NCERT Class XII Chapter
Nuclei
Questions With Solutions

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Question : 13
Total: 31
The radionuclide
11
6
C
decays according to
11
6
C
11
5
B
+e+
+ v ; T12 = 20.3 min
The maximum energy of the emitted positron is 0.960 MeV.
Given the mass values:
m (
11
6
C
)
= 11.011434 u and m (
11
5
B
)
= 11.009305 u
Calculate Q and compare it with the maximum energy of the positron emitted
Solution:  
The given equation,
11
6
C
11
5
B
+e+
+ v + Q
The Q value is, Q =
[m(
11
6
C
)
6me
m(
11
5
B
)
+5me
me
]
c2

Q = [11.011434 – 11.009305 – 2 × 0.000548] c2
931.5 MeV ≈ 0.96 MeV
As we know that different positrons comes out with different possible energies shared between daughter nucleus and positron.
So, the Q value of reaction is almost same as the maximum energy of positron emitted.
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