Low-lying excited states of
46
Ar have been studied via inverse-kinematics proton scattering with a thick
target. Coupled-channels calculations have been used to extract the deformation length of the 2
+
1
state. This
result, combined with existing Coulomb excitation data, yields a ratio of the neutron-to-proton transition matrix
elements of
M
n
/M
p
=
1
.
19(25)
N/Z
, showing a departure from the proton dominance observed in the
N
=
28
isotones above
48
Ca. The status of the
N
=
28 shell below
48
Ca is discussedstatus: publishe
