P6 Radioactivity

OCR Gateway (OCR A) GCSE Flashcards from PMT.

Describe the arrangement of protons, neutrons and electrons in an atom.

• The protons and neutrons are found in the atom’s nucleus. - The electrons are found in discrete energy levels around the nucleus.

What type of charge does the nucleus of an atom have? Why?

• Positive charge - The nucleus contains protons and neutrons - Protons have a positive charge - Neutrons have no charge

Give two ways that an atom’s electron arrangement can be changed.

1. Absorbing electromagnetic radiation. 2. Emitting electromagnetic radiation.

Explain how an atom’s electron arrangement changes when it absorbs EM radiation.

• Electrons move further away from the nucleus. - They move to a higher energy level.

Explain how an atom’s electron arrangement changes when it emits EM radiation.

• Electrons move closer to the nucleus. - They move to a lower energy level.

How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

• The number of protons is equal to the number of electrons. - Protons and electrons have equal and opposite charges, so charge cancels.

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

The number of protons.

What is the name given to the number of protons in an atom?

Atomic Number

What is an atom’s mass number?

The total number of protons and neutrons in the atom.

What is an isotope of an atom?

An atom of an element that has a different number of neutrons, but the same number of protons.

How do atoms turn into positive ions?

• They lose one or more of their outer electrons. - Electrons are negatively charged, so the resultant charge of the atom is positive.

Why do unstable nuclei give out radiation?

• Unstable nuclei undergo decay to become more stable. - As they release radiation their stability increases.

What is the name of the process in which an unstable nucleus gives out radiation to become more stable?

Radioactive decay.

State four types of nuclear radiation.

1. Alpha particles 2. Beta particles 3. Gamma rays 4. Neutrons

What are the constituents of an alpha particle?

• Two protons and two neutrons. - It is the same as a helium nucleus.

Give the equation for an α particle.

α 4 2

What is the range of an alpha particle through air?

A few centimetres (normally in the range of 2-10cm).

What will stop beta radiation from passing through a point?

• A thin sheet of aluminium. - Several metres of air.

Give the equation for a ß particle.

ß 0 -1

What will stop gamma radiation from passing through a point?

• Several centimetres of lead. - A few metres of concrete.

Give the equation for γ radiation.

γ 0 0 (γ radiation is an EM wave).

Which type of radiation is most ionising?

Alpha radiation.

Which type of radiation is least ionising?

Gamma radiation.

State any changes to mass or charge that occur due to the emission of a gamma ray.

Both mass and charge remain unchanged.

Describe the nature of radioactive decay.

• Random. - Which nuclei decays and when is determined only by chance. - It is impossible to predict which nuclei will decay and when.

Define the half-life of a radioactive isotope.

• The time it takes for the number of unstable nuclei in a substance to halve. - The time it takes for the count rate from a sample to fall to half its initial level.

What is radioactive contamination?

The presence of unwanted radioactive nuclei on other materials.

What is irradiation?

• The process of exposing a material to nuclear radiation. - The material does not become radioactive.

Give 3 practical applications of radioactive materials.

• Medical tracers - Radiotherapy - Smoke alarms

What kind of radiation is used in smoke alarms?

Alpha radiation

How do smoke alarms work?

Alpha radiation is emitted into the air, reaching a detector and completing the circuit. If smoke is present, it blocks alpha radiation so it does not reach the detector and the circuit is broken, causing an alarm to sound.

Give a use of beta emitters.

Thickness monitoring of paper.

How does thickness monitoring work?

A source and receiver are placed on either side of the sheet. If there is a drop or rise in the number of particles detected, the thickness has changed and needs adjusting.

Why are isotopes with long half-lives particularly harmful?

• They remain radioactive for much longer periods of time. - They must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long.

State two uses of nuclear radiation in the field of medicine.

1. Examining of internal organs. 2. Controlling and destroying unwanted tissue.

How is radiation used in sterilisation?

Gamma emitters are used to kill bacteria/parasites on equipment.

What kind of radiation is used for radiotherapy?

Gamma radiation.

Explain the process of radiotherapy.

• Gamma emitters direct gamma rays onto specific areas with cancerous cells. - The cells absorb the radiation and die.

What are the risks of ionising radiation to people?

It can damage living cells, causing them to die or mutate and become cancerous.

What is nuclear fusion?

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

Name two isotopes of hydrogen which are commonly used in nuclear fusion.

Deuterium and Tritium

Which releases more energy, nuclear fission or nuclear fusion?

Nuclear fusion.

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.

What can mass be converted into?

Energy

What is nuclear fission?

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

What usually needs to happen to induce fission?

• The unstable nuclei must absorb a neutron. - Spontaneous fission (where no neutron absorption occurs) is rare.

Alongside two smaller nuclei, what else is emitted in a fission reaction?

• Two or three neutrons - Gamma rays - Energy

What takes place during a chain reaction in a nuclear reactor?

• 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.