(1). Heavy water is used in nuclear reactors

• (a). to absorb neutrons to sustain controlled reaction
• (b). to absorb neutrons to stop the chain reaction
• (c). to reduce hazardous radiation from nuclear reaction
• (d). to slow down the neutrons to thermal energies.
• (e). None of these

(2). Pick out the incorrect statement from the following.

• (a). β -emission from the nucleus is always accompanied with a neutrino.
• (b). The energy of the ? -particle emitted from a given nucleus is always constant.
• (c). γ-ray emission makes the nucleus more stable.
• (d). Nuclear force is charge-independent.
• (e). None of these

(3). Consider the following statements. S1: The nuclear force is independent of the charge nucleons. S2: The number of nucleons in the nucleus of an atom is equal to the number of electrons in the atom. S3: All nuclei have masses that are less than the sum of masses of constituent nucleons. S4: Nucleons belong to the family of leptons while electrons are members of the family of hadrons. Choose the correct statement/statements from these.

• (a). S1 only
• (b). S1 and S4
• (c). S2, S3 and S4
• (d). S1 and S3
• (e). None of these

(4). A radioactive element X with half life 2 h decays giving a stable element Y. After a time I, ratio of X and Y atoms 1:16. Time t is

• (a). 6h
• (b). 4h
• (c). 8h
• (d). 16h
• (e). None of these

(5). lf the binding energies of a deuteron and an alpha particle 1.125 MeV and 7.2 MeV respectively, then the more stable of the two is

• (a). deuteron
• (b). alpha particle
• (c). both (a) and (b)
• (d). sometimes deuteron and sometimes alpha particle
• (e). None of these

(6). Which of the following statements are true? (I) All radioactive element decay exponentially with time. (II) Half life time of a radioactive element is the time required for one half of the radioactive atoms to distintegrate (III) Age of the earth can be determined by radioactive dating. (IV)Half life time of a radioactive element is fifty percent of its average life period. Select the correct answer using the codes given below.

• (a). I and II
• (b). I, III and IV
• (c). I, II and III
• (d). II and III
• (e). None of these

(7). Half-life of a radioactive substance is 20 minutes. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately

• (a). 10 min
• (b). 20 min
• (c). 30 min
• (d). 40 min
• (e). None of these

(8). In the Bohr model of the hydrogen atom. the lowest orbit corresponds to

• (a). infinite energy
• (b). maximum energy
• (c). minimum energy
• (d). zero energy
• (e). None of these

(9). A freshly prepared radioactive sample of half-life 4 hours emits radiation of intensity which is 64 times the safe level. The minimum hours after which it would be safe to work with it is

• (a). 4
• (b). 6
• (c). 12
• (d). 24
• (e). None of these

(10). A radioactive decay can form an isotope of the original nucleus with the emission of particles

• (a). one of and four γ
• (b). one of and two γ
• (c). one of and one γ
• (d). four of and one γ
• (e). None of these

• (a). 1
• (b). 2
• (c). 3
• (d). 4
• (e). None of these

• (a). 1
• (b). 2
• (c). 3
• (d). 4
• (e). None of these

• (a).
• (b).
• (c).
• (d).
• (e). None of these

• (a). 1
• (b). 2
• (c). 3
• (d). 4
• (e). None of these

• (a). 7.57 Me-v
• (b). 8.36 Mev
• (c). 9.12 Mev
• (d). 9.56 Mev
• (e). None of these

• (a). 1
• (b). 2
• (c). 3
• (d). 4
• (e). None of these

• (a). 1
• (b). 2
• (c). 3
• (d). 4
• (e). None of these

• (a). 26.7 MeV
• (b). 216 MeV
• (c). 3.27 MeV
• (d). 1 MeV
• (e). None of these

• (a). 1
• (b). 2
• (c). 3
• (d). 4
• (e). None of these

• (a). 1
• (b). 2
• (c). 3
• (d). 4
• (e). None of these