Atomic structure

How large is the radius of an atom?

1×10^-10m

What are the 3 subatomic particles of an atom?

• Proton

• Electron

• Neutron

Where is most of the mass in an atom concentrated?

In the nucleus

In terms of size, what proportion of the atom is the nucleus?

1/10,000

What is an atoms electronic arrangement

An atom’s electronic arrangement (or electron configuration) is the way its electrons are distributed into different shells or energy levels around the central nucleus.

How can an atom’s electron arrangement change?

By absorption or emission of electromagnetic radiation

What is an isotope?

An atom with the same amount of protons / electrons, but a different number of neutrons

What do all forms of the same elements have in common?

They have the same number of protons

Explain the alpha particle scattering experiment and what the conclusions were and why they were made

• Most passed through

• Some got deflected by a large angle

• Some bounced straight back

This says the atom is mostly empty space, with a dense positive nucleus and a cloud of electrons

What is the difference between the plum pudding model of the atom and the nuclear model of the atom?

• Dense small positive nucleus

• Electrons orbiting in a cloud

What is radiation?

Radiation is the emission of particles or electromagnetic waves from an unstable nucleus.

Why do some nuclei emit radiation?

They are unstable, so they undergo decay and emit radiation to become stable

What is radioactive decay?

The process in which an unstable nucleus gives out radiation to become more stable

What is the activity of an unstable nucleus?

Activity is the rate of decay of an unstable nuclei, measured in becquerel (Bq)

What is count rate?

The number of radioactive decays per second for a radioactive source

What device could measure count-rate?

Geiger-Muller tube

What are the 4 types of radiation that can be emitted?

• Alpha particles

• Beta particles

• Gamma rays

• NeutronW

What makes up an alpha particle?

Basically a helium nucleus, 2 neutrons 2 protons

How far can an alpha particle travel in the air?

A few centimetres ~ 2-10cm

What can stop alpha particles through a point?

• Paper

• Human skin

• 2-10cm of air

What is a beta particle?

AW high speed electron ejected from the nucleus as a neutron turns into a proton

What will stop beta radiation from passing through a point?

• A thin aluminium sheet

• Several metres of air

What will stop gamma radiation from passing through a point?

• Several centimetres of lead

• Metres of concrete

What is the most and least ionising?

Alpha radiation and gamma radiation

Are there any changes when a gamma ray is emitted?

Both mass and charge remain unchanged

What is the nature of radioactive decay?

• Completely random

• Which nuclei decays is by chance

• It is impossible to predict when a nuclei will decay and when

What is the half-life of a radioactive isotope?

The time it takes for the unstable nuclei to halve, or the time taken for the count rate to fall to half of its initial level

What are radioactive contaminants?

Unwanted radioactive nuclei on other materials

What is irradiation?

Exposing a material to nuclear radiation, however this does not mean that the material is now radioactive

What are 4 sources of backround radiation?

• Rocks

• Cosmic rays from space

• Nuclear weapon testing

• Nuclear accidents

What is the unit used to measure radiation dosage?

Sieverts (Sv)

What factors affects the fatality of a radioactive isotope?

The half-life of the isotope, longer ones being more harmful

What are two uses of nuclear radiation in medicine?

• Examining internal organs

• Controlling and destroying unwanted tissue

How can gamma rays be used?

As sterilisers, killing bacteria and parasites on the object

Explain the process of radiotherapy.

• Gamma emitters direct gamma rays at the cancerous cells

• The cancerous cells absorb the radiation and are killed

How are medical tracers chosen?

They should have a short half life and decay into a stable isotope which can be excreted. They should only release gamma radiation since it is weakly ionising and can easily pass through body tissue without damaging it.

What is nuclear fission?

The splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons), e.g. Uranium 235

• An unstable nucleus absorbs a neutron

• The nucleus undergoes fission and releases 2 or 3 further neutrons

• These induce more fission, which results in a chain reaction

What usually needs to happen to induce binary fission?

The unstable nuclei must abosrb. Spontaneous fission so i said that commotation

What could happen in an unctontolled chain reaction?

• The rate of fission events becomes to high and results in the production of too much energy

• This can lead to a nuclear explosion

What are the 3 components in a nuclear reactots

What is nuclear fusion?

The joining of two light nuclei to produce a heavier nuclei and release energy

What is nuclear fusion

Nuclear fusion is the process where two small atomic nuclei join together to form a larger nucleus, releasing a large amount of energy.

Explain the difficulty of generating energy through nuclear fusion?

Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them

Why is nuclear fusion is currently not a viable way to produce energy on Earth?

With current equipment/techniques, the energy required is greater than the energy produced, resulting in a net energy loss