Radioactivity: R = radioactivity Ro = radioactivity at time zero t = time H = \'

Question

Radioactivity: R = radioactivity Ro = radioactivity at time zero t = time H = 'half-life' a time for half of the substance to decay. Isotope half-life tritium 12.3 years carbon-14 5568 years phosphorus-32 14.3 days Cobalt-60 5.3 years iodine-131 8.1 days radium-226 1600 years uranium-238 4.5 billion years For Problems #6-#12, one point each: how long do each of these substances take to decay to one millionth of the original amount? #6. tritium #7. carbon-14 #8. phosphorus-32 #9. cobalt-60 #10. iodine-131 #11. radium-226 #12. uranium-238

Explanation / Answer

t = -H * ln(R/R0) / ln(2)

6) Tritium :

t = -12.3 * ln(1/1000000) / ln(2)
t = 245.16 years

7)C -14 :

t = -5568 * ln(1/1000000) / ln(2)
t = 110978.97 years

8) P - 32 :

t = -14.3 * ln(1/1000000) / ln(2)
t = 285.02 days

9) Co - 60 :

t = -5.3 * ln(1/1000000) / ln(2)
t = 105.64 years

10) I - 131 :

t = -8.1 * ln(1/1000000) / ln(2)
t = 161.45 days

11) Ra - 226 :

t = -1600 * ln(1/1000000) / ln(2)
t = 31890.51 years

12) U - 238 :

t = -4.5 * ln(1/1000000) / ln(2)
t = 89.69 billion years

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