Question

Write the balanced nuclear equations for the positron emission of Si-27.

Write the balanced nuclear equations for the beta decay of Si-31.

How many hours are needed for a sample of Si-31 with an activity of 16 μCi to decay to 2.0 μCi?

Answer 1

Q1.

Write the balanced nuclear equations for the positron emission of Si-27.

Positron emissoin is esentially --> mass number is kept; proton number decrease, there is positron emission (ve) + energy

²⁷₁₄Si = ²⁷₁₃Al + e + ve

Q2

beta decay -->

mass number is kept, atomic number increases by +1, there is beta particle ( 0-1 e ) + 0 0 ve (neutrino)

³¹₁₄Si --> ³¹₁₅P +´⁰_-1e- + ^0₀ve

Q3.

time in h required for

acitivty from 16 micro Ci to 2 micro Ci

if this is 1st order, then

Half life for Si 31 = 2.62 h

Cfinal = Cinitial*(1/2)^(time/Half life)

2 = 16 * (1/2)^(t/2.62 )

t =2.62 * ln(2/16) / ln(1/2)

t = 7.86 hours required