topic 4 - atomic structure: atoms and nuclear radiation Flashcards
What happens with the nucleus of an atom when it tries to become more stable?
It gives out radiation in a process called radioactive decay.
What is radioactive decay?
A random process in which a nucleus gives out atomic radiation to become more stable?
Do stable or unstable atoms give out radioactive decay?
Unstable atoms.
What is activity?
The rate at which a source of unstable nuclei decays.
What is activity measured in?
Becquerel (Bq).
What is count rate?
The number of decays recorded each second by a detector.
Give an example of a detector used to measure count rate.
A Geiger-Muller tube.
What are the 4 types of ionising radiation which can be released from a nucleus?
- Alpha
- Beta
- Gamma
- Neutron
What is ionising radiation?
Radiation which knocks electrons off atoms.
What does ionising radiation create.
Positively charged ions.
What does the ‘ionising power’ of a radiation source mean?
How easily is can perform ionising radiation.
What is the symbol for an alpha particle/
α
What are alpha particles made up of?
2 protons and 2 neutrons.
What element has the same nucleus as an alpha particle?
Helium.
What is the penetration through materials of alpha particles like?
Don’t penetrate very far into materials and are stopped quickly - they are absorbed into a sheet of paper.
What is the range of alpha particles in air?
A few cm.
What is the ionising power of alpha particles like?
Strongly ionising.
Give a practical use of alpha particles.
Smoke detectors
How do alpha particles work in smoke detectors?
Smoke detectors ionise air particles, causing a current to flow. If there is smoke in the air, it binds to the ions, meaning the current stops and the alarm sounds.
What is the symbol for a beta particle?
β
What is a beta particle made up of?
A high-speed electron ejected from the nucleus as a neutron turns into a proton.
What is the mass of a beta particle?
Virtually none.
What is the charge of a beta particle?
-1
What is the penetration through materials of beta particles like?
They penetrate moderately far before colliding.
What is the range of beta particles in air?
A few metres.
What material can be used to absorb beta particles?
A sheet of aluminium.
How ionising are beta particles?
Moderately ionising.
Give a use of beta particles.
Testing the thickness of sheets of metal.
What is the symbol for gamma rays?
γ
What is a gamma ray made up of?
Electromagnetic radiation from the nucleus.
What is the pentration through materials of gamma rays like?
Penetrate far into materials without being stopped.
How far can gamma particles travel through air?
A long distance.
How ionising are gamma particles?
Weakly ionising.
What can gamma particles be absorbed by?
Thick sheets of lead or metres of concrete.
What are nuclear equations used to represent?
Radioactive decay.
In nuclear equations, what symbol may an alpha particle be represented by?
He (mass no.=4, atomic no.=2)
In nuclear equations, what symbol may a beta particle be represented by?
e (mass no.=0, atomic no.=-1)
What is the general form of a nuclear equation?
atom before decay –> atom after decay + radiation emitted
What must be equal on both sides of a nuclear equation?
The total mass and atomic numbers.
How does alpha decay change the charge and mass of the nucleus?
It decreases both the charge and mass.
How does beta decay affect the charge of a nucleus?
It increases the charge.
How does the emission of a gamma ray affect the mass and charge of a nucleus?
It doesn’t affect it.
Is radioactive decay predictable or random?
Random.
What is the half life of a radioactive isotope?
The time it takes for the number of nuclei in a sample of the isotope to halve.
OR
The time it takes for the count rate from a sample containing the isotope to fall to half its initial level.
What half-life be used to find?
The rate at which a source decays (its activity).
Each time a radioactive nucleus decays to become a stable nucleus, what decreases?
The total activity.
What does a short half-life mean for activity and why?
The activity decreases quickly because the nuclei arevert unstable and rapidly decay.
What does a long half-life mean for activity and why?
The activity decreases slowly because most of the nuclei don’t decay for a long time.
Why can sources with a short half-life be dangerous?
They emit a high amount of radiation at the start.
Why can sources with a long half-life be dangerous?
Nearby areas are exposed to radiation for years.
(got up to
radioactive contamination)
