The quality of our product has been tested in several ways. Precision of the first AMS spectrometer (Compact Carbon AMS ser. no. 003) was tested on modern samples in the NEC factory and after installation in Poznań. In September 2003 we significantly reduced the background of that spectrometer. Precision of the second spectrometer (Compact Carbon AMS ser. no. 012) was tested on modern standards and on background samples after installation of the spectrometer in Poznan. We also compared results of 14C measurements performed with our two spectrometers.
Compact Carbon AMS 003 – factory test results
Precision of our AMS machine has been tested in NEC by AMS 14C measurements of three cathodes prepared from the same sample (ANU sucrose standard). The results below show excellent reproducibility of 13C/12C and 14C/12C measurements
|
Cathode
|
Time (s)
|
14C counts
|
13C/12C
|
14C/12C
|
|
ANU
|
500
|
136558
|
1,1025e-2
|
1,3772e-12
|
|
ANU
|
500
|
140410
|
1,1019e-2
|
1,3791e-12
|
|
ANU
|
500
|
131027
|
1,1017e-2
|
1,3775e-12
|
|
Precision of single measurement
|
0.4 permil
|
0,1 percent
|
||
Compact Carbon AMS 003 – acceptance test results
Precision of the machine in our Laboratory has been tested by AMS 14C measurements of three cathodes prepared from the same sample (OXII standard) and provided by NEC. The results below show excellent reproducibility of 13C/12C and 14C/12C measurements.
|
Cathode
|
Time (s)
|
14C counts
|
13C/12C
|
14C/12C
|
|
OxII
|
750
|
177833
|
1,0694e-2
|
1,3289e-12
|
|
OxII
|
750
|
194300
|
1,0716e-2
|
1,3313e-12
|
|
OxII
|
750
|
146583
|
1,0694e-2
|
1,3346e-12
|
|
Precisin of single measurement
|
0.12 permil
|
0.28 percent
|
||
Compact Carbon AMS 003 – reduction of the machine background
A simple way of background reduction in the “Compact Carbon AMS” spectrometer has been proposed by J. Southon (Irvine, California, USA). Application of this discovery in Poznań reduced our machine background by a factor of 2-3. At present, this background corresponds to a 14C age > 60000 BP.
|
Date
|
Current (μA)
|
14C counts (2.5 min)
|
14C (pMC)
|
Age 14C
|
|
Before modification
|
||||
|
01-05-2003
|
12.8
|
20
|
<0.159
|
51800
|
|
01-05-2003
|
13.0
|
19
|
0.148
|
52300
|
|
01-05-2003
|
13.2
|
11
|
0.085
|
56800
|
|
01-05-2003
|
13.7
|
9
|
0.067
|
58700
|
|
01-05-2003
|
11.3
|
16
|
0.144
|
52600
|
|
01-05-2003
|
13.8
|
14
|
0.103
|
55200
|
|
01-05-2003
|
137
|
18
|
0.133
|
53200
|
|
01-05-2003
|
13.5
|
11
|
0.083
|
57000
|
|
05-05-2003
|
12.8
|
17
|
0.135
|
53100
|
|
05-05-2003
|
13.9
|
8
|
0.059
|
59800
|
|
05-05-2003
|
14.1
|
13
|
0.093
|
56000
|
|
05-05-2003
|
13.2
|
19
|
0.146
|
52500
|
|
05-05-2003
|
13.4
|
13
|
0.098
|
55600
|
|
05-05-2003
|
10.3
|
10
|
0.098
|
55600
|
|
After modification
|
||||
|
24-09-2003
|
17.5
|
6
|
0.035
|
63900
|
|
24-09-2003
|
17.5
|
3
|
0.018
|
69200
|
|
03-10-2003
|
15.7
|
6
|
0.039
|
63100
|
|
03-10-2003
|
15.8
|
7
|
0.046
|
61800
|
|
03-10-2003
|
15.7
|
5
|
0.032
|
64600
|
|
20-10-2003
|
12.0
|
5
|
0.042
|
62500
|
|
27-10-2003
|
18.6
|
6
|
0.033
|
64300
|
|
30-10-2003
|
11.2
|
7
|
0.055
|
60300
|
|
06-11-2003
|
16.4
|
5
|
0.031
|
64800
|
|
17-11-2003
|
21.5
|
7
|
0.034
|
64100
|
|
23-11-2003
|
20.6
|
7
|
0.036
|
63700
|
|
26-11-2003
|
19.5
|
11
|
0.056
|
60100
|
|
15-12-2003
|
19.2
|
8
|
0.043
|
62300
|
The background tests were made using aliquots of 14C-free commercial graphite (Alfa-graphite), kindly supplied by the Leibniz-Labor für Altersbestimmung, Kiel, Germany.
Compact Carbon AMS 012 – acceptance tests
Precision of the spectrometer was tested after its installation in our Laboratory, by 14C measurements on three portions of graphite prepared from the sample of modern standard (Oxalic Acid II).
|
Sample
|
Time (s)
|
Counts 14C
|
13C/12C
|
14C/12C*
|
|
OxII
|
600
|
169078
|
1,1050e-2
|
1,4711e-12
|
|
OxII
|
600
|
172851
|
1,1049e-2
|
1,4669e-12
|
|
OxII
|
600
|
137709
|
1,0940e-2
|
1,4661e-12
|
|
Precision of single graphite measurement
|
0.6 per mil
|
0.26 percent
|
||
* – values corrected for isotopic fractionation, basing on the measured ratios 13C/12C
Compact Carbon AMS 012 – background
Tło spektrometru zmierzono przy pomocy próbki grafitu komercyjnego (alfa-graphite). Dodatkowo wykonano pomiary na porcjach grafitu przygotowanych w laboratorium radiowęglowym z miligramowych próbek węgla kamiennego (coal).
|
Sample
|
Time (s)
|
Counts 14C
|
14C (pMC)
|
Wiek 14C
|
|
Alfa-graphite
|
900
|
37
|
0.029
|
65400
|
|
Coal
|
900
|
213
|
0.175
|
51000
|
|
Coal
|
900
|
426
|
0.228
|
48900
|
Test dating – comparison of results obtained with our two spectrometers
The tests indicated good agreement of 14C dates obtained with the two spectrometers.
|
CAMS 003 (BP)
|
CAMS 012 (BP)
|
Difference
|
Diff./error
|
|
|
1
|
660±25
|
650±24
|
10
|
0,28
|
|
2
|
4525±30
|
4583±34
|
57
|
-1,26
|
|
3
|
560±30
|
608±26
|
-48
|
-1,21
|
|
4
|
17270±80
|
17292±84
|
-22
|
-0,19
|
|
5
|
110±30
|
149±25
|
-39
|
-0,99
|
|
6
|
12020±60
|
11976±55
|
44
|
0,54
|
|
7
|
8245±35
|
8247±33
|
-2
|
-0,04
|
|
8
|
-549±28
|
-515±26
|
-34
|
-0,89
|
|
9
|
5420±40
|
5350±26
|
70
|
1,47
|
|
10
|
5335±35
|
5327±26
|
8
|
0,18
|
|
11
|
2715±30
|
2707±23
|
8
|
0,21
|
Our precision of 14C dating depends also on the quality of sample preparation in the Poznań Radiocarbon Laboratory
See the results of the sample preparation tests: