**NUCLEI QUIZ-15**

**NUCLEI QUIZ-15**

**Dear Readers,**

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.

**Q2. A helium atom, a hydrogen atom and a neutron have masses of 4.003 u, 1.008 u and 1.009 u (unified atomic mass units), respectively. Assuming that hydrogen atoms and neutrons can fuse to form helium, what is binding energy of a helium nucleus?**

Solution

(d)
Refer to the definition of mass defect

**Q3.The rest mass of a deuteron is equivalent to an energy of 1876 MeV, that of a proton to 939 MeV and that of a neutron to 940 MeV A deuteron may disintegrate to a proton and a neutron if it**

**Q4. The activity of a radioactive element decreases to one-third of the original activity A_0 in a period of 9 years. After a further lapse of 9 years, its activity will be**

**Q5. There are n number of radioactive nuclei in a sample that undergoes beta decay. If from the sample, n’ number of Î²-particles are emitted every 2 s, then half-life of nuclei is**

Solution

(b) t(1/2)=0.639/Î»

(b) t(1/2)=0.639/Î»

**Q6. A radioactive nucleus undergoes a series of decays according to the scheme A□(→┴( Î± ) A_1 □(→┴( Î² ) A_2 □(→┴( Î± ) A_3 □(→┴( Î³ ) A_4 )) ) ) If the mass number and atomic number of A are 180 and 72, respectively, then what are these number for A_4?**

Solution

(a) Two Î±-particles reduce mass number by 8 Therefore, new mass number =180-8=172 Emission of two Î±-particles reduces charge number by 4 Emission of Î²-particles increases charge number by 1 Therefore, the new charge number =72-4+1=69

(a) Two Î±-particles reduce mass number by 8 Therefore, new mass number =180-8=172 Emission of two Î±-particles reduces charge number by 4 Emission of Î²-particles increases charge number by 1 Therefore, the new charge number =72-4+1=69

**Q7. When an atom undergoes Î²^+ decay,:**

Solution

(b)
A nucleus contains protons and neutrons with no antiprotons and antineutrons. Hence, answer can be either (b) or (d). Due to conservation of spin, the answer is (b)

**Q8. From a newly formed radioactive substance (Half life 2 hours), the intensity of radiation is 64 times the permissible safe level. The minimum time after which work can be done safely from this source is**

**Q9. Stationery nucleus ^238 U decays by a emission generating a total kinetic energy T: _92^238 U → _90^234 Th+ _2^4 Î± What is the kinetic energy of the Î±-particle?**

**Q10. A freshly prepared radioactive source of half-life 2 h emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is**