桑福德地下研究设施戴维斯洞穴中Gamma Ray背景的测量
Measurement of the Gamma Ray Background in the Davis Cavern at the Sanford Underground Research Facility
摘要：
由于宇宙射线通过地球时会衰减，深地下环境是低背景搜索的理想场所。然而，它们受到周围岩石中$^{40}$ K和$^{238}$ U和$^{232}$ Th衰变链发射的$γ$ -射线的背景影响。LUX-ZEPLIN（LZ）实验将寻找暗物质粒子与位于南达科他州Lead的Sanford Underground Research Facility的Davis校园内的液体氙TPC的相互作用，该实验位于4，850英尺的高度。为了确定洞穴背景，在不同位置用碘化钠探测器和铅屏蔽进行了现场$γ$射线测量。对于无屏蔽测量，积分计数率（0- 3300 keV）在596 Hz到1355 Hz之间变化，对应于$1.9\pm0.4$ ~ $γ~$ cm $^{-2}$ s $^{-1}$ .洞穴壁中产生的放射性可表征为$220\pm60$ ~Bq/kg的$^{40}$ K、$29\pm15$ ~Bq/kg的$^{238}$ U和$13\pm3$ ~Bq/kg的$^{232}$ Th。
英文摘要：
Deep underground environments are ideal for low background searches due to the attenuation of cosmic rays by passage through the earth. However, they are affected by backgrounds from $γ$-rays emitted by $^{40}$K and the $^{238}$U and $^{232}$Th decay chains in the surrounding rock. The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a liquid xenon TPC located within the Davis campus at the Sanford Underground Research Facility, Lead, South Dakota, at the 4,850-foot level. In order to characterise the cavern background, in-situ $γ$-ray measurements were taken with a sodium iodide detector in various locations and with lead shielding. The integral count rates (0--3300~keV) varied from 596~Hz to 1355~Hz for unshielded measurements, corresponding to a total flux in the cavern of $1.9\pm0.4$~$γ~$cm$^{-2}$s$^{-1}$. The resulting activity in the walls of the cavern can be characterised as $220\pm60$~Bq/kg of $^{40}$K, $29\pm15$~Bq/kg of $^{238}$U, and $13\pm3$~Bq/kg of $^{232}$Th.
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