Flashcards in module 4 Deck (46):
What did John Dalton Dalton and Democritus agree on?
matter was made up of tiny spheres (atoms) that couldn't be broken up, be Dalton thought each element was made from different types of atoms.
What did J.J. Thomson discover?
electrons, these could be removed from charge. Dalton's theory wasn't quite right. Thomson suggested atoms were spheres of positive charge with tiny negative electrons stuck in them-plum pudding model
What did Rutherford discover?
he fired alpha particles at thin gold foil-alpha scattering experiment. From plum pudding model expected them all to go through sheet or slightly deflected. Most went through some more deflected more than expected, few deflected back the way they came. Plum pudding model proved wrong.
How did Rutherford's experiment change the shape of the atom?
due to some alpha particles coming back scientist knew most mass of atom was concentrated in centre in tiny nucleus. Nucleus had positive charge since repelled positive alpha particles. Because nearly all went through most of atom was empty space-first nuclear atom
How did the atom look after Rutherford?
positively charged nucleus surrounded by cloud of negative electrons.
What did Niels Bohr discover?
electrons orbiting nucleus do it in certain distances called energy levels. His theoretical calculations agreed with experimental data. After Bohr further experiments found protons subatomic particle to make the nucleus positively charged.
What did James Chadwick discover?
proved existence of proton explained imbalance between atomic and mass numbers.
What does the current model of an atom look like?
the nucleus' radius is 10,000 times smaller than the atom. radius of atom is 1*10 to the power of -10 m. if electrons gain energy by absorbing EM radiation have to move to higher energy level far from nucleus (oppsite with other way round).
What is the atomic number?
number of protons.
What is an isotope?
an atom with different number of neutrons, all elements have different isotopes usually 1 or 2 stable ones. unstable decay and try to become stable by emitting radiation=radioactive decay. spit out 1 or more types of ionising radiation form nucleus, also release neutrons when decay. ionising radiation=radiation that knocks off electron-positive charged.
What is ionising power?
of radiation source is how easily it can knock off electrons.
How do alpha particles work?
emitted from nucleus. 2 protons and 2 neutrons. Don't penetrate far into materials stopped quickly. Can only travel a few CMs in air can be absorbed by paper. Large-most ionising. Used in smoke detectors. ionises air particles causes current to flow. Smoke-binds to ions, current stops and alarm sounds.
How do beta particles work?
fast moving electron. moderately ionising, penetrate moderately far into materials before colliding-range=few Meters. absorb by aluminium (5 mm thick). Per beta particle neutron turns to proton in nucleus. Used to test thickness of sheets of metals.
How do gamma rays/EM waves work?
electromagnetic radiation released by nucleus, penetrate far, have long range. weak at ionising tend to pass through than collide, eventually hit and do damage. Absorbed by thick sheets of lead or meters of concrete.
What are nuclear equations?
showing radioactive decay by using element symbols written: atom before decay=atom after decay+radiation emitted. Total mass and atomic numbers must be equal on both sides.
What is alpha decay?
atomic number reduces by 2 and mass number reduces by 4. proton is positive neutron is neutral so charge decreases. equation wirtten as helium nucleus top:4 bottom:2 He
When are gamma rays sometimes emitted?
When a nucleus decays by alpha or beta decay.
What is beta decay?
protons increase by 1-increase positive charge by 1. Nucleus lost electron but gained proton so no mass changes.
How does gamma decay work?
Gamma rays are a way of getting rid of excess energy from a nucleus. There is no change of the atomic mass or atomic number of an atom.
What is a radioactive substance and how do you measure radiation?
A substance that gives out radiation from nuclei of their atoms. Measured with Geiger-Muller tube and counter, records count-rate, number of radiation counts reaching per second.
What is radioactive decay?
Random. Can't predict which nucleus in sample will decay next, or when 1 will decay. Can find out time takes for amount of radiation emqitted by source to halve, known as half-life. Can be used to make predictions about radioactive sources, though decays are random. Half-life can be used to find rate which source decays-activity. Activity is measured in becquerels, Bq
What happens when a nucleus decays to become a stable nucleus?
Activity as a whole will decrease (older sources emit less radiation). For some isotopes it takes a few hours before nearly a unstable nuclei have decayed, others last millions of years.
What is the problem with trying to measure radioactivity?
Activity never reaches zero, this is why we have to use idea of half-life to measure how quickly activity drops off.
What is the half life?
Time taken for number of radioactive nuclei in an isotope to halve. Also time taken for activity, and so count-rate to halve. Short half-life means activity falls quickly, because nuclei are very unstable and rapidly decay. Sources with short half-life are dangerous because of high amount of radiation they emit at start, but quickly become safe.
What is a long half-life?
Activity falls more slowly because most of nuclei don't decay for long time, source just sits there, releasing small amounts of radiation for long time. This can be dangerous because nearby areas are exposed to radiation for years or millions of years.
How do you plot half-life?
Activity against time. Found from graph by finding time interval on bottom axis corresponding to halving of activity on vertical axis.
What is background radiation?
Low-level radiation around all the time.
Where does the meaurments and subtraction of background radiation come from?
Radioactivity of naturally ocuring unstable isotopes all around us. Radiation from space called cosmic rays, mostly from sun, earth's atmosphere protects us. Human activity: fallout, nuclear explosions, nuclear waste-only represents tiny proportion of radiation.
What does the radiation dose tell you?
Risk of harm of body tissue due to exposure to radiation. Measured in sieverts (Sv). Dose from background radiation is small, so millisieverts often used (1Sv=1000 mSv). Your radiation dose varies depending on where live, what job.
What is irradiation, and how is it prevented?
Objects near radioactive source are irradiated by it-exposed to it. Irradating something doesn't make it radioactive. Keeping sources in lead-lined boxes, standing behind barriers, or being in different room and using remote-controlled arms reduce effects or irradiation.
What is contamination?
If unwanted radiactive atoms get onto or into object, object is said to be contaminated. Contaminating atoms might then decay, releasing radiation-could cause harm. Contamination especially dangerous because radioactive particles get inside your body.
How is contamination prevented?
Gloves and tongs should be used when handling sources, to avoid particles getting stuck in skin or under nails. Some workers wear protective suits to stop breathing in particles.
How are beta and gamma rays harmful outside the body?
Can penetrate body and get to delicate organs. Alpha less dangerous-can't penetrate skin, easily blocked by samll air gap. High levels of irradiation from all sources are dangeous, especially from beta and gamma.
How are alpha particles dangerous inside the body?
Do damage in very iocalised areas. So contamination rather than irradiation, majour concern when working with alpha sources. Beta less damaging inside body, radiation absorbed over wider areas, some passes out body. Gamma least dangerous inside body, mostly pass straight out, lowest ionising power.
What are the risks of using radiation?
Can enter living cells and ionise atoms/molecules. Can lead to tissue damage. Lower doses cause minor damage without killing cells. Can give rise to mutant cells-divide uncontrollably-cancer. Higher doses kills cells-raidation sickness if lot of cells get blatted at once.
How are gamma sources useful?
Certain raioactive isotopes injected, progress around body, can be followed using an external detector. Computer converts reading to a display showing where strongest reading is coming from.
How is iodine useful in radiation?
Iodine-123 absorbed by thyroid gland like normal iodine-127, but gives out radiation-can be detected to indicate whether thuroid gland is taking in iodine as should.
How are isotopes useful in radiation in the body?
Isotopes taken into the body-usually gamma (never alpha), radiation passes out of body withou causing much ionisation. Have short half-life, so radioactivity inside patient quickly disappears.
What is radiotherapy?
High doses of ionising radiation kills all living cells, can treat cancer. Gamma rays directed carefully, at just right dosage to kill cancer cells and not damagind normal cells. Radiation-emmiting implants also be put next to or inside tumors. Some damage inevitably done to normal cells-sickness.
How do you weigh up the risks and benefits of radiation?
traces can be used to diagnose life-threatinig conditions, risk of cancer from 1 of tracer is small. Prolonged exposure to radiation pose risk in future, cause side effects. Many people with cancer have radiotherapy. Preceived risk-how risky a person thinks something is. Not same as actual risk of procedure and percieved risk can vary from person to person.
What is nuclear fission?
Type of nuclear reaction, releases energy from large unstable atoms, by splitting them into smaller atoms.
What are the steps involved in nuclear fission?
Spontaneous fission rarely happens. Nucleus absorbs neutron before splits. When splits 2 lighter elements roughly same size form. 2/3 neutrons also released when atom splits. If any slow enough moving neutrons-absorbed by other nucleus, cna cause more fission-chain reaction. Energy not transferred to kinetic energy stores of products is carried away by gamma rays. Energy carried by gamma rays an in kinetic energy stores of remaining free neutrons and other decay products used to heat water making steam-turn turbines and generators. Energy produced by fission controlled by changing how quickly chain reaction can occur-using control rods-lowered and raised in nuclear reactor. They abosrb neutrons.
What can an uncontrolled chain reaction cause?
Lots of energy being released as explosion-nuclear weapons.
What is nuclear fusion?
2 light nuclei collide at high speed and fuse, creates larger heavier nucleus.
What do heavier nucleus produced in fusion have?
Not as much weight as 2 separate light nuclei had. Some mass converted to energy-released as radiation. Fusion releases a lot of energy