据《物理评论快报》10日报道，英国牛津大学牵头的科学家团队首次观测到太阳中微子在地下探测器中 触发罕见核反应，使碳原子转化为氮原子。长期以来，中微子因几乎不与物质相互作用而难以被直接观 测，这次突破显示科学家已具备在极低能区间研究中微子—原子核相互作用的能力，为核物理和粒子物 理相关研究打开了新窗口。 中微子是宇宙中最神秘的粒子之一，中微子的直接探测长期以来一直是粒子物理领域的一大挑战。 此次实验依托深埋在加拿大萨德伯里地下约两千米处的SNO+中微子探测器。研究团队关注的是一种极 为罕见的相互作用，即高能太阳中微子撞击实验介质中的碳-13原子核，使其转变为放射性的氮-13。 氮-13会在约10分钟后发生衰变。为识别这一过程，团队采用了"延迟符合"探测方法，先捕捉中微子撞 击碳-13原子核时产生的瞬时闪光，再寻找数分钟后由氮-13放射性衰变产生的第二次闪光。两个信号在 时间上的明确关联，为区分真实中微子事件与背景噪声提供了可靠依据。 结果显示，在2022年5月4日至2023年6月29日的231天观测期内，实验共观测到约5.6个相关事件，与太 阳中微子理论预期产生的4.7个事件在统计上相符。这标志着科学家首次在实 ...

Core Insights - The research team from the Institute of Modern Physics of the Chinese Academy of Sciences has made significant progress in the study of rare decay modes of atomic nuclei, successfully observing the new nuclide aluminum-20 and its decay through a rare three-proton emission mode [1][2] Group 1: Research Findings - Over 3,300 nuclides have been discovered, with fewer than 300 being stable nuclides found in nature; the rest are unstable and undergo radioactive decay [1] - Common decay modes include alpha decay, beta decay, beta-plus decay, electron capture, gamma transition, and fission, with many of these modes identified before the mid-20th century [1] - Recent advancements in nuclear physics experiments have led to the discovery of various new decay modes, particularly in neutron-deficient nuclei [1] Group 2: Specific Observations - The aluminum-20 nuclide, located outside the proton drip line and lacking seven neutrons compared to stable aluminum isotopes, is the lightest aluminum isotope observed experimentally to date [2] - The decay of aluminum-20 occurs through a two-step process involving the emission of a proton and then a double proton, with magnesium-19 acting as an intermediate state [2] - The research utilized the Gamow shell model and Gamow coupling method for theoretical calculations, successfully reproducing the decay energy of aluminum-20 and predicting its ground state spin parity [2] Group 3: Theoretical Implications - The study explores isospin symmetry, a fundamental principle in nuclear physics, indicating that mirror nuclei with the same mass number but swapped proton and neutron numbers should exhibit similar energy level structures [2] - The findings suggest a breaking of isospin symmetry in the aluminum-20 and nitrogen-20 mirror nucleus system, which has significant implications for nuclear structure research [2]