Physics - Radioactivity

Relative mass and charge of a Proton, Neutron and Electron

Proton: 1, +1

Neutron: 1, 0

Electron: 1/2000, -1

Difference between a mass number and an atomic number

Mass Number = Protons + Neutrons

Atomic Number = Protons

What happens when an electron absorbs EM radiation?

1: Jumps to a higher energy level/shell (Exciting)

2: Quickly drops back down (De-Exciting)

3: Releases the energy as an EM wave

EM Spectrum from the longest to shortest wavelength

Radio Waves

Micro Waves

Infrared Light

Visible Light

Ultraviolet Light

X-Rays

Gamma Rays

What did Rutherford’s gold foil experiment show?

1: Most alpha particles passed straight through the foil, proving the atom was mostly empty space

2: A few alpha particles were deflected, proving the nucleus has a positive charge

3: A very small number of alpha particles rebounded, showing the nucleus was very small and dense

Why does a nucleus emit each type of energy?

Alpha: The nucleus is too big

Beta-: There are too many Neutrons

Beta+: There are too many Protons

Gamma: There is too much energy

What happens in Beta+ and Beta- Decay?

Beta+: A proton turns into a neutron and a positron (the antiparticle of an electron) is emitted

Beta-: A neutron turns into a proton, and a high energy electron is emitted

Order of penetration from lowest to highest and what stops each type of radiation

Alpha: Stopped by skin or paper

Beta: Stopped by aluminium

Gamma: Stopped by lead

Order of Ionising power from highest to lowestand definition of Ionisation.

Alpha, Beta, Gamma

Ionisation is radiation giving enough energy to an atom that it rips off an electron, so it becomes an ion with a charge

Alpha Decay Rule

Mass Number -4

Atomic Number -2

Alpha Particle Emitted

Beta Decay Rule

Mass Number Unchanged

Atomic Number +1 (Beta-) or -1 (Beta+)

Electron/Positron Emitted

Is Radioactive Decay predictable?

No

Define Half Life

The time it takes for the number of nuclei of a radioactive isotope to halve.

Unit of Radioactive Activity

Becquerel (Bq)

Unit of Radiation dose recieved

Sievert (Sv)

What detects radiation?

A GM tube

How to measure the radioactivity of a sample

1: Measure the background count

2: Measure the sample count

3: Sample count - Background Count = Radiation

How does a radiation badge work?

Photographic film darkens the more radiation hits it

Paper, Aluminium and lead shows what type of radiation reached it.

What is background radiation and give three sources

Continuous, low level, natural and unavoidable radiation.

Radon Gas (From Mining)

Cosmic Rays (From Space)

Human Activity (From Medical Equipment)

Irradiation vs Contamination

Irradiation:

Exposure to radiation outside the body

Object does not become radioactive

Contamination:

Radioactive material on or inside the body

Object stays radioactive as long as its contaminated

How can you reduce exposure?

•Limit time spent near radioactive materials

•Handle with tongs to keep a safe distance

How does a smoke alarm work?

1: An Alpha source ionises the air

2: Ions have a charge, so current flows

3: Smoke absorbs the Alpha particles

4: The current drops and the alarm sounds

How is beta radiation used in aluminium manufacturing?

1: A detector counts the beta particles passing through a sheet

2: If the aluminium is to thick, few er get through

3: Rollers Squash the aluminium

How is gamma used to test for leaks?

1: Weak gamma emitter flows through water pipes

2: Escaping water causes gamma to accumulate around the soil

3: On the surface, many GM tubes detect localised high radioactivity to detect the leak

It must have a short half life to keep everyone safe

What makes a good medical tracer?

• A short half life to stay safe

• Beta or Gamma for it to be detected outside the body

• Blockages show up as built up radiation

What half life suits a radioactive implant?

• Short enough to be safe

• Long enough to kill the tumour

• Must be Beta or Gamma

What is a PET scan?

1: A Beta+ source is used

2: The positrons emitted annihilate with electrons

3: The mass is converted into energy

4: The gamma rays detected on either side of the tumour shows its location

What is nuclear fission?

The splitting of a large, unstable atom into two daughter nuclei

Describe the fission chain reaction

1: A neutron is absorbed by a uranium nucleus

2: This becomes unstable and splits into two daughter nuclei, neutrons and gamma rays

3: Those neutrons go on to cause more fission

What do control rods and graphite moderators do?

Control Rods: Absorb neutrons. Lowering them reduces the rate of fission and raising them increases it.

Graphite Moderator: Slows neutrons down so they’re more likely to be absorbed by fuel rods.

Equation linking energy, mass change and speed of light

E=mc²

Pros and cons of fission

Pros:

Most energy per kg

No greenhouse gases

Not weather dependent

Cons:

Waste stays radioactive for ages

Huge startup cost

Non-renewable

Accidents are disastrous

Used for weapons

What is nuclear fusion?

Two light nuclei (hydrogen isotopes) fuse into one heavier nucleus, releasing a lot of energy

Why does fusion release a lot of energy

The reactants have more mass than the products, as some mass is converted into energy

What conditions does fusion need?

• Extremely high temperatures

• Enough pressure to make plasma

• Strong magnetic fields to contain it and stop it from touching the reactor walls

Why is fusion so hard to achieve and how does the sun do it?

The strong electrostatic repulsion between the positive nuclei has to be overcome

•The suns huge gravity forces protons close together

• Extreme temperatures make them accelerate

• This greatly increases the number of collisions

Benefits of fusion

• Vastly more energy output than fission

• Virtually limitless fuel supply

• Clean

• Safe Design