In-flight Positron Annihilation Research Articles

Fully Geant4 compatible package for the simulation of Dark Matter in fixed target experiments

We present the package for the simulation of DM (Dark Matter) particles in fixed target experiments. The most convenient way of this simulation (and the only possible way in the case of beam-dump) is to simulate it in the framework of the Monte-Carlo program performing the particle tracing in the experimental setup. The Geant4 toolkit framework was chosen as the most popular and versatile solution nowadays.Specifically, the package includes the codes for the simulation of the processes of DM particles production via electron and muon bremsstrahlung off nuclei, resonant in-flight positron annihilation on atomic electrons and gamma to ALP (axion-like particles) conversion on nuclei. Four types of DM mediator particles are considered: vector, scalar, pseudoscalar and axial vector. The total cross sections of bremsstrahlung processes are calculated numerically at exact tree level (ETL).The code handles both the case of invisible DM decay and of visible decay into e+e− (μ+μ− for Z′, γγ for ALP).The proposed extension implements native Geant4 application programming interfaces (API) designed for these needs and can be unobtrusively embedded into the existing applications.As an example of its usage, we discuss the results obtained from the simulation of a typical active beam-dump experiment. We consider 5×1012 100 GeV electrons impinging on a lead/plastic heterogeneous calorimeter playing a role of an active thick target. The expected sensitivity of the experiment to the four types of DM mediator particles mentioned above is then derived. Program summaryProgram Title: DMG4CPC Library link to program files:https://doi.org/10.17632/6m3yhx4ssw.1Licensing provisions: GNU General Public License 3Programming language: c++Nature of problem: The optimal way to simulate Dark Matter production processes in fixed target experiments in most cases is to do it inside the program for the full simulation of the experimental setup and not separately, in event generators. The code that can be easily embedded in such programs is needed. The code should be able to simulate various DM production processes that happen in a thick target, in particular on nuclei, with maximal accuracy.Solution method: We created a Geant4 compatible DM simulation package for this purpose. The choice of this simulation framework is suggested by its popularity and versatility. The code includes the cross sections precalculated at exact tree level for a wide variety of DM particles.

Fluxes and spectra of quasimonochromatic annihilation photons for studying E1 giant resonances in nuclei

The fluxes and spectra of quasimonochromatic photons originating from the in-flight annihilation of positrons interacting with electrons of targets are analyzed in the energy region characteristic of the excitation of E1 giant resonances in nuclei. Targets of small thickness and low atomic number are used. The dependences of the spectra on the energy and angle (and their scatter) for positrons incident to the target, on the collimation angle for photons, and on the target thickness are studied.

Photofission of 238U in the giant-resonance region

Data on cross sections for the reaction 238U(γ,F) in the giant-resonance region were analyzed in connection with the preparation of new experiments aimed at studying 238U photofission—in particular, in beams of photons from in-flight positron annihilation on internal targets of positron storage rings. These data were taken from measurements also performed with annihilation photons but from positron beams external to the accelerators used. The procedures applied in such measurements and based both on processing the multiplicity of detected neutrons and on detecting fission fragments were also analyzed.

Coincidence Doppler Broadening of Positron Annihilation Radiation in Fe

We measured the Doppler broadening annihilation radiation spectrum in Fe, using 22NaCl as a positron source, and two Ge detectors in coincidence arrangement. The two-dimensional coincidence energy spectrum was fitted using a model function that included positron annihilation with the conduction band and 3d electrons, 3s and 3p electrons, and in-flight positron annihilation. Detectors response functions included backscattering and a combination of Compton and pulse pileup, ballistic deficit and shaping effects. The core electrons annihilation intensity was measured as 16.4(3) %, with almost all the remainder assigned to the less bound electrons. The obtained results are in agreement with published theoretical values.

Statistical analysis of the Doppler broadening coincidence spectrum of electron–positron annihilation radiation in silicon

We report a statistical analysis of Doppler broadening coincidence data of electron–positron annihilation radiation in silicon using a 22Na source. The Doppler broadening coincidence spectrum was fit using a model function that included positron annihilation at rest with 1s, 2s, 2p, and valence band electrons. In-flight positron annihilation was also fit. The response functions of the detectors accounted for backscattering, combinations of Compton effects, pileup, ballistic deficit, and pulse-shaping problems. The procedure allows the quantitative determination of positron annihilation with core and valence electron intensities as well as their standard deviations directly from the experimental spectrum. The results obtained for the core and valence band electron annihilation intensities were 2.56(9)% and 97.44(9)%, respectively. These intensities are consistent with published experimental data treated by conventional analysis methods. This new procedure has the advantage of allowing one to distinguish additional effects from those associated with the detection system response function.

Positron Annihilations at the Galactic Center: Generating More Questions Than Answers

The bulge of our Galaxy is illuminated by the 0.511 MeV gamma-ray line flux from annihilations of nonrelativistic positrons. The emission is strongly concentrated at the Galactic Center (GC), in contrast to gamma-ray maps tracing nucleosynthesis (e.g., the 1.809 MeV line from decaying 26 Al) or cosmic ray processes (e.g., the 1–30 MeV continuum), which reveal a bright disk with a much less prominent central region. If positrons are generated at relativistic energies, higher-energy gamma rays will also be produced from inflight annihilation of positrons on ambient electrons. The comparison of the gamma-ray spectrum from inflight annihilation to the observed diffuse Galactic gamma-ray data constrains the injection energies of Galactic positrons to be less than 3 MeV.

Positron Annihilations at the Galactic Center: Stringent Constraint on Positron Injection Energies

The intense 0.511 MeV gamma-ray line emission from the Galactic Center observed by INTEGRAL requires a large annihilation rate of nonrelativistic positrons. The emission is strongly concentrated at the Galactic Center (GC), in contrast to gamma-ray maps tracing nucleosynthesis (e.g., the 1.809 MeV line from decaying 26Al) or cosmic ray processes (e.g., the 1-30 MeV continuum), which reveal a bright disk with a much less prominent central region. If positrons are generated at relativistic energies, higher-energy gamma rays will also be produced from inflight annihilation of positrons on ambient electrons. The comparison of the gamma-ray spectrum from inflight annihilation to the observed diffuse Galactic gamma-ray data constrains the injection energies of Galactic positrons to be less than 3 MeV.

Statistical analysis of the Doppler broadening coincidence spectrum of the electron–positron annihilation radiation in aluminum

We report a new, simplified and more efficient modeling on the statistical analysis of Doppler broadening coincidence data of the electron–positron annihilation radiation in aluminum, when compared with previous works. The Doppler broadening coincidence spectrum was fitted using a model function. The model function included positron annihilation at rest with the conduction band, 2p, 2s and 1s electrons. In-flight positron annihilation was also fitted. The response functions of the detectors included backscattering, combinations of Compton effects, pileup, ballistic deficit and pulse shaping problems. The annihilation intensities obtained in this work were, for the conduction band 94.0(3)%, for the 2p electrons 5.7(3)%, for the 2s electrons 0.29(16)%, for the 1s electrons 0.0126(13)%. The intensity of the in-flight positron annihilation was 0.064(3)%, and the three Fermi cutoff parameters obtained were 6.758(9), 10.013(11) and 15.532(10), in 10 −3 m 0 c units. The obtained results are compared with published data.

Study of the Doppler broadening of positron annihilation radiation in silicon

We report the measurement of Doppler broadening annihilation radiation in silicon, using 22Na as a positron source, and two Ge detectors arrangement. The two-dimensional coincidence energy spectrum was fitted using a model function. The model function included at rest positron annihilation with valence band, 2p, 2s, and 1s electrons. In-flight positron annihilation was also fitted. The detectors response functions included backscattering, and a combination of Compton effects, pileup, ballistic deficit, and pulse shaping problems. The obtained results agree well with the literature.

Doppler broadening of positron annihilation radiation: fitting the coincidence spectrum

The profile of the annihilation radiation in aluminum using positrons from a 22 Na source was observed in a two-HPGe-detectors arrangement. The coincidence photon energy spectrum was fitted using a model function, accounting for both Doppler broadening and detector system response. Intensities of the thermalized positron annihilation with band, 2p, 2s, and 1s electrons, and in-flight positron annihilation were fitted. The binding energies of the 1s, 2s, and 2p electrons and the Fermi cutoff parameters of the band electrons were also fitted.

Study of the electron-positron annihilation coincidence peak two-dimensional pofile

Positron annihilation radiation profi le in aluminum was observed with a pair of Ge detectors in coincidence. 22Na was used as a source of positron and the two-dimensional gamma energy spectrum wasfi tted using a model function. Annihilation components of positron at rest with conduction band, 1s, 2s, and 2p electrons were observed. The in-flight positron annihilation was also observed. The model function also took into account the detector response function, relative effi ciency corrections and the gamma backscattering. Coincidences involving a combination of Compton effect, pileup, ballistic defi cit, and pulse shaping problems were treated as well.

Total cross section measurement of π0 photoproduction near threshold on complex nuclei

Total cross section measurements of π 0 photoproduction have been performed on 4He, C and Ca for photon energies ranging up to 40 MeV above threshold. The experiment utilized tagged in-flight positron annihilation monochromatic photons and an almost 4 π lead-glass π 0 detector. Our results are compared to those of previous experiments and they are discussed in connection with available theoretical predictions.

Charged-pion photoproduction measurement on deuterium in the Δ(1236) region using a quasi-monochromatic photon beam

Abstract Charged-pion photoproduction spectra on hydrogen and deuterium have been measured using an in-flight positron annihilation photon beam. Pions were detected in magnetic spectrometers. The experiment consisted of π ± angular distributions at 300 MeV, and fixed-angle excitation curves at 20° ( π ± ) and 55° ( π ± ) in the photon energy range 300–460 MeV. Experimental data are compared to a calculation by Laget which includes final-state nucleon-nucleon interaction and Pauli correlations. The overall agreement is satisfactory; however, the model slightly overestimates the nucleon-nucleon rescattering contribution.

Recent experimental studies of the total photonuclear cross-sections between 30 and 140 MeV

Recent experimental data concerning the total photonuclear cross-section from 30 to 140 MeV have recently been obtained at the ALS linac of Saclay by means of quasi-monochromatic photons produced by in-flight annihilation of positrons. This total photonuclear cross-section was obtained in the case of heavy nuclei as the sum of all the measured cross-sections for the partial photoneutron decay channels. The integrated cross-section, integrated up to 140 MeV, shows an enhancement factorK≈0.76 above the classicalE1 sum rule. This largeK value is well explained by the effect of the tensor force and the tensor correlations. The dependence of σ(γ, tot;Eγ) upon the energyEγ agrees well with the new quasi-deuteron models.

Fission of Bi induced by a quasi-monochromatic photon beam at energies from 100 MeV to 280 MeV

The photofission yields of Bi induced by the quasi-monochromatic photon beam from in-flight annihilation of positrons of the Frascati linac were measured. The experiment was performed at sixteen different positron energies, from 120 MeV up to 280 MeV, by collecting the annihilation photons at angles 0.5° < θ < 1°. Fission fragments were detected with glass sandwiches. Photofission cross-section values were deduced by means of an appropriate unfolding method.

Photoneutron cross sections ofNi58andNi60

Photoneutron cross sections of $^{58}\mathrm{Ni}$ and $^{60}\mathrm{Ni}$ have been measured, using separated isotopes and nearly monoenergetic photons from in-flight annihilation of positrons. Both ($\ensuremath{\gamma},n$) and ($\ensuremath{\gamma},2n$) cross sections have been obtained; the ($\ensuremath{\gamma},3n$) cross section for both isotopes was found to be essentially negligible up to the highest energy measured, 33.5 MeV. The peak cross section of 27 mb for $^{58}\mathrm{Ni}$ occurs at 17.3 MeV, while for $^{60}\mathrm{Ni}$ the peak cross section of 74 mb occurs at 16.3 MeV. The ($\ensuremath{\gamma},2n$) cross section of $^{58}\mathrm{Ni}$ is small, never exceeding 1.5 mb, whereas in the case of $^{60}\mathrm{Ni}$ the ($\ensuremath{\gamma},2n$) cross section rises to a peak value of just over 10 mb at approximately 24 MeV, where it constitutes over 30% of the total photoneutron cross section. In both nuclei the ($\ensuremath{\gamma},2n$) cross section appears essentially to vanish above 33 MeV, whereas the single-neutron cross sections of both appear to remain nearly constant from about 25 MeV to the maximum measured energy. Considerable structure appears in the total cross section of both nuclei throughout the giant-resonance region. Structure is also evident in the ($\ensuremath{\gamma},2n$) cross sections, particularly in the case of $^{60}\mathrm{Ni}$. Integrated total photoneutron cross sections up to 33.5 MeV were determined to be 286 MeV mb for $^{58}\mathrm{Ni}$ and 704 MeV mb for $^{60}\mathrm{Ni}$. Our results are compared with those from previous photoneutron experiments, and, combined with measured photoproton cross sections, are used to test theoretical predictions based on shell-model calculations.NUCLEAR REACTIONS $^{58,60}\mathrm{Ni}(\ensuremath{\gamma},n)$, ($\ensuremath{\gamma},2n$), $E=12\ensuremath{-}34$ MeV; measured $\ensuremath{\sigma}(E)$; deduced integrated cross sections, symmetry energies. Enriched targets, monoenergetic photons, resolution 75-160 keV.

Pr141(γ,n)Cross Section from Threshold to 24 MeV

The $^{141}\mathrm{Pr}(\ensuremath{\gamma},n)$ cross section was measured from threshold to 24 MeV with a photon beam produced by the in-flight annihilation of positrons. The photon beam resolution was determined to be 1.2% (full width at half maximum) by elastically scattering the $\ensuremath{\gamma}$ rays from the 15.1-MeV level in $^{12}\mathrm{C}$. The ($\ensuremath{\gamma},n$) cross section was found to have a maximum value of \ensuremath{\sim}348 mb and an integrated value up to 24 MeV of 1.72 \ifmmode\pm\else\textpm\fi{} 0.16 MeV b. Within the statistics and the photon resolution of the measurement, the results indicate that there is no structure in the cross section, with the possible exception of a weak bump at approximately 17.5 MeV. The results are compared with previous measurements and with theory; the latter comparison indicates that the widths of states in the dynamic collective theory should be considerably broader than those which have been typically used.

The SLAC monochromatic photon beam

A multi-GeV monochromatic photon beam is operational at SLAC. The energy spectrum consists of a monochromatic part, derived from the in-flight annihilation of positrons, superimposed on the usual thin target bremsstrahlung. The beam has been successfully utilized in the study of photoproduction processes by both bubble chamber and spark chamber techniques.

Measurements of theCu63(γ, n)and (γ, 2n) Cross Sections

The $^{63}\mathrm{Cu}(\ensuremath{\gamma}, n)$ cross section was measured over the energy range from threshold to 25 MeV with a photon beam of 2.0% resolution which was produced by the inflight annihilation of positrons. The ($\ensuremath{\gamma}, n$) cross section was found to have a maximum value of 75\ifmmode\pm\else\textpm\fi{}6 mb at about 17.1 MeV and an integrated value up to 25 MeV of 490\ifmmode\pm\else\textpm\fi{}40 MeV mb. No structure was observed in these measurements or in additional ($\ensuremath{\gamma}, n$) measurements which were made in the region of the peak of the giant resonance with 1.5% $\ensuremath{\gamma}$-ray resolution. The ($\ensuremath{\gamma}, n$) data from the present experiment were combined with the $(\ensuremath{\gamma}, n)+(\ensuremath{\gamma}, pn)$ data from Livermore to obtain the $^{63}\mathrm{Cu}(\ensuremath{\gamma}, pn)$ cross section, which was found to have a maximum value of 15\ifmmode\pm\else\textpm\fi{}4 mb at about 23 MeV and an integrated value up to 25 MeV of 60\ifmmode\pm\else\textpm\fi{}15 MeV mb. In addition, the $^{63}\mathrm{Cu}(\ensuremath{\gamma}, 2n)$ cross section was measured at three representative energies between threshold and 26 MeV. The maximum ($\ensuremath{\gamma}, 2n$) cross section obtained was 10.0\ifmmode\pm\else\textpm\fi{}1.6 mb at 23.7 MeV. The results of the experiments are compared with previous measurements and with theory. A small bump in the $(\ensuremath{\gamma}, n)+(\ensuremath{\gamma}, pn)+(\ensuremath{\gamma}, 2n)$ cross section at about 23 MeV may possibly be attributed to an analog giant resonance.