Atoms & Nuclear Radiation (AQA GCSE Physics): Flashcards

Going from alpha to gamma radiation, range increases, penetrating power increases and ionisation decreases.

True.

Beta particles are only stopped by aluminium if it is a few millimetres thick; thinner aluminium will not stop them.

Alpha radiation is the most ionising, because alpha particles have the largest charge (+2).

Gamma radiation is very weakly ionising, so it barely reacts with the air it passes through. Alpha is strongly ionising, so it reacts with air quickly and loses its energy over a short distance.

Alpha radiation is stopped by paper. Beta radiation is stopped by a few millimetres of aluminium.

Any three from:

• Producing electricity through nuclear fission

• Medical diagnosis and treatment

• Testing materials

• Determining the age of ancient artefacts

• Checking the thickness of materials

• Smoke detectors

Alpha radiation.

Beta and gamma radiation would pass straight through the smoke without being absorbed, so the alarm would not be triggered. Alpha radiation is absorbed by smoke, making it the most suitable choice.

The properties of the different types of radiation determine which one is used in a particular application.

True.

This is one of the many uses of radiation, alongside things like producing electricity, medical procedures and checking material thickness.

Alpha decay is the process where an unstable nucleus emits an alpha particle, forming a new element.

Two protons and two neutrons (a helium nucleus).

It decreases by 4.

It decreases by 2.

In a decay equation, the sum of the mass and atomic numbers before the reaction must be the same as the sum after the reaction.

True.

An alpha particle is identical to a helium nucleus (two protons and two neutrons), and the two terms are interchangeable.

Because the emitted alpha particle carries away two protons, and protons have a charge of +1 each, so the nucleus's charge decreases by 2.

Beta decay is the process where a neutron in the nucleus changes into a proton and an electron. The electron is emitted as a beta particle, and the proton remains in the nucleus.

It stays the same, because the emitted electron has a negligible mass compared to protons and neutrons.

It increases by 1, because a neutron (atomic number 0) changes into a proton (atomic number 1).

Beta decay often happens in unstable nuclei that have too many neutrons.

True.

Because the atomic number changes during beta decay, the nucleus becomes a different element.

Nitrogen-14 and a beta particle.

Gamma decay is the emission of a gamma ray from an unstable nucleus. It makes the nucleus less energetic but does not change its structure.

They both remain the same.

A gamma ray has a lot of energy but no mass and no charge.

Gamma decay usually happens at the same time as alpha and beta decay.

False.

Gamma decay does not change the nucleus's structure (mass number and atomic number stay the same), so the element remains the same. Only the nucleus's energy reduces.

An analogy is a way of understanding an idea by using a different but similar situation.

There is an equal probability of any nucleus decaying; it cannot be known which particular nucleus will decay next, or at what time it will decay.

The rate of radioactive decay is unaffected by the surrounding conditions.

Just as you cannot predict the result of a single dice roll but can state the probability of rolling a particular value (e.g. 1/6 for a six), you cannot predict when a single nucleus will decay but can estimate the probability of decay in a given time.

When a GM tube is placed near a radioactive source, the counts recorded are irregular and cannot be predicted; these fluctuations in count rate provide evidence for the randomness of radioactive decay.

False.

It cannot be predicted when a particular unstable nucleus will decay; it is only possible to estimate the probability of a nucleus decaying in a given time period.

Half-life is the time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half (or for the activity of the sample to fall to half its original level).

Different isotopes have different half-lives, ranging from a fraction of a second to billions of years.

After two half-lives (11 400 years), 25% of the original carbon-14 remains.

False.

The half-life is constant for a particular isotope.

Measure the initial activity, A₀, of the sample; measure how the activity changes with time; the time taken for the activity to decrease to half its original value is the half-life.

6 hours. Each further halving (to 2 × 10⁷ Bq, then 1 × 10⁷ Bq) also takes 6 hours, confirming the half-life is constant.

The sample has undergone two half-lives (2 000 000 → 1 000 000 → 500 000). Since two half-lives take one year, the half-life is 6 months.

Method 1 (Halving): multiply 1 by half for each half-life elapsed (e.g. 1 × ½ × ½ × ½ × ½ for four half-lives).

Method 2 (Raising to a power): raise ½ to the power of the number of half-lives elapsed (e.g. (½)⁴).

After four half-lives, the ratio of remaining nuclei to original nuclei is 1:16.

15 ÷ 3 = 5 half-lives.

(1/2)⁵ = 1/32 of the original nuclei remain.

31 decayed : 1 remaining (31:1).

True.

This follows directly from the definition of half-life.

Contamination is the unwanted presence of materials containing radioactive atoms on other materials.

Irradiation is the process of exposing a material to nuclear radiation.

False.

Irradiating a material does not make it radioactive, although it can kill living cells.

It is often difficult to remove the contaminating radioactive isotope, so the material continues to emit radiation and expose its surroundings for as long as the isotope remains.

Screening the source, or moving further away from it.

Irradiating surgical equipment to kill micro-organisms before surgery; irradiating food to kill micro-organisms and make it last longer without going mouldy.

Contamination causes continuous exposure to radiation because the radioactive isotope remains on or in the material, unlike a one-off exposure from irradiation.

The internal organs will be irradiated as the source emits radiation as it moves through the body.

Lead-lined suits are worn by people working with radioactive materials; the lead absorbs most of the radiation that would otherwise hit the person.

An airtight suit prevents radioactive atoms from getting inside the person, reducing the risk of contamination.

The only way a material can become radioactive is if that material becomes contaminated.

Peer review is the process by which a scientist's findings and conclusions are looked at by other scientists before being accepted.

Other scientists can learn from the findings, and the original scientist's work is checked for accuracy.

Marie Curie discovered radium in 1898.

Marie Curie was the only person ever to win the Nobel Prize in two fields.

Any two from: cosmetics, toothpaste, cleaning products, chocolate.

False.

At the time, people thought radium was good for human health; it was not until 1927 that findings showed radiation exposure increased the risk of cancer.