SMSH-PROJECTS-HALF LIFE CALCULATIONS-10/12/23
element
A pure substance made of only one kind of atom
neutron
A small particle in the nucleus of the atom, with no electrical charge
radioactive decay
A spontaneous process in which unstable nuclei lose energy by emitting radiation
electron
A subatomic particle that has a negative charge
20
Initially, there are how many parent atoms? (Write answer as a number)
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
15 mg
Ac-228 has a half life of 6.13 hours. Approximately how much of a 240.0 mg sample would remain after one day? (Hint: round 6.13 to the nearest whole number)
5700
Approximately what is the half-life of carbon 14?
88
Approximately what percentage of daughter material is present when the third half life is reached.
75
Approximately what percentage of daughter material is there in ninety-four days?
isotopes
Atoms of the same element having different masses because they contain different numbers of neutrons.
25 grams
Chromium-48 decays. After 25 half-lives, what part of 800 grams would remain?
47 days
How long is the half-life of mercury-203?
30 minutes
If 20.0 g of a radioactive isotope are present at 1:00 PM and 5.0 g remain at 2:00 PM, what is the half life of the isotope?
protons
Positively charged particles
stable
Radioactive decay stops when the nucleus becomes ___.
50%
The half life of Uranium-238 is 4.5 billion years and the age of earth is 4.5 X 109 years. What fraction of Uranium-238 that was present when Earth was formed still remains?
75 mg
The half life of iodine-125 is 60 days. If the initially sample is 4800 mg, how much will of iodine-125 would be left after 360 days?
3200
The half life of radium 226 is 1602 years. If you have 500 grams of radium today how many grams would have been present 9612 years ago?
15
The halflife of Na-25 is how many hours?
parent element
The original element before it turns into another element through decay.
half life
Time it takes for half of an isotope to decay
gamma rays
Which are more dangerous: gamma rays, alpha particles or beta particles?
gamma rays
_____ is produced during radioactive decay in the form of energy from the nucleus.
alpha particles and beta particles
______ and _____ are given off when a nucleus has too many protons or an unstable ratio of protons to neutrons
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
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
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
daughter element
the new element that results from the radioactive decay of the parent element
