(show all your works and please do all questions from part a to part c. Sorry fo

Question

(show all your works and please do all questions from part a to part c. Sorry for long questions, but I will thanks to anyone who can help me all questions from part a to part c)

a. nuclear disarmament could be accomplished if weapons were not replenished. the tritium in hydrogen bomb warheads decays to helium-3 with a half life of 12.26yrs and must be replaced or the weapon is useless

(i) write a balanced equation for the tritium decay reaction

(ii) what fraction of the tritium is lost in 5.50yrs

b. what is the probably mode of decay for each of the following: silver-111, carbon-15, chromium-48, thorium-224, uranium-238, xenon-120

c. circle which isotopes in each pair is more stable and explain your reason: 55140Cs or 55133Cs, 3579Br or 3578Br, 1228Mg or 1224Mg

Explanation / Answer

Decay

a. (i) Tritium decay reaction : 3H1 ---> 3He2 + 0beta-1

(ii) First order rate equation,

ln[A] = ln[Ao] - kt

k = 0.693/12.26 yr = 0.0565 yr-1

fraction left aftr 5.50 yr [A] is,

ln[A] = ln(100) - 0.0565 x 5.50

[A] = 73.29%

b. Probable mode of decay for nucelus

Ag-111 : beta(-) decay

C-15 : beta(-) decay

Cr-48 : beta(+) decay

Th-224 : alpha decay

U-238 : alpha decay

Xe-120 : beta(+) decay

c. Most stable isotope are ones with optimum ratio of neutron to protons in it to stabilize the net internuclear force existing between electrons and nucleus,

(55/133)Cs is more stable than (55/140)Cs

(35/79)Br is more stable than (35/78)Br

(12/24)Mg more stable than (12/28)Mg

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