  A variation of the relative content of (54Fe+58Ni) versus 56Ni may be
responsible for the observed scatter of Type Ia Supernovae (SNe Ia) about a
mean relation between their intrinsic brightness and the shape of their light
curve. Synthetic light curves are computed of parametrised Chandrasekhar-mass
explosion models of constant kinetic energy, where the ejecta are divided into
an inner NSE zone, composed of (54Fe+58Ni) inside and 56Ni outside, an outer
zone with Intermediate Mass Elements and a CO zone. Both the size of the NSE
zone and the fraction of (54Fe+58Ni) v. 56Ni are varied systematically. Models
with the same original NSE content but different (54Fe+58Ni)/56Ni ratios reach
different peak brightness but have similar light curve shapes. Synthetic
spectra indicate that the V-band decline rate is not affected by the
(54Fe+58Ni)/56Ni ratio. While the 56Ni mass and the total NSE mass are the
dominant parameters determining the peak luminosity and the shape of the light
curve, respectively, a variation in the (54Fe+58Ni)/56Ni ratio, which may
depend on the metallicity of the progenitor (Timmes, Brown & Truran 2003) is
likely to account for a significant part of the observed scatter of local SNe
Ia about the mean brightness--decline rate relation.
