  The D0/D4 system with a Neveu-Schwarz B-field in the spatial directions of
the D4-brane has a tachyon in the spectrum of the (0,4) strings. The tachyon
signals the instability of the system to form a bound state of the D0-brane
with the D4-brane. We use the Wess-Zumino-Witten like open superstring field
theory formulated by Berkovits to study the tachyon potential for this system.
The tachyon potential lies outside the universality class of the D-brane
anti-D-brane system. It is a function of the B-field. We calculate the tachyon
potential at the zeroth level approximation. The minimum of the tachyon
potential in this case is expected to reproduce the mass defect involved in the
formation of the D0/D4 bound state. We compare the minimum of the tachyon
potential with the mass defect in three cases. For small values of the B-field
we obtain 70% of the expected mass defect. For large values of the B-field with
Pf$(2\pi\alpha' B) >0$ the potential reduces to that of the D-brane
anti-D-brane reproducing 62% of the expected mass defect. For large values of
the B-field with Pf$(2\pi\alpha' B) <0$ the minimum of the tachyon potential
gives 25% of the expected mass defect. At the tachyon condensate we show that
the (0,4) strings decouple from the low energy dynamics.
