P6 Flashcards
What are atomic nuclei made of?
Protons and neutrons.
What is the relative charge of a proton?
+1.
What is the charge of a neutron?
0 (no charge).
What is the overall charge of the nucleus?
Positive, due to protons.
What are isotopes?
Atoms of the same element with different numbers of neutrons
What remains the same in all isotopes of an element?
The atomic number (protons).
What differs between isotopes?
The mass number (due to different numbers of neutrons).
Give an example of isotopes.
Carbon-12, Carbon-13, Carbon-14.
In nuclear notation, what does A represent?
Mass number = protons + neutrons.
What does Z represent?
Atomic number = number of protons (defines the element).
What does X represent?
The chemical symbol of the element.
What is the charge N in a nuclear symbol?
• If there are N more electrons than protons, the charge is –N.
• If there are N fewer electrons, the charge is +N.
What is the defining feature of an element?
The number of protons — it is fixed for each element.
Why are some nuclei unstable?
They have too many protons or neutrons, or excess energy.
What happens to unstable nuclei?
They undergo radioactive decay to become more stable.
Is radioactive decay predictable?
No — it is completely random. You cannot predict when a specific nucleus will decay.
What is alpha decay?
Emission of an alpha particle (2 protons + 2 neutrons = helium nucleus). Happens when nucleus is too large.
What is beta decay?
A neutron turns into a proton, and an electron (beta particle) is emitted. Happens when there are too many neutrons.
What is electron capture?
The nucleus absorbs a neutron and emits a neutron. Happens when the nucleus is too large.
What is gamma emission?
Emission of a gamma ray when the nucleus has too much energy.
Do gamma emissions change proton or neutron number?
No — they only release energy, not particles.
What is a nuclear equation?
A way of representing radioactive decay by showing the changes to the atomic and mass numbers.
What happens to atomic and mass number in alpha decay?
• Atomic number: –2
• Mass number: –4
(The nucleus loses 2 protons and 2 neutrons)
Example of alpha decay equation:
Pu 239/94 —> U 235/92 + He 4/2
What happens to atomic and mass number in beta decay?
• Atomic number: +1 (neutron becomes a proton)
• Mass number: stays the same
Example of beta decay equation:
C 14/6 —> N 14/7 + e 0/-1
What happens to atomic and mass number in gamma decay?
• No change in atomic or mass number
• Only energy is released
What is ionisation?
The process where radiation knocks electrons off atoms, turning them into ions.
What makes a radiation more ionising?
If it collides easily with atoms and has more mass/charge.
What is the most ionising type of radiation?
Alpha — but it has low penetration.
What stops alpha radiation?
A few cm of air or paper.
What is the penetration level of beta radiation?
Medium — it can pass through air but is stopped by 5 mm of aluminium.
What is the penetration level of gamma radiation?
High — it passes through most materials and requires thick lead or concrete to reduce it.
What is the most penetrating type of radiation?
Gamma rays.
What is half-life?
The time it takes for half the radioactive nuclei in a sample to decay.
What else can half-life mean?
The time for the count rate or activity to fall by half.
Is half-life affected by external conditions?
No — it’s constant and not affected by temperature or pressure.
What is activity?
The rate of decay of radioactive nuclei, measured in Becquerels (Bq).
What is count rate?
The number of decays detected per second by a Geiger-Müller tube.
What is irradiation?
Exposure to radiation from a radioactive source.
What is contamination?
Radioactive particles getting on or inside an object.
What’s the difference between contamination and irradiation?
• Contamination: radioactive material is present
• Irradiation: exposed to radiation, not particles
How can contamination occur?
Touching or inhaling radioactive material.
Which is more dangerous: contamination or irradiation?
Contamination, because the source remains inside the body.
What type of radiation is used in smoke alarms?
Alpha radiation — it ionises air, which is interrupted by smoke.
What is gamma radiation used for in medicine?
• Sterilising equipment
• Medical tracers
• Cancer treatment
Why is beta used to measure thickness (e.g. paper)?
It partially penetrates, so changes in count rate reflect thickness.
How do we stay safe when using radioactive sources?
• Use lead-lined containers
• Tongs to handle sources
• Limit exposure time
• Increase distance
What is nuclear fission?
The splitting of a large unstable nucleus into two smaller nuclei + neutrons + energy.
What triggers nuclear fission?
Absorption of a neutron.
What does fission release?
• 2–3 neutrons
• Kinetic energy
• Gamma radiation
What is a chain reaction?
The neutrons released go on to cause more fission events.
What is nuclear fusion?
Two small nuclei join to form a larger nucleus, releasing lots of energy.
Why is fusion difficult on Earth?
Nuclei repel each other due to positive charge — requires extremely high temperature and pressure.
Where does fusion naturally occur?
In stars, including the Sun.
What makes fusion safer than fission?
It doesn’t produce long-lived radioactive waste and can’t go out of control.
What happens when electrons absorb or emit radiation?
• Absorb: Electrons gain energy and move to a higher level.
• Emit: They drop back and release energy as EM radiation.
• Ionisation occurs if outer electrons are lost.
What types of radiation can atomic changes produce?
They can produce radiation from across the EM spectrum, including gamma rays.
How do you calculate net decline from radioactive decay?
Use half-life graphs to find how many half-lives have passed, then apply
remaining amount = (1/2)^n
n is number of half lives
What’s the difference between irradiation and contamination?
• Irradiation = exposed to radiation
• Contamination = radioactive material on/in the object
Contamination is more dangerous long-term.
How does half-life affect radiation hazard?
• Short half-life = intense, short-lived risk
• Long half-life = low-level but persistent hazard
What are uses of radiation in medicine?
• Internal imaging (tracers)
• Controlling tumours
• Sterilisation
All use carefully selected isotopes.
