Project 2.1 (Reference 9). However, there is still some uncertainty on this point, and
the curves presented may be off in absolute magnitude, although the shape of the curves
as a function of time is probably correct.
The initial-gammavalues given represent those observed at the detector and should
be multiplied by a factor of approximately 1.2 to correct for station shielding.
This
factor of 1.2 is a measured value of the attenuation of the blast shield for Co” radiation;
the attenuation is a function of the energy of the incident radiation. Time is a factor
only in that after one minute there is little gamma radiation in this energy range (>1
Mev).
Figures 3.23 through 3.28 should be multiplied by 1.2 to give free-field values.
*
The data in Figure 3.26 is in reasonable agreement with similar data in Reference
9, especially after the data of Figure 3.26 has been extrapolated to a time equivalent to
that reported by Operation Redwing Project 2.1.
Figures 3.27 and 3.28 show that approximately "fy of the total-initial exposure for
Shot Flathead 221.04 and Shot Navajo 221.05 was delivered after the arrival of the shock
front. Most of this exposure was due to the enhancement caused by the hydrodynamic
effect because the exposure rate was decay.ng rapidly before the arrival of the shock
front.
Reference 9 compares measured-initial-gamima exposure -versus-distance curves
with curves computed from TM 23-200. For the purpose of comparison with published
data, integrated-initial-gamma-rate data from Figures 3.26, 3.27, and 3.28 of this
report have been plotted cn the corresponding curves from Heference 9. In addition,
extrapolation of Project 2.2 measu.ed data (integrated-initial-gamma rate) to include
initial-gamma dose delivered ufter the end of project records has been made using
information and 1acthods in Reference 1U.
Exposure received prior to stari of project
records has been neglected, since the e-.posure was relatively insignificant. The abovementioned plots for Shot Zuni are sneown in Figure 3.29 and for Shots Flathead and
Navajo in Figure 3.30.
3.3
BEACH-BALL MEASUREMENTS
The objective of measuring the exposure rute at the lip of the crater from Shot Zuni
was assumed by Project 2.2 at u lute Stuge in tne preparations for Operation Redwing.
The beach-ball instrument was dropped ontu the Shot Zuni crater lip at H + 6 hours.
The fall apparently caused a change in the calibration of the system, because the received data indicated an exposure rate ar high as 50,C00 r/brat this late trme. Furthermore, rotor interference mace reception of the transmitted signal difficult.
3.4
THERMAL-RADIATION DETECTOR
The thermal-radiation detector wus instalicd on Ste Nan for Shot Tewa at a range
of approximately 20 miles, and the detonation was satisfactorily detected.
49