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39 Cards in this Set

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  • Back
At what point will atomic elements start to undergo radioactive decay
generally above with a Z greater than or equal to Po (84)
From what point are atomic elements considered artificial (not naturally occurring)
at Z greater than 92
nuclear stability ratio in smaller nuclei
stability achieved when (A-Z)/Z is 1
nuclear stability for larger nuclei
(A-Z)/Z is greater than 1 (1.2-1.4), need greater number of protons
which element has the most stable isotopes
Tin (Sn) with 10 stable isotopes
2 points of view from which to consider nuclear stability
thermodynamic (PE of a particular nucleus as compared with PE sum of its component protons and neutrons) and kinetic (proba that nucleus will undergo radioactive decay)
what combinations of protons and neutrons seem to confer special stability
nuclides with even numbers of protons and neutrons (more stable than odd counterparts), magic numbers (2,8, 20,28,50,82,126) patterns similar to atoms (noble gases)
beta particle
represents an electron, neg. charge and no mass, emitted during nuclear decay, but does not exist inside nucleus, is a product of reaction (a given quantity of energy can become a particle under certain circumstances)
beta particle production
occurs in smaller nuclei, as mass number stays same, neutron/proton ratio decreases (only reaction where this occurs)
what is the net effect of beta particle production
to change a neutron to a proton (therefore expect nuclides that lie above zone of stability (more neutrons than protons) to be beta particle producers
gamma ray
refers to high-energy photon, freq. accompany nuclear decays and particle reactions, 2 gamma rays of diff. E are produced with an alpha particle
how can a nucleus with excess E relax to its ground state
emitting a gamma ray (pure energy)
positron production
occurs for nuclides below zone of stability (few neutrons compared to protons), its net effect is to raise the neutron proton ratio by changing proton to neutron (emit +1)
positron
particle with same mass (0) of electron, but opposite charge
annihilation
when particle (beta particle) and antiparticle (positron) collide, the particulate matter is changed to electromagnetic radiation in form of gamma ray (high E photon)
electron capture
process in which one of inner-orbital electrons is captured by nucleus, results in 1 less proton (higher neutron/proton ration), might have interested alchemists if faster rate
rate of decay
negative in the change in the number of nuclides per unit time (-ΔN over Δt), directly proportional to number of nuclides in a given sample (neg. bc nuclides decreasing)
danger of Sr-90
Sr-90 is absorbed in grass, hay, and passed to humans through cow's milk, lodges in bones and bc of long half life (28.8yrs) causes radiation damage that may lead to cancer
another possibility of nuclear decay besides beta and alpha particle production
nuclear fission (splitting of heavy nuclei into smaller nuclides) and fusion (joining lighter nuclides into a heavier nuclei)
alpha particle
similar to He nucleus (4 mass, 2 protons)
alpha decay
results in ejection of positive particles, typically occurs in heavier nuclei
radiotracers and radiolabels
used to measure the speed of chemical processes and to track the movement of a substance through a natural system such as a cell or tissue
E=mc2
demonstrates a possible conversion btwn E and mass, for a small change in mass (mass defect), there is a corresponding change in E (binding E)
binding energy
represents how much E is needed to break down a nucleus into its components (nucleons)
binding E trends for nucleus vs. nucleons
total binding energy for nucleus is higher the greater the atomic number, but if you look at binding E per nucleon, trends are diff. (56-Fe is upper limit, most stable)
decay series
successive radioactive processes until a stable nucleus is achieved, usually a combo of alpha and beta decays
abundance and rates of reaction
diamond is more stable than graphite, but graphite is more abundant because its rate of reaction is faster
first order nuclear processes
all nuclear processes are first order processes, meaning the rate of reaction is directly proportional to the concentration of the reactant
nuclear transmutation
conversion of one chemical element or isotope into another. This occurs either through nuclear reactions (in which an outside particle reacts with a nucleus), or through radioactive decay (where no outside particle is needed)
nuclear fission
releases a tremendous amount of energy, typically initiated by neutron, (NB for every neutron used, 3 neutrons are produced, leads to supercritical situation if uncontrolled)
chain reaction
a self-sustaining process
subcritical
process dies out (less than 1 neutron causes another fission event)
critical
process sustains itself at an even level (exactly 1 neutron from each fission event causes another fission event)
supercritical
process escalates rapidly (if more than 1 neutron from each fission event goes on to cause another fission event)
critical mass
amount of substance that allows a critical reaction
geometric series
describes progression of nuclear fission reactions, (number of neutrons released increases in geometric progression)
how many neutrons are produced for every neutron used in a nuclear fission reaction
3 neutrons for every 1 neutron used (need a material to absorb other 2 neutrons produced)
nuclear fusion
occurs on sun, believed to be primary source of helium on earth, cannot be replicated because required extremely high temps (4x10 to the 7 K)
What does E=mc2 show
that there is a possible conversion btwn energy and mass