After 8 half-lives what percentage of the initial radioactive material remains?

Question

After 8 half-lives what percentage of the initial radioactive material remains? A. 0.2% B. 0.4% C. 1.25% D. 3.125% What was the approximate half-life of the radioactive material examined and plotted during class on Monday 4/17? (See the Excel file with raw data in the "Assignments folder" if necessary) A. 10 seconds B. 25 minutes C. 23 minutes D. 14.3 hours Which of the following involves the emission of electromagnetic radiation? A. Alpha decay B. Beta decay C. Gamma decay Reset Selection Mass is conserved for an alpha decay A. True B. False Which of the following would be the least likely to penetrate a piece of cardboard? A. Alpha decay B. Beta decay C. Gamma decay

Explanation / Answer

1. After each half life, amount remains half of amount present initily.

After first amount remined is 1/2, then 1/2(1/2)=1/4, after third- 1/2(1/4)= 1/8. Then 1/16, then 1/32, then 1/64, then 1/128, then 1/256.

So 100/256= 0.39,which is close to 0.4?.

3.

Gamma decays are high energy EM rays, so Gamma decay involves EM emission.

4.

True: Mass is conserved in Alpha decay.

5.

Alpha particles are least likely to penetrate cardboard: Gamma can penetrate lead, beta can penetrate blocks of metals, while alpha are least energetic.

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