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.

The longer the half-life of a nucleus, the lower the radioactive activity. A nucleus with a half-life that is a million times greater than another will be a million times less radioactive. A ‘half-life’ is defined as the amount of time taken for the number of nuclei present in a sample at a given time to exactly halve.

No, the half-life defines the ratio and the number of stable atoms. The percent of decrease is the same no matter how many atoms you start with. By looking at the ratio of carbon-12 to carbon-14, they can calculate back to the amount of original carbon-14 using the carbon-14 half-life of 5,730 years.

The half-life of a radioactive isotope is the amount of time it takes for one-half of the radioactive isotope to decay. The half-life of a specific radioactive isotope is constant; it is unaffected by conditions and is independent of the initial amount of that isotope.

Half-life (symbol t1⁄2) 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.

Scientists can use their knowledge of radioactive decay and half-lives to determine the age of many things, including skeletal remains. One method used to determine the age of bones is the Carbon-14 method. Carbon-14 is a radioactive isotope of carbon that is found in all living things.

After 6 hours, there will be only 50-mg of technetium-99m. After 12 hours, the amount will half again and there will be 25-mg of technetium left.

Radioactive decay law: N = N.e-λt The rate of nuclear decay is also measured in terms of half-lives. The half-life is the amount of time it takes for a given isotope to lose half of its radioactivity. If a radioisotope has a half-life of 14 days, half of its atoms will have decayed within 14 days.

Half-life (t½) is the time required to reduce the concentration of a drug by half. The formula for half-life is (t½ = 0.693 × Vd /CL) Volume of distribution (Vd) and clearance (CL) are required to calculate this variable.

As you can see from this table, the amount of reactant left after n half-lives of a first-order reaction is (1/2) n times the initial concentration….Half-Lives.

Average number of radioactive decays per unit time (rate) • or – Change in number of radioactive nuclei present: A = -dN/dt • Depends on number of nuclei present (N). During decay of a given sample, A will decrease with time.

An example will show the use of this equation. For the decay reaction 238U → 234Th + 4He, the mass values for 238U and 4He are in Table 3.1; for 234Th it is 234.043 594. Thus we obtain Qα = –931.5 (234.043 594 + 4.002 603 – 238.050 7785) = 4.274 MeV.

The rate of decay, or activity, of a sample of a radioactive substance is the decrease in the number of radioactive nuclei per unit time.

Suppose N is the size of a population of radioactive atoms at a given time t, and dN is the amount by which the population decreases in time dt; then the rate of change is given by the equation dN/dt = −λN, where λ is the decay constant.

decay chainThe series of decays or transformations that radionuclides go through before reaching a stable form. For example, the decay chain that begins with Uranium-238 culminates in Lead-206, after forming intermediates such as Uranium-234, Thorium-230, Radium-226, and Radon-222. Also called the “decay series.”.

When a radioactive substance decays, it emits particles from the nucleus in a effort to become a stable atom. To fill in the chart, a periodic table of the elements is needed. If an alpha particle is emitted, the atomic number decreases by 2 which will produce a new element.

Definition. The decay constant (symbol: λ and units: s−1 or a−1) of a radioactive nuclide is its probability of decay per unit time. The number of parent nuclides P therefore decreases with time t as dP/P dt = −λ.

Half-life is the time required for half the atoms in a sample to decay. Example (answers may vary): For C-14, the half-life is 5770 years. A 10-g sample of C-14 would contain 5 g of C-14 after 5770 years; a 0.20-g sample of C-14 would contain 0.10 g after 5770 years.

A more precise definition of half-life is that each nucleus has a 50% chance of living for a time equal to one half-life t1/2. Thus, if N is reasonably large, half of the original nuclei decay in a time of one half-life.

25 percent

Explanation: The “half-life” of a sample of radioactive isotope is defined as the amount of time it takes for half of the nuclei in the sample to decay. This is called Carbon Dating, and is accurate out to about 50,000 years (about 10 half-lives).