Is γ-ray emission from novae affected by interference effects in the 18F(p,α)15O reaction?
Is γ-ray emission from novae affected by interference effects in the 18F(p,α)15O reaction?
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新星发射的γ射线是否受到18F(p,α)15O反应中干扰效应的影响？
DOI：
10.1103/physrevlett.110.032502
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发表时间：
2012
影响因子：
8.6
通讯作者：
H. Wirth
中科院分区：
文献类型：
--
作者：
A. Laird;A. Parikh;A. Murphy;K. Wimmer;K. Wimmer;A. Chen;C. Deibel;C. Deibel;T. Faestermann;S. Fox;B. Fulton;R. Hertenberger;D. Irvine;Jordi José;R. Longland;D. Mountford;B. Sambrook;D. Seiler;H. Wirth
（18）F（p，α）（15）O反应速率对于限制新星中产生的γ射线可观测放射性同位素（18）F的模型预测至关重要。由于复合核（19）Ne的能级结构的特殊特征，该速率的确定具有挑战性，这导致干扰效应可能发挥重要作用。这个速率的主要不确定性来自质子阈值附近（S（p）=6.411 MeV）的J（π）=3/2（+）态与阈值以上665 keV的宽J（π）=3/2（+）态之间的干扰。这个未知的干扰项导致新星温度下天体物理S因子的不确定性高达40倍。本文报道了利用（19）F（（3）He，t）（19）Ne反应对该能区态的一种新的测量。与先前的假设形成鲜明对比，我们发现质子阈值和E（cm）=50 keV之间至少有3个共振，所有这些共振都具有不同的角分布。这些都不符合J（π）=3/2（+）角分布。我们发现，现在的主要不确定性来自未知的质子宽度的48千电子伏共振，而不是从可能的干扰效应。进行的流体动力学新星模型计算表明，在所考虑的模型中，这个未知的宽度对（18）F产生的影响至少为2倍。
The (18)F(p,α)(15)O reaction rate is crucial for constraining model predictions of the γ-ray observable radioisotope (18)F produced in novae. The determination of this rate is challenging due to particular features of the level scheme of the compound nucleus, (19)Ne, which result in interference effects potentially playing a significant role. The dominant uncertainty in this rate arises from interference between J(π)=3/2(+) states near the proton threshold (S(p)=6.411 MeV) and a broad J(π)=3/2(+) state at 665 keV above threshold. This unknown interference term results in up to a factor of 40 uncertainty in the astrophysical S-factor at nova temperatures. Here we report a new measurement of states in this energy region using the (19)F((3)He,t)(19)Ne reaction. In stark contrast to previous assumptions we find at least 3 resonances between the proton threshold and E(cm)=50 keV, all with different angular distributions. None of these are consistent with J(π)=3/2(+) angular distributions. We find that the main uncertainty now arises from the unknown proton width of the 48 keV resonance, not from possible interference effects. Hydrodynamic nova model calculations performed indicate that this unknown width affects (18)F production by at least a factor of two in the model considered.