Characterization of Italian tile samples using comparative neutron activation analysis in the Penn State Breazeale Nuclear Reactor

Open Access
Author:
Durrant, Chad Bredthauer
Graduate Program:
Nuclear Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Kenan Unlu, Thesis Advisor
  • Amanda Melia Johnsen, Thesis Advisor
  • Karen Ann Thole, Thesis Advisor
Keywords:
  • neutron activation analysis
  • comparative NAA
Abstract:
Comparative neutron activation analysis (CNAA) is a powerful method that is used to determine trace element compositions of unknown samples by comparing them with known samples. This is accomplished by the activation of the samples with thermal neutrons and then subsequently measuring the corresponding delayed gamma rays. There are three principal goals achieved from this research: developing an irradiation fixture with suitable neutron fluences and large sample number capacity, characterizing the thermal neutron flux of the irradiation fixture, and determining the trace element composition of 15 Italian tiles. The Italian tiles come from two archeological sites, Tarquinia and Veii in Italy. By determining the trace element composition of the samples, the tiles can be separated into groups based on their composition. Archeologists then use the composition data to determine where material used to make these tiles and other similar artefacts originated from. Once the origins of these samples are determined other conclusions such as trade and technology transfer in the region can be drawn. In order to use CNAA at the Radiation Science and Engineering Center to determine the trace element composition of 15 Italian tile samples, an irradiation fixture and sample holder were designed and built for the Penn State Breazeale Reactor (PSBR). This sample holder allows up to 28 samples to be irradiated simultaneously at relatively similar thermal neutron fluences. A short irradiation with a total neutron fluence of ~ 6.1 x 10^14 neutrons/cm2 and a long irradiation with total neutron fluence of ~ 5.8 x 10^17 neutrons/cm^2 were performed. The irradiation fixture is also durable and made mostly with high purity aluminum, thereby minimizing the impurities that can increase the activity of the sample holder across multiple irradiations. An encapsulation method for the samples was developed using high purity quartz ampoules to minimize the interferences in the gamma spectra as well as minimize the activity produced. The thermal and epithermal neutron flux profile of the sample holder was characterized using bare gold-aluminum wires and cadmium covered gold-aluminum wires. The total variation from highest to lowest thermal neutron flux was ~30%. Lastly, the trace element compositions of the 15 Italian tile samples were determined by CNAA. Between 13 and 16 trace elements were determined for each sample including: sodium, potassium, manganese, strontium, europium, scandium, titanium, chromium, iron, zinc, rubidium, antimony, barium, hafnium, calcium, and zirconium. The concentrations of the trace elements determined ranged from hundreds of part per billion (ppb) for antimony to tens of milligrams per gram for potassium, titanium, and iron. All other trace elements had concentrations within that range. After the trace element compositions for each sample were determined, the samples were analyzed and clustered into two groups of similar composition. Group 1 is composed of samples 139B-148B and Group 2 is composed of samples 149B-153B. Based upon comparisons with previous work Group 1 samples likely originate from Tarquinia and Group 2 samples likely originate from Veii. The elements primarily responsible for these groupings are europium, chromium, hafnium, scandium, rubidium and zirconium. Scatter plots with europium and chromium as one of the trace elements concentrations give the most distinct separation between the groupings. One exception is the zirconium plot of sample 145B, which appears to suggest that sample 145B is part of neither group. This research also corroborates the findings of previous studies and demonstrates the efficacy of CNAA as an analytical technique for determining the trace element composition of Italian tile samples.