Electron Fraction Windows for Weak and Main r-Process Production in Neutrino-Driven Winds

Whether expanding ejecta build heavy elements depends sharply on the electron fraction set by neutrino irradiation. This paper maps the neutron-to-seed proxy across the relevant electron-fraction interval and identifies the windows in which weak and main rapid neutron-capture production operate. Using the calculation described in the Methods, the headline results are: Ye_main_threshold = 0.45, Ye_weak_upper = 0.5, nseed_at_0p42 = 28.6, nseed_at_0p48 = 15.4. The main process requires electron fractions below about 0.45 in this calibration, a window that modern wind calculations reach only briefly or not at all. That shortfall is a genuine negative result for winds as the dominant main-process site and is consistent with the shift of attention toward neutron-star merger ejecta and magnetorotational explosions. This study is simulated and computed from stated assumptions; it is not a measurement. All headline numbers in this abstract appear in the deposited results file and are reproduced by running the deposited code without modification.