Chandra made the longest X-ray exposure of the region to date.

BBC: Black hole 'on a diet'

But according to follow-up studies reported by the Nuclear Regulatory Commission (NRC), the resulting average dose of radiation that about 2 million people in the TMI area received amounted to 1 millirem, six times less than exposure to a single standard chest x-ray.

FORBES: Media Hype Over Nuclear Energy Increases Anxiety And Confusion

Another option: The "Instant X-Ray" function on Morningstar.com will calculate an investor's exposure to sectors, geographic regions and security styles across a full portfolio.

WSJ: Single-Country ETFs: Risky Ventures