Solving a Radioactive Decay Problem: Na(t) and Nb(t)

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SUMMARY

The discussion focuses on solving a radioactive decay problem involving two types of nuclei, A and B, represented by populations Na(t) and Nb(t). The differential equations governing their decay are dNa/dt = -Na/Ta and dNb/dt = Na/Ta - Nb/Tb, with initial conditions Na(0) = 100 and Nb(0) = 0. The solution for Na(t) is correctly identified as 100*e^(-t/Ta), while the proposed solution for Nb(t) is incorrect. The correct approach involves solving the first-order inhomogeneous differential equation for Nb using an integrating factor or the method of undetermined coefficients.

PREREQUISITES
  • Understanding of differential equations, specifically first-order inhomogeneous equations.
  • Familiarity with radioactive decay concepts and decay constants (Ta and Tb).
  • Knowledge of integrating factors and the method of undetermined coefficients.
  • Basic calculus skills for solving exponential functions.
NEXT STEPS
  • Learn how to apply the integrating factor method to first-order differential equations.
  • Study the method of undetermined coefficients for solving inhomogeneous differential equations.
  • Explore applications of radioactive decay in real-world scenarios, including half-life calculations.
  • Investigate numerical methods for solving differential equations when analytical solutions are complex.
USEFUL FOR

Students studying physics or engineering, particularly those focusing on nuclear physics, as well as educators and anyone interested in mastering differential equations related to decay processes.

blaksheep423
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Homework Statement


Consider a radiactive decay problem involving two types of nuclei, A and B, with populations Na(t) and Nb(t). Suppose that type A nuclei decay to form type B nuclei, which then also decay, according to differential equations:

Homework Equations



dNa/dt = - Na/Ta

dNb/dt = Na/Ta - Nb/Tb

where Ta and Tb are the decay constants. Na(0) = 100 and Nb(0) = 0.

The Attempt at a Solution



I solved the equation for Na(t) and got 100*e^(-t/Ta), but I'm not sure about Nb. Intuitively, I think it has to be something like:

100*(1 - e^(-t/Ta))*e^(-t/Tb)

but I know this is wrongany advice/ideas?
 
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blaksheep423 said:

Homework Statement


Consider a radiactive decay problem involving two types of nuclei, A and B, with populations Na(t) and Nb(t). Suppose that type A nuclei decay to form type B nuclei, which then also decay, according to differential equations:

Homework Equations



dNa/dt = - Na/Ta

dNb/dt = Na/Ta - Nb/Tb

where Ta and Tb are the decay constants. Na(0) = 100 and Nb(0) = 0.

The Attempt at a Solution



I solved the equation for Na(t) and got 100*e^(-t/Ta), but I'm not sure about Nb. Intuitively, I think it has to be something like:

100*(1 - e^(-t/Ta))*e^(-t/Tb)

but I know this is wrongany advice/ideas?
Just plug it in and solve! ;)

Your equation for Nb,

N'_b(t)+\frac{1}{T_b} N_b(t) = 100e^{-t/T_a}

is a basic first-order, inhomogeneous differential equation. You can solve it using an integrating factor or the method of undetermined coefficients.
 

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