posted by .

Beryllium-7 has a half-life of 53 D. A sample was observed for one minute and there were 26,880 decays.
a.) what is the activity level of the sample?
b.) what will the activity level of the sample be after 265 d?
c.) after how many days will be activity level of the sample be 112 Bq?
d.) what was activity level 106 d before the sample was observed?
e.) how many days earlier was activity level 8 times greater than the observed level?

  • Radioactivity -

    a. The rate of decay = 26,880 dpm (decays/min)
    k = 0.693/t1/2
    Solve for k and substitute into the below equation.
    ln(No/N) = kt
    No = 26880
    N = ?
    k from above
    t = 265 days

    1 Bq = 1 dps
    Your sample is 26,880 dpm so
    26,880 decays/min x (1 min/60 sec) = about 448 dps.
    ln(No/N) = kt
    No = 448
    N = 112
    k from above
    Solve for t in days.

    ln(No/N) = kt
    No = ?
    N = 26,880
    k from above
    t = 106

    e. see d.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. physics-Radioactivity

    1) The number of radioactive nuclei in a particular sample decreases over a period of 15 days to one-seventeenth the original number. What is the half-life (in days) of these nuclei?
  2. physics

    Suppose 32000 radioactive nuclei are in a sample. About how many remain after two days if the half-life is 22 hrs?
  3. college physics part 2

    the activity of a sample of carbon has one-eighth of the initial activity. carbon-14 has a half-life of 5730 yr. how old is the sample in yr?
  4. Physics

    University students, studying the activity of a particular radioactive isotope which had a half-life of 12.0 hours. If the original activity of the sample was 448 kBq, what would the activity be 3.00 days later?
  5. college Geol 101

    Suppose you have a sample of clamshell at a Paleoindian site and you measure the 14C activity of a 100-gram sample of carbon as 320 disintegrations per minute (or 3.2 disintegrations per gram of carbon per minute). a.What was the activity …
  6. chemistry

    The half-life for the radioactive decay of calcium-47 is 4.5 days.If a sample has an activity of 4.00uCi after 13.5 days, what was the initial activity of the sample?
  7. math

    An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent. a)(a) What is the half-life of the element?
  8. chem

    A sample of radon has an activity of 80,000 Bq. If the half-life of radon is 15 h, how long before the sample's activity is 5,000 Bq?
  9. Chemistry - Radioactivity

    The activity of a sample of Ba-137m has decreased by 75% from its initial activity after 5.10 minutes. What is the half-life of Ba-137m?
  10. Physics

    The activity of a sample of 31Si (T1/2 = 9.43×103 s) is 7.88×105 decays per second. What is the mass of sample present?

More Similar Questions