P9: Atomic Structure and Radioactivity Flashcards
what is radioactivity?
The particles released by an unstable nucleus as it breaks down.
Define Activity in radioactivity
the rate at which a radioactive nuclei decays
what is the unit of activity
the Becquerel (Bq)
what is the result of radioactivity on the atom?
a new element is formed
what are the 3 different types of nuclear radiation?
alpha, beta and gamma radiation
what are alpha particles?
helium nulceus
what are beta particles?
electrons
what is gamma radiation or gamma rays?
a form of electromagnetic radiation. It is a high energy photon.
what are isotopes?
Elements with different nucleon or mass numbers
what is the nucleon number?
mass number
what are nuclides?
nuclei that have the same number of protons and neutrons
difference between a nuclide and an isotope?
isotopes are atoms have different nucleon numbers. nuclides are simply nuclei with a particular number of protons and neutrons
what are the 3 radiation types?
alpha, beta, gamma
which radiation type is not affected by electrical or magnetic fields and why?
gamma radiation. Because it has no charge
which form of radiation has the strongest ionizing power?
Alpha particles.
which form of radiation travels furthest
gamma radiation because it is electromagnetic radiation
which form of radiation results in change in the mass number of the atom?
alpha and beta
which form of radiation is electromagnetic?
gamma
what is meant by ionizing radiation?
particles emitted by an unstable nucleus which are capable of stripping electrons from other atoms.
how is ionizing radiation bad for living things?
atoms of the different molecules in the body such as DNA and proteins are ionized and so the molecule loses its function resulting in radiation sickness where the organism becomes ill and may even die.
why is radiation sickness difficult to treat
the ionized atoms remain in the body for many years.
which form of radiation can be blocked by paper of skin?
alpha
which form of radiation can be stopped by metal foil?
beta
which form of radiation can be stopped only by a thick metal plating such as lead?
gamma radiation
A neutron can break up to produce a (1)__________ and a (2)_________
- electron
- proton
what kind of atoms are considered radioactive?
atoms that dont have the correct balance of proton and neutrons
which part of the atom is responsible for radioactivity?
its nucleus
what are the changes that occur in a nucleus undergoing alpha radioactive decay?
- The parent nucleus has incorrect balance of protons and neutrons
- the nucleus emits an alpha particle (helium nucleus)
- the atomic number decreases by 2 and the nucleon number decreases by 4.
- A new daughter nucleus is formed and therefore a different element is formed
what are the changes that occur in a nucleus undergoing beta radioactive decay?
- The parent nucleus has incorrect balance of protons and neutrons
- a neutron in the nucleus decays into a proton and an electron
- The electron is emitted from the atom as a high velocity beta particle.
- the atomic number increases by 1.
- A new daughter nucleus is formed and therefore a different element is formed
What changes occur during gamma decay?
- Gamma decay does not cause any changes in the nuceus of the nuclide
- Gamma radiation is the energy released as electromegnetic waves as a result of alpha or beta decay.
written equation for radioactive decay
unstable parent nucleus —–> new daughter nucleus(new element) + apha or beta particles + gamma radiation.
what is nuclear fission?
Process by which a neutron is used to break up a nucleus into 2 smaller nucei resulting in the release of large amounts of energy
Explain nuclear fission
- a neutron is used to hit a nucleus which absorbs it.
- the nucleus becomes unstable and breaks up because it has too many neutrons.
- The decay of the nucleus produces more neutrons which are then used to split more nucei and and so a chain reaction results.
- A large amount of energy is released and used eg to generate electricity.
How is nuclear fission important?
- The energy released from nuclear fission is used to generate electricity.
what is nuclear fusion?
process by which two nuclei are merged to produce one larger nucleus, resulting in the release of energy
eg the energy from the sun is produced by nuclear fusion between of hydrogen isotopes to form helium
what is background radiation?
radiation form natural and artificial materials that exist around us.
What is radioactive decay?
A spontaneous process where an unstable nucleus breaks up, releasing alpha, beta and gamma radiation, to form a more stable nucleus.
general graph for radioactive decay
definition radioactive decay rate
radioactive decay rate is defined as the number of nuclei that decay per unit time.
How is radioactive half-life defined?
The time it takes for half of the active nuclides or isotopes to decay
why is half life important?
- each isotope has its own unique half life
Important names in the discovery of the atom and radioactivity
- Democritus - suggested matter consisted of small invisible particles call ‘atomos’
- Joseph John Thompson - suggested the plum pudding model of the atom where the atom was a positively charged sphere with fixed negative charged particles interspersed within it resulting n a net charge of 0.
- Ernest Rutherford: Suggested most of the Atom was empty space, with a positive nucleus surrounded by a cloud of electrons. surrounign
- Neils Bohr: Suggested that the electrons orbit the nucleus in particular shells
- James Chadwick: Discovered the Neutron
- Marie Currie: most important name in the study of radioactivity - she discovered that radioactivity is an atomic phenomenon and that the intensity of the radioactive rays was only dependent on the mass of the emitting radioactive sample and not on environmental conditions. She discovered the elements polonium and radium
What is the Geiger-Marsden or Rutherford Scattering Experiment?
- Alpha particles fired at a thin sheet of gold foil in a vaccum.
- The alpha particles that passed through the foil would then strike a Zinc Sulphide screen causing small flashes.
- It was observed that most of the alpha particles passed throught the foil without defection and few were deflected
Conclusion:
- Most of the atom is empty space.
- The nuclues is extremely dense with positive charges that repelled the positively charged alpha particles.
Of the 3 radiation types, (1)___________ travel only a few cm in air, (2)__________ travel a few meters and (3)____________ have a very long range
- alpha particles
- beta particles
- gamma rays
Of the 3 radiation types, (1)___________ is absorbed by paper or skin, (2)__________ is absorbed by thin foil of aluminium, and (3)____________ can be abdorbed by thick sheet of lead.
- alpha
- beta
- gamma
Of the 3 radiation types, (1)___________ travels a few cm, (2)__________ travels a few meters and (3)____________ can travel many Kms
- alpha particles
- beta particles
- gamma particles
which radioactive emmision has the strongest ionizing power?
Alpha particles
diagram showing the 3 types of radioactive decay
Comparison of the the 3 types of radioactive emissions
The 3 types of radioactive emissions compared
what is the nuclear symbol for the alpha particle?
what is the nuclear symbol for the beta particle?
nuclear symbol for the gamma particle
What are the tests to identify the different types of radiation
- Absorbtion test
- Electric field test
- Magnetic field test
- Cloud Chamber test
The GM tube did not detect any radioactive emisson when paper was placed in front of the emitting source except the background radiation. What type of radioactive emission is coming from the source?
alpha emissions
The GM tube detected increased radioactive emissons when paper was placed in front of the emitting source. What type of radioactive emission is coming from the source?
beta or gamma
The GM tube did not detect any radioactive emisson when a thin sheet of foil was placed in front of the emitting source except the background radtion. What type of radioactive emission is coming from the source?
beta radiation
The GM tube detected increased radioactive emissons when a thin sheet of foil was placed in front of the emitting source. What type of radioactive emission is coming from the source?
gamma radiation
Identify the the different radioactive emission in the diagram
What method of identification of the radiation type is seen here?
Electric field deflection test
Identify the the different radioactive emission in the diagram
What method of identification of the radiation type is seen here?
Magnetic field deflection test
Identify the the different radioactive emission in the diagram
What method of identification of the radiation type is seen here?
Diffusion Cloud Chamber Test
Identify the the different radioactive emission in the diagram
What method of identification of the radiation type is seen here?
Absorption test
what instrument is used to detect radioactive emissions?
the Geiger-Muller (GM) tube
How to work out the number of half lives that a radioactive isotope will go through in a given time.
divide the given time by the half life.
eg an isotope has a half life of 5 years. After 20 years it will have passed through 20/5 = 4 half lives
Uses of radioisotopes
- In Medicine:
- radiotherapy
- radioactive tracing
- Non-Medical uses
- gama radiation used to detect weak areas in metals
- radiocarbon dating
- sterilization of objects
- to measure the thickness of an object
what is radio-carbon dating used for?
to determine the age of old organic materials based on the amountof carbon 14 that remains in them.
Explain the principle behind radio-carbon dating with Carbon-14
- some of the carbon dioxide used by plants in photosynthesis contains radioactive carbon-14
- Animals incooperate carbon-14 in their bodies when they eat the plants
- When the plant or animal dies it stops incooperating any more carbon-14.
- the amount of C-14 in the dead body begins to decrease over time by radioactive decay
- the half life of carbon-14 is 5730 years
- measuring the amount of carbon-14 remaining in a dead body is used to estimate as to when the body died
what is Einsteins equation of mass-energy equivalence
E=mc2
- E is energy output
- m is mass defect
- c speed of light in a vacuum
