Atomic Structure and Radioactivity Flashcards
Who first came up with the atom and when?
Democritus in the 5th Century BCE. He said that all matter was made up of different lumps.
Who agreed with Democritus and when? What did he conjecture?
John Dalton agreed in 1804 that matter is made up of tiny spheres but argued that each element would have its own atom.
Who developed the plum pudding model? What was it?
J J Thomson. His plum pudding model showed a positively charged sphere with negative electrons stuck in it like plums in a plum pudding.
What did Rutherford and Marsden do in 1909?
They fired a beam of alpha particles at thin gold foil. They kept a circular detector screen around the gold foil and alpha beam source to detect the reflection of alpha particles.
What did Rutherford and Marsden expect to see from their experiment?
Very little deflection.
What happened when the alpha beam was fired at the gold foil?
Most of the particles went straight through apart from the odd one that shot back at them.
What did Rutherford conclude from their experiment?
- Most of the atom must be empty space as alpha particles passed right through the foil.
- The nucleus must be positively charge to deflect the positively charged alpha particles so much.
- The nucleus must be very small as very few alpha particles were deflected at all.
What three particles are found in an atom? What are their charges?
- Electrons (-)
- Protons (+)
- Neutrons (none)
What does the nucleus of an atom contain?
Neutrons and protons which gives it its positive charge.
Where are the electrons found in an atom?
Orbiting the nucleus in energy shells.
Hay are the relative masses of the three particles in an atom?
Proton / 1
Neutron - 1
Electron - Negligible
Why do atoms have no overall charge?
Because they have the same amount of protons and electrons which cancel each others’ charges out.
What is an ion? The
A charged atom.
What is atomic number?
The number of protons in the nucleus of an atom
What is the mass number?
The number of protons plus the number of neutrons in the nucleus of an atom.
What are isotopes?
Forms of the same elements with different numbers of neutrons in their nuclei.
What are radioactive substances?
Substances that give out radiation from the nuclei of their atoms at all times.
What is the purpose of radioactive decay?
For unstable isotopes to decay into stable isotopes.
What are the three types of radioactive decay?
Alpha, beta and gamma.
What is an alpha particle made of?
Two neutrons and two protons - the same as a helium nucleus.
What happens when an atom undergoes alpha decay?
Two neutrons and two protons are lost from its nucleus.
How penetrative are alpha particles?
Not very. They are stopped quickly because they are big, heavy and slow.
How ionising are alpha particles and why?
They are strongly ionising beside of their size. They knock into a lot of atoms and knock electrons off them which created a lot of ions.
What is a beta particle?
An electron.
What happens when an atom undergoes beta decay?
A neutron turns into a proton and an electron is released.
What are five qualities of a beta particle?
- Moderately fast
- Quite small
- Moderately penetrative
- Long range in air
- Moderately ionising
What are gamma rays?
Very short wave RM waves with no mass or charge.
What are three qualities of gamma rays?
- Very penetrative
- Pass straight through air
- Weakly ionising as they usually pass atoms but are extremely destructive when they do hit something
How are alpha particles shown in equations?
Either as He or α with an atomic number of 2 and a mass number of 4.
How are beta particles shown in equations?
Either as e or β with a mass number of 0 and an atomic number of -1.
How are alpha and beta particles affected by magnetic fields?
- They re deflected in opposite directions
* Alpha particles are deflected less than beta particles because of their greater masses despite feeling a larger force
What is half-life?
The average time it takes for the number of nuclei of a radioactive isotope in a sample to halve.
What does a short half life mean?
The activity falls quickly because lots of the nuclei decay quickly.
What does a long half-life mean?
The activity falls slowly because most of the nuclei don’t decay for a long time.
What is a Geiger counter?
A particle detector that measures activity.
How is half life found on a graph?
By finding the time interval in the x axis corresponding to the halving of the activity on the y axis.
What is a radiation dose?
The amount of energy absorbed by your body from radioactive radiation.
What two factors affect radiation dose?
- The type of radiation you’re exposed to
* The amount of radiation you are exposed to
What are three sources of background radiation?
- Radioactivity of naturally occurring unstable isotopes in air, food, rocks and building materials
- Cosmic rays
- Nuclear waste and other man made sources
What two locational factors affect the amount of radiation you are exposed to?
- Certain underground rocks give off more radiation at the surface
- People at high altitudes are exposed to more cosmic rays
What four occupational factors can lead to you being exposed to more radiation?
- Nuclear industry workers are exposed to 10% the normal amount of radiation
- Radiographers are exposed to lots of radiation
- People who work at high altitudes are exposed to more cosmic waves
- Underground work increases radiation dose
What can the effects of low doses of radiation be on cells?
They can cause minor damage without killing cells which can give rise to mutant cells which divide uncontrollably and form a tumour.
What can the effects of high doses of radiation be on cells?
The cells can die leading to radiation sickness.
What forms of radiation are most dangerous outside the body?
Beta and Anna because they are very penetrative.
What form of radiation are most dangerous inside the body?
Alpha because it is the most ionising.
What precautions can be taken when working with radioactive materials?
- Only use them for short amounts of time
- Never allow skin to come into contact with the source - use tongs
- Hold the source at arms length to decrease the amount of radiation that hits you
- Keep the source pointing away from you and avoid looking directly at it
What element absorbs all three types of radiation?
Lead
What are three uses of lead to protect you from radiation?
- Radioactive sources are kept in lead boxes
- Medical professionals wear lead aprons and stand behind lead screens
- During a medical procedure, the patient is covered with lead anywhere the radiation does not need to act
What are four uses of radioactivity?
- Smoke detectors
- Medical tracers
- Radiotherapy
- Sterilisation
What type of radiation do smoke detectors use?
Alpha
How do smoke detectors work?
A weak source of alpha radiation is placed in the detector close to two electrodes. The alpha particles cause ionisation of molecules in the air which frees electrons allowing a current to flow between the two electrodes. If there is smoke, the smoke will absorb the radiation and the current will be broken, causing an alarm to sound.
Why can’t beta and gamma sources be used in smoke detectors?
Their range is too long so try pose a threat to homeowners,
Why should the alpha source in a smoke detector have a long half-life?
So that the source doesn’t need to be replaced too often.
What are medical tracers?
Certain radioactive isotopes that can be injected into people and then followed around the body using an external display.
What type of radiation is used for medical tracers?
Gamma or beta so that the radiation passes out of the body.
Why shouldn’t alpha radiation be used for medical tracers?
Because they are too ionising
What is radiotherapy?
The treatment of cancerous cells using ionising radiation.
What type of radiation is used for radiotherapy?
Gamma
Why does the radiation in radiotherapy need to be directed carefully?
So that only the target cells are killed.
What type of radiation is used for sterilisation?
Gamma rays which kill all microbes.
What is an advantage of using radiation over boiling for sterilisation?
Radiation doesn’t involve high temperatures so objects like apples and plastic instruments can be sterilised without being harmed.
What qualities should the isotope used for sterilisation have?
- Should be very strong
* Should have a good half life
