Values: [01] 3.71E+16 [02] 1.93 [03] 8.56E+17 [04] 2.31 Correct answers will be

Question

Values:

[01] 3.71E+16 [02] 1.93 [03] 8.56E+17 [04] 2.31

Correct answers will be in these ranges:

19-1. 1.00e10, 2.50e10 Bq

19-2. 10:0, 20.0 million

19-3. 1.00, 1.60 h

19-4. 200; 500

The half-life of an isotope of phosphorus is 14.2 days. If a sample contains [01] _______such nuclei, determine its activity. Rn-222 has a half-life of 3.83 days. If 25.8 million Rn-222 nuclei are present at time t = 0, how many of those nuclei will remain after [02] ________days have passed? 3. Suppose that you start with 2.52 Times 1018 radioactive nuclei and 2.09 h later determine that only [03] _______nuclei of the substance remains. What is the half-life of this substance? Consider a sample containing 3.91 Times 1019 92238 nuclei. The half-life of 92238U is 4.47 billion years. How many of these nuclei will decay during a [04] ______-s interval?

Explanation / Answer

a) lambda = ln(2)/14.2*60*60*24 = 5.65E-7

activity = n*lambda = 5.65E-7*3.71E16 = 2.09E10

b) N=N0*2^(-t/half life) = 25.8*10^5*2^(-1.93/3.83) = 18.19 million

c) 8.5E17 = 2.52E18*2^(-2.09/t) or t = 1.333 hr

d) N = 3.91E19*2^(-2.31/4.47*365*24*3600E8)

or decomposition is nearly equal to 470 nuclei

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