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 [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

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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 [2002]

(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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