atomic physics Flashcards
What does Rutherford’s nuclear model of an atom state
- an atom consists of a positively charged centrally located nucleus which makes up almost the entire mass of the atom
- it is surrounded by orbits filled with negatively charged electrons that remain in a circular path around the nucleus due to the strong electrostatic force of attraction between the positive nucleus and the negatively charged electrons
What are the observations and conclusions of the greiger-marsden alpha-particle scattering experiment
(through a thin gold foil)
- the majority of particles go straight through without deflection (conclusion: this happens because majority of the space inside the atom is empty)
- some are deflected at angles less than 90deg (conclusion: this is because there is a positive charge in the atom)
- very few are deflected at angles greater than 90/backscattered
(conclusion: the nucleus with positive charge takes up a very small space inside the atom)
what is nuclear fission
when large unstable nuclei break up into smaller nuclei and the process releases energy. This occurs in power stations
what is nuclear fusion
nuclear fusion takes place in stars like the sun and is the process in which smaller nuclei collide with each other at high speeds to form larger nuclei and release energy in the process.
what is a nuclear reaction
the nucleus reacts and we balance mass numbers and atomic numbers
what is background radiation
background radiation is always present in the environment around us
natural sources of background radiation
radioactive argon gas present in the atmosphere, radioactive rocks and minerals beneath the earth’s surface and background cosmic radiation from outer space
artificial sources of background radiation
uses of radioactive isotopes in medicine, radioactive waste from nuclear power stations and nuclear weapons
ways to detect radiation
- photographic film
- geiger-muller tube/counter (GM tube)
- gold-lead electroscope
- scintillation counters
- spark counters
properties of radioactive emission
- spontaneous: can occur without excitation or external factors
- random: we do not know which radioactive atom is going to decay at a certain point of time but we know that a fixed proportion of atoms will decay in a period of time
what are alpha particles
- consists of 2 protons and 2 neutrons
- essentially a helium nucleus
charge of alpha particles
2+
range of alpha particles in air
2cm
penetration of alpha particles
stopped by paper
ionization of alpha particles
high
what is a beta particle
a high speed electron
charge of beta particles
-1
range of beta particles in air
few 10s of cm
penetration of beta particles
stopped by few mm of aluminium
ionization of beta particles
medium
what are gamma rays
electromagnetic waves
charge of gamma rays
0
range of gamma rays in air
infinite
penetration of gamma rays
reduced by few mm lead
ionization of gamma rays
low
deflection of gamma rays in electrical field
passes straight through
deflection of alpha radiation in electric field
deflected towards negatively charged plate
deflection of beta radiation in electric field
deflected towards positively charged plate
deflection of gamma radiation in magnetic fields
gamma radiation passes straight through without any deviation
deflection of alpha and beta radiation in magnetic fields
- both deflected in opposite directions (which can be found using Flemings left hand rule)
- beta particles deflect more than alpha particles as they are much lighter
what is ionisation
the process by which electrons are removed or added to a substance by applying energy
why does alpha ionise the most
-greater mass and charge
why do alpha particles have the shortest range
- they ionise virtually every atom they pass
- so they lose energy quickly and have a short range
why do beta particles have a moderate range
- the particles create a less dense trail of ions than alpha, and consequently have a longer range
- they tend to be more dangerous than alpha because they are able to travel further and penetrate skin yet are still ionizing enough to cause damage
why do gamma rays have unlimited range
they are the least ionizing form of radiation
common uses of radiation
- controlling thickness of material
- medical tracers to detect blood clots
- industrial tracers to detect leaks in pipes
- cancer treatment
- sterilization
- smoke detectors
what is radioactive decay
-occurs due to the presence of unstable nuclei in some isotopes, as a result they emit radiation to become stable
alpha/beta radiation in radioactive decay
affects the composition of the nucleus and changes to that of a different element
gamma radiation in radioactive decay
does not affect the composition of the nucleus and is released only after alpha or beta emission to get rid of excess energy in the nucleus
what is the half life of an isotope
the time taken for the number of original nuclei to drop to half of its initial value/the time taken for half a radioactive substance to decay (can be found from a nuclide graph)
what can radioactive radiation cause to living cells
- mutations
- breed cancerous cells
- may kill living cells
safety precautions for radioactive radiation
- store the sources in lead-lined boxes
- minimise the amount of time you handle sources for and return them to their boxes as soon as you have finished using them
- stay at a safe distance from the radioactive source
- when handling sources do so at an arm’s length, using a pair of tongs or forceps and other source-handing tools
- wear protective clothing
