Calibration sources for proton spectroscopy in neutron decay

中子衰变产生的质子的最大能量只有751电子伏特。因此，质子光谱学需要对从中子衰变位置到探测器的整个质子轨道上的静电势有很好的了解。例如，aSPECT延迟谱仪对电子-反中微子相关系数a的尝试精度为0.3%，需要了解7 mV水平下衰变体积和分析面的静电势。对于PERC质子光谱，这些电位必须以类似的精度已知，全部沿着PERC光谱仪内部的中子导流器。由于质子的能量分布很广，用衰变中的质子来表征光谱仪的特性是有限的。需要单能源。此外，在光谱仪中调试的探测器将从能量范围在0到800 eV之间的质子源中受益匪浅。这种来源的可用性将使探测器和光谱仪的开发独立于反应堆操作，并使这项工作更有效率。为此，我们建议开发两种单能正粒子源。具有小能量宽度的质子源将允许光谱仪表征和探测器调试，而不需要中子，并将用于PERC二级质子光谱仪的离线开发。慢化正电子源将提供单能正电子束，其极好的能量宽度低于100 meV，仅受热展宽的限制。此外，该源将提供一个明确的正电子束的角分布。与电子相比，正电子不需要改变光谱仪中的电位。光源非常紧凑，可以安装在光谱仪内部。这两种提议的源是互补的：质子源可能具有更大的能量宽度，在使用上不太灵活，但对于表征探测器和依赖于质量/电荷比的光谱仪特性是必不可少的。慢化正电子源具有良好的能量宽度和稳定性，非常适合于表征静电势分布、透射函数和光谱仪的稳定性。光源应针对延迟光谱仪进行优化，并使用该光谱仪进行测试。在将质子源连接到aSPECT之前，它将用于表征PERKEO-III的质子探测器。在用aSPECT完成测量后，源可用于表征PERC及其次级质子光谱仪。

Protons from neutron decay have a maximum energy of 751 eV only. Proton spectroscopy therefore requires a very good knowledge of the electrostatic potentials along the full proton trajectory, from the position of the neutron decay to the detector. For example, the attempted accuracy of the aSPECT retardation spectrometer of 0.3% for the electron-antineutrino correlation coefficient a requires knowledge of the electrostatic potentials of decay volume and analyzing plane at the level of 7 mV. For proton spectroscopy with PERC, these potentials have to be known at similar accuracy, all along the neutron guide inside the PERC spectrometer. Characterization of the spectrometers by protons from the decay is limited because of the broad energy distribution of the protons. Monoenergetic sources are required. Furthermore, detector commissioning in the spectrometers would profit enormously from a proton source in the energy range between 0 and 800 eV. The availability of such a source would allow detector and spectrometer development independent on reactor operation and make this work much more efficient. We propose to develop two monoenergetic sources of positive particles for these purposes. A proton source with small energy width will allow spectrometer characterization and detector commissioning without neutrons and will be used for the off-line development of secondary proton spectrometers for PERC. A source of moderated positrons will provide a monoenergetic positron beam with an excellent energy width of below 100 meV, only limited by the thermal broadening. Furthermore, this source will provide a well-defined angular distribution of the positron beam. Compared to electrons, the potentials in the spectrometer do not need to be changed for positrons. The source is very compact and can be installed inside a spectrometer. Both proposed sources are complementary: The proton source has probably a larger energy width and is less flexible in use but is indispensable to characterize the detectors and those spectrometer properties that depend on the ratio mass/charge. The source of moderated positrons with its excellent energy width and stability is ideally suited to characterize the electrostatic potential distribution, the transmission function, and the stability of the spectrometer. The sources shall be optimized for the retardation spectrometer aSPECT and tested with this spectrometer. Before connecting the proton source to aSPECT it will be used to characterize the proton detectors of PERKEO-III. After finishing the measurements with aSPECT, the sources are available for characterizing PERC and its secondary proton spectrometers.