Capabilities of the Gamma-400 Gamma-ray Telescope for Observation of Electrons and Positrons in the TeV Energy Range

The space-based GAMMA-400 gamma-ray telescope will measure the fluxes of gamma rays in the energy range from ∼20 MeV to several TeV and cosmic-ray electrons and positrons in the energy range from several GeV to several TeV to investigate the origin of gamma-ray sources, sources and propagation of the Galactic cosmic rays and signatures of dark matter. The instrument consists of an anticoincidence system, a converter-tracker (thickness one radiation length, 1 X₀), a time-of-flight system, an imaging calorimeter (2 X₀) with tracker, a top shower scintillator detector, an electromagnetic calorimeter from CsI(Tl) crystals (16 X₀) with four lateral scintillation detectors and a bottom shower scintillator detector. In this paper, the capability of the GAMMA-400 gamma-ray telescope for electron and positron measurements is analyzed. The bulk of cosmic rays are protons, whereas the contribution of the leptonic component to the total flux is ∼10⁻³ at high energy. The special methods for Monte Carlo simulations are proposed to distinguish electrons and positrons from proton background in the GAMMA-400 gamma-ray telescope. The contribution to the proton rejection from each detector system of the instrument is studied separately. The use of the combined information from all detectors allows us to reach a proton rejection of up to ∼1 × 10⁴.

     

Low dose production studies of platinum at irradiation temperature of 140 K

An ansatz is developed to find out an analytical expression for energy levels of the anharmonic oscillators, of the typeV(X) =X²/2 + λX2m (m = 2, 3) which is valid for all values ofn and all regimes of parameter space. The procedure is extended to find out an analytical expression for the energy levels of the oscillatorV(X) =X²/2 + λ1X4 + λ₂X⁶. As a practical application, it has been applied to calculate characteristics of radiation emitted due to channeling of relativistic positrons channeled between (100) planes in silicon.     

Observations of Trapped Electrons and Positrons with E > 50 MeV in the Inner Radiation Belt by the PAMELA Magnetic Spectrometer

Geomagnetically trapped electrons and positrons with energy above 50 MeV were observed in PAMELA experiment on board Resurs DK satellite. The instrument consists of magnetic spectrometer, imaging electromagnetic calorimeter, time-of-flight system, anticoincidence and neutron detectors that provide unique particle identification and background rejection. PAMELA was collecting data since June 2006 till January 2016. The satellite orbit with initial altitude 350–600 km and inclination 70° crosses the inner radiation belt in South Atlantic Anomaly at L-shell ∼1.2. The trapped electrons and positrons were selected on the basis of a trajectory simulation in the Earth magnetic field. Features of the energy spectra of electrons and positrons at low energies are analyzed.

     

Low temperature electron irradiation of tellurium

Abstract

Tellurium single crystal samples with a hole concentration of 3 × 10¹⁴/cm² were irradiated at 10 K with electrons with an energy of 0.6 and 1 MeV. In the range investigated resistivity and Hall-coeficient R_H both decreased linearly with the integrated electron flux. The hole generation rate was 0.09 cm^?1 and 0.47 cm^?1 for 0.6 and 1 MeV electrons, respectively. The Hall-mobility R_H/P increased with irradiation.

Annealing of the radiation damage by raising the temperature clearly revealed three recovery stages in the resistivity- and Hall-data. At 180K p and R_H returned to their pre-irradiation values. The original Hall-mobility was already restored close to 90 K.

A more detailed study of the first recovery stage, which occurs at about 50 K, revealed an activation energy of 170±40meV. It is most likely, that the observed lattice defects are Frenkel-defects. There are indications, that the point defects interact with dislocations.     

Production of intense positron beams at the VEPP-5 injection complex

A source of positrons allowing 5 × 10⁸ positrons accelerated to the energy of 70 MeV to be produced per pulse has been developed. The process of electron-positron pair production in an electromagnetic shower is used for production of positrons. The electromagnetic shower is generated in a tantalum target by a beam of 2 × 10¹⁰ electrons with energy 270 MeV. A high efficiency of positron collection (positron yield Y ≈ 0.1 GeV^?1) is ensured by a unique design of the matching device.     

Positron studies of hydrogen-defect interactions in proton irradiated molybdenum

Molybdenum single crystals are irradiated at 20 K with 6 MeV protons. The radiation damage and lattice defect annealing is studied by positron lifetime spectroscopy in the temperature range from 15 to 720 K. Loss of vacancies due to recombination with mobile interstitials is observed at 40 K (Stage I) in agreement with resistivity measurements. This is the first time Stage I is observed by positrons below 77 K. The implanted hydrogen decorates the vacancies around 100 K, which is consistent with a hydrogen migration energy in molybdenum:E _M ^H = 0.3–0.4 eV. Clustering of spatially correlated vacancies takes place in a wide temperature region below the usual vacancy clustering stage (Stage III). Stage III is observed at rather low temperatures (400–480 K) due to the very high vacancy concentration. Hydrogen bound to vacancies and vacancy clusters is released above 540 K, which puts an upper limit to the hydrogen binding energy:E _B ^H 1.4 eV. The present work emphasizes the advantage of employing a vacancy sensitive technique to study hydrogen in metals, where its intrinsic solubility is low. In such metals (as molybdenum) both the effective solubility and the effective mobility of hydrogen are strongly influenced by the presence of vacancies.     

Intense source of slow positrons from pulsed electron accelerators

A pulsed LINAC is used for pair production in a tantalum target of 2.5 radiation lengths in an energy range from 80 to 260 MeV. Several well-annealed tungsten vanes are placed immediately behind the target and thermalize a small fraction of the fast positrons. The slow positrons are extracted from the target region and magnetically guided over a distance of 17 m to the detector at the end of an S-shaped solenoid. Two Nal detectors with well-known detection efficiency are used to register the 511 keV annihilation-rays. To reduce pile-up effects 50 mm of Pb were placed in front of the detectors. At an average electron current of 1 A we could detect about 10⁷ slow positrons per second. The positron yield is proportional to the electron current, and shows an increase with the electron energy for our target. The positron energy distribution has a FWHM of 1.8 eV.     

A study of the effect of gamma and laser irradiation on the thermal,optical and structural properties of CR-39 nuclear track detector

A comparative study of the effect of gamma and laser irradiation on the thermal, optical and structural properties of the CR-39 diglycol carbonate solid state nuclear track detector has been carried out. Samples from CR-39 polymer were classified into two main groups: the first group was irradiated by gamma rays with doses at levels between 20 and 300 kGy, whereas the second group was exposed to infrared laser radiation with energy fluences at levels between 0.71 and 8.53 J/cm². Non-isothermal studies were carried out using thermogravimetry, differential thermogravimetry and differential thermal analysis to obtain activation energy of decomposition and transition temperatures for the non-irradiated and all irradiated CR-39 samples. In addition, optical and structural property studies were performed on non-irradiated and irradiated CR-39 samples using refractive index and X-ray diffraction measurements. Variation in the onset temperature of decomposition T _o, activation energy of decomposition E _a, melting temperature T _m, refractive index n and the mass fraction of the amorphous phase after gamma and laser irradiation were studied.

It was found that many changes in the thermal, optical and structural properties of the CR-39 polymer could be produced by gamma irradiation via degradation and cross-linking mechanisms. Also, the gamma dose has an advantage of increasing the correlation between thermal stability of the CR-39 polymer and bond formation created by the ionizing effect of gamma radiation. On the other hand, higher laser-energy fluences in the range 4.27–8.53 J/cm² decrease the melting temperature of the CR-39 polymer and this is most suitable for applications requiring molding of the polymer at lower temperatures.     

Spatial distribution of albedo particles on altitudes ∼500 km

Spatial distributions of energetic charged particles, neutrons and gamma rays at altitude 500 km (below the radiation belts of the Earth), obtained by the measurements of two apparatuses on board the Intercosmos-17 satellite, are presented. The latitudinal dependences, [i.e. the variation of flux with vertical cut-off rigidity of the measurement point], for neutrons (E _n = 1 –30 MeV), gamma rays (E =0·15–6 MeV), secondary electrons (E _e > 100 MeV) and for primary protons coming from the west and the east, respectively, are given. The main characteristic, the ratioN _p/N _e of the counting rate of the particles in the polar regionN _p(R_vert< <0·1 GeV/c) and on the equatorN _e(R_vert > 16 GeV/c), is obtained for the various types of particles. This value is 10 for neutrons, 3.7 for gamma rays, 1·8 for electrons, 11 for protons in westward direction, 10 for protons in eastward direction. The latitude profile of neutrons and gamma rays is in a good agreement with calculations assuming their production by nuclear reactions of primary cosmic rays with nuclei of the atmosphere. The weakening of rigidity dependence of protons coming from east in comparison with those coming from the west, is interpreted as the cause of additional proton albedo flux. The equality of albedo electron fluxes (E_e = 100–3500 MeV) from these directions is observed. With the use of the shadowing effect the obtained data on electron-positron component are consistent with the flux of albedo positrons (E_e + > 3·5 GeV) of the value (0·5±0·2) m^–2. s^–1. ster^–1. The possibility of abundance of albedo positrons above electrons at these altitudes for the energy intervalE=0·2÷0·3 GeV is indicated.     

New experimental limits on the probabilities of pauli-forbidden transitions in the <Superscript>12</Superscript>C nucleus from data obtained with the borexino detector

The Pauli exclusion principle was tested for nucleons in the ¹²C nucleus by using data from the Borexino detector. The approach used consisted in seeking photons, neutrons, and protons, as well as electrons and positrons, emitted in the Pauli-forbidden transitions of nucleons from the 1P _3/2 shell to the filled 1S _1/2 shell. Owing to a uniquely low background level in the Borexino detector and its large mass, the currently most stringent experimental limits were obtained for the probabilities and relative intensities of Pauli-forbidden transitions for the electromagnetic, strong, and weak channels.     

Monte Carlo calculation of electron spectra produced in water phantoms by 20 keV-1 GeV photons

Abstract

A Monte Carlo calculation for the energy spectra of electrons and positrons produced in infinite and semiinfinite water phantoms by photons ranging in energies from 20 keV to 1 GeV are presented. The dominant processes considered are the photoelectric effect, Auger effect, Compton effect, pair, and triplet production. Bremsstrahlung produced by electrons and positrons with energies greater than 1 MeV is also included. The effect of multiple Compton scattering, not considered in the earlier calculation, for the infinite phantom for photon energies higher than 2 MeV has been incorporated. For a semi-infinite phantom, multiple Compton scattering and backscattering through the top are considered. The results are compared with the earlier calculations for the first-collision spectrum. It is found that the inclusion of multiple Compton scattering significantly increases the average number of electrons/cm³ per photon/cm² at all energies considered whereas bremsstrahlung reduces the number of high energy electrons and produces more low energy electrons in the spectrum.     

199Hg+光频标的黑体辐射频移

光学频率标准会受到环境温度的黑体辐射影响发生频移,进而影响其准确度. 本文估算了¹⁹⁹Hg⁺的超精细能级5d¹⁰6s²S_1/2 (F=0)和5d⁹6s^{2 2}D_5/2 (F=2)的极化率,得到了室温(300 K)下黑体辐射引起的相对频移为-5.4×10^-17, 最后讨论了低温环境下黑体辐射对¹⁹⁹Hg⁺光频标的影响.     

On The Contribution of the P and D Partial-Wave States to the Binding Energy of the Triton in the Bethe-Salpeter-Faddeev Approach

The influence of the partial-wave states with nonzero orbital moment of the nucleon pair on the binding energy of the triton T(nnp) in the relativistic case is considered. The relativistic generalization of the Faddeev equation in the Bethe-Salpeter formalism is applied. Two-nucleon t matrix is obtained from the Bethe-Salpeter equation with separable kernel of nucleon-nucleon interaction of the rank one. The kernel form factors are the relativistic type of the Yamaguchi functions. The following two-nucleon partial-wave states are considered: ¹S₀, ³S₁, ³D₁, ³P₀, ¹P₁, ³P₁. The system of the integral equations are solved by using the iteration method. The binding energy of the triton and three-nucleon amplitudes are found. The contribution of the P and D states to the binding energy of triton is given.

     

An identification method of positron production in laser beam interaction with targets

A simple electromagnetic transport system was constructed to identify very rare positrons produced in a powerful laser beam interaction with a target. Testing experiments were carried out with CO₂-laser (10¹² W/cm²) beam pulses (τ=50 ns,f=0.01 Hz) focused on the copper target, as well as with a 96 MeV alpha-particle beam irradiated carbon target. The results showed that the developed system could be effectively used for positron identification and evaluation of their energy by means of a time-of-flight method. The computerized system to deal with this problem, together with others related to the power laser beam interaction with targets, has been constructed.     

Electron and positron work functions of Cr(100)

We report measurements of the electron and positron work functions of submonolayer contaminated single crystal surfaces of Cr(100) in ultra high vacuum. The positron work function ø₊ is obtained by measuring the spectrum of slow positrons reemitted by the Cr(100) surface when it is bombarded with keV energy positrons. The electron work function ø_- is measured relative to Al(100) by comparing the target biases at which the slowest emitted positrons are recollected by the target. We obtain ø₊ = ?1.76(10) eV and ø_- = 4.46(6) eV for our Cr(100) surface using the value ø_- = 4.41(3) eV for Al(100) reported by Grepstad, Gartland and Slagsvold. The ø₊ value is in agreement with the ?2.2 eV calculated by Nieminen and Hodges. The positronium work function for Cr implied by these results is ?4.10(10) eV; the positronium negative ion (Ps^-) work function for this surface is calculated to be + 0.37(7) eV. A search for Ps^- showed that at a 90% confidence level less than one in 10³ thermalized positrons reaching the Cr surface are emitted as Ps^-. The slow positron emission spectrum was observed not to change over the 70–300 K range in contrast to recent theoretical predictions.     

Positron annihilation and Hall effect in electron irradiatedn-InP crystals

Positron annihilation and Hall effect inn-InP crystals as a function of electron irradiation up to 1 · 10¹⁹ cm^–2 and post-irradiated isochronal annealing up to 550 °C have been studied. It is concluded that in irradiatedn-InP samples positrons interact with negatively charged acceptor-type defect with level atE _c –0.33 eV, probablyV _In (primary defect). In post-irradiated isochronal annealed (up to 330 °C) samples ofn-InP positron trapping occurs preferably in secondary defects-vacancy clusters, which are formed in the temperature range (150–300 °C). Inn-InP crystals containing radiation induced defects the trapping rate was found to decrease with temperature in the range (300–77) K.     

Laser-cooled positron source

We examine, theoretically, the feasibility of producing a sample of cold (⩽4 K), high-density (≈10¹⁰/cm³) positrons in a Penning trap. We assume⁹Be⁺ ions are first loaded into the trap and laser-cooled to approximately 10 mK where they form a uniform density column centered on the trap axis. Positrons from a moderator are then injected into the trap along the direction of the magnetic field through an aperture in one endcap of the trap so that they intersect the⁹Be⁺ column. Positron/⁹Be⁺ Coulomb collisions extract axial energy from the positrons and prevent them from escaping back out the entrance aperture. Cooling provided by cyclotron radiation and sympathetic cooling with the laser-cooled⁹Be⁺ ions causes the positrons to eventually coalesce into a cold column along the trap axis. We present estimates of the efficiency for capture of the positrons and estimates of densities and temperatures of the resulting positron column. Positrons trapped in this way may be interesting as a source for antihydrogen production, as an example of a quantum plasma, and as a possible means to produce a bright beam of positrons by leaking them out along the axis of the trap. Contribution of the National Institute of Standards and Technology; not subject to US copyright.     

Investigation into the rotational bands of 185Pt with the particle-rotor model

Theoretical calculations have been performed for the ν9/2⁺[624](i _13/2) and ν7/2⁻[503]( f _7/2) bands of ¹⁸⁵Pt in the framework of particle-rotor model. The band properties of signature splitting and configuration mixing have been analyzed. The level energy and signature splitting before the band crossing can be well interpreted by introducing triaxiality. The positive-parity yrast band is proposed to be dominated by the ν9/2⁺[624](i _13/2) component, while the negative-parity band shows strong mixing of ν7/2⁻[503](f _7/2) and ν9/2⁻[505](h _9/2) configurations.