Alan, I experimented a little bit. At the moment, using your code and
also (now that I know what to look for) POV-Ray's example files, I am
ending up with this:

sphere
{
 < 0.0, 0.0, 0.0 > 10.0
 pigment { rgbt 1.0 } //makes it invisible
 hollow // enable it to contain your media
 interior // the "magic" starts here
 {
  media
  {
   emission 0.5
   intervals 1
   samples 5
   method 3
   density
   {
    spherical
	color_map
	{
	 [ 0.0 color rgb < 0.0,     0.0,     0.0 >        ]
	 [ 0.1 color rgb < 0.74902, 0.34118, 0.22353 > /4 ]
	 [ 1.0 color rgb < 0.74902, 0.34118, 0.22353 >    ]
	}
   } // starts at 1 at <0,0,0> and drops to zero at radius 1
  }
 }
 scale 10.0
 translate < 0.0, 0.0, 0.0 >
}

cylinder
{
 < 0.0, 0.0, -50.0 > < 0.0, 0.0,  50.0 > 2.50
 pigment { rgb < 1.0, 0.5, 0.0 > }
}

The media sphere, and for test purposes a cylinder.
I am quite happy, but would like still to have the same high density
within 1.0 units from the center, and then a fading out from 1.0 to 1.3.
The fading out I achieve, is not regular enough - it seems to end quite
fast.

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