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优化神经网络模型精确预测镥及铼同位素链的质子分离能

Exactly Predicting the Proton Separation Energy of Lu and Re Isotope Chain via Optimized Neural Network Models

  • 摘要: 原子核质量在核结构和核天体物理中起到重要作用。对于远离稳定线的奇特核,由质量得到的几百keV的分离能差别可能引起半衰期至少3个数量级差异。目前,^149\rmLu是实验上可探测到的寿命最短的质子发射核;其周围未被探测核素的分离能将影响核合成路径。为此,采用人工神经网络(Artificial Neural Network, ANN)和贝叶斯神经网络(Bayesian Neural Network, BNN)用于约束质子分离能,实践表明两种方法分别存在过拟合和精度的问题。为提高精度和缓解过拟合问题,基于BNN模型,同时考虑标签值不确定度及模型的集成不确定度,发展了BNN-Beihang (BH)模型。该模型预测的^148-151\rmLu, ^160-161\rmRe质子分离能不确定度首次达到100 keV以下,这些结果将有效约束镥及铼同位素链质子发射核的寿命。

     

    Abstract: Nuclear mass plays an important role on nuclear structure and nuclear astrophysics. For the exotic nuclei far away from the stability valley, at least three orders of the magnitude for the half lives of emitters might be arisen by hundreds of keV difference of the separation energy given by the nuclear mass. At present, ^149\rmLu is the proton emitter with shortest lives discovered in experiments. The separation energies of the neighbor undetected nuclei will influence the nucleosynthesis path. To this end, we apply Artificial Neural Network (ANN) model and Bayesian Neural Network (BNN) model to constrain the proton separation energy, and the practice indicates that the two approaches have the overfitting and precision problems respectively. In order to improve the precision and mitigate the overfitting problem, based on BNN model, and take the uncertainties of the labels and the ensemble uncertainty of the models into account simultaneously, we develop the BNN-Beihang (BH) model. The uncertainties of ^148\rmLu and ^160-161\rmRe predicted by the model decreased to less than 100 keV for the first time. These results will effectively improve the precision of the theoretical predictions to the Lu and Re chain proton emitters' lives.

     

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