  We propose a sensitive measurement of the charm total cross-section at RHIC
through muon identification from charm semileptonic decay at low transverse
momentum ($p_T$). This can test the binary-collision scaling ($N_{bin}$)
properties of the charm total cross-section and be used to study whether
heavy-flavor quarks, which are used as a probe, are produced exclusively at the
initial impact in hadron-hadron collisions. The effect of the charm
semileptonic decay form factor on extracting the total charm cross section and
on the shape of the lepton spectra are also discussed in detail. We conclude
that lepton spectra from charmed hadron decays at transverse momentum
$p_T\simeq1.0$ GeV/$c$ are sensitive to the charmed hadron spectrum shape.
Therefore, the interactions of heavy quarks with the medium created in
relativistic heavy-ion collisions, especially the flow effects, can be
extracted from the lepton spectra from charmed hadron decays at low $p_T$.
