Revision as of 10:51, 22 June 2012

Amount of radioactive material (number of nuclei <-> number of moles <-> weigth) and law of radioactive decay

Written and developed by Prof. Per Hoff (uio) 

1:

1. 3.2  • 10⁸ Bq
2. 383 Bq
3. 2.3  • 10⁹ Bq
4. 8  • 10⁴ Bq

2:

1. 1.78  • 10¹³ atoms.
2. 2  • 10¹¹ atoms.

3: 2.40 g ⁶⁰Co.

4:

1. 2.53  • 10⁵ Bq.
2. 7.19 years = 7 years and 68 days.

5: The mass of ^99mTc is 20.5 ng. After one week 28 half-times will have past, and the activity will be the following:

D = D₀  • (½)²⁸ = 4  • 10⁷ Bq  • (½)²⁸ = 0.15 Bq.

All ^99mTc has disintegrated and turned into ⁹⁹Tc. The number of ⁹⁹Tc atoms will therfore be the same as the original number of ^99mTc atoms.

[math]N=\frac{D}{\lambda} \rightarrow \frac{4\cdot 10^{7}Bq}{3.21\cdot 10^{-5}s^{-1}}=1.25\cdot 10^{12}atoms[/math]

6:

1. 1 g natural Lu contains 0.0259 g ¹⁷⁶Lu, with a half-life equal to 3.8 • 10¹⁰ år. This gives D = 51 Bq
   
2. There are two naturally occuring radioisotopes of Sm, ¹⁴⁷Sm and ¹⁴⁸Sm, which gives D = 127.24 Bq + 0.001 Bq = 127 Bq.

7: 3002 kg

8:

1. 18.5 kg
2.  After 2.455 • 10⁵ years it will be 2.299 • 10⁸ Bq ²³⁸U left, which is equal to 18.49 kg.