Annihilation In Flight Of Positrons Research Articles

Photoactivation experiment of 197Au(γ, n) performed with 9.17-MeV γ-ray from 13C(p, γ)14N**Project supported by the National Natural Science Foundation of China (Grant No. 11655003).

High energy γ-ray can be used for nuclear waste transmutation by using the giant dipole resonance (GDR). The photonuclear reaction 197Au(γ, n) is known as a standard for studies on photoactivation experiments. The previous experiments on 197Au(γ, n) have been performed with bremsstrahlung, positron annihilation in flight or laser Compton scattering γ-ray. In this work, a new mono-energetic γ-ray source based on 13C(p, γ)14N reaction is used to measure the cross section of 197Au(, n) and the measured value is compared with the results obtained with other ways.

Positron annihilation in flight: experiment with slow and fast positrons

A novel digital coincidence Doppler broadening (D-CDB) spectrometer was employed for energy resolved investigations of two-quantum annihilation-in-flight (TQAF). The TQAF phenomenon was studied using monoenergetic positrons produced in a slow positron beam and also using fast positrons. Because of a low background the measurements on the slow positron beam could be performed in a close geometry and the TQAF contribution in the two-dimensional gamma ray energy spectra fills a 'bowl-like' area delimited by a hyperbolic curve and a kinematical cut-off determined by the kinetic energy of positrons. With decreasing positron energy the area of TQAF contribution becomes smaller and disappears completely for slow positrons with energies below ~ 100 eV. The measurements with fast positrons were restricted to a limited range of angles between the annihilation gamma rays and the TQAF events contribute to a hyperbolic band in gamma ray energy spectrum.

Photoneutron Cross Sections for Au Revisited: Measurements with Laser Compton Scattering γ-Rays and Data Reduction by a Least-Squares Method

Photoneutron cross section measurements were made for Au in the entire energy range of the (γ,n) channel based on a direct neutron counting with quasi-monochromatic γ-rays produced in inverse Compton scattering of laser photons with relativistic electrons. The data were analyzed by a least-squares method to deduce photoneutron cross sections. The analysis significantly reduced experimental uncertainties compared with those resulting from the photon difference method. The result is compared with the previous data by direct neutron counting with γ-rays produced in positron annihilation in flight and by photoactivation with bremsstrahlung. The present data are in good agreement with the previous data near the neutron threshold, while there remain some discrepancies between the present and the previous data above 10 MeV.

New Experimental Approach to the Detection of Positron Annihilation in Flight Process

Positron annihilation in flight, when mainly positron contributes to the energy and momentum of the annihilating pair, is rarely observed in condensed matter due to its small probability. Additionally, this process does not manifest itself by any characteristic features, which would help in observation. Hence, our knowledge about that process is poor. In the paper we propose the new experimental method which allows us to detect this process. We applied the conventional positron lifetime spectrometer, which after changing photon energy ranges and layout of detectors was suitable for that detection. The first measurements allow us to estimate that in pure aluminum almost 4.76% of all implanted positrons from isotope source Na annihilate in flight.

An undergraduate experiment to test relativistic kinematics using in flight positron annihilation

The basic theoretical tenants of special relativity can be presented in introductory physics courses. However, because special relativistic effects only become apparent at velocities close to the speed of light, there are few experiments at the undergraduate level that involve special relativistic effects. We show that it is possible to experimentally verify the relation E2=p2c2+m02c4 in an undergraduate student laboratory using commercially available equipment. The experiment uses the annihilation of positrons in flight.

Energy-Resolved Positron Annihilation in Flight in Solid Targets

Energy-resolved two-quantum annihilation in flight of positrons with energies ranging from 10 to 71.6 keV was observed. An energy-dispersive two-detector coincidence system was used to observe the sum and difference energies of the {gamma} rays from annihilating positron-electron pairs. For positrons penetrating carbon foils the c/v dependence of the annihilation cross section is confirmed. Spectra obtained from gold-coated carbon foils show evidence of in-flight annihilation with gold M-shell electrons. (c) 1999 The American Physical Society.

Energy spectra of electrons and positrons produced in semi-infinite and infinite water phantoms irradiated by photons with energies up to 1 GeV.

Previous Monte Carlo calculations for the energy spectra of electrons produced in water irradiated by photons are extended to 1 GeV. All of the physical processes believed to be important in the transport of electrons and positrons above 100 keV and photons starting with the ejection of L photoelectrons are considered. The results are presented in tabular form and can be conveniently used to compute kerma in water. The contributions of several physical processes, such as Compton scattering and pair-production to electron spectra, are separately tabulated. The results are compared with those of Todo et al. (1982) for the single interactions of monoenergetic photons. It is found that the inclusion of processes such as multiple Compton scattering, bremsstrahlung production, positron annihilation in flight, Møhiller and Bhabha scattering from electrons and Molière multiple scattering from atomic nuclei make a considerable difference in the inferred electron spectrum in water.

High-energy processes in solar flares

view Abstract Citations (210) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Energy Processes in Solar Flares Murphy, R. J. ; Dermer, C. D. ; Ramaty, R. Abstract A detailed study of high-energy processes in solar flares is reported, including the production of neutrons and pions, and incorporating isobaric and scaling models and a recent compilation of pion production data (Dermer, 1986). The broad-band gamma-ray spectrum resulting from the decay of neutral pions, the bremsstrahlung of positrons and electrons from the decay of charged pions, and the annihilation in flight of positrons is evaluated. Also evaluated is the 0.511 MeV gamma-ray line resulting from the annihilation of the positrons which survive annihilation in flight. Calculations were based on an isotropic, thick-target model using the best available nuclear data and models. Results are compared with extensive observation of the June 3, 1982 flare (10-120 MeV gamma rays), 0.511 and 2.2 MeV line emission, nuclear line emission, high-energy neutrons, and interplanetary charged particles. Publication: The Astrophysical Journal Supplement Series Pub Date: March 1987 DOI: 10.1086/191180 Bibcode: 1987ApJS...63..721M Keywords: Gamma Ray Spectra; High Energy Interactions; Particle Acceleration; Solar Corpuscular Radiation; Solar Flares; Bremsstrahlung; Neutron Spectra; Particle Production; Pions; Positron Annihilation; Radioactive Decay; Solar Atmosphere; Solar Physics; GAMMA RAYS: GENERAL; NUCLEAR REACTIONS; PARTICLE ACCELERATION; SUN: FLARES full text sources ADS |

Inclusive photoproton spectra from 12C at intermediate energies

Inclusive photoproton spectra have been measured at five laboratory angles and two photon energies: 159 and 198 MeV. A quasi-monochromatic photon beam, obtained by positron annihilation in-flight on a liquid hydrogen target, was used and the photon spectrum was measured on-line by a pair spectrometer. The experimental proton spectra are well described by assuming a dominant photon absorption mechanism by np quasi-deuteron pairs in the nucleus, provided that rescattering effects are taken into account.

The development of a Monte Carlo code simulating electron-photon showers and its evaluation by various transport benchmarks

The author has developed a Monte Carlo program which simulates electron-photon showers. The physical processes necessary for accurate calculations have been considered. The slowing down process of electrons consists of two components; continuous energy loss while being deflected and discrete energy loss. The discrete electron reactions included inelastic scattering, bremsstrahlung production and positron annihilation in-flight. All the photon interactions including coherent and incoherent scattering, and the emission of characterisitc X-rays have been taken into account. The shower code has been completed by linking the treatments for electrons and photons. Choosing the optimal parameter set, calculations of miscellaneous transport problems have been carried out for the examination of code. The response functions of photon and electron detectors, the electron transport in an Al foil and the electron depth-dose in water have been compared to the benchmarks obtained with the ETRAN and the EGS. The validity of the developed shower code has been confirmed in the energy range up to 30 MeV.

Double Gamma Decay inCa40andZr90

The rare double gamma decay of the first excited ${0}^{+}$ state in $^{40}\mathrm{Ca}$ and $^{90}\mathrm{Zr}$ has been measured with a segmented $4\ensuremath{\pi}$ NaI detector system, which allows suppression of the perturbing background due to positron annihilation in flight. In both cases the directional correlation of the two photons is found to be asymmetric around 90\ifmmode^\circ\else\textdegree\fi{}, which is explained by an interference of $2E1$ and $2M1$ transitions. The deduced $M1$ quenching factors agree with those from ($e$,${e}^{\ensuremath{'}}$) and ($p$,${p}^{\ensuremath{'}}$) measurements.

Monochromatic nuclear photon scattering experiment

A facility for the measurement of absolute cross sections and angular distributions of photons scattered elastically from nuclei has been set up in the Mainz Linac Laboratory. Quasimonoenergetic photons of 8–100 MeV are produced by the method of the positron annihilation in flight. The scattered photons can simultaneously be detected in four NaI(Tl) spectrometers, which are installed at different scattering angles. The performance of the system and test measurements are discussed.

Continuous Radiation Spectra of Positron Annihilation in Flight

Continuous radiation spectra of positron annihilation in flight were measured with a Ge(Li) detector. Positrons emitted from 22 Na and 68 Ga were stopped in aluminum, copper and lead. Observed spectra were in good agreement with theoretical ones. It was shown that the intensity of annihilation in flight depends on the atomic number of the stopping material and on the positron energy.

Photon Mass Attenuation and Mass Energy-Absorption Coefficients for H, C, N, O, Ar, and Seven Mixtures from 0.1 keV to 20 MeV

coherent and incoherent scattering, atomic photoeffect, and positron-electron pair and triplet production; the energy-absorption cross sections for these interactions are also listed. From this cross-section data base, mass energy-absorption coefficients pen/p, taking into account bremsstrahlung losses and positron annihilation in flight, Compton-scattered and fluorescence photons, and mass-attenuation coefficients p/p, are tabulated for the above elements and for the mixtures: air, water, polystyrene, methyl methacrylate (Lucite, Perspex, Plexiglass, etc.), polyethylene, bakelite, and amber over the range from 0.1 keV to 20 MeV. For application to cavity ionization detector metrology the ratio pen/p in air to that in carbon and to that in the above six remaining mixtures is tabulated over the same energy range. The air and carbon p,/p values and air/carbon ratios are compared with those in ICRU Report 17 and other earlier compilations.

Photoneutron cross sections for 18O

Absolute ( γ, xn) cross sections for 18O were measured up to 33 MeV, using a quasimonoenergetic photon beam from positron annihilation in flight. The cross sections show pronounced structure in particular at energies below the main giant dipole resonance. The (γ, 2n) cross section is large in the whole energy region. The integrated total photoneutron cross section amounts to 0.53 in units of the classcial dipole sum. No pronounced isospin splitting could be observed in the photoneutron decay channel.

A study of the photoneutron reactions in 10B and 11B

Absolute ( γ, xn) cross sections for 10B and 11B were measured up to 35 MeV using a quasi-monoenergetic photon beam from positron annihilation in flight. The experimental cross sections were compared with many-particle shell-model calculations and data from previous bremsstrahlung experiments. The 11B photoneutron cross section is discussed with respect to possible isospin splitting. A systematic review of the photoneutron cross sections of the p-shell nuclei integrated up to about 30 MeV seems to show a strong influence of the α-cluster structure of the target nuclei.

Monte Carlo calculation of the intrinsic gamma ray efficiencies of cylindrical NaI(Tl) detectors

Intrinsic total absorption peak efficiencies, intrinsic efficiencies corresponding to energy losses in the detector material of more than E γ −1.5 MeV, and total intrinsic efficiencies for gamma rays of energy E γ ranging from 0.5 MeV to 16 MeV for a 7.62 cm × 7.62 cm NaI(Tl) detector, were determined using Monte Carlo methods. The calculations were carried out under the assumption of an isotropic point source placed on the symmetry axis of the crystal at a distance of 10 cm from the front face, taking multiple scattering of secondary particles, creation of bremsstrahlung, and positron annihilation in flight into account. The comparison of the calculated data with experimental values shows a very satisfactory agreement in the whole energy region. Some exploratory calculations have therefore been carried out for a 26.67 cm × 33.02 cm NaI(Tl) crystal in the energy region up to 40 MeV, the results of which should be reasonable, despite the high gamma ray energy.

The quasimonoenergetic photon facility at the Giessen 65 MeV electron linear accelerator

The method of the positron annihilation in flight is used to produce quasimonoenergetic photons of variable energy. The photon facility (8–40 MeV) at the Giessen accelerator is described. The positron production, the beam transport, and monitor system are discussed. The absolute calibrations and the 4 π neutron detector used in ( γ, xn)-reactions are explained The performance of the facilities is demonstrated by test measurements of the total photoneutron cross sections σ(γ, Tn) for 12C and 16O.

Photoneutron cross sections for 9Be obtained with quasi-monoenerget1c photons

Absolute ( γ, xn) cross sections for 9Be were measured with monochromatic photons from positron annihilation in flight in the energy range from 17 to 37 MeV. No pronounced structure was found in the cross sections in contrast to recent experiments performed with bremsstrahlung sources. The results are compared with many-particle shell model calculations.

Three-body photodisintegration ofHe3

The photoneutron cross section for $^{3}\mathrm{He}$ has been measured from threshold to 30 MeV using monochromatic photons from positron annihilation in flight. The cross section reaches its maximum of about 0.95 mb at about 15 MeV. Several distinct structures are apparent, some correlated with observed fore-aft asymmetry of the photoneutrons. The integrated cross section is 13.0 MeV mb, and the $\frac{1}{E}$ integrated cross section is 0.77 mb. With reasonable extrapolations to higher energies this is consistent with sum-rule predictions, well within experimental uncertainties. Current theoretical calculations are capable of accounting for the over-all size and shape of the cross section, but not for the fine details of the present measurement.NUCLEAR REACTIONS $^{3}\mathrm{He}(\ensuremath{\gamma},n)$, $E=7.7\ensuremath{-}30.2$ MeV; measured $\ensuremath{\sigma}(E)$, fore-aft photoneutron asymmetry with monoenergetic photons.