First direct limit on the 334 keV resonance strength in $$^{22}$$Ne($$\alpha $$,$$\gamma $$)$$^{26}$$Mg reaction
D. Piatti, E. Masha, M. Aliotta, J. Balibrea-Correa, F. Barile, D. Bemmerer, A. Best, A. Boeltzig, C. Broggini, C. G. Bruno, A. Caciolli, F. Cavanna, T. Chillery, G. F. Ciani, Alessandro Compagnucci, P. Corvisiero, L. Csedreki, T. Davinson, R. Depalo, A. Di Leva, Z. Elekes, F. Ferraro, E. M. Fiore, A. Formicola, Zs. Fülöp, G. Gervino, A. Guglielmetti, C. Gustavino, Gy. Gyürky, G. Imbriani, M. Junker, Maria Lugaro, Paola Marigo, R. Menegazzo, V. Mossa, F. R. Pantaleo, V. Paticchio, R. Perrino, P. Prati, D. Rapagnani, L. Schiavulli, J. Skowronski, K. Stöckel, O. Straniero, T. Szücs, M. P. Takács, S. Zavatarelli
Abstract
Abstract In stars, the fusion of $$^{22}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>22</mml:mn> </mml:msup> </mml:math> Ne and $$^4$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>4</mml:mn> </mml:msup> </mml:math> He may produce either $$^{25}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>25</mml:mn> </mml:msup> </mml:math> Mg, with the emission of a neutron, or $$^{26}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>26</mml:mn> </mml:msup> </mml:math> Mg and a $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> ray. At high temperature, the ( $$\alpha ,n$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>,</mml:mo> <mml:mi>n</mml:mi> </mml:mrow> </mml:math> ) channel dominates, while at low temperature, it is energetically hampered. The rate of its competitor, the $$^{22}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>22</mml:mn> </mml:msup> </mml:math> Ne( $$\alpha $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> , $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> ) $$^{26}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>26</mml:mn> </mml:msup> </mml:math> Mg reaction, and, hence, the minimum temperature for the ( $$\alpha ,n$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>,</mml:mo> <mml:mi>n</mml:mi> </mml:mrow> </mml:math> ) dominance, are controlled by many nuclear resonances. The strengths of these resonances have hitherto been studied only indirectly. The present work aims to directly measure the total strength of the resonance at $$E_{\text {r}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mtext>r</mml:mtext> </mml:msub> </mml:math> = 334 keV (corresponding to $$E_{\text {x}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mtext>x</mml:mtext> </mml:msub> </mml:math> = 10949 keV in $$^{26}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>26</mml:mn> </mml:msup> </mml:math> Mg). The data reported here have been obtained using high intensity $$^4$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>4</mml:mn> </mml:msup> </mml:math> He $$^+$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mo>+</mml:mo> </mml:msup> </mml:math> beam from the INFN LUNA 400 kV underground accelerator, a windowless, recirculating, 99.9% isotopically enriched $$^{22}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>22</mml:mn> </mml:msup> </mml:math> Ne gas target, and a 4 $$\pi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>π</mml:mi> </mml:math> bismuth germanate summing $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> -ray detector. The ultra-low background rate of less than 0.5 counts/day was determined using 63 days of no-beam data and 7 days of $$^4$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>4</mml:mn> </mml:msup> </mml:math> He $$^+$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mo>+</mml:mo> </mml:msup> </mml:math> beam on an inert argon target. The new high-sensitivity setup allowed to determine the first direct upper limit of 4.0 $$\,\times \,$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mspace/> <mml:mo>×</mml:mo> <mml:mspace/> </mml:mrow> </mml:math> 10 $$^{-11}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>11</mml:mn> </mml:mrow> </mml:msup> </mml:math> eV (at 90% confidence level) for the resonance strength. Finally, the sensitivity of this setup paves the way to study further $$^{22}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>22</mml:mn> </mml:msup> </mml:math> Ne( $$\alpha $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> , $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> ) $$^{26}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>26</mml:mn> </mml:msup> </mml:math> Mg resonances at higher ener