Dr. David L. Cook first introduced briefly the application of W isotopes in limiting isotopic heterogeneity at the nebula scale and the effects of radioactive decay and cosmic rays on meteorites. Then, he showed us his work. A suite of IIAB iron meteorites was studied in order to accurately determine the contribution from galactic cosmic rays (GCR) and from potential decay of ¹⁸⁴Os to measured excesses in the minor isotope ¹⁸⁰W. In addition to W isotopes, trace element concentrations (Re, Os, Ir, Pt, W) were determined on the same samples, as well as their cosmic ray exposure ages, using ³⁶Cl-³⁶Ar systematics. These data were used in combination with an improved model of GCR effects on W isotopes to correct effects resulting from neutron capture and spallation reactions. After these corrections, the residual ¹⁸⁰W excesses correlate with Os/W ratios and indicate a clear contribution from 184Os decay. A newly derived decay constant is equivalent to a half-life for ¹⁸⁴Os of (3.38 ± 2.13) × 10¹³ a. Furthermore, when the data are plotted on an Os–W isochron diagram, the intercept (ε¹⁸⁰W= 0.63 ± 0.35) reveals that the IIAB parent body was characterized by a small initial nucleosynthetic excess in ¹⁸⁰W upon which radiogenic and GCR effects were superimposed. This is the first cogent evidence for p-process variability in W isotopes in early Solar System material.

  The report was excellent and Dr. David L. Cook often interacted with us during the report. Each key point was presented in detail, and all the teachers and students listened attentively.

  After the report, the exchange and discussion took place. Dr. David L. Cook communicated with teachers and students about the causes and correction of isotope anomalies, and answered students' questions actively and patiently. Everyone benefited greatly from the report.

                                contributor: Tianli Zhang