Preliminary Analysis of Wipe Samples


(Status 8/7/2000)

14 KamLAND wipe samples have been neutron activated at HFIR. The activation was done in 1 min increments on 7/6/2000 and 7/7/2000. In the following only long lived isotopes are analyzed. It is assumed that a 2 min irradiation was perforemd on 7/7/2000 9:00 am. The applied neutron flux was 4e14 cm**-2 s**-1. I assume an epithermal flux component of 1/185 of the thermal flux.
On 7/14/2000 14 of those samples were received at UA. All of them were counted for 10 min using our shielded Ge detector. 4 of them were kept at UA for further analysis the rest of them was sent to Caltech for counting.
The following activities were identified in the gamma spectra: 24Na, 46Sc, 51Cr, 58Co(?), 59Fe, 60Co, 65Zn, 82Br, 122Sb(?), 124Sb(?). Due to the large activities the activation products of K, U and Th were not observed. The data is consistent with the 82Br coming from the alcohol soaked paper. The counting efficiency was determined using calibrated point sources.
For wipe samples 1, 2 and 3 counting was repeated several times. The time dependent activities show a 10% reproducibility of the solid angles. The 59Fe and 82Br activities determined for wipe sample 1 for the various gamma lines give a 15% reproducibility in the energy dependent efficiency.
The analysis of the combined runs for those three samples yielded siginificant activities. Background obtained through an activated alcohol soaked paper sample has been subtracted.

Wipe sample 1 (15-2 subtracted), counting time: 1.84 d:
Isotope Activity Total mass of element
[Bq] [g]
45Sc 1.04+/-0.05 (7.0+/-0.3)e-10
51Cr 9350+/-50 (9.0+/-0.05)e-5
59Fe 129+/-0.3 (4.0+/-0.01)e-4
60Co 78+/-0.2 (1.1+/-0.003)e-6
65Zn 60+/-0.4

All errors are statistical. The systematic error is of the order 20%.

Wipe sample 2 (15-2 subtracted), counting time: 2.38 d:
Isotope Activity Total mass of element
[Bq] [g]
45Sc 0.03+/-0.02 (2.0+/-1.3)e-11
51Cr 540+/-1 (5.4+/-0.01)e-6
59Fe 6.9+/-0.07 (2.1+/-0.02)e-5
60Co 4.0+/-0.04 (5.9+/-0.06)e-8
65Zn 60+/-0.3


Wipe sample 3 (15-2 subtracted), counting time: 2.89 d
Isotope Activity Total mass of element
[Bq] [g]
45Sc 0.34+/-0.03 (2.3+/-0.2)e-10
51Cr 348+/-1 (3.5+/-0.01)e-6
59Fe 4.7+/-0.06 (1.4+/-0.02)e-5
60Co 2.7/-0.03 (4.0+/-0.04)e-8
65Zn 141+/-0.4


Wipe sample 14 (15-2 subtracted), counting time: 1.09 d
Isotope Activity Total mass of element
[Bq] [g]
45Sc 1.4+/-0.1 (9.4+/-0.7)e-10
51Cr 16000+/-8 (1.5+/-0.001)e-4
59Fe 217+/-0.6 (6.7+/-0.02)e-4
60Co 128/-0.3 (1.8+/-0.004)e-6
65Zn 88.3+/-0.6

Wipe sample 15-2 (no background subtracted), counting time: 3.41 d
Isotope Activity Total mass of element
[Bq] [g]
45Sc 0.15+/-0.01
51Cr 3.1+/-0.1
59Fe 0.21+/-0.02
60Co 0.12+/-0.01
65Zn 14.9+/-0.1

With the exception of Sc the listed elements can be attributed to the residue of the stainless steel grinding. The ratio of Co and Cr might confirm this if we can get it from Mitsui. David Glasgow mentioned that he observed 45Sc only in the mine dust but not in the welding fumes. This element might hence give us a handle on the determination of the amount of dust removed per cleaning. We would need from David the [Bq] of 45Sc per gram of dust as determined by his counting. It is intersting to note, that there seems to be a large jump in activity after the first cleaning but from then on only little difference. Also the 46Sc seems unchanged. The Caltech data would be need to understand this behaviour. Finally 45Sc is also observed in the activated blanck paper which rises the question on how repersentative this background is. Has the Sc been deposited on the paper during handling in Kamioka? The Zn doesn't seem to follow any systematics. Has that also been observed at Caltech?
The input of David Glasgow and Bryan Tipton would be most important.

Results of the initial 10 min runs (15-2 subtracted)
Sample 46Sc 51Cr 59Fe 60Co 65Zn
[Bq] [Bq] [Bq] [Bq] [Bq]
Wipe sample 1 -0.2+/-0.1 9830+/-81 181+/-30 70+/-4 54+/-6
Wipe sample 2 -0.3+/-0.7 639+/-21 10+/-2 3.4+/-1.2 59+/-6
Wipe sample 3 -2.9+/-0.7 509+/-19 5.8+/-1.6 2.8+/-0.8 150+/-9
Wipe sample 4 -1.6+/-0.7 338+/-16 8.5+/-2.4 2.5+/-0.8 101+/-7.5
Wipe sample 5 281+/-15 6.4+/-1.6 3.9+/-1.2 46+/-6
Wipe sample 6 -0.6+/-0.6 308+/-15 8.5+/-1.6 1.5+/-1.0 10+/-4
Wipe sample 7 -0.1+/-0.6 443+/-18 78+/-2 2.7+/-0.7 9+/-4
Wipe sample 8 -0.4+/-0.6 250+/-14 5.9+/-1.4 2.1+/-1 16+/-5
Wipe sample 9 -0.4+/-0.6 328+/-16 3.2+/-1 2.5+/-0.7 15+/-4
Wipe sample 10 -0.3+/-0.5 253+/-14 5.2+/-1.3 2.1+/-0.6 15+/-4
Wipe sample 12 0.02+/-0.7 517+/-19 6.6+/-1.6 3.1+/-1.2 94+/-7
Wipe sample 14 -0.1+/-1.2 15900+/-1000 216+/-11 111+/-51 86+/-8
Background sample 15 0.8+/-0.5 3.6+/-3.1 1.4+/-1.1 0+/-0.5 11+/-2.4
Background sample 15-2 0.6+/-0.4 6.8+/-3.7 -1.3+/-0.6 -0.4+/-0.2 14+/-2.6

No other run has been subtracted from the two background spectra. Background sample 15-2 has been suntracted from all other wipe samples. This table serves to compare the Caltech and Alabama systematics.

Sample description. Samples were collected by Yuri Kamyshkov and Johannes Ritter

Samples of the surface impurities were made with Whatman 42 ashless paper pads send to Mozumi by Bryan. These pads have a diameter of ~ 40 mm and, as we saw with Johannes Ritter, do not remove the dirt from the surface as efficient as regular JK-Wipers used for the regular cleaning.
Samples were made by wetting pads with alcohol and wiping the cleaned surfaces as described below. We worked in rubber gloves. At this time only cleaned surfaces were available; in the future when the installation level in the sphere will be lowered, Johannes will make also samples before cleaning. After wiping samples were transfered into plastic zip bags (as clean as one can get from the grocery store).

#1 Inside sphere area "A" 10x10 cm2. Area was wiped with wet pad (about 5 strokes were needed to cover the area once) 15 times in alternating x-y directions.

#2 Same area "A" wiped with the wet pad again 10 times.

#3 Same area "A" wiped with the wet pad again 10 times.

#4 Same area "A" wiped with the wet pad again 10 times.

#5 Same area "A" wiped with the wet pad again 10 times.
Comment: the idea of repetitive wiping (many samples) is to determine from the amount detected on the pad (by extrapolation and integration) the total amount of impurities on the surface (assuming that the process removes some amount of dirt from the surface).

#6 Inside sphere area "B" 10x10 cm2. All area was wiped with wet pad (about 5 strokes were needed to cover the area once) 15 times in alternating x-y directions.

#7 Same area "B" wiped with the wet pad again 10 times.

#8 Same area "B" wiped with the wet pad again 10 times.

#9 Same area "B" wiped with the wet pad again 10 times.

#10 Same area "B" wiped with the wet pad again 10 times.

#11 Inside sphere along the welded plate joint. Length of joint of ~ 20 cm (width of one pad) was wiped 10 times up and down.

#12 repeate #11 on the same spot.

#13 Area along the joint at a distance of about 2-3 cm (where usually dark remanents of the welding rods are still deposited after grinding. These remanents are very difficult to remove by the methods used for cleaning). Area of the width of a pad and length of 20 cm was wiped up and down 10 times.

#14 repeate #13 on the same spot.

#15 2 empty samples (wetted with alcohol)

#16 area 10x10 cm2 on the floor of the vessel deck near lifting cage entrance. Area wiped 10 times.