Research Facilities and Projects

Black Hills Underground Campus (BHUC)

The BHUC is a unique, multidisciplinary research facility located at the Ross Campus of the 4850’ level of SURF with ~4300 meter water equivalent shielding from cosmic rays.

4850’, 7400’ levels of SURF

BHUC Campus Cavern

The facility is comprised of two separate cleanroom spaces and an outside staging area for research and development activities. The 200 sq. ft. class 10,000 cleanroom houses lab benches and the 600 sq.ft. class 1,000 cleanroom space is partially occupied with low background counters.

The BHUC has available standard power outlets within the cleanroom and the work area, access to a ‘star’ ground within the cleanroom, standard internet connections (ethernet and wifi), N2 gas distribution and an automated liquid nitrogen (LN2) system. Below is a proposed configuration of the counting cleanroom. Currently, only about half of this cleanroom is utilized.

BHUC Counting Clean Room

Four 180 L dewars outside the cleanroom supply each counting station with liquid nitrogen via vacuum-jacketed piping that runs along three walls of the cleanroom and out into the work area. These liquid nitrogen dewars also supply gaseous nitrogen via their boil-off which is in turn is also supplied to each counting station as radon purge gas by stainless steel tubing running along the walls.

There are currently three single-crystal low background counting stations in the BHUC: Morgan, Maeve, and Mordred. BHSU manages these detectors on behalf of LBNL. Each of these current counting stations are HPGe detectors surrounded by lead and copper shielding and purged with low activity N2 gas.

BHUC Crystal Counting Stations

Pictured above are the current single-crystal counting stations in the BHUC counting room. From left to right are Mordred, SOLO (now above-ground), Maeve, Morgan HPGe detectors inside their shielding castles. The rack of electronics to the right provides the DAQ and networking for all four detectors. Along the walls of the clean room can be seen the LN2 and N2 lines.

In addition to the three traditional, single, HPGe crystal detectors, the Twins is a dual detector low background counting station in development. Access to a dual-crystal system in development by LLNL is also possible.

Twins Detector installed at the BHUC

Top view of schematic showing two crystals in one shield

Here are the current HPG's underground at BHUC.

Resources

BHUC Publications

Background determination for the LUX-ZEPLIN dark matter experiment, [LZ Collaboration], Phys. Rev. D 108, 012010 (2023).

Counting Facilities at the Black Hills Underground Campus, D. Tiedt, B. Mount, A. Rodriguez, AIP Conf. Proc. 2908, 020003 (2023).

Supporting Capabilties for Underground Facilities, A. Kamaha, B.J. Mount, R.W. Schnee, Snowmass UF4 Topical Group Report

The LUX-ZEPLIN (LZ) Radioactivity and Cleanliness Control Programs, [LZ Collaboration], Phys. J. C, 80, 1044 (2020).

Black Hills State University Underground Campus, J. Mount et al., Appl Radiat Isot., 126, 130 (2017).

Identification of Radiopure Titanium for the LZ Dark Matter Experiment and Future Rare Event Searches, [LZ Collaboration], Astropart. Phys. 96, 1 (2017).

Spectroscopy Lab

The Physics department at BHSU has created a state-of-the-art spectroscopy laboratory for ongoing research in association with the Sanford Underground Lab. The spectroscopy lab is building a custom Cavity Ring-Down Spectroscopy system for detecting very low levels of chemical impurities in Argon gas. This gas will be employed as the detection medium in future dark matter experiments in Lead, SD at the Sanford Underground Research Facility (SURF).

Above Ground Lab

There is 1100 sq ft of dedicated lab space available for SURF projects in the newly-renovated Jonas Science Building at BHSU. This space houses a 12’x12’ cleanroom (class 1,000) room as well as a sample prep area for ICP-MS. It also includes fume hoods and access to a Nanopure deionized water system.

Pictured above is a BHSU dedicated lab for SURF-focused research (including the ICP-MS lab)

Additionally, this lab houses a High Purity Germanium (HPGe) detector, SOLO. SOLO will be used as a pre-screener for the BHUC detectors and as a training ground for undergraduate students.

ICP-MS Lab

The BHSU ICP-MS lab is located in the Jonas Science Building on the BHSU campus. The lab houses a class 10,000 cleanrooms and an Agilent 7900 ICP-MS with SPS 4 Autosampler. In addition to liquid samples, the BHSU ICP-MS is also able to handle solid samples with its ESI NWR 213 laser ablation sample introduction system.

Please contact Brianna Mount (Brianna.Mount@BHSU.edu, (605)642-6094) with any questions related to the ICP-MS or any analysis requests.

About ICP-MS

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is a technique which allows users to obtain sensitive measurements of concentrations of a range of elements down to the sub parts-per-trillion (ppt) level. With varying applications in diverse fields, this fast, multi-element technique has become an indispensable tool in ultra-trace elemental analysis [Reference 1, Reference 2].

First commercialized in the early 1980’s, the ICP-MS technique has grown rapidly in the subsequent decades [Reference 1, Reference 3]. Its sensitivity to elements from the sub-ppt to ppm range make it the ideal instrument for many applications.

In the standard ICP-MS technique, liquid samples are pumped into a nebulizer where it is mixed with argon gas to form a fine aerosol and sent into the plasma torch. The molecules of the aerosol are broken into ions by the plasma and sent through the mass spectrometry interface consisting of sampling and skimmer cones and into an ion focusing system which directs the ions into the mass separation device and finally onto the detector [Reference 1]

Sample schematic of an ICP-MS instrument

The particular ICP-MS mass separation technique in the Agilent 7900 utilizes a quadrupole, which is the technology with which most ICP-MS instruments operate. An auto-sampler is included for fast, automated data acquisition. In addition to the standard liquid sample introduction system, the ICP-MS facility is also be equipped with a removable laser ablation sample introduction system.

The laser ablation add-on has the ability to analyze solid materials without the need for acid digestion. This is of use in samples which are not easily dissolved. It is also able to spatially resolve analytes on a sample. Laser ablation has the advantage of being able to pinpoint an area on a sample to analyze and be fairly non-destructive due to its small spot size ~4-200 μm. However, with the addition of laser ablation comes a reduction in sensitivity. Laser ablation systems are only sensitive down to the ppb level. The laser ablation add-on is removable in about 30 minutes. This removable sample introduction system enables the ICP-MS at BHSU to flexibly analyze more samples in diverse applications.

Previous Projects

Geology/Environmental Applications

Uranium and Thorium Levels in Geological Samples

Uranium mining is widespread in western South Dakota and northwestern Nebraska, and the potential environmental disturbance derived from this activity is of serious concern to the Oglala Sioux Tribe of the Pine Ridge Indian Reservation. The BHSU group was approached by faculty and students from the Oglala Lakota College (OLC) to participate in a study to evaluate the background levels of U and Th in nine geological samples. The leachable and bioavailable fractions of U and Th were determined in the samples using the BHSU ICP-MS. The found levels in the leachable fraction varied from 0.35 mg kg-1 to 21.4 mg kg-1 U and from 2.0 to 12.6 mg kg-1 Th. The bioavailable fractions were below 3.1 % of the leachable fraction for U and lower than 0.15 % for Th. The OLC group will collect more geological samples from distinct rock outcrops in order to provide the background levels of other potentially toxic elements. Of particular relevance will be the elemental analysis of the collected plant material aiming at finding potential biomonitoring organisms of the studied area.

Antarctic Lichen samples

Antarctica has been recognized as the last pristine environment on Earth. Environmental monitoring assessment programs are active in several Antarctic scientific stations and the most frequently selected samples are soils, sediments, mosses and lichens. Lichens are especially interesting as they enjoy longevity, immobility, and a perennial nature. Another important feature of these sentinel organisms is their well-known capacity of absorbing contaminants from the atmosphere. Airborne pollutants, such as toxic metals, can be directly absorbed by lichen anatomical structures, and have been used for tracking atmospheric pollution over the time. The toxic elements, notably As, Cd, Cr, Pb, Hg, and Ni are persistent in the environment, and they can induce several drastic disturbances, such as imbalances in the food chain, and the development of adverse effects on the organisms as the inhibition of their growth, metabolism and reproduction. Lichen samples have been collected around four Antarctic stations: Arctowski (Polish), Bellingshausen (Russian), Escudero (Chilean), and Comandante Ferraz (Brazilian). The BHSU ICP-MS group will analyze these samples in the coming year and plans to submit a proposal to study lichens in other areas of Antarctica as well.

Physics

Silicon and Sapphire for DARKSIDE

The BHSU ICP-MS group was requested to perform their first low background analysis of a silicon substrate by the DARKSIDE direct matter detector group. Dr. Guerra designed a sample preparation procedure and was able to establish limits for uranium and thorium in the silicon. DARKSIDE has also requested the group analyze sapphire samples with their laser ablation sample introduction system and ICP-MS.

Germanium Analysis

The BHSU group has received germanium samples from the University of South Dakota to analyze. Growing detector-grade germanium crystals requires numerous steps to convert bulk germanium into ultra-pure material used in detectors of rare event experiments. The characterization of materials used in crystal growth is crucial to the crystal growth process, both before and after the crystal has been formed.

If the impurity concentration is too low, it could result in a highly, non-uniform electric field. Conversely, if it is too high, it could result in excessively high depletion voltage and risk a breakdown. The BHSU ICP-MS group will analyze the germanium samples for their B, Al and P content in the coming months to enable USD to better understand their crystal growing process.

Chemistry

ICP-MS Study of Environmental Toxicity of Nanomaterials used in Renewable Energy Generation

Optimization procedures were performed to study nanomaterial degradation in different media. Initial work has focused on characterization of the synthesized nanomaterials. Two undergraduate students, Amber Borkovec and Rachel Stevens spent this summer synthesizing nanomaterials for digestion. The digestion procedure initially showed inconsistent recoveries, which is understandable with the complex chemistry surrounding the nanomaterial. Both students received introductory training and sample preparation training from Dr. Asunskis and Dr. Guerra. This project has been funded in part for the upcoming year through NIH to analyze the material toxicity and the effects on cellular growth. The ICP-MS will continue to be a focal point of this project to analyze the leachable species from the material in media. The bioaccumulation of elements in the cell will also be studied in this upcoming year using the ICP-MS.

Chemical Characterization of Underground Water at Sanford Lab

In the labyrinth of tunnels that comprise the Sanford Lab, there are numerous water microenvironments that are hypothesized to contain unique microbial communities of potential interest to microbiologists. The objective of this study was to characterize water chemistry at distinct and previously unsampled locations, with particular emphasis on those areas undergoing microbial study. Test sites were located at the 4100’ level and 4850’ level of the Sanford Lab. Filtered and unfiltered samples were taken above-ground and analyzed using the BHSU ICP-MS. This study found interesting differences in water composition between levels of the Sanford Lab and more research is ongoing.

Biology

Otolith and Water Chemistry Studies with McNenny State Fish Hatchery

McNenny State Fish Hatchery provides trout and salmon for stocking in the Black Hills, Missouri River Reservoirs and Eastern South Dakota lakes and streams. McNenny is somewhat unique in that the hatchery has a history and culture of research. The BHSU ICP-MS group was approached by the hatchery to provide laser ablation ICP-MS analysis of otoliths as well as analysis of water. The BHSU ICP-MS group has toured the hatchery and discussion are ongoing to determine possible research paths.

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LUX-ZEPLIN (LZ Collaboration)

LZ Dark Matter Experiment

Narrator

People have always been fascinated by the beauty and richness of the night sky, and scientists have been studying the cosmos for many centuries. But we still don't know a whole lot about what the universe is made of. In fact, 85% of all the matter in the universe, called dark matter, can't be seen even with our most advanced scientific instruments. Scientists know it's there because it bends light and affects how galaxies rotate. It's also a crucial part of galaxy formation, and our world wouldn't exist without it. Identifying the building blocks of dark matter is one of the highest priorities of modern physics. Most scientists believe it's made of ghostly particles that rarely bump into their surroundings. That's why billions of dark matter particles might zip right through our bodies every second without us even noticing. Leading candidates for dark matter particles are WIMPS, or weakly interacting massive particles. Now, SLAC is helping to build and test one of the biggest and most sensitive detectors ever designed to catch a WIMP- the LUX-ZEPLIN, or LZ detector. LZ's heart is a tank filled with ten tons of liquid xenon. If a particle streaks through the tank and strikes a xenon nucleus, two things will happen: the xenon will emit a flash of light, and it will also release electrons, which drift in an electric field to the top of the tank, where they produce a second flash of light. A WIMP will produce a characteristic combination of flashes, which will be detected with nearly 500 light-sensitive tubes at the top and bottom of the tank. But to have any hope of seeing a potential WIMP signal, LZ scientists will have to deal with a lot of background noise, such as unwanted signals from cosmic rays from spaces, and gamma rays and neutrons released in natural radioactive decay in the environment and detector materials. Therefore, the detector core will be surrounded by several layers that eliminate this noise as much as possible. First, the researchers will purify the xenon to an incredible degree, to get rid of traces of radioactive krypton. The goal is less than one krypton atom per 100 trillion xenon atoms. Next, they'll use only the innermost 80% of the purified xenon in the tank to detect dark matter. The outer 20% will serve as a radiation shield. Another think layer of xenon, called the xenon skin, will reject signals from gamma rays and neutrons. The tank that holds the xenon will be made of ultraclean, medical-grade titanium that generates very few background signals. The titanium tank will sit inside a bigger tank filled with a liquid that, like the xenon skin, detects gamma rays and neutrons. And both of those tanks will be inside a third tank, filled with 70,000 gallons of water the outer radiation shield. All of this will be located nearly a mile underground at the Sanford Underground Research Facility in South Dakota, where it's protected from cosmic rays. With LZ going online in early 2020, researchers hope for a breakthrough in the search for dark matter to learn more about ourselves, our galactic home, and the entire universe.

Dark matter constitutes about 85% of the mass in the universe [1-4], but its composition and nature remain unknown. Leading theories continue to postulate that dark matter is formed of Weakly Interacting Massive Particles (WIMPs) with masses between ~ 2 and at least 1000 GeV/c². The 2023 P5 recommendations highlighted the significance of identifying dark matter for the Office of Science High Energy Physics program. Recommendation 1 emphasizes the importance of the LUX-ZEPLIN (LZ) experiment as it has entered its primary WIMP discovery phase; stating “as one of the highest priorities independent of budget scenario”, that the LZ detector at the Sanford Underground Research Facility (SURF) [5-7] in Lead, SD be one of the experiments to continue to receive support from DOE for “ongoing experiments and research to enable maximum science[8].” Additionally, “an ultimate Generation 3 (G3) dark matter direct detection experiment reaching the neutrino fog, in coordination with international partners and preferably sited in the US” was also recommended by the P5 panel.

The LZ collaboration is a merging of the LUX [9] and ZEPLIN [10] experiments and is searching for the elusive WIMP signal [11-14]. The experiment is located in SURF’s Davis cavern on the 4850L, which provides 4300 meter water equivalent shielding.

The LZ detector consists of a 7-tonne active mass liquid xenon target in a dual-phase Time Projection Chamber (TPC), see Figure 1.

Figure 1: Rendering of the LZ experiment, showing the major detector subsystems. At the center is the liquid xenon TPC (1), monitored by two arrays of PMTs and serviced by various cable and fluid conduits (upper and lower). The TPC is contained in a double-walled vacuum insulated titanium cryostat and surrounded on all sides by a GdLS Outer Detector (2). The cathode high voltage connection is made horizontally at the lower left (5). The GdLS is observed by a suite of 8” PMTs (3) standing in the water (4) which provides shielding for the detector. The pitched conduit on the right (6) allows for neutron calibration sources to illuminate the detector [15].

Interactions occurring within the TPC fiducial volume will create two bursts of light, each at separate times, which reach the Photomultiplier tubes (PMTs) located at the top and the bottom of the TPC. The first signal, S1, is the prompt scintillation signal from the original interaction between a particle and the xenon. The second signal, S2, is created when electrons from the original interaction are drifted to the gas phase of the TPC through an applied uniform electric field, where they produce a second scintillation signal through electroluminescence. These two signals allow for three-dimensional reconstruction of the location of the event as well as the determination of its energy. Interactions with the xenon nucleus (nuclear recoils, NR) are differentiated from interactions with the xenon electron cloud (electron recoil, ER) through the ratio of these S1 and S2 signals.

LZ’s TPC is surrounded by a thin layer of instrumented xenon within the titanium cryostat, which is called the Skin. The cryostat is then surrounded by the outer detector (OD), which are large acrylic tanks filled with gadolinium-doped liquid scintillator. Both the Skin and OD have dedicated PMTs. The entire system is then contained in a water tank. The combination of the Skin and the OD form a system which detects gamma and neutron emissions from within the detector materials themselves, which allows these background signals to be vetoed.

Construction was completed in 2021 and the first results were published in 2023 (see Figure 2 and [16]). Data-taking is ongoing! The LZ experiment will achieve detection limits close to the neutrino fog.

Figure 2: The 90 % confidence limit (black line) for the spin independent WIMP cross section vs. WIMP mass. The green and yellow bands are the 1σ and 2σ sensitivity bands. The dotted line shows the median of the sensitivity projection. Also shown are the PandaX-4T [17], XENON1T[18], LUX[19], and DEAP-3600[20] limits [16].