In 2009 the EoI-12-2009-CUNA "A Nuclear Astrophysics facility for LSC: The sources of neutrons in the stars and other reactions of astrophysical interest" was submitted to the LSC Scientific Committee by Spanish groups and international partners. In that document, the idea to develop an underground facility at the Laboratorio Subterráneo de Canfranc (LSC) to measure reactions of importance in nuclear astrophysics was advanced.
With such a facility, it was proposed to measure, in particular, the neutron sources for the weak and main s-processes, namely the 22Ne(α,n)25Mg and the 13C(α,n)16O reactions. The possibilities for direct measurement of the reaction cross sections at the relevant astrophysical energies in surface laboratories are exhausted, and therefore underground measurements are indispensable.
Since the submission of the Expression of Interest we have continued developing the Physics case and investigating the main elements of such a facility, founded on the expertise of the groups involved in the proposal. In October 2012 a Letter of Intent was submitted to the Scientific Committee of the LSC.
In this document the Physics case was reviewed and the experimental details and challenges for the two key 22Ne(α,n)25Mg and 13C(α,n)16O reactions examined. A realistic estimate of the expected count rates, the energy range of interest and an example of the anticipated impact of the measurements was provided. The possibilities that a new facility will offer to experimentally measure other reactions of astrophysical interest were also examined.
The possible locations inside the LSC were explored. The excavation of a new underground cave was discussed based on the preliminary study requested by LSC. The option offered by LAB2500, which seems advantageous in terms of costs and reduced background, was also discussed.
Then the options for the accelerator were detailed, with special emphasis in the beam current and operation stability. The properties of the targets for the success of the measurements were briefly examined.
We have performed Monte Carlo simulations to support the proposal and measurements of the neutron background, with emphasis on the shielding conditions to get the same level of background as the existing one at the LSC, and on the neutron background measurements with 3He proportional counters.
Moreover the instrumentation required for the measurements has been addressed. We have investigated the 4π neutron counter for (α,n) reactions, setting the requirements for underground measurements based on the background measurements and the experience with experiments at ground level. We have also examined the measurement of radiative capture cross-sections with large coverage gamma ray spectrometers.
Finally, the implementation of the underground accelerator facility has been presented, with the requests to LSC and the first order estimates of the time and investment required.
Canfrac Underground Laboratory
Paseo de los Ayerbe s/n
22880 Canfranc Estación