Double Escape Research Articles

Selection and characterization of human respiratory syncytial virus escape mutants resistant to a polyclonal antiserum raised against the F protein

A human respiratory syncytial virus (HRSV) neutralization escape mutant was obtained after 56 serial passages in the presence of a polyclonal antiserum raised against the F protein. Nucleotide sequence analysis of this escape mutant virus revealed two amino acid substitutions: Asn268Ile and Val533Met. When this virus was allowed to grow in the absence of the anti-F polyclonal serum, only the mutation Asn268Ile was stably maintained. Both the double and single escape mutant viruses lost reactivity with mAbs belonging to antigenic site II of the fusion protein of RSV. Mutation Asn268Ile has already been reported in RS viruses that are resistant to mAbs 47F and 11 and palivizumab (PZ). We have thus identified a novel mutation (Val533Met) in the transmembrane domain of the F protein that was selected under immune pressure.

Immunity to Protozoan Parasites

Immunity to Protozoan Parasites

A Mathematical Approach to Determine Escape Peak Efficiencies of High-Purity Germanium Cylindrical Detectors for Prompt Gamma Neutron Activation Analysis

Determining single-escape (SE), double-escape (DE), and full-energy (FE) peak efficiencies is helpful in prompt gamma-ray neutron activation analysis, in which identifying complicated gamma peaks as well as quantifying spectra is crucial. The FE peak efficiency was measured at the National Institute of Standards and Technology for a closed-end, n-type high-purity germanium (HPGe) cylindrical detector using standard point sources, whereas SE and DE peak efficiencies and the SE-to-DE peak ratio for the HPGe detector were calculated using compact analytical expressions.

Signal modeling of high-purity Ge detectors with a small read-out electrode and application to neutrinoless double beta decay search in Ge-76

The GERDA experiment searches for the neutrinoless double beta decay of76Ge using high-purity germanium detectors enriched in76Ge. The analysis of the signal time structure provides a powerfultool to identify neutrinoless double beta decay events and to discriminate themfrom gamma-ray induced backgrounds. Enhanced pulse shape discriminationcapabilities of Broad Energy Germanium detectors with a small read-outelectrode have been recently reported. This paper describes the full simulationof the response of such a detector, including the Monte Carlo modeling ofradiation interaction and subsequent signal shape calculation. A pulse shapediscrimination method based on the ratio between the maximum current signalamplitude and the event energy applied to the simulated data shows quantitativeagreement with the experimental data acquired with calibration sources. Thesimulation has been used to study the survival probabilities of the decays whichoccur inside the detector volume and are difficult to assess experimentally.Such internal decay events are produced by the cosmogenic radio-isotopes68Ge and 60Co and the neutrinoless double beta decay of76Ge. Fixing the experimental acceptance of the double escape peakof the 2.614 MeV photon to 90%, the estimated survival probabilitiesat Qββ = 2.039 MeV are (86±3)% for 76Geneutrinoless double beta decays, (4.5±0.3)% for the 68Gedaughter 68Ga, and (0.9+0.4−0.2)% for 60Codecays.

A Mathematical Approach to Determine Escape Peak Efficiencies of High-Purity Germanium Cylindrical Detectors for Prompt Gamma Neutron Activation Analysis

Determining single-escape (SE), double-escape (DE), and full-energy (FE) peak efficiencies is helpful in prompt gamma-ray neutron activation analysis, in which identifying complicated gamma peaks as well as quantifying spectra is crucial. The FE peak efficiency was measured at the National Institute of Standards and Technology for a closed-end, n-type high-purity germanium (HPGe) cylindrical detector using standard point sources, whereas SE and DEpeak efficiencies and the SE-to-DEpeak ratio for the HPGe detector were calculated using compact analytical expressions.

A Pulse Shape Analysis technique for the MAJORANA experiment

In order to achieve background count rates sufficiently low so as to allow the observation of rare events such as neutrinoless double beta (0νββ) decay, background suppression techniques are routinely employed. In this paper we present details of a novel Pulse Shape Analysis algorithm, which allows single-site events such as 0νββ decay to be distinguished from multi-site background events in germanium detectors. The algorithm, which is based on the event-by-event χ 2 fitting of experimental signals to a basis data set of unique single-site pulse shapes, has been developed through simulation studies and tested experimentally using a Broad Energy Germanium detector. It is found experimentally that the technique is able to successfully identify and reject 99% of multi-site events in the single escape peak associated with the gamma decay of 208Tl, whilst maintaining a survival probability of 98% for neutrinoless double-beta-decay-like double escape peak events.

Reciprocal recognition of an HLA-Cw4-restricted HIV-1 gp120 epitope by CD8+ T cells and NK cells

The HIV-1 Nef protein selectively downregulates human leukocyte antigen (HLA)-A and HLA-B but not HLA-C molecules on the surface of infected cells. This allows HIV-infected cells to evade recognition by most cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. We investigated the recognition of an HLA-Cw4-restricted HIV-1 gp120 epitope SFNCGGEFF (SF9) and its variant SFNCGGEFL (SL9) by T cells and NK receptors. Recognition of HIV-1 gp120 peptides (SF9 and SL9) by T-cell clones was measured by staining with HLA-Cw4-peptide tetrameric complexes and cytolytic assays using target cell pulsed with either peptides. KIR2DL1 binding to these two peptides was measured using surface plasmon resonance and tetramer staining of an NK cell line. : CTLs could recognize SF9 better than the variant SL9, as shown by both tetramer staining and cytolytic assays. Intriguingly, an HLA-Cw4 tetramer folded with the 'escape' variant SL9 could bind to KIR2DL1 on NK cell lines with higher affinity than HLA-Cw4-SF9. The binding of KIR2DL1 to its ligand results in inhibition of NK cell function. Our results indicate that the HIV-1 gp120 variant peptide SL9 could potentially escape both from NK cell and CTL recognition by increasing its affinity for KIR2DL1 binding. These data suggest that HIV-1 can acquire mutations that are capable of escaping from both CTL and NK cell recognition, a phenomenon we have termed 'double escape'.

Dynamics of the direct double ionization of helium by two XUV photons

As a highly correlated process, direct two-photon double onization of helium represents a very challenging theoretical problem. A wide rande of computational methods have been used to evaluate generalized cross sections. However, despite considerable efforts, a quantitative agreement between all calculations has not been reached. In this contribution, we address several issues regarding the origin of the discrepancies in the total cross section and the behaviour of this cross section close to the sequential regime. Our ab initio calculations are based on the numerical solution of the time-dependent Schrödinger equation by means of a spectral method combined with Jacobi-matrix calculations. This method which, in principle, takes fully into account electron correlations, provides also a consistent physical picture of the double escape mechanism.

Neutron inelastic scattering processes as a background for double-β decay experiments

We investigate several Pb$(n,{n}^{'}\ensuremath{\gamma}$) and Ge$(n,{n}^{'}\ensuremath{\gamma}$) reactions. We measure \ensuremath{\gamma}-ray production from Pb$(n,{n}^{'}\ensuremath{\gamma}$) reactions that can be a significant background for double-\ensuremath{\beta} decay experiments which use lead as a massive inner shield. Particularly worrisome for Ge-based double-\ensuremath{\beta} decay experiments are the 2041-keV and 3062-keV \ensuremath{\gamma} rays produced via Pb$(n,{n}^{'}\ensuremath{\gamma}$). The former is very close to the $^{76}\mathrm{Ge}$ double-\ensuremath{\beta} decay endpoint energy and the latter has a double escape peak energy near the endpoint. We discuss the implications of these \ensuremath{\gamma} rays on past and future double-\ensuremath{\beta} decay experiments and estimate the cross section to excite the level that produces the 3062-keV \ensuremath{\gamma} ray. Excitation \ensuremath{\gamma}-ray lines from Ge$(n,{n}^{'}\ensuremath{\gamma}$) reactions are also observed. We consider the contribution of such backgrounds and their impact on the sensitivity of next-generation searches for neutrinoless double-\ensuremath{\beta} decay using enriched germanium detectors.

THEORETICAL INVESTIGATION OF PULSE SHAPES OF DOUBLE BETA EVENTS IN A 76Ge DETECTOR, THEIR DEPENDENCE ON PARTICLE PHYSICS PARAMETERS, AND THEIR SEPARABILITY FROM BACKGROUND GAMMA EVENTS

For the first time the expected pulse shapes to be observed for neutrinoless double beta events in a big 76 Ge detector have been calculated starting from their Monte Carlo calculated time history and spatial energy distribution. It is shown that with the spatial resolution of a large size Ge detector for the majority of 0νββ events it is not possible to differentiate between the contributions of different particle physics parameters entering into the 0νββ decay process — in the mass mechanism the effective neutrino mass and the right-handed weak current parameters λ, η. It is shown that on the other hand it is possible in a 76 Ge double beta decay experiment to reject a background of larger sizes (high multiplicity) gamma events by selecting low size (low multiplicity) events. First comparison of the theoretical ββ pulses to events from the line observed at3,4Qββ shows very good agreement. It is shown further that a rather good radial position determination of ββ events in the detector is possible. By the same type of calculation it is shown that use of the pulse shapes of the 1592 keV double escape line of the 2614 keV γ-transition from 228 Th for calibrating a neuronal net for search of events of neutrinoless double beta decay should be helpful.

Microscopic calculations of signals of double beta decay in a 76Ge detector and first application to the Heidelberg–Moscow experiment

The identification of signals of neutrinoless double beta decay is a question of extreme interest. Starting from the Monte Carlo calculated time history and spatial energy distribution of neutrinoless double beta events, for the first time the expected pulse shapes to be observed in a big 76Ge detector have been calculated ‘microscopically’, by using the Poisson Superfish code for determination of the field distribution in the detector. It is shown, that for the majority of 0νββ events it is not possible to differentiate between the contributions of different particle physics parameters entering into the 0νββ decay process—in the mass mechanism the effective neutrino mass and the right-handed weak current parameters 〈λ〉, 〈η〉. It is shown, that on the other hand it is possible in a 76Ge double beta decay experiment to reject a background of larger sizes (high multiplicity) gamma events by selecting low size (low multiplicity) events. First application of the theoretical ββ pulses to events from the line observed at Qββ [H.V. Klapdor-Kleingrothaus, I.V. Krivosheina, A. Dietz, et al., Phys. Lett. B 586 (2004) 198; H.V. Klapdor-Kleingrothaus, A. Dietz, I.V. Krivosheina, et al., Nucl. Instrum. Methods A 522 (2004) 371] shows very good agreement. It is shown further, and confirmed by measurements with a collimated source, that a rather good radial position determination of ββ events in the detector is possible. By the same type of calculation it is shown that use of the pulse shapes of the 1592 keV double escape line of the 2614 keV γ-transition from 228Th for calibrating a neuronal net for search of events of neutrinoless double beta decay can be helpful.

THEORETICAL DESCRIPTION OF DOUBLE BETA DECAY TRACKS IN A GERMANIUM DETECTOR AND OF THEIR DEPENDENCE ON PARTICLE AND NUCLEAR PHYSICS — A REVIEW

In this review for the first time a theoretical description of the tracks of events of nuclear double beta decay in a large Ge detector is presented. It is obvious that in principle the shapes and sizes of these tracks — and the corresponding time structure of pulses — depend on particle physics and nuclear physics parameters such as neutrino mass, right-handed current parameters, and nuclear matrix elements. The knowledge of this dependence is of importance, since the key to probe the existence of 0νββ decay beyond observation of a signal at the Q value of the process, Qββ, is the discrimination of ββ events from background γ events (or other events), in almost any double beta decay experiment (see Refs. 2 and 3). In this review Monte-Carlo simulations of tracks of neutrino-accompanied (2νββ) and neutrinoless double beta decay (0νββ) events, and of various kinds of background processes such as multiple and other γ interactions are reported for a large Ge detector. The time history of the evolution of the individual events is followed and the sizes of the events (volumes in the detector inside which the energy of the event is released) are investigated. Effects of the angular correlations of the two electrons in ββ decay, which again depend on the above nuclear and (for 0νββ decay) particle physics parameters, are taken into account and have been calculated for this purpose for the first time on basis of the experimental half-life of 76 Ge and of realistic nuclear matrix elements. It is shown for ββ decay of 76 Ge , that 0νββ events are to a large extent separable from Compton scattering of γ events of the same energy, while double escape peaks of γ-lines show very similar behavior as 0νββ events, and in that sense can be useful for corresponding "calibration" of pulse shapes of the detector. The possibility to distinguish 0νββ events from γ events is found to be essentially independent of the particle physics parameters of the 0νββ process. A brief outlook is given on the potential of future experiments with respect to determination of the particle physics parameters 〈mν〉, 〈λ〉, 〈η〉. It is suggested, that the strategy in future 0νββ research should be, to combine confirmation of the HEIDELBERG-MOSCOW result with determination of the mechanism of the dominating decay, instead of repeating earlier experiments or ideas. The future experiment thus should not use 76 Ge or 136 Xe , but instead 124 Xe .

Dynamics of the helium atom close to the full fragmentation threshold: Double ionization

A complete set of cross sections is presented for photodouble ionization of He at $0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ above the threshold. Special care is taken to clear the asymmetry parameter and the energy differential cross section of any ionization-excitation contribution. As a result, their limiting behaviors for the fully asymmetric partitionings of the excess energy are elucidated, thus shedding light on pending discussions in the field. A reliable scheme follows for computing the fully integrated cross section. Very good agreement is observed between the calculated and measured fully differential cross sections after a detailed reassessment of the experimental normalization procedure. The present findings are compared with the assumptions underlying the Wannier picture of near-threshold double escape.

Suitability of nuclear medicine gamma cameras as gamma spectrometers in the event of a radiological emergency

Nuclear medicine gamma cameras are large area NaI(Tl) scintillation detectors that measure both the position and energy of incident gamma rays. A typical, commercial, large field-of-view (LFOV), gamma camera has about 2000 cm 3 of useful detector volume with an entrance window of 50×40 cm 2 by 1 cm thickness. A 3″×3″ NaI(Tl) detector, by comparison, has 17.4% of the volume and 2.3% of the area of the LFOV gamma camera. A 2002 survey reported 11,700 gamma cameras as being installed in hospitals and clinics in the US. In the event of a radiological emergency, the ability to utilize some of this installed detector capacity would be desirable. This work investigates the feasibility of using the gamma camera as a large area gamma spectrometer for detecting and quantifying isotopes likely to be involved in a radiological emergency caused by dispersion of radioactivity by a so called “dirty bomb.” Monte Carlo modeling was used to analyze detection sensitivity as a function of energy for the camera vs. the 3″×3″ cylinder. For a point source positioned 100 cm from the face of the detector, the ratio of total extrinsic efficiency of the camera to that of the 3″×3″ cylinder varied from 40.3 at 140 keV to 7.3 at 5 MeV. Ratios for extrinsic efficiency of peaks (including the full energy peak, single escape, and double escape peaks) varied from 41.1 at 140 keV to 5.5 at 5 MeV. Modifications that will be required to enable the cameras to function as spectrometers over a wide energy range are described and discussed. Given the large sensitivity advantage, the fact that the camera is shielded on three sides, and that cameras are already present at many locations to where victims of a disaster would be transported, it is desirable that such system capabilities be investigated.

Monte Carlo assessment of soil moisture effect on high-energy thermal neutron capture gamma-ray by 14N

Among many conventional techniques, nuclear techniques have shown to be faster, more reliable, and more effective in detecting explosives. In the present work, neutrons from a 5 Ci Am–Be neutron source being in water tank are captured by elements of soil and landmine (TNT), namely 14N, H, C, and O. The prompt capture gamma-ray spectrum taken by a NaI (Tl) scintillation detector indicates the characteristic photo peaks of the elements in soil and landmine. In the high-energy region of the gamma-ray spectrum, besides 10.829 MeV of 15N, single escape (SE) and double escape (DE) peaks are unmistakable photo peaks, which make the detection of concealed explosive possible. The soil has the property of moderating neutrons as well as diffusing the thermal neutron flux. Among many elements in soil, silicon is more abundant and 29Si emits 10.607 MeV prompt capture gamma-ray, which makes 10.829 MeV detection difficult. The Monte Carlo simulation was used to adjust source–target–detector distances and soil moisture content to yield the best result. Therefore, we applied MCNP4C for configuration very close to reality of a hidden landmine in soil.

Screened Wannier Exponent in Weakly Coupled Plasmas

The plasma screening effect on the ionization threshold law for double electron escape into the continuum of a residual ion is investigated in weakly coupled plasmas. The screened re-normalized electron charge due to the electron-electron interaction and the plasma screening effect is obtained as a function of the Debye length, position, and nuclear charge. The screened Wannier exponent for the double ionization cross section is obtained as a function of the Debye length and nuclear charge. It is found that the plasma screening effect significantly reduces the re-normalized electron charge. It is also found that the screened Wannier exponent slightly increases with increasing the Debye length.

Numerical escape criteria for a symmetric four-body model

Numerical escape criteria is presented for the Caledonian Symmetric Four-Body problem (CSFBP). The numerical experiments show that escapes can be detected very early with the help of the method. Integrating a huge amount of orbits of the symmetric four-body system we found that for the equal mass case the double binary escape, and in the planetary case the single bodies escape are the most likely outcome of the disintegration of the system.

Effect of addition of new oligosaccharide chains to the globular head of influenza A/H2N2 virus haemagglutinin on the intracellular transport and biological activities of the molecule.

The haemagglutinin (HA) of influenza A/H2N2 virus possesses six antigenic sites (I-A to I-D, II-A and II-B), and sites I-A, I-B and I-C are located in the regions corresponding to sites A, B and D on the H3 HA. We demonstrated previously that most escape mutants selected by mAbs to site I-A, I-B or I-C had acquired a new oligosaccharide at position 160, 187 or 131, respectively, but this has never occurred during circulation of A/H2N2 virus in humans. Here, to examine whether the H2 HA has the potential to gain two new oligosaccharides on its tip, 31 double escape mutants were isolated by using a single escape mutant with an oligosaccharide at position 160, 187 or 131 as a parental virus and a mAb to an antigenic site different from that to which the mAb used for selection of the parental virus was directed as a selecting antibody, but there were no mutants with two new oligosaccharides. Glycosylation-site HA mutants containing one to three oligosaccharides at positions 160, 187 and 131 were also constructed and their intracellular transport and biological activities were analysed. The results showed that all of the mutant HAs were transported to the cell surface but exhibited a decrease in both receptor-binding and cell-fusing activities. Thus, influenza A/H2N2 virus may have failed to increase the number of oligosaccharides on the HA because, if this happens, the biological activities of the HA are reduced, decreasing the ability of the virus to replicate in humans.

Software for Calculating Nuclear Reaction Cross Sections

A software package is proposed for determining cross sections of spallation, fission, or fragmentation by activation methods. Various additions have been made to the method, including correction for single and double escape peaks on the areas of the γ lines for the residual nuclei, and for the dead time of the measurement system, with a proposal for the complete identification of all lines of each nuclide observed on the basis of the internal intensity ratios derived from a nuclear database.

Halogen determination in Arctic aerosols by neutron activation analysis with Compton suppression methods

The study of halogens particularly bromine and chlorine in Arctic aerosolshas received a great deal of attention in the past decade in ozone depletionduring polar sunrise studies. Iodine has also been studied as part of geochemicalcycling. We have shown that all three of the above elements can be determinedsimultaneously with very low detection limits using epithermal NAA in conjunctionwith Compton suppression methods. Besides lowering the background considerably,Compton suppression can eliminate or minimize the overlapping peak of the620 keV photopeak arising form the 1642 keV double escape peak of 38Cl interfering with the 616.9 keV photopeak of 79Br(n,γ) 80 Br reaction. Iodine is ideally determined by epithermal NAAbecause of its very good resonance integral cross-section. Although chlorineis usually determined using thermal neutrons via the 37Cl(n,γ) 38Cl reactions, epithermal NAA is still feasible for the Arcticaerosol, since it has a major sea-salt component.