the rubidium isotope 87Rb is a beta emitter with a half-life of 4.9E10 y that decays into 87Sr. It is used to determine the age of rocks and fossils. Rocks containing the fossils of early animals contain a ration of 87Sr to 87Rb of 0.090. Assuming that there was no 87Sr present when the rocks were formed, calculate the age of these fossils. Answer in units of y.

Assume we start with 100 atoms Rb87 @ t=0 when the fossil just started to form. Then after some time, y will have disintegrated and formed Sr87. Thus 100-y will be the number of Rb87 atoms left.
(Sr87/Rb87)=0.090 from the problem.
Solve for y and 100-y

k = 0.693/t1/2= ??
ln(No/N) = kt
No = 100
N = 100 - y from above.
k = from above
solve for t, the age of the fossil.

  1. 👍 0
  2. 👎 0
  3. 👁 147
asked by Star

Respond to this Question

First Name

Your Response

Similar Questions

  1. physics

    The rubidium isotope 87Rb is a β emitter that has a half-life of 4.9 x 1010 y that decays into 87Sr. It is used to determine the age of rocks and fossils. Rocks containing the fossils of early animal have a ratio of 87Sr to 87Rb

    asked by Anonymous on October 10, 2012
  2. chemistry

    the longest lived radioactive isotope yet discovered is the beta-emitter has been determinded that it would take 2.4 x 10^21 years for 99.9% of this isotope to decay. write the equation for this reaction, and

    asked by penelope on July 12, 2010
  3. Chemistry

    Radioactive iodine-131 decays (beta emitter) to form Xenon-131. Iodine-131 has a half-life of 8.07 days. If a thyroid gland absorbed 20.0 microcuries of I-131 today, how many microcuries would remain after 30.0 days. Microcuries

    asked by Ceamus Angelina on July 1, 2018
  4. college chemistry

    The half-life of 13252Te is 3.26 days. This isotope decays by beta emission to a highly unstable intermediate that decays rapidly to a stable product by beta emission. (a) What is the ultimate product obtained from Te-132? Write a

    asked by brody on May 3, 2010
  5. Chemistry

    Tc-99 is a radioactive isotope that decays by beta emission and is used by radiologists in the diagnosis of liver disease. Its decay behavior is shown by the activity-time table. What is its half-life?

    asked by Jennifer on December 10, 2011
  6. Chemistry

    Gallium65, a radioactive isotope of gallium, decays by first order-kinetics. The half-life of this isotope is 15.2 min. How long would it take for 7/8 of a sample of this isotope to decay? 15.2 min 30.4 min 45.6 min 48.0 min I'm

    asked by Val on March 28, 2010
  7. Chemistry

    When is an isotope considered stable? _(Select all that apply.)_ The isotope does not emit a form of radiation. The isotope’s half-life is longer than the average human life. The isotope emits some form of radiation. The

    asked by Quinn on October 22, 2018
  8. Chemistry

    The strontium-90 isotope decays by the reaction below. It has a half-life of 28 yr. If the initial activity of this isotope was 168dpm, what would the activity be after 28.0 yr?

    asked by Morgan on September 27, 2015
  9. modern physics

    A radioisotope P has a half-life of 3 s. At t = 0, a given sample of this isotope contains 8000 atoms. Calculate (i) its decay constant, (ii) average life, (iii) the time t1 when 1000 atoms of the isotope P remain in the sample,

    asked by gourav on March 19, 2017
  10. chemistry

    What is the half-life of an isotope if it decays to 12.5% of its radioactivity in 18 minutes?

    asked by fatin on September 14, 2010

More Similar Questions