Q. No.The half-life of a radioactive substance is 30 minutes. The time (in minutes) taken between 40% decay and 85% decay of the same radioactive substance is:
1. 15
2. 30
3. 45
4. 60
For radioactive material, the half-life is 10 minutes. If initially, there are 600 number of nuclei, the time taken (in minutes) for the disintegration of 450 nuclei is :
1. 20
2. 10
3. 30
4. 15
1. \(\frac{1}{\sqrt{m}}\)
2. \(\frac{1}{m^2}\)
3. \(m\)
4. \(\frac{1}{m}\)
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A nucleus of uranium decays at rest into nuclei of thorium and helium. Then,
1. The nucleus helium has more kinetic energy than the thorium nucleus
2. The helium nucleus has less momentum than the thorium nucleus
3. The helium nucleus has more momentum than the thorium nucleus
4. The helium nucleus has less kinetic energy than the thorium nucleus
A radioisotope 'X' with a half-life 1.4 × 109 years decays to 'Y' which is stable. A sample of the rock from a cave was found to contain 'X' and 'Y' in the ratio 1:7. The age of the rock is :
1. 1.96 x 109 years
2. 3.92 x 109 years
3. 4.20 x 109 years
4. 8.40 x 109 years
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| 1. | \(26.7\) MeV | 2. | \(6.675\) MeV |
| 3. | \(13.35\) MeV | 4. | \(2.67\) MeV |
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2. 80 years
3. 100 years
4. 40 years
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If the nuclear radius of 27Al is 3.6 Fermi, the approximate nuclear radius of 64Cu in Fermi is:
1. 2.4
2. 1.2
3. 4.8
4. 3.6
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A mixture consists of two radioactive materials A1 and A2 with half-lives of 20 s and 10 s respectively. Initially, the mixture has 40 g of A1 and 160 g of A2. The amount of the two in the mixture will become equal after:
1. 60 s
2. 80 s
3. 20 s
4. 40 s
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