• mean lifetime — symbol τ — … a. To determine the activity, we first need to find the number of nuclei present. For a particular decay mechanism, the radioactive decay constant for a nuclide is defined as the probability per unit time that a given nucleus of that nuclide will decay by that mechanism. Strategy. The Lambda logo (λ) is a symbol found frequently in the Half-Life universe. The decay rate, or activity, of a radioactive substance are characterized by: Constant quantities: • half life — symbol t1/2 — the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value. 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. We can find the decay constant directly from Equation \ref{eq8}. Potassium-40 (40 K) is a radioactive isotope of potassium which has a long half-life of 1.251 × 10 9 years. It represents the Greek letter "Λ" (lowercase "λ"), and is a radioactive decay constant used in the half-life equation. A = activity in becquerel (Bq) N = the number of undecayed nuclei l = decay constant (s-1) Radioactive decay law. The value of the decay constant depends on the nature of the particular decay process. "Λ" is the 11th letter in the Greek alphabet. The probability to decay/time is termed the ”decay constant”, and is given the symbol λ. Find (a) its decay constant and (b) the initial activity of 1.00 g of the material. activity = decay constant x the number of undecayed nuclei. This method will work with any of the symbols above, substituting the appropriate code before typing ALT+X. Solution. Here, the symbol k is the radioactive decay constant, which has units of inverse time (e.g., s −1, yr −1) and a characteristic value for each radioactive isotope. * mean lifetime - symbol τ - the average lifetime of any given particle. A half-life is the time it takes for half of the nuclei to disappear. The decay constant l is the probability that a nucleus will decay per second so its unit is s-1. The decay constant is found to be P = λ Δt If you have the Lucida Sans Unicode font available, this will type the equilibrium symbol without going to the insert symbol menu. The half-life of strontium-90, $$\ce{_{38}^{90}Sr}$$, is 28.8 y. The energies involved in the binding of protons and neutrons by the nuclear forces are ca. 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