Question

99Mo is made in nuclear reactors for medical use, because it decays to 99Tc with a half-life of 2.75 days. If a 0.5 kg sample of 99Mo is left alone for 11 days, what mass of 99Tc will be present?

A

0.063 kg

B

0.033 kg

C

0.47 kg

D

0.44 kg

Answer 1

Solution:

Using decay equation,

Find the amount of Mo left after 11 days,

N = N_o e^-t where = ln2/t_1/2 = 0.693/2.75 = 0.252/days.

For 11 days,

N = 0.5 e^-0.252*11

= 0.03125.

0.03125 kg of Mo is still available ,means,

the mass of Tc is, = Initial mass of Mo - Final mas of Mo [converted to Tc ]

= 0.5 - 0.03125

= 0.46875

= 0.47 kg Ans: C .

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