Secondary Γ-rays Research Articles

Evaluation of relative biological effectiveness for diseases of the circulatory system based on microdosimetry.

In the next decade, the International Commission on Radiological Protection (ICRP) will issue the next set of general recommendations, for which evaluation of relative biological effectiveness (RBE) for various types of tissue reactions would be needed. ICRP has recently classified diseases of the circulatory system (DCS) as a tissue reaction, but has not recommended RBE for DCS. We therefore evaluated the mean and uncertainty of RBE for DCS by applying a microdosimetric kinetic model specialized for RBE estimation of tissue reactions. For this purpose, we analyzed several RBE data for DCS determined by past animal experiments and evaluated the radius of the subnuclear domain best fit to each experiment as a single free parameter included in the model. Our analysis suggested that RBE for DCS tends to be lower than that for skin reactions, and their difference was borderline significant due to large variances of the evaluated parameters. We also found that RBE for DCS following mono-energetic neutron irradiation of the human body is much lower than that for skin reactions, particularly at the thermal energy and around 1MeV. This tendency is considered attributable not only to the intrinsic difference of neutron RBE between skin reactions and DCS but also to the difference in the contributions of secondary γ-rays to the total absorbed doses between their target organs. These findings will help determine RBE by ICRP for preventing tissue reactions.

HESS J1809-193: Gamma-Ray Emission by Cosmic Rays from a Past Explosion

The very-high-energy γ-ray source HESS J1809-193 has been detected by the LHAASO and HAWC observatory beyond 100 TeV energy. It is an interesting candidate for exploring the underlying mechanisms of γ-ray production due to the presence of supernova remnants, pulsars, and molecular clouds close to it. We have considered the injection of the energetic cosmic rays from a past explosion, whose reminiscent may be SNR G011.0-00.0, which is located within the extended γ-ray source HESS J1809-193. We explain the multiwavelength data from the region of HESS J1809-193 with synchrotron, inverse Compton, and bremsstrahlung emission of cosmic-ray electrons and secondary γ-ray production in interactions of cosmic-ray protons with the cold protons in the local molecular clouds within a time-dependent framework including the diffusion loss of cosmic rays. The observational data have been modeled with the secondary photons produced by the time-evolved cosmic-ray spectrum assuming the age of the explosion is 4500 yr.

A simulation study of a collimating shield structure in a vertical neutron camera on HL-3

A shield structure with five collimating tubes has been designed in a vertical neutron camera (VNC) on HL-3. Polyethylene is used to screen scattered neutrons, and the lead layer is applied to obstruct the stray X-rays and γ-rays in the environment, as well as secondary γ-rays produced by neutrons interacting with materials. The shielding effect of the structure is studied by using GEANT4. The energy spectra of the incident neutrons and the rate of direct neutrons at the end of five channels are obtained, which demonstrates that the design of shield achieve the criteria as we excepted.

A lower bound on intergalactic magnetic fields from time variability of 1ES 0229+200 from MAGIC and Fermi/LAT observations

Context. Extended and delayed emission around distant TeV sources induced by the effects of propagation of γ ray s through the intergalactic medium can be used for the measurement of the intergalactic magnetic field (IGMF). Aims. We search for delayed GeV emission from the hard-spectrum TeV γ-ray emitting blazar 1ES 0229+200, with the goal of detecting or constraining the IGMF-dependent secondary flux generated during the propagation of TeV γ rays through the intergalactic medium. Methods. We analysed the most recent MAGIC observations over a 5 year time span, and complemented them with historic data of the H.E.S.S. and VERITAS telescopes, along with a 12-year-long exposure of the Fermi/LAT telescope. We used them to trace source evolution in the GeV–TeV band over a decade and a half. We used Monte Carlo simulations to predict the delayed secondary γ-ray flux, modulated by the source variability, as revealed by TeV-band observations. We then compared these predictions for various assumed IGMF strengths to all available measurements of the γ-ray flux evolution. Results. We find that the source flux in the energy range above 200 GeV experiences variations around its average on the 14-year time span of observations. No evidence for the flux variability is found in the 1 − 100 GeV energy range accessible to Fermi/LAT. The non-detection of variability due to delayed emission from electromagnetic cascade developing in the intergalactic medium imposes a lower bound of B > 1.8 × 10−17 G for the long-correlation-length IGMF and B > 10−14 G for an IGMF of cosmological origin. Though weaker than the one previously derived from the analysis of Fermi/LAT data, this bound is more robust, being based on a conservative intrinsic source spectrum estimate and accounting for the details of source variability in the TeV energy band. We discuss implications of this bound for cosmological magnetic fields that might explain the baryon asymmetry of the Universe.

Account of the baryonic feedback effect in γ-ray measurements of intergalactic magnetic fields

Aims. Intergalactic magnetic fields in the voids of the large-scale structure can be probed via measurements of secondary γ-ray emission from γ-ray interactions with extragalactic background light. Lower bounds on the magnetic field in the voids were derived from the nondetection of this emission. It is not clear a priori what kind of magnetic field is responsible for the suppression of the secondary γ-ray flux: a cosmological magnetic field that might be filling the voids, or the field spread by galactic winds driven by star formation and active galactic nuclei. Methods. We used IllustrisTNG cosmological simulations to study the effect of magnetized galactic wind bubbles on the secondary γ-ray flux. Results. We show that within the IllustrisTNG model of baryonic feedback, galactic wind bubbles typically provide energy-independent secondary flux suppression at a level of about 10%. The observed flux suppression effect has to be due to the cosmological magnetic field in the voids. This might not be the case for the special case when the primary γ-ray source has a hard intrinsic γ-ray spectrum that peaks in the energy range above 50 TeV. In this case, the observational data may be strongly affected by the magnetized bubble that is blown by the source host galaxy.

The research of the energy and the fluence of the primary and the secondary γ-ray in the n/γ hybrid radiation field

According to the "little boy" data from the United States, this paper simulates the primary γ-ray of the nuclear explosion and the secondary γ-ray produced by neutron, γ-ray and material interaction. At the same time, the linear attenuation coefficient spectra of 0.001mev to 100mev was calculated. The information was obtained from the point of the source projection of 500 meters to 1km. The results showed in the observation distance: The attenuation of the primary γ-ray energy was in line with the spectral γ-ray passing through the law of shielding the decay of the material. and it showed the phenomenon of the "hardening" of the energy spectrum. The fluence decreases an order of magnitude. The energy of the secondary γ-ray does not showed obvious attenuation laws, and the fluence decreases by about two orders of magnitude. It was worth noting that the average energy of the two kinds of γ-ray was around 2.100 MeV, and the fluence was in the same order of magnitude at 1km from the distance simulation.

HESS J1943+213: An Extreme Blazar Shining through the Galactic Plane

Abstract HESS J1943+213 is a very high energy (VHE; >100 GeV) γ-ray source in the direction of the Galactic plane. Studies exploring the classification of the source are converging toward its identification as an extreme synchrotron BL Lac object. Here we present 38 hr of VERITAS observations of HESS J1943+213 taken over 2 yr. The source is detected with a significance of ∼20 standard deviations, showing a remarkably stable flux and spectrum in VHE γ-rays. Multifrequency Very Long Baseline Array (VLBA) observations of the source confirm the extended, jet-like structure previously found in the 1.6 GHz band with the European VLBI Network and detect this component in the 4.6 and 7.3 GHz bands. The radio spectral indices of the core and the jet and the level of polarization derived from the VLBA observations are in a range typical for blazars. Data from VERITAS, Fermi-LAT, Swift-XRT, the FLWO 48″ telescope, and archival infrared and hard X-ray observations are used to construct and model the spectral energy distribution (SED) of the source with a synchrotron self-Compton model. The well-measured γ-ray peak of the SED with VERITAS and Fermi-LAT provides constraining upper limits on the source redshift. Possible contribution of secondary γ-rays from ultra-high-energy cosmic-ray-initiated electromagnetic cascades to the γ-ray emission is explored, finding that only a segment of the VHE spectrum can be accommodated with this process. A variability search is performed across X-ray and γ-ray bands. No statistically significant flux or spectral variability is detected.

Two-Millimeter Radiation from Stratospheric Nuclear Explosions

The dependence of the spectral power of radiation in the transmission window of air near wavelength 2 mm on the altitude of stratospheric nuclear explosions is investigated. One of the rotational transition lines of nitrogen oxide NO is studied. Calculations of the time dependence of the nitrogen oxide concentration were performed by the method of mathematical modeling of plasma. It is shown that a large amount of nitrogen oxide is formed by explosion γ-rays in the partial-ionization region ahead of the shock wave front; the nitrogen oxide concentration reaches a quasistationary level and remains almost constant for hundreds of microseconds. The quasistationariness is maintained by secondary γ-rays arising in inelastic scattering of explosion neutrons. Estimates of the spectral power of radiation near wavelength 2 mm are obtained. It is shown that at altitude 45 km above the ground the spectral power of the radiation is 105 times greater than for ground-level explosions.

SENSITIVITY OF THE CHERENKOV TELESCOPE ARRAY TO THE DETECTION OF INTERGALACTIC MAGNETIC FIELDS

ABSTRACT Very high energy (VHE; energy E ≳ 100 GeV) γ-rays originating from extragalactic sources undergo pair production with low-energy photons of background radiation fields. These pairs can inverse-Compton-scatter background photons, initiating an electromagnetic cascade. The spatial and temporal structure of this secondary γ-ray signal is altered as the pairs are deflected in an intergalactic magnetic field (IGMF). We investigate how VHE observations with the future Cherenkov Telescope Array, with its high angular resolution and broad energy range, can potentially probe the IGMF. We identify promising sources and simulate γ-ray spectra over a wide range of values of the IGMF strength and coherence length using the publicly available ELMAG Monte Carlo code. Combining simulated observations in a joint likelihood approach, we find that current limits on the IGMF can be significantly improved. The projected sensitivity depends strongly on the time a source has been γ-ray active and on the emitted maximum γ-ray energy.

Detector shielding materials for fast neutron analysis system

Owing to its unique advantage, neutron detection technology has attracted much attention as a method for real-time detection of various elements. However, neutron has strong penetrating ability and can react with the surrounding materials to form a lot of secondary γ-rays; as a result, insufficient detector shielding will have a significant impact on the measurement results. In this paper, a series of experiments were performed to investigate the shielding effect based on the simulation, Three kinds of heavy metals including tungsten, iron and lead, together with four kinds of hydrogen-rich materials concluding polyethylene, paraffin, water and polyethylene with boron were compare for neutron shielding. A detailed set-up of the detector shielding system was described and advantages were discussed.

γ-Ray Emission from the Extreme Blazar 1ES 0229 + 200

Based on the traditional Synchrotron Self-Compton (SSC) model, we consider a secondary γ-ray emission component to an extreme blazar 1ES 0229 + 200 for the multiwavelength radiation. By assuming a suitable electron spectra and Inter-Galactic Magnetic Field (IGMF), we obtained excellent fits to observed spectra of the source. This indicated that the observed excess GeV γ-rays emission can be explained by secondary γ-rays produced through inverse Compton scattering of e± pairs against Cosmic Microwave Background (CMB) photons.

Monte Carlo Simulation of Low-Energy Neutron Attenuation Performance in Boron Steel

In this paper, KTA-304 boron steel for low-energy neutron absorption and attenuation is studied by Monte Carlo method, and compared with the traditional SUS304 stainless steel. Taking into account some factors, such as processing conditions, corrosion resistance, hot ductility, etc. we may reasonably come to the conclusion that 1.13% boron concentration in the steel has a better absorption capacity to the low-energy neutron and can effectively reduce the secondary γ-ray effect, meeting the request of radiation protection with reduced material thickness. Besides, low-energy neutron attenuation coefficient was calculated at different boron concentrations of the steel in different energies, providing a reasonable basis for selecting the neutron shielding materials. The γ-rays released in the neutron capture process were considered, too.

CRPropa 2.0

Recently CRPropa 2.0 has been released as a public software package to simulate the extragalactic propagation of ultra-high energy nuclei. It includes deflections by extragalactic magnetic fields and all relevant interactions with ambient photon backgrounds. Furthermore it provides the possibility to track secondary γ-rays and neutrinos produced in the different reactions. This allows for the investigation of their connection with the primary nuclei, the so called multi-messenger approach. In this paper CRPropa 2.0 is introduced, its different components are discussed and two example applications are presented.

CRPropa 2.0 – A public framework for propagating high energy nuclei, secondary gamma rays and neutrinos

Version 2.0 of CRPropa [CRPropa is published under the 3rd version of the GNU General Public License (GPLv3). It is available, together with a detailed documentation of the code, at https://crpropa.desy.de.] is public software to model the extra-galactic propagation of ultra-high energy nuclei of atomic number Z⩽26 through structured magnetic fields and ambient photon backgrounds taking into account all relevant particle interactions. CRPropa covers the energy range 7×1016<E/eV<A×1022 where A is the nuclear mass number. CRPropa can also be used to track secondary γ-rays and neutrinos which allows the study of their link with the charged primary nuclei – the so called multi-messenger connection. After a general introduction we present several sample applications of current interest concerning the physics of extragalactic ultra-high energy radiation.

Relative intensities of prompt γ-rays from the 35Cl(n,γ)36Cl reaction with thermal neutrons as secondary γ-ray intensity standards

The relative intensities of 16 prompt γ-rays from the 35Cl(n,γ)36Cl reaction with a thermal neutron were precisely determined as secondary γ-ray intensity standards with HPGe detectors. The detection efficiencies were calibrated from 0.2 to 10.8MeV using the standard sources 152Eu and 56Co and the 14N(n,γ)15N reaction. We performed appropriate analyses for the evaluation of doublet peaks, subtraction of mixing with escape γ-rays and other corrections; consequently, the values were determined within 1% accuracy. Relative intensities in the range of 0.7 to 8.6MeV are proposed as reliable secondary standards for 16 γ-rays.

Revised production cross-section of γ-rays in p–p collisions with LHC data for the study of TeV γ-ray astronomy

We present the production cross-section of γ-rays based on data of p–p collisions at the Large Hadron Collider (LHC), revising the previous semi-empirical formula mainly for (1) the inelastic cross-section in p–p collisions, σpp(E0), and 2) the inclusive γ-ray spectrum in the forward region, σpp→γ(E0,Eγ). We find that the previous cross-section gives a significantly softer spectrum than found in the data of LHC. In this paper, we focus our interest mainly upon the LHC forward (LHCf) experiment, giving γ-ray spectra in the very forward region with the pseudo-rapidity η∗≳8.8 in the center of mass system (CMS), which have not been reported so far. We also give the pseudo-rapidity distribution of charged hadrons with -3⩽η∗⩽3 obtained by ALICE and TOTEM experiments, both with LHC. We find that the revised cross-section reproduces quite well the accelerator data over the wide energy range from GeV to 30PeV for projectile protons, corresponding approximately to 100MeV to 3PeV for secondary γ-rays. The production cross-section of γ-rays produced in the forward region is essential for the study of γ-ray astronomy, while not important are those produced in the central region in CMS, and of much less importance in the backward. We discuss also the average transverse momentum of γ-rays, p¯t, and the average inelasticity transferred to γ-rays, k¯γ∗, obtaining that the former increases very slowly with p¯t=100∼220MeV/c for E0=1GeV∼26PeV, and the latter is almost independent of E0, with k¯γ∗≈1/6, while we cannot exclude the possibility of a small increase of k¯γ∗.

A study of the γ-ray flux during the total solar eclipse of 1 August 2008 at Novosibirsk, Russia

In the past, there have been reports of the observation of decrease in the flux of secondary cosmic γ-rays during a total solar eclipse. We have measured the flux of secondary cosmic γ-rays during the total solar eclipse that occurred at Novosibirsk in Russia, on 1 August 2008. Highly sensitive measurements were carried out by using a detector system with built-in redundancy. The system consisted of two independent, large volume NaI(Tl) scintillator detectors for sensitive and reliable measurements. The data display significant variability in the flux of secondary γ-rays in the energy range 50–4600 keV. Just prior to the total solar eclipse a change ∼9% in the flux was observed, followed by a small but steady decrease ∼4% during the eclipse. The temporal variation in the observed flux of γ-rays were found to be nearly identical for the two detectors. The energy dependence of the variation was further studied by binning the yield in three energy ranges, namely, 100–200, 200–400 and 400–4600 keV. The nearly identical time variation observed in the two independent measurements provides confidence that the measured variation is real and not an artifact of the instrumentation. Systematic observations during the future eclipses are required to study this fascinating phenomenon which is not yet understood.

Time of arrival of the first relativistic solar protons to the Earth

The anticoincidence system of the spectrometer onboard the INTEGRAL spacecraft (ACS SPI) is sensitive to primary and secondary γ-rays with energies higher than 150 keV and effectively responds to the arrival of solar protons and electrons. When the flux of primary γ-rays is small, ACS SPI registers the arrival of solar protons much earlier than the network of neutron monitors (NMs). For example, on December 13, 2006, ACS SPI registered the arrival of solar protons approximately 10 min earlier than the CR intensity started increasing on the Earth according to the NM data. However, when the flux of solar γ-rays is sufficiently high, ACS SPI observes the arrival of solar protons simultaneously with NMs (the event of January 20, 2005) or later (October 28, 2003). Found times of arrival of relativistic solar protons to the Earth do not contradict proton acceleration during γ-ray flares.

First results obtained by RUNJOB campaign

We report experimental results obtained by using a wide-gap type emulsion chamber flown in the first Japanese-Russo joint balloon project, called RUNJOB ( RU ssia- N ippon JO int B alloon-program). Two balloons were launched from Kamchatka in July 1995, and both were recovered successfully near the Volga River. The exposure time was 130 hours for the first flight and 168 hours for the second. The mean ceiling altitude, in both flights, was 32 km corresponding to 10 g/cm 2 . Total area of the emulsion chamber was 0.8 m 2 , and the thickness 0.385 and 2.28 collision m.f.p.'s for vertically incident proton- and iron-primaries, respectively. We detected 381 showers using Fuji-#200-type X-ray film; of these 174 showers were due to atmospheric secondary γ-rays, and the rest 207 came from nuclear components. The energy range covers 20∼200 TeV for proton-primary, 3∼30 TeV/nucleon for helium-primary, and 0.7∼5 TeV/nucleon for iron-primary. We give the energy spectra for various elements (proton, helium, …, iron) as well as the all-particle spectrum and the average mass of the cosmic-ray primaries.

Gamma-ray and neutrino flares produced by protons accelerated on an accretion disc surface in active galactic nuclei

We discuss the consequences of almost rectilinear acceleration of protons to extremely high energies in a reconnection region on the surface of an accretion disc that surrounds a central black hole in an active galaxy. The protons produce γ-rays and neutrinos in interactions with the disc radiation as considered in several previous papers. However, in this model the secondary γ-rays can initiate cascades in the magnetic and radiation fields above the disc. We compute the spectra of γ-rays and neutrinos emerging from regions close to the disc surface. Depending on the parameters of the reconnection regions, this model predicts the appearance of γ-ray and neutrino flares if protons take most of the energy from the reconnection region. In contrast, if leptons take most of the energy, they produce pure γ-ray flares. The γ-ray spectrum expected in the case of hadronic cascading is compared with the spectrum observed during the flare in 1991 June from 3C 279. The neutrino flares that should accompany these γ-ray flares may be detected by future large-scale neutrino telescopes sensitive at ∼ 105 TeV.