Page 64 - ILL Annual Report 2019

NUCLEAR AND PARTICLE PHYSICS
Carlos Guerrero. Spanish
Universidad de Sevilla, Seville, Spain Centro Nacional de Aceleradores (CNA), Seville, Spain
‘I am a Ramón y Cajal researcher currently working at the CNA (Spain) after a six-year period working at the n_TOF facility at CERN
(Switzerland). In the field of experimental nuclear physics I perform cross section measurements, in most cases induced by neutrons, that are of interest to astrophysics, nuclear technology and medical physics.’
From the ILL reactor core
to the LiLiT neutron beam:
a nuclear astrophysics experiment to better understand the nucleosynthesis of elements in the universe
V4 beam tube at the ILL, the PSI radiochemistry laboratory and the SARAF accelerator facility
Among the nuclear reactions occurring in the stars, neutron capture is the driving force behind the production of more than half of the isotopes in our universe. The study of this reaction is key to a better understanding of stellar nucleosynthesis; and it is particularly interesting in the case of reactions in unstable nuclei
that act as branching points along
the so-called slow (or s-) process.
AUTHORS
C. Guerrero, J. Lerendegui-Marco and J. M. Quesada (Universidad de Sevilla & Centro Nacional de Aceleradores CNA, Spain)
M. Tessler, M. Paul, S. Halfon, T. Palchan-Hazan and L. Weissman (Hebrew University & SNRC, Israel)
S. Heinitz, E. A. Maugeri, R. Dressler, N. Kivel and D. Schumann (Paul Scherrer Institut PSI, Switzerland)
C. Domingo-Pardo (Instituto de Física Corpuscular IFIC-CSIC, Spain) U. Köster (Institut Laue-Langevin ILL, France)
ARTICLE FROM
Phys. Rev. B (2019)—doi: https://doi.org/10.1016/j. physletb.2019.134809
REFERENCES
[1] J.A. Johnson, Science 363 (2019) 474
[2] F. Käppeler, R. Gallino, S. Bisterzo and W. Aoki, Rev. Mod. Phys.
83 (2011) 157
[3] W. Ratynski and F. Käppeler, Phys. Rev. C 37 (1988) 595 [4] D. Studer, S. Heinitz, R. Heinke, P. Naubereit, R. Dressler,
C. Guerrero, U. Köster, D. Schumann and K. Wendt, Phys. Rev. A 99 (2019) 062513
The chemical elements of our universe are created through nuclear reactions occurring in the stars. The vast majority of elements heavier than iron are made through various forms
of neutron capture, a process in which a neutron is absorbed and retained by a nucleus thereby increasing its mass number by one unit. This process occurs sequentially until the newly formed nucleus becomes unstable; when this happens, a branching point is reached and competition arises between additional neutron capture and the beta-decay of the nucleus. The latter means the production of a different chemical element. The sequence of neutron captures and beta-decays taking place mostly in AGB (Asymptotic Giant Branch) stars is known as the s-process and is responsible for the production of about half of the elements in our universe.
In this context, the study of neutron capture reactions in the laboratory provides a key quantity for nucleosynthesis network calculations: the Maxwellian-Averaged Cross Section (MACS). This quantity is related to the probability of a neutron capture reaction occurring for a neutron with the equivalent kinetic energy of those in the stellar sites where the s-process takes place. Experiments to determine this quantity, the MACS, produce neutron beams of the appropriate energy distribution that are used to irradiate a target made up of the isotope of interest. Then, the number of reactions that have taken place is determined by looking at the decay of newly formed nuclei.
Figure 1
A planetary nebula like the Cat’s Eye one shown here is created when
an AGB star blasts part of its content via strong stellar winds into the environment. Thus, the elements formed in the s-process contribute to the normal chemical composition of the universe. [Picture from NASA (public)]
ANNUAL REPORT 2019