Soudan Mine Research Articles

Aqueous Co removal by mycogenic Mn oxides from simulated mining wastewaters

Naturally occurring manganese (Mn) oxide minerals often form by microbial Mn(II) oxidation, resulting in nanocrystalline Mn(III/IV) oxide phases with high reactivity that can influence the uptake and release of many metals (e.g., Ni, Cu, Co, and Zn). During formation, the structure and composition of biogenic Mn oxides can be altered in the presence of other metals, which in turn affects the minerals’ ability to bind these metals. These processes are further influenced by the chemistry of the aqueous environment and the type and physiology of microorganisms involved. Conditions extending to environments that typify mining and industrial wastewaters (e.g., increased salt content, low nutrient, and high metal concentrations) have not been well investigated thus limiting the understanding of metal interactions with biogenic Mn oxides. By integrating geochemistry, microscopic, and spectroscopic techniques, we examined the capacity of Mn oxides produced by the Mn(II)-oxidizing Ascomycete fungus Periconia sp. SMF1 isolated from the Minnesota Soudan Mine to remove the metal co-contaminant Co(II) from synthetic waters that are representative of mining wastewaters currently undergoing remediation efforts. We compared two different applied remediation strategies under the same conditions: coprecipitation of Co with mycogenic Mn oxides versus adsorption of Co with pre-formed fungal Mn oxides. Co(II) was effectively removed from solution by fungal Mn oxides through two different mechanisms: incorporation into, and adsorption onto, Mn oxides. These mechanisms were similar for both remediation strategies, indicating the general effectiveness of Co(II) removal by these oxides. The mycogenic Mn oxides were primarily a nanoparticulate, poorly-crystalline birnessite-like phases with slight differences depending on the chemical conditions during formation. The relatively fast and complete removal of aqueous Co(II) during biomineralization as well as the subsequent structural incorporation of Co into the Mn oxide structure illustrated a sustainable cycle capable of continuously remediating Co(II) from metal-polluted environments.

Diverse subterranean fungi of an underground iron ore mine.

Mines and caves are unusual ecosystems containing unique fungi and are greatly understudied compared to other environments. The Soudan Mine in Tower, MN, an iron ore mine that closed in 1963 after operating for 80 years, was sampled to explore fungal diversity and to investigate taxa that tolerate heavy metals for potential bioprocessing technologies or as sources of bioactive molecules for drug discovery and possible biocontrol for white-nose syndrome (WNS) of bats. The mine is 714 m deep, has 18 levels and contains large quantities of wooden timbers, in contrast to many other oligotrophic subterranean environments. Fungi were cultured from samples and the ITS region was sequenced for identification and phylogenetic analysis. Results show Ascomycota are the dominant fungi followed by Basidiomycota and Mucoromycota. Out of 164 identified taxa, 108 belong to the Ascomycota and 26 and 31 to Basidiomycota and Mucoromycota, respectively. There are also 46 taxa that do not match (<97% BLAST GenBank identity) sequenced fungal species. Examples of the most commonly isolated Ascomycota include Scytalidium sp., Mariannaea comptospora, Hypocrea pachybasidioides, Oidiodendron griseum and Pochonia bulbillosa; Basidiomycota include Postia sp., Sistotrema brinkmannii, Calocera sp., Amylocorticiellum sp.; Mucoromycota include Mortierella parvispora, M. gamsii, M. hyaline, M. basiparvispora and Mortierella sp. Unusual growth forms were also found including large quantities of black rhizomorphs of Armillaria sinapina and white mycelial cords of Postia sp. mycelium, as well as Pseudogymnoascus species growing over large areas of mine walls and ceiling. The mine environment is a relatively extreme environment for fungi, with the presence of high levels of heavy metals, complete darkness and poor nutrient availability. Several genera are similar to those isolated in other extreme environments but phylogenetic analyses show differences in species between these environments. Results indicate this subterranean environment hosts a wide diversity of fungi, many of them not found in above ground environments.

Timing in the NOvA detectors with atomic clock based time transfers between Fermilab, the Soudan mine and the NOvA Far detector

The NOvA experiment uses a GPS based timing system both to internally synchronize the readout of the DAQ components and to establish an absolute wall clock reference which can be used to link the Fermilab accelerator complex with the neutrino flux that crosses the NOvA detectors. We describe the methods that were used during the commissioning of the NOvA DAQ and Timing systems to establish the synchronization between the Fermilab beam and the NOvA far detector. We present how high precision atomic clocks were trained and transported between the MINOS and NOvA detectors during a Northern Minnesota blizzard to validate the absolute time offsets of the experiments and make the first observation of beam neutrinos in the NOvA far detector.

Measuring muon-induced neutrons with liquid scintillation detector at Soudan mine

We report a direct detection of muon-induced high-energy neutrons with a 12-liter neutron detector fabricated with EJ-301 liquid scintillator operating at Soudan mine for about two years. The detector response to energy from a few MeV up to $\ensuremath{\sim}20\text{ }\text{ }\mathrm{MeV}$ has been calibrated using radioactive sources and cosmic-ray muons. Subsequently, we have calculated the scintillation efficiency for nuclear recoils, up to a few hundred MeV, using Birks' law in the Monte Carlo simulation. Data from an exposure of 655.1 days were analyzed and neutron-induced recoil events were observed in the energy region from 4 to 50 MeV, corresponding to fast neutrons with kinetic energy up to a few hundred MeV, depending on the scattering angle. Combining with the Monte Carlo simulation, the measured muon-induced fast neutron flux is determined to be $(2.23\ifmmode\pm\else\textpm\fi{}0.52(\text{sta})\ifmmode\pm\else\textpm\fi{}0.99(\text{sys}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (${E}_{n}\text{ }&gt;20\text{ }\text{ }\mathrm{MeV}$), in a reasonable agreement with the model prediction. The muon flux is found to be ($1.65\ifmmode\pm\else\textpm\fi{}0.02(\text{sta})\ifmmode\pm\else\textpm\fi{}0.1(\text{sys}))\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0ex}{0ex}}{10}^{\ensuremath{-}7}\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (${E}_{\ensuremath{\mu}}\text{ }&gt;1\text{ }\text{ }\mathrm{GeV}$), consistent with other measurements. As a result, the muon-induced high-energy gamma-ray flux is simulated to be $7.08\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ (${E}_{\ensuremath{\gamma}}\text{ }&gt;\text{ }1\text{ }\text{ }\mathrm{MeV}$) for the depth of Soudan.

Fast neutron measurement at Soudan Mine using a large liquid scintillation detector

Fast neutron measurement at Soudan Mine using a large liquid scintillation detector

MINOS neutrino oscillation results

Neutrinos interact only weakly with other matter and had been thought to be massless. However, if their mass is non-zero, they could change flavors as they propagate. Recent results from observations of atmospheric, solar, and reactor neutrinos indicate that they do change flavor and these observations have provided measurements of two of the three possible mixings. The MINOS experiment is now making precise measurements of the ν μ ↔ ν τ oscillations seen in atmospheric neutrinos, and extends our reach towards the so far unseen angle θ 1 3 by looking for ν e appearance from the ν μ beam. It does so by using the intense, well-understood NuMI neutrino beam created at Fermilab and observing it 735 km away at the Soudan Mine in Northeast Minnesota. This combination also allows investigation of the oscillation properties of anti-neutrinos, as the NuMI beam can focus opposite-charged pions to produce the anti-neutrinos, and the MINOS detectors are magnetized, allowing event-by-event discrimination of the resulting muon charge-sign.

A BRIEF REVIEW OF MINOS NEUTRINO OSCILLATION RESULTS

The MINOS long-baseline experiment is using the NuMI neutrino beam to make precise measurements of neutrino flavor oscillations in the "atmospheric" neutrino sector. MINOS observes the νμ disappearance oscillations seen in atmospheric neutrinos, tests possible disappearance to sterile ν by measuring the neutral current flux, and extends our reach towards the so far unseen θ13 by looking for νe appearance in this νμ beam. The magnetized MINOS detectors also allow tests of CPT conservation by discriminating between neutrinos and anti-neutrinos on an event-by-event basis. The intense, well-understood NuMI neutrino beam created at Fermilab is observed 735 km away at the Soudan Mine in Northeast Minnesota. High-statistics studies of the neutrino interactions themselves and the cosmic rays seen by the MINOS detectors have also been made. MINOS started taking beam data in May 2005 and is now nearing the end of its five-year run. This paper reviews results published based on the first several years of data.

Current MINOS neutrino oscillation results

The MINOS experiment is now making precise measurements of the νμ disappearance oscillations seen in atmospheric neutrinos, tests possible disappearance to sterile ν by measuring the neutral current flux, and has extended our reach towards the so far unseen θ13 by looking for νe appearance in the νμ beam. It does so by using the intense, well-understood NuMI neutrino beam created at Fermilab and observing it 735km away at the Soudan Mine in Northeast Minnesota. High-statistics studies of the neutrino interactions themselves and the cosmic rays seen by the MINOS detectors have also been made. Results from MINOS' first three years of operations will be presented.

The Cryogenic Dark Matter Search (CDMS) experiment: Results and prospects

Weakly Interacting Massive Particles (WIMPs) are a strong candidate for the Cold Dark Matter of the Universe. CDMS-II is a direct-search WIMP search experiment, operating at 50 mK and housed at the Soudan mine, Minnesota. The 250 gram Ge detectors utilize athermal phonon sensors where tungsten transition edge sensors are operated in negative electrothermal feedback. The search at Soudan is ongoing with an expected final reach of CDMS-II by the end of 2008 of a WIMP-nucleon cross-section sensitivity of 2.1 x10-44 cm2, at a WIMP mass of 60 GeV/c2. To proceed further, we have proposed the SuperCDMS program.

CDMS, Supersymmetry and Extra Dimensions

The CDMS experiment aims to directly detect massive, cold dark matter particles originating from the Milky Way halo. Charge and lattice excitations are detected after a particle scatters in a Ge or Si crystal kept at ∼30 mK, allowing to separate nuclear recoils from the dominating electromagnetic background. The operation of 12 detectors in the Soudan mine for 75 live days in 2004 delivered no evidence for a signal, yielding stringent limits on dark matter candidates from supersymmetry and universal extra dimensions. Thirty Ge and Si detectors are presently installed in the Soudan cryostat, and operating at base temperature. The run scheduled to start in 2006 is expected to yield a one order of magnitude increase in dark matter sensitivity.

Direct dark matter searches with CDMS and XENON

The cryogenic dark matter search (CDMS) and XENON experiments aim to directly detect dark matter in the form of weakly interacting massive particles (WIMPs) via their elastic scattering on the target nuclei. The experiments use different techniques to suppress background event rates to the minimum, and at the same time, to achieve a high WIMP detection rate. The operation of cryogenic Ge and Si crystals of the CDMS-II experiment in the Soudan mine reported spectrum-weighted exposures of 34 (12) kg-d for the Ge (Si) targets after cuts, over the recoil energies 10–100 keV for a WIMP mass of 60 GeV/ c 2. It gives an upper limit (90% C.L.) of spin-independent WIMP-nucleon cross-section at 1.6 × 10 −43 cm 2 for a WIMP mass of 60 GeV/ c 2, starting to constrain predications in supersymmetry models. The two-phase xenon detector of the XENON10 experiment is currently taking data in the Gran Sasso underground lab and promising preliminary results were recently reported. Both experiments are expected to increase their WIMP sensitivity by a one order of magnitude in the scheduled science runs for 2007.

Search for Weakly Interacting Massive Particles with CDMS and XENON

The Cryogenic Dark Matter Search (CDMS) and XENON experiments aim to directly detect dark matter in the form of weakly interacting massive particles (WIMPs) via their elastic scattering on the target nuclei. The experiments use different techniques to suppress background event rates to the minimum, and at the same time, to achieve a high WIMP detection rate. The operation of cryogenic Ge and Si crystals of the CDMS-II experiment in the Soudan mine has yielded the most stringent spin-independent WIMP-nucleon crosssection (∼ 10-43 cm2) at a WIMP mass of 60 GeV/c2. The two-phase xenon detector of the XENON10 experiment is currently taking data in the Gran Sasso underground lab and promising preliminary results were recently reported. Both experiments are expected to increase their WIMP sensitivity by a one order of magnitude in the scheduled science runs for 2007.

First observations of separated atmosphericνμandν¯μevents in the MINOS detector

The complete 5.4 kton MINOS far detector has been taking data since the beginning of August 2003 at a depth of 2070 meters water-equivalent in the Soudan mine, Minnesota. This paper presents the first MINOS observations of muon neutrino and muon anti-neutrino charged-current atmospheric neutrino interactions based on an exposure of 418 days. The ratio of upward to downward-going events in the data is compared to the Monte Carlo expectation in the absence of neutrino oscillations giving: R_data(up/down)/R_MC(up/down) = 0.62^{+0.19}_{-0.14} (stat.) +- 0.02 (sys.). An extended maximum likelihood analysis of the observed L/E distributions excludes the null hypothesis of no neutrino oscillations at the 98 % confidence level. Using the curvature of the observed muons in the 1.3 T MINOS magnetic field muon neutrino and muon anti-neutrino interactions are separated. The ratio of muon neutrino to muon anti-neutrino events in the data is compared to the Monte Carlo expectation assuming neutrinos and anti-neutrinos oscillate in same manner giving: R_data(numubar/numu)/R_MC(numubar/numu) = 0.96^{+0.38}_{-0.27} (stat.) +- 0.15 (sys.), where the errors are the statistical and systematic uncertainties. Although the statistics are limited, this is the first direct observation of atmospheric neutrino interactions separately for muon neutrinos and muon anti-neutrinos.

Using pyrosequencing to shed light on deep mine microbial ecology

BackgroundContrasting biological, chemical and hydrogeological analyses highlights the fundamental processes that shape different environments. Generating and interpreting the biological sequence data was a costly and time-consuming process in defining an environment. Here we have used pyrosequencing, a rapid and relatively inexpensive sequencing technology, to generate environmental genome sequences from two sites in the Soudan Mine, Minnesota, USA. These sites were adjacent to each other, but differed significantly in chemistry and hydrogeology.ResultsComparisons of the microbes and the subsystems identified in the two samples highlighted important differences in metabolic potential in each environment. The microbes were performing distinct biochemistry on the available substrates, and subsystems such as carbon utilization, iron acquisition mechanisms, nitrogen assimilation, and respiratory pathways separated the two communities. Although the correlation between much of the microbial metabolism occurring and the geochemical conditions from which the samples were isolated could be explained, the reason for the presence of many pathways in these environments remains to be determined. Despite being physically close, these two communities were markedly different from each other. In addition, the communities were also completely different from other microbial communities sequenced to date.ConclusionWe anticipate that pyrosequencing will be widely used to sequence environmental samples because of the speed, cost, and technical advantages. Furthermore, subsystem comparisons rapidly identify the important metabolisms employed by the microbes in different environments.

MINOS: Design & detectors

MINOS is a 735 km long-baseline neutrino oscillation experiment from Fermilab (IL, USA) to the Soudan mine (MN, USA). The experiment measures ν μ at various energies from Fermilab’s NuMI beam. The near and far detectors are almost identical steel–scintillator sandwich tracking calorimeters. MINOS has been running in atmospheric mode since 2003 and in beam mode since February 2005. MINOS is designed to make precision measurements of the neutrino oscillation parameters in the atmospheric sector while also being able to improve the current limit on reactor sector oscillations. Several stages of calibration have to be performed to achieve this.

Exclusion limits on the WIMP-nucleon cross section from the first run of the Cryogenic Dark Matter Search in the Soudan Underground Laboratory

The Cryogenic Dark Matter Search (CDMS-II) employs low-temperature Ge and Si detectors to seek Weakly Interacting Massive Particles (WIMPs) via their elastic scattering interactions with nuclei. Simultaneous measurements of both ionization and phonon energy provide discrimination against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.99% efficiency. Electromagnetic events very near the detector surface can mimic nuclear recoils because of reduced charge collection, but these surface events are rejected with >96% efficiency by using additional information from the phonon pulse shape. Efficient use of active and passive shielding, combined with the the 2090 m.w.e. overburden at the experimental site in the Soudan mine, makes the background from neutrons negligible for this first exposure. All cuts are determined in a blind manner from in situ calibrations with external radioactive sources without any prior knowledge of the event distribution in the signal region. Resulting efficiencies are known to ~10%. A single event with a recoil of 64 keV passes all of the cuts and is consistent with the expected misidentification rate of surface-electron recoils. Under the assumptions for a standard dark matter halo, these data exclude previously unexplored parameter space for both spin-independent and spin-dependent WIMP-nucleon elastic scattering. The resulting limit on the spin-independent WIMP-nucleon elastic-scattering cross-section has a minimum of 4x10^-43 cm^2 at a WIMP mass of 60 GeV/c^2. The minimum of the limit for the spin-dependent WIMP-neutron elastic-scattering cross-section is 2x10^-37 cm^2 at a WIMP mass of 50 GeV/c^2.

Underground science research facilities in the United States, the transition from mine tenant to facility operator

The underground physics research community (UPRC) in the United States has historically conducted research in underground mines. Because underground mines exist for the purposes of ore extraction, research activities sometimes take a secondary role. Underground science has matured, as second and third generation experiments have demonstrated the continuing benefit of such research. Success breeds interest, so the demand for underground research space has increased. Hence the need for a dedicated underground laboratory has been recognized and pursued. Underground physics research in the United States began with several cosmic ray studies in the 1950s. In the 1960s, future Nobel Prize winner Fred Reines and his associates observed cosmic-ray produced neutrinos at the famous East Rand Proprietary Gold Mine near Johannesburg, South Africa. The first large-scale US detector was located at the Homestake gold mine in Lead, South Dakota. The detector was a 380,000-liter tank of perchloroethylene, a cleaning fluid. Subsequent experiments included: the water Cerenkov detector for the Irvine-Michigan-Brookhaven (IMB) experiment, located 600 m underground in the Morton salt mine near Cleveland, OH; the Harvard-Purdue-Wisconsin (HPW) experiment 650 m underground in Park City, UT; and the Soudan 2 proton decay experiment located 713 m underground at the Soudan Underground Mine State Park in northeastern Minnesota. International underground physics laboratories include: Gran Sasso, Pyhasalmi mine, Kamioka Mozumi mine, Sudbury Neutrino Observatory at the INCO Creighton mine, and the Boulby mine. The underground physics research community in the US is pursuing a sole-purpose National Underground Science Laboratory. Candidate sites are: Homestake mine, Mount San Jacinto, Soudan mine, WIPP site and the Henderson mine. The next-generation nucleon decay experiment, tentatively called UNO, will require a cavern 60 m wide by 60 m high by 180 m long at a depth on the order of 1,500 m. The transition from a single experiment facility to a multiple experiment facility requires development of a separate operating authority. The authority must deal with the new institutional issues associated with balancing the laboratory versus experiment issues, including different sources of funding, shared responsibilities and liabilities, experiment rights and conflict resolution, decommissioning, and provided services. In all inhabitable building spaces, whether above- or underground, providing fire and life safety is the most important design requirement. For the underground science laboratories, this must be accomplished in the underground environment, and in the framework of several mining, occupational and building codes. The underground environment, while inhospitable in some ways, is a necessity for current and future high-energy physics research. Deep underground space can be developed to make regular human occupation safe, functional and appealing. The benefits are clear for a single-purpose underground facility, where underground science is the sole reason for being underground. Sites for an US National Underground Science Laboratory are many and varied. The challenge remains to develop and fund the best site. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Status and prospects of the MINOS experiment

The MINOS long-baseline neutrino oscillation experiment has completed the installation and commissioning of the Far Detector at the Soudan mine, while the construction of the Near Detector at the Fermi National Accelerator Laboratory is under way. We report on the current status of the experiment, the projected schedule, and its physics capabilities.

Installation and commissioning of the CDMSII experiment at Soudan

In the past year and a half, the Cryogenic Dark Matter Search (CDMS) collaboration has been active at the Soudan mine in installing a system for running ZIP detectors that will be used to search for dark matter in the form of Weakly Interacting Massive Particles. Presently, there is an operating cryogenic system, working electronics, a functional data acquisition and analysis system, passive shielding, an active muon veto, and 12 ZIP detectors. Six of the 12 ZIP detectors have been tested in situ and are fully operational with acceptable noise profiles. CDMS is in the process of commissioning the experiment and expects to be making a background measurement by the end of summer 2003.

MINOS: THE PHYSICS PROGRAM AND THE CONSTRUCTION STATUS

The MINOS experiment will study muon neutrino oscillations in the range of parameter space implied by the measurements with atmospheric neutrinos. The two magnetized toroidal tracking calorimeters, 1 kton at Fermilab and 5.4 kton in the Soudan Mine 735-km away, are constructed out of extruded scintillator strips and use wavelength-shifting and clear fibers read out by multi-anode photomultipliers. The far detector is now more than 3/4 completed and commenced collecting cosmic ray data. The neutrino beamline and the near detector will be finished by the end of 2004. In addition, a calibration detector was also constructed and exposed to the test beams. Over the last two years the entire project has progressed on schedule and budget and with most of the civil construction out of the way the road to this interesting physics program is finally cleared.