On the production of cosmogenic nuclides in meteoroids by galactic protons

Underground radioactivity measurements of meteorites: Development of methods suitable to determine precise terrestrial age of recent falls

The L6 chondritic meteorite, HaH-346, fell in Libya. However, neither the exact date of the fall nor the exact size of the original meteoroid or asteroid is known. A specimen of the meteorite, weighing 488 g, was measured using ultra low-background gamma-ray spectrometry in the 225 m deep underground facility HADES. Activation products ²²Na, ²⁶Al, ⁶⁰Co, ⁵⁷Co, ⁵⁴Mn and ⁴⁴Ti were detected. The detection efficiency was determined by 3D scanning the meteorite and introducing this in the computer model of the detector and sample implemented in the MCNP6.2 Monte Carlo code. The activities of ²²Na and ²⁶Al support the hypothesis that the fall took place on 26 August 2018. Furthermore, the ⁶⁰Co and ²⁶Al activities indicate that the original radius of meteoroid was between 50 and 80 cm, which suggests the mass prior to atmospheric entry was between 2400 and 7300 kg.

Supernova-Produced ^{53}Mn on Earth

For the time period from 1.5 to 4 Myr before the present we found in deep ocean ferromanganese crusts a ^{53}Mn excess concentration in terms of ^{53}Mn/Mn of about 4×10^{-14} over that expected for cosmogenic production. We conclude that this ^{53}Mn is of supernova origin because it is detected in the same time window, about 2.5 Myr ago, where ^{60}Fe has been found earlier. This overabundance confirms the supernova origin of that ^{60}Fe. For the first time, supernova-formed ^{53}Mn has been detected and it is the second positively identified radioisotope from the same supernova. The ratio ^{53}Mn/^{60}Fe of about 14 is consistent with that expected for a SN with a 11-25  M_{⊙} progenitor mass and solar metallicity.

Galactic-cosmic-ray-produced 3He in a ferromanganese crust: any supernova 60Fe excess on earth?

An excess of 60Fe in 2.4-3.2 x 10(6) year old ferromanganese crust (237 KD) from the deep Pacific Ocean has been considered as evidence for the delivery of debris from a nearby supernova explosion to Earth. Extremely high ;{3}He/;{4}He (up to 6.12 x 10(-3)) and 3He concentrations (up to 8 x 10(9) atoms/g) measured in 237 KD cannot be supernova-derived. The helium is produced by galactic cosmic rays (GCR) and delivered in micrometeorites that have survived atmospheric entry to be trapped by the crust. 60Fe is produced by GCR reactions on Ni in extraterrestrial material. The maximum (3)He/(60)Fe of 237 KD (80-850) is comparable to the GCR (3)He/(60)Fe production ratio (400-500) predicted for Ni-bearing minerals in iron meteorites. The excess 60Fe can be plausibly explained by the presence of micrometeorites trapped by the crust, rather than injection from a supernova source.