Atomic Structure and Radiation Flashcards
What is the radius of the nucleus compared to the radius of the atom?
The radius of the nucleus is less than 1/10,000th of the radius of the atom
Where is most of the atoms’ mass concentrated?
The nucleus
Energy levels that are further from the nucleus have a _____ energy level than those closer
higher
What can happen to an electron if an atom absorbs electromagnetic radiation?
It can move from a lower to a higher energy level.
What is an isotope?
An isotope is an atom of the same element that has a different number of neutrons.
What is the overall charge of an atom?
Neutral / No charge
What is an ion?
A charged particle
What did the Ancient Greeks believe about atoms?
They believed that everything is made up of small indivisible spheres called atoms.
What did JJ Thomson discover in 1897?
That atoms contained negatively charged particles called electrons. This showed that atoms are not indivisible and have an internal structure.
What did the plum pudding model suggest?
That an atom is a ball of positive charge with negative electrons embedded in it.
Describe the Alpha scattering experiment
Scientists used a piece of gold foil and fired alpha particles at it. They found that most of the fast moving α-particles passed straight through the gold foil. Some of the α-particles were deflected by the foil by small angles. Surprisingly one out of every 12,000 alpha particles appeared to rebound (bounce straight back)
Why did they use gold for the alpha scattering experiments?
Because gold can be hammered into a very thin sheet; only a few atoms thick.
What is an alpha particle?
A helium nucleus
What did the alpha scattering experiment tell scientists about the atom?
• Since most of the alpha particles passed through the foil, most of the atom must be empty space
• Some of the alpha particles were deflected, therefore the centre of an atom must be positively charged, repelling the alpha particles.
• Some of the alpha particles bounced straight back meaning that most of the mass must be concentrated in the centre (nucleus) of the atom
What did Niels Bohr propose about electrons?
He suggested that electrons orbit the nucleus at specific distances called shells or energy levels
What did James Chadwick suggest about the nucleus?
That it contains neutrons, particles with no charge, that contribute to the weight of the atom.
What are radioisotopes?
Isotopes of an atom which give out radiation in a bid to become stable.
What is radioactive decay?
Some isotopes have an unstable nucleus. To become stable that nucleus gives out radiation. This is called radioactive decay.
Radioactive decay is a ______ process
random
What is activity and how is it measured?
The activity is the rate at which a source of unstable nuclei decay. Activity is measured in becquerel (Bq)
What is a Beta particle?
An electron which is ejected from the nucleus at a high speed.
Which is the most ionising radiation?
Alpha
Which is the least ionising radiation?
Gamma
Gamma radiation is an ________
electromagnetic wave
What material can stop alpha radiation?
A sheet of paper
What material stops beta radiation?
3-5mm of aluminium
What material stops gamma radiation?
5-10cm of lead of metres or concrete
How do we measure count rate?
With a Geiger-Muller counter
Why are alpha particles strongly ionising?
Because the positive charge of the particle attracts the electrons
What is the range in air of alpha radiation?
5cm
What is the range in air of beta radiation?
15cm
What is the range in air of gamma radiation?
Several meters
What happens when radiation collides with atoms?
It can cause the atom to lose electrons and form ions
What happens to the atomic number during alpha decay?
It decreases by 2
What happens to the mass number during alpha decay?
It decreases by 4
What happens to the atomic number during beta decay?
It increases by 1
How are beta particles represented?
How are alpha particles represented?
What is the half-life of a radioactive isotope?
Half-life is the time it takes for the amount of unstable nuclei in a sample to decay to half its’ initial amount.
What does ionising radiation increase the risk of?
It increases the risk of cancer
What is irradiation?
Irradiation is exposing an object to nuclear radiation.
Is an irradiated object radioactive?
No, the object only comes into contact with with radiation and not the isotope itself
Give a precaution one should take when handling materials contaminated with alpha radiation
• Wear gloves
• Wear a face mask to avoid breathing in materials
Give a precaution one should take when handling materials contaminated with beta or gamma radiation
• Wear a lead apron
• Wear a face mask to avoid breathing in materials
What is radioactive contamination?
When unwanted radioactive isotopes end up on other materials.
What is the difference between contamination and irradiation?
When an object is irradiated it means that is has come into contact with the radiation given out by radioactive isotopes, but it is not radioactive. A contaminated object comes into contact with the radioactive isotopes themselves. These objects are radioactive.
True or False: Alpha emitters can be dangerous if inhaled or swallowed
True
Why do Geiger-Muller tubes still detect radiation without a radioactive source present
Background radiation
List two natural sources of background radiation:
• Radioactive rocks
• Cosmic rays
List two manmade sources of background radiation:
• Fall out from nuclear weapons testing
• Nuclear accidents
What can affect your exposure to background radiation?
Location & Occupation
What is the does of radiation measured in?
Sieverts
What type of radiation does radioactive iodine emit?
Gamma
What things should we consider before using radioactive materials as a tracer?
- The tracer must emit radiation that can pass out of the body and be detected (beta or gamma)
- It must not be highly ionising to minimise damage to body tissue
- The tracer must not decay into another radioactive isotope
- The tracer must have a short half life so it is not present in the body for a long time
What is the disadvantage of using gamma radiation to destroy unwanted tissue?
Healthy tissue may also be damaged as the radiation passes through the body.
Describe the process of nuclear fission
A large uranium nucleus absorbs a neutron, which triggers the nucleus to undergo fission (spilt). When the nucleus splits, it forms two smaller nuclei, which are roughly equal in size. The nucleus also emits two or three neutrons, gamma radiation and energy. All the fission products have kinetic energy.
What causes a fission chain reaction?
The neutrons emitted by the nucleus during a chain reaction are absorbed by other nuclei and trigger fission again.
A ______ chain reaction is used to release energy in a nuclear reactor
controlled
Describe the process of nuclear fusion
Two light nuclei are joined to form a heavier nucleus. Some of the mass of the nuclei can be converted into energy, which is released as radiation.
Is nuclear fusion a chain reaction?
No
What type of reaction is this?
A fission chain reaction
