Ch8: Radioactivity Flashcards
Name the 3 scientists who contributes to the discovery of radioactivity?
-Henri Becquerel
-Marie Curie
-Pierre Curie
How did Becquerel contribute to the discovery of radioactivity?
He observed that some form of radiation, emitted by uranium was able to penetrate paper and affect a photographic plate. He later found that radiation was emitted continuously and spontaneously (did not need to be treated by light/heat)
-Left uranium salts resting on a photographic plate that was wrapped in black paper
-Plate became darkened in the area near uranium salt
How did the Curies contribute to the discovery of radiation
They extracted two new radioactive elements from an ore (of uranium) pitchblende
-Polonium
-Radium
What is radioactivity?
The spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation
What are3 types of radiation?
-Alpha particles
-Beta particles
-Gamma radiation
Alpha particles:
1. Composition
2. Charge
3. Mass? Speed?
4. Penetrating power
5. Name an alpha emitter
6. Risk
- 2 protons, 2 neutrons
- Positive
- Relatively large mass, relatively slow
- Low penetrating power, stopped by a few cm of air or a sheet of paper
- Americium-241 (smoke detectors)
- Harmless bc low penetrating power but harmful of inhaled or ingested
Beta Particles:
1. Composition
2. Charge
3. Mass? Speed?
4. Penetrating power
5. Name a beta emitter
- Results when a neutron in a nucleus splits into a proton and an electron. Proton stays in the nucleus but electron is ejected from the nucleus. This high speed electron is a beta particle
- Negative
- Lighter, high speed
- More penetrating than alpha, can penetrate up to 5mm of aluminium
- Carbon-14 (radiocarbon dating)
How does radioactivity disprove Dalton’s Atomic Theory?
The only place that the alpha and beta particles could be coming from is within the atoms of the radioactive-isotope
Explain gamma radiation
-Simply high-energy electromagnetic radiation similar to x-rays
-Does not consist of particles, does not have a mass
-Does not consistof charged particles therfore not deflected by electric or magnetic fields
-An unstable nucleus emits gamma radiation in order to lose surplus energy
Gamma radiation
1. Penetrating power
2. Name a gamma radiation emitter
3 . Risk
- High penetrating ability, only stopped by a thick slab of lead
- Cobalt-60 (used to kill cancer cells by focusing radiation on cancerous tissue)
- Most dangerous type of radiation due to high penetrating ability
How is radiation detected?
Geiger-Muller tube, connected to a ratemeter
What is a nuclear reaction?
Process that alters the composition, structure or energy of an atomic nucleus
Differences between chemical vs. Nuclear reactions
Chem: involves electrons rather than nucleus
Nucl: Changes take place in nucleus
C: no new element formed
N: New element formed (transmutation)
C: No release of nuclear energy
N: Nuclear energy released
C: Chemical bonds broken and formed
N: no chemical bonding involved
What type of radiation does not make new atoms when lost?
Loss of gamma radiation doesnot give rise to any new atoms, the energy is simply lost from the nucleus
What is half-life?
The time taken for half of the nuclei in any given sample to decay
What section of the periodic table contains many radioactive elements?
Lanthanide and Actinide series
What is a radioisotope?
Radioactive isotope
What are different uses for radioisotopes?
-Medical uses: radiotherapy, sterilisation
-Archaeology: radiocarbon dating
-Food irradiation: kills germs
What is radiocarbon dating?
Technique used to determine the age of an object containing carbon. It is based on the ratio of carbon-14 to carbon-12 in the object
