Answer:
The approximate difference in the half-lives of the isotopes is 66 days.
Step-by-step explanation:
The decay of an isotope is represented by the following differential equation:
![\frac{dm}{dt} = -\frac{t}{\tau}](https://tex.z-dn.net/?f=%5Cfrac%7Bdm%7D%7Bdt%7D%20%3D%20-%5Cfrac%7Bt%7D%7B%5Ctau%7D)
Where:
- Current mass of the isotope, measured in kilograms.
- Time, measured in days.
- Time constant, measured in days.
The solution of the differential equation is:
![m(t) = m_{o}\cdot e^{-\frac{t}{\tau} }](https://tex.z-dn.net/?f=m%28t%29%20%3D%20m_%7Bo%7D%5Ccdot%20e%5E%7B-%5Cfrac%7Bt%7D%7B%5Ctau%7D%20%7D)
Where
is the initial mass of the isotope, measure in kilograms.
Now, the time constant is cleared:
![\ln \frac{m(t)}{m_{o}} = -\frac{t}{\tau}](https://tex.z-dn.net/?f=%5Cln%20%5Cfrac%7Bm%28t%29%7D%7Bm_%7Bo%7D%7D%20%3D%20-%5Cfrac%7Bt%7D%7B%5Ctau%7D)
![\tau = -\frac{t}{\ln \frac{m(t)}{m_{o}} }](https://tex.z-dn.net/?f=%5Ctau%20%3D%20-%5Cfrac%7Bt%7D%7B%5Cln%20%5Cfrac%7Bm%28t%29%7D%7Bm_%7Bo%7D%7D%20%7D)
The half-life of a isotope (
) as a function of time constant is:
![t_{1/2} = \tau \cdot \ln2](https://tex.z-dn.net/?f=t_%7B1%2F2%7D%20%3D%20%5Ctau%20%5Ccdot%20%5Cln2)
![t_{1/2} = -\left(\frac{t}{\ln\frac{m(t)}{m_{o}} }\right) \cdot \ln 2](https://tex.z-dn.net/?f=t_%7B1%2F2%7D%20%3D%20-%5Cleft%28%5Cfrac%7Bt%7D%7B%5Cln%5Cfrac%7Bm%28t%29%7D%7Bm_%7Bo%7D%7D%20%7D%5Cright%29%20%5Ccdot%20%5Cln%202)
The half-life difference between isotope B and isotope A is:
![\Delta t_{1/2} = \left| -\left(\frac{t_{A}}{\ln \frac{m_{A}(t)}{m_{o,A}} } \right)\cdot \ln 2+\left(\frac{t_{B}}{\ln \frac{m_{B}(t)}{m_{o,B}} } \right)\cdot \ln 2\right|](https://tex.z-dn.net/?f=%5CDelta%20t_%7B1%2F2%7D%20%3D%20%5Cleft%7C%20-%5Cleft%28%5Cfrac%7Bt_%7BA%7D%7D%7B%5Cln%20%5Cfrac%7Bm_%7BA%7D%28t%29%7D%7Bm_%7Bo%2CA%7D%7D%20%7D%20%5Cright%29%5Ccdot%20%5Cln%202%2B%5Cleft%28%5Cfrac%7Bt_%7BB%7D%7D%7B%5Cln%20%5Cfrac%7Bm_%7BB%7D%28t%29%7D%7Bm_%7Bo%2CB%7D%7D%20%7D%20%5Cright%29%5Ccdot%20%5Cln%202%5Cright%7C)
If
,
and
, the difference in the half-lives of the isotopes is:
![\Delta t_{1/2} = \left|-\left(\frac{33\,days}{\ln 0.90} \right)\cdot \ln 2 + \left(\frac{43\,days}{\ln 0.90} \right)\cdot \ln 2\right|](https://tex.z-dn.net/?f=%5CDelta%20t_%7B1%2F2%7D%20%3D%20%5Cleft%7C-%5Cleft%28%5Cfrac%7B33%5C%2Cdays%7D%7B%5Cln%200.90%7D%20%5Cright%29%5Ccdot%20%5Cln%202%20%2B%20%5Cleft%28%5Cfrac%7B43%5C%2Cdays%7D%7B%5Cln%200.90%7D%20%5Cright%29%5Ccdot%20%5Cln%202%5Cright%7C)
![\Delta t_{1/2} \approx 65.788\,days](https://tex.z-dn.net/?f=%5CDelta%20t_%7B1%2F2%7D%20%5Capprox%2065.788%5C%2Cdays)
The approximate difference in the half-lives of the isotopes is 66 days.