Nuclear Chemistry (SQA National 5 Chemistry): Flashcards
Exam code: X813 75
1/360Still learning
Know0
- FrontRadiation
What is a radioisotope?
Was this flashcard helpful?
Cards in this collection (36)
What is a radioisotope?
A radioisotope is an atom with an unstable nucleus that emits radiation during radioactive decay in order to become more stable.
What are the three types of radiation emitted during radioactive decay?
The three types of radiation are:
Alpha (α)
Beta (β)
Gamma (γ)
True or False?
Alpha radiation is stopped by a single sheet of paper.
True.
Alpha radiation has low penetrating power. It is the least penetrating of the three radiation types and is stopped by paper.
What is an alpha particle made of?
An alpha particle is identical to a helium nucleus. It consists of two protons and two neutrons, and carries a charge of 2+.
Beta particles are fast-moving .......... produced when a .......... in the nucleus changes into a proton. Beta radiation is stopped by a thin sheet of .......... .
Beta particles are fast-moving electrons produced when a neutron in the nucleus changes into a proton. Beta radiation is stopped by a thin sheet of aluminium.
Why is gamma radiation not deflected by an electric field?
Gamma radiation carries no electric charge (charge = 0). It is neutral, so it experiences no force in an electric field and passes straight through without deflection.
True or False?
Beta particles are deflected towards the negative plate in an electric field.
False.
Beta particles carry a negative charge (−1), so they are deflected towards the positive plate. It is the positively charged alpha particles that are attracted to the negative plate.
What material is needed to stop each type of radiation, in order of increasing penetrating power?
In order of increasing penetrating power:
Alpha: stopped by paper
Beta: stopped by thin aluminium
Gamma: only stopped by thick lead or concrete
What is a nuclear equation?
A nuclear equation uses nuclide notation to show the changes in an atomic nucleus during radioactive decay, with mass numbers and atomic numbers balanced on both sides.
What are the two conservation rules for balancing a nuclear equation?
The two rules are:
Conservation of mass number: the sum of mass numbers (top numbers) must be equal on both sides
Conservation of atomic number: the sum of atomic numbers (bottom numbers) must be equal on both sides
True or False?
In alpha decay, the mass number of the decaying nucleus decreases by 4 and the atomic number decreases by 2.
True.
An alpha particle has mass number 4 and atomic number 2. When it is emitted, those numbers are subtracted from the parent nucleus, forming a new element.
How does beta decay change the mass number and atomic number of the nucleus?
In beta decay, the mass number stays the same (the beta particle has mass number 0). The atomic number increases by 1, because a neutron converts into a proton inside the nucleus.
An alpha particle consists of .......... protons and two neutrons. It has a mass number of .......... and an atomic number of .......... .
An alpha particle consists of two protons and two neutrons. It has a mass number of 4 and an atomic number of 2.
What effect does gamma decay have on the mass number and atomic number of the nucleus?
Gamma decay has no effect on the mass number or atomic number. A gamma ray carries no mass or charge, so the nucleus is unchanged in composition. Only energy is released.
True or False?
During beta decay, the atomic number of the nucleus increases by 1.
True.
A neutron in the nucleus converts into a proton and an electron. The electron (beta particle) is emitted, and the extra proton remains, increasing the atomic number by 1.
A beta particle has a mass number of .......... and an atomic number of .......... . This means that in beta decay the mass number of the nucleus .......... and the atomic number increases by 1.
A beta particle has a mass number of 0 and an atomic number of −1. This means that in beta decay the mass number of the nucleus stays the same and the atomic number increases by 1.
How do you identify the new element formed during radioactive decay when balancing a nuclear equation?
After balancing the mass numbers and atomic numbers, find the atomic number of the unknown product. Use the Data Booklet to identify the element with that atomic number — this is the new element formed.
What is half-life?
A half-life is the time taken for half of the nuclei in a sample of a particular radioisotope to decay. It is given the symbol t1/2.
What happens to the amount of a radioisotope after each successive half-life?
After each half-life, the amount of the radioisotope remaining is halved. For example, starting at 100%: after one half-life 50% remains, after two half-lives 25% remains, and so on.
True or False?
The half-life of a radioisotope is affected by temperature and pressure.
False.
Half-life is a nuclear property and is constant. It is unaffected by physical conditions such as temperature or pressure or by the chemical compound the isotope is part of.
How does the arrow method work for half-life calculations?
Each arrow represents one half-life passing, during which the amount is halved. For example:
80 g → 40 g → 20 g → 10 g
Counting the arrows gives the number of half-lives elapsed.
Half-life is defined as the time taken for .......... of the nuclei in a sample to .......... . After each half-life, the amount of the radioisotope remaining is .......... .
Half-life is defined as the time taken for half of the nuclei in a sample to decay. After each half-life, the amount of the radioisotope remaining is halved.
How do you find the half-life of a radioisotope from a decay curve?
Read the initial value on the y-axis at time = 0. Divide it by two to find the halfway value. Draw a horizontal line from that value to the curve, then a vertical line down to the x-axis. The time read from the x-axis is the half-life.
True or False?
After exactly two half-lives, 25% of the original radioisotope remains.
True.
After the first half-life, 50% remains. After the second half-life, half of that remains, giving 25% of the original amount.
To calculate the number of half-lives from a given time, divide the .......... by the .......... . To find the half-life from the number of half-lives, divide the .......... by the number of half-lives.
To calculate the number of half-lives from a given time, divide the total time by the half-life. To find the half-life from the number of half-lives, divide the total time by the number of half-lives.
How do you calculate the amount of a radioisotope that has decayed, rather than the amount remaining?
First use the arrow method to find the amount remaining. Then subtract the remaining amount from the starting amount:
amount decayed = starting amount − amount remaining
A sample starts at 80 mg and falls to 5 mg after 60 hours. How do you calculate its half-life?
Use the arrow method to count the number of half-lives:
80 mg → 40 mg → 20 mg → 10 mg → 5 mg = 4 half-lives
Then: half-life = total time ÷ number of half-lives = 60 ÷ 4 = 15 hours
What two key properties must be considered when evaluating a radioisotope for a particular use?
The two key properties are:
The type of radiation emitted (alpha, beta or gamma)
The half-life of the isotope
Why is an alpha-emitting radioisotope unsuitable for use as an injected medical tracer?
Alpha radiation has very low penetrating power and is stopped by the body's tissues. It cannot pass out of the body to be detected by a scanner. It would also deliver a high radiation dose to the surrounding tissue.
True or False?
A radioisotope used as an injected medical tracer needs a long half-life to remain active in the body long enough to be detected.
False.
A medical tracer needs a short half-life (hours or days). It must last long enough for the scan to be completed but decay quickly afterwards to minimise the radiation dose to the patient.
Why is gamma radiation used for treating internal tumours rather than alpha or beta radiation?
Gamma radiation has the highest penetrating power and can pass through the body to reach internal tumours. Alpha and beta radiation cannot penetrate deeply enough to reach internal targets.
Smoke detectors use .......... radiation because it has .......... penetrating power and is stopped by smoke particles, triggering the alarm. The source requires a .......... half-life so it works reliably for a long time.
Smoke detectors use alpha radiation because it has low penetrating power and is stopped by smoke particles, triggering the alarm. The source requires a long half-life so it works reliably for a long time.
Why is beta radiation suitable for monitoring the thickness of aluminium foil in a factory?
Beta radiation has medium penetrating power and is stopped by aluminium. If the foil becomes too thick, less radiation reaches the detector. If it becomes too thin, more radiation passes through. This allows the thickness to be monitored and adjusted.
True or False?
Industrial thickness gauges and smoke detectors both require radioisotopes with very long half-lives.
True.
Both applications require a long half-life so the source works reliably over many years without needing to be replaced. Short half-lives are needed for medical tracers inside the body.
A suitable medical tracer should emit .......... radiation so it can .......... the body and be detected. It should have a .......... half-life to minimise the radiation dose to the patient.
A suitable medical tracer should emit gamma radiation so it can pass through the body and be detected. It should have a short half-life to minimise the radiation dose to the patient.
How do you decide whether a radioisotope is suitable for a specific medical or industrial use?
Consider two factors:
Type of radiation — match the penetrating power to the job (e.g. gamma for body imaging, beta for thin material monitoring, alpha for smoke detectors)
Half-life — long for industrial/smoke detector use; short for medical tracers inside the body
Sign up to unlock flashcards
or