atomic structure & radioactivity

What is an atom?

The smallest part of an element that can exist. $

What are the three subatomic particles?

Protons, neutrons and electrons. $

Where are protons found?

In the nucleus. $

Where are neutrons found?

In the nucleus. $

Where are electrons found?

In shells (energy levels) around the nucleus. $

What is the relative charge of a proton?

+1 $

What is the relative charge of a neutron?

0 $

What is the relative charge of an electron?

-1 $

What is the relative mass of a proton?

1 $

What is the relative mass of a neutron?

1 $

What is the relative mass of an electron?

About 1/1836 (negligible). $

What is the atomic number?

The number of protons in the nucleus. $

What does the atomic number determine?

The element. $

What is the mass number?

The total number of protons and neutrons in the nucleus. $

How do you calculate the number of neutrons?

Mass number − atomic number. $

What is an isotope?

Atoms of the same element with different numbers of neutrons. $

Why do isotopes have the same chemical properties?

They have the same number of electrons. $

Why do isotopes have different masses?

They have different numbers of neutrons. $

What is radioactive decay?

The spontaneous and random emission of radiation from an unstable nucleus. $

Is radioactive decay random?

Yes, you cannot predict which nucleus will decay next. $

What is activity?

The rate at which radioactive nuclei decay. $

What is the unit of activity?

Becquerel (Bq). $

What does 1 becquerel mean?

One decay per second. $

What is count rate?

The number of radioactive particles detected each second. $

Why is count rate not always equal to activity?

Not all radiation is detected. $

Why should background radiation be subtracted?

To obtain the corrected count rate from the source alone. $

What is alpha radiation?

A helium nucleus containing 2 protons and 2 neutrons. $

What is the symbol for an alpha particle?

⁴₂He (α). $

What is the charge of an alpha particle?

+2 $

What is the relative mass of an alpha particle?

4 $

How far can alpha radiation travel in air?

A few centimetres. $

What stops alpha radiation?

Paper or human skin. $

How ionising is alpha radiation?

Very strongly ionising. $

Why is alpha radiation weakly penetrating?

It loses energy quickly through ionisation. $

What happens to the atomic number during alpha decay?

It decreases by 2. $

What happens to the mass number during alpha decay?

It decreases by 4. $

State the uranium alpha decay equation.

²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He $

What is beta radiation?

A fast-moving electron emitted from the nucleus. $

What is the symbol for a beta particle?

⁰₋₁e (β⁻). $

What is the charge of a beta particle?

-1 $

What is the relative mass of a beta particle?

Negligible. $

How far does beta radiation travel in air?

A few metres. $

What stops beta radiation?

About 5 mm of aluminium. $

How ionising is beta radiation?

Moderately ionising. $

What happens to the atomic number during beta decay?

It increases by 1. $

What happens to the mass number during beta decay?

It stays the same. $

State the carbon-14 beta decay equation.

¹⁴₆C → ¹⁴₇N + ⁰₋₁e $

What is gamma radiation?

High-energy electromagnetic radiation emitted from the nucleus. $

Does gamma radiation have mass?

No. $

Does gamma radiation have charge?

No. $

How far can gamma radiation travel in air?

Hundreds of metres. $

What stops gamma radiation?

Thick lead or metres of concrete. $

How ionising is gamma radiation?

Weakly ionising. $

What happens to the atomic and mass numbers during gamma emission?

They do not change. $

Why is gamma radiation highly penetrating?

It has no mass or charge. $

What is neutron radiation?

Emission of a neutron from an unstable nucleus. $

How is neutron radiation shielded?

Thick concrete or water. $

What must always balance in a nuclear equation?

Total mass number and total atomic number. $

What is half-life?

The time taken for the number of unstable nuclei, activity or count rate to halve. $

What happens after one half-life?

Half the radioactive nuclei remain. $

What fraction remains after two half-lives?

1/4 $

What fraction remains after three half-lives?

1/8 $

What percentage remains after three half-lives?

12.5% $

How do you calculate the remaining fraction after n half-lives?

(1/2)ⁿ $

If the initial activity is 640 Bq, what is it after two half-lives?

160 Bq. $

How do you determine half-life from a graph?

Measure the time for the activity or count rate to fall to half its value. $

What are the main natural sources of background radiation?

Radon gas, rocks, soil, cosmic rays and food. $

What are the main man-made sources of background radiation?

Medical uses, nuclear fallout and nuclear waste. $

What unit is radiation dose measured in?

Sievert (Sv). $

What unit is commonly used for radiation dose?

Millisievert (mSv). $

How many millisieverts are in one sievert?

1000 mSv. $

Why does background radiation vary between places?

Differences in altitude, geology and occupation. $

What device detects radiation by counting ionising events?

A Geiger–Müller tube. $

What does photographic film measure?

Radiation dose received over time. $

What is irradiation?

Exposure to radiation passing through the body. $

Can irradiation be removed by washing?

No. $

What is contamination?

Radioactive material on or inside a person or object. $

Can contamination be removed?

Yes, if it is on the surface it can often be washed or wiped away. $

Why is alpha contamination especially dangerous?

Alpha particles are strongly ionising inside the body. $

Which types of radiation are most dangerous outside the body?

Beta and gamma. $

How can radiation exposure be reduced?

Reduce time, increase distance and use shielding. $

Why does increasing distance reduce radiation dose?

Radiation spreads out as it travels. $

Why is lead used for shielding?

It absorbs ionising radiation effectively, especially gamma rays. $

How does ionising radiation damage living cells?

It removes electrons from atoms, causing ionisation. $

What can low doses of ionising radiation cause?

Mutations that may lead to cancer. $

What can high doses of ionising radiation cause?

Cell death and radiation sickness. $

How does a smoke alarm use alpha radiation?

Alpha particles ionise the air, allowing a small current to flow; smoke reduces the current and triggers the alarm. $

Why is alpha radiation suitable for smoke alarms?

It is stopped by a short distance of air and is not highly penetrating. $

How is gamma radiation used in radiotherapy?

It is directed at tumours to kill cancer cells. $

Why is gamma radiation suitable for radiotherapy?

It penetrates deep into the body. $

Which radiation is used for thickness monitoring?

Beta radiation. $

Why is beta radiation used for thickness monitoring?

Some is absorbed by the material, allowing thickness to be measured. $

Why is alpha unsuitable for thickness monitoring?

It is absorbed too easily. $

Why is gamma unsuitable for thickness monitoring?

It passes through too easily. $

What are radioactive tracers used for?

Following the movement of substances through the body. $

Why do medical tracers usually have a short half-life?

They minimise the patient's radiation dose. $

What type of radiation is usually detected from medical tracers?

Gamma radiation. $

Why are gamma emitters used as tracers?

Gamma rays can escape the body and be detected outside it. $

How is gamma radiation used in sterilisation?

It kills bacteria on medical equipment and food without heating them. $

Why doesn't gamma sterilization make objects radioactive?

Gamma rays do not leave radioactive material behind. $