Speaker
Description
Ultra-high-energy cosmic rays (UHECRs) are among the most energetic particles
observed in nature, yet their origin and propagation through extragalactic space
remain open questions. In order to understand the propagation, it is necessary to
study how the UHECR nuclei interact electromagnetically with the Cosmic Microwave
Background via the electric dipole (E1) response which dominates the photoabsorption
cross-section, governing the energy loss and mass decomposition processes. To address
this matter, the PANDORA project aims at measuring photo-nuclear reactions and
decay branching ratios systematically in light nuclei [1].
In this contribution, preliminary results for the measurement of the electric dipole
response of 10,11 B from the first PANDORA experiment will be presented. The
measurements were done using inelastic proton scattering of 392 MeV proton beams
at zero degrees at the RCNP facility in Osaka, Japan, where the Grand Raiden (GR)
spectrometer was used at forward angles, 0, 4.5 and 6.6 degrees, to measure the
scattered protons. The GR was coupled with the Scγlla Array [2] for gamma decay
coincidence analysis. Scγlla consists of 8 large volume LaBr3 detectors placed on the
scattering chamber, 4 at 90 degrees and 4 at 135 degrees, with respect to the beam.
The distance from the target position to the front surface of the detectors is 200 mm,
corresponding to a photopeak efficiency of 2% for 1.3 MeV γ rays.
The 10 B and 11 B nuclei were chosen to be part of these first measurements due to
their odd-A and odd-odd character, exhibiting complex structures such as clustering,
they also show a fragmented and non-trivial total E1 response, where the isospin
selection rule plays a crucial role. Moreover, they contribute to significant changes
in the mass-distribution during their disintegration. This makes them a important
challenge for theoretical models necessary to extrapolate the E1 response to other
nuclei in the light mass region. In this contribution, preliminary results for excitation-
energy spectra and angular distributions, as well as some γ-ray decay characteristics
will be presented.
References
[1]A. Tamii et al. “PANDORA project: photo-nuclear reactions below $A=60$”. In: 2022. url:
https://api.semanticscholar.org/CorpusID:253397902.
[2]G. Gosta et al. “Response function and linearity for high energy -rays in large volume LaBr3:Ce
detectors”. In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators,
Spectrometers, Detectors and Associated Equipment 879 (2018), pp. 92–100. issn: 0168-9002. doi:
https://doi.org/10.1016/j.nima.2017.10.018.
This work was supported by the Romanian Ministry of Research, Innovation, and
Digitalization under contract 10N/PN 23 21 01 06. PAS was supported by the ELI-
RO program funded by the Institute of Atomic Physics, Măgurele, Romania, ctr. no.
ELI-RO/RDI/2024-002 (CIPHERS) and DLB, ELI-RO/RDI/2024-007 (ELITE).