Two radioactive materials X1 and X2 have decay constants 10λ and λ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of X1 to that of X2 will be 1e after a time

1. 110 λ 

2. 111 λ

3. 1110 λ   

4. 19 λ

Subtopic:  Radioactivity (OLD NCERT) |
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A radioactive material has mean-lives of 1620 yr and 520 yr for α and β-emission. The material decays by simultaneous α and β-emission. The time in which 1/4th of the material remains intact is 

1. 4675 yr 

2. 720 yr

3. 545 yr 

4. 324 yr

Subtopic:  Radioactivity (OLD NCERT) |
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The radioactivity of an element becomes 164th of its original value in 60 seconds. Then the half value period is

1. 5 sec 

2. 10 sec 

3. 20 sec

4. 30 sec

Subtopic:  Radioactivity (OLD NCERT) |
 91%
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A nucleus of P84210o originally at rest emits α particle with speed ν. What will be the recoil speed of the daughter necleus. [DCE 2002]

1. 4ν / 206

2. 4ν / 214

3. ν / 206 

4. ν / 214

Subtopic:  Types of Decay |
 75%
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An atom of mass number 15 and atomic number 7 captures an α-particle and then emits a proton. The mass number and atomic number of the resulting product will respectively be

1. 14 and 2

2. 15 and 3

3. 16 and 4 

4. 18 and 8

Subtopic:  Types of Decay |
 78%
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Solar energy is mainly caused due to [2003]

1. fusion of protons during synthesis of heavier elements

2. gravitational contraction

3. burning of hydrogen in the oxygen

4. fission of uranium present in the sun

Subtopic:  Mass-Energy Equivalent |
 83%
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A sample of radioactive elements contains 4×1010 active nuclei. If half-life of element is 10 days, then the number of decayed nuclei after 30 days is 

1. 0.5×1010   

2. 2×1010

3. 3.5×1010

4. 1×1010

Subtopic:  Radioactivity (OLD NCERT) |
 54%
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A and B are two radioactive substances whose half-lives are 1 and 2 years respectively. Initially 10 g of A and 1 g of B is taken. The time (approximate) after which they will have the same quantity remaining is:

1. 6.62 yr

2. 5 yr   

3. 3.2 yr 

4. 7 yr

Subtopic:  Radioactivity (OLD NCERT) |
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A sample of radioactive element has a mass of 10 gm at an instant t = 0. The approximate mass of this element in the sample after two means lives in [CBSE PMT/PDT 2003]

1. 3.70 gm

2. 6.30 gm

3. 1.35 gm 

4. 2.50 gm

Subtopic:  Radioactivity (OLD NCERT) |
 51%
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PMT - 2003
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Given a sample of Radium-226 having half-life of 4 days. Find the probability, a nucleus disintegrates after 2 half lives [IIT-JEE 2006]

1. 1 

2. 1/2 

3. 1.5 

4. 3/4

Subtopic:  Radioactivity (OLD NCERT) |
 71%
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