~

and ther hodograph forecaue sucn-particles tsetrpive ay this positios e@ _.
plua five hour, A second possible sourve wee fallou® from & highes por=

ties of the eloud (perhape as higha# twenty thousand feet). Inthis.
event the particles wuld have moved first ta the nort& and thes havo beer ©
earrévdtuck to- tiie west by the "easterlies".

The former source ip. ~= ~~

believedemst likaly since the time of arrival correlates auch bettes in
that case, Had tits contamination continued te move at its original specd
and dimastion, it would have arrived in the vicinity of SNTETOK Atolk

at approximately plus lixteen hours. The fact that ne such contaminatioss
was reported there is beliaved due to continued fallout and to dispersion.
Sinee
further contamination was reported in the patterrr, "ILSON THRES

was difsctcd by Rad Safe to begin an orca search to the northeast at plus
six (0200Z) hours. This search was conducted at nine thousand facet. A

contamination contact of 50 ar/hr waa aide at OLL7 Z (plus 7 hours) 100

milesnortheast of BIXKII.

This contaets tallics well with the forecast

position of fallout from tho twenty and thirty thousand foot levels = especi-

ally when it is considred that as a particle fall it was influcneed by

winds which were sligntly less strong.

No further contacts were reported

by 7ILSON THRES. This was to bo axpectud since the remainder of the search
wos. to the corth and aast of the cloud's path.
c. “ILSON TO, flying at 10,000 fect, nade no contamination con=
tacta in the ractrack pattern prior to his departure at 225QZebrea. Three

contacts were reported, however, between 2348 and OOLCGZ in the area search

to the east of Ground ceroe The maximm reading of 250 Ur/ir waa reported
at 2353 Zebra, 100 miles east-northeast of Bikini, at alaost exactly the
forecast 0020-Zebra position of the twenty and thirty thousand foot part=

tele trajectories. This fallout almost certainly produced the appreeio@
able (but not hazardous) contamination. of RONGERIK and nONGELAP Atolls.
Subsequent reports were only aircrart radinticn backgreounde
de

Subsequent “ILSON flights were cancelled: whem it appeared

that no ap regicble air contamination oxistec in the vicinity of the test
site.

6.

"ZA THER RECONNAISSANCE FLIGHTS:
A POUTREL LILA weather r.cam aissa ce flight on plus one day mde a

cont:c& of aporoximately 3 Mr/Hr, 520 2ilcs southwest of Ground Zero at

plus 28 hours,

This position grees well with the plus 28 hour position

of the very low levels of tho cloud.

It is sore likuly however that this

moterial, which wis encountersd at tun thousand fect, was actu lly fall~
cut from a much higher levol. In that case thc mturial would Anve moved
to the northeast and then have been carried boek to the wust when tha

prevailing “eastcriics" reestablished themselves after KOON.

A second

contest, this time of 4 Mr/Hr at twenty t-ouaand feet, nas-ma-do five hours
later narth—northoast of ENIVETOK.

Similar to thet just discussed.

This mterial aust havo had a history

In both enrsos tha contamination appears

to have bBcon confined to a rol.tively small creay,.

Mel?

Select target paragraph3