Neutron capture experiment sheds light on ancient stardust

Niobium-94, an isotope with 41 protons and 53 neutrons, plays a crucial role in the formation of heavy elements in dying stars. In a recent study published in Physical Review Letters, the n_TOF Collaboration has made the first-ever measurement of the probability of niobium-94 undergoing neutron capture. This discovery sheds light on a long-standing puzzle regarding the composition of ancient stardust, known as presolar grains, which were formed before the sun and carried to Earth by primitive meteorites.

By analyzing these grains, researchers can gain insights into the nuclear makeup of our galaxy during the formation of heavy elements. The mystery lies in the fact that presolar grains contain more molybdenum-94 than current theoretical models can explain. To investigate this issue, scientists examined niobium-94, which behaves similarly to molybdenum-94 but with one less proton and one extra neutron.

Within a dying star, niobium-94 can either undergo beta decay to become molybdenum-94 or neutron capture to become niobium-95. Understanding the competition between these two processes is essential for deciphering why there is an excess of molybdenum-94 in presolar grains. Previous attempts to measure the neutron capture probability of niobium-94 faced significant challenges, but the n_TOF Collaboration overcame these obstacles through a collaborative effort involving multiple institutes.

The researchers used a highly intense neutron source at CERN's n_TOF facility to irradiate a pure niobium-94 sample and detect the faint signal of neutron capture. The results of this measurement align closely with previous theoretical estimates, indicating that the discrepancy between models and stardust data is not due to inaccurate estimates but rather limitations in older stellar models.

When incorporated into the most advanced stellar models, the new result significantly reduces uncertainty and successfully explains the observed molybdenum-94 abundances in ancient stardust. However, there is still a crucial piece of the puzzle missing. The researchers have only theoretical estimates for the beta decay process of niobium-94, and future experiments will aim to make precise measurements of this nuclear process to better understand the origin of molybdenum-94 and ultimately gain a clearer picture of how stars create heavy elements.