Abstract / Summary
A 1998 University of Athens physics dissertation analysing energetic-particle measurements from the Pioneer 10 and Pioneer 11 Charged Particle Instruments reported recurrent structures in autocorrelation and cross-correlation analyses, including features near 469-470 and 340-341 nominal days. The original MATLAB code and processed data files were later lost. This report reconstructs the historical computation from the dissertation and official NASA archival data, then records a modern AI-assisted computational reassessment of the physical interpretation. The historical 11-20 MeV proton results are reproduced to rounding precision, including the Pioneer 10 autocorrelation near 469 samples and the principal Pioneer 10/Pioneer 11 cross-correlation features. Reconstruction also shows that the historical correlation axis represented displacement in a gapped retained-sample sequence, not uniformly elapsed calendar days: 341 common samples correspond to a median separation of 365 d, a mean of 412.7 d, and a range of 342-1160 d. The modern reassessment therefore uses actual observation times, calendar-lag correlation, Lomb-Scargle spectra, observation-window spectra, mask-preserving red-noise surrogates, multiple-testing corrections, and a final time-localized joint test. Several quasi-annual and approximately 1.3-year structures appear descriptively, but the strongest locked candidates do not meet the final corrected significance criteria. A detrended He 20-24 MeV/n feature near 459 d during 1973-1981 gives nominal p=0.027 but Holm-adjusted p=0.054 and is not reproduced in the corresponding raw-log analysis. The robust conclusion of this report is therefore historical and methodological: the 1998 numerical results are computationally reproducible, but their lag values cannot be treated directly as fixed calendar-time periodicities. The advanced modern analyses are provided as an auditable AI-assisted robustness assessment and should not be interpreted as independently specialist-validated signal analysis.