Direct and Indirect Studies of Astrophysical Reactions

组成我们周围世界的绝大多数元素都是通过恒星中发生的核反应和衰变序列形成的。这些核过程负责在静止的恒星燃烧中产生能量，以及恒星爆炸，如新星、超新星和X射线爆发。与此同时，这些反应/衰变链将最初的“种子”元素(在大爆炸中形成的氢和氦)转化为更重的元素--最终几乎填满了整个元素周期表。 这一研究项目的首要目标是更好地了解在恒星燃烧和恒星爆炸中对核合成和/或能量产生有重大影响的关键反应的速率。在涉及计算机模拟恒星过程的灵敏度研究中确定的关键反应的速率将通过使用TRIUMF/ISAC加速器设施的稳定和稀有同位素束进行直接和间接测量来研究。 直接测量将使用世界领先的龙反冲分离器，包括升级的实验室射线探测器阵列，以测量主导恒星质子和阿尔法俘获速率的关键共振的强度和能量。在这些直接测量实验中，共振强度将通过将重离子束撞击到扩展的、无窗口的氢或氦气体目标上来确定，并将光束能量调整为共振。产生的反应产物(重反冲和射线)将被计数并用于确定反应产率，该反应产率与共振强度成正比。同时，将利用延伸靶内反应的位置来精确确定共振能量。在许多情况下，共振能量测量将利用一种新的“共振计时”技术，该技术利用了LABR闪烁体优越的计时分辨率。 对于太弱而无法在实验室测量的反应，或者没有足够的稀有同位素束流强度，将使用间接技术来确定感兴趣的共振强度。特别是，转移反应将被用来测量重要共振的光谱因子--与共振强度成正比的量。该提案的间接测量部分将包括在TRIUMF开发一个新的逆运动学(d，n)实验方案，使用目前正在建造的IRIS固体氢靶和tex NEUT中子探测器阵列。这项前景看好的技术提供了一个机会，可以间接确定一系列反应的关键共振强度，这些反应目前还不能进行直接测量。

The vast majority of the elements making up the world around us were formed through sequences of nuclear reactions and decays occurring in stars. These nuclear processes are responsible for energy generation in quiescent stellar burning, as well as stellar explosions such as novae, supernovae, and X-ray bursts. At the same time, these reaction/decay chains transmutate the initial “seed” elements (hydrogen and helium, formed in the Big Bang) into heavier species - eventually filling nearly the entire periodic table. The overarching goal of this research project is to better understand the rates of key reactions which have a significant impact on nucleosynthesis and/or energy generation in stellar burning and stellar explosions. The rates of key reactions - which have been identified in sensitivity studies involving computer simulations of stellar processes - will be studied through direct and indirect measurements using stable and rare-isotope beams from the TRIUMF/ISAC accelerator facility. Direct measurements will employ the world-leading DRAGON recoil separator, including an upgraded LaBr -ray detector array, to measure the strengths and energies of key resonances that dominate stellar proton and alpha capture rates. In these direct-measurement experiments, resonance strengths will be determined by impinging a heavy-ion beam onto an extended, windowless hydrogen or helium gas target, with the beam energy tuned to be on resonance. The resulting reaction products (heavy recoils and rays) will be counted and used to determine the reaction yield, which is proportional to the resonance strength. At the same time, the position of the reaction within the extended target will be used to precisely determine the resonance energy. In many cases, the resonance energy measurement will make use of a novel “resonance timing” technique, which capitalizes on the superior timing resolution of LaBr scintillators. For reactions that are too weak to measure in the laboratory, or for which sufficient rare-isotope beam intensities are not available, indirect techniques will be used to determine the resonance strengths of interest. In particular, transfer reactions will be used to measure spectroscopic factors for important resonances - quantities which are directly proportional to the resonance strength. The indirect-measurement component of the proposal will include development of a new program of inverse-kinematics (d,n) experiments at TRIUMF, using the IRIS solid H2 target and the TexNEUT neutron detector array currently under construction. This promising technique offers an opportunity to indirectly determine key resonance strengths for a wide array of reactions for which direct measurements are not presently feasible.