  We calculate the HBT radius Rs for {\pi}+ particles with the Coulomb
interaction by using the string melting version of a multiphase transport(AMPT)
model. We study the relationship between the single-particle space-momentum
angle and the particle sources and discuss HBT radii without single-particle
space-momentum correlation. Additionally, we study the Coulomb interaction
effect on the numerical connection between the single-particle space-momentum
angle distribution and the transverse momentum dependence of Rs.
