The half-life of a radioactive substance is 48 hours. How much time will it take to disintegrate to its $\frac{1}{16}$th part

(a) 12 h             (b) 16 h
(c) 48 h             (d) 192 h

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A radioactive substance has an average life of 5 hours. In a time of 5 hours
(a) Half of the active nuclei decay
(b) Less than half of the active nuclei decay
(c) More than half of the active nuclei decay
(d) All active nuclei decay

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Which of the following radiations has the least wavelength

(a) X-rays              (b) $\mathrm{\gamma }$-rays
(c) $\mathrm{\beta }$-rays              (d) $\mathrm{\alpha }$-rays

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Types of decay
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A radioactive sample at any instant has its disintegration rate 5000 disintegration per minute. After 5 minutes, the rate is 1250 disintegrations per minute. Then, the decay constant (per minute) is
(a) 0.8 In 2                (b) 0.4 In 2
(c) 0.2 In 2                (d) 0.1 In 2

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A nucleus with Z = 92 emits the following in a sequence:
$\mathrm{\alpha },{\mathrm{\beta }}^{-},{\mathrm{\beta }}^{-},\mathrm{\alpha },\mathrm{\alpha },\mathrm{\alpha },\mathrm{\alpha },\mathrm{\alpha },{\mathrm{\beta }}^{-},{\mathrm{\beta }}^{-},\mathrm{\alpha },{\mathrm{\beta }}^{+},{\mathrm{\beta }}^{+},\mathrm{\alpha }$. The Z of the resulting nucleus is
(a) 74              (b) 76
(c) 78              (d) 82

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Types of decay
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Radioactive nuclei that are injected into a patient collect at certain sites within its body, undergoing radioactive decay and emitting electromagnetic radiation. These radiations can then be recorded by a detector. This procedure provides an important diagnostic tool called
(a) Gamma camera
(b) CAT scan
(d) Gamma ray spectroscopy

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A radioactive decay chain starts from ${}_{93}{}^{237}\mathrm{Np}$ and produces ${}_{90}{}^{229}\mathrm{Th}$ by successive emissions. The emitted particles can be
(a) Two $\mathrm{\alpha }$-particles and one $\mathrm{\beta }$-particle
(b) Three ${\mathrm{\beta }}^{+}$ particles
(c) One $\mathrm{\alpha }$ particle and two ${\mathrm{\beta }}^{+}$ particles
(d) One $\mathrm{\alpha }$ particle and two ${\mathrm{\beta }}^{-}$ particles

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The half-life of a sample of a radioactive substance is 1 hour. If $8×{10}^{10}$ atoms are present at t = 0, then the number of atoms decayed in the duration t = 2 hour to t = 4 hour will be
(a) $2×{10}^{10}$          (b) $1.5×{10}^{10}$
(c) Zero               (d) Infinity

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Carbon dating is best suited for determining the age of fossils if their age in years is of the order of
(a) ${10}^{3}$             (b) ${10}^{4}$
(c) ${10}^{5}$             (d) ${10}^{6}$

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A count rate meter shows a count of 240 per minute from a given radioactive source. One hour later the meter shows a count rate of 30 per minute. The half-life of the source is

(a) 120 min                   (b) 80 min
(c) 30 min                     (d) 20 min