Speaker
Description
The abundances of the light elements produced in the early stages of the Universe are accurately predicted by Big Bang Nucleosynthesis (BBN). However, following the observations on low-metallicity stars, the measured 𝐿𝑖7 abundance is 3-4 times lower than expected. Due to this discrepancy, known as “cosmological Li problem”, it can be assumed that either the measurements are leading to anomalous results, or an error is present in the theoretical models.
Since two main reactions are responsible for the production of mass 7 elements, 𝐻(𝛼, 𝛾) 𝐿𝑖73 and especially 𝐻𝑒(𝛼, 𝛾) 𝐵𝑒73 , the error can be related to the WMAP baryonic density. A lower value for this quantity corresponds to a higher effect of the 𝐻(𝛼, 𝛾) 𝐿𝑖73 reaction. While 𝐻𝑒(𝛼, 𝛾) 𝐵𝑒73 reaction have been well studied, only a few experiments were performed over the 𝐻(𝛼, 𝛾) 𝐿𝑖73 reaction. Although an experiment implying a tritium target cannot be performed anymore, the 𝐻(𝛼, 𝛾) 𝐿𝑖73 reaction can still be studied by its inverse reaction: 𝐿𝑖(𝛾, 𝑡) 𝐻𝑒47 . A measurement of the photodisintegration of 𝐿𝑖7 was performed in 2017 by our team at High Intensity γ-ray Source (HIγS) Laboratory at Duke University (USA). The detection of the alpha-triton coincidences was performed using an array of segmented silicon detectors. The considered energies of the gamma beam were between 4.4 and 10 MeV, but the coincidences have been clearly separated only for energies higher than 6 MeV and especially in the thinner detectors. As a continuation, a similar experimental campaign took place at HIγS in the first part of April 2023, to measure the cross section and the angular distributions of 𝐻(𝛼, 𝛾) 𝐿𝑖73 reaction at energies lower than 6 MeV. The study used a 𝐿𝑖𝐹 target and an improved array of segmented silicon detectors with a similar arrangement but thinner than in the previous set-up such as the coincidences were properly separated for those lower energies.
The preliminary results of the experimental campaign performed at HIγS in the beginning of April 2023 problem will be presented.
