Nuclear Excitation by Single-Quantum Annihilation of Positrons

当正电子释放的电磁能量在原子核的库仑场中与被束缚的原子电子在飞行中湮灭，满足共振吸收的能量标准时，原子核的激发可能是一种结果。这种现象的计算结果与现有的实验数据有很大的出入。迄今为止进行的各种实验都有共同的缺点。他们利用了来自放射源和厚靶的整个正电子光谱。原子核的亚稳态研究了几个生命周期。结果是不准确的，并且易于含糊不清的解释。鉴于此，人们要求进行使用单能正电子和薄靶的实验。这些研究将利用布鲁克海文的Dynamitron和橡树岭国家实验室的ORELA进行。将研究短寿命态，这将使连续运行的束流实验成为可能。将使用不同厚度的薄靶。将探讨由不同理论模型提出的可能有助于单量子湮灭的核激发的次要效应。预期可以得到可获得的数据，以便作出明确的解释，并使人们清楚地了解这一现象背后的物理过程。＊＊＊

9505886 Palathingal When the electromagnetic energy released as a positron gets annihilated in flight with a bound atomic electron in the Coulomb field of the nucleus, meets the energy criterion for resonance absorption, the excitation of the nucleus could be a possible result. There are major discrepancies between the results of calculations of this phenomenon and the available experimental data. The various experiments conducted so far have all suffered from common disadvantages. They utilized whole spectra of positrons derived from radioactive sources and thick targets. Metastable states of the nucleus were studied for periods of a few life times. The results were not accurate, and were prone to ambiguities for interpretation. In view of this, experiments have been called for that would use monoenergetic positrons and thin targets. Such studies will be undertaken utilizing the Dynamitron at Brookhaven and at ORELA at Oak Ridge National Lab. Short-lived states will be studied, that would make a continuous- running beam experiment possible. Thin targets of varied thickness will be used. Secondary effects that might contribute to the nuclear excitation alongside the single-quantum annihilation, proposed by differing theoretical models, would be explored. It is expected that data could be derived that would be accessible for unambiguous interpretation, and would lead to a clear understanding of the physical processes underlying the phenomenon. ***