Preparation test results – background
Reliability of our sample preparation lines has been tested by AMS 14C measurements of cathodes prepared from coal (14C-free). Most of the 14C counts are supposed to reflect contamination with modern carbon introduced during production and storage of the cathodes.
|
Cathode
|
Time (s)
|
14C counts
|
14C (pMC)*
|
Libby age 14C
|
|
P7
|
450
|
150
|
0,167±0,020
|
51300
|
|
P13
|
600
|
309
|
0,256±0,009
|
47900
|
|
P14
|
1500
|
382
|
0,160±0,012
|
51700
|
|
P9
|
1200
|
349
|
0,171±0,017
|
51200
|
|
P10
|
1350
|
504
|
0,206±0,014
|
49700
|
|
P8
|
1200
|
389
|
0,198±0,014
|
50000
|
|
P13+14
|
1050
|
459
|
0,222±0,020
|
49100
|
|
P12
|
1200
|
379
|
0,176±0,014
|
50900
|
* the error represents only standard deviation of the mean value of single measurements
Each coal sample was pretreated, combusted and graphitised separately. The results show very low contamination with modern carbon, excellent reproducibility of sample preparation and suggest our ability of dating samples up to 50000 years old.
Preparation test results – standard
Reliability of our sample preparation lines has been tested by AMS 14C measurements of cathodes prepared from standard sample (Oxalic Acid II). Samples for each cathode were combusted and graphitised separately. In each run, a few cathodes were measured. Low spread of results from within run confirms reproducilibty of our preparation procedures.
|
Run date
|
Cathode
|
12C current (μA)
|
14C counts
|
14C (pMC)*
|
|
12-01-2002
|
P44
|
26,1
|
176059
|
134,07±0,60
|
|
P46
|
25,8
|
206315
|
133,28±0,58
|
|
|
P471
|
27,5
|
222281
|
134,07±0,41
|
|
|
Standard deviation of single cathode result (pMC)
|
0,46
|
|||
|
Run date
|
Cathode
|
12C current (μA)
|
14C counts
|
14C (pMC)*
|
|
25-01-2002
|
P(43+44)
|
19,8
|
265436
|
133,99±0,73
|
|
P(43+44)II
|
28,2
|
380448
|
133,56±0,69
|
|
|
P(47+50)
|
20,9
|
278282
|
134,22±0,63
|
|
|
P(52+55)
|
23,8
|
288882
|
134,08±0,62
|
|
|
P47
|
26,7
|
362487
|
134,77±0,60
|
|
|
P49
|
25,5
|
226374
|
133,97±0,59
|
|
|
P53
|
8,7
|
58299
|
136,10±1,13
|
|
|
P541
|
24,0
|
324777
|
134,07±0,45
|
|
|
Standard deviation of single cathode result (pMC)2
|
0,40
|
|||
|
Run date
|
Cathode
|
12C current (μA)
|
14C counts
|
14C (pMC)*
|
|
30-01-2002
|
P(58+64)
|
19,1
|
176150
|
133,86±0,67
|
|
P56
|
20,7
|
192375
|
134,72±0,49
|
|
|
P57
|
15,8
|
144047
|
134,88±0,53
|
|
|
P59A1
|
22,9
|
211347
|
134,07±0,32
|
|
|
Standard deviation of single cathode result (pMC)
|
0,49
|
|||
|
Run date
|
Cathode
|
12C current (μA)
|
14C counts
|
14C (pMC)*
|
|
06-02-2002
|
P48
|
22,6
|
206807
|
133,83±0,74
|
|
P66
|
22,0
|
171147
|
134,28±0,73
|
|
|
P49A1
|
18,0
|
148451
|
134,07±0,57
|
|
|
Standard deviation of single cathode result (pMC)
|
0,23
|
|||
1 – measurement of this cathode was used as a reference for other cathodes
2 – calculated without cathode P53, which produced very low 12C current
These results suggest that using single cathode measurements we can 14C date young samples with a precision of ±40 years.
Preparation test results – charcoal
Reproducibility of our 14C measurements has been tested by AMS 14C measurements of samples collected from a batch of well homogenised modern charcoal. Samples for each cathode were combusted and graphitised separately. In each run, a few cathodes were measured. Concentration of 14C (in pMC) was determined using measurements of modern standard (Oxalic Acid II) and background (coal) for particular runs as reference values.
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
30-01-2002
|
P67A
|
119,47±0,68
|
-1430±451
|
|
P76
|
120,96±0,71
|
-1529±46
|
|
|
P77
|
120,45±0,70
|
-1495±46
|
|
|
P75B
|
120,56±0,77
|
-1502±51
|
|
|
P75A
|
120,06±0,68
|
-1469±45
|
|
|
P74A
|
119,46±0,68
|
-1429±45
|
|
|
Weighted mean
|
120,13±0,29
|
-1474±19
|
|
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
06-02-2002
|
P(43+44)
|
120,22±0,68
|
-1480±45
|
|
P(68+71)B
|
120,98±0,72
|
-1530±47
|
|
|
P67
|
121,15±1,00
|
-1542±66
|
|
|
P74
|
121,07±0,61
|
-1536±40
|
|
|
P77A
|
120,78±0,71
|
-1517±47
|
|
|
P49
|
120,22±0,59
|
-1480±39
|
|
|
P53
|
120,41±0,73
|
-1492±48
|
|
|
P(68+71)A
|
121,26±0,82
|
-1549±54
|
|
|
P84
|
119,85±0,85
|
-1455±39
|
|
|
Weighted mean
|
120,63±0,24
|
-1507±15
|
|
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
11-02-2002
|
P75
|
121,63±0,56
|
-1573±36
|
|
P89A
|
120,82±0,52
|
-1520±34
|
|
|
Weighted mean
|
121,20±0,39
|
-1545±25
|
|
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
14-02-2002
|
P88
|
121,13±0,53
|
-1540±35
|
|
P85A
|
119,71±0,56
|
-1446±37
|
|
|
P81B
|
120,46±0,54
|
-1496±36
|
|
|
Weighted mean
|
120,46±0,31
|
-1496±20
|
|
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
20-02-2002
|
P72
|
119,41±0,52
|
-1425±35
|
|
P82A
|
120,43±0,56
|
-1493±37
|
|
|
P85
|
120,06±0,52
|
-1468±34
|
|
|
Weighted mean
|
119,94±0,31
|
-1461±20
|
|
|
Weighted mean of all runs2
|
120,31±0,152
|
-1486± 92
|
|
1 – the age is conventional only, and for modern material cannot be interpreted as the real age of sample
2 – calculated without run on 11-02, which gave outlying result
Low spread of results within runs and excellent agreement of results obtained for different runs confirms reliability of our measurements of 14C concentration. These results show that using single cathode we can 14C date young samples with a precision of ±40 years, and that measuring a few cathodes we can improve the precision up to ±25 years.
Preparation test results – sample of known age
Reliability of our 14C measurements has been tested by AMS 14C measurements of samples of known 14C age. These were the samples distributed in frame of the IAEA 14C Quality Assurance Program. Analysis of results obtained in a few tens of 14C laboratories resulted in Consensus Values of the IAEA materials (Różański et al. 1992. Radiocarbon 34, 506). Samples for each cathode were combusted and graphitised separately. Concentration of 14C (in pMC) was determined using measurements of modern standard (Oxalic Acid II) and background (coal) for particular runs as reference values.
|
Sample
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
IAEA C1
|
11-02-2002
|
IAEA C1/A
|
0,07±0,11
|
—
|
|
carbonate
|
11-02-2002
|
IAEA C1/F
|
-0,12±0,111
|
—
|
|
14-02-2002
|
IAEA C1/B
|
-0,10±0,111
|
—
|
|
|
14-02-2002
|
IAEA C1/C
|
-0,20±0,111
|
—
|
|
|
14-02-2002
|
IAEA C1/D
|
-0,17±0,111
|
—
|
|
|
14-02-2002
|
IAEA C1/E
|
-0,10±0,111
|
—
|
|
|
Weighted mean
|
-0,10±0,051
|
—
|
||
|
Consensus Value
|
0,00±0,02
|
|||
|
Sample
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
IAEA C3
|
11-02-2002
|
IAEA C3/B
|
128,44±0,63
|
-2011±392
|
|
cellulose
|
11-02-2002
|
IAEA C3/C
|
130,68±0,67
|
-2150±41
|
|
11-02-2002
|
IAEA C3/D
|
129,64±0,53
|
-2086±32
|
|
|
Weighted mean
|
129,55±0,34
|
-2080±21
|
||
|
Consensus Value
|
129,41±0,06
|
-2072± 3
|
||
|
Sample
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
IAEA C4
|
11-02-2002
|
IAEA C4/2A
|
0,35±0,11
|
45400±2500
|
|
subfossil wood
|
11-02-2002
|
IAEA C4/2B
|
0,38±0,11
|
44800±2400
|
|
11-02-2002
|
IAEA C4/3A
|
0,37±0,11
|
45000±2600
|
|
|
11-02-2002
|
IAEA C4/3B
|
0,23±0,11
|
48800±3800
|
|
|
14-02-2002
|
IAEA C4/3
|
0,17±0,11
|
51200±5200
|
|
|
20-02-2002
|
IAEA C4/5
|
0,54±0,13
|
41900±2000
|
|
|
Weighted mean
|
0,33±0,05
|
45900±1200
|
||
|
Consensus Value
|
0,32±0,12
|
46100±3000
|
||
|
Sample
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
IAEA C5
|
06-02-2002
|
IAEA C5
|
23,18±0,22
|
11740±75
|
|
subfossil wood
|
11-02-2002
|
IAEA C5/2
|
23,45±0,21
|
11650±70
|
|
11-02-2002
|
IAEA C5/2A
|
23,28±0,23
|
11710±80
|
|
|
18-03-2002
|
IAEA C5/4
|
23,03±0,15
|
11795±52
|
|
|
18-03-2002
|
IAEA C5/5A
|
23,00±0,17
|
11823±73
|
|
|
18-03-2002
|
IAEA C5/7
|
22,95±0,21
|
11805±59
|
|
|
Weighted mean
|
23,12±0,08
|
11763±26
|
||
|
Consensus Value
|
23,05±0,02
|
11788± 6
|
||
|
Sample
|
Run date
|
Cathode
|
14C (pMC)
|
Libby age (BP)
|
|
IAEA C6
|
06-02-2002
|
IAEA C6
|
151,55±0,75
|
-3340±39
|
|
sucrose
|
20-02-2002
|
IAEA C6/2
|
150,54±0,62
|
-3286±33
|
|
20-02-2002
|
IAEA C6/2A
|
150,40±0,64
|
-3279±34
|
|
|
20-02-2002
|
IAEA C6/2B
|
149,56±1,02
|
-3234±54
|
|
|
20-02-2002
|
IAEA C6/3
|
150,40±0,59
|
-3279±31
|
|
|
20-02-2002
|
IAEA C6/3A
|
151,01±0,66
|
-3312±35
|
|
|
Weighted mean
|
150,63±0,28
|
-3291±14
|
||
|
Consensus Value
|
150,61±0,11
|
-3290± 5
|
||
1 – measurements of this sample gave 14C activity lower than for the background sample. This is reasonable, since significant contamination is introduced during combustion, which is performed for the background samples (coal), but not for carbonates
2 – the age is conventional only, and for modern material cannot be interpreted as the real age of sample
These results confirm our ability to date reliably young as well as old samples.
Objective tests – program VIRI
Reliability of our 14C dating has been controlled by participation in the program VIRI (V-th International Radiocarbon Inter-comparison). IN each of 3 stages of that program (in years 2001-2007), several tens of 14C laboratories all around the world, were receiving the same samples for analysis. After collecting results of analyses, the program organizer calculated so called Consensus values, i.e. averages obtained after rejecting of drastic outliers results (Scott et al. 2007. Radiocarbon 49, 409, http://www.radiocarbon.org/Consensus values for VIRIjuly2009.pdf). Results of the program are partly confidential in such a sense, that VIRI does not publish the results obtained by individual laboratories.
Results of VIRI confirm reliability of our dating.
| Stage VIRI-1 | ||||
|
Sample
|
Our result (BP)
|
Consensus value
|
Difference
|
Diff./Error
|
|
VIRI A
|
-735±27
|
-700±2
|
-35
|
-1,29
|
|
barley mash
|
-745±27
|
-700±2
|
-45
|
-1,66
|
|
VIRI B
|
2785±30
|
2820±4
|
-35
|
-1,16
|
|
grains
|
2839±32
|
2820±4
|
19
|
0,59
|
|
VIRI C
|
-853±26
|
-817±2
|
-36
|
-1,38
|
|
barley mash
|
-830±44
|
-817±2
|
-13
|
-0,30
|
|
VIRI D
|
2829±31
|
2836±4
|
-7
|
-0,22
|
|
grains
|
2825±30
|
2836±4
|
-11
|
-0,36
|
|
Stage VIRI-2
|
||||
|
Sample
|
Our result (BP)
|
Consensus value
|
Difference
|
Diff./Error
|
|
VIRI E
|
35100±700nu
|
38915±150
|
—
|
—
|
|
mammoth bone
|
42300±2400u
|
38915±150
|
3385
|
1,41
|
|
VIRI F
|
2500±35nu
|
2520±5
|
—
|
—
|
|
horse bone
|
2620±40u
|
2520±5
|
100
|
2,48
|
|
VIRI G
|
980±30nu
|
970±5
|
10
|
0,33
|
|
human bone
|
—-u,1
|
970±5
|
—
|
—
|
|
VIRI H
|
9290±50nu
|
9530±7
|
—
|
—
|
|
whale bone
|
9560±60u
|
9530±7
|
30
|
0,50
|
|
VIRI I
|
8340±50nu
|
8337±6
|
—
|
—
|
|
whale bone
|
8300±60u
|
8337±6
|
-37
|
-0,61
|
|
Stage VIRI-3
|
||||
|
Sample
|
Our result (BP)
|
Consensus value
|
Difference
|
Diff./Error
|
|
VIRI J
|
41900±1300
|
43200±180
|
-1300
|
-0,99
|
|
humic acid
|
||||
|
VIRI K
|
>50000
|
59600±1400
|
—
|
—
|
|
wood
|
||||
|
VIRI L
|
2281±29
|
2234±4
|
47
|
1,61
|
|
wood
|
||||
|
VIRI M
|
2453±30
|
2429±4
|
24
|
0,79
|
|
wood
|
||||
|
VIRI N
|
2418±30
|
2436±4
|
-18
|
-0,59
|
|
wood
|
||||
|
VIRI O
|
120±26
|
124±2
|
-4
|
-0,15
|
|
cellulose
|
||||
|
VIRI Q
|
627±27
|
636±4
|
-9
|
-0,33
|
|
charcoal
|
||||
|
VIRI R
|
2522±29
|
2490±4
|
32
|
1,09
|
|
shell
|
||||
|
VIRI S
|
-724±24
|
-763±2
|
39
|
1,62
|
|
barley mash
|
||||
|
VIRI T
|
3395±33
|
3359±3
|
36
|
1,09
|
|
humic acid
|
||||
|
VIRI U
|
11774±59
|
11778±6
|
-4
|
-0,07
|
|
humic acid
|
nu, u, 1 – samples were prepared first not-including (nu) and then including (u) ultrafiltration. As a rule, results obtained without ultrafiltration were not used in assessment of our reliability. In one exception (1), amount of material remained, was too small for credible dating including ultrafiltration.
Objective tests – program SIRI
Reliability of our 14C dating has been controlled by participation in the program SIRI (Sixth International Radiocarbon Inter-comparison). In that program (in years 2013-2014), several tens of 14C laboratories all around the world, received the same samples for analysis. After collecting results of analyses, the program organizer calculated so called Consensus values, i.e. averages obtained after rejecting of drastic outliers results. Results of the program are partly confidential in such a sense, that SIRI does not publish the results obtained by individual laboratories.
Results of SIRI confirm reliability of our dating.
|
Sample
|
Our result (BP)
|
Consensus value
|
Difference
|
Diff./error
|
|
SIRI A
|
>48000
|
51697
|
—
|
—
|
|
wood
|
>48000
|
>50864
|
—
|
—
|
|
SIRI B
|
36309±966
|
39165±298
|
-2856
|
-2,83
|
|
bone
|
38497±1302
|
39165±298
|
-668
|
-0,50
|
|
SIRI C
|
44423±2617
|
45347
|
-924
|
—
|
|
bone
|
>42000
|
>46550
|
—
|
—
|
|
SIRI D
|
-316±26
|
-307±6
|
-9
|
-0,34
|
|
barley mash
|
-298±24
|
-307±6
|
9
|
0,36
|
|
SIRI E
|
10746±60
|
10827±9
|
-81
|
-1,34
|
|
wood
|
10823±63
|
10827±9
|
-4
|
-0,06
|
|
SIRI F
|
324±27
|
370±4
|
-46
|
-1,69
|
|
wood
|
350±29c
|
370±4
|
-20
|
-0,68
|
|
SIRI G
|
399±26
|
378±5
|
21
|
0,79
|
|
wood
|
399±26c
|
378±5
|
12
|
0,38
|
|
SIRI H
|
415±26
|
385±4
|
30
|
1,14
|
|
wood
|
390±29c
|
385±4
|
5
|
0,17
|
|
SIRI I
|
9998±55
|
9987±6
|
11
|
0,20
|
|
wood
|
9930±58
|
9987±6
|
-57
|
-0,98
|
|
SIRI J
|
32734±629
|
31768±123
|
966
|
1,51
|
|
charcoal
|
32151±576
|
31768±123
|
383
|
0,65
|
|
SIRI K
|
>50000
|
53532
|
—
|
—
|
|
carbonate
|
>47000
|
>51603
|
—
|
—
|
|
SIRI L
|
>44000
|
50195
|
—
|
—
|
|
wood
|
>43000
|
>51989
|
—
|
—
|
|
SIRI N
|
3360±33
|
3370±7
|
-10
|
-0,30
|
|
humic acid
|
3403±34
|
3370±7
|
33
|
0,95
|
c – preparation of wood included extraction of cellulose. In other cases, simple AAA method was applied
Replicate sample measurements
Reliability of our one-sigma precision is further confirmed by dating replicate samples. Examples of those replicates are given below.
|
First results BP
|
Replicate BP
|
|
123±25
|
159±35
|
|
668±26
|
694±35
|
|
1080±29
|
1118±25
|
|
1467±25
|
1448±37
|
|
2181±35
|
2215±33
|
|
2739±30
|
2787±32
|
|
3878±28
|
3841±31
|
|
3876±40
|
3933±43
|
|
3897±33
|
3921±35
|
|
4213±41
|
4242±40
|
|
5529±36
|
5566±38
|
|
5990±52
|
5936±45
|
|
11504±77
|
11484±73
|
|
22680±750
|
23703±291
|
The precision of our 14C dates depends also on the quality of the spectrometer working in the AMS Laboratory.
See the results of the AMS spectrometer tests: