Atomic Physics - Paper 1 Flashcards
To revise Atomic physics (paper 1)
State the typical size of an atom
1 x 10-10 m
Describe the structure of an atom
A positively charged nucleus containing protons and neutrons surrounded by negatively charged electrons in shells.
State the size of a typical nucleus?
1 x 10-15 m
State the size of a nucleus compared to an atom
The radius of the nucleus is less than 1/10000 of the radius of an atom
How can electrons move to a higher energy shell/level
By absorbing energy in the form of electromagnetic radiation. This is called excitation.
How can electrons move to a lower energy shell/level
By releasing energy in the form of electromagnetic radiation. This is called relaxation.
What is the charge on an atom why?
Atoms are neutral as the number of positive protons is equal to the number of negative electrons
What is an Ion?
A charged atom that has gained or lost electrons
The same element must always have the same number of…?
Protons
Define the atomic number
Number of protons = number of electrons for an atom
Define nucleon number
mass mummer = Number of protons + number of neutrons
Define an isotope
The same element with the same number of protons but with a different number of neutrons.
Describe how the model of the atom has changed with new experimental evidence
Atoms were originally though to be tiny spheres that couldn’t be divided.
The discovery of the electron led to the plum pudding model of the atom.
The alpha particle scattering experiment led to the nuclear model of the atom - a positive nucleus which contained the majority of the mass.
Neils Bohr suggested that electrons orbited the nucleus in shells.
James Chadwich discovered the neutron
Describe the plum pudding model of the atom
A positive sphere with negative electrons dotted throughout it.
Describe the alpha particle scattering experiment.
Alpha Particles were fired at thin gold in a vacuum.
Describe and explain the observations from the alpha particle experiment.
- The majority of alpha particles went straight though the gold. So atoms are mainly empty space.
- Some alpha particles were defected by the gold foil. There must be something positive which contained the majority of the mass in an atom (the nucleus)
- A tiny fraction of alpha particles bounced back where they came from. The nucleus must be a tiny part of the atom
How can an unstable nucleus become more stable?
By giving out radiation (alpha, beta or gamma)
Define activity
The rate at which a source of unstable nuclei decays
State the units of activity
Becquerel (Bq)
Define count rate
The number of decays recorded by a detector (GM tube)
Describe a alpha particle
Two protons and two neutrons together. A helium nucleus
Describe a beta partice
A fast moving electron ejected from the nucleus. This happens after a neutron has decayed into a proton
Describe a gamma ray
An electromagnetic wave with no charge or mass.
Define penertrating abilty
Penetrating power is what can stop the radiation.
State the penetrating power of alpha, beta and gamma radiation.
Penetrating power is what can stop the radiation.
Alpha - skin, paper 5 - 10 cm of air
Beta - mm’s of aluminium, 1 meter of air
Gamma - reduced by cm’s of lead or m’s of concrete
Define Ionisation ability
Ionising ability is the ability to do damage to our living cells and tissues.
State the ionising ability of alpha, beta and gamma radiation.
Ionising ability is the ability to do damage to our living cells and tissues. Alpha - highly ionising
Beta - moderately ionising
Gamma - very weakly ionising
In decay equations what is the mass number and proton number for an alpha particle?
mass number = 4
proton number = 2
In decay equations what is the mass number and proton number for a beta particle?
mass number = 0
proton number = -1
In decay equations what is the mass number and proton number for a gamma wave?
mass number = 0
proton number = 0
how can the rate of radioactive decay be increased?
It can’t be affected by physics quantities such as temperature or pressure. it is completely random.
Define half life
The time taken for the number of radioactive nuclei in a sample to half.
Define contamination
Unwanted presence of radioactive atoms on other materials such as clothes, buildings etc
Define irradiation
The process of exposing an object to radiation. The object does not become radioactive. e.g. killing bacterial on fruit to increase its shelf life.
How should radioactive sources be used safely?
Use only for a short period of time.
Keep source at arms length.
Point source away from yourself.
Stored in a lead lined box with a radioactive symbol
What is background radiation?
Radiation that is around us all the time
State some sources of natural background radiation?
Rocks, cosmic rays, food
State some sources of man made background radiation
X-rays, nuclear bombs, nuclear power stations
What factors can affect the level of background radiation a person receives?
occupation e.g. radiotherapist, pilot
Location - Background radiation increase with altitude.
State the units of radiation dose
Sieverts (Sv)
What type of radiation and half life should be used with a medical tracer.
Gamma with a short half life - 6 hours.
Gamma is the least ionising so wil cause the least amount of damage to the patient.
What type of radiation and half life should be used with a smoke detector.
Alpha with a long half life - 400 years
Alpha particles are highly ionising so they can be easily stopped by smoke and set the alarm off.
Describe nuclear fission
Splitting of a large unstable nucleus eg Uranium or plutonium
What is required to start fission
The unstable nucleus must absorb a neutron
What is released after fission
2 or 3 neutrons and lots of energy
What is a chain reaction?
One neutron is absorbs by one Uranium nucleus. This undergoes fission and releases 2 or 3 neutrons. These neutrons can cause fission in 2 or 3 more uranium nuclei. the process can keep repeating.
Describe nuclear fusion
The joining of two light nuclei to form a heavier nucleus.
Where does fusion take place naturally?
In all stars
What is released by fusion
Energy
Where is the majority of the mass of an atom?
The nucleus, as the mass of an electron is almost zero compared to the mass of protons and neutrons
What was Dalton’s theory about the atom?
all matter is made of small invisible units called atoms
What was Thomson’s theory about the atom?
He discovered the electron and therefore knew the atom was made up of charged particles. He introduced the Plum Pudding Model
What was Rutherford’s theory about the atom?
following the alpha particle scattering experiment he updated the plum pudding model to the Nuclear Model; that most of the mass of the atom was concentrated in the nucleus which carries a positive charge
What was Bohr’s theory about the atom?
Bohr updated the Nuclear model to show that electrons orbit the nucleus in certain energy levels
What was Chadwick’s theory about the atom?
He discovered the neutron
Why did the discovery of electrons mean that Dalton’s model of the atom needed to be updated?
That atoms were not the smallest thing anymore, as the electron was smaller than the atom
What are the different types of nuclear radiation?
Alpha, Beta, Gamma and Neutron
What happens to the mass and charge of the nucleus during alpha decay?
Mass (nucleon) number goes down by 4
Number of protons goes does by 2
What happens during beta decay?
A neutron decays into a proton creating the beta particle which is fired out of the nucleus
What happens to the mass and charge of the nucleus during beta decay?
Mass (nucleon) number stays the same
Number of protons goes up by 1
What happens to the mass and charge of the nucleus during gamma decay?
Mass (nucleon) number stays the same
Number of protons stays the same
What happens when radioactive radiation strikes an atom?
It can knock an electron off an atom - ionisation
What is the safest type of radiation to have inside the body?
Gamma as it’s the least ionising and escapes easily
What is the most dangerous type of radiation to have inside the body?
Alpha as it’s most ionising and cannot escape
What is the safest type of radiation to have outside the body?
Alpha as it’s least penetrating and can’t penetrate our skin
