A radioactive material has mean-lives of 1620 yr and 520 yr for $\alpha$ and $\beta$-emission. The material decays by simultaneous $\alpha$ and $\beta$-emission. The time in which 1/4th of the material remains intact is

(a) 4675 yr                                 (b) 720 yr

(c) 545 yr                                   (d) 324 yr

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The radioactivity of an element becomes $\frac{1}{64}th$ 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

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A nucleus of ${}_{84}{}^{210}Po$ originally at rest emits $\alpha$ particle with speed $\nu$. What will be the recoil speed of the daughter necleus. [DCE 2002]

(1) 4$\nu$ / 206                          (2) 4$\nu$ / 214

(3) $\nu$ / 206                            (4) $\nu$ / 214

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Types of decay
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An atom of mass number 15 and atomic number 7 captures an $\alpha$-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

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Types of decay
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If radius of the ${}_{13}{}^{27}\mathrm{Al}$ nucleus is estimated to be 3.6 fermi then the radius of ${}_{52}{}^{125}Te$ nucleus be nearly

(a) 4 Fermi                                     (b) 5 Fermi

(c) 6 Fermi                                     (d) 8 Fermi

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Mass-energy equivalent
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Solar energy is mainly caused due to 

(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

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Mass-energy equivalent
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A sample of radioactive elements contains $4×{10}^{10}$ active nuclei. If half-life of element is 10 days, then the number of decayed nuclei after 30 days is 

(1) $0.5×{10}^{10}$                   (2) $2×{10}^{10}$

(3) $3.5×{10}^{10}$                   (4) $1×{10}^{10}$

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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

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In radioactive decay process, the negatively charged emitted $\beta$-particles are

(a) the electrons present inside the nucleus

(b) the electrons produced as a result of the decay of neutrons inside the nucleus

(c) the electrons produced as a result of collisions between atoms

(d) the electrons orbiting around the nucleus

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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

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