Cloud samples

The over-all distribution function consists of a linear combination of two lognormal functions. This is based on the observation that size distribution from very early aerial clouds samples from subsurface detonations are described accurately by the lognormal form of distribution. (This is shown below in connection with subsurface detonation analyses.) It is also supported by the work of particle analysts in industry, who find that particle population produced by crushing or grinding are described by lognormal distributions. 

As in the case of the land surface burst, complete characterization of the particle population requires only that particle mass, a volatile species, and a refractory species distribution with particle size be determined. All other isotopic distributions may be deduced from the istotope partition calculations described above. In the subsurface detonation, the earliest aerial cloud sample was obtained in the cloud 15 minutes after detonation. The early sample was, therefore, completely representative of the aerial cloud particle population. In Figure 5 the results of the size analysis on a weight basis are shown. Included for comparison is a size distribution for the early, local fallout material. The local fallout population and the aerial cloud population are separated completely from the time of their formation. 

In considering the correlation results, it is well to keep in mind the range of fractionation, as indicated by the values of the r89,95 ratio, shown by the samples in question. For the Small Boy event most of the gross samples from the collecting stations in the local fallout field yielded values of 189,95 in the range between 0.1 and 0.2. However, when cloud samples, sieve fraction samples, and samples from the peripheral stations are also considered, the range of the ratio runs from about 0.01 to about 7.0. 

Units are in fissions for the cloud samples and fissions/gram for all other samples. 

Cloud sample results are in ma. or fissions all other results are in ma./gram or fissions/gram. The exponent in the last column applies to all columns. 

Cloud samples 245 were collected between 40 and 45 minutes after detonation at a height of 15,000 feet. Cloud samples 827 were collected one hour after detonation between 16,500 and 17,500 feet. Cloud samples 837 were collected one hour after detonation between 16,500 and 17,500 feet. Cloud samples 837 were collected at 16,000 feet approximately 1.5 hours after shot time. Cloud sample 842 was collected at 16,700 feet approximately 2 hours after shot time. 

Figure 1. Particles from the cloud sample KC-1, showing both spherical and irregular particles...

Finally, the ionization current per gram, sy, has been calculated for 21 days after the event and compared with s95. Unlike the cloud sample, the KH sample was fractionated. The standardized (i.e., corrected to a reading of 560 X 10"9 ma. for a 100-/xgram radium standard) unfractionated value of this ratio at 21 days has been determined by Mackin to be 4.7 X 10"21 ma. per fission (10). The value determined here is only half of the theoretical value. Crockers calculations show that 140La contributes 60% of the ionization rate from an unfractionated sample at this time (2). Depletion in 140La therefore undoubtedly contributes to the... 

The Particle Size Distribution of Nuclear Cloud Samples... 

The size distributions of the particles in cloud samples from three coral surface bursts and one silicate surface burst were determined by optical and electron microscopy. These distributions were approximately lognormal below about 3/x, but followed an inverse power law between 3 and ca. 60 or 70p. The exponent was not determined unequivocally, but it has a value between 3 and 4.5. Above 70fi the size frequency curve drops off rather sharply as a result of particles having been lost from the cloud by sedimentation. The effect of sedimentation was investigated theoretically. Correction factors to the size distribution were calculated as a function of particle size, and theoretical cutoff sizes were determined. The correction to the size frequency curve is less than 5% below about 70but it rises rather rapidly above this size. The corrections allow the correlation of the experimentally determined size distributions of the samples with those of the clouds, assuming cloud homogeneity. 

In this paper we report on the results of size distribution measurements of cloud samples from three coral surface bursts and one silicate surface burst and present the results of the calculations of the sedimentation correction. 

Table II. Sampling Data for Some Cloud Samples from Ground Surface Bursts...

The size and mass frequency curves of the complete cloud samples, derived from those of the fractions and the fraction weights, are shown in Figures 2 through 6. The sedimentation corrections have been applied. They are quite small for all but the largest particles found. 

The size frequency curves for debris in cloud samples from surface and near-surface nuclear bursts generally has a lognormal shape below a few microns but obeys an r p law between a few microns and about 70 /x. The value of p is probably about 4 but is still subject to some conjecture. Removal of large particles prior to sampling as a result of sedimentation does not allow for any definitive conclusions about the shape of the size frequency curve in the cloud. 

A Comparison between Cloud Samples and Close-In Ground Fallout Samples from Nuclear Ground Bursts... 

Choice of Zuni is dictated partly by the fact that prompt fallout samples were obtained near the test site and that a fallout collection ship was located about 85 km. from ground zero. Thus, the opportunity exists to compare samples in the same size range but collected under quite different conditions. The Zuni cloud samples were obtained at an altitude of 12.5 km. about 3 hours after the explosion. The Zuni cloud at stabilization extended from approximately 15 to 24 km. vertically. 

With respect to the cloud samples, which were analyzed 11 years after collection, their chemical form may have been altered. Also, it is... 

Figure 5 is a similar plot for "Mo that also includes data for 147Pm (7) in the Zuni cloud. This cloud sample shows remarkable agreement with the distant Zuni fallout sample. In other respects the comments on Figure 4 are applicable to Figure 5. 

Magnitude of Specific Activity in Cloud Samples. The specific activities of all nuclides—refractory and volatile—show higher values in the cloud samples and in the 85-km. downwind fallout samples from Zuni. It is to be emphasized that these are undifferentiated samples—i.e., no attempt is made to distinguish between radioactive and nonradioactive particles—and that both the cloud and the downwind fallout samples are not representative of the core of the nuclear cloud but only of its lower fringes. Accordingly, specific activities within the core of the cloud should be even higher than those observed. 

Figure 10. Phase diagram of PS-1.2SK / PMMA-6.3SK. (x) - cloud samples, (°) transparent samples,...

---