Page 738 - SUBSEC October 2017_Neat

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02238020/CAPE SPEC/MS/2017

Question 3 KC UK XS

(c) E = mc (1) 1
2

m = 3.017 u – (2.015 u + 1.008 u)
= - 0.006 u (1)
= 0.006 x 1.66 x 10 -27
= 9.96 x 10 -30 kg (1) 3
E = 9.96 x 10 -30 x (3 x 10 )
8 2
= 8.97 x 10 -13 J (1)

(d)
(i) Half-life is the time taken for half the number of particles
to disintegrate (1). 2

Decay constant : is a characteristic of the atoms that
decay such that

 = - 1 dN
N dt (1)

(ii) T½ = 0.693 (1) 1


 = 0.693 (1)
3
1.6 x 10 2

-4
-1
= 4.33 x 10 s (1)

(iii) A = -  N (1)
1
= -4.33 x 10 x 5 x 10 x 10
-4
16
-4
1
= 2.17 x 10 Bq (1)
13

4
(iv) 226 Ra  222 X + He (1) 2
88 86 2

226 Ra  226 X + e (1)
0

88 89 -1