Define background radiation .

Low levels of radiation from environmental sources, which are always present around us

What are the two categories of background radiation source?

Natural sources and man-made (artificial) sources

Give four natural sources of background radiation.

radon gas from rocks and soil cosmic rays from space carbon-14 in biological material radioactive material in food and drink (e.g. potassium-40 in bananas)

Give four man-made sources of background radiation.

medical sources (X-rays, CT scans, tracers, radiotherapy) nuclear waste nuclear fallout from nuclear weapons nuclear accidents (e.g. Chernobyl)

How is the corrected count rate obtained?

By subtracting the background count rate (measured with no source present) from the count rate measured with the source present

Uranium in rocks and soil decays into .......... gas, which is an .......... emitter and is dangerous if inhaled.

Uranium in rocks and soil decays into radon gas, which is an alpha emitter and is dangerous if inhaled

True or False? A count rate that never drops to zero, even far from a source, means the detector is faulty.

False. A count rate that levels off above zero is due to background radiation , which is always present — not a faulty detector

Define an alpha (α) particle .

A high energy particle made up of 2 protons and 2 neutrons (the same as a helium nucleus ), usually emitted from nuclei that are too large

Define a beta-minus (β⁻) particle .

A high energy electron emitted from the nucleus, produced by nuclei that have too many neutrons

Define a gamma (γ) ray .

A high energy electromagnetic wave emitted by a nucleus that needs to lose energy — it has no mass and no charge

Rank alpha, beta and gamma by ionising power .

Alpha most ionising → beta moderately ionising → gamma least ionising

What stops each type of radiation, from least to most penetrating?

alpha — least penetrating, absorbed by a few cm of air (range ~3–7 cm) beta — stopped by a few mm of aluminium (range ~20 cm–3 m in air) gamma — most penetrating

Alpha particles are the .......... but the .......... type of radiation.

Alpha particles are the most ionising but the least penetrating type of radiation

True or False? Gamma radiation is the most dangerous to cells because it is the most ionising.

False. Alpha is the most ionising radiation (highest charge, most ion pairs per cm), so it does the most damage to cells over a short range; gamma is the least ionising

What does an alpha particle consist of?

2 protons and 2 neutrons (a helium-4 nucleus), emitted from large unstable nuclei

In alpha decay , how do the mass and atomic numbers change?

nucleon (mass) number decreases by 4 proton (atomic) number decreases by 2

Why is a beta-minus particle given an atomic number of −1 in a decay equation?

Here the atomic number is being used to measure charge : protons are positive (positive atomic number), so the electron , being negative, is given a negative number

In gamma decay , how do the mass and atomic numbers change?

Neither changes — gamma decay makes the nucleus less energetic but does not change its structure

What must balance in a nuclear decay equation?

the mass (nucleon) numbers on each side must be equal the atomic (proton) numbers on each side must be equal

The gamma ray emitted during gamma decay carries a lot of energy, but has no .......... and no .......... .

The gamma ray emitted during gamma decay carries a lot of energy, but has no mass and no charge

True or False? Gamma decay changes the atomic number of the nucleus.

False. Gamma decay changes neither the mass number nor the atomic number — the nucleus simply loses energy

What is the aim of Core Practical 15: Investigating Gamma Radiation Absorption?

To investigate the absorption of gamma rays by different thicknesses of lead

State the independent , dependent and control variables in Core Practical 15.

independent — thickness of lead dependent — count rate control — radioactive source, distance of GM tube to source, location / background radiation

Why is background radiation measured (with no source present) before the main readings?

So it can be subtracted from later readings to give the corrected count rate , since background radiation is always present

How do you know the gamma radiation has been fully absorbed ?

When the count rate falls to background levels (allowing for a little random variation)

The thickness of each lead absorber is measured at three points using .......... .

The thickness of each lead absorber is measured at three points using Vernier calipers

State the safety precautions when handling the radioactive source.

store in a lead-lined container when not in use keep a good distance (~1 m) from the source in use handle with tweezers/tongs , pointing the source away from you wash hands and remove your outer layer of clothing afterwards

Why should the source have a long half-life and an activity well above background ?

It improves accuracy — the activity stays roughly constant during the experiment and is high enough to stand out clearly against background radiation

True or False? Background radiation can be ignored when analysing the results of this experiment.

False. Background radiation must be measured and subtracted to give the corrected count rate; ignoring it makes the absorption results inaccurate

Define radioactive decay .

The spontaneous disintegration of a nucleus to form a more stable nucleus , resulting in the emission of an alpha, beta or gamma particle

Define a spontaneous process .

A process which cannot be influenced by environmental factors (such as temperature, pressure or chemical conditions)

Define a random process .

A process in which the exact time of decay of a nucleus cannot be predicted — each nucleus has a constant probability of decaying in a given time

How does a Geiger-Muller tube provide evidence for the randomness of decay?

The counts are irregular and unpredictable — the fluctuations in count rate near a source show that decay happens at random

Although the decay of a single nucleus is random, with large numbers of nuclei it is possible to statistically .......... the behaviour of the whole group.

Although the decay of a single nucleus is random, with large numbers of nuclei it is possible to statistically predict the behaviour of the whole group

True or False? Heating a radioactive sample increases its rate of decay.

False. Radioactive decay is spontaneous — it is unaffected by temperature, pressure or chemical conditions

Define the decay constant (λ) .

The probability, per second, that a given nucleus will decay (units: s -1 )

Define the activity of a radioactive sample.

The number of decays per unit time , measured in becquerels (Bq) , where 1 Bq = 1 decay per second (1 s -1 )

The time taken for half the number of nuclei in a sample to decay — equivalently, the time for the activity to halve (since A ∝ N )

The shorter the half-life, the .......... the decay constant and the .......... the decay.

The shorter the half-life, the larger the decay constant and the faster the decay

True or False? After two half-lives, all of the radioactive nuclei in a sample have decayed.

False. Decay is exponential and never reaches zero — after two half-lives a quarter of the original nuclei remain

A LevelPhysicsEdexcelFlashcards11. Nuclear RadiationRadioactivity Decay

Radioactivity Decay (Edexcel A Level Physics): Flashcards

Exam code: 9PH0

1/43

0Still learning

Know0

FrontBackground Radiation
Define background radiation.
FrontBackground Radiation
Give four natural sources of background radiation.
BackBackground Radiation
radon gas from rocks and soil
cosmic rays from space
carbon-14 in biological material
radioactive material in food and drink (e.g. potassium-40 in bananas)

Was this flashcard helpful?

Cards in this collection (43)

Define background radiation.
Low levels of radiation from environmental sources, which are always present around us
What are the two categories of background radiation source?
Natural sources and man-made (artificial) sources
Give four natural sources of background radiation.
- radon gas from rocks and soil
- cosmic rays from space
- carbon-14 in biological material
- radioactive material in food and drink (e.g. potassium-40 in bananas)
Give four man-made sources of background radiation.
- medical sources (X-rays, CT scans, tracers, radiotherapy)
- nuclear waste
- nuclear fallout from nuclear weapons
- nuclear accidents (e.g. Chernobyl)
How is the corrected count rate obtained?
By subtracting the background count rate (measured with no source present) from the count rate measured with the source present
Uranium in rocks and soil decays into .......... gas, which is an .......... emitter and is dangerous if inhaled.
Uranium in rocks and soil decays into radon gas, which is an alpha emitter and is dangerous if inhaled
True or False?
A count rate that never drops to zero, even far from a source, means the detector is faulty.
False.
A count rate that levels off above zero is due to background radiation, which is always present — not a faulty detector
Define an alpha (α) particle.
A high energy particle made up of 2 protons and 2 neutrons (the same as a helium nucleus), usually emitted from nuclei that are too large
Define a beta-minus (β⁻) particle.
A high energy electron emitted from the nucleus, produced by nuclei that have too many neutrons
Define a gamma (γ) ray.
A high energy electromagnetic wave emitted by a nucleus that needs to lose energy — it has no mass and no charge
Rank alpha, beta and gamma by ionising power.
Alpha most ionising → beta moderately ionising → gamma least ionising
What stops each type of radiation, from least to most penetrating?
- alpha — least penetrating, absorbed by a few cm of air (range ~3–7 cm)
- beta — stopped by a few mm of aluminium (range ~20 cm–3 m in air)
- gamma — most penetrating
Alpha particles are the .......... but the .......... type of radiation.
Alpha particles are the most ionising but the least penetrating type of radiation
True or False?
Gamma radiation is the most dangerous to cells because it is the most ionising.
False.
Alpha is the most ionising radiation (highest charge, most ion pairs per cm), so it does the most damage to cells over a short range; gamma is the least ionising
What does an alpha particle consist of?
2 protons and 2 neutrons (a helium-4 nucleus), emitted from large unstable nuclei
In alpha decay, how do the mass and atomic numbers change?
- nucleon (mass) number decreases by 4
- proton (atomic) number decreases by 2
Why is a beta-minus particle given an atomic number of −1 in a decay equation?
Here the atomic number is being used to measure charge: protons are positive (positive atomic number), so the electron, being negative, is given a negative number
In gamma decay, how do the mass and atomic numbers change?
Neither changes — gamma decay makes the nucleus less energetic but does not change its structure
What must balance in a nuclear decay equation?
- the mass (nucleon) numbers on each side must be equal
- the atomic (proton) numbers on each side must be equal
The gamma ray emitted during gamma decay carries a lot of energy, but has no .......... and no ...........
The gamma ray emitted during gamma decay carries a lot of energy, but has no mass and no charge
True or False?
Gamma decay changes the atomic number of the nucleus.
False.
Gamma decay changes neither the mass number nor the atomic number — the nucleus simply loses energy
What is the aim of Core Practical 15: Investigating Gamma Radiation Absorption?
To investigate the absorption of gamma rays by different thicknesses of lead
State the independent, dependent and control variables in Core Practical 15.
- independent — thickness of lead
- dependent — count rate
- control — radioactive source, distance of GM tube to source, location / background radiation
Why is background radiation measured (with no source present) before the main readings?
So it can be subtracted from later readings to give the corrected count rate, since background radiation is always present
How do you know the gamma radiation has been fully absorbed?
When the count rate falls to background levels (allowing for a little random variation)
The thickness of each lead absorber is measured at three points using ...........
The thickness of each lead absorber is measured at three points using Vernier calipers
State the safety precautions when handling the radioactive source.
- store in a lead-lined container when not in use
- keep a good distance (~1 m) from the source in use
- handle with tweezers/tongs, pointing the source away from you
- wash hands and remove your outer layer of clothing afterwards
Why should the source have a long half-life and an activity well above background?
It improves accuracy — the activity stays roughly constant during the experiment and is high enough to stand out clearly against background radiation
True or False?
Background radiation can be ignored when analysing the results of this experiment.
False.
Background radiation must be measured and subtracted to give the corrected count rate; ignoring it makes the absorption results inaccurate
Define radioactive decay.
The spontaneous disintegration of a nucleus to form a more stable nucleus, resulting in the emission of an alpha, beta or gamma particle
Define a spontaneous process.
A process which cannot be influenced by environmental factors (such as temperature, pressure or chemical conditions)
Define a random process.
A process in which the exact time of decay of a nucleus cannot be predicted — each nucleus has a constant probability of decaying in a given time
How does a Geiger-Muller tube provide evidence for the randomness of decay?
The counts are irregular and unpredictable — the fluctuations in count rate near a source show that decay happens at random
Although the decay of a single nucleus is random, with large numbers of nuclei it is possible to statistically .......... the behaviour of the whole group.
Although the decay of a single nucleus is random, with large numbers of nuclei it is possible to statistically predict the behaviour of the whole group
True or False?
Heating a radioactive sample increases its rate of decay.
False.
Radioactive decay is spontaneous — it is unaffected by temperature, pressure or chemical conditions
Define the decay constant (λ).
The probability, per second, that a given nucleus will decay (units: s^-1)
Define the activity of a radioactive sample.
The number of decays per unit time, measured in becquerels (Bq), where 1 Bq = 1 decay per second (1 s^-1)
State the equation linking activity, decay constant and number of undecayed nuclei.
$A = \frac{Δ N}{Δ t} = λ N$
where A = activity (Bq), λ = decay constant (s^-1), N = number of undecayed nuclei
The greater the decay constant or the more undecayed nuclei, the greater the activity
State the radioactive decay equation for the number of undecayed nuclei.
$N = N_{0} e^{- λ t}$
where N₀ = initial number of undecayed nuclei, λ = decay constant, t = time
Define half-life.
The time taken for half the number of nuclei in a sample to decay — equivalently, the time for the activity to halve (since A ∝ N)
State the equation relating half-life and the decay constant.
$t_{1 / 2} = \frac{\ln 2}{λ}$
Half-life and decay constant are inversely proportional
The shorter the half-life, the .......... the decay constant and the .......... the decay.
The shorter the half-life, the larger the decay constant and the faster the decay
True or False?
After two half-lives, all of the radioactive nuclei in a sample have decayed.
False.
Decay is exponential and never reaches zero — after two half-lives a quarter of the original nuclei remain

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Nuclear Fusion & FissionNext:Gravitational Fields