How can i update an differential equation variable during the odeint operation using 'if" condition in python?

Question

I have these differential equations:

a=5*2.17*(10**-6)*n1*nx 
b=4*2.17*(10**-6)*n1*ni
c=n1/(0.154*(10**-7))
h=((8*(10**-7))/(3.14*t))**0.5
dn1dt=((1.7565*(10*