Physics Topic 5 Radioactivity

What happens when an electron moves to a higher orbit? -

The atom absorbs EM radiation and becomes excited.

What happens when an electron falls to a lower orbit? -

EM radiation is emitted.

What is ionising radiation? -

Radiation that can knock electrons out of atoms.

What happens if an electron gains just enough EM energy? -

It can leave the atom, to form an ion.

What is used to detect radiation? -

A Geiger-Müller tube or photographic film.

How does a Geiger-Muller detect radiation? -

It clicks each time it detects radiation(can be attached to a counter, to display the count rate)

How does photographic film detect radiation? -

It goes darker as it absorbs more radiation, usually worn by doctor to check the exposure they've had

What is meant by the "activity" of a radioactive source? -

The rate at which it decays (measured in becquerels, Bq)

What happens to activity over time? -

Initially high but decreases exponentially as isotopes decay.

What are the three main types of radiation? -

Alpha (α), Beta (β), and Gamma (γ).

What is an alpha particle made of and how is it stopped? -

2 protons and 2 neutrons, highly ionising, weakly penetrating, absorbed by paper

What is beta minus and how is it stopped? -

A fast-moving electron, medium ionising/penetration, stopped by a few mm of aluminium.

What is beta plus and how is it stopped? -

Fast moving positron, medium ionising/penetration

What is gamma radiation and how is it stopped? -

Electromagnetic radiation; lowly ionising, highly penetrating requires thick lead or concrete to reduce.

What happens in beta-minus decay? -

A neutron becomes a proton, and an electron is emitted.

What happens in beta-plus decay? -

A proton becomes a neutron, and a positron is emitted.

Does gamma decay change the element? -

No, it only releases excess energy.

What is half-life? -

The time for half the radioactive nuclei in a sample to decay or for activity to halve.

Risks of short half-life -

Less risk as it does not remain radioactive for long

Risks of long half life -

Weakly radioactive for a long period, exposed to radiation longer

How are radioactive isotopes used in smoke alarms? -

Americium-241 emits alpha particles that ionise air, producing a current of charged particles flowing. Smoke blocks the current, triggering the alarm.

How are radioactive tracers used in medicine? -

Radioactive tracer injected into body. External detector traces where tracer has collected in body.

How about in irradiation? -

Gamma waves transfer energy to bacteria, killing them and sterilising food(delaying ripening of food)

How about in sterilisation? -

gamma rays exposed on equipment to kill all microbes present on equipment

How about in tracing -

Beta source and receiver placed on either side of the paper during production. A change in amount of recieved electrons means thickness of paper has been changed.

Safety measures for patients -

Tracers with a short half life so it can be quickly removed from body - less long term effect

Safety measures for medical staff -

leave the room during radioactive tests as everyday proximity puts their health at risk, photographic film

What is background radiation and examples of it? -

Low level of radiation thats around us at all times (Cosmic rays, Rocks, Nuclear waste, Medical rays)

What's the difference between contamination and irradiation? -

Contamination = radioactive material on/in body and lasts for a long period while irradiation is exposure to radiation without contact.

What is nuclear fission? -

Unstable nucleus splits into smaller daughter nuclei, releasing lots of energy and neutrons.

How is fission triggered? -

By absorbing a neutron.

What happens in a chain reaction? -

Released neutrons cause further fission events.

What is used in nuclear power stations? -

Uranium - 235

What does fission produce? -

Two daughter nuclei that are radioactive

What is nuclear fusion? -

Two small nuclei collide at high speed to form a larger nucleus, releasing large amounts of energy.

What conditions are needed for nuclear fusion? -

High temperatures and pressure

What happens at a nuclear reactor? -

Unstable nuclei absorbs a slow moving neutron, undergoing fission, releasing 2 to 3 neutrons, inducing more fission

What are control rods used for? -

Lower rate of fission by absorbing excess neutrons in between fuel rods

What does a moderator do? -

It slows down the fast neutron so it travels at the speed that allows fission

What are the pros of fusion? -

No radioactive waste, abundant fuel, high energy yield.

What do nuclear reactors do /produce? -

Reactions release thermal energy, which is used to boil water and create steam. The steam is used to turn the turbine, which starts the generator that generates electricity.

What are the cons of nuclear power? -

Risk of nuclear waste leaking, waste disposal is difficult- high temp, long half life

What are the pros of nuclear power? -

No CO2 emissions - no global warming, lots of energy from a small amount, doesn't release harmful gases like sulphur dioxide

What is a PET scanner used for? -

To produce 3D images showing metabolic activity or tissues/organ function using radioactive tracers that emit positrons.

How does a PET scanner work? -

Radioactive tracer injected(tagged to a specific chemical) so tracer travels in body to specific chemical. Scanner records where tracer emits radiation.

How does a PET scanner identify cancer cells? -

BY showing metabolic activity in tissues- cancer cells have high metabolic activity