron and electron hit each other
They destroy each other and produce gamma radiation in process called annihilation
(used in PET scanning)
Describe Gamma radiation
Electromagnetic radiation with a short wavelength
released by nucleus they penetrae far without being stopped
weakly ionising because of this so tend to pass through than collide, eventually hit something causing damage
absorbed by thick lead or concrete
How does the activity of a substance change over time
the rate something decays is called its activity and you can predict this with a samples half-life
What is activity measured in
becquerels Bq
1 Bq= 1 decay per second
How can amount of radioactivity be measure with photographic film
The more radiation the film is exposed to the darker it becomes (just like it does when exposed to light)
How is radioactivity used in smoke alarms
- a weak source of alpha radiation is placed in a smoke detector close to two electrodes
- the source causes ionisation and a current flows
- when there is a fire the smoke will absorb the radiation
- this makes the current stop and the alarm sounds
How is radioactivity used to irradiate food
high dose of gamma rays to kill microbes
this means the food doesnt go off as quickly
How is radioactivity used to sterilise medical equipement
Using gamma rays to kill microbes by irradiation
Why is irradiation a good method of sterilisation
its doesnt include boiling at high temperatures so the instruments/ food can be sterilised without damage
it needs a reasonably long half life so it doesnt need replacing
how is radioactivity used in tracing and thickness gauging
(Gamma is used in industry to detect leaky pipes)
Beta radiation is used in thickness control
you direct the radiation through the material being made with a detector on the other side
-if the amount of detected radiation changes then control the rollers to give right thickness
-it must be beta as the paper needs to partly block the radiation
Which two radiations must be the only ones that can pass through the body in medicine
beta or gamma NEVER ALPHA as its strongly ionising
beta and gamma can pass through without too much damage
How is radioactivity used in cancer diagnosis
In PET scanners- inject person with positron in glucose with a low half life to act as a tracer
- positrons meet the electrons in the organ with cancer cells and annihilate giving off gamma radiation which can be detected accurately on screen
- distribution of radioactivity matches up with metabolic rate as radioactive glucose is used by cells so an increases metabolism
Why must PET scanner be on site of a hospital
because if they were off site the isotopes would have to travel a greater distance and wouldnt work as well as activity would decrease
What are the hazards of ionising radiation
It can cause tissue damage and cell mutations which can cause tumors and cancer
How is radioactivity used to treat cancer internally
Internally- radioactive material (alpha) place near or in tumour and do damage to the cancerous cells but not as much nearby tissue as its short range
Beta used in implants too but can damage healthy cells due to long range
How is radioactivity used to treat cancer externally
gamma rays aimed at tumour which penetrate body and is carefully focused on tumour
- damages healthy cells
- long half life so doesnt need replacing
- doctors must stay in shielded room to protect
Advantages and disadvantages of treating Cancer internally
+damges cancer cells
-can damage other tissues
+/-short half life to reduce time its in their body
Advantages and disadvantages of treating Cancer externally
+damages cancerous cells
+long half life means doesnt need to keep replacing
-can cause burning
-can kill healthy cells
Describe some advantages and disadvantages of nuclear power
+reliable
+relatively safe
+0 emissions of fossil fuels
+huge amounts of energy from small source
- very expensive
- must be carefully controlled
- negative public perception
- waste has long half life
- risk of catastrophe
Describe the process of nuclear fission
- A slow moving neutron is fired at a large unstable nucleus (uranium 235)
- this makes it unstable so splits into 2 lighter nuclei and lots of energy is released
- as well as this 2 or 3 slow moving neutrons are released setting off a chain reaction
What are are the products of the fission of Uranium- 235
Krypton and Barium (radioactive)
How is a chain reaction controlled
- uranium fuel rods are placed in moderator such as water to slow down the fast moving neutrons
- boron control rods absorb excess neutrons to control and keep rate steady
How is thermal energy from chain reaction converted to electrical energy
-energy is transferred to thermal store of moderator which is transferred to boiler to heat water making steam which powers a turbine which turns to kinetic energy and powers generator creating electrical energy
Describe the process of nuclear fusion
- joining together small nuclei to creat a larger heavier nucleus such as two hydrogen to make a helium nuclei
- as mass of new nucleus doesnt have as much mass as the lighter nuclei did so some is converted into energy and radiation
How do stars create energy
In nuclear fusion reactions
Why are high temperatures and pressures needed for fusion
because strong force of electrostatic compulsion needs to be overcome to make 2 positively charged nuclei close enough to fuse at 10,000,000 degrees
Why is it difficult to make the conditions of fusion reactions
Because any material at those temperatures would be incinerated/ vaporised so reactors are very expensive to build and hard.
What are the different bodies that make up the solar system
Sun Planets Asteroids dwarf planets moons artificial satellites comets
How have ideas about the solar system changed over time
geocentric model- sun moon and everything orbited the earth because we didnt have telescopes and you saw the sun and moon travelling across the sky everyday.
Heliocentric- the sun is at the centre of the solar system and all planets orbit the sun in perfect circles (this was explained with galileo’s jupiters moons and proved geocentric model wrong
Gradually evidence increased for this model as we got more technology
We have elliptical orbits not circle
What factors effect strength of gravitational field
mass of the body creating field, larger=stronger
distance- closer= stronger=more instantaneous velocity needed to balance it
Why does gravity have different values on different bodies of the solar system
Because it depends on the gravitational field strength
weight force due to gravity
What are the orbits of moons, planets, comets and artificial satalites
Moons- orbit their planet almost circular, natural satalite
Planets orbit the sun in elliptical orbit
Comets- highly elliptical orbit round sun to edge of solar system
Artificial satallites-orbit earth in fairly circle orbit
Why does velocity of an object change even if orbiting at steady speed
constant speed means its constantly accelerating
this force is called the centripetal force
-the instantaneous velocity keeps it travelling in a “circle” at right angle to acceleration
-force is from the gravitational force
How does a changing speed of a body in orbit affect its radius of its orbit
If the speed of the object changes, the size/radius of its orbit changes too
More stable orbits have a smaller radius
Describe the life cycle of a star like our sun
nebula, protostar, main sequence, red giant, white dwarf
Describe the life cycle of a star much larger than our sun
nebula, protostar, main sequence, red supergiant, supernova, black hole/ neutron star
How does the movement of a wave source affect the observed frequency and wavelength
Obserevd increase in wavelength of light from distant galaxies and patterns have been shifted to red end of the spectrum
(when the observed frequency changes so does the wavelength)
Explain what red-shift is
- Different elements absorb different wavelength and frequencies of visible light.
- Each element produces a specific pattern of dark lines at frequencies it absorbs on spectrum
- as wavelength increases the patterns have been shifted towards the red end of the spectrum
Why does red shift provide evidence that the universe is expanding
by measuring red shift, we can see that all distant galaxies are moving away from us. these galaxies have greater red shifts and show greater increase in wavelength
this means the universe is expanding
What is the steady state theory
matter is always being created as the universe expand but density of universe stays the same, there is no beginning or end to the universe
supported by red shift
What is the big bang theory
All matter started in tiny dense hot space whch exploded and space started expanding and keeps doing
gives us finite age of universe around 13.7 billion years
supported by CMB and Red shift
Why do both theories account red shift
Because red shift shows objects are moving away from observer so could be observed for either model
What is CMB radiation
Cosmic microwave background radiation- detected low frequency EM radiation from Microwave part of spectrum
It is the left over energy from the initial explosion
Why has CMB led to the Big Bang theory being our current model
Because it shows left over energy from an initial explosion which shows the universe had a beginning
-Radio telescopes helped detect this
