Radioactive Decay & Half-Life Calculations, Fission and Fusion

radioactive decay

A spontaneous process in which unstable nuclei lose energy by emitting radiation

alpha decay

A nuclear reaction in which a nucleus ejects an alpha particle. the radioactive decay process in which the nucleus of an atom emits an alpha particle

A 208. g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 h. What is the half-life of this radioactive isotope?

15.0 h

All isotopes of technetium are radioactive, but they have widely varying half-lives. If an 800.0 g sample of technetium-99 to 100.0 g of technetium-99 in 639,000 y, what is its half-life?

213,000 years

What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 21.6 s?

7.2 s

mass number

the sum of the number of neutrons and protons in an atomic nucleus

The half-life of Iodine-131 is 8.07 days. If 25.0 g are left after 40.35 days, how many grams were in the original sample?

800. g

isotope

Atoms of the same element that have different numbers of neutrons

Half Life Graph - 2 hours

How long is one half life?

How much of a 500. g sample of potassium-42 is left after 62 hours?

The half-life of potassium-42 is 12.4 hours.half-life = 12.4 hours total time of decay = 62.0 hours initial amount = 500. g number of half-lives past: 62.0/12.4 = 5 half-lives 5 half-lives = 1/32 remains 500. g x 1/32 = 15.625 g ~15.6 g

alpha particle

a charged particle consisting of 2 protons and 2 neutrons emitted from the nucleus during radioactive decay

gamma ray

a high energy photon emitted by a nucleus during fission and radioactive decay

beta particle

an electron (or positron) that is emitted from a nucleus during radioactive decay

half-life

the time required for one-half of the atoms of a radioactive substance to decay

The half-life of hafnium-156 is 0.025 s. How long will it take a 500. g sample to decay to ¼ its original mass?

half-life = 0.025 s total time of decay = ? s initial amount = 500 .g 1/4 remains = 2 half-lives 2 x 0.025 s = 0.05 s

The half-life of radon-222 is 3.8 days. How much of a 100. g sample is left after 15.2 days?

half-life = 3.8 days total time of decay = 15.2 days initial amount = 100. g number of half-lives past: 15.2/3.8 = 4 half-lives 4 half-lives = 1/16 remains 100. g x 1/16 = 6.25 g

Carbon-14 has a half-life of 5,715 years. If a sample contains 70 mg originally, how much is left after 17,190 years?

half-life = 5,715 years total time of decay = 17,190 years initial amount = 70.0 mg number of half-lives past: 17,190/5,715 = 3 half-lives 3 half-lives = 1/8 remains 100.mg x 1/8 = 12.5 mg

The half-life of cobalt-60 is 5.26 years. If 50.0 g are left after 15.8 years, how many grams were in the original sample?

half-life = 5.26 years total time of decay = 15.8 years final amount = 50.0 g number of half-lives past: 15.8/5.26 = 3 half-lives 3 half-lives = 1/8 remains = 50.0 g 50.0 g x 8 = 400. g

If half-life of iodine-131 is 8.10 days, how long will it take a 50.00 g sample to decay to 6.25 g?

half-life = 8.10 days total time of decay = ? days initial amount = 50.00 g final amount remaining = 6.25 g 1/8 remains = 3 half-lives 3 x 8.10 days = 24.3 days

If 100 g of gold-198 decays to 6.25 g in 10.8 days, what is the half-life of gold-198?

half-life = ? days total time of decay = 10.8 days initial amount = 100. g final amount = 6.25 g 1/16 remains = 4 half-lives past 10.8 days/4 = 2.7 days = 1 half-life

25 kg.

how much remains after 3 half lives pass?

fission

process of a nucleus splitting into 2 or more fragments and releases neutrons and energy

beta decay

radioactive decay in which an electron is emitted.

nuclear energy

the energy stored in atomic nuclei The potential energy stored in the nucleus of an atom

Why are some isotopes radioactive?

the nucleus is unstable

fusion

the process of lighter nuclei combining at extremely high temperatures to form heavier nuclei and release energy