Silisyum-26 Üzerinde Proton Yakalama İçin Doğrudan Yakalama Hızının ANC Temelli Dolaylı Değerlendirilmesi

Abstract

²⁶Si üzerinde gerçekleşen radyatif proton yakalama reaksiyonu sonucunda ²⁷P oluşumu, ²⁶Al’nin tükenme yolunu etkilediği için patlayıcı hidrojen yanması nükleosentezi açısından önemlidir. ²⁶Si’nin kısa ömürlü olması ve yıldızsal enerji bölgesinde beklenen tesir kesitlerinin çok küçük olması, bu reaksiyon hızının doğrudan deneysel olarak belirlenmesini zorlaştırmaktadır. Bu nedenle reaksiyon, ²⁶Mg ve ²⁷Mg ile ilişkili ayna nötron sistemi kullanılarak ANC yöntemiyle dolaylı olarak sınırlandırılmıştır. ¹³C hedefi üzerinde ²⁶Mg elastik saçılma kanalı ve ²⁷Mg’yi besleyen nötron-kapma kanalı ölçümleri, MDM spektrometresi ve onun odak düzlemi dedektör sistemi ile gerçekleştirilmiştir. Analiz sonucunda ²⁷Mg’nin temel durumu için C²s1/2(²⁷Mg) = 29.19 ± 3.94 fm−1 nötron ANC değeri elde edilmiştir. Ayna simetrisi uygulanarak, ²⁷P için karşılık gelen proton ANC değeri C²s1/2(²⁷P) = 1126 ± 152 fm−1 olarak, spektroskopik faktör ise 0.64 ± 0.09 olarak belirlenmiştir. RADCAP hesaplamaları daha sonra doğrudan yakalama bileşeni için sıfır enerjide astrofiziksel S-faktörünü S(0) = (5.6 ± 0.8) × 10−2 MeV b olarak vermiştir. Elde edilen doğrudan yakalama reaksiyon hızı, önceki tahminden yaklaşık iki kat daha yüksektir; ancak T9 > 0.1 için toplam reaksiyon hızı esas olarak ²⁷P’nin en düşük uyarılmış durumu üzerinden gerçekleşen rezonans yakalama tarafından kontrol edilmektedir.

Keywords

• Silisyum-26
• asimptotik normalizasyon katsayısı
• ayna çekirdek sistemi
• doğrudan yakalama
• astrofiziksel S-faktörü

An ANC-Based Indirect Evaluation of the Direct-Capture Rate for Proton Capture on Silicon-26

Abstract

Radiative proton capture on 26Si, leading to the formation of 27P, is relevant to explosive hydrogen-burning nucleosynthesis because it affects the depletion pathway of 26Al. The short lifetime of 26Si, together with the very small cross sections expected in the stellar energy region, makes a direct determination of this rate experimentally difficult. For this reason, the reaction was constrained indirectly through the ANC, using the mirror neutron system associated with 26Mg and 27Mg. Measurements of the ²⁶Mg elastic-scattering channel on ¹³C and the neutron-pickup channel populating ²⁷Mg were carried out with the MDM spectrometer and its focal-plane detector system. The analysis gave a neutron ANC of C²s1/2(27Mg) = 29.19 ± 3.94 fm−1 for the ground state of 27Mg. By applying mirror symmetry, the corresponding proton ANC for 27P was obtained as C²s1/2(27P) = 1126 ± 152 fm−1, with a spectroscopic factor of 0.64 ± 0.09. RADCAP calculations then gave a zero-energy astrophysical S-factor of S(0) = (5.6 ± 0.8) × 10−2 MeV b for the direct-capture component. The deduced direct-capture rate is nearly a factor of two higher than the earlier estimate, although for T9 > 0.1 the total rate is mainly controlled by resonant capture through the lowest excited state of 27P.

Keywords

• Silicon-26
• asymptotic normalization coefficient
• mirror nuclear system
• direct capture
• astrophysical S-factor

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