certainty in the readings, owing to general com-
tamination of the environment. However, if elf the
observed radiation is ascribed to radioactive iodine
in the thyroid, the exposure amounted to a peak
value of a few thousandths of a roentgen per
day (9). The peak values for other human measurements in the United States for tests both in
Nevada andin the Pacific have been generaily onetenth or less of this level.
These data indicate that the highest measured
radiation dose to the thyroids of animals has been
below the level that might produce harmful effects
and that the highest measured radiation exposure
to the thyroid of human beings has been far below
that needed to produce any detectable effects.
—a value considered safe. These posible wands.
will becontinually checked by the Atomic Enesgy
Commission's extensive monitoring program new
in operation.
Neutrons (particles) that are released from a
nuclear detonation react with a nitrogen atom ia
the air to form radioactive carbon,called carbon-14,
which has a longhalf-life of about 5600 years. This
radioactive carbon enters into the biosphere (the
environmentofliving things) alongside normal car.
bon and thus finds its wayinto all living tissues and
irradiates the surrounding cells. Since carbon is
foundin ail living matter, the effects are similar to
those when the whole body is irradiated by an ex
ternal source.
logically important elements in fallout is strontium-
Because of its long half-life the amount of carbon-i4 in the world would accumulate until it
posited in the bones and continues to irradiate the
surrounding cells for long periods of time, since it
has a half-life of about 27.7 vears. The deposition
of relauvely large amounts of strontium-90 in the
bone would be expected eventually tw produce
the rate of production is equal to its rate of loss by
radioactive decay. Assuming a constant rate of preduction through yearly nuclear tests, an equilibrium
condition might be approached afver 30,000 years.
One-half of the equilibrium value would be reached
Owing to its relatively long half-life the amount
of strontium-90 will accumulate in the environment if more is continually added. Assuming a constam rate of yearly addition and no los through
weathering, an equilbrium condition would be ap-
A nominal-szed bomb produces about 1/45
pound of neutroms (/). If it is amsumed that each
peutron wil] react with a axrogen atom to produss
carbon-14, thea the total amount of this clement
produced would Se about 1/3 pound. It has been
suggested that a large thermonucicar weapen might
Internal exposure (long term). One of the bio-
90. If it is taken into the body, it is selectively de-
bone tumors (//).
proached after 150 vears— 1 sate un which the rase
of addition = equal eo the rate of los through
radiological decay. About aee-half of this equilibriuss amount would be reached m 78 vears. The
equilsbrura amount would be about 40 tenes the
aneual addition.
Az the present came the
contammnstoe
ef wrontiim-930 @ the Used Sas
about
15°100,000 macrocune per square foot. {A micro-
curie & a ‘ast for meamering the radboacuvity of 3
material. By defimiuom, a cune w 37x 10° dumm
sormal radamm comernt (/2
and | 1300 of the
reached an equilibrium state, a condition in which
in 5600 years.
produce as such as 140 pounds of carbon-1¢ (/3).
30,000 years, the aear eqpalibr:um amount of com
boe-14 thus creseed m the werid would be about
20 umes greater than the amount now prewnt.
There are about 180,000 pounds of carben-14
mamtand curremiy a asture m an equisbrem
sunee, owing w natural production by acutrams
(ereaerd by commec rays) reacting with enregm
of the am (1¢). However, tis amount comtribusm.
analy abo | percent to the wtal satura] redietien
dose recerwed by the body ‘weal natural rachetion
3 sbowt 3.1000 rormeses per week) (/5). Thus,
the equilbeor: acer: af carboe-14 (approached
ra 30,000 ears omght mcrease the eormel radia-
om dose to the body by 20 percent of the preset
value (9). The comchesion suust be aade that this
eflect 8 inconsequential.
Av, wate, and fish. Am amd woser usually con-
proach 73 10,000 eucronarie per tqaare hoon (9).
This is about |. 27 of the ammount of radium thar B
usually present and 1/150 of the amount estumased
to result eventually m the body's accumulating a
maxiszum permumesible body burden of strontiam-90
December 1955
so forth) (16). Inhalation of these radioactive say
terials present im the air resales im a radsetion deup
af 3,100 w 8/100 roentgen par week being dalle
ered to the hungs. The radbonctive camtent in water