I experimented with ISZS and found out how to stop it decaying.  It decays on it's own because it emits it's own negative pressure.  I drew increasingly large squares of ISZS and it turns out that ISZS drawn in 17x17 squares or smaller don't decay and 18x18 or larger can be kept in a PUMP box; the positive pressure keeps it from decaying; you'll have to experiment with pressure values depending on the area of the shape of ISZS your trying to contain.  ISZS also heats up a little under negative pressure, so if you want the photon decay to be a more controlled, you have to keep the ISZS cold as it decays.  ISZS containment is demonstrated in this save:

EDIT:  Now that I linked my save here, this thread now belongs in "Creations"; please move it there.