SESSION I DISCUSSION
247
effect of older debris, with Sr concentrations becoming higher with
increasing altitudes.
FREILING: In looking at Dr. Drevinsky’s slides, I got the impres-
sion that, as the altitude decreased, there was moreactivity in the
larger particles and less activity inthe smaller particles. I am wonder-
ing whether the large particles you collected are large single particles
or
composites of smaller particles.
an electron microscope?
Have you examined these with
DREVINSKY: It is generally true that with decreasing altitude an
increasingly higher percentage of activity was found to be carried by
particles with 0.02 u<r<0.15 u relative to those with r< 0.02u.
[r is radius.} However, we have not studied our samples by optical
techniques to determine their physical nature.
FREILING: If they were formed by agglomeration pracesses, there
would be no reason to expect larger sizes to have a different radiochemical composition than the smaller particles.
Dr. Nielsen, do you have any comments ?
NIELSEN: No, I might ask Dr. Lockhart a similar question, i.e.,
whether or not he has looked at the larger particles he collects to
see if they are single particles.
LOCKHART: One nice thing about filter collection is that the
investigator does not have to worry about Single particles. He can
treat them all as a group the same way that Dr. Drevinsky did. Therefore we have not looked at individual particles at all.
.
I have a question for Dr. Nielsen about the ®*y and !4Sb. We have
seen no ‘Sb that stands out among the large quantity of ‘°Sb. The
8y is very low, but it is detectable, having about the sameactivity
as the small amount of gamma associated with the beta-emitting aly
Do you have any idea how these isotopes of antimony and yttrium
compare at ground level?
NIELSEN: The '*Sb concentration according to our figures was
about 5 dis, min, and the '4Sb was about 0.1 dis/min per 1000 cu ft.
It is less at the present time. Our latest figures show about 0.009
dis/min for ‘Sb and about 1 dis/min for !"5Sb,
The ®8y concentration is presently
about 0.005 dis/min. It has
fallen off quite a bit. For about two years the concentration was about
0.03 dis/min per 1000 cuft.
FREILING: I have a question for Mr. Benson. You mentioned the
activity per unit volume of the particles was such that you would infer
devices of greater mass producing these particles than was actually
the case. Since some of these high-yield bursts engulf many cubic