aan,
soentgens, when an aircraft with a speed of at least 0.8 mach is used, and when
sanoling is performed later than two hours after shot time.
¢.
Collection Times
.
As mentioned in .aragraph 1, the amount of radioactive material
collected for a fixed pilot exposure (3.5R total) increases with how auch radio-
‘active decay has taken place by the time sampling is performed. Opposing delay
in samoling is the risk of failure which increases as cloud dircersal takes place
according to the effects of the vertical velocity gradient and angular shear of
the wince structure in the region of the desired altitudes. Jor Mike Shot on IVY
a slow rate of cloud dispersal due to a favorable wind structure permitted suc:
cessful sampling as late as six hours at about 7,000 feet true altitude, while
for Kine Shot that portion of the’main body of the cloud which lay between 359,000
and 15,000 feet dispersed so rapidly that sam>ling at these altitudes was in-
effective three hours after shot time.
Later samples had to be collected at
lower altitudes where the wind structure did not disperse the cloud so rapidly.
Although dispsrsal effects can be estimated from tho wind structure predicted for
shot time, a wind structure which is predicted to be unfavorable may not offer a
very powerful argument for a change in shot schedule. In order to achieve maximm
gtc.cle Bises, operational planning for CASTLEcloud sampling should be based on
acuvsl cloud penetrations conducted in three phases over the followinz appropriate
tine intervais:
let phase:
2nd phase:
3rd phase:
H/¢ 2:00 to Hf 3:00 Hours
H?# 3:00 to He 4:00 Hours
Hf 4:00 to Hf 5:30 Hours
Thnees times are chosen on the basis of favorable cloud dispersal
aod recistion intensities as the minimum times to ceach an in-cloud radiation
ex205uTe eauivalent to a total exocsure of 3.5R on landing.
In the event of
micvcrabic wind structure, the first flight will certainly collect the desired
- géccolze, the second will srobably do sc, and if necessary the third can bc
fiou:, at other, soseibly lower, altitudes where the cloud persists longer. On
the basis they the above minimum time for the third flight may frequently bc insufficient under operationel conditions, e longer flight time would be desirable.
Since cloud cissersal appears to be less ranid at 50,000 feet or above, a higher
eltitude would also be desirable for this flight, if this were pogzcible. An
elternative to the above schedule, in the event of an extremely unfavoreble wind
corditicn, would be to start to obtain all samoles at not later than two hours
aftez shot tine and to sacrifice a possible increase in aamole size.
Gd.
Collection Altitudes
Tne degree to which a samole is representative of the totel bomb
detris is normally found to depend on how far below the main cloud mass it is
collecitsd. for this reason, it is desirable to collect sammles either in the
main cloud mics or es close to it as possible.
For bombs with yields up to 509
kiiotons, anc perhaps to 1000 kilotons, satisfactory samplinz of the main cloud
mace can be cchieved at altitudes up to about 45,000 feet true (usually not lover
then 35,000 rect except for very small yields) on tests conducted at the Enixetcl:
Proving Grourc where the mean tropopause height is ebout 55,000 feet.
For the
higher yield: of the really "super" devices the desirable seamsling altitude should
be at least 55,000 feet to permit collection of materia? more representative of
tne main clouc mass.
~X- S-
| COPIED/DOE
f LANL RC
a.
343F