P6 Flashcards
What are subatomic particles
Particles found inside atoms, like neutrons protons and ekectrons
What are isotopes
Atoms of the same elements with different numbers of neutrons
What are the mass and charges of neutrons protons and electons
Charge:
E = -1
P = +1
N = 0
Mass
E = 1/1835 (taken as 0)
P = 1
N = 1
What does the mass number of an atom show
The number of protons and neutrons
What does the atomic number show
Number of protons in the nucleus
Or electrons in the outer shell
What happens if a nuclei is unstable
It xan emit radiation
What does it mean if a nuclei is unstable
A nucleus that decays by emitting radiation or by fission
Why do the nuclei of atoms decay
If a change in the atoms configuration it will become unstable (as it is no longer balanced)
And it will attempt to become stable by decaying
What are the 5 main types of Radiation and their symbols
Alpha (a)
Beta (β + or -)
Gamma (y)
Neutron decay
What is an alpha particle
A charged particle with no electrons
It is the nucleus of a helium atom
(+2 charge and a mass of 4)
What is a beta minus particle
A high speed energy electron
It has a charge of -1 and a mass of 0 (1/1835)
It is released from the nucleus when a neutron transforms into a proton
What is a beta plus particle
A particle with a +1 charge and a mass of 0 (1/1835)
It is a high speed POSITRON
(Same characteristics as an electron but positive)
It is released from the nucleus when a proton transforms into a neutron
What is gamma radiation
High energy + high frequency electromagnetic wave
It has a mass of 0 and a charge of 0
What is penetrating power
The ability to travel through a material
What is the ionising power, range and penetration power of, alpha, beta and gamma
Alpha - high ionising power, short range (a few cm) and small penetrating power (stopped by a few sheets of paper)
Beta - Moderate ionising power, medium range (a few m) and a low penetrating power (stoped by a few mm of aluminium)
Gamma - little ioninsing power, far range (a few km) and a great penetrating power (a few m of lead or concrete)
How can radiation be detected
Using a geiger counter
This device ‘clicks’ when radiation enters it, as the radiation ionised the gas inside the tube
What happens in alpha decay
The atomic number decreases by 4
The mass number decreases by 2
E.g 240 Pu → 236 U + 4 He
94 92 2
Helium nucleus is limited
What happens in beta - decay
A neutron becomes a proton and an electron is emitted
The mass number stays the same, but the atomic number increases by 1
E.g
218 Po → 218 At + 0 e
84 85 -1
What happens in beta + decay
Opposite of beta -
A proton transforms into a neutron and releases a positron
Mass number stays the same
Atomic number decreases by 1
218 Po → 218 Bi + 0 β
84 83 +1
What happens in gamma decay
There is no change in the atom / isotope as gamma radiation has no mass or charge
It is normally emitted WITH alpha or beta particles
What happens in neutron decay
A neutron is emitted, so the mass decreases by 1
The charge remains the same
5 He → 4 He + 1 n
2 2 0
Is the way a material decays uniform
No it is random
What can a geiger counter measure
The radiation emitted per second (called activity)
It is measured in becquerels
1 becquerel = 1 count (wave or particle) per minute
What is half life
The time taken for the activity to halve in a material
Half life is measured in time and shows how wuickly a material decays
How are graphs used to calculate half life
Time is plotted (x axis) against activity
When the activity is halved we can read down to see how long it took
what is net decline
The ratio showing the ratio of final to initial activity
What is the net decline after two half lives
1:4 - it has halved twice (it is a quarter its original size)
How are electrons arranged
In fixed energy levels around the nucleus of an atom known as electrong shells
What does the photon model show
How electromagnetic radiation is emitted and absorbed as packets of enegy called photons
The energy of each photon is proportional to its frequency
What happens when photons excite electrons
When photons have enough energy electrons can be excited
This causes the electron to move up an energy level
Other than collisions with photons how can electrons be excited
Passing an electric current through electrons in a gas
What happens when electrons move from a higher energy level to a lower one
Radiation is emitted
The frequency of the radiation depends on the difference in energy levels
The change in energy levels can be between multiple levels not just one
How do absorption spectrums work and what do they show
When light of all frequencies is passed through hydrogen gas some frequencies are absorbed.
The spectrum shows a set of frequencies of radiation absorbed by an atom when excited electrons move to higher energy levels
Which photons (pieces of the electromagnetic spectrum) have enough energy to ionise atoms
Ultraviolet, X-ray and Gamma
What does an emission spectrum shown
Shows a set frequency of radiation emitted when excited ekctrins move to lower energy levels
What is contamination (radiation)
When the radioactive material is inside the body or skin
(Or an object)
What is irradiation
Being exposed to radiation from an external source
What is background radiation
A measure of the level of ionising radiation present in the environment
What happens when you move away from a source of radiation that is irradiating
It no longer effects you
When is irradiation used
Used in x-rays
Foods are irradiated to improve their shelf life
Irradiation vs contamination
Irradiation :
Object exposed to radiation outside the body
Can cause cancer
Exposure stops when source is removed
Object doesnt become radioactive
Contamination
Object exposed to a source of radiation in or around the body
Can cause cancer
The object is radioactive as long as its contaminated
Difficult to remove contamination
What are the medical uses of irradiation
Gamma knife → moveable ray of gamma radiation that is focused onto tumors
This kills cancerous cells or inhibits their growth
Can be used to sterilize equipment (kills microorganisms e.g bacteria)
What are the medical uses of contamination
Radioactive tracers are injected into patients
These are absorbed by organs and through the releasing of gamma radiation show images of organs
Why is gamma radiation used for radioactive tracers
They have a high penetrating power so less radiation would be absorbed by the patient
Why are alpha particles not used for radioactive tracers
They have a low penetrating power so the patient would absorb the radiation
(Causing cancer)
Why are radiotracers with a short half life chosen
To minimise the time of exposure to radiation
The radiotracer would have to have a long enough half life to be effective
What is the conservation of mass
Mass is conserved in physical and chemical reactions
What is nuclear fission
A nuclear reaction where mass is not conserved
Nuclear fission reactions are used to generate energy in nuclear reactors
When a neutron hits a nucleus the nuclei split into two smaller nuclei, which also release neutrons (release 2 or 3 between them)
These neutrons then hit other nuclei, which release more neutrons
Causing a chain of reactions
How are nuclear fission reactions controlled
Control rods are made of a material that can absorb neutrons
This prevents the chain reaction from continuing
How / why are neutrons slowed down during nuclear fission reactions
The neutrons are emitted at high speeds, and slowed down by moderators which absorb energy from the neutrons
This is done so the control rods can absorb neutrons faster
What does it mean if a material is fissionable + examole
Uranium - 235 is fissionable
This means that it can split easily
What are the benefits of nuclear fission reactions
1g of uranium is equal to 3000kg of coal in energy
What are the dangers of using nuclear fission reactions
Long half lives of radioactive waste (100+ years some over 200,000)
Chernobyl disaster, making land unusable due to radioactive waste
Radioactive waste emits beta and alpha particles
How is radiation prevented from entering the environment during nuclear fission reactions
The reactor is sealed in a metal container, encased in concrete and then fused in glass and sealed in a metal casing
This prevents all types of radiation escaping to the environment
What is mass energy equivalence
The fact that during nuclear reactions not all mass is conserved
Some is converted to energy
What famous equation did Einstein make relating to mass energy equivalence
Energy = mass × speed of light²
E=mc²
This equation shows the energy released when an objects mass is fully converted into energy
What is the speed of light
3×10⁸ m/s
What is nuclear fusion
The joining of two lighter nuclei to form a larger nucleus which releases energy
How does the size of a nuclei depend on what nuclear reaction will occur to it
Larger nuclei split when hit with electrons
Smaller nuclei fuse to form a more stable nuclei
What atoms are used for most fusion reactions
Isotopes of hydrogen
Two protons are fused to make hydrogen-2 (deuterium)
Hydrogen-3 is formed by fusing deuterium
(Also forms hydrogen)
What do hydrogen-2 and hydrogen-3 fuse to form
They join to form a helium atom and a neutron
What is the heaviest nucleus of an element that can be made through fusion
Iron
It is formed in a supernova
Why are fusion reactions possible in the sun
High temperatures keep the nuclei moving at high speeds
High pressures keep the nuclei close enough to fuse
Why is energy released during nuclear fusion
Energy is released by radiation
Calculated using e=mc²
Why is hydrogen a good fuel for nuclear fusion
It is the most abundant element on the earth
Why does nuclear fusion not create radioactive waste
The nucleus formed is stable
