NUCLEI QUIZ-16

JEE Advanced Physics Syllabus can be referred by the IIT aspirants to get a detailed list of all topics that are important in cracking the entrance examination. JEE Advanced syllabus for Physics has been designed in such a way that it offers very practical and application-based learning to further make it easier for students to understand every concept or topic by correlating it with day-to-day experiences. In comparison to the other two subjects, the syllabus of JEE Advanced for physics is developed in such a way so as to test the deep understanding and application of concepts.

Q1.The fission of a heavy nucleus gives, in general, two smaller nuclei, two or three neutrons, some Î²-particles, and some Î³-radiation. It is always true that the nuclei produced
•   Have a total rest-mass that is greater off the greater part of the original nucleus
•   Have large kinetic energies that carry off the greater part of the energy released
•   Travel in exactly opposite directions
•   Have neutron-to-proton ratios that are too low for stability
Solution
(b) The nuclear fission differs from other nuclear reaction in three respects 1. The nucleus is deeply divided into two large fission fragments or nuclei of roughly equal mass. The nuclei or fission fragments fly apart at great speed and thus posses large kinetic energies that carry off the greater part of the energy released 2. The mass decrease is appreciable and hence large energy is released 3. Other neutrons, called fission neutrons, are emitted in the process. Small amount of energy is released in the form of radiation

Q2. Fast neutrons can easily be slowed down by
•   The use of lead shielding
•   Passing them through water
•   Elastic collision with heavy nuclei
•   Applying a strong electric field
Solution
(b) Fast neutrons can be easily slowed down by passing them through water. This is because of comparable masses the energy passed by neutron to water molecule is high

Q3.The rate of decay of a radioactive element at any instant is 10^3 disintegrations s^(-1). If the half-life of the elements is 1 s, then the rate of decay after 1 s will be A deuteron may disintegrate to a proton and a neutron if it
•   500 s^(-1)
•   1000 s^(-1)
•   250 s^(-1)
•   2000 s^(-1)
Solution

Q4. Which of the following statements is incorrect for nuclear forces?
•   These are strongest in dependent
•   They are charge dependent
•   They are effective only for short ranges
•   They result from interaction of every nucleon with the nearest limited number of nucleons
Solution
(b) Nuclear forces are charge independent

Q5. A radioactive nucleus is being produced at a constant rate Î± per second. Its decay constant is Î». If N_0 are the number of nuclei at time t=0, then maximum number of nuclei possible are

•   Î±/Î»
•   N_0 Î±/Î»
•   N_0
•   Î±/Î»+N_0
Solution
156 (a) Maximum number of nuclei will be present when rate of decay = rate of formation Or Î»N=Î± ∴N=Î±/Î»

Q6. In the nuclear reaction 〖 _1 H〗^2+〖 _1 H〗^2→〖 _2 H〗^3+〖 _0 n〗^1 If the mass of the deuterium atom =2.014741 a.m.u., mass of 〖 _2 He〗^3 atom =3.016977 a.m.u. and mass of neutron =1.008987 a.m.u., then the Q value of the reaction is nearly
•  0.00352 MeV
•   3.27 MeV
•   0.82 MeV
•   2.45 MeV
Solution

Q7. An Î±-particle of 5 MeV energy strikes with a nucleus of uranium at stationary at an scattering angle of 180°. The nearest distance upto which Î±-particle reaches the nucleus will be of the order of:

•  1 â„«
•   10^(-10) cm
•   10^(-12) cm
•   10^(-15) cm
Solution

Q8. A radionuclide A_1 with decay constant Î»_1 transform into a radioactive A_2 with decay constant Î»_2. Assuming that at the initial moment the preparation contained only the radioactive A_1, then the time interval after which the activity of the radioactive A_2 reaches its maximum value is
•   ln⁡〖(Î»_2/Î»_1)〗/(Î»_2-Î»_1 )
•   ln⁡〖(Î»_1/Î»_2)〗/(Î»_2-Î»_1 )
•   ln⁡〖(Î»_2-Î»_1)〗
•   None of these
Solution
(d) Conserve the number of nucleons

Q9. Consider one of fission reactions of ^235 U by thermal neutrons _92^235 U+n→ _38^94 Sr+ _54^140 Xe+2n. The fission fragments are however unstable and they undergo successive Î²-decay until _38^94 Sr becomes _40^94 Zr and _54^140 Xe becomes _58^140 Ce. The energy released in this process is [Given m( _ ^235 U)=235.439 , m(n)=1.00866 u,m( _ ^94 Zr)=93.9064 u, m( _ ^140 Ce)=139.9055 u,1 u=931 MeV
•   Slightly less than T/2
•   T/2
•   Slightly less than T
•   Slightly greater than T
Solution

Q10. A free nucleus of mass 24 a.m.u. emits a gamma photon (when initially at rest). The energy of the photon is 7 MeV. The recoil energy of the nucleus in keV is
•  2.2
•   1.1
• 3.1
• 2.2

Solution
(b) Use conservation of linear momentum

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