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Research output: Thesis › Doctoral Thesis
Research output: Thesis › Doctoral Thesis
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TY - BOOK
T1 - Estimates of the local contribution to trace plutonium in soils from Blelham Tarn and Windermere
AU - Madina, Argaia
PY - 2025
Y1 - 2025
N2 - The assessment of trace environmental actinide quantities in Blelham Tarn and Fell Foot samples is described. This research comprises the assessment of trace quantities of americium and plutonium in soil samples taken in the environments surrounding these two lakes in the English Lake District, using broad-energy, High-Resolution Gamma-ray Spectroscopy (HRGS) and compact Accelerator Mass Spectrometry (AMS). It targets the concentration of trace radioactivity, mass abundance and isotopic fraction in soils and aims to discern the global and local proportions that constitute this quantity. The x-ray spectrometry studies indicate that the 241Am (and hence 241Pu) content in Lake District samples studied in this research is consistent with the prior art [1]. The average 240Pu/239Pu ratio (0.181 ± 0.002) measured in this research is observed to be consistent with the global fallout average reported in several previous studies, such as the global fallout average [2], and with that, the sediments in Lake Ontario [3].The average 244Pu/239Pu ratio for the Blelham Tarn and Fell Foot data, not measured previously for Lake District samples [4], has been compared with data from Erie Lake, Salzburg, the Enewetak and Bikar atolls samples to estimate the local contribution to trace plutonium deposited (F_(L_239 ) / %), from the atmosphere at these sites [4] [5] [6] [7], respectively. Further Analysis of this local contribution, derived in terms of its 244Pu/239Pu and accounting for (18 ± 13) at % of the majority isotope 239Pu for the combined data from both sites, indicates that it has a 240Pu/239Pu ratio of (0.21 ± 0.08) consistent with the prior measurement of samples from the Irish Sea [5]. In addition, this suggests that the local material deposition is more consistent with reprocessed Magnox materials rather than fallout from either the Windscale or Chernobyl accidents, notwithstanding significant uncertainties and the potential for a shortfall in assessment due to the resistance of the refractory component in fallout residues.The dependence with depth of trace environmental plutonium measured in this research is observed to be consistent with the trend that combines the phenomena of convection and dispersion, as per the Convection-Dispersion Equation (CDE). Using the CDE for a single deposition (the traditional application of the CDE) yields a deposition period consistent with the peak fallout from nuclear weapons tests in 1963. Using a modified version of the CDE comprising two deposition components, each with time spans distinct from one another, yields timescales for the local distribution of approximately (30± 12) years and for the global fallout component of approximately (57 ±10) years, consistent with the era of permitted discharges at Sellafield and peak global fallout, respectively.Finally, a consideration of the potential for there to be a refractory-based reserve that is resilient to some preparatory processes has been explored and the implications for this work considered.
AB - The assessment of trace environmental actinide quantities in Blelham Tarn and Fell Foot samples is described. This research comprises the assessment of trace quantities of americium and plutonium in soil samples taken in the environments surrounding these two lakes in the English Lake District, using broad-energy, High-Resolution Gamma-ray Spectroscopy (HRGS) and compact Accelerator Mass Spectrometry (AMS). It targets the concentration of trace radioactivity, mass abundance and isotopic fraction in soils and aims to discern the global and local proportions that constitute this quantity. The x-ray spectrometry studies indicate that the 241Am (and hence 241Pu) content in Lake District samples studied in this research is consistent with the prior art [1]. The average 240Pu/239Pu ratio (0.181 ± 0.002) measured in this research is observed to be consistent with the global fallout average reported in several previous studies, such as the global fallout average [2], and with that, the sediments in Lake Ontario [3].The average 244Pu/239Pu ratio for the Blelham Tarn and Fell Foot data, not measured previously for Lake District samples [4], has been compared with data from Erie Lake, Salzburg, the Enewetak and Bikar atolls samples to estimate the local contribution to trace plutonium deposited (F_(L_239 ) / %), from the atmosphere at these sites [4] [5] [6] [7], respectively. Further Analysis of this local contribution, derived in terms of its 244Pu/239Pu and accounting for (18 ± 13) at % of the majority isotope 239Pu for the combined data from both sites, indicates that it has a 240Pu/239Pu ratio of (0.21 ± 0.08) consistent with the prior measurement of samples from the Irish Sea [5]. In addition, this suggests that the local material deposition is more consistent with reprocessed Magnox materials rather than fallout from either the Windscale or Chernobyl accidents, notwithstanding significant uncertainties and the potential for a shortfall in assessment due to the resistance of the refractory component in fallout residues.The dependence with depth of trace environmental plutonium measured in this research is observed to be consistent with the trend that combines the phenomena of convection and dispersion, as per the Convection-Dispersion Equation (CDE). Using the CDE for a single deposition (the traditional application of the CDE) yields a deposition period consistent with the peak fallout from nuclear weapons tests in 1963. Using a modified version of the CDE comprising two deposition components, each with time spans distinct from one another, yields timescales for the local distribution of approximately (30± 12) years and for the global fallout component of approximately (57 ±10) years, consistent with the era of permitted discharges at Sellafield and peak global fallout, respectively.Finally, a consideration of the potential for there to be a refractory-based reserve that is resilient to some preparatory processes has been explored and the implications for this work considered.
KW - thesis-1
U2 - 10.17635/lancaster/thesis/2785
DO - 10.17635/lancaster/thesis/2785
M3 - Doctoral Thesis
PB - Lancaster University
ER -