\Rightarrow dr=\lambda dx$, $r=\lambda x$
$\Rightarrow
I_c=j_c(R)2\pi \lambda^2 \exp(-R/\lambda) \int_0^R d(\frac{r}{\lambda})
\Rightarrow dr=\lambda dx$, $r=\lambda x$
$\Rightarrow
I_c=j_c(R)2\pi \lambda^2 \exp(-R/\lambda) \int_0^R d(\frac{r}{\lambda})