In the attached image, it looks like their whole shield is lined with copper. Am I wrong in having assumed that the copper shield is only needed around the detector? Or is this a different case because, as described in the woodshole article, it is a well detector?
http://ourradioactiveocean.org/results- ... l#analysisDetection limit:
Our current detection limit using this method is about 0.1 Bq/m3 for 137Cs and 0.2 Bq/m3 for 134Cs. Values below this are reported as “below detection,” but this detection limit will vary with the sample size, the methods and detector used, and the total time each sample spends on the gamma detector. In general, larger sample sizes (we process a relatively large 20 liter sample), longer counting times (we typically leave a sample on for 48 hours or more), and more efficient detectors (we use some of the world’s most sensitive gamma detectors) lead to the lowest possible detection limits.
great summary here: http://www.whoi.edu/page.do?pid=83397&t ... &cid=94989
tests results here: http://ourradioactiveocean.org/results.html