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Bananas (K-40)



Dear Radsafers,

Inspired by the recent discussion we had about BBq (bananabecquerels) I 
wonder if you could help me with a calculation. Going back to the data, 
bananas should contain about 100 Bq (K-40) per kilo. My mind then went 
to boat transports of bananas. A boat for Sweden may typically come with 
6000 tons of bananas in one transport.

The reason for this reflection is that we presently have a political 
"discussion" (in a few newspapers) about Bq:s on the surface of 
containers with nuclear fuel waste – containers that should have less 
than 4 Bq/cm2 -these are shipped by boats – I don’t know what kind of 
Bq:s there typically are but according to a couple of sources, 2% of 
surface tests were recently above 4 Bq/cm2 and at least one spot had 40 
Bq/cm2 (scenario: touch it – pick your nose and get 40 Bq). The 
containers are 6.15 m high and have a diameter of 1.95 m (cylindrical 
shape) in case somebody wants to play with numbers there.

Now, Swedes eat about 135 million kilos of bananas per year (almost 9 
million people, 15 kg/capita, side topic – not necessary info. for my 
question below). BTW: After joining the European market – our banana 
consumption has fallen by 25%. This is probably bad health news 
considering vitamins, tryptophan and other essentials that bananas 
contain.

My question concerns the K-40 related dose rate for someone working 
close to the bananas on the boat. The bananas come in boxes so for 
simplicity, I think one can assume that the "critical group/person" is 
standing 1 meter from the wall of a "cube" or "rectangular superbox" 
with bananas (symmetrical position – same distance to the right as to 
the left corner). I realize that some assumptions must be made here 
about density, self-absorption etc –but I still ask: Can anyone simplify 
the problem and give me a realistic estimate of the K-40 dose rate? I 
don't expect any megadoses to come out from this - it is more of 
curiosity in the question.
(And then the cylinder above, with say 4 "equal" Bq:s/cm2 on a 1 m 
distance could be a perhaps more complex task. The cylinders are made 
out of steel and lead – from preliminary info – one can assume that the 
contribution outside from the spent fuel is zero).

I may mention that the 40 Bq/cm2 have been reported to the police by a 
member of our green party. After the Chernobyl accident she drove by car 
at least 200 km to buy "becquerel free" milk (she has at least six 
children – I am thinking about the high responsibility to stay alive as 
a parent – that factor should be sixfold).

These lines reflect my most personal considerations and thoughts that 
others may not necessarily share.

Bjorn

bjorn_cedervall@hotmail.com
Depts. Medical Radiation Biology and Medical Radiation Physics,
Karolinska Institutet, Box 260,
S-171 76 Stockholm, Sweden
Ph/fax: Int + 468 343525 (Med. Radiation Physics)
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