Secondary Photons Research Articles

Application of phase space file secondary computation method in cell dose distribution

Phase space files can store the particle information in one or more planes of radiation particles simulated by the Monte Carlo (MC) method. The secondary calculation method based on phase space files is commonly used to improve the efficiency of MC simulations. However, it is still unclear whether phase space files are applicable for microdosimetric evaluations. In this study, voxel-type and mesh-type monolayer cell population models of different sizes were constructed, and phase space files of secondary electrons generated by photons with different initial energies were obtained using the MC software -- PHITS. The overall average dose caused by the secondary electron phase space files in the region of interest and their microdosimetric distribution within cells were calculated and compared with the results caused by the initial photons under the same geometric conditions. The results showed that the adoption of secondary electron phase space files had almost no impact on the evaluation of macroscopic average dose, with deviations lower than 3% compared to the overall dose caused by the initial photons in the Petri dish. For microdosimetric distributions of the voxel-type model and the two different morphologies of mesh-type cell models, with a macroscopic accumulated dose of 1 mGy, the relative deviation of the cell dose distribution generated by the initial photons and the phase space files was below 10% and the total computation time of phase space files was below 2% of initial photon's. For accumulated doses of 10, 50, and 100 mGy, the relative deviation of the cell nucleus specific energy obtained by secondary electrons and initial photons was greater than 10%. As the size of the culture dish increased, the differences in cell dose distributions also increased, with the root mean square error (RMSE) and coefficient of variation (Cv) of dose distributions both exceeding 30%. In conclusion, this study assessed the effectiveness of the secondary calculation method utilizing phase space files for dose evaluation at the cellular scale. This research offers essential technical support and theoretical foundations for the utilization of this approach in microdosimetric investigations at the cellular level.

Assessment of secondary cancer risks within non-target organs during proton therapy for lung cancer: A Monte Carlo study

Proton therapy is a rapidly progressing modality with a significant impact on lung cancer treatment. However, there are concerns about the subsequent effects of secondary radiation in out-of-field organs. Thus, the present study aimed to evaluate the risk of subsequent secondary cancers within non-target organs during proton therapy for lung cancer. A Monte Carlo model of the International Commission on Radiological Protection (ICRP) 110 male phantom was employed to calculate the absorbed dose associated with secondary photons and neutrons within out-of-field organs for different tumor locations. The risk of induced secondary cancers was then estimated using the Biological Effects of Ionizing Radiation Committee (BEIR) VII and National Council on Radiation Protection and Measurements (NCRP) 116 risk models. Organs close to the tumor, such as the heart, esophagus, thymus, and liver, received the highest equivalent doses. The calculated equivalent doses increased as the tumor depth increased from 4–8 cm to 12–16 cm. The contribution of neutrons to the total equivalent dose was dominant (up to 90%) in most of the organs studied. The calculated risks of secondary cancers were higher in the liver and esophagus compared with other organs when using the BEIR risk model. The maximum risk value was obtained for the left lung when the NCRP 116 risk model was used. Furthermore, the estimated risks of secondary malignancies increased with the tumor depth using both risk models. The calculated risks of radiation-induced secondary cancers were relatively lower than the baseline cancer risks. However, extra attention is warranted to minimize subsequent secondary cancers after proton therapy for lung cancer.

Optical nanotransceivers in photonics

The analogy used in nanophotonics with radiophysics, on the basis of which the notion of an optical nanoantenna was introduced and fruitfully used, is extended to the case of two-step processes with optical excitation of a quantum emitter (scatterer) and subsequent emission of secondary photons and the concept of an “optical nanotransceiver” (transceiver), i. e. a device receiving primary and generating secondary photons is introduced. The nanotransceiver efficiency parameter is introduced, which is defined by the product of the primary radiation intensity factor and the local density of photonic states at the secondary radiation frequency. This nanotransceiver parameter determines scattered radiation intensity enhancement and a maximum possible value of photoluminescence enhancement. The latter is achieved for emitters with low intrinsic quantum yield.

Fluorine Doping Mediated Epitaxial Growth of NaREF4 on TiO2 for Boosting NIR Light Utilization in Bioimaging and Photodynamic Therapy

AbstractBy integrating TiO2 with rare earth upconversion nanocrystals (NaREF4), efficient energy transfer can be achieved between the two subunits under near‐infrared (NIR) excitation, which hold tremendous potential in the fields of photocatalysis, photodynamic therapy (PDT), etc. However, in the previous studies, the combination of TiO2 with NaREF4 is a non‐epitaxial random blending mode, resulting in a diminished energy transfer efficiency between the NaREF4 and TiO2. Herein, we present a fluorine doping‐mediated epitaxial growth strategy for the synthesis of TiO2‐NaREF4 heteronanocrystals (HNCs). Due to the epitaxial growth connection, NaREF4 can transfer energy through phonon‐assisted pathway to TiO2, which is more efficient than the traditional indirect secondary photon excitation. Additionally, F doping brings oxygen vacancies in the TiO2 subunit, which further introduces new impurity energy levels in the intrinsic band gap of TiO2 subunit, and facilitates the energy transfer through phonon‐assisted method from NaREF4 to TiO2. As a proof of concept, TiO2‐NaGdF4 : Yb,Tm@NaYF4@NaGdF4 : Nd@NaYF4 HNCs were rationally constructed. Taking advantage of the dual‐model up‐ and downconversion luminescence of the delicately designed multi‐shell structured NaREF4 subunit, highly efficient photo‐response capability of the F‐doped TiO2 subunit and the efficient phonon‐assisted energy transfer between them, the prepared HNCs provide a distinctive nanoplatform for bioimaging‐guided NIR‐triggered PDT.

Fluorine Doping Mediated Epitaxial Growth of NaREF4 on TiO2 for Boosting NIR Light Utilization in Bioimaging and Photodynamic Therapy.

By integrating TiO2 with rare earth upconversion nanocrystals (NaREF4), efficient energy transfer can be achieved between the two subunits under near-infrared (NIR) excitation, which hold tremendous potential in the fields of photocatalysis, photodynamic therapy (PDT), etc. However, in the previous studies, the combination of TiO2 with NaREF4 is a non-epitaxial random blending mode, resulting in a diminished energy transfer efficiency between the NaREF4 and TiO2. Herein, we present a fluorine doping-mediated epitaxial growth strategy for the synthesis of TiO2-NaREF4 heteronanocrystals (HNCs). Due to the epitaxial growth connection, NaREF4 can transfer energy through phonon-assisted pathway to TiO2, which is more efficient than the traditional indirect secondary photon excitation. Additionally, F doping brings oxygen vacancies in the TiO2 subunit, which further introduces new impurity energy levels in the intrinsic band gap of TiO2 subunit, and facilitates the energy transfer through phonon-assisted method from NaREF4 to TiO2. As a proof of concept, TiO2-NaGdF4 : Yb,Tm@NaYF4@NaGdF4 : Nd@NaYF4 HNCs were rationally constructed. Taking advantage of the dual-model up- and downconversion luminescence of the delicately designed multi-shell structured NaREF4 subunit, highly efficient photo-response capability of the F-doped TiO2 subunit and the efficient phonon-assisted energy transfer between them, the prepared HNCs provide a distinctive nanoplatform for bioimaging-guided NIR-triggered PDT.

Skin Absorbed Dose Coefficients for Human Legs from Beta Radiation as a Function of Height

External exposure to skin from beta-emitter radionuclides following severe reactor accidents or nuclear testing can result in beta burning and other health complications. The skin absorbed dose coefficient (SADC) measures the energy deposition into the skin during such accidents. The U.S. Environmental Protection Agency has published several reports to measure the possible energy deposition into the skin in such accidents. However, the most recent SADC published by Federal Guidance Report (FGR) 12 was computed only at one meter above the contaminated surface. Therefore, it was necessary to develop a model to estimate the absorbed dose coefficients for skin at different heights. In this manuscript, Geant4, a Monte Carlo simulator toolkit, was used to estimate the absorbed dose coefficients from electron sources located on the soil surface with energies ranging from 0.1 to 4 MeV. The energy deposited from primary electrons, secondary electrons, and photons in a 50 µm thick layer of epidermis tissue (Basal Cells Layer) located at a depth of 50 µm from the skin surface was estimated at several discrete heights of human leg phantom. More than 40% of the total energy deposited comes from secondary electrons and photons in energy sources of 0.1 and 0.2 MeV on average, but for higher energies, this percentage is less than 1%, which indicates primary electrons are the main source of the deposited energy in the skin. Furthermore, the results showed the energy deposited into skin closer to the ground was 50–100% higher than the previously estimated doses for 1 m above the ground. The results from Geant4 showed a great correlation (R2 = 0.972) with the FGR 12 data at one meter height, and they were aligned with the published values from FGR 12, which validated the simulation results. Therefore, the calculated dose coefficients for different energy sources and different heights could be used in radiation protection measurements.

Radiosensitization with metallic nanoparticles under MeV proton beams: local dose enhancement.

In addition to specific dosimetric properties of protons, their higher biological effectiveness makes them superior to X-rays and gamma radiation, in radiation therapy. In recent years, enrichment of tumours with metallic nanoparticles as radiosensitizer agents has generated high interest, with several studies attempting to confirm the efficacy of nanoparticles in proton therapy. In the present study Geant4 Monte Carlo (MC) code was used to quantify the increased nanoscopic dose deposition of 50nm metallic nanoparticles including gold, bismuth, iridium, and gadolinium in water upon exposure to 5, 25, and 50MeV protons. Dose enhancement factors, radial dose distributions in nano-scale, as well as secondary electron and photon energy spectra were calculated for the studied nanoparticles and proton beams. The obtained results demonstrated that in the presence of metallic nanoparticles an increase in proton energy leads to a decrease in secondary electron and photon production yield. Additionally, an increase in the radial dose enhancement factor from 1.4 to 16 was calculated for the studied nanoparticles when the proton energy was increased from 5 to 50MeV. It is concluded that the dosimetric advantages of proton beams could be improved significantly in the presence of metallic nanoparticles.

Formation of N–bearing complex organic molecules in molecular clouds: Ketenimine, acetonitrile, acetaldimine, and vinylamine via the UV photolysis of C2H2 ice

Context. The solid-state C2H2 chemistry in interstellar H2O-rich ice has been proposed to explain astronomically observed complex organic molecules (COMs), including ketene (CH2CO), acetaldehyde (CH3CHO), and ethanol (CH3CH2OH), toward early star-forming regions. This formation mechanism is supported by recent laboratory studies and theoretical calculations for the reactions of C2H2+OH/H. However, the analog reaction of C2H2+NH2 forming N-bearing species has been suggested to have a relatively low rate constant that is orders of magnitude lower than the value of C2H2+OH. Aims. This work extends our previous laboratory studies on O-bearing COM formation to investigate the interactions between C2H2 and NH3 ice triggered by cosmic ray-induced secondary UV photons under molecular cloud conditions. Methods. Experiments were performed in an ultra-high vacuum chamber to investigate the UV photolysis of the C2H2:NH3 ice mixture at 10 K. The ongoing chemistry was monitored in situ by Fourier-transform infrared spectroscopy as a function of photon fluence. The IR spectral identification of the newly formed N-bearing products was further secured by a quadrupole mass spectrometer during the temperature-programmed desorption experiment. Results. The studied ice chemistry of C2 H2 with NH2 radicals and H atoms resulting from the UV photodissociation of NH3 leads to the formation of several N-bearing COMs, including vinylamine (CH2CHNH2), acetaldimine (CH3CHNH), acetonitrile (CH3CN), ketenimine (CH2CNH), and tentatively ethylamine (CH3CH2NH2). The experimental results show an immediate and abundant CH2CHNH2 yield as the first-generation product, which is further converted into other chemical derivatives. The effective destruction and formation cross-section values of parent species and COMs were derived, and we discuss the chemical links among these molecules and their astronomical relevance.

New developments in the MCUNED-Plus code for radiation transport and coupled transport-activation computational simulations in accelerator-based facilities

The radiation hazard is one of the major aspects of concern in the design of a facility where it exists a risk of exposure to ionizing radiation. The nuclear analysis for radioprotection purposes requires an accurate description of the radiation fields. This is especially true in accelerator-based facilities where several types of particles are producing the radiation fields. Radiation fields exist during the accelerator operation, but delayed radiation may also be significant for a long time after operation ends. The radiation fields of concern present during the operation are due to the secondary neutrons and photons emitted by the interaction of accelerated particles with the accelerator components (beam leakage) or with the target. The radiation present after the operation is the residual photon field produced by activated materials, these materials being activated by both accelerated particles and secondary neutrons. This residual radiation field is relevant in high intensity accelerators like IFMIF-DONES.In order to address these complex radiation transport simulations, the D1SUNED code has been updated and the new code release renamed as MCUNED-Plus. The new developments include improvements in the light-ion transport like the implementation of a variance reduction for the production of secondary particles, and a new kinematics to reproduce the angular distribution of secondary particles emitted after deuteron breakup reaction. The calculation of the residual photon field in accelerator facility has also been improved by allowing to evaluate both light-ions and secondary neutrons induced shutdown dose rate in a single coupled simulation.

Observations of GRB 221009A by the MAVEN-SEP Instrument at Mars

We report on the detection of the Brightest Of All Time (the BOAT) gamma-ray burst (GRB) 221009A by the MAVEN Solar Energetic Particle (SEP) silicon (Si) detectors. The SEP instrument on board the MAVEN spacecraft at Mars is designed to measure charged particle fluxes and energies. In this work, we show that the SEP Si detectors have detected populations of secondary charged particles and low-energy primary photons from the GRB. Our analysis relies on a series of simplified Geant4 Monte Carlo simulations. We show that electromagnetic and hadronic interactions between the GRB photons and the spacecraft’s passive material and Si detectors produced the detected secondary particles.

Geant4 simulation of secondary photons generated by laser–solid interaction in the presence of external magnetic field

A parametric study of the average energy and scattering angle distribution of Bremsstrahlung x-ray photons generated in over-dense fuel were investigated using the Geant4 simulation toolkit in fast ignition concept. In our simulation, over-dense fuel with the mass ρc∼(300−1000)g.cm−3, and fast ignitor with the intensity I=(1021,1023)W.cm−2 and wavelength λ=(0.35,0.53)μm were considered in the presence of an external magnetic field with the strength Bext=(0−10)kT. Further, for the produced MeV electrons in pre-plasma, two types of energy distribution functions, i.e., exponential and quasi two-temperature, were considered. The simulation results show that by applying an external magnetic field strength Bext∼(1−2)kT, a smooth increase was observed in the x-ray photon average energy and a considerable increase in scattering angle and photon counts in over-dense plasma obtained, so that the peak values mostly obtained for Bext∼1kT. Meanwhile, between the two energy distribution functions for electrons, the optimal average energy and scattering angle values were obtained by considering the quasi-two-temperature energy distribution function and for the fast igniter intensity and wavelength, I=1021W.cm−2,λ=0.35μm respectively, and the fuel density ρc∼300g.cm−3. Finally, regarding to the obtained optimal average photon energy (i.e., Ebph<0.4MeV), which could be considered as minimum photon energy loss and maximum electron penetration toward the fuel, the minimum thickness of lead and concrete shields required to reduce the flux of photons to its one-tenth value were found to be 1.5 cm and 30.7 cm, respectively.

Performance of a first full-size WOM-based liquid scintillator detector cell as prototype for the SHiP Surrounding Background Tagger

As a prototype detector for the SHiP Surrounding Background Tagger (SBT), we constructed a cell (120 cm × 80 cm × 25 cm) made from corten steel that is filled with liquid scintillator (LS) composed of linear alkylbenzene (LAB) and 2,5-diphenyloxazole (PPO). The detector is equipped with two Wavelength-shifting Optical Modules (WOMs) for light collection of the primary scintillation photons. Each WOM consists of an acrylic tube that is dip-coated with a wavelength-shifting layer on its surface. Via internal total reflection, the secondary photons emitted by the molecules of the wavelength shifter are guided to a ring-shaped array of 40 silicon photomultipliers (SiPMs) coupled to the WOM for light detection. The granularity of these SiPM arrays provides an innovative method to gain spatial information on the particle crossing point. Several improvements in the detector design significantly increased the light yield with respect to earlier proof-of-principle detectors. We report on the performance of this prototype detector during an exposure to high-energy positrons at the DESY II test beam facility by measuring the collected integrated yield and the signal time-of-arrival in each of the SiPM arrays. The resulting detection efficiency and reconstructed energy deposition of the incident positrons are presented, as well as the spatial and time resolution of the detector. These results are then compared to Monte Carlo simulations.

On the way to increase osseointegration potential: Sequential SI-ATRP as promising tool for PEEK-based implant nano-engineering

In the search of the ideal bone implant material, surface initiated atom transfer radical polymerization (SI-ATRP) techniques were successfully employed to modify the polyetheretherketone (PEEK) surface with complex architecture nanolayers featuring hydrophilic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) or poly(2-hydroxyethyl methacrylate) (PHEMA) branches. As a result, polymer layers with height up to over 300 nm were synthesized to decrease the water contact angle from 92.8° to 23.0°. In-depth analysis of layer topography, structure and elemental composition realized with atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), time-of-flight secondary ions mass spectroscopy (TOF-SIMS) and X-ray photon spectroscopy (XPS) confirmed successful surface modification. Additionally, to demonstrate the applicability of proposed PEEK functionalization, the biomineralization assay in simulated body fluid (SBF) solution was conducted. The high density of hydroxyl and amine groups in branched polymer brushes structure enhanced the rate of hydroxyapatites (HAp) formation substantially. Compared to untreated PEEK, modification with polymer brushes resulted in the creation of cauliflower-like structures with high specific surface area and Ca/P ratio equal to 1.83–1.87 for PEEK grafted with brushes composed of PHEMA backbone segment and PDMAEMA or PHEMA as block polymer branches (PEEK-g-PHEMA-g-PDMAEMA or PEEK-g-PHEMA-g-PHEMA) after 2 weeks. Finally, the process of the hydroxyapatite formation and increase of the layer thickness in a range of 14 days to 6 weeks of immersion in SBF was thoroughly visualized by scanning electron microscopy (SEM).

The TES-based Cryogenic AntiCoincidence Detector (CryoAC) of ATHENA X-IFU: A Large Area Silicon Microcalorimeter for Background Particles Detection

We are developing the Cryogenic AntiCoincidence detector (CryoAC) of the ATHENA X-IFU spectrometer. It is a TES-based particle detector aimed to reduce the background of the instrument. Here, we present the result obtained with the last CryoAC single-pixel prototype. It is based on a 1 cm2 silicon absorber sensed by a single 2 mm × 1 mm Ir/Au TES, featuring an on-chip heater for calibration and diagnostic purposes. We have illuminated the sample with 55Fe (6 keV line) and 241Am (60 keV line) radioactive sources, thus studying the detector response and the heater calibration accuracy at low energy. Furthermore, we have operated the sample in combination with a past-generation CryoAC prototype. Here, by analyzing the coincident detections between the two detectors, we have been able to characterize the background spectrum of the laboratory environment and disentangle the primary (i.e. cosmic muons) and secondaries (mostly secondary photons and electrons) signatures in the spectral shape.

Effects of thunderstorms electric field on secondary photons of cosmic ray at large high altitude air shower observatory

Large high altitude air shower observatory (LHAASO) is a complex of extensive air shower (EAS) detector arrays, located on the Mt. Haizi (29°21' N, 100°08' E) at an altitude of 4410 m a. s. l., Daocheng, Sichuan Province, China. The information about primary cosmic rays can be obtained by using data from secondary particles measured at LHAASO, with photons make up the majority among these secondary particles. During thunderstorms, the atmospheric electric field can affect secondary charged particles (mainly positrons and electrons), thus changing the information of photons on the ground. In this work, Monte Carlo simulations are performed to investigate the effects of near-ground thunderstorm electric fields on cosmic ray secondary photons at LHAASO. A simple model with a vertical and uniform atmospheric electric field in a layer of atmosphere is used in our simulations. During thunderstorms, the number and energy of photons are found to significantly change and strongly depend on the electric field strength. In a field of –1000 V/cm (below the threshold of the relativistic runaway electron avalanche (RREA) process), the number of photons is increased by 23%. Also, the spectrum of photons softens, and the increased number of photons with energy less than 2 MeV exceeds 29%. In an electric field of –1700 V/cm (above the threshold of the RREA process), the number of photons experiences exponential growth, with an increase of 279%. The spectrum of photons becomes softer than that at –1000 V/cm, and the increased number with energy less than 2 MeV is more than 361%. It is consistent with the theory of RREA. For these phenomena of photons at LHAASO, the main factor is that the number of positrons and electrons are increased due to the acceleration of negative electric field on electrons, with increase of 65% in –1000 V/cm and 992% in –1700 V/cm, and the spectrum of positrons and electrons soften. Newborn free positrons/electrons may undergo bremsstrahlung and deposit part of their energy into photons, causing the change of number and energy of photons to follow roughly the same pattern as positrons and electrons. The simulation results can provide the information for understanding the variations of the data detected by LHAASO during thunderstorms and the acceleration mechanisms of secondary charged particles caused by an atmospheric electric field.

A relook at the GZK neutrino-photon connection: impact of extra-galactic radio background & UHECR properties

Ultra-high energy cosmic rays (UHECRs) beyond the Greisen-Zatsepin-Kuzmin (GZK) cut-off provide us with a unique opportunity to understand the universe at extreme energies. Secondary GZK photons and GZK neutrinos associated with the same interaction are indeed interconnected and render access to multi-messenger analysis of UHECRs. The GZK photon flux is heavily attenuated due to the interaction with Cosmic Microwave Background (CMB) and the Extra-galactic Radio Background (ERB). The present estimate of the ERB comprising of several model uncertainties together with the ARCADE2 radio results in large propagation uncertainties in the GZK photon flux. On the other hand, the weakly interacting GZK neutrino flux is unaffected by these propagation effects. In this work, we make an updated estimate of the GZK photon and GZK neutrino fluxes considering a wide variation of both the production and propagation properties of the UHECR like, the spectral index, the cut-off energy of the primary spectrum, the distribution of sources and the uncertainties in the ERB estimation. We explore the detection prospects of the GZK fluxes with various present and upcoming UHECR and UHE neutrino detectors such as Auger, TA, GRAND, ANITA, ARA, IceCube and IceCube-Gen2. The predicted fluxes are found to be beyond the reach of the current detectors. In future, proposed IceCube-Gen2, Auger upgrade and GRAND experiments will have the sensitivity to the predicted GZK photon and GZK neutrino fluxes. Such detection can put constraints on the UHECR source properties and the propagation effects due to the ERB. We also propose an indirect limit on the GZK photon flux using the neutrino-photon connection for any future detection of GZK neutrinos by the IceCube-Gen2 detector. We find this limit to be consistent with our GZK flux predictions.

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.

Why would you put a flashlight in a dark matter detector?

Silicon photomultipliers (SiPMs) are solid-state, single-photon sensitive, pixelated sensors whose usage for scintillation detection has rapidly increased over the past decade. It is known that the avalanche process within the device, which renders a single photon detectable, can also generate secondary photons which may be detected by a separate device. This effect, known as external crosstalk, could potentially degrade the science goals of future xenon dark matter experiments. In this article, we measure the effect of external crosstalk in a dual-phase, liquid xenon time projection chamber fully instrumented with SiPMs. We then consider the implications for a future xenon dark matter experiment utilizing SiPMs and discuss possible solutions.

Modelling atomic relaxation and bremsstrahlung in the deterministic code STREAM

STREAM, developed by the Computational Reactor Physics and Experiment laboratory (CORE) of the Ulsan National Institute of Science and Technology (UNIST), is a deterministic neutron- and photon-transport code primarily designed for light water reactor (LWR) analysis. Initially, the photon module in STREAM did not account for fluorescence and bremsstrahlung photons. This article presents recent developments regarding the integration of atomic relaxation and bremsstrahlung models into the existing photon module, thus allowing for the transport of secondary photons. The photon flux and photon heating computed with the newly incorporated models is compared to results obtained with the Monte Carlo code MCS. The incorporation of secondary photons has substantially improved the accuracy of photon flux calculations, particularly in scenarios involving strong gamma emitters. However, it is essential to note that despite the consideration of secondary photon sources, there is no noticeable improvement in the photon heating for LWR problems when compared to the photon heating obtained with the previous version of STREAM.

Sterile neutrinos from dark matter: a ν nightmare?

We provide a comprehensive study of observable spectra from dark matter pair-annihilation or decay into sterile (right-handed) neutrinos. This occurs, for instance, in neutrino portal dark matter models, where a sterile neutrino acts as the portal between dark matter and the Standard Model sector. The subsequent decays of right-handed neutrinos produce detectable Standard Model particles, notably photons, positrons, and neutrinos. We study the phenomenology of models where the right-handed neutrino masses are below the GeV scale, as well as models where they are at, or significantly heavier than, the TeV scale. In both instances, and for different reasons, the standard tools, including Monte Carlo simulations, are both inadequate and inaccurate. We present the complete framework to compute the relevant branching ratios for right-handed neutrino decays and the spectra of secondary photons, positrons, and neutrinos for a broad range of dark matter and right-handed neutrino masses. We discuss the general features of such signals, and compare the spectra to standard signals from dark matter annihilation/decay into bottom quarks. Additionally, we provide open source code (The code is available at https://github.com/LoganAMorrison/blackthorn) that can be used to compute such spectra.