The theory of nuclear astrophysics is that all the heavy elements like uranium are formed in the interior of massive stars. These stars eventually explode, releasing the elements into space. If we assume that at the time of explosion there were equal amounts of 235 U and 238 U, how long ago were the elements that formed our Earth released, given that the present 235U/238U ratio is 0.007? (The half-lives of 235U and 238U are 0.70 × 109 yr and 4.47 × 109 yr, respectively.)

A piece of charcoal (totally carbon) from an ancient campsite has a mass of 262 grams.  It is measured to have an activity of 29 Bq from 14C decay.  Use this information to determine the age of the campfire.   Your answer is required to be in years. Information:    14C half-life is 5730 years. 1 gram of living carbon has 6.52x1010 atoms of 14C

The radioactive isotope of lead ^209Pb decays according to the differential equation dN/dt=-kN.  The isotope has a half-life of 3.3 Hours.  If 1 gram is presented initially, how long will it take for 78% of the lead to decay?

One of the ways that 235U can fission is by means of the following reaction: In +235 U 141 Ba + Kr + 3 n 56 Atomic masses of the reactants and products are as follows: n 235 U 92 92 Kr 36 141 Ba 56 1.008665 u 235.043930 u 91.926156 u 140.9144035 u a) Determine the energy in MeV that is released when one 23592U nucleus fissions. Assume that the incoming neutron is very slow. b) Find the total energy released in MeV if 2.8 kg of 23592U were to undergo fission entirely by this reaction.