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TL-dating of archaeological samples from Carnuntum
NucL Tracks Radiat. Meas., Vol. 14, Nos 1/2, pp. 295-298, 1988 Int. J. Radiat. Appl. lnstrum., Part D Printed in Great Britain
0191-278X/88 $3.00 + 0.00 Pergamon Press plc
TL-DATING OF A R C H A E O L O G I C A L SAMPLES FROM CARNUNTUM R. ERLACH
Institut fiir Silikatchemie und Arch/iometrie, Hochschule ffir angewandte Kunst, Oskar Kokoschka-Platz 2, A-1010 Wien, Austria and N. VANA Atominstitut der Osterreichischen Universit/iten, Schiittelstral3e 115, A-1020 Wien, Austria
(Received 1 August 1987; in final form 31 December 1987) Abstraet--A dating project was carried out aimed at optimizing the standard TL procedure for pottery samples from Carnuntum, Austria. More than 70 samples of different types of pottery were analysed using the fine-grain technique. The environmental dose-rate at the excavation site was measured by different methods and a test programme with archaeologically well-dated samples was used to find the best procedure for dating. Bricks from a bath, a lime-kiln and pieces of pottery from the fill of a post hole were dated to an accuracy ranging from _+3 to _+14%.
1. INTRODUCTION THE AREA of Carnuntum, situated at the southern bank of the river Danube approximately 45 km east of Vienna, is the largest and most important excavation site of Roman origin in Austria. This Roman city (in its time housing approximately 50,000 inhabitants) and its military complex guarded the "limes" at the place where the ancient "amber road" crossed the Danube. The ceramic samples dated in this project originate from a rather small part of the excavation area representing a temple district with adjacent business area and public baths. The object of the dating project was to investigate the feasibility of TL-dating the ceramic samples from this particular site and to find out whether the TL-dates would help the excavating archaeologists to solve some of their puzzles. The Roman sites usually are well dated by archaeological evidence but in cases where the only evidence is everyday pottery with stylistic features scarcely changing through the centuries, TL-dating should be more useful. Other problems for the archaeologists were the determination of the time of utilization of a kiln and the time of filling of some post holes containing pottery fragments.
This led to wrong TL-ages for the samples of known archaeological age if all datapoints and linear extrapolation were used for the calculation of equivalent dose (El)) and second glow intercept (I). The error in age was dependent on the range of additional beta doses used for establishing the growth characteristic of the samples and the intercept amounting to as much as 50% of the archaeological dose (P) (Fig. 2a). To cope with this problem, and as the extrapolation of a nonlinear fit to the growth curve data was considered to be problematic, a mode of evaluation was adopted in which only fine grain disks with their total dose (D) restricted to a range of approximately 0.5 x P < D < 2.5 x P were used (Fig. 2b). Subsequent checks performed with samples of known age showed good agreement with archaeological date. Samples of "terra sigillata", however, consistently produced TL-ages that were low compared with their known age and this may be due to their high firing temperature.
2. TEST P R O G R A M M E ON ARCHAEOLOGICALLY DATED S A M P L E S To start with, a test programme was carried out using samples of well known archaeological age. These samples and the great majority of the other ceramic samples to be dated in the course of the project showed a slight supralinear behaviour of the TL-growth characteristic throughout the observed range of applied dose. 295
3. E N V I R O N M E N T A L DOSE-RATE
MEASUREMENT The measurement of the external gamma dose-rate at the excavation site was carried out using conventional TL dosimeters (Harshaw T L D 200, CaF2: Dy, 6 × 6 x I mm 3) over various periods of time ranging from three weeks up to one year and at different locations on the site. The method of measurement and evaluation of dose-rate is described below and in more detail by Tschirf and Vana (1982). Using 20 assorted and annealed dosimeter chips the procedure comprises the following steps.
296
R. E R L A C H and N. V A N A
Copper lid~ PlastiC~mece~ 1_.cap@ .~..~. ~
site. The dosimeter chips were contained in plastic i capsules and sealed in a copper capsule to correct for the different energy dependence of the C a F 2 relative to quartz. (See Fig. 1 for the arrangement of the dosimeters). (c) The remaining five irradiated and five nonirradiated TL-dosimeters were read out (simultaneously with burying the dosimeter capsule) and the calibration factor K (equation (1)) for the dosimeters, as well as the limit of detection, calculated. (l)
K = (Io - LW)/Do
Styropor
where I 0 = TL of preirradiated dosimeters (dose Do) and L W = TL of nonirradiated dosimeters (background).
Plastic capsule
(d) After the measurement time, T, the buried dosimeters were recovered, read out and from the resulting data the fading correction (F) (equation (2)) and finally the gamma dose-rate (D,) (equation (3)) at the measurement location calculated (corrected for different stopping power of the TL-phosphor relativt~ to quartz).
Copper capsule
F = (Io - L W ) / ( I
- I~)
(2)
where I = TL of preirradiated dosimeters after time T and lu = TL of nonirradiated dosimeters after time T; D , = (lu - - L W ) F / ( K
FIG. 1. Exploded view of dosimeter arrangement used for environmental dose-rate measurement.
(a) Ten of the chips were irradiated with a calibration dose D o in the radiation field of a calibrated gamma source (Co-60); the other 10 chips were used without preirradiation. The irradiation is performed with the TL-chips in the dosimeter capsules as used for the measurements on the excavation site. (b) Five of the irradiated and five of the nonirradiated TL-chips were buried at the archaeological
TL
y
/ /
N(,/ /
/
/
T).
The gamma dose-rates derived from these measurements were checked against the readings of a proportional counter and tallied with one another within the error of measurement.
4. DATING RESULTS In the following tables a few of the dating results of this project are summarized. All TL-samples were prepared according to the fine grain technique as described by Zimmerman (1971) and analyzed on a D A Y B R E A K TL-dating system (Bortolot e t al.,
./
Tk
./
7/
7 ./.// ./ /
#, /
~ED (a)
(3)
+/ //
(b)
FIG. 2. TL-growth curve: determination of E l ) and I by linear extrapolation (a) using all points, (b) using only datapoints (full circles) with total dose restricted to approximately 0.5 x P < D < 2,5 × P.
TL-DATING
OF SAMPLES FROM
CARNUNTUM
297
Table I. Dating results for samples taken from the tiles which made up a conduit in the public baths adjacent to the temple district. Archaeological evidence dates this building to sometime after the middle of the 3rd century AD, a more precise dating could not be gained from the excavation P Sample
[Gy]
I/P
Sips
ZBI ZB2 ZB3 ZB4 ZB5 ZB6 ZB7a ZB7b ZB8
6.00 6.95 6.65 7.45 6.80 7.20 7.35 6.85 6.60
0.18 0.17 0.17 0.14 0.19 0.19 0.19 0.20 0.10
1.23 1.31 1.78 1.46 1.27 1.23 1.26 1.20 1.09
D a-val [mGy/a]
a [%]
fl [%]
), + c [%]
W [%]
TL-date AD
0.112 0.115 0.115 0.130 0.105
28.1 28.0 30.2 32.8 28.7 33.0 29.1 30.1 23.3
40.3 39.3 38.5 37.8 39.5 39.4 38.2 38.2 43.7
31.6 32.7 31.3 29.4 31.8 27.6 32.7 32.7 33.0
18 19 19 20 18 20 20 21 24
501 5:178 227-+ 163 374-+ 160 290-+ 164 311 -+ 150 451 _+ 168 130-+ 153 331 -+ 142 297-+ 166
0.125 0.116 0.105 0.093
4.04 3.95 4.13 4.40 4.06 4.69 3.96 4.14 3.91
TL context date: 305 AD (_+40, _+110, VHTL-CZB).
Table 2. TL-dates for samples of different types of ceramic taken from the fill of a post hole which usually does not contain any archaeologically significant material that would allow the dating of these holes. The results for samples PFL 3 and 4 surprisingly indicate the existence of urban activities in this area after the retreat of the Romans, a period that is hard to grasp by archaeological means Sample
[Gy]
P
I/P
Sips
D a-val [mGy/a]
r, [%]
fl [%]
y+ c [%]
W [%]
TL-date AD
PFLI PFL2 PFL3 PFL4 PFL5 PFL6 PFL7 PFL8 PFL9 PFLI0
10.55 9.85 6.90 7.20 7.90 7.15 6.80 7.10 8.15 6.95
0.13 0.24 0.02 0.22 0.22 0.17 0.13 0.18 0.23 0.18
0.91 0.83 0.97 1.01 1.10 1.23 !.30 l.ll 1.13 1.13
0.205 0.186 0.165 0.125 0.145 0.I15 0.086 0.103 0.115 0.125
54.6 54.2 53.0 44.3 37.7 32.3 24.8 32.1 31.2 33.9
31.6 31.8 31.1 39.4 41.2 45.0 52.1 47.6 47.5 44.1
13.9 13.9 15.9 16.3 21.1 22.7 23.1 20.4 21.2 21.9
5 9 14 5 18 18 17 14 12 12
387 _+ 158 467_+ 148 774-+ 170 682_+ ll5 152_+130 191 _+339 253_+ 173 379_+ 116 71 _+ 161 300_+ 146
6.60 6.49 5.69 5.52 4.31 3.98 3.92 4.45 4.26 4.12
Table 3. TL-dates for samples taken from the inner layer of a lime-kiln. The end of utilisation could be established by these dates which are in good correlation with archaeological evidence. The buildings of this area have been destroyed by an earthquake around the middle of the century with hardly any building activities afterwards Sample
P [Gy]
I/P
D Sips a-val [mGy/a]
~t [%]
fl [%]
~+ c [%]
W [%]
TL-date AD
ZBRI ZBR2
5.75 5.80
0.17 0.15
1.16 0.095 1.20 0.093
27.0 27.5
39.7 39.4
33.2 33.1
18 19
331 _+ 177 315 4- 156
3.48 3.47
1982) with a n E M I 9635B p h o t o m u l t i p l i e r a n d C o r n i n g 7-59 a n d 4-69 filters. The effective a n n u a l dose-rate D comprises the external dose-rate determined by T L - d o s i m e t r y as described a b o v e a n d the internal dose-rate determined by a l p h a c o u n t i n g a n d assessment of potassium content by ICPspectroscopy. R a d o n e m a n a t i o n o f the samples a n d w a t e r c o n t e n t o f the e n v i r o n m e n t have not been measured. E v a l u a t i o n o f the T L - d a t e s a n d e r r o r analysis was performed according to the procedures given by A i t k e n (1976). 5. C O N C L U S I O N In the course o f the dating project a n u m b e r o f results were o b t a i n e d which proved to be very valuable to the archaeologists. As these still represent N.T. ]4/I-2--T
individual dates a m o r e c o m p r e h e n s i v e investigation of ceramic samples from this excavation site would be desirable as well as further investigation o f certain groups o f ceramics (e.g. terra sigillata, bricks) or archaeological complexes to get the right feel for the p r o b l e m s associated with them.
Acknowledgements--We want to thank Dr P. Dolezel for determination of potassium content of the ceramic samples. The dating project was supported by the "Fonds zur F6rderung der wissenschaftlichen Forschung" under project number P5214.
REFERENCES Aitken M. J. (1976) Thermoluminescent age evaluation and assessment of error limits: revised system. Archaeometry 18, 233-238.
298
R. E R L A C H and N. V A N A
Bortolot V. J. and Carriveau G. W. (1982) An integrated TL measurement and computer system. PACT J. 6, 272-280. Tschirf E. and Vana N. (1982) Umgebungsiiberwachung
beziiglich/iuBerer Strahlung-Ger/ite und MeBresultate Acta phys. hung. 52, 363-372. Zimmerman D. W. (1971) Thermoluminescence dating using fine grains from pottery. Archaeometry 13, 29-52
0191-278X/88 $3.00 + 0.00 Pergamon Press plc
TL-DATING OF A R C H A E O L O G I C A L SAMPLES FROM CARNUNTUM R. ERLACH
Institut fiir Silikatchemie und Arch/iometrie, Hochschule ffir angewandte Kunst, Oskar Kokoschka-Platz 2, A-1010 Wien, Austria and N. VANA Atominstitut der Osterreichischen Universit/iten, Schiittelstral3e 115, A-1020 Wien, Austria
(Received 1 August 1987; in final form 31 December 1987) Abstraet--A dating project was carried out aimed at optimizing the standard TL procedure for pottery samples from Carnuntum, Austria. More than 70 samples of different types of pottery were analysed using the fine-grain technique. The environmental dose-rate at the excavation site was measured by different methods and a test programme with archaeologically well-dated samples was used to find the best procedure for dating. Bricks from a bath, a lime-kiln and pieces of pottery from the fill of a post hole were dated to an accuracy ranging from _+3 to _+14%.
1. INTRODUCTION THE AREA of Carnuntum, situated at the southern bank of the river Danube approximately 45 km east of Vienna, is the largest and most important excavation site of Roman origin in Austria. This Roman city (in its time housing approximately 50,000 inhabitants) and its military complex guarded the "limes" at the place where the ancient "amber road" crossed the Danube. The ceramic samples dated in this project originate from a rather small part of the excavation area representing a temple district with adjacent business area and public baths. The object of the dating project was to investigate the feasibility of TL-dating the ceramic samples from this particular site and to find out whether the TL-dates would help the excavating archaeologists to solve some of their puzzles. The Roman sites usually are well dated by archaeological evidence but in cases where the only evidence is everyday pottery with stylistic features scarcely changing through the centuries, TL-dating should be more useful. Other problems for the archaeologists were the determination of the time of utilization of a kiln and the time of filling of some post holes containing pottery fragments.
This led to wrong TL-ages for the samples of known archaeological age if all datapoints and linear extrapolation were used for the calculation of equivalent dose (El)) and second glow intercept (I). The error in age was dependent on the range of additional beta doses used for establishing the growth characteristic of the samples and the intercept amounting to as much as 50% of the archaeological dose (P) (Fig. 2a). To cope with this problem, and as the extrapolation of a nonlinear fit to the growth curve data was considered to be problematic, a mode of evaluation was adopted in which only fine grain disks with their total dose (D) restricted to a range of approximately 0.5 x P < D < 2.5 x P were used (Fig. 2b). Subsequent checks performed with samples of known age showed good agreement with archaeological date. Samples of "terra sigillata", however, consistently produced TL-ages that were low compared with their known age and this may be due to their high firing temperature.
2. TEST P R O G R A M M E ON ARCHAEOLOGICALLY DATED S A M P L E S To start with, a test programme was carried out using samples of well known archaeological age. These samples and the great majority of the other ceramic samples to be dated in the course of the project showed a slight supralinear behaviour of the TL-growth characteristic throughout the observed range of applied dose. 295
3. E N V I R O N M E N T A L DOSE-RATE
MEASUREMENT The measurement of the external gamma dose-rate at the excavation site was carried out using conventional TL dosimeters (Harshaw T L D 200, CaF2: Dy, 6 × 6 x I mm 3) over various periods of time ranging from three weeks up to one year and at different locations on the site. The method of measurement and evaluation of dose-rate is described below and in more detail by Tschirf and Vana (1982). Using 20 assorted and annealed dosimeter chips the procedure comprises the following steps.
296
R. E R L A C H and N. V A N A
Copper lid~ PlastiC~mece~ 1_.cap@ .~..~. ~
site. The dosimeter chips were contained in plastic i capsules and sealed in a copper capsule to correct for the different energy dependence of the C a F 2 relative to quartz. (See Fig. 1 for the arrangement of the dosimeters). (c) The remaining five irradiated and five nonirradiated TL-dosimeters were read out (simultaneously with burying the dosimeter capsule) and the calibration factor K (equation (1)) for the dosimeters, as well as the limit of detection, calculated. (l)
K = (Io - LW)/Do
Styropor
where I 0 = TL of preirradiated dosimeters (dose Do) and L W = TL of nonirradiated dosimeters (background).
Plastic capsule
(d) After the measurement time, T, the buried dosimeters were recovered, read out and from the resulting data the fading correction (F) (equation (2)) and finally the gamma dose-rate (D,) (equation (3)) at the measurement location calculated (corrected for different stopping power of the TL-phosphor relativt~ to quartz).
Copper capsule
F = (Io - L W ) / ( I
- I~)
(2)
where I = TL of preirradiated dosimeters after time T and lu = TL of nonirradiated dosimeters after time T; D , = (lu - - L W ) F / ( K
FIG. 1. Exploded view of dosimeter arrangement used for environmental dose-rate measurement.
(a) Ten of the chips were irradiated with a calibration dose D o in the radiation field of a calibrated gamma source (Co-60); the other 10 chips were used without preirradiation. The irradiation is performed with the TL-chips in the dosimeter capsules as used for the measurements on the excavation site. (b) Five of the irradiated and five of the nonirradiated TL-chips were buried at the archaeological
TL
y
/ /
N(,/ /
/
/
T).
The gamma dose-rates derived from these measurements were checked against the readings of a proportional counter and tallied with one another within the error of measurement.
4. DATING RESULTS In the following tables a few of the dating results of this project are summarized. All TL-samples were prepared according to the fine grain technique as described by Zimmerman (1971) and analyzed on a D A Y B R E A K TL-dating system (Bortolot e t al.,
./
Tk
./
7/
7 ./.// ./ /
#, /
~ED (a)
(3)
+/ //
(b)
FIG. 2. TL-growth curve: determination of E l ) and I by linear extrapolation (a) using all points, (b) using only datapoints (full circles) with total dose restricted to approximately 0.5 x P < D < 2,5 × P.
TL-DATING
OF SAMPLES FROM
CARNUNTUM
297
Table I. Dating results for samples taken from the tiles which made up a conduit in the public baths adjacent to the temple district. Archaeological evidence dates this building to sometime after the middle of the 3rd century AD, a more precise dating could not be gained from the excavation P Sample
[Gy]
I/P
Sips
ZBI ZB2 ZB3 ZB4 ZB5 ZB6 ZB7a ZB7b ZB8
6.00 6.95 6.65 7.45 6.80 7.20 7.35 6.85 6.60
0.18 0.17 0.17 0.14 0.19 0.19 0.19 0.20 0.10
1.23 1.31 1.78 1.46 1.27 1.23 1.26 1.20 1.09
D a-val [mGy/a]
a [%]
fl [%]
), + c [%]
W [%]
TL-date AD
0.112 0.115 0.115 0.130 0.105
28.1 28.0 30.2 32.8 28.7 33.0 29.1 30.1 23.3
40.3 39.3 38.5 37.8 39.5 39.4 38.2 38.2 43.7
31.6 32.7 31.3 29.4 31.8 27.6 32.7 32.7 33.0
18 19 19 20 18 20 20 21 24
501 5:178 227-+ 163 374-+ 160 290-+ 164 311 -+ 150 451 _+ 168 130-+ 153 331 -+ 142 297-+ 166
0.125 0.116 0.105 0.093
4.04 3.95 4.13 4.40 4.06 4.69 3.96 4.14 3.91
TL context date: 305 AD (_+40, _+110, VHTL-CZB).
Table 2. TL-dates for samples of different types of ceramic taken from the fill of a post hole which usually does not contain any archaeologically significant material that would allow the dating of these holes. The results for samples PFL 3 and 4 surprisingly indicate the existence of urban activities in this area after the retreat of the Romans, a period that is hard to grasp by archaeological means Sample
[Gy]
P
I/P
Sips
D a-val [mGy/a]
r, [%]
fl [%]
y+ c [%]
W [%]
TL-date AD
PFLI PFL2 PFL3 PFL4 PFL5 PFL6 PFL7 PFL8 PFL9 PFLI0
10.55 9.85 6.90 7.20 7.90 7.15 6.80 7.10 8.15 6.95
0.13 0.24 0.02 0.22 0.22 0.17 0.13 0.18 0.23 0.18
0.91 0.83 0.97 1.01 1.10 1.23 !.30 l.ll 1.13 1.13
0.205 0.186 0.165 0.125 0.145 0.I15 0.086 0.103 0.115 0.125
54.6 54.2 53.0 44.3 37.7 32.3 24.8 32.1 31.2 33.9
31.6 31.8 31.1 39.4 41.2 45.0 52.1 47.6 47.5 44.1
13.9 13.9 15.9 16.3 21.1 22.7 23.1 20.4 21.2 21.9
5 9 14 5 18 18 17 14 12 12
387 _+ 158 467_+ 148 774-+ 170 682_+ ll5 152_+130 191 _+339 253_+ 173 379_+ 116 71 _+ 161 300_+ 146
6.60 6.49 5.69 5.52 4.31 3.98 3.92 4.45 4.26 4.12
Table 3. TL-dates for samples taken from the inner layer of a lime-kiln. The end of utilisation could be established by these dates which are in good correlation with archaeological evidence. The buildings of this area have been destroyed by an earthquake around the middle of the century with hardly any building activities afterwards Sample
P [Gy]
I/P
D Sips a-val [mGy/a]
~t [%]
fl [%]
~+ c [%]
W [%]
TL-date AD
ZBRI ZBR2
5.75 5.80
0.17 0.15
1.16 0.095 1.20 0.093
27.0 27.5
39.7 39.4
33.2 33.1
18 19
331 _+ 177 315 4- 156
3.48 3.47
1982) with a n E M I 9635B p h o t o m u l t i p l i e r a n d C o r n i n g 7-59 a n d 4-69 filters. The effective a n n u a l dose-rate D comprises the external dose-rate determined by T L - d o s i m e t r y as described a b o v e a n d the internal dose-rate determined by a l p h a c o u n t i n g a n d assessment of potassium content by ICPspectroscopy. R a d o n e m a n a t i o n o f the samples a n d w a t e r c o n t e n t o f the e n v i r o n m e n t have not been measured. E v a l u a t i o n o f the T L - d a t e s a n d e r r o r analysis was performed according to the procedures given by A i t k e n (1976). 5. C O N C L U S I O N In the course o f the dating project a n u m b e r o f results were o b t a i n e d which proved to be very valuable to the archaeologists. As these still represent N.T. ]4/I-2--T
individual dates a m o r e c o m p r e h e n s i v e investigation of ceramic samples from this excavation site would be desirable as well as further investigation o f certain groups o f ceramics (e.g. terra sigillata, bricks) or archaeological complexes to get the right feel for the p r o b l e m s associated with them.
Acknowledgements--We want to thank Dr P. Dolezel for determination of potassium content of the ceramic samples. The dating project was supported by the "Fonds zur F6rderung der wissenschaftlichen Forschung" under project number P5214.
REFERENCES Aitken M. J. (1976) Thermoluminescent age evaluation and assessment of error limits: revised system. Archaeometry 18, 233-238.
298
R. E R L A C H and N. V A N A
Bortolot V. J. and Carriveau G. W. (1982) An integrated TL measurement and computer system. PACT J. 6, 272-280. Tschirf E. and Vana N. (1982) Umgebungsiiberwachung
beziiglich/iuBerer Strahlung-Ger/ite und MeBresultate Acta phys. hung. 52, 363-372. Zimmerman D. W. (1971) Thermoluminescence dating using fine grains from pottery. Archaeometry 13, 29-52