An ultra-low background PMT for liquid xenon detectors Akerib, D. S.; Bai, X.; Bernard, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2012, Letnik:
703, Številka:
C
Journal Article
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Results are presented from radioactivity screening of two models of photomultiplier tubes designed for use in current and future liquid xenon experiments. The Hamamatsu 5.6 cm diameter R8778 PMT, ...used in the LUX dark matter experiment, has yielded a positive detection of four common radioactive isotopes: 238U, 232Th, 40K, and 60Co. Screening of LUX materials has rendered backgrounds from other detector materials subdominant to the R8778 contribution. A prototype Hamamatsu 7.6 cm diameter R11410 MOD PMT has also been screened, with benchmark isotope counts measured at <0.4 238U / <0.3 232Th / < 8.340K / 2.0+-0.2 60Co mBq/PMT. This represents a large reduction, equal to a change of x $\frac{1}{24}$ 238U / x $\frac{1}{9}$ 232Th / x $\frac{1}{8}$ 40K per PMT, between R8778 and R11410 MOD, concurrent with a doubling of the photocathode surface area (4.5 cm to 6.4 cm diameter). 60Co measurements are comparable between the PMTs, but can be significantly reduced in future R11410 MOD units through further material selection. Assuming PMT activity equal to the measured 90% upper limits, Monte Carlo estimates indicate that replacement of R8778 PMTs with R11410 MOD PMTs will change LUX PMT electron recoil background contributions by a factor of x $\frac{1}{25}$ after further material selection for 60Co reduction, and nuclear recoil backgrounds by a factor of \times $\frac{1}{36}$. The strong reduction in backgrounds below the measured R8778 levels makes the R11410 MOD a very competitive technology for use in large-scale liquid xenon detectors.
The LUX detector is currently in operation at the Davis Campus at the 4850’ level of the Sanford Underground Research Facility (SURF) in Lead, SD to directly search for WIMP dark matter. Knowing the ...type and rate of backgrounds is critical in a rare, low energy event search, and LUX was designed, constructed, and deployed to mitigate backgrounds, both internal and external. An important internal background are decays of radon and its daughters. These consist of alpha decays, which are easily tagged and are a tracer of certain backgrounds, and beta decays, some of which are not as readily tagged and present a background for the WIMP search. We report on studies of alpha decay and discuss implications for the WIMP search.
The Large Underground Xenon (LUX) experiment Akerib, D. S.; Bai, X.; Bedikian, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2012, Letnik:
704, Številka:
C
Journal Article
Recenzirano
Odprti dostop
The Large Underground Xenon (LUX) collaboration has designed and constructed a dual-phase xenon detector, in order to conduct a search for Weakly Interacting Massive Particles (WIMPs), a leading dark ...matter candidate. The goal of the LUX detector is to clearly detect (or exclude) WIMPS with a spin independent cross-section per nucleon of 2×10-46 cm2, equivalent to ∼1event/100kg/month in the inner 100-kg fiducial volume (FV) of the 370-kg detector. The overall background goals are set to have <1 background events characterized as possible WIMPs in the FV in 300 days of running. This paper describes the design and construction of the LUX detector.
Data acquisition and readout system for the LUX dark matter experiment Akerib, D. S.; Bai, X.; Bedikian, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2011, Letnik:
668, Številka:
C
Journal Article
Recenzirano
Odprti dostop
LUX is a two-phase (liquid/gas) xenon time projection chamber designed to detect nuclear recoils from interactions with dark matter particles. Signals from the LUX detector are processed by ...custom-built analog electronics which provide properly shaped signals for the trigger and data acquisition (DAQ) systems. The DAQ is comprised of commercial digitizers with firmware customized for the LUX experiment. Data acquisition systems in rare-event searches must accommodate high rate and large dynamic range during precision calibrations involving radioactive sources, while also delivering low threshold for maximum sensitivity. The LUX DAQ meets these challenges using real-time baseline sup- pression that allows for a maximum event acquisition rate in excess of 1.5 kHz with virtually no deadtime. This work describes the LUX DAQ and the novel acquisition techniques employed in the LUX experiment.
Neuropathic pain is commonly seen in cancer patients, either as a direct result of the malignancy or as a consequence of the treatment rendered. In recent years, methadone has been utilized in the ...treatment of neuropathic pain because of its additional mechanism of action as an NMDA-receptor antagonist. In this paper we discuss the etiology of neuropathic pain in cancer patients, unique properties of methadone, and prior studies on methadone in this patient population. While methadone has been established as a cheap and effective agent in treating cancer pain, specific studies are needed comparing methadone to other opioids in the management of cancer-related neuropathic pain.
The efficiency of stable gene transfer and expression in NIH3T3 cells has been shown to be significantly enhanced by a brief treatment with the phorbol ester tetradecanoylphorbol 12,13-acetate (TPA) ...immediately following calcium-phosphate transfection. Several lines of evidence indicated that this effect was mediated through protein kinase C activation. These studies were expanded to determine whether this was a consistent and widespread phenomenon among other cell lines. The efficiency of transfection in two other established fibroblast lines, LMtk- and 2A3 3T3, was unaffected by TPA treatment, and primary human foreskin fibroblasts were similarly unaffected. Transfection was inhibited by TPA treatment in the transformed cell lines EJ and HeLa. Protein kinase C enzyme assays indicated that TPA causes a translocation of the enzyme from cytosol to membrane in both NIH3T3 and EJ cells, suggesting that the PKC translocation event does not account for the TPA effect on transfection. The TPA-mediated inhibition of transfection in EJ cells was not blocked by sphingosine, suggesting that this phenomenon is unrelated to PKC activation. The results suggest that TPA treatment may either enhance, inhibit, or have no effect on transfection, depending on the cell line.
The design of effective subunit vaccines requires the inclusion of both B and T cell epitopes. The best mechanism for including both types of epitopes within an Ag is dependent upon how the Ag is ...processed by the APC for presentation to a responsive Th cell. If it is more efficient to process a single molecule for both helper and primary epitopes, than covalent linkage of B cells and T cell epitopes for intramolecular presentation of help would be recommended. If however, separate peptides containing either B or Th cell epitopes could be included within a single complex for the elicitation of intermolecular/intrastructural help, more antigenically diverse structures could be designed. This paper reports that it is possible to generate intermolecular/intrastructural help within an antigenic peptide-phospholipid (PL) complex. These peptide-PL complexes use well defined epitopes from Plasmodium falciparum as Ag. In addition to generating intrastructural help, we have shown that the Ir to these peptide-PL complexes is controlled by Ir genes and is similar to the Ir to the circumsporozoite protein of this pathogen.
For more than a decade our laboratories have been combining concepts in biochemistry, virology, and immunology in order to develop a conceptual basis for vaccine design. Our long-term goals have been ...to construct simple and well-defined immunogens that would stimulate specific immune responses in vivo. Using this approach, we hypothesized that it should be possible to define the structural and biochemical parameters of an immunogen that are necessary and sufficient to stimulate designated effector arms of the immune system. Through the use of covalently coupled peptide complexes, we have been able to define minimal requirements for the induction of humoral immune responses (Mannino et al., 1992). This represents a significant advance in eliciting an immune response to peptides, because it requires only peptides and phospholipids in the absence of additional adjuvants. It is different from the previous use of peptides and liposomes since here the peptides are covalently linked to a hydrophobic anchor and integrated into the phospholipid complex, rather than passively adsorbed or encapsulated. The presentation of peptide as part of a peptide-phospholipid complex (in contrast to encapsulation or nonspecific absorption) may be more similar to the natural presentation of an epitope in the context of an in vivo antigenic challenge. This technology also allows us to incorporate B and Th epitopes in a number of forms--as a single peptide, as two peptides in the same liposome, or as a peptide with viral glycoproteins in the same liposome. These data also demonstrate that Th epitopes do not have to be covalently linked to the B-cell epitope in order to provide help for that epitope. The implications of the data reported here are significant for both basic science and applied technologies. In basic science, the peptide-phospholipid complexes are potentially useful for analyzing the cooperative effects of B- and T-cell epitopes in the in vivo immune response. Since the peptide-phospholipid complexes are totally synthetic and highly immunogenic, they may be constructed in any formulation required to answer questions on the roles of B and T cells in promoting an immune response. Furthermore, since the number of antigenic sites is limited only by the number of peptides included in the peptide-phospholipid complexes, these constructs may be useful in producing antisera or monoclonal antibodies to weakly antigenic regions of a large protein, since the lack of antigenic competition should enhance the immunogenicity of these regions. Clinically, this technology will expand the potential for subunit vaccines.
The role that individual determinants play in modulating the immune response of an organism to a pathogen is often obscured because of the complexity of the pathogen. In order to gain a better ...appreciation of the role of individual determinants in the immune response, a pathogen may be dissociated into smaller components, for example peptides representing specific epitopes. These isolated components are often poorly immunogenic and historically have required the use of adjuvants to stimulate antibody production. This report defines the minimal essential requirements for antibody production to a peptide in this system. These are the ability to stimulate both B- and T-helper lymphocytes, anchorage in a phospholipid complex and multivalency within the complex. When these conditions are met, no additional adjuvants are necessary. This procedure has allowed us to identify three distinct T-helper cell epitopes from HIV gp160. In addition, this information has been used to produce a simple, totally synthetic and highly immunogenic preparation for the production of antibodies to peptides.
Proteoliposome delivery vesicles can be prepared by the protein-cochleate method Gould-Fogerite and Mannino, Anal. Biochem. 148 (1985) 15-25; Mannino and Gould-Fogerite, Biotechniques 6 (1988) ...682-690. Proteins which mediate the entry of enveloped viruses into cells are integrated in the lipid bilayer, and materials are encapsulated at high efficiency within the aqueous interior of these vesicles. We describe proteoliposome-mediated delivery of proteins and drugs into entire populations of cells in culture. Material can be delivered gradually by Sendai-virus-glycoprotein-containing proteoliposomes. Alternatively, synchronous delivery to a population can be achieved by exposing cell-bound influenza glycoprotein vesicles briefly to low pH buffer. When DNA is encapsulated, chimeric proteoliposome gene-transfer vesicles (chimerasomes), which mediate high-efficiency gene transfer in vitro and in vivo, are produced. Stable expression of a bovine papilloma virus-based plasmid in tissue-cultured cells, at 100,000 times greater efficiency than Ca.phosphate precipitation of DNA, with respect to the quantity of DNA used, has been achieved. Stable gene transfer and expression in mice has been obtained by subcutaneous injection of chimerasomes containing a plasmid expressing the early region of polyoma virus. In one experimental group, 50% of the mice developed tumors which were shown to express polyoma virus early proteins and contain the transferred DNA. This is the first report of stable gene transfer in animals mediated by a liposome- or proteoliposome-based system.
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