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Dating bricks of the last two millennia from Newcastle upon Tyne: a preliminary study
Radiation Measurements 32 (2000) 615±619
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Dating bricks of the last two millennia from Newcastle upon Tyne: a preliminary study I.K. Baili*, N. Holland Luminescence Dating Laboratory, Department of Archaeology, University of Durham, South Road, Durham DH1 3LE, UK Received 30 October 1999; accepted 3 December 1999
Abstract Bricks from a group of four independently dated late medieval buildings in Newcastle upon Tyne have been tested to establish their suitability for luminescence dating as part of a wider study of the dating of post-Roman and medieval brick buildings. The luminescence characteristics of quartz extracted from the bricks were determined using TL (2108C peak) and OSL measurement procedures. Both TL and OSL measurement procedures based on SAR and SARA protocols were applied to determine the palaeodose. The luminescence dates for three sampled locations are in good agreement with the assigned architectural dates; the fourth appears to be older raising doubts concerning the architectural assessment of the sampled phase. 7 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction At present the only methods available for determining the age of much of the brickwork of standing buildings of the late medieval and early modern periods in Britain (i.e. 14th±19th centuries A.D.) are based on either surviving historical records or on typological comparisons. Depending on the region concerned, typological dating may at best only enable dating within 50 years and in many cases the uncertainty exceeds a century. This paper presents the preliminary results of a study that aims to develop procedures for the routine dating of bricks from standing medieval buildings in Britain. Brick samples were taken from late medieval buildings in Newcastle upon Tyne (see Table 1) where dates have been assigned by architectural historians. A further excavated brick of putatively Roman age from
* Corresponding author. Tel.: +44 (0)191 374 3741. E-mail address: ian.baili@durham.ac.uk (I.K. Baili).
the nearby archaeological site of the medieval Jarrow Monastery was also examined. It was included to test the properties of brick from the same region but manufactured under dierent conditions and with substantially higher palaeodose. 2. Sample preparation and measurement conditions HF etched quartz grains within the size range 90± 150 mm were extracted from the bricks using standard quartz inclusion separation procedures. A 1 cm thick slice was cut from each brick and the outer 2 mm removed from all faces using a water-cooled diamond saw and abrasive wheel; the slice was mechanically crushed by hand. Part of the crushed material was sieved into three fractions (<90 mm, 90±150 mm and >150 mm) and the remainder ball-milled for use in dose-rate assessment. The 90±150 mm sieved fraction was etched in HF (40%, 45 min) followed by washing in HCl (32%, 45 min). The measurement sample comprised inclusions of size >90 mm and densities between
1350-4487/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 0 - 4 4 8 7 ( 9 9 ) 0 0 2 8 6 - 3
616
I.K. Baili, N. Holland / Radiation Measurements 32 (2000) 615±619
2.63 and 2.67 g cmÿ3 (separated using a solution of sodium polytungstate). Luminescence measurements were performed with 01 mg aliquots of inclusions, deposited as a monolayer onto stainless steel discs, previously coated with a thin layer of silicone oil. In the case of TL (performed with a Risù DA-12 reader), preliminary tests were performed with dierent colour glass ®lters. For the measurements discussed here the signal was maximised by placing no colour ®lter in the detection system. For OSL measurements (performed with aDA-15 reader) the standard stimulation (0450±570 nm) con®guration and detection ®lter pack (2 Hoya U-340) were employed; the incident stimulation power was adjusted to 30 mW cmÿ2. Radiation doses were administered using a calibrated Sr90/Y90 beta source (GoÈksu et al., 1995). 3. Measurements and results TL and OSL measurements were performed using regenerative and additive±regenerative procedures applied to single aliquots based on those developed previously for application with OSL (SARA, Mejdahl and Bùtter-Jensen, 1994), SAR (Murray and Roberts, 1998) and TL (Baili and Petrov, 1999). 3.1. TL TL glow curves typical of the samples discussed here are shown in Fig. 1(a); the 02108C TL peak was used for dosimetry. The regenerative procedure applied (referred to here as SAR±TL to provide consistency in terminology) was similar to that described by Baili and Petrov (1999; procedures C and D). By terminating the glow curve below 3008C (we used 2808C) it was possible in the case of the late medieval bricks to avoid signi®cant changes in sensitivity when measurement aliquots were subjected to a limited number of repeated dose/measurement cycles. However, sensitisation eects were apparent for cumulative dose exceeding several gray. To check for sensitivity changes on ®rst heating
(alone), an additive dose procedure was employed, referred to here as SARA TL, which is similar in principle to that used in the pre-dose technique (modi®ed additive dose procedure) and the SARA OSL procedure. Corrections for changes in sensitivity were necessary when using this procedure and they were calculated on the basis of a separate set of tests with several aliquots. In these tests repeated measurements were performed with dierent levels of dose to characterise the change in sensitivity with the size of the regenerative dose and the cumulative dose. 3.2. OSL Fig. 1(b) shows two OSL decay curves: the ®rst corresponding to the natural dose (N) and the second measured following a further pre-annealing treatment to check for thermal transfer eects (referred to here as a pre-heat monitor, PHM). In the case of the late medieval brick samples the intensity of the PHM decay curve and the degree of sensitivity change were small compared with the preceding OSL decay curve in the sequence of measurements, tested for cumulative doses up to 08 Gy. However, for the brick from Jarrow (P 1 5 Gy), both the PHM signals were signi®cant [Fig. 1(b)] and sensitisation eects more marked, depending on the severity of the pre-annealing treatment (Fig. 2). The PHM decay curve was taken to represent the best estimate of the background for the preceding OSL measurement. For this sample supralinear behaviour in the regenerative growth characteristic is obtained if the background signal is assumed to be that obtained after prolonged bleaching or that extrapolated from the `tail' of the OSL decay curve. 3.3. Age calculation To provide a basis for assessing the reliability of the various dose evaluation procedures, the associated measurements for annual dose assessment were performed and preliminary luminescence dates are listed in Table 2.
Table 1 Details of the brick samples tested Location
Laboratory reference
Architectural date A.D.
The Cooperage 28/30 The Close, Level 2 Alderman Fenwick's House Holy Jesus Hospital Jarrow Monastery
225 227 228 257 JA98-1
1620±1680 1620±1680 1680±1720 1670±1710
±
I.K. Baili, N. Holland / Radiation Measurements 32 (2000) 615±619
617
Fig. 1. (a) TL glow curves measured (58/s) with sample 228 where N and b represent the natural and regenerative (1 Gy) glow curves respectively; (b) OSL decay curves measured with sample JA98-1 (held at 1258C) where N and PHM represent the natural and pre-heat monitor (see main text) decay curves, respectively.
4. Discussion In general the quartz tested had adequate TL and OSL luminescence sensitivity for dating measurements, although in one case (Holy Jesus Hospital, 257) the natural OSL signal was not measurable. Both TL and OSL sensitivities varied widely between samples. This
Fig. 2. Relative change in OSL response to a small monitor beta dose in a regenerative sequence vs incremental dose. The OSL monitor was measured before and after the administration of a beta dose (the incremental dose). The same preheat speci®cation was applied throughout the regenerative sequence for each of four aliquots (represented by dierent symbols). The pre-heats range in severity from 10 s at 2208C combined with 10 s at 1508C associated with the monitor dose (cross) to 10 s at 2608C (open triangles) throughout.
is not surprising in view of previous studies (e.g. Petrov and Baili, 1997) which indicated that the sensitivity of the 110 and 2108C TL peaks and their emission spectrum were strongly in¯uenced by the atmosphere surrounding quartz during high temperature annealing. Quartz extracted from sample 228 (Alderman Fenwick's House) had signi®cantly higher luminescence sensitivity and this may be linked with the introduction of coal as a fuel during the late 17th century in north east Britain leading to more uniform and fully oxidising ®ring conditions in the kiln. With the detection systems as speci®ed above, the integrated TL signal (peak temperature 2208C) was about an order of magnitude higher than the integrated OSL signal (0±20 s; applying a 10 s pre-heat at 2608C). The choice of pre-heat treatment can also signi®cantly aect the suitability of samples for dating where the natural OSL is weak, as was found with the mid-17th century bricks (225 and 227). For example, in one case the natural OSL signal dropped by a factor of 10 following a pre-heat treatment of 2808C for 10 s. With the exception of the Cooperage (225), the preliminary dating results for bricks from two buildings, The Close (227) and Alderman Fenwick's House (228) indicate that the SAR and SARA OSL and SARA TL dates Ð and for Holy Jesus Hospital the SARA TL date Ð are in good agreement with the assigned architectural age for the phases sampled. For all three sampled locations the central values of the SAR TL dates are on average 5% younger than the assigned age. If the P values are reliable, this dierence is signi®cantly smaller than that predicted using currently available trap parameter data to estimate the mean
a
b
A pre-heat was applied (RT-1408C @ 28/s) before measurement of the TL glow curve. Several pre-heat treatments were applied (10 s at 220, 260 and 2808C) before OSL measurements; the values of P were obtained using a 10 s pre-heat at 2608C. c The total eective dose-rate was calculated on the basis of b-TLD, thick source alpha counting and in situ g-TLD measurements. d The uncertainties associated with the calculated luminescence dates are the overall errors (1s). e The brick was thought to be of either late Roman or early medieval age.
e
1500295 1660250 1655245 ± 1430285 1640240 1710230 ± 3202190 3.71 3.56 3.19 3.15 3.04 2.3520.28 1.1020.06 0.9620.05 0.8420.07 ± 2.1720.10 0.8520.05 0.8020.03 0.6820.06 ± 225 227 228 257 JA98-1
2.1220.21 1.2820.05 0.9320.02 ± 5.120.3
1.8520.30 1.2220.13 1.1020.09 ± ±
1415270 1760230 1750230 1785225
13652100 1690235 1700235 1730235
SARA OSL dated (A.D.) SAR OSL dated (A.D.) SARA TL dated (A.D.) SAR TL dated (A.D.) Eective total doseratec (mGy/a) SARA OSLb P (Gy) SAR OSLb P (Gy) SARA TLa P (Gy) SAR TLa P (Gy) Sample ref.
Table 2
1620±1680 1620±1680 1680±1720 1670±1710
I.K. Baili, N. Holland / Radiation Measurements 32 (2000) 615±619 Architectural date (A.D.)
618
lifetime of the trap(s) associated with the 2108C TL peak. The latter ranges from 0750 to 2000 years at 208C (Baili and Petrov, 1999). This was an unexpected outcome and is to be investigated further. Both the OSL and TL dates for The Cooperage are much older than the assigned architectural age. This suggests that the phase of the building sampled may be signi®cantly earlier than expected or that the manufacturing date of the brick predates the phase construction, i.e. the brick was re-used. This underlines the need for detailed examination of building history when seeking known age material. Other samples will be taken from this location to investigate the reliability of the age evaluation.
5. Summary This study, although at a preliminary stage and of limited range of samples, has demonstrated the feasibility of applying TL and OSL techniques to quartz inclusions to obtain luminescence ages for late medieval bricks. The selection of known age samples and the possibility of applying two techniques based on dierent luminescence mechanisms both oer a methodological advantage, the latter providing a means of checking the consistency of palaeodose evaluations. Such checks are needed in view of the underlying complexity of changes in sensitivity that are encountered when using regenerative procedures. With one exception the luminescence ages are consistent with their assigned architectural age and in the case of The Cooperage it appears that the sampled phase may be older than the ®rst architectural assessment.
Acknowledgements We are pleased to acknowledge the collaboration of Mr D. Heslop, Tyne and Wear County Archaeologist, and Dr C.P. Graves, Department of Archaeology, University of Durham, concerning archaeological aspects of this project. Financial assistance was provided from the Nueld Foundation (to NH), the University of Durham and the Society of Antiquaries of Newcastle upon Tyne.
References Baili, I.K., Petrov, S.A., 1999. The use of the 2108C TL peak in quartz for retrospective dosimetry. Radiation Protection Dosimetry 84, 551±554. GoÈksu, H.Y., Baili, I.K., Bùtter-Jensen, L., HuÈtt, G., Stoneham, D., 1995. Interlaboratory beta source cali-
I.K. Baili, N. Holland / Radiation Measurements 32 (2000) 615±619 bration using TL and OSL with natural quartz. Radiation Measurements 24, 479±484. Mejdahl, V., Bùtter-Jensen, L., 1994. Luminescence dating of archaeological materials using a new technique based on single aliquot measurements. Quaternary Science Reviews (Quaternary Geochronology) 7, 551±554.
619
Murray, A.S., Roberts, R.G., 1998. Measurement of the equivalent dose in quartz using a regenerative-dose singlealiquot protocol. Radiation Measurements 29, 503±515. Petrov, S.A., Baili, I.K., 1997. Determination of trap depths associated with TL peaks in synthetic quartz (350±550 K). Radiation Measurements 27, 185±191.
www.elsevier.com/locate/radmeas
Dating bricks of the last two millennia from Newcastle upon Tyne: a preliminary study I.K. Baili*, N. Holland Luminescence Dating Laboratory, Department of Archaeology, University of Durham, South Road, Durham DH1 3LE, UK Received 30 October 1999; accepted 3 December 1999
Abstract Bricks from a group of four independently dated late medieval buildings in Newcastle upon Tyne have been tested to establish their suitability for luminescence dating as part of a wider study of the dating of post-Roman and medieval brick buildings. The luminescence characteristics of quartz extracted from the bricks were determined using TL (2108C peak) and OSL measurement procedures. Both TL and OSL measurement procedures based on SAR and SARA protocols were applied to determine the palaeodose. The luminescence dates for three sampled locations are in good agreement with the assigned architectural dates; the fourth appears to be older raising doubts concerning the architectural assessment of the sampled phase. 7 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction At present the only methods available for determining the age of much of the brickwork of standing buildings of the late medieval and early modern periods in Britain (i.e. 14th±19th centuries A.D.) are based on either surviving historical records or on typological comparisons. Depending on the region concerned, typological dating may at best only enable dating within 50 years and in many cases the uncertainty exceeds a century. This paper presents the preliminary results of a study that aims to develop procedures for the routine dating of bricks from standing medieval buildings in Britain. Brick samples were taken from late medieval buildings in Newcastle upon Tyne (see Table 1) where dates have been assigned by architectural historians. A further excavated brick of putatively Roman age from
* Corresponding author. Tel.: +44 (0)191 374 3741. E-mail address: ian.baili@durham.ac.uk (I.K. Baili).
the nearby archaeological site of the medieval Jarrow Monastery was also examined. It was included to test the properties of brick from the same region but manufactured under dierent conditions and with substantially higher palaeodose. 2. Sample preparation and measurement conditions HF etched quartz grains within the size range 90± 150 mm were extracted from the bricks using standard quartz inclusion separation procedures. A 1 cm thick slice was cut from each brick and the outer 2 mm removed from all faces using a water-cooled diamond saw and abrasive wheel; the slice was mechanically crushed by hand. Part of the crushed material was sieved into three fractions (<90 mm, 90±150 mm and >150 mm) and the remainder ball-milled for use in dose-rate assessment. The 90±150 mm sieved fraction was etched in HF (40%, 45 min) followed by washing in HCl (32%, 45 min). The measurement sample comprised inclusions of size >90 mm and densities between
1350-4487/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 0 - 4 4 8 7 ( 9 9 ) 0 0 2 8 6 - 3
616
I.K. Baili, N. Holland / Radiation Measurements 32 (2000) 615±619
2.63 and 2.67 g cmÿ3 (separated using a solution of sodium polytungstate). Luminescence measurements were performed with 01 mg aliquots of inclusions, deposited as a monolayer onto stainless steel discs, previously coated with a thin layer of silicone oil. In the case of TL (performed with a Risù DA-12 reader), preliminary tests were performed with dierent colour glass ®lters. For the measurements discussed here the signal was maximised by placing no colour ®lter in the detection system. For OSL measurements (performed with aDA-15 reader) the standard stimulation (0450±570 nm) con®guration and detection ®lter pack (2 Hoya U-340) were employed; the incident stimulation power was adjusted to 30 mW cmÿ2. Radiation doses were administered using a calibrated Sr90/Y90 beta source (GoÈksu et al., 1995). 3. Measurements and results TL and OSL measurements were performed using regenerative and additive±regenerative procedures applied to single aliquots based on those developed previously for application with OSL (SARA, Mejdahl and Bùtter-Jensen, 1994), SAR (Murray and Roberts, 1998) and TL (Baili and Petrov, 1999). 3.1. TL TL glow curves typical of the samples discussed here are shown in Fig. 1(a); the 02108C TL peak was used for dosimetry. The regenerative procedure applied (referred to here as SAR±TL to provide consistency in terminology) was similar to that described by Baili and Petrov (1999; procedures C and D). By terminating the glow curve below 3008C (we used 2808C) it was possible in the case of the late medieval bricks to avoid signi®cant changes in sensitivity when measurement aliquots were subjected to a limited number of repeated dose/measurement cycles. However, sensitisation eects were apparent for cumulative dose exceeding several gray. To check for sensitivity changes on ®rst heating
(alone), an additive dose procedure was employed, referred to here as SARA TL, which is similar in principle to that used in the pre-dose technique (modi®ed additive dose procedure) and the SARA OSL procedure. Corrections for changes in sensitivity were necessary when using this procedure and they were calculated on the basis of a separate set of tests with several aliquots. In these tests repeated measurements were performed with dierent levels of dose to characterise the change in sensitivity with the size of the regenerative dose and the cumulative dose. 3.2. OSL Fig. 1(b) shows two OSL decay curves: the ®rst corresponding to the natural dose (N) and the second measured following a further pre-annealing treatment to check for thermal transfer eects (referred to here as a pre-heat monitor, PHM). In the case of the late medieval brick samples the intensity of the PHM decay curve and the degree of sensitivity change were small compared with the preceding OSL decay curve in the sequence of measurements, tested for cumulative doses up to 08 Gy. However, for the brick from Jarrow (P 1 5 Gy), both the PHM signals were signi®cant [Fig. 1(b)] and sensitisation eects more marked, depending on the severity of the pre-annealing treatment (Fig. 2). The PHM decay curve was taken to represent the best estimate of the background for the preceding OSL measurement. For this sample supralinear behaviour in the regenerative growth characteristic is obtained if the background signal is assumed to be that obtained after prolonged bleaching or that extrapolated from the `tail' of the OSL decay curve. 3.3. Age calculation To provide a basis for assessing the reliability of the various dose evaluation procedures, the associated measurements for annual dose assessment were performed and preliminary luminescence dates are listed in Table 2.
Table 1 Details of the brick samples tested Location
Laboratory reference
Architectural date A.D.
The Cooperage 28/30 The Close, Level 2 Alderman Fenwick's House Holy Jesus Hospital Jarrow Monastery
225 227 228 257 JA98-1
1620±1680 1620±1680 1680±1720 1670±1710
±
I.K. Baili, N. Holland / Radiation Measurements 32 (2000) 615±619
617
Fig. 1. (a) TL glow curves measured (58/s) with sample 228 where N and b represent the natural and regenerative (1 Gy) glow curves respectively; (b) OSL decay curves measured with sample JA98-1 (held at 1258C) where N and PHM represent the natural and pre-heat monitor (see main text) decay curves, respectively.
4. Discussion In general the quartz tested had adequate TL and OSL luminescence sensitivity for dating measurements, although in one case (Holy Jesus Hospital, 257) the natural OSL signal was not measurable. Both TL and OSL sensitivities varied widely between samples. This
Fig. 2. Relative change in OSL response to a small monitor beta dose in a regenerative sequence vs incremental dose. The OSL monitor was measured before and after the administration of a beta dose (the incremental dose). The same preheat speci®cation was applied throughout the regenerative sequence for each of four aliquots (represented by dierent symbols). The pre-heats range in severity from 10 s at 2208C combined with 10 s at 1508C associated with the monitor dose (cross) to 10 s at 2608C (open triangles) throughout.
is not surprising in view of previous studies (e.g. Petrov and Baili, 1997) which indicated that the sensitivity of the 110 and 2108C TL peaks and their emission spectrum were strongly in¯uenced by the atmosphere surrounding quartz during high temperature annealing. Quartz extracted from sample 228 (Alderman Fenwick's House) had signi®cantly higher luminescence sensitivity and this may be linked with the introduction of coal as a fuel during the late 17th century in north east Britain leading to more uniform and fully oxidising ®ring conditions in the kiln. With the detection systems as speci®ed above, the integrated TL signal (peak temperature 2208C) was about an order of magnitude higher than the integrated OSL signal (0±20 s; applying a 10 s pre-heat at 2608C). The choice of pre-heat treatment can also signi®cantly aect the suitability of samples for dating where the natural OSL is weak, as was found with the mid-17th century bricks (225 and 227). For example, in one case the natural OSL signal dropped by a factor of 10 following a pre-heat treatment of 2808C for 10 s. With the exception of the Cooperage (225), the preliminary dating results for bricks from two buildings, The Close (227) and Alderman Fenwick's House (228) indicate that the SAR and SARA OSL and SARA TL dates Ð and for Holy Jesus Hospital the SARA TL date Ð are in good agreement with the assigned architectural age for the phases sampled. For all three sampled locations the central values of the SAR TL dates are on average 5% younger than the assigned age. If the P values are reliable, this dierence is signi®cantly smaller than that predicted using currently available trap parameter data to estimate the mean
a
b
A pre-heat was applied (RT-1408C @ 28/s) before measurement of the TL glow curve. Several pre-heat treatments were applied (10 s at 220, 260 and 2808C) before OSL measurements; the values of P were obtained using a 10 s pre-heat at 2608C. c The total eective dose-rate was calculated on the basis of b-TLD, thick source alpha counting and in situ g-TLD measurements. d The uncertainties associated with the calculated luminescence dates are the overall errors (1s). e The brick was thought to be of either late Roman or early medieval age.
e
1500295 1660250 1655245 ± 1430285 1640240 1710230 ± 3202190 3.71 3.56 3.19 3.15 3.04 2.3520.28 1.1020.06 0.9620.05 0.8420.07 ± 2.1720.10 0.8520.05 0.8020.03 0.6820.06 ± 225 227 228 257 JA98-1
2.1220.21 1.2820.05 0.9320.02 ± 5.120.3
1.8520.30 1.2220.13 1.1020.09 ± ±
1415270 1760230 1750230 1785225
13652100 1690235 1700235 1730235
SARA OSL dated (A.D.) SAR OSL dated (A.D.) SARA TL dated (A.D.) SAR TL dated (A.D.) Eective total doseratec (mGy/a) SARA OSLb P (Gy) SAR OSLb P (Gy) SARA TLa P (Gy) SAR TLa P (Gy) Sample ref.
Table 2
1620±1680 1620±1680 1680±1720 1670±1710
I.K. Baili, N. Holland / Radiation Measurements 32 (2000) 615±619 Architectural date (A.D.)
618
lifetime of the trap(s) associated with the 2108C TL peak. The latter ranges from 0750 to 2000 years at 208C (Baili and Petrov, 1999). This was an unexpected outcome and is to be investigated further. Both the OSL and TL dates for The Cooperage are much older than the assigned architectural age. This suggests that the phase of the building sampled may be signi®cantly earlier than expected or that the manufacturing date of the brick predates the phase construction, i.e. the brick was re-used. This underlines the need for detailed examination of building history when seeking known age material. Other samples will be taken from this location to investigate the reliability of the age evaluation.
5. Summary This study, although at a preliminary stage and of limited range of samples, has demonstrated the feasibility of applying TL and OSL techniques to quartz inclusions to obtain luminescence ages for late medieval bricks. The selection of known age samples and the possibility of applying two techniques based on dierent luminescence mechanisms both oer a methodological advantage, the latter providing a means of checking the consistency of palaeodose evaluations. Such checks are needed in view of the underlying complexity of changes in sensitivity that are encountered when using regenerative procedures. With one exception the luminescence ages are consistent with their assigned architectural age and in the case of The Cooperage it appears that the sampled phase may be older than the ®rst architectural assessment.
Acknowledgements We are pleased to acknowledge the collaboration of Mr D. Heslop, Tyne and Wear County Archaeologist, and Dr C.P. Graves, Department of Archaeology, University of Durham, concerning archaeological aspects of this project. Financial assistance was provided from the Nueld Foundation (to NH), the University of Durham and the Society of Antiquaries of Newcastle upon Tyne.
References Baili, I.K., Petrov, S.A., 1999. The use of the 2108C TL peak in quartz for retrospective dosimetry. Radiation Protection Dosimetry 84, 551±554. GoÈksu, H.Y., Baili, I.K., Bùtter-Jensen, L., HuÈtt, G., Stoneham, D., 1995. Interlaboratory beta source cali-
I.K. Baili, N. Holland / Radiation Measurements 32 (2000) 615±619 bration using TL and OSL with natural quartz. Radiation Measurements 24, 479±484. Mejdahl, V., Bùtter-Jensen, L., 1994. Luminescence dating of archaeological materials using a new technique based on single aliquot measurements. Quaternary Science Reviews (Quaternary Geochronology) 7, 551±554.
619
Murray, A.S., Roberts, R.G., 1998. Measurement of the equivalent dose in quartz using a regenerative-dose singlealiquot protocol. Radiation Measurements 29, 503±515. Petrov, S.A., Baili, I.K., 1997. Determination of trap depths associated with TL peaks in synthetic quartz (350±550 K). Radiation Measurements 27, 185±191.