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Poznan Radiocarbon Laboratory

PRL Quality Tests

Poznan Radiocarbon Laboratory Cathode

The quality of our product has been tested in several ways. Reproducibility of preparation procedures in our Laboratory was tested on background and modern standard samples as well as on samples collected from a batch of well homogenised modern charcoal. Ultimately, we 14C dated samples of well known radiocarbon age. Reliability of our precision is additionally confirmed by several replicate datings of normal samples.
In years 2001-2009 wer took part in the interlaboratory comparison program VIRI, and in 2013-2014 – in the program SIRI.

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
* the error represents standard deviation of the mean value of single measurements
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±40
 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±60
  9530±7
30
0,50
VIRI I
  8340±50nu
  8337±6
whale bone
  8300±60
  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±29
  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: