Physics - Atoms and Radiation

What was Democritus’ atomic theory (500bc)?

Everything is made up of particles, which are separated by empty space and cannot be broken down any further

What was John Dalton’s solid sphere model (1800s)?

Everything is made up of solid spheres, and there are different types of spheres (which are the elements we now know today)

What was JJ Thompson's plum pudding model (1897)

The ‘solid spheres’ could not be solid, and they must’ve contained negatively charged particles. An atom was a general ball of positive charge, with negatively charged electrons stuck in the middle

What was Ernest Rutherford's nuclear model, and what experiment did he do to prove this (1909)? (what is the problem with this model)

He fired alpha particles through a very thin sheet of gold. If JJ Thompson was correct, then the particles should have passed straight through, as the positive charge would have been equally spread out through the material, and would not have been strong enough at any point to affect the alpha particles. However, some of the particles bounced back the way they came, some passed through but were deflected, and few passed through in a straight line.

Because of this, he proposed that atoms must have a positive central nucleus, with a negative ‘cloud’ around the outside. The problem with this was that there was nothing stopping the cloud from rushing in towards the centre, meaning that the atom should automatically collapse

What was Niels Bohr’s Nuclear theory (1913)?

The electrons orbit the nucleus in shells, which prevent them from collapsing inward

Who proved that neutrons exist in the atom?

James chadwick

Why are some nuclei unstable

The protons in an atom will naturally repel each other, while the neutrons provide a nucleic force of attraction which holds the nucleus together. If there are too many or too few neutrons, the nucleus can become unstable as the forces holding it together and forces repelling become out of balance Also, if the nucleus becomes too large, the nucleic force of attraction cannot hold the outer protons in.

What does an unstable nucleus need to do and why

Emit radiation in order to become stable

What is activity

The rate at which a source of unstable nuclei decays

What is activity measured in

Becquerels

What is IS alpha radiation?

Two neutrons and two protons

Charge of alpha radiation

2+ (positive)

mass of alpha radiation

4 (large)

Ionising power of alpha radiation

high

Penetrating power of alpha radiation and what is blocked by

Low - blocked by a few cm of air, or paper

If a nucleus emits alpha radiation, what is the effect on the nucleus’ atomic number

Down by 2

If a nucleus emits alpha radiation, what is the effect on the nucleus’ neutron number

Down 2

If a nucleus emits alpha radiation, what is the effect on the nucleus’ mass number

Down 4

If a nucleus emits alpha radiation, what is the effect on the nucleus’ electron number

none

What is IS beta radiation?

High speed electrons

Charge of beta radiation

-1 (negative)

mass of beta radiation

1/2000 (tiny)

Ionising power of beta radiation

small

Penetrating power of beta radiation and what is blocked by

A metre in air or a few mm of aluminium

If a nucleus emits beta radiation, what is the effect on the nucleus’ atomic number and why?

Up by one (a neutron in the nucleus changes into a proton)

If a nucleus emits beta radiation, what is the effect on the nucleus’ neutron number and why

Down 1 (a neutron in the nucleus changes into a proton)

If a nucleus emits beta radiation, what is the effect on the nucleus’ mass number

None (technically -1/2000)

If a nucleus emits beta radiation, what is the effect on the nucleus’ electron number

Down 1

What is IS gamma radiation?

Electromagnetic wave

Charge of gamma radiation

none

mass of gamma radiation

none

Ionising power of gamma radiation

tiny

Penetrating power of gamma radiation and what is blocked by

kilometres in air, metres in concrete

If a nucleus emits gamma radiation, what is the effect on the nucleus’ atomic number

none

If a nucleus emits gamma radiation, what is the effect on the nucleus’ neutron number

none

If a nucleus emits gamma radiation, what is the effect on the nucleus’ mass number

none

If a nucleus emits gamma radiation, what is the effect on the nucleus’ electron number

none

Define radioactive decay

The process by which a nucleus of an unstable atom loses energy by emitting ionising radiation. It is a completely random process.

Define ionisation

The process by which an atom gains or loses an electron, becoming charged (in the case of radiation, a radioactive particle can crash into another one and cause it to lose electrons for instance)

How does photographic film work (who might use it)

Radiation passes through windows Window 1 allows all radiation through Window 2 has aluminium, to show if beta radiation is present Window 3 has lead, so gamma radiation can be detected When exposed to radiation, the film turns from transparent to dark coloured and opaque (called a Film Badge). This allows people to detect different types of radiation, depending on where the film badge is, and the level of radiation, depending on the extent of the colour change People who work in industries where they might be exposed to radiation wear these badges to ensure that they are not exposed to a dangerously high dose

How does a gold leaf electroscope work

When the electroscope is charged, the gold leaf sticks out of it, because the particles of gold are repelled by the negative charge Air is normally a good insulator, so the charge does not leak When ionisation radiation is brought near, it starts to ionise the air particles, which they can conduct electricity The charge is able to leak, so the electroscope is no longer negatively charged This means that the gold leaf is no longer repelled, so it fallsDe

How does a spark counter work

A metal gauze is placed about a mm above a wire. A strong current (5000V) is passed through the gauze and wire causing them to spark The voltage is reduced until it stops sparking An alpha radiation source is brought close to the gauze, ionising the air around it This means that the air is now able to conduct electricity, so electricity can pass between the wire and the gauze This creates sparks, which are counted. The more frequent the sparks, the stronger the radiation.

How does a cloud chamber work

The chamber contains supersaturated vapours (often alcohol) Ionising radiation strips an electron away from an atom, disturbing the particles This causes the particles to condense together. This forms visible bubbles or tracks which can be used to show where and in what direction radiation is occurring

How does a geiger muller tube work

A tube is filled with argon gas at a very low pressure. There is a window made of mica at one end and an electrode at the other. It is connected to a circuit which allows it to count pulses of electricity If radiation enters the tube through the mica window, it ionises one of the argon particles, ripping away an electron This will collide with other argon atoms, also knocking other electrons from these atoms The free electrons rush towards the electrode This allows the tube to conduct electricity One ionising radiation entering the tube generates a pulse of electricity which can be counted, using a counter The counter emits clicks The faster the clicks, the more radiation

Define half life

The time taken for 1 half of the radioactive nuclei to decay

Which is more dangerous: a radioactive material with a half life of 50 years, or a radioactive material with a half life of 50 seconds? Why?

A radioactive material with a half life of 50 seconds is more dangerous as it releases radiation more quickly, so being around it means that you will be exposed to more radiation

Why do we use half life? (as opposed to a full life or predicting singular nuclei)

The decay of radioactive nuclei is completely random, so it is impossible to predict when any single nucleus will decay A large group of atoms will behave in a statistical pattern, so you can predict when a half of them will have decayed The process never fully reaches 0 so you can’t have a full life

In a nuclear equation, how is an alpha particle represented

4/2 He (4 is above the two, there is no line)

In a nuclear equation, how is a beta particle represented

0/-1 e (0 is above -1, there is no line

Write a nuclear equation for 219/86 radon, emitting alpha radiation

219/86 radon → 215/84 polonium + 4/2 He

Write a nuclear equation for 14/6 carbon emitting beta radiation

14/6 carbon → 14/7 nitrogen + 0/-1 e

Symbol for alpha radiation

ɑ

Symbol for beta radiation

β

Symbol for gamma radiation

γ

What is irradiation

The process by which an object is exposed to radiation

What is contamination

When radioactive particles get onto an object (this includes if you ingest them)

Is contamination a problem? Why/why not?

Not directly, as it doesn’t cause harm. However, if the radioactive particles decay, then you become irradiated, which is a problem

Why is ionising radiation dangerous for humans

It can interact with DNA molecules, causing mutations which can develop into cancer

If the source is outside the body, which type of radiation is the most harmful and why?

Beta and gamma, as they can penetrate human skin, whale alpha can’t.

If the source is inside the body, which type of radiation is most harmful and why

Alpha as it is the most ionising so can cause the most harmful mutations in cells

Which of these types of radiation are ionising: radiowaves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays. Alpha, beta

X-rays, gamma rays, alpha, beta

What impacts the danger of being exposed to radiation?

How much radiation you receive, the type of radiation (e.g. alpha), where the radioactive material is (inside or outside the body)

What determines how large a dosage of radiation you receive

How far away you are from the source How long you are exposed to it for How radioactive the source is

What precautions can you take to minimise irradiation and avoid contamination

Wear a lead apron, overalls, and gloves Use tongs and do not point them towards anybody Keep the item in a leadlined box

What is radiation sickness (causes, effects)

If you are exposed to lots of radiation over a long period of time, then cells can be destroyed or damaged. This causes radiation sickness, where the person may experience vomiting, hair loss, and tiredness

Why can radiation cause cancer AND treat it

Radiation can destroy and damage cells → it can destroy cancer cells It can cause dna mutations that lead to cancer

How does external radiotherapy work and which type of radiation is used

A radioactive source is placed outside the body, with its radiation directed towards the cancer site from different angles. Normally, gamma radiation is used here as it can pass through human skin

How does internal radiotherapy work, and which type of radiation is used

A radioactive source is placed inside the body, either inside the cancer site, or next to it. Normally, beta radiation is used, which is more damaging than gamma rays, but can’t pass through the body as far

Why do patients feel sick after radiotherapy

The radiation also damages nearby healthy cells, causing radiation sickness

Positives of radiotherapy

Can literally save a person's life

Negatives of radiotherapy

Sickness lowers quality of life. Radiotherapy may not be able to save a life, only to extend it.

What can medical tracers do

Help us diagnose diseases

How can we limit the negative impacts of medical tracers

Giving a low dose with a short half life

How can radioactive material be used as medical tracers

A person is asked to swallow/injected with a radioactive substance. This substance then travels around the body, so can be tracked as medical scanners can trace which parts of the body are emitting radiation. This can be used to see if an organ is working properly (e.g. it can be used to see if the thyroid gland it absorbing things as it should be, as the amount of radiation it emits tells us how much of the substance it has absorbed)

Which type of radiation is used in medical tracers

Normally gamma as it is the least ionising and the least harmful, and it can penetrate human skin so can be detected easily

Is a long or short half life better for medical tracers

Short half life as the material is only emitting radiation for a short time, so will not expose the patient to radiation long term Though long enough that it can be used for an investigation

Give some examples of sources of background radiation

Rocks and cosmic rays Man made sources kike fallout from nuclear weapons testing and nuclear accidents

What is nuclear fusion

The fusion of two small nuclei into one large nucleus

Nuclear fusion requires high/low energy. Why?

High – this means that the particles have more energy and will move so fast the the positive charges have no time/ are not powerful enough to repel each other

Is nuclear fusion used in nuclear reactors? Why/why not?

No as it is too hard to control, and requires extremely high temperatures and pressures

Why does nuclear fusion produce so much energy

Some of the mass of the two smaller nuclei is converted to energy when they join together

What is nuclear fission

The splitting of one large nucleuse into two of more smaller nuclei

What are the two types of nuclear fission? Which one is used in nuclear reactors and why?

Spontaneous - when an unstable nucleus splits into two or more smaller ones randomly By absorbing a neutron - neutrons are fired at an unstable nucleus to make it even less stable so it splits

The second method is used in nuclear reactors because spontaneous is quite rare, so to generate lots of energy quickly, the second method is preferred.

Nuclear fission can lead to a BLANK reaction

chain

How does the nuclear fission chain reaction work

A relatively slow moving neutron is fired at an unstable nucleus, causing it to split into daughter nuclei, as well as releasing energy in the form of gamma radiation and 2 or 3 more neutrons These neutrons collide with and are absorbed by other unstable nuclei, causing them to split, again, releasing energy and more neutrons, which means that the process repeats.

How is electricity generated from nuclear fission

As the nucleus splits it releases gamma radiation. This is used to heat up water flowing through pipes, evaporating it into steam. The steam rises and turns a turbine which in TURN (hahaha) turns a generator which creates electricity.

Why is nuclear fission dangerous

The chain reaction means it can speed up very quickly and get out of control, releasing massive amounts of energy. This is essentially what happens in a nuclear bomb

What are control rods used for in nuclear reactors

Absorbing neutrons to slow down the chain reaction and stop it getting out of control

What is coolant for in a nuclear reactor

Carry thermal energy away from the core of the reactor

What are fuel rods used for in nuclear reactors

Often made of uranium 235, a fissionable material

What is a moderator rods used for in nuclear reactors

Slow down fast neutrons so they are more likely to be absorbed by other uranium atoms (if they are too fast they will bounce off)

Pros of nuclear energy

Fuel is cheap. Clean as it does not produce greenhouse gases. Produces a large and steady amount of energy

Cons of nuclear energy

Risk of a major disaster if the plant malfunctions. Power plants are very expensive to build. This waste is difficult and expensive to get rid of, as it has to be stored deep underground