Composition and size of nucleus, atomic masses
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See all →- ^290_82X α Y e^+ Z β^- P e^- QIn the nuclear emission stated above, the mass number and atomic number of the product Q respectively, are : Answer: 1. 286, 81 Key idea: α emission lowers A by 4 and Z by 2; β^+ (positron) lowers Z by 1; β^- (electron) raises Z by 1. The mass numbe... 1
- The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to ≤ft(1/16)^th of its initial value? Answer: 1. 80 minutes Activity falls by half every half-life. dfrac116=(1/2)⁴ , so 4 half-lives are needed. t=4×20=80 minutes. The answer is... 1
- A nucleus of mass number 189 splits into two nuclei having mass number 125 and 64. The ratio of radius of two daughter nuclei respectively is : Answer: 4. 5 : 4 Nuclear radius is R=R₀A^(1/3) . R₁/R₂=(125/64)^(1/3)=5/4 The ratio is 5:4 . Option (4). 1
- In the given nuclear reaction, the element X is :^22_11Na → X + e^+ + Answer: 4. ²²₁₀Ne The emission of a positron is beta-plus decay: a proton turns into a neutron, so the mass number stays the same and the at... 1
- A radioactive nucleus ^A_ZX undergoes spontaneous decay in the sequence^A_ZX → _Z-1B → _Z-3C → _Z-2D, where Z is the atomic number of element X. The possible decay particles in the sequence are : Answer: 3. β^+, α, β^- Key idea: α decay lowers Z by 2; β^- raises Z by 1; β^+ lowers Z by 1. Z→ Z-1 : β^+ . Z-1→ Z-3 : α . Z-3→ Z-2 : β^- .... 1
- The half-life of a radioactive nuclide is 100 hours. The fraction of original activity that will remain after 150 hours would be : Answer: 2. 1/2√(2) Key idea: activity decays as A=A₀(1/2)^t/T_(1/2) . dfrac AA₀=(1/2)^(150/100)=(1/2)^(3/2)=dfrac12sqrt2 . Option 2. 1