1 additional deposition of particles carrying their lead from somewhere 



2 else. 



3 You can't really distinguish between those two. 



4 DR. HECKER: That's what I was trying to ask. 



5 DR. BOTHNER: You actually can distinguish between the two, and I 



6 think the way you can do that is to look at the lead-210 values, the 



7 inventories. The inventories is the amount of lead-210 that's there. 



8 You've integrated over a core or something, and you say that's a 



9 certain number of dpm's/cm^, integrated for the whole depth in which 



10 you'd find excess lead-210, which I'm going to say is about 30 



11 centimeters. So there's x number, say it's 30. 



12 If you look at the samples and you compare that inventory with 



13 somewhere on the slope and where it's, say half as much, then you look 



14 at the specific activity of the lead-210, that is how much lead per gram 



15 of sediment, and we find that on a per gram basis, the lead-210 is much 



16 higher in the canyon axis. 



17 That's says it's not that lead-210 is carrying in more particles, 



18 but it's of a higher concentration on the particles. I think that's the 



19 argument that suggests that the scavenging is greater in the canyon 



20 axis. 



21 I can't do that for total lead, because I don't know--I can't get 



22 inventories of total lead because it's part of the real world, I mean 



23 it's part of the natural.... I can't subtract the background very well 



24 in these particular samples. I suppose it's possible, but the signal is 



25 pretty small . 



26 The enrichment in the bottom sediments is only about 1.5 above 



27 what you'd find in average shales, whereas excess lead-210 in 



28 particularly plutonium, there is nothing there, the background is zero, 



29 it's a non-natural isotope. 



30 So, that's where the isotopes are really helping us out. 



31 DR. MACIOLEK: Any other questions? Thanks, Mike. 



32 That concludes the presentations for this morning. I'd like to 



33 thank all of the speakers for very interesting and informative talks, 



34 and to ask them once again to please let Jim Hain as the senior 



73 



