Thermal neutron background measurement in CJPL

Zeng, Zhi; Gong, H.; Yue, Qian; Li, J.M.

doi:10.1016/j.nima.2015.09.043

Cited by 16 publications

(9 citation statements)

References 7 publications

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“…Table II summarizes measurements of ambient radiation background by the main experiment hall in CJPL-I. Standard detector techniques [12,[58][59][60] were adopted to perform these measurements.…”

Section: Low-background Facilitiesmentioning

confidence: 99%

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The China Jinping Underground Laboratory and Its Early Science

Cheng

Kang

et al. 2017

Annu. Rev. Nucl. Part. Sci.

104

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The China Jinping Underground Laboratory, inaugurated in 2010, is an underground research facility with the deepest rock overburden and largest space by volume in the world. The firstgeneration science programs include dark matter searches conducted by the CDEX and PandaX experiments. These activities are complemented by measurements of ambient radioactivity and installation of low-background counting systems. Phase II of the facility is being constructed, and its potential research projects are being formulated. In this review, we discuss the history, key features, results, and status of this facility and its experimental programs, as well as their future evolution and plans.

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Section: Low-background Facilitiesmentioning

confidence: 99%

“…3 He-proportional tube[60] (4.00 ± 0.08) × 10 −6 cm −2 s −1 Multiple Bonner spheres [61] (7.03 ± 1.81) × 10 −6 cm −2 s −1…”

mentioning

confidence: 99%

The China Jinping Underground Laboratory and Its Early Science

Cheng

Kang

et al. 2017

Annu. Rev. Nucl. Part. Sci.

104

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“…Thus, precise information about the neutron background is of crucial importance. Neutron fluxes in deep laboratories are typically at the level of 10 −8 ∼ 10 −6 n/cm 2 /s [1][2][3][4][5], several orders of magnitude lower than that at ground level. In the case of measurement of such low neutron flux, the intrinsic background of detectors should be taken into account.…”

Section: Introductionmentioning

confidence: 98%

A thermal neutron detection system based on boron-coated straw detector with prompt gamma coincidence

Pan¹,

Shen²,

Fu³

et al. 2022

J. Inst.

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Accurate measurement of the neutron flux is of crucial importance for rare event search experiments in underground laboratories. The intrinsic radioactive background of the detector becomes the limiting factor for the detection of extremely low neutron flux. In this study, a thermal neutron detection system aimed at low flux measurement was developed based on boron-coated straw (BCS) neutron detectors. The neutron events can be distinguished from the detector background by coincidence measurement of neutron and the prompt gamma ray. With state-of-the-art BCS neutron detectors and NaI(Tl) gamma detector, a system sensitivity of ∼120 cps/nv was achieved, comparable to that of the commonly used 3He counters. Based on the selected coincidence criteria, the background events were rejected to 0.1% with 45.3% of the neutrons preserved. The background accidental coincidence count rate of the system was measured as 2.3×10-5 cps, corresponding to a lower limit of measurable thermal neutron flux of 1.9×10-7 n/cm2/s. The performance of the system can be further improved by using other gamma scintillator with lower neutron absorption (such as BGO) and adding extra shielding for ambient gamma rays.

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“…1. The thermal neutron flux was measured with a gaseous 3 He proportional ionization chamber in the Hall A of CJPL, giving a flux of (4.00 ± 0.08) × 10 −6 cm −2 s −1 [10]. The same measurement was performed inside the PE room.…”

Section: Introductionmentioning

confidence: 99%

Measurement of the fast neutron background at the China Jinping Underground Laboratory

Lin

Liu

et al. 2018

Nuclear Instruments and Methods in Physics Research Section A:

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We report on the measurements of the fluxes and spectra of the environmental fast neutron background at the China Jinping Underground Laboratory (CJPL) with a rock overburden of about 6700 meters water equivalent, using a liquid scintillator detector doped with 0.5% gadolinium. The signature of a prompt nuclear recoil followed by a delayed high energy γ-ray cascade is used to identify neutron events. The large energy deposition of the delayed γ-rays from the (n, γ) reaction on gadolinium, together with the excellent n-γ discrimination capability provides a powerful background suppression which allows the measurement of a low intensity neutron flux. The neutron flux of (1.51±0.03 (stat.)±0.10 (syst.))×10 −7 cm −2 s −1 in the energy range of 1 -10 MeV in the Hall A of CJPL was measured based on 356 days of data. In the same energy region, measurement with the same detector placed in a one meter thick polyethylene room gives a significantly lower flux of (4.9 ± 0.9 (stat.) ± 0.5 (syst.)) × 10 −9 cm −2 s −1 with 174 days of data. This represents a measurement of the lowest environmental fast neutron background among the underground laboratories in the world, prior to additional experiment-specific attenuation. Additionally, the fast neutron spectra both in the Hall A and the polyethylene room were reconstructed with the help of GEANT4 simulation. 1 Main contributor underground site is produced in the rock through the spontaneous fission of 238 U and the (α, n) reactions of light nuclei bombarded by the α-particles emitted in the U/Th decay chains. An additional neutron background is taken along with the infrastructure and the experimental setup of laboratories. Nuclear recoils and other interactions due to the environmental neutron background can restrict experimental sensitivities or bring false positive signals in the studies of rare phenomena. Therefore, the understanding of neutron spectrum and identifying neutron sources are substantial issues for background reduction and guide the design of shielding systems for the next generation of large-scale experiments.The China Jinping Underground Laboratory

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Thermal neutron background measurement in CJPL

Cited by 16 publications

References 7 publications

The China Jinping Underground Laboratory and Its Early Science

The China Jinping Underground Laboratory and Its Early Science

A thermal neutron detection system based on boron-coated straw detector with prompt gamma coincidence

Measurement of the fast neutron background at the China Jinping Underground Laboratory

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