The half life of radioactive Radon is 3.8 days. The time at the end of which 1/20 th of the Radon sample will remain undecayed is
(Given log10e=0.4343
(a) 3.8 days               (b) 16.5 days
(c) 33 days                (d) 76 days

Concept Questions :-

Radioactivity
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If 10% of a radioactive material decays in 5 days, then the amount of original material left after 20 days is approximately
(a) 60%              (b) 65%
(c) 70%              (d) 75%

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Radioactivity
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A radioactive isotope X with a half-life of 1.37×109 years decays to Y which is stable. A sample of rock from the moon was found to contain both the elements X and Y which were in the ratio of 1 : 7. The age of the rock is
(a) 1.96×108 years         (b) 3.85×109 years
(c) 4.11×109years          (d) 9.59×109 years

Concept Questions :-

Radioactivity
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From a newly formed radioactive substance (Half life 2 hours), the intensity of radiation is 64 times the permissible safe level. The minimum time after which work can be done safely from this source is

(a) 6 hours            (b) 12 hours
(c) 24 hours          (d) 128 hours

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Radioactivity
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The half life of radium is 1620 years and its atomic weight is 226 kgm per kilomol. The number of atoms that will decay from its 1 gm sample per second will be

(a) 3.61×1010     (b) 3.6×1012
(c) 3.11×1015     (d) 31.1×1015

(Avogardo's number N = 6.02×1026 atpm/kilomol)

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A radioactive material decays by simultaneous emission of two particles with respective half lives 1620 and 810 years. The time (in years) after which one- fourth of the material remains is 
(a) 1080         (b) 2430
(c) 3240         (d) 4860

Concept Questions :-

Radioactivity
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The half life period of a radioactive element X is same as the mean life time of another radioactive element Y. Initially both of them have the same number of atoms. Then

(a) X and Y have the same decay rate initially
(b) X and Y decay at the same rate always
(c) Y will decay at a faster rate than X
(d) X will decay at a faster rate than Y

Concept Questions :-

Radioactivity
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For a substance the average life for α-emission is 1620 years and for β emission is 405 years. After how much time the 1/4 of the material remains after α and β emission

1. 1500 years            2. 300 years
3. 449 years              4. 810 years

Concept Questions :-

Types of decay
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A radioactive nucleus undergoes α-emission to form a stable element. What will be the recoil velocity of the daughter nucleus if v is the velocity of α-particle and A is the atomic mass of radioactive nucleus ?


1. 4VA-4             2. 2VA-4
3. 4VA+4             4. 2VA+4

Concept Questions :-

Types of decay
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Half life of a radio-active substance is 20 minutes. The time between 20% and 80% decay will be 
1. 20 minutes          2. 40 minutes
3. 30 minutes          4. 25 minutes

Concept Questions :-

Radioactivity
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