aldered separately. For canisters Nos. 2, 3, and 5, the mean effective yield, determined by
using Eqs. 3.4 and 3.5 for 1 Kt as described previously, is found to be 790 Kt. Thia is considerably greater than the currently reported radiochemical yield of 550 + 15 Kt. For the
canisters in the Mach region, the mean effective yield is found to be 1400 Kt, and it will be
noted that the overpressure vs distance curve computed on this basis gives very satisfactory
agreement with the Sa’ dia ground-pressure measurementsplotted in Fig. 3.8, except that, as
in the case of Mike shot and presumably fo.. the same reason, the overpressure measured on
the ground at very long range Js quite low compared to the equivalent reduced values from the
high-altitude gauges.
wrteed at AetinenbeteMnon anes tialSalta
before the arrival of the reflected wave and those measured at the other canistera represent
the superposition of direct and reflected waves in the Mach stem, the two groups are con-
8.3.2
Thermal Radiation
stra
The data frora the canisters in the Mach region are consistent with the free-air values
measured at canisters Nos. 2, 3, and 5 if it is assun:ed that the overpressure in the Mach stem
at points far below the triple point is equal to that which would resutt from a surface burst
with a reflection factor of 1400/790 = 1.77, Whether this vatue of the energy-reflection factor
is consistent with the observed reflected-shock-pressure increments at canisters Nos. 2, 3,
and 5 cannot be determined since there is not available a theoretical treatment of the pressure
distribution in the neighborhood of the triple point that wuuld permit a comparison between the
two.
The root-.nean-square percentage deviation of the spserved values from the computed
curves is 6.8 per cent including the data from caniste. No. 6 and 3.1 per cent omitting this
point.
3
Measurements at Operation Ivy. The points and referenced data are given in Fig. 3.9. For the
UCLA data the mean of the two values from the B-36 was used. From this single point an
“attenuated” curve and a “vacuum”plot of intensity vs distance are estimated. Since only pre-
_
Lf
liminary data are involved, crude assumptions were usedfor the effective attenuation without
attempt at refinement.
Both these comparisons and the bomb-radiation yielda would lead to estimates of higher
thermal-radiation intensities than recorded by the canister thormocouple. {t is therefore
necessary to review possible sources of error. Among these possibilities are the following:
Yt was known that a bare thermocouple, i.e., unenclosed by a translucent envelope, is sub-
jected t. wind effects. V*...i blowing across a hot junction causesit to give low readings because the junction ig cooled. (A possible type, as yet not thoroughl:7 tested and which could not
be procured in time to use on this operation, is described in Sec. 4.2.) As controlled by the
parachutes, the descent rate is approximately 30 ft/sec. Horizontal wind and Llast winds add
to the uncertainties of the data.
The hot, radiation-sensing junction is a minute bead. The directional sensitivity of a
spherical receiver differs from that of a plane receiver. The radiometers nearest the burst
cannot be assi.med to be “looking” at the point source; hence the dependence onthe inverse
square of the aictance may deviate somewhat.
Changes in the spectral character of the burst resulting from absorption by the products of
photochemical reactions and by radiation degeneration to the infrared would tend to result in
lower thermal yields.
Reflection of radiation from ground (earth and water) and from clouds would increase the
intensities; a cloud between the burst and a radiometer would decrease the intensity.
In comparison with an air burst, for a surface burst the effects of reflection from the
ground are even moredifficult to assess.
35
RESTRICTED DATA (ND SECURITY INFORMATION
weg
The information on thermal radiation may be most conveniently examined by comparing it
with the best data now avaiable from Tumbler shots Nos. 1 to 4 and the preliminacy information from Mike shot as given in the report from the University of California,* Thermal-radiation