  An affine manifold is a manifold with torsion-free flat affine connection. A
geometric topologist's definition of an affine manifold is a manifold with an
atlas of charts to the affine space with affine transition functions; a radiant
affine manifold is an affine manifold with holonomy consisting of affine
transformations fixing a common fixed point. We decompose an orientable closed
radiant affine 3-manifold into radiant 2-convex affine manifolds and radiant
concave affine 3-manifolds along mutually disjoint totally geodesic tori or
Klein bottles using the convex and concave decomposition of real projective
$n$-manifolds developed earlier. Then we decompose a 2-convex radiant affine
manifold into convex radiant affine manifolds and concave-cone affine
manifolds. To do this, we will obtain certain nice geometric objects in the
Kuiper completion of holonomy cover. The equivariance and local finiteness
property of the collection of such objects will show that their union covers a
compact submanifold of codimension zero, the complement of which is convex.
Finally, using the results of Barbot, we will show that a closed radiant affine
3-manifold admits a total cross section, confirming a conjecture of Carri\`ere,
and hence every radiant affine 3-manifold is homeomorphic to a Seifert fibered
space with trivial Euler number, or a virtual bundle over a circle with fiber
homeomorphic to a torus.
