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A potential method for mass estimation of shielded special nuclear materials (SNM) is proposed. The method uses fast and epithermal neutrons, generated by an external pulsed neutron source, to induce fission in SNM. The subsequent β-delayed γ-rays and neutrons, emitted by the fission products, are measured simultaneously by two 3He slab detectors and a coaxial high purity germanium (HPGe) detector, located around the tested material. Measuring simultaneously both, β-delayed γ-rays and neutrons measurement, offers improved sensitivity for fissile materials detecting. Laboratory examination of the method was performed in the Pulsed Neutron Interrogation Test Assembly (PUNITA), using CBNM (Central Bureau for Nuclear Measurements) samples of Uranium.

Low-level radioactive surface-contamination measurements require lightweight, large-area, and high-efficiency detectors. In the previous work, we utilized wavelength shifting (WLS) fibers, coupled to a beta-sensitive plastic scintillator (PS) layer on one side, and to an alpha-sensitive ZnS(Ag) layer on both sides, for detecting both alpha and beta particles. In this work, the main goal was to improve the light collection (maximizing the number of photons reaching the PMT) by optimizing the WLS fibers structure, for getting better signal-to-noise ratio and to minimize the low-energy threshold of the detector. In most cases, improving the light collection mostly influenced the detector resolution. In our case, improving the light collection will improve the detection efficiency by ability to detect more events at low-energy spectrum, which is limited by the noise level. Aiming to improve the scintillation light-collection efficiency, we investigated and compared four different detector configurations. Two of them described in the previous work presents utilization of WLS fibers, with different diameters ( $1~\hbox{mm}\phi $ , $1.5~\hbox{mm}\phi $ ), coupled on the PS. Two other configurations present utilization of WLS fibers ( $1.5~\hbox{mm}\phi $ ) installed into a flat groove on the PS layer, while in one configuration we utilized straight WLS fibers and in the other we utilized bent WLS fibers. It was found that the utilization of WLS fibers in bent configuration gives the highest light-collection efficiency. Additionally, there is improved light collection achieved by using WLS fibers with wider diameter ( $1.5~\hbox{mm}\phi $ ), which maximizes the capture fraction. Additionally, since ZnS(Ag) and PS have different decay times (200 ns and 2.4 ns, respectively), we were able to separate alpha from beta events. An algorithm script was developed to calculate the full width at half maximum (FWHM) of each pulse and a histogram was generated of the FWHM values for the pulse shape discrimination (PSD). Efficient PSD was achieved for alpha energies above 100 keV with figure of merit (FOM) of 1.92. GEANT4 simulation was carried out and compared with experimental results. The results of both were matched, showed that the light-collection efficiency from the bent WLS fibers configuration was the best. The simulation results and the experiments, including full description of the detector structure, ionization stage, and the WLS light collection, are presented.

In this paper, a method is presented for the detection of special nuclear materials (SNMs) in shielded containers, which is both sensitive and applicable under field conditions. The method uses an external pulsed neutron source to induce fission in SNM and subsequent detection of the fast prompt fission neutrons. The detectors surrounding the container under investigation are liquid scintillation detectors able to distinguish gamma rays from fast neutrons by means of pulse shape discrimination method (PSD). One advantage of these detectors, besides the ability for PSD analysis, is that the analog signal from a detection event is of very short duration (typically few tens of nanoseconds). This allows the use of very short coincidence gates for the detection of the prompt fission neutrons in multiple detectors, while benefiting from a low background coincidence rate, yielding a low detection limit. Another principle advantage of this method derives from the fact that the external neutron source is pulsed. By proper time gating, the interrogation can be conducted by epithermal source neutrons only. These neutrons do not appear in the fast neutron signal following the PSD analysis, thus providing a fundamental method for separating the interrogating source neutrons from the sample response in the form of fast fission neutrons. This paper describes laboratory tests with a configuration of eight detectors in the Pulsed Neutron Interrogation Test Assembly (PUNITA). Both the photon and neutron signature for induced fission is observed, and the methods used to isolate these signatures are described and demonstrated.

A study of irradiation-induced damage in HAVAR® foils was initiated in order to extract the highest proton dose the foils can sustain. The lattice structure of HAVAR® foils in different metallurgic conditions is presented, as well as visible internal structure, measured by Transmission Electron Microscopy (TEM). Positron Annihilation Spectroscopy (PAS) techniques were used to investigate these foils, and another foil that had been irradiated to the maximal proton dose limit, set by the manufacturer to a total charge of 1 mAh (= 3.6 C). PAS techniques included Doppler broadening (DB) measurement in the SPONSOR beam and lifetime (LT) measurements, both carried at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Both positron spectroscopy methods show clear differences between the investigated foils, with distinguished characteristics for annealed, cold-rolled and irradiated foils. The advantages of using a slow positron beam to study thin foils and defect profiles, over a table-top LT spectrometer, are discussed and demonstrated by the HAVAR® measurements.

HAVAR foils are used in the medical industry as a window material for the production of 18FDG for PET scans. First comparative measurements of HAVAR foils, 25 μm thick, are presented. Three samples were measured: cold rolled (CR), annealed (AN), and proton irradiated (IR). These HAVAR foils were studied by means of Slow Positron Implantation Spectroscopy (SPIS), Positron Annihilation Lifetime spectroscopy (PAL), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). TEM and XRD results show that HAVAR has a fcc structure with a small amount of dislocations in the AN sample and a high density of dislocation nets in the CR sample. The positron diffusion lengths, extracted from the SPIS measurements, are ∼8 nm and ∼66 nm in the CR and AN samples, respectively, in agreement with TEM observations. The results of PAL measurements show significant differences between positron mean lifetimes in the three samples. Differences of ∼50 ps and ∼70 ps were measured between the mean lifetime in the AN sample and these in the CR and IR samples, respectively. GEANT4 simulations were used for the first time in PAL analysis. The simulation method and its benchmarking against previous measurements are described. Lifetime results obtained using conventional PAL analysis and GEANT4 based analysis are consistent within uncertainties for both the HAVAR and a Si reference sample.

Coherent Λπ− production on Pb of 600 GeV Σ− hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width Γ[Σ(1385)−→Σ−γ] s ≈1.385 GeV to be 56±16 μb.

The production of $D_s^-$ relative to $D_s^+$ as a function of $x_F $ with 600 GeV/c $\Sigma^-$ beam is measured in the interval $0.15 < x_F < 0.7$ by the SELEX (E781) experiment at Fermilab. The integrated charge asymmetries with 600 GeV/c $\Sigma^-$ beam ($0.53\pm0.06$) and $\pi^-$ beam ($0.06\pm0.11$) are also compared. The results show the $\Sigma^-$ beam fragments play a role in the production of $D_s^-$, as suggested by the leading quark model., Comment: 11 pages, 5 figures, submitted to Physics Letter B

We report on the measurement of the one-dimensional charged kaon correlation functions using 600~GeV/{\it c} $\Sigma^-$, $\pi^-$ and 540~GeV/{\it c} $p$ beams from the SELEX~(E781) experiment at the Fermilab Tevatron. $K^{\pm}K^{\pm}$ correlation functions are studied for three transverse pair momentum, $k_T$, ranges and parameterized by a Gaussian form. The emission source radii, $R$, and the correlation strength, $\lambda$, are extracted. The analysis shows a decrease of the source radii with increasing kaon transverse pair momentum for all beam types., Comment: 8 pages, 4 figures, 1 table

We present data from Fermilab experiment E781 (SELEX) on the hadroproduction asymmetry for anti-Lambda_c compared to Lambda_c+ as a function of xF and pt2 distributions for Lambda_c+. These data were measured in the same apparatus using incident pi-, sigma- beams at 600 GeV/c and proton beam at 540 GeV/c. The asymmetry is studied as a function of xF. In the forward hemisphere with xF >= 0.2 both baryon beams exhibit very strong preference for producing charm baryons rather than charm antibaryons, while the pion beam asymmetry is much smaller. In this energy regime the results show that beam fragments play a major role in the kinematics of Lambda_c formation, as suggested by the leading quark picture.

Made available in DSpace on 2022-04-28T19:55:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-12-13 The σ- mean squared charge radius has been measured in the space-like Q2 range 0.035-0.105 GeV2/c2 by elastic scattering of a σ- beam off atomic electrons. The measurement was performed with the SELEX (E781) spectrometer using the Fermilab hyperon beam at a mean energy of 610 GeV/c. We obtain (rch2σ- = (0.61 ± 0.12(stat.) ± 0.09(syst.)) fm2. The proton and π- charge radii were measured as well and are consistent with results of other experiments. Our result agrees with the recently measured strong interaction radius of the σ-. © 2001 Elsevier Science B.V. All rights reserved. Ball State University, Muncie, IN 47306 Bogazici University, Bebek 80815 Istanbul Carnegie-Mellon University, Pittsburgh, PA 15213 Centro Brasiliero de Pesquisas Físicas, Rio de Janeiro Fermilab, Batavia, IL 60510 Institute for High Energy Physics, Protvino Institute of High Energy Physics, Beijing Institute of Theoretical and Experimental Physics, Moscow Max-Planck-Institut für Kernphysik, 69117 Heidelberg Moscow State University, Moscow Petersburg Nuclear Physics Institute, St. Petersburg Tel Aviv University, 69978 Ramat Aviv Universidad Autónoma de San Luis Potosó, San Luis Potosi Universidade Federal da Paraiba, Paraíba University of Bristol, Bristol BS8 1TL University of Iowa, IA City, IA 52242 University of Michigan-Flint, Flint, MI 48502 University of Rome 'La Sapienza' and INFN, Rome University of SãoPaulo, São Paulo University of Trieste and INFN, Trieste Imperial College, London SW7 2BZ Boston Consulting Group, Munchen Siemens Medizintechnik, Erlangen Deutsche Bank AG, Eschborn Infineon Technologies AG, München University of Karlsruhe, Karlsruhe Instituto de Fisica da Universidade Estadual de Campinas UNICAMP, SP Universität Freiburg, Freiburg Physik-Department Technische Universität München, Garching Lucent Technologies, Naperville, IL Instituto de Física Teórica da Universidade Estadual Paulista, São Paulo Max-Planck-Institut fur Physik, Munchen SPSS Inc., Chicago, IL University of Alabama at Birmingham, Birmingham, AL 35294, London DOE, Germantown, MD Instituto de Física Teórica da Universidade Estadual Paulista, São Paulo

We report new precision measurements of the lifetimes of the {Lambda}{sup +}{sub c} and D{sup 0} from SELEX, the charm hadroproduction experiment at Fermilab. Based upon 1630 {Lambda}{sup +}{sub c} and 10210 D{sup 0} decays we observe lifetimes of {tau}[{Lambda}{sup +}{sub c}]=198.1{+-} 7.0{+-}5.6 fs and {tau}[D{sup 0}]=407.9{+-}6.0{+-}4 .3 fs .

Total cross sections for Sigma- and pi- on beryllium, carbon, polyethylene and copper as well as total cross sections for protons on beryllium and carbon have been measured in a broad momentum range around 600GeV/c. These measurements were performed with a transmission technique adapted to the SELEX hyperon-beam experiment at Fermilab. We report on results obtained for hadron-nucleus cross sections and on results for sigma_tot(Sigma- N) and sigma_tot(pi- N), which were deduced from nuclear cross sections.

We report the first observation of the Cabibbo-suppressed charm baryon decay Xi(+)(c)-->pK(-)pi(+). We observe 150+/-22+/-5 events for the signal. The data were accumulated using the SELEX spectrometer during the 1996-1997 fixed target run at Fermilab, chiefly from a 600 GeV/c Sigma(-) beam. The branching fractions of the decay relative to the Cabibbo-favored Xi(+)(c)-->Sigma+K-pi(+) and Xi(+)(c)-->Xi(-)pi(+)pi(+) are measured to be B(Xi(+)(c)-->pK(-)pi(+))/B(Xi(+)(c)-->Sigma+K-pi(+)) = 0.22+/-0. 06+/-0.03 and B(Xi(+)(c)-->pK(-)pi(+))/B(Xi(+)(c)-->Xi(-)pi(+)pi(+)) = 0.20+/-0.04+/-0.02, respectively.

The design and performance of the Fermilab E781 (SELEX) Hardware Scattering Trigger (HST) are described. This trigger functioned by distinguishing beam scattering at small angles ( >150 μ rad) from non-interacting beam. Six 50 μ m pitch silicon planes grouped in three ( x , y ) stations, two before and one after the target, were used as the particle detectors. The triggering system involved 1920 channels of readout providing data to the Fast Encoding and Readout System (FERS) with programmable trigger logic processor. The overall system was tested successfully at Fermilab during the 1996-1997 fixed target run. The encoding time of the readout part of the FERS device was 30 ns and the processor decision time was 55 ns. The HST provided an output signal 250 ns after beam traversal of the target.

Gammas from induced fissions were measured and separated into prompt and delayed particles. To this end, a dedicated detector was realized, based on a plastic scintillator, a wavelength shifter fiber and a silicon photomultiplier (SiPM). Results are presented from the interrogation of Special Nuclear Materials (SNM), employing a pulsed neutron generator in the PUNITA graphite moderator incorporating the above detector assembly. The detector response is presented, as well as the sensitivities for prompt and delayed processes within the same experimental setup., JRC.E.8-Nuclear security

The feasibility of using a pulsed neutron generator in a graphite assembly together with a single liquid scintillation detector for the detection of special nuclear materials is investigated. Thermal source neutrons induce fission in fissile material present in the sample. By means of pulse shape discrimination the detector signals from fast fission neutrons are easily identified among the signals from gamma rays and the interrogating thermal neutrons. The method has potential in applications for detection of special nuclear materials in shielded containers., JRC.E.8-Nuclear security

A study of irradiation-induced damage in HAVAR® foils was initiated in order to extract the highest proton dose the foils can sustain. The lattice structure of HAVAR® foils in different metallurgic conditions is presented, as well as visible internal structure, measured by Transmission Electron Microscopy (TEM). Positron Annihilation Spectroscopy (PAS) techniques were used to investigate these foils, and another foil that had been irradiated to the maximal proton dose limit, set by the manufacturer, of 1 mAh. PAS techniques included Doppler Broadening (DB) measurement in the SPONSOR beam and Lifetime (LT) measurements, both carried at Helmholtz Zentrum Dresden-Rossendorf (HZDR). Both positron spectroscopy methods show clear differences between the investigated foils, with distinguished characteristics for annealed, cold-rolled and irradiated foils. The advantages of using a slow positron beam to study thin foils and defect profiles, over a table-top LT spectrometer, are discussed and demonstrated by the HAVAR® measurements.

HAVAR ist ein sehr festes, nicht magnetisches und korrosionsbeständiges Material. In der Medizintechnik wird es als Fenster für Targetkammern zur Produktion von Fluordesoxyglucose (FDG) benutzt. Das in der FDG enthaltene 18F findet Verwendung in der Positronen-Emissions-Tomographie als beta+-Strahler. Die Herstellung des 18F erfolgt dabei durch Protonenbestrahlung von 18O angereicherten Wassertargets entsprechend der Reaktion 18O(p,n)18F. Der wachsende Bedarf an 18FDG erfordert eine intensivere Protonenbestrahlung und damit eine höhere Beanspruchung der HAVAR-Folie als Targetfenster. Für eine Prognose der Beständigkeit der HAVAR-Folien gegenüber Protonenbestrahlung sind Informationen über die Defektstruktur innerhalb der Folien und deren strahlungsinduzierte Veränderungen erforderlich. Deshalb wurden 25 µm dicke HAVAR-Folien sowohl im Ausgangszustand, nach Wärmebehandlung und nach Protonenbestrahlung hinsichtlich der Ausbildung von leerstellenartigen Defekten mittels konventioneller Positronen-Lebensdauermessungen untersucht. Oberflächennahe Untersuchungen bis in Tiefen von ca. 3 µm erfolgten mit einer mono-energetischen Positronenstrahlapparatur durch Messung der Doppler-Verbreiterung der Annihilationslinie. Unterschiede in der Ausbildung der Defekte in Abhängigkeit von der Probenpräparation und –beanspruchung werden dargestellt und mit Ergebnissen, erhalten aus der Transmissions-Elektronenmikroskopie, verglichen.

The HAVAR alloy was originally developed in the late 1940. It is a high strength, nonmagnetic and corrosion resistant material. One of its applications is in the medical industry, in the process of fluorodeoxyglucose (FDG) production for Positron Emission Tomography (PET). The 18F positron emitting isotope is produced by the reaction 18O(p,n)18F in proton cyclotrons. In Soreq NRC, 25 µm foils of HAVAR are used as a window material for the 18O enriched water targets, contained in Al vessels. With the increasing demand for 18F-FDG, an accelerated production rate is planned, with much higher intense proton beam from the new SARAF accelerator at Soreq NRC [1]. This initiated a research effort to study radiation damage in HAVAR that can predict its radiation hardness in the ~2-4 mA SARAF proton beam. We measured four 25 µm thick HAVAR samples: cold rolled (CR), cold rolled and heat treated (HT), annealed (AN) and CR irradiated (IR). The latter was a window taken apart from the target 7 years ago after irradiation in the cyclotron to 10MeV protons of total charge 1mA-h. The first three samples were metallurgically characterized by means of Transmission Electron Microscope (TEM). Positron Annihilation Spectroscopy (PAS) measurements were preformed on all four samples. These included Doppler Broadening (DB) and Positron Annihilation Lifetime ( PAL) measurements in the slow positron beam and in the table top lifetime spectrometer at HZDR [2]. We present preliminary results from these PAS measurements, that show clear differences between the four samples. Positron lifetimes of the HAVAR types change between ~80ps for the annealed sample to ~175ps for the irradiated sample. The positron diffusion length changes from (8 ± 1) nm (CR) to (66 ± 1) nm (AN) in these samples. We also compare between the metallurgical characteristics of the different types of HAVAR measured with TEM to PAS results. The PAS measurements show a clear increase of the mean lifetime with the increase of the density of dislocations in the CR sample compared to that of AN HAVAR foils. [1] L. Weissman et al., "The Status of the SARAF Linac Project", WE102 in Proceedings of Linac 2010, Tsukuba, September 12-17, 2010 [2] W. Anwand, H. - R. Kissener, and G. Brauer, Acta Phys. Pol. A 88, 7 (1995).

1. 1. Recordings of dendritic potentials and sustained potential shifts (SPS) were made from the brain of immobilised frogs during surface tectal electrical stimulation. 2. 2. Single pulses evoked dendritic responses; trains caused decay of dendritic responses on the background of the evoked SPS. 3. 3. The tectal surface SPS declined with distance from the stimulating electrode. 4. 4. The negative surface SPS declined with tectal depth to ca 300 μm, then reversed polarity and increased in amplitude with depth up to 700 μm.

A single-spin asymmetry in the inclusive π 0 production at small x F was measured. In the experiment 40 GeV/c π − mesons were incident on transversely polarized protons and deutrons. An asymmetry of (40–50)% has been revealed in the hard scattering region.