ATOMIC PHYSICS COMBINED

half life

the half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve

beta particle

a fast moving electron

isotopes

forms of the same element that have the same nuber of protons and electrons but a different number of neutrons

alpha particle

a particle containing two neutrons and two protons, also known as helium nucleus

gamma rays

electromagnetic radiation of short wave length but high frequency

proton

positively charged particle found in the nucleus

neutron

neutral particle found in the nucleus

electron

negatively charged particle found orbiting the nucleus

ion

formed when atoms gain or lose electrons

atomic number

number of protons or electrons found in an atom

mass number

number of protons and neutrons found in an atom

alpha decay

mass number decreases by 4 and the atomic number decreases by 2

beta decay

mass number stays the same and the atomic number increases by 1

JJ Thomson

Plum pudding model : he proposed that atoms were a general ball of positive charge with discrete electrons stuck in it

Rutherford and Marsden

they took positively charged alpha particles and fired it at a thin sheet of gold

if the positive charge was spread out as Thompson said then the particles should pass straight through as the weak positive charge spread out wouldn't be enough to affect/repel them

instead the alpha particles deflected back proving thompson wrong

what did rutherford conclude from his experiment

- atoms are mostly empty space

- the mass of the atom is concentrated at the centre with a positive nucleus

- the negative charge was in some sort of cloud around the nucleus

what was the fault in rutherford's nuclear model

there was nothing stopping the negative cloud of electrons from rushing towards the positive nucleus which would make the atom collapse

Geiger-Muller

device used to measure radiation counts

what stops alpha

Skin/Paper/ a few cm of air stops this type of radiation

what stops gamma radiation

lead or concrete

what stops beta radiation

thin sheet of aluminium

what are some natural sources of background radiation

- radon gas from rocks and buildings

- cosmic rays from space

what are some man made sources of background radiation

- exposure from medical testing

- fallout from nuclear weapons testing and accidents

When are gamma rays emitted?

after alpha or beta radiation as a way of the nucleus getting rid of extra energy

Rank alpha, beta- and gamma in terms of their ionising power (lowest to highest).

gamma

beta

alpha

Rank alpha, beta- and gamma in terms of their penetration power (lowest to highest).

alpha

beta

gamma

what makes alpha particles so ionising

their large size and strong charge

why are gamma rays so penetrative

they have no mass or charge so they pass straight through making them weakly ionising., this means that they can penetrate really far into materials before being stopped

what is the difference between irradiation and contamination

irradiation is the process by which objects are exposed to radiation of any type ( this doesn't mean that the object has been contaminated)

contamination is when radioactive particles get onto other objects ( can't harm others unless you're contaminated)

Why does radioactive decay occur?

Radioactive decays allows the nucleus of an unstable element to spontaneously convert into a more stable element while emitting a radioactive particle

Is radioactive decay random or systematic?

Random - you can't predict which nucleus in a sample will decay next

what are some precautions to avoid exposure to radiation

- keeping the item in a lead lined box

- wearing gloves or overalls

- handling the substance with tools eg. tongs and not habdling directly

why is ionising radiation dangerous

because it can enter our body and damage tissues and cells, in worser cases they can ionise our DNA and cause mutations in them causing them to divide uncontrollably forming a tumour

why does alpha radiation stop being harmful when the source is outside the skin

because alpha radiation can't penetrate skin

what are two uses of radiation in medicine

- medical tracers

- radiotherapy

how do medical tracers work

- we use isotopes with a short half life so that they only emit radiation for a short period

- how it works is we place radioactive material inside the patient's body via injecting them, then we track the movement of the isotope around the body by tracking the radiation they emit

- we can also check is organs are working well by seeing if they absorb the right amount of a substance

eg. giving people iodine-123 which emits gamma radiation we can see if the thyroid glands are absorbing the iodine as they should be

how does radiotherapy work

Cancer cells are destroyed by targeted doses of radiation to stop mitosis, so that they stop dividing and growing.

However sometimes healthy cells are also targeted. It is worth it though as it can save a person's life however it doesn't stop the cancer coming back in other areas.

what is activity and what is it measured in

activity is the rate at which unstable nuclei decay and it's measured in becqurels ( which is one decay per second)

what is half life

the average number of time taken for the count rate and so the number of nuclei in a radioactive isotope to fall by half

what is nuclear fission

The splitting of a large, unstable nucleus into two smaller daughter nuclei

which two isotopes undergo fission and are used as fuel in nuclear power stations

uranium and plutonium

During fission, when a _______ collides with an unstable nucleus, the nucleus splits into two smaller ________ as well as two or three neutrons

neutron

daughter nuclei

In a fission reaction energy transferred is from _______ potential energy to kinetic energy

nuclear

why is induced fission more common than spontaneous fission and how does it work

Because it is rare for nuclei to undergo fission without additional energy being put into the nucleus, as nuclear fission requires lots of energy

Usually, for fission to occur the unstable nucleus must first absorb a neutron.

This makes the isotope very unstable and splits by nuclear fission almost immediately. So energy is readily available and often radioactive isotopes take millions of years to decay so induced fission is useful here

What is a chain reaction?

When the emitted neutrons from the fission reaction collide with other unstable nuclei and cause further fission reactions

where do controlled chain reactions occur

in a nuclear reactor, as chain reactions are needed to keep the reactor running

where do uncontrolled chain reactions occur

A nuclear weapon uses an uncontrolled chain reaction to release a huge amount of energy in a short period of time as an explosion

why are uncontrolled chain reactions dangerous

Because each new fission reaction releases energy, uncontrolled chain reactions can be dangerous

The number of neutrons available increases quickly, so the number of reactions does too

what is nuclear fusion

When two light nuclei join to form a heavier nucleus

why is nuclear fusion hard to reproduce on earth

because it requires extremely high temperatures to maintain

where does nuclear fusion happen naturally

Nuclear fusion takes place in the centres of stars

Hydrogen nuclei fuse into helium nuclei and release a large amount of energy