altTokyo.com

Part 1:  Designing the equipment:
You cannot simply point a geiger counter at a plate of food and expect to find anything, you really need a lab to test with far more sensitive equipment and procedures.
     Fellow longterm expat, Allan, has been determined to find a way to do this cheapily.  Using the very sensitive pancake detectors (2x LND 7318 GM tubes – sensitivity 35.45cpm (each) at background of 0.10uSv/Hr) pointed at each other in a copper tube which is then encased in at least 50mm of lead to shield out any external radiation.     Dried food samples can then be placed in the tube to determine any beta radiation.

Twin pancake geiger sensors in a lead capsule for food testing.

 Part of the aim is to establish how low the threshold will be. Obviously it would be nice to get readings below 10Bq/Kg but this is unlikely.
Bananas are 150Bq/Kg and the average banana is 150g. So if we can take one (or more) banana(s) and dry it(them) out and measure any increase we know we are on the right track, but far from our target as we would like to be more than 10 times this sensitivity.
Also keep in mind that the pancake will have a different sensitivity to K40 (the Isotope in a banana) than it will to Cs 137.
So in order to be useful our calibration must be based on Cs137/134. This means we look for food contaminated with Cs137/134 and test that. Once we are able to detect an increase in reading we then need to test that same sample in a lab and this will enable us to calibrate our display directly in Bq. To get Bq/Kg we simply divide by the pre-dried weight (in Kg) of the sample.

One of the LND 7318 GM tubes

Considerable effort has been made melting lead and moulding a thick shell 50mm thick to encase the copper pipe shell which itself contains  sensors and testing area.   The completed “bucket weighs 50kg and the lid 10kg!

 

Lead casing that encloses sensors, electronics, and dried food samples.

 

Next step is to perform tests empty to determine self count and calibration, then to obtain suspect greens and dehydrate them for test samples.     More info on progress to come soon.   Please direct any technical advice,  to the forums, this is only a simple  explanation here.   We really look forward to the test results hopefully soon.