Nuclear reaction studies

Nuclear structure has a profound impact in shaping the elemental abundance in the Universe. We work in the Nuclear Physics line at CMAM in the use of alternatives reactions to shed light in long standing problems such the cross section of 12C(α,γ)16O at 300 keV or the primordial 7Li abundance in the Universe. These reactions play a fundamental role in the nuclear astrophysics since, for instance the former determines the ratio of carbon to oxygen in the universe and thus an important influence in the nucleosynthesis of the heavy elements. The nuclei and the states of interest are populated in low energy reactions, and studied by particle and gamma detection. The reactions that are still of interest to be studied have, in general, extremely low cross sections. Therefore, we have designed a set of detector setups easily interchangeable.

To this aim, we address the breakup of unbound states near the particle threshold in 16O that has a very relevant impact in the determination of cross-sections of astrophysical interest. In this context we study the 19F(p,αγ)16O to populate the states of 16O near the alpha breakup threshold. For the case of the primordial abundance of 7Li we study the 7Li(3He,p)9Be to estimate the cross section of the reaction of 7Li(3H,n)9Be much more difficult to determine accurately. The latter is expected from simulations to play an important role in understanding the primordial 7Li abundance.

Recently the 45º beamline was made operative for the study of other nuclear reactions. Neutron production through α-induced nuclear reactions is relevant in several fields. Specifically, (α,n) reactions are interesting in nuclear astrophysics as a source of neutrons for the slow neutron capture nucleosynthesis (the s-process) and in the α-particle capture process. The MANY (Measurement of Alpha Neutron Yields and spectra) collaboration is an effort by Spanish research groups (IFIC, UPC, UCM, CIEMAT, US, IEM) with the aim to carry out measurements of (α,xn) reactions using CMAM (Madrid) and CNA (Seville) α-beams with complementary neutron detection systems: one 4π neutron counter with nearly flat response up to 10 MeV, MINIBELEN and a second detector based on BC501/EJ301 liquid scintillator modules, MONSTER which can operate as a time-of-flight spectrometer. Both systems are also complemented by γ-spectroscopy measurements for (α,xnγ) reactions using an array of fast scintillators. All instruments are coupled to high performance digital electronics. Commissioning of the beam-line has been achieved with well-known 27Al(α,n)30P reaction.

The MANY (Measurement of Alpha Neutron Yields and spectra) collaboration is an effort by Spanish research groups to carry out measurements of (α,xn) reactions of different physical interests:

  • Source of neutrons for the slow neutron capture nucleosynthesis (the s-process) [TAI16].
  • α-particles capture process (the α-process) [WOO92, BLI17].
  • Neutron-induced background
  • in underground laboratories LSC Canfranc [BET10].
  • in nuclear facilities such as particle accelerators and nuclear reactors [MUR02].
  • [BET10] A. Bettini, Nucl. Instrum. Methods A 626 - 627 (2010) S64 – S68
  • [BLI17] J. Bliss et al. J. Phys. G.: Nucl. Part. Phys. 44 (2017) 054003
  • [MUR02] T. Murata and K. Shibata, J. Nucl. Sci. Technol. 39 (2002) 76 – 79
  • [TAI16] J.L. Tain et al., J. Phys.: Conf. Ser. 665 (2016) 012031