roots of the bessel function of the first kind of zero order

Hi everyone,

I'm quite new to matlab and in order to plot a diffusion equation, I need the "roots of the bessel function of the first kind of zero order".

I've read so many things and tried so many options but I can't seem to get it right. I need for 1:1000.

Basically this is the equation I'm trying to put to work

I think I got the rest right but I can't seem to get that part right.

Thank you in advance!