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Description
Flashcards by Aaishah Din, updated more than 1 year ago
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Created by Aaishah Din
about 6 years ago
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| Question | Answer |
| What is a radioactive substance? | Radioactive substances are substances that emit radioactivity. |
| Why are some nuclei unstable? | In unstable nuclei, the strong nuclear forces do not generate enough binding energy to overcome the repulsion force inside the nucleus. Or, substances could be radioactive if the proton:neutron ratio is too big or small. |
| An unstable nucleus becomes stable by. . . | . . . emitting alpha, beta, or gamma radiation- decays. Decaying is a random event that happens with nothing being done to the nucleus |
| What is decaying? | emitting radiation. |
| Give two properties of radioactive subtsances. | 1) Decaying is completely random. 2) The probability of decay is the same for each nucleus |
| What is a geiger counter and how does it work | A Geiger counter is a machine used to detect radioactivity. The counter clicks each time a particle of radiation enters the tube. |
| What was Rutherford's alpha particle scattering experiment? | Rutherford's experiment involved a vacuum chamber, to prevent air molecules absorbing the alpha particles. Each time an alpha particle was shot, a small dot of light was observed. |
| What were the results of this experiment? | --> Most of the particles went straight through --> some were partly deflected --> very, very few were deflected at angles over 90 degrees. |
| What did the results show | 1) atoms are mostly empty space 2) a positive, concentrated, central, small nucleus 3) electrons are very light |
| Why was it accepted | 1) Rutherford + co were respected 2) it predicted the existence of the neutron 3) explained radioativity |
| what determines if a nucleus is unstable | - too many protons or neutrons disturb the balance, disrupting the binding energy from the strong nuclear forces causing the nucleus to be unstable. |
| Nuclei with atomic no above __ are radioactive | 83. |
| ALPHA | - same as a helium atom - proton no goes down by 2 - mass no goes down by 4 - travels a few cms in air - stopped by paper - most ionizing, least penetrating - slightly deflected in field |
| BETA | - a high speed, energy electron - mass no. of 0, atomic no. -1 - mass no doesn't change, atomic no goes up by one - medium penetration/ionization highly deflected in field travels ms stopped by aluminum |
| GAMMA | - electromagnetic ray - unlimited range of air stopped by lead (thick) - isn't deflected in field |
| What is background radiation? | radiation from unstable nuclei in materials around us and in the atmosphere |
| how to take background radiation into account | 1) measure count rate without source 2) measure count rate with source ans to step 2) minus ans to step 1 |
| how to test different materials | place material between Geiger Counter and source add more layers till the count rate is 0 the radiation had been stopped |
| How to test the range | move the source away from the tube. when the source is beyond the range of radiation, the count rate will be 0. |
| Define ionization. | when electrons are knocked out of atoms, making them have a charge, because of radiation. |
| define irradiated | when an object is exposed to ionising radiation |
| define contamination | unwanted presence of materials containing radioactive atoms on other materials |
| how to avoid radiation | keep as far away as possible spending little time at at-risk areas shielding yourself with concrete barriers long tools, special handles |
| Define peer review | when findings are published and shared with other scientists so they can check them |
| define activity | The number of unstable atoms emitted per second or the decay of a substance per second |
| half life | the period of time it takes for the number of radioactive nuclui of isotops in a sample to halve. |
| count rate | number of counts per second |
| count rate after N half lives | Initial count rate / 2^n |
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