what is nuclear half life?

Question

it has a connectioon with chenistry. just definition,cause, effects and what does it have to do with us.

Answer 1

Under most conditions, radioactive substances decay into something else at a rate dependent only on the amount of substance still present. The half-life of a radioactive isotope is the time necessary for half of the substance to decay.

After one half-life, one half of the substance originally present will still be around. After a second half life, half of the substance present at the end of the first half-life will still be present, or one quarter of the original substance will still be present. After n half lives, (1/2)^n of the substance at the beginning of the experiment will still be around. This relationship also holds true value for nonnegative values of n that are not whole numbers.

Half-life is characteristic of the nucleus only. Changes in electron configuration, temperature, pressure, or the presence of surrounding nonradioactive nuclei do not affect this half-life. A high concentration of neutron-emitting isotopes can hasten the decay of certain isotopes, sometimes with very explosive results. The fission bomb is based on this principle. However, that is about the only exception I can think of that would change the rate of nuclear decay that would happen outside of the laboratory.

Aside from fission reactions precipitated by neutron bombardment, radioactive decay is the only known way to get rid of radioactive material. This occurs at a fixed and highly predictable rate, so locking the stuff away for a minimum amount of time is the only known way to get rid of it. Fortunately, the really hot stuff has a short half-life and the stuff with a long half-life doesn't produce much radioactivity in a given amount of time. It is the stuff with a half-life of years or decades that is the most troublesome to be rid of - long-lived enough to be troublesome but still radioactive enough to be dangerous.

One use of isotopes with long half-lives is in dating archeological artifacts or materials. Certain radioactive isotopes, notably carbon-14, are continuously generated naturally. As long as organisms are alive, they take in this carbon 14 and renew it within themselves. This process stops when the organism dies, thereby starting a radioactive clock by which the remains of the organism can later be dated.

This includes such things as wood, leather, cloth, animal bones, and other artifacts from which manmade objects can be constructed. Because the organisms from which artifacts are made are usually killed within a few months of constructing the artifact, this makes a good way of dating artifacts from organic materials. This also includes the ashes from long-dead campfires.

Radioactive isotopes, usually very small amounts with short half-lives, are also used in medical diagnosis and in medical and biochemical research as tracers and stand-ins for their nonradioactive counterparts. Larger amounts, carefully placed, have also been used for destroying otherwise inoperable tumors and for other medical treatments. Small amounts of radioactive isotopes are also key parts of many smoke detectors, particularly battery-operated ones.

Answer 2

Half-Life = The time it takes for the released radiation of a nuke to decrease 50%.

Answer 3

Half Life is the amount of time it takes for a radioactive substance to lose half of its radioactivity.

For example, if the half life of something is 10,000 years, then it will take 10,000 years for the substance to lose half of its radioactivity. It will then take another 10,000 years to lose half of its remaining radioactivity, and another 10,000 years to lose half of that, and so on, and so on.

Answer 4

RADIOACTIVE HALF-LIFE
Not all of the atoms of a radioisotope decay at the same time, but they decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life. The half-life of a radioisotope describes how long it takes for half of the atoms in a given mass to decay. Some isotopes decay very rapidly and, therefore, have a high specific activity. Others decay at a much slower rate.

How do you measure the decay of radioactive isotopes?

Now that we have an idea of how radioactive isotopes decay, let's look at how this is measured and apply the terms we just learned.

The basic unit of measure for describing the activity (radioactivity) of a quantity of radioactive material is the curie, named after Marie Curie. A quantity of radioactive material is considered to have an activity of 1 curie or 1 C, when 37 billion of its atoms decay (disintegrate) in one second. In scientific terms, this is expressed by the equation: 1C = 3.7 X 1010 disintegrations/sec. Remember that we said each isotope has its own decay pattern. If the rate of decay is greater than 37 billion atoms in one second, then the source would have an activity greater than one curie, and if that source had fewer than 37 billion atoms decaying in one second, its activity would be less than one curie.

Now that you know that the activity of a radioactive source is the measure of the number of atoms that decay each second and that the activity varies as a function of the size of the source, let's see why half-life is important.



As we have mentioned before each radioactive isotope has its own decay pattern. Not only does it decay by giving off energy and matter, but it also decays at a rate that is characteristic to itself. The rate at which a radioactive isotope decays is measured in half-life. The term half-life is defined as the time it takes for one-half of the atoms of a radioactive material to disintegrate. Half-lives for various radioisotopes can range from a few microseconds to billions of years. See the table below for a list of radioisotopes and each of unique their half-lives.

Radioisotope Half-life
BPolonium-215 0.0018 seconds
ismuth-212 60.5 seconds
Sodium-24 15 hours
Iodine-131 8.07 days
Cobalt-60 5.26 years
Radium-226 1600 years
Uranium-238 4.5 billion years

How does the half-life affect an isotope?

Let's look closely at how the half-life affects an isotope. Suppose you have 10 grams of Barium-139. It has a half-life of 86 minutes. After 86 minutes, half of the atoms in the sample would have decayed into another element, Lanthanum-139. Therefore, after one half-life, you would have 5 grams of Barium-139, and 5 grams of Lanthanum-139. After another 86 minutes, half of the 5 grams of Barium-139 would decay into Lanthanum-139; you would now have 2.5 grams of Barium-139 and 7.5 grams of Lanthanum-139.

How is half-life information used in carbon dating?

The half-lives of certain types of radioisotopes are very useful to know. They allow us to determine the ages of rocks and fossils. Scientists can use the half-life of Carbon-14 to determine the approximate age of organisms and objects less than 40,000 years old. By determining how much of the carbon-14 has transmutated, scientist can calculate and estimate the age of a substance. This technique is known as Carbon dating. Isotopes with longer half-lives such as Uranium-238 can be used to date objects millions of years old.