1 : the time required for half of something to undergo a process : such as. a : the time required for half of the atoms of a radioactive substance to become disintegrated.
What definition describes a half-life?
Half-life (symbol t 1 ⁄ 2 ) is the time required for a quantity to reduce to half of its initial value . The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive.
What are the 2 definitions of half-life?
Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve . Count-rate is the number of decays recorded each second by a detector, such as the Geiger-Muller tube. ... The half-life of radioactive carbon-14 is 5,730 years.
What is the scientific term for half-life?
or half life, half·life
Physics. the time required for one half the atoms of a given amount of a radioactive substance to disintegrate. Also called biological half-life . ... the time required for the activity of a substance taken into the body to lose one half its initial effectiveness.
What are the types of half-life?
The range of half-lives is boundless . There are isotopes with half-lives of nsec, μsec, msec, sec, hr, min, days, weeks, months, years, centuries, millennia, and even as long as a billion years (half-life of K-40 = 1.28 x 109 years).
What is the best definition of half-life?
Half-life, in radioactivity, the interval of time required for one-half of the atomic nuclei of a radioactive sample to decay (change spontaneously into other nuclear species by emitting particles and energy), or, equivalently, the time interval required for the number of disintegrations per second of a radioactive ...
What does half-life mean for drugs?
The half-life of a drug is the time it takes for the amount of a drug's active substance in your body to reduce by half . This depends on how the body processes and gets rid of the drug. It can vary from a few hours to a few days, or sometimes weeks.
How do you calculate half-lives?
How to calculate half life? To find half-life: Divide ln 2 by the decay constant of the substance .
How does half-life work?
The half-life of a drug is an estimate of the period of time that it takes for the concentration or amount in the body of that drug to be reduced by exactly one half (50%). ... For example, if 100mg of a drug with a half-life of 60 minutes is taken, the following is estimated: 60 minutes after administration, 50mg remains.
Why is it called a half-life?
It's easy misinterpret half-life to mean “one half of the time it takes for whatever atoms you're looking at to decay,” but it actually means “ the length of time it takes for one half of the atoms you're looking at to decay .” The measurement is useful in radiometric dating, says Dee, because exponential decay means “it ...
Why is half-life important?
Knowing about half-lives is important because it enables you to determine when a sample of radioactive material is safe to handle . ... They need to be active long enough to treat the condition, but they should also have a short enough half-life so that they don't injure healthy cells and organs.
Why do radioisotopes differ in the length of their half lives?
Different radioisotopes may vary greatly in their rate of decay. That's because they vary in how unstable their nuclei are . The more unstable the nuclei, the faster they break down.
Who is the main character of half-life?
Gordon Freeman, Ph. D. , is the silent protagonist of the Half-Life series and the playable character in Half-Life and all games in the Half-Life 2 series. He is a theoretical physicist and holds a Ph. D.
What does a 30 year half-life mean?
Physical Half Life is the time for a quantity of radioisotope to decay by half (Cs-137 = 30 years) Biological Half Life is the time for 1/2 of the amount of a radionuclide to be expelled from the body (CS-137 = 70 to 100 days)
What is effective half time?
The time required for the activity of a particular radioisotope deposited in a living organism , such as a human or an animal, to be reduced by 50 percent as a result of the combined action of radioactive decay and biological elimination.
