~~
as a result of the sediment deposited in the water and could be evaluated adequately using only
an AN/PDR-39 survey type meter. The maximum contamination encountered in the lagoon
anchorages was 8,4 x 107° microcurie per milliliter. The average activity varied from 1 x
107¢ to 3x 1074 microcurie per milliliter. No ship’s drinking water was found to contain any
detectable radioactive material.
Air samples collected in fall-out areas by vacuum typeair filters and cascade-impactor
slides constituted another type of sample analyzed in the field laboratory. Upon those occasions
when fall-out was detected on board the USS Bairoko, portable air samplers were periodically
turned on as a meansto determine whether fall-out was still occurring. The entire filter paper
was counted and the activity was noted in counts/min per cu ft of air. Air samplers were also
used by the initial survey party. A cascade impactor, installed in the radiac repair shop on
board the Bairoko, was utilized to evaluate the inhalation hazard associated with the radioactive particulate matter by determining the percentage of the total activity associated with
particles less than 5 p in diameter. The air samples collected on March 1, when the USS
Bairoko received a substantial fall-out from
indicated activities ranging from 455 to
2740 counts/min per cu ft of air. The only cdscade-impactor data were also obtained during
the fall-out that occurred on the Bairoko. An average of 65 per cent of the activity was found
to be associated with particles less than 5 p in diameter.
4 ey
un
:
Decay-rate measurements and energy determinations were made on various types of
nples throughout the cperation in an effort to obtain detailed information on the fundamental
_serties of the radioactive particulate matter. Gamma energies were difficult to obtain acucately due to the low counting efficiency of G-M tubes for gammaradiation and the apparent
ty ¥ energies involved, The latter also made beta-energy determinations more difficult. Gamma
energies measured on very active samples varied from 600 to 25 kev. The low gammaenergies
measured were somewhat surprising. Beta energies varied from 0.2 to 2.2 Mev.
Log-log plots of counts per minute vs time after detonation were utilized to obtain decayrate data. Samples studied included fall-out samples on the Bairoko, water samples from the
lagoon and drinking-water samples from Rongelap, crater samples, and air samples. The following results represent a-cross section of the different types of sainples studied and the calculated slope of the line obtained by plotting the log of the activity vs the log of the time after
detonation.
1, Fall-out sample on the flight deck of the Bairoko, RuntI, 1.62.
2, Lagoon sample collected 1220 Apr. 7,
1.03 at +8 days and 1.31 at +25
days.
ee
3, Air sample collected Apr. 26,
~
© 1.19
The six drinking-water samples from-Rongelap indicated an average slope of —1.48 from
CH ewe) 4eae oo. © > Anerpenatiacene SAR syptlce Ha
“Se
.
___fr4.2 days to’
+10 days and a slope of ~—1.80 until last counted.
~~Miscellaneous tasksassigned to the radiation-analysis section included the analysis of
urine samples for tritium content; examination of food, soil, and water samples obtained ona
resurvey mission to Rongelap and Uterik; a study of the decay characteristics of contaminating
material on vans being shipped to the United States; and analysis of water samples obtained
during a water survey following Zombie event.
4.6.10
Conclusions and Recommendations
(a) Conclusions, The present maximum permissible exposure of 3.9 r per 13-week test
period is not a realistic MPE in co.sideration of heavy work loads in extensively contaminated
areas, The use of waivers to-cover exposures in excess of this MPE Lecomes a needless routine without much significance when operations are conducted in large contamination areas
without much interval between detonations. A large number of individuals did exceed 3.9 r, but
very few exceeded 6.0 r.
The utilization of project personnel as monitors proved itself with few exceptions.
Procurement and ciearance of personnel must be accomplished at least four months in
advance of operations in order that selection and training can be completed and in order that
the unit can be completely assembled prior to movement overseas,
72