Atomic Structure (P4) Flashcards
What happens to unstable atoms?
Some atoms are unstable. They will eventually radioactively decay to form a more stable atom.
What are the three types of radiation?
Alpha, beta and gamma.
What is an alpha particle?
Two protons and two neutrons that are expelled from the nucleus of an atom.
What is a beta particle?
A neutron turns into a proton and an electron is ejected.
What is a gamma radiation?
The nucleus emits electromagnetic ray but does not change. No particle is lost.
What is an isotope?
An isotope is an atom with a different amount of protons (to the average) but the same amount of protons.
Who proved the modern atomic structure and how?
Ernest Rutherford proved the modern atomic structure using the alpha scattering experiment.
What is the alpha scattering experiment?
In the alpha scattering experiment, Rutherford set up a source of alpha particles in front of gold foil that was only an atom thick. Around the experiment was a detector to see where the particles ended up. Most went straight through some where deflected of at odd angles and a few where deflected right back. He did this to prove the current atomic model.
What did the alpha scattering experiment prove?
That atoms have a tiny, dense, positively charged centre and negative subatomic particles around it.
Which is the most ionising radiation?
Alpha
What is the most penetrating radiation?
Gamma
Describe the structure of a nucleus?
(1/10000 the size of the atom)
Contains protons and neutrons
Contains most of the mass of the atoms
Positively charged
What is the size of an atom?
1x10^-10m
Where are electrons in an atom?
They orbit at specific energy levels about the nucleus
What happens to the energy levels as they get further from the nucleus?
The further the shell is from the nucleus, the higher the energy
How can electrons move up an energy level?
If they absorb electromagnetic radiation they may increase energy level
How can electrons move down an energy level?
If they emit electromagnetic radiation they may decrease energy level
What is the charge of a proton?
+1
What is the charge of an electron?
-1
What is the charge of a neutron?
0
Define Atomic Number
Number of protons in an atoms nucleus
Why do atoms have no overall charge?
Number of protons= Number of electrons
Why is there an equal number of protons as electrons in an atoms?
Cancel out the positive charge
Atoms with the same number of protons are always the same….
Element
Atoms with different numbers of protons are…
Different elements
What does Mass Number tell us?
Number of protons + neutrons
mass of a nucleus
Define isotope
Atoms of the same element that have a different number of neutrons
Define ion
When atoms (gain or) loose electrons to become charged
When was the electron discovered?
1897
What did the discovery of the electron show?
Atoms are not spheres and have have an internal structure
What was the first (modern) model of an atom?
Plum pudding model
Describe the plum pudding model
A ball of positive charge with negative electrons embedded in it
What material was used for the alpha scattering experiment and why?
Gold foil
Easily hammered into foil that is only a few atoms thick
What is the charge of an alpha particle?
Positive
What did the nuclear model look like?
Small positive nucleus, empty space and a ring of negative electrons around it
What is the name of the model derived from the alpha scattering experiment?
Nuclear Model
What did Niels Bohrs propose
Electrons orbit at specific energy levels
What did James Chadwick discover?
The uncharged neutron
Describe radioactive decay
When an isotope has an unstable nucleus and to become stable it gives out radiation
In which order and when do radioactive nuclei decay?
None
Radioactive decay is a random process
Define activity
when related to radioactivity
Activity is the rate at which a source of unstable nuclei decay
What do we measure activity in?
Becquerel (Bq)
What is 1 Bq equal to?
1 decay per second
What do we use to measure activity?
Geiger-Muller meter
What does the count rate tell us?
Number of decays recorded each second by a detector (i.e.: a Geiger-Muller tube)
Why are count rate and activity not the same?
Background radiation
Describe an alpha particle
α
2 neutrons and 2 protons
(Helium Nucleus)
Positive charge
Describe a beta particle
Describe how it is formed
β
An electron ejected from the nucleus at very high speed
It is formed when a neutron changes into a proton and an electron
Describe gamma rays
γ
A type of electromagnetic radiation from the nucleus
not a particle
What are the 4 types of nuclear radiation?
Neutron
Alpha particle
Beta particle
Gamma rays
What type of atoms tend to be radioactive?
Isotopes
How far do alpha particles travel in air? Why?
Not very far (<5cm)
Because they are large and collide with air
How far do beta particles travel in air? Why?
Further than alpha (<15cm)
Because they are small they can go quite far but will eventually collide with air
How far do gamma rays travel in air? Why?
Several meters as it is not a particle
What is the penetrating power of alpha particles?
Very low
stopped by a single sheet of paper
What is the penetrating power of beta particles?
Medium
stopped by a few millimetres of aluminium
What is the penetrating power of gamma radiation?
High
stopped by several centimetres of lead
What is ionising power?
When radiation collides with atoms, that can cause atoms to loose electrons and form ions
What is the ionising power of alpha particles?
Very ionising
What is the ionising power of beta particles?
Quite ionising
What is the ionising power of gamma rays?
Weakly ionising
How do we represent an alpha particle?
4/2He
(Helium symbol)
(not a fraction, just 4 over 2)
What is the atomic number of an atom that undergoes alpha particle decay?
The initial element is Ra and has a mass number of 226 and atomic number of 88
226Ra->222Rn+4He
88 Ra->86 Rn +2He
No longer Radium
What happens to the atomic and mass numbers during alpha decay?
Atomic number decreases by 2
Mass number decreases by 4
How do we represent a beta particle?
0/-1e
(electron symbol)
(not a fraction, just 0 over -1)
What is the atomic number of an atom that undergoes beta particle decay?
The initial element is Al and has a mass number of 29 and atomic number of 13
29Al-> 29Si+ 0e
13Al -> 14Si + -1e
What happens to the atomic and mass numbers during beta decay?
The atomic number increases by 1 but the mass number does not change
What happens to the atomic and mass numbers during gamma decay?
Both atomic and mass number stay the same and are unchanged
Define Half-life
Two possible definitions:
1) The time taken for the number of nuclei of the isotope in a sample to half
2) The time it takes for the count rate from a sample containing the isotope to fall to half its initial level
This is Random! It’s an estimation…
Define Irradiation
Exposing an object to irradiation
Define Contamination
When unwanted radioactive isotopes end up on other materials
Give an example of useful irradiation?
Sterilising equipment using gamma rays
How do we sterilise equipment using radiation?
Place the object in sealed plastic (to prevent bacteria entering when it it taken out)
Place it in a chamber with a radioactive isotope that emits gamma radiation
It should have a lead shield to protect workers
What happens to the radioactivity of an object after it it irradiaited?
Nothing
It does not become radioactive
What happens to the radioactivity of an object after it it irradiaited?
Nothing
It does not become radioactive
Why do objects that are irradiated not become radioactive?
They come in contact with the radiation but not the radioactive isotope itself
What protection may someone take to protect themselves against alpha radiation?
Gloves
What protection may someone take to protect themselves against low levels of beta radiation?
Lead Apron
What protection may someone take to protect themselves against low levels of gamma radiation?
Lead Apron
How may someone protect themselves from high levels of beta and gamma radiation?
Lead walls
Lead glass screen
What should people who work with radiation also carry?
Radiation monitor
When is alpha contamination dangerous?
If inhaled or swallowed as they are highly ionising
When is alpha contamination not dangerous?
When created by an external force as dead skin cells easily stop it
Why is beta particle contamination quite dangerous?
They are quite ionising and penetrating enough to enter the body
Why is gamma contamination not very dangerous?
They are weakly ionising and penetrating enough to pass straight through the body
What is the name of the process by which scientists share and publish studies and why do they do it?
They do it so that others will check their findings
This is called peer review
Describe Background Radiation
The radiation that is constantly around us
Give examples of man-made radiation
Fallout form Nuclear Weapons testing
Nuclear accidents
Give examples of natural radiation
Radioactive rock (Granite)
Cosmic rays
(from space)
What is the source of cosmic rays?
Supernovas
What affects your exposure to background radiation?
Location
Occupation
What do we measure radiation dosage in?
Sieverts (Sv)
1 millisieverts is 1/1000 of a sieverts
What do we use radioactive isotopes for in medicine?
Exploring internal organs
Controlling or destroying unwanted tissue
How can we explore tissues or organs using radioactive isotopes?
The patient consumes or is injected with (usually gamma) radiation. As it is emitted it can be detected and we can see areas where specific isotopes are more or less abundant
What are the issues involved in using radioactive tracers to explore the body?
Must emit a radiation which can pass out of the body (gamma or beta)
Must not be strongly ionising
Must not decay into another radioactive isotope
Must have a short half life
Which common disease can often be controlled or destroyed using radiotherapy?
Cancer
What is the main issue with radiotherapy?
Healthy tissue may also be damaged
What is the advantage of doing radiotherapy from within a patients body?
More accurate and less damage to healthy tissue
Define Nuclear Fission
Large, unstable nuclei are split
Give two examples of large, unstable nuclei
Uranium
Plutonium
What initiates nuclear fission?
It can be spontaneous (this is rare)
Usually the nucleus needs to absorbs a neutron
What happens when a radioactive isotope of uranium absorbs a neutron?
It undergoes nuclear fission
Energy, two daughter nuclei, 2/3 neutrons and gamma radiation
What are the relative sizes of daughter nuclei?
Roughly equal
During Nuclear fission of uranium, neutrons are released, what may happen because of this?
They may be absorbed by other uranium isotopes triggering the process to happen again - Chain Reaction
How do we generate energy in a nuclear reactor?
Controlled fission chain reaction
How do we create nuclear weapons that explode?
Uncontrolled fission chain reaction
Define Nuclear Fusion
When two light nuclei are joined to form a heavier nucleus
Some of the mass can be converted into energy, which is released as radiation
Describe the chain reaction in nuclear fusion
There is none
Describe the chain reaction in nuclear fission
A neutron is often needed to trigger the process
However, one of the products is also several neutrons which are released and can be absorbed by another nuclei setting off another reaction
