Re: human-human K-40 dose- Reduction due to shielding of background

[RADPROJECT@aol.com]

In a message dated 12/8/99 9:41:50 AM Eastern Standard Time, m-woo@uiuc.edu 
writes: [quoting an earlier post about K-40 incremental dose to two partners 
in close proximity]:

<< According to UNSCEAR (1988) the annual effective dose equivalent from
 the body's K-40 is an estimated 180 uSv (18 mrem).  Now, in the case
 where two people share the same bed for 8 hrs/day, and assuming a
 geometry factor of 0.16 (this is probably subject to considerable
 variation; I don't want to discuss it), then each person would receive
 an additional annual radiation dose of approximately 10 uSv (1 mrem)
 from the other person's K-40.  This does not take into account any
 backscatter from a slab floor (a NORM problem itself!).
  >>
==============
Radsafers:

Any realistic calculation of incremental dose to an individual from K-40 flux 
due to K-40 within the body of an "other" person needs to take into 
consideration a missing refinement. The point being overlooked is  that 
having an other in close proximity to a person for some period of time 
doesn't just increase dose from the "other" but shields the person being 
irradiated from background flux from all natural decay series  including K-40 
and cosmic based on the solid angle one might assume between the parties and 
their average orientation in space.

If in bed, is the other shielding cosmic rays from the person by spending a 
lot of time between the person and space, or is the other spending a goodly 
fraction of time shielding the person from terrestrial gammas by shielding 
photon flux from the ground?

Having calibrated high pressure ionization chambers using the so-called 
"shadow shield technique", I know how much photon flux from a source can be 
attenuated by an object like a lead brick or a body placed between a source 
and a detector. This effect would likely significantly reduce any net 
exposure from K-40 flux from an other to an individual to the point there 
might not be any net exposure. I haven't done the calculation but this seems 
intuitively right.

BTW, IF there is any net exposure from K-40 in an other's  body, the exposure 
would be higher between two males [higher muscle mass in males vs. females 
due to more K-40 content in males] than that from a female to a male, and 
least to both individuals on average between two females.

Would ALARA considerations thereby be an argument against male homosexual 
relationships, and provide support for female  homosexual relationships? 
Obviously, if there is incremental K-40 dose due to in-body K-40 content, 
male/female average exposure would fall between male/male and female/female.

With tongue in cheek,
Stewart Farber
Public Health Sciences
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