Production Yield of Muon-Induced Neutrons in Lead by Holger Kluck

Author:Holger Kluck
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Another trade off exists between the coverage of large targets and high moderation efficiency on one hand and a high efficiency of scintillation light collection on the PMTs on the other hand, as the latter is degraded in large volume detectors by internal absorption in the liquid scintillator and increased light trajectories due to multiple reflections on the detector walls. It can be further degraded by a chemical long term instability of the scintillator, leading to an increased light absorption. For the actually used liquid scintillator this is further discussed in Sects. 4.2.1, 4.3 and 4.4.3.

The efficiency may further decrease by the finite time resolution of the NMM, resulting in pile up of delayed signals, the dead time [23] of the NMM, resulting in missed signals, and the ionization quenching (Eq. 4.14a), suppressing the prompt signals from proton recoils. This is further discussed in Sect. 4.2.6. Also the measured multiplicity can get further distorted by secondary neutron production in the liquid scintillator via , [33, 75]. A selection of the related cross sections are shown in Fig. 4.1b. This effect is also evident in Fig. 4.4 for the two lines of 20 and 50 MeV neutrons: The increased detection efficiency with respect to the three lower energetic neutrons is caused by the neutron multiplication via inelastic scatterings, not only on the carbon in the scintillator but also on the lead target.

As the detection efficiency for all investigated neutron energies reaches a plateau at , this is the optimal thickness for the active volume with respect to the neutron detection. Here a neutron detection efficiency of 40 % can be expected for this configuration.

As all these effects are energy dependent, measurements of poly-energetic neutrons, like muon-induced neutrons, are not easily to correct for detection efficiencies. It is more appropriate to convolve simulated results with the detector efficiency and compare it afterwards with the measurements [33]. For this reason the next Sect. 4.2 will document in detail the detector properties, serving as input for the model of detector response in Sect. 5.​4, which is then folded by the simulated neutron production in Sect. 5.​5 and finally compared in Chap. 6 with the measurements in Sect. 4.5.

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