Dr. Gerard Barrett

Research Fellow - 14CHRONO

Address

14CHRONO (Centre for Climate, the Environment and Chronology)

School of Geography, Archaeology and Palaeoecology (GAP)

Queen's University Belfast

Belfast, BT7 1NN

Northern Ireland, UK

Contact

g.barrett@qub.ac.uk

+44 (0)28 9097 5377

Research and Interests

I work on and conduct research into the operation, optimization, and maintenance of the accelerator mass spectrometer (AMS, NEC compact 0.5MV) used in radiocarbon dating at 14CHRONO. Continual examination of approaches to improve the accuracy and precision while maintaining the production of high quality dates is a core element of this work.

Additional interests focus on the application of scientific methods to archaeology with special emphasis on dating methods and their use in relation to ceramics and chronology building. These are best summarised as follows:


Qualifications and Training

Ph.D. Rehydroxylation Dating Queen's University Belfast 2015

M.Sc. Dating and Chronology Queen's University Belfast 2011

M.Sc. Atomic and Molecular Cluster Physics National Univ. Ireland, Maynooth 2008

B.Sc. Experimental Physics Trinity College Dublin 2004

Cert. British Prehistoric Pottery Oxford Univ. Dep. Cont. Education 2011

Cert. Vacuum Physics and Techniques Univ. Cat. de Louvain 2005


Ph.D Research (part of an on-going examination of the RHX method):

Rehydroxylation Dating: Assessment for Archaeological Application (unpublished 2015 - Queen's University Belfast)

A series of publications are in preparation to distribute the findings of this work with the abstract included below.


Abstract:

Investigations are carried out into the mass gain behaviour of fired clay ceramics following drying (130°C) and reheating (500°C), and the application of these mass gain properties to the dating of archaeological ceramics using a modified rehydroxylation dating (RHX) methodology, a component based approach. Gravimetric analysis is conducted using a temperature and humidity controlled glove box arrangement (featuring a top-loading balance) on eighteen samples of varied known ages and contexts; this occurs following transfer from environmentally controlled chambers where subsamples of these samples are aged at three temperatures (25°C, 35°C, 45°C) following drying and reheating. The sample set consists principally of post-medieval bricks, but also includes some post-medieval pottery as well as both Etruscan and Roman ceramics. A suite of techniques are applied to characterise these ceramics, including XRD, FTIR, p-XRF, thin-section petrography, BET analysis, TG-MS, permeametry.

It is demonstrated that almost all samples exhibit issues with a prolonged and indefinite period of drying, exceeding two months at 130°C. Methods are presented for treating this issue as well as an interpretation of the processes involved. As well as this, one third of samples (abnormal samples) are shown to have problematic mass gain behaviour that is revealed to be correlated with high specific surface area/pore volume and the likely result of pore condensation issues.

It is confirmed that, as for reheating at 500°C, samples exhibit a two-stage mass gain behaviour following drying at 130°C, with the second of these stages continuing indefinitely and approximately linear as a function of t1/4. The first stage, Stage 1, is shown to have similar magnitude and duration following both drying and reheating, and is associated with physisorption of water on the surface and pores of the ceramic. The second stage, Stage 2, following both drying and reheating, is demonstrated to be better described by a t1/n model, where 1/n varies from 1/6 - 1/2, dependent on the sample; a correlation with the specific surface area/pore volume, connecting the diffusion mechanism of the process with the pore structure of the ceramic, will be presented. As well as this, it is established that the curvature (1/n value of t1/n model) has similar values for all subsamples of a sample aged at different temperatures and following both drying and reheating. The mass gain in Stage 2 following drying is shown to have an Arrhenius temperature dependence with activation energies of the order of those for mass gain following reheating at 500°C; a notable difference from the activation energies of rehydroxylation will be demonstrated. It is hypothesised that Stage 2 mass gain following drying is due to the recombination of chemisorbed water previously removed during drying, and support for this argument is presented. The rate of Stage 2 mass gain following drying will be shown to have a linear relationship with the rate following reheating at 500°C, and it will be argued that the underlying mass gain processes (chemisorption/rehydroxylation) are either the same and governed by the heating procedure or, more likely, different chemisorption processes but with some fundamental and compositional relationship.

For RHX dating, a component based approach is presented and applied. The results are inconclusive, with the estimated ages of most samples generally far too large, neither confirming the effectiveness of a component based approach nor the use of a t1/4 or t1/n model. The effects of a range of factors on the estimated ages are examined and discussed, including: uncertainties due to the experimental setup, data quality and resolution, uncertainty in the effective lifetime temperature (ELT), issues with the incomplete drying of samples, the presence of organic matter, the presence of problematic minerals, and the effects of short term elevated temperature events (STETEs). Of note, it is shown that organic matter contamination is present in significant quantities in all samples, regardless of retrieval context, and uncertainties in this quantity, particularly the organic matter to organic carbon ratio (OM/OC), have considerable effects on the estimated ages. The presence of gypsum is identified as a possible large source of uncertainty due to its dehydration and lower physisorption levels following reheating. The need for a better understanding of the nature of the drying processes and water not removed during drying is also highlighted. For samples with large activation energies, it is shown that STETEs, for example post-firing cooling of a brick or heating/cooling cycles during the use of a cooking pot, can add considerable quantities of (re)hydroxyl mass to the sample, detrimental to any dating estimations.

Finally, two contrasting methods of dealing with uncertainty and certainty in the temperature history of a ceramic are proposed, with examples of their use presented: an age-temperature curve approach is recommended for the visual interpretation of the ages and age ranges of samples where the ELT is less certain; the activation energy temperature history (AETH) approach is recommended for use where the temperature history of a sample is very well understood.

M.Sc. Research

Rehydroxylation Dating: Investigating the Effects of Diurnal and Annual Temperature Cycles within Ireland and Great Britain (unpublished 2011 - Queen's University Belfast)

Utilising instrumental temperature data from across Ireland and Great Britain, computer modelling was carried out to explore the temporal and spatial effects diurnal and annual temperature cycles have on average rehydroxylation rates (left below). These effects, found to be significant, were also examined for several long temperature records extending back to the 1880s (right below) A methodology for correcting these effects was developed and proposed for future use.

Journal Publications

Van der Burgt, P.J.M., Mahon, F., Barrett, G. and Gradziel, M.L. 2014. Electron impact fragmentation of thymine: partial ionization cross sections for positive fragments. European Physical Journal D. 68 151

Barrett, G. 2013. Rehydroxylation dating of fired clays: an improved time-offset model to account for the effect of cooling on post-reheating mass gain. Journal of Archaeological Science. 40 3596-3603

Barrett, G. and van der Burgt, P.J.M. 2008. A new apparatus for the study of electron impact fragmentation of molecular clusters. J. Phys. Conf. Ser. 101 012008

Conference Paper Presentations

Barrett, G. 2013. A new setup for testing the mass gain (rehydroxylation characteristics of fired clay ceramics. World Archaeology Congress-7. Dead Sea. Jordan (January 2013)

Barrett, G. 2007. Electron Impact Fragmentation of Biomolecular Clusters. AMIG07 - Atomic and Molecular Interactions Group conference. Maynooth

Conference Poster Presentations

Barrett, G. 2013. A new setup for testing the mass gain (rehydroxylation characteristics of fired clay ceramics. World Archaeology Congress-7. Dead Sea. Jordan (January 2013)

Barrett, G. 2012. Rehydroxylation dating: a new setup for testing the mass gain characteristics of fired clay ceramics. Insight from Innovation: New Light on Archaeological Ceramics. University of Southampton (October 2012)

Barrett, G. and van der Burgt, P.J.M. 2007. A New Apparatus for the Study of Electron Impact Fragmentation of Molecular Clusters. RADAM07 - Radiation Damage in Biomolecular Systems conference. Dublin.

Barrett, G. and P.J.M. van der Burgt. 2006. Electron impact fragmentation of molecular cluster. Biomolecules - From Gas Phase Properties to Reaction relevant in Living Cells (ESF Conference). Obergl, Austria (June 2006)

Awards

The Kerr's Master's Prize 2011
Queen's University Belfast, Belfast, Co. Antrim, Northern Ireland

Awarded by the School of Geography, Archaeology and Palaeoecology for best overall performance across all Master's level taught programs.

The Kerr's Master's Dissertation Prize 2011
Queen's University Belfast, Belfast, Co. Antrim, Northern Ireland

Awarded by the School of Geography, Archaeology and Palaeoecology for best dissertation across all Master's level taught programs.