
   Fallout Fundamentals
   Fallout   consists of dust particles that have been coated with  radioactive
by-products  from atomic explosions.   This occurs when the nuclear  or  atomic
blast  is a ground rather than air-burst (air-burst meaning that  the fireball
is   far  enough   from the earth's surface that there is  no  ground  material
uptake  into the high temperature portion of the mushroom cloud).   In an  air-
burst the bomb products condensate into such very small particles that they are
aloft  for  such a long time that they are mostly non-radioactive by  the  time
they  come  down,  typically months or years.  The fission  process  gives  off
hundreds  of  different  radioactive elements and isotopes.   Also,  a  certian
portion  of the fission mass does not fission.  The fussion portion of  nuclear
bombs  is  clean and gives off only helium, the atomic bomb  trigger  (fission)
which starts the nuclear bomb (fussion) is the portion of the bomb that  leaves
radioactive by-products.
   These   by-products   can  be classified  by  their  characteristics.    One
characteristic is half-life.   The half-life is the length of time it takes for
an element to give off one-half of its total radioactivity.  This would also be
the  length  of  time required for a given amount to  change  to  one-half  the
radioactive  level, in other words if something was giving off  radiation  that
would yield 3 Rads/hours, after one half-life it would give off 1.5  Rads/hour.
An unstable  isotope  only  emits radioactivity  when  one  atom   decays   to 
another  isotope  or element (which may or not be stable,   stable  being  non-
radioactive).    Therefore  the  portions of the element that are  not  in  the
process  of  decaying  are  not  giving  off  any radioactivity.   If you  have
"X"  number of atoms of a radioactive element,  "X/2" of those atoms will  give
off their radioactivity in the half-life period and become a different  element
or isotope.  If an element has a half-life of 1 day, a given amount of it  will
give off 1/2 of its total radiation during the 1st day,  1/4  during the second
day,  1/8 the 3rd day,  1/16th the 4th, 1/32 the 5th, 1/64 the 6th, 1/128th the
7th,  et cetra. If you have a short half-life like Iodine 131  of 8, days  most
of  the radioactivity (99+%) will be emitted in two months.   In a  long  half-
life element like plutonium 239 with a 24,400 year half-life,  1,000,000  atoms
would in 24,400 years give of 1/2 of their radioactivity  leaving 500,000 atoms
of plutonium 239 at the end of those 24,400 years.  500,000 decays over  24,400
years equals approx. 21 decays per one year.
   Another characteristic is the type of radiation given off, Alpha, Beta, or
Gamma radiation.  Neutron radiation is only given off by the actual blast 
itself and is not given off by the fallout itself.  Only neutron radiation
can MAKE something that is not radioactive become radioactive.  This is why 
fallout can not cause something (like food inside a can) to become radioactive.
Alpha, beta, and gamma radiation can NOT make anything become radioactive.
Alpha radiation (helium nucleus,  2 protrons and  2  neutrons),  like  from 
plutonium, can be shielded with one layer of Cellophane or newspaper or several
inches of air.   Beta radiation (an electron) can  be  shielded  by  a layer of
drywall, or several feet of air.  Gamma radiation is electromagnetic radiation.
Neutron radiation is a neutron and is about twice as hard to stop as Gamma.
Gamma and neutron are harder to stop, you need several feet of dirt or 
concrete to absorb them. See below for specifics for stopping Gamma radiation.
   One  factor  that most people don't realize about fallout is   how  fast  it
decays.   Fallout follows the t-1.2 law which states that for  every  sevenfold
increase in time after detonation there is a tenfold drop in radiation output.
Example,  a  reading of X level of radioactivity at Y  hours  after  detonation
would  indicate a level of radioactivity of .1X at 7Y hours  after  detonation.
This  is  accurate  for  2,500  hours  (14  weeks)  following  the   explosion,
thereafter  the doserate is lower  than  t-1.2 would predict.   Example,  if  a
dose  rate of 100 REM/hr was found at 1 hour after detonation(this assumes  all
significant  fallout  from the bomb has fallen,  therefore  starting  with  the
seven hour point  is  probably  more realistic) would be 10 REM/hr at 7  hours,
1  REM/hr at 49 hours(2 days),  .1 REM/hr at 343 hours(2 weeks), .01 REM/hr  at
2401 hours (14 weeks).  A "survival safe" dose of radiation (this being defined
as no short term effects or disability) is  3 to 12 Rads/day. This dose rate of
3-12 Rads/day can only be taken to an accumulated dose of 150-200 rads if  done
day  after  day. This would occur (assume 6 Rads/day) in this  example  at  150
hours  for 24 hour exposure,  or at 49 hours for a 6 hours per day  outside  of
shelter.  Note though that since the level of activity is decreasing  the  time
spent  outside every day would increase.  If you increase the  radiation  by  a
factor of 10 for another  example would be where you would have 1,000 Rem/hr at
1 hr, 100 Rem/hr at 7 hrs., 1 Rem/hr at 343 hrs., .1 Rem/hr at 2401 hrs. The 24
hour  exposure would be at 1,000 hours(41 days) and 6 hour work day outside  of
shelter at 300 hours(12 days).
   For various levels of contamination a "no short term effects" dose of 6 Rads
per day would be something like this: (for 80 col. printout)(measurements at 
boundries of the oval shaped pattern)
 
Hours from   Dose rate   Hours of "safe" work outside per day, medical effect
explosion   
   EXAMPLE A   An area 10 miles wide by 30 miles downwind directly downwind
               from of a missle field that gets dozens of hits
1 hr.      10,000 R/hr  None, 100% dead at 6 minutes of exposure
7 hrs.      1,000 R/hr  None, 100% dead at 1 hour of exposure
2 days        100 R/hr  None, 50% dead within 3-4 hour continuous exposure
2 weeks        10 R/hr  36 minutes. 50% dead for 2 day continuous exposure.
14 wks(3 mo)    1 R/hr  6 hours/day. 50% dead for 1 month continuous exposure
                        5% dead for 15 day continuous exposure, no medical care
                        and no deaths for 1 week continuous exposure.
   EXAMPLE B  An area 10 miles wide by 30 miles downwind of a single 1 MT
              ground burst
1 hr        1,000 R/hr  None, 100% dead at 1 hour of exposure
7 hrs.        100 R/hr  None, 50% dead within 7-8 hour of continuous exposure
2 days         10 R/hr  36 minutes. 50% dead for 5 days of continuous exposure.
2 week          1 R/hr  6 hours/day. 50% dead for 1 month continuous exposure.
14 weeks      0.1 R/hr  All day.  0% deaths from radiation hereafter.
    EXAMPLE C An area 12 miles wide by 95 miles downwind for a single 1 MT
              ground burst
1 hr         radiation has not arrived yet.
7 hrs.         50 R/hr  12 minutes, 50% dead for 18 hour continuous exposure
2 days          5 R/hr. 1 hour, 5% dead for 2 week continuous exposure
2 weeks       0.5 R/hr  12 hours/day.
14 weeks     0.05 R/hr  Unlimited.
  The above three examples indicate conditions and exposures that would only
be acceptable in wartime.  In these examples the wind is continuous in
direction and velocity.  A real wind would not make such nice neat ovals.  It
should be noted that even in real wind conditions, marching perpendicular to
the depositing wind will remove you from a individual fallout zone.

  Here is an example of the levels of contamination from a single 1 MT ground
burst with a 15 MPH wind
Area downwind Arrival  Accumulated total radiation dose   Dose Rate in Rads/hr
(boundries)   time for                                          at
in miles      fallout  1 week  4 weeks  15 weeks  100 yrs 7 hrs. 2 days(14 hrs)
33 x 7        1.5 hrs  3000 R  3300 R   3600 R    4600 R  100 R/hr   10 R/hr
95 x 12       5 hrs.   900 R   1200 R   1400 R    1700 R  ~50 R/hr    5 R/hr
160 x 18      10 hrs.  300 R   400 R    460 R     650 R not there yet 2 R/hr
245 x 20      16 hrs   90 R    120 R    150 R     240 R not there yet 0.7 R/hr

   For shelter from Gamma radiation the standard rule of thumb is 150 pounds of
mass per square foot of cross section of shelter wall yields a PF, protection
factor, of 40.  This means if you had two shelters on a flat contaminated field
with  one  having walls of one layer of cellophane and the other of  walls  and
ceiling  of  something that had for its thickness 150 lbs/sq.  ft.(  note  this
would  be  a thickness of 2.5" of lead, 4" of steel, 12" of  concrete,  18"  of
soil,  30" of water, 200' of air) you would recieve 1/40th the dose in the  150
lb/sq.ft. walled shelter.  This effect can be multiplied.  If the sq. ft. cross
section  was  300  lbs.  that would be 1/40th of 1/40th  or  1/1,600th  of  the
unprotected  dose.   Take for example a dose rate starting at 100 Rem/hr  at  1
hr.,10Rem/hr  at 7 hrs.,1 Rem/hr at 49 hours,  etc.  If exposure started  at  1
hour the total dose would be 240 R in 1 day, 310 R in 1 week, 350 R in 4 weeks,
390  R in 15 weeks.  The same in a PF 40 shelter would be 6 R in 1 day,  7.7  R
in  1  week,   8.7 R in 4 weeks.  The difference would  be  5%  fatalities-most
others  suffering from nausea and taking about 1 month to recover  without  the
protection  versus  0% fatalities-0% sickness with protection of PF40  in  this
case.
   Another  example  with a dose rate starting at 1,000 Rem/hr at 1  hr.,   100
Rem/hr at 7 hrs., 10 Rem/hr at 49 hours, etc. If exposure started at 1 hour the
total  dose would be 2,400 R in 1 day, 3,100 R in 1 week, 3,500 R in  4  weeks,
3,900 R in 15 weeks.  This in a 40 PF shelter would be 60 R in 1 day, 77 R in a
week,  87  R in 4 weeks. In a 1,600 PF shelter this would be 1.5 R  in  1  day,
about 2 R in 2 weeks, about 2.5 R in 15 weeks.  The differences here would be -
no  protection = 100% fatalities in several hours - PF 40 = 0% fatalities,  25%
suffer nausea(at the most) with total recovery in 7 days, - PF 1600 no effects.
   Please note that protection factor increases as a multiple.  If 150  lbs/ft.
sq.  = a PF of 40(1/40th or 2.5%), 300 lbs/ft sq. = a PF of 1,600(1/1,600th  or
0.0625%), and 450 lbs/ft. sq. = a PF of 64,000(1/64,000th or 0.0015625%)

Typical Swiss domestic shelters have a PF of 16,000 to over 2,500,000.

