A radioactive sample had an initial activity of 56 dpm . After 69.3 minutes, it was found to have an activity of 28 dpm . Find the number of atoms in a sample having an activity of 100 dpm.

A radioactive sample has initial activity of 28 dpm 30 minutes later its activity 14 dpm . How many atoms of nuclide were present initially?

._11^24Na (half-life=15hrs.) is known to contain some radioactive impurity (half-life=3hrs.) in a sample. This sample has an intial activity of 1000 counts per minute, and after 30 hrs it shows an activity of 200 counts per minute. what percent of the intial activity was due to the impurity ?

A radioactive sample has N_0 active at t = 0 . If the rate of disintegration at any time is R and the number of atoms is N , them the ratio R//N varies with time as.

A 0.2 mL sample of a solution containing 1.0xx10^(-7) curie of ._(1)^(3)H is injected to the blood stream of an animal. After sufficient time for circulatory equilibrium to be established, 0.10 mL of blood is found to have an activity of 20 dp m . Calculate the volume of blood in animal, assuming no change in activity of sample during circulatory equilibrium.

Half-life of radioactive sample, when activity of material initially was 8 counts and after 3 hours it becomes 1 count is

A radioactive sample S_1 having an activity of 5muCi has twice the number of nuclei as another sample S_2 which has an activity of 10muCi . The half-lives of S_1 and S_2 can be

A radioactive sample is alpha- emitter with half life 138.6 days is observed by a student to have 2000 disintegration/sec. The number of radioactive nuclei for given activity are.

A freshly prepared sample of a certain radioactive isotope has an activity of 10mCi. Afte 4.0h its activity is 8.00 mCi. (a) Find the decay constant and half-life How many atoms of the isotope were contained in the freshly preapared sample? (c) What is the sample's activity 30.0 h after it is prepared?

At some instant, a radioactive sample S_(1) having an activity 5 muCi has twice the number of nuclei as another sample S_(2) which has an activity of 10 muCi . The half lives of S_(1) and S_(2) are :

Two radioactive substances have half-lives T and 2T. Initially, they have equal number of nuclei. After time t=4T , the ratio of their number of nuclei is x and the ratio of their activity is y. Then,