FLUKA Monte Carlo Simulations Research Articles

Novel Bragg peak characterization method using proton flux measurements on plastic scintillators.

\textit{Objective}. Bragg peak measurements play a key role in the beam quality assurance in proton therapy. Used as base data for the treatment planning softwares, the accuracy of the data is crucial when defining the range of the protons in the patient, for the sparing of healthy tissue but also for a correct volumetric dose distribution. \textit{Approach} In this paper a protocol to reconstruct a Pristine Bragg Peak exploring the direct correlation between the particle flux and the dose deposited by particles is presented. Proton flux measurements at the HollandPTC and FLUKA Monte Carlo simulations are used for this purpose. This new protocol is applicable to plastic scintillator detectors developed for Quality Assurance applications. In order to obtain the Bragg curve using a plastic fiber detector, a PMMA phantom with a decoupled and moveable stepper was designed. The step phantom allows to change the depth of material in front of the fiber detector during irradiations. The Pristine Bragg Peak reconstruction protocol uses the measured flux of particles at each position and multiplies it by the average dose obtained from the Monte Carlo simulation at each position. \textit{Main Result} The results show that with this protocol it is possible to reconstruct the Bragg Peak with an accuracy of about 470 µm, which is in accordance with the tolerances set by the AAPM. Improvements to the protocol and further applications are also discussed. \textit{Significance} It has the advantage to be able to overcome the quenching problem of scintillators in the high ionization density region of the Bragg peak.
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The FLUKA Monte Carlo simulation of the magnetic spectrometer of the FOOT experiment

The FOOT experiment of INFN is devoted to the measurement of the nuclear fragmentation double differential cross sections useful for the improvement of calculation models adopted in hadrontherapy and radioprotection. A detailed Monte Carlo simulation of the FOOT magnetic spectrometer has been implemented in order to optimize the design and to guide data analysis. This task has been accomplished by means of the FLUKA Monte Carlo code. The input files of the FLUKA simulations are created from the software framework of the experiment, in order to have a consistent generation and description of geometry and materials in both simulation and data analysis. In addition, this ensures the possibility of processing both simulated and real data with the same data analysis procedures. Databases containing specific parameters describing the setup employed in each different data taking campaign are used. A customized event-by-event output of the Monte Carlo code has been developed. It can be read out by the general software framework of FOOT, enabling access to the generation history of all particles in the same event. This output structure therefore gives the possibility to perform a detailed analysis and study of all relevant processes, allowing the detailed tracking reconstruction of all individual particles. Examples of results are presented.

A comparative analysis of the NaI detector response function using GAMOS and FLUKA Monte Carlo simulations

This work aims to study the response function of a 2″×2″ NaI(Tl) scintillation detector using Monte Carlo simulations. A precise mathematical model of the NaI(Tl) scintillator was developed using both FLUKA and GAMOS Monte Carlo simulation software. The photon pulse height distributions of the NaI(Tl) without influence of its energy resolution, obtained with FLUKA and GAMOS codes, were converted into a real NaI(Tl) response function using the necessary conversion process. Spectral characteristics such as full-energy peak efficiency, energy resolution, peak-to-Compton ratio, and peak-to-total ratio were investigated by simulation at different gamma-ray energy obtained from 109Cd, 137Cs, 54Mn, 65Zn, and 60Co sources. The simulated spectra from the GAMOS code were consistent with those generated by the FLUKA code. Additionally, the comparison between simulated results and experimental data demonstrated good agreement. The validation of the computational models used for the NaI(Tl) detector in both FLUKA and GAMOS software was successfully achieved, confirming the accuracy of the simulations in replicating the detector's response.

Photon and thermal neutron shielding behaviors of aluminum calcium fluoroborate glass modified with barium oxide: FLUKA Monte Carlo, XCOM and experimental investigations

The borate glass system was prepared using the melt-quenching method. The XRD was used to confirm the amorphous structure of present samples, the FTIR was utilized to observe vibration modes, and the UV–Vis-NIR spectrophotometer was employed to measure transmittance spectra. The radiation shielding properties were examined by FLUKA Monte Carlo simulation, XCOM programs, and experimental methods. The density increased, while the molar volume decreased as the BaO content increased. For the X-ray and gamma-ray radiation, indicate that the addition of BaO instead of B2O3 improve the shielding properties, while the Σ is decreased for thermal neutron radiation. According to the results, adding BaO enhanced the X-ray and gamma-ray shielding properties. However, adding BaO led to the reduces its ability of shielding the thermal neutrons of the glass samples. These data are expected to be accommodate to considering for any applications which requires high efficiency of photon or thermal neutrons shielding.

Radiation shielding parameterizations of FeSO4, CuSO4, NiSO4 and ZnSO4 Compounds: using (XRF) technique & Monte Carlo FLUKA approach

The mass attenuation coefficient (MAC) for different sulphate compounds can be estimated by using the Energy Dispersive X-ray Fluorescence (EDXRF), also known as X-ray Fluorescence (XRF) technique. The X-ray photons emitted have different energies depending on incident photon energy, atomic weight, and molecular structure of tested material. The excitation energy of the gamma rays source with 59.53 keV was obtained by using 241Am (40 µci). The (MAC) for sulphate compounds of a different element (Fe, Ni, Cu, Zn) have been calculated by measuring the intensity difference for kα in pure elements and their compounds. The determined results showed that the maximum value for (µm) was in FeSO4. These results are consistent with the theoretical value obtained by the XCOM software in addition to investigating the wide energy response of photon interaction with the introduced compounds using the FLUKA Monte Carlo simulation software. The mass attenuation coefficient (MAC) of these compounds is numerically evaluated in the energy range 0.015-15 MeV using the FLAIR code. The computed (µm) is used to generate significant radiation protection factors such as the linear attenuation coefficient (LAC), half-layer value (HVL), effective (Zeff), and equivalent (Zeq) atomic number. For studying the shielding effectiveness and efficiency, for fast and thermal neutron radiation, the removal cross-section ƩR was given.

Experimental, theoretical, and Monte Carlo simulation study of radiation shielding properties of La2O3-Added lithium borate glasses

The La2O3-added lithium borate glasses in the composition of (80-x)B2O3: xLa2O3: 10Li2O: 10Al2O3 (x = 10, 15, 20, 25, and 30 mol%) were prepared by the melt quenching process. The gamma-ray shielding properties of glasses were measured experimentally at various gamma-ray energies acquired from sources of 133Ba, 137Cs, and 60Co and compared with the FLUKA Monte Carlo simulation. FLUKA was also utilized for investigation and compared with the theoretical values obtained using the WinXCom program across the energy range from 0.015 MeV to 15 MeV. The mass attenuation coefficient (μm), effective atomic number (Zeff), effective electron density (Neff), mean free path (MFP) and half-value layer (HVL) were reported. From the results, it was found that adding La2O3 to the glass structure increased μm, Zeff, and Neff, while MFP and HVL decreased. The glasses exhibited the lowest HVL value, indicating improved shielding ability when compared with some shielding materials. PHITS has been utilized to simulate the variations in the absorbed dose resulting from interaction of protons within the modelled phantom. These findings demonstrate the suitability of La2O3-added lithium borate glasses as radiation shielding materials.

Monte Carlo simulation and optimization of neutron ray shielding performance of related materials

Polymers have become widely used substrate materials for shielding neutron rays because of their high hydrogen content and easy processing procedures. Rare-earth materials are also being gradually adopted as neutron absorbers because of their considerable thermal neutron absorption cross-sections. This paper utilizes the FLUKA Monte Carlo simulation program to compare the shielding effects of various polymers and rare-earth oxides on neutron rays across different energy ranges. The study investigates the superior shielding materials for neutron radiation in each energy range. Subsequently, a series of materials are simulated by combining the preferred shielding materials for neutron rays in each energy range, exploring the influence of material composition and composite structure on the effectiveness of neutron ray shielding. It is revealed that the preferred material for shielding neutron rays changes for different energy ranges. For low-energy neutron rays, rare-earth oxides such as Sm2O3 and Gd2O3 demonstrate the most effective shielding, whereas for high-energy neutron rays, polyethylene (PE) provides the best shielding performance. Materials with different compositions show varying preferred structures when dealing with a 252Cf neutron source. However, in mitigating the secondary gamma rays generated during the neutron shielding process, stacked-type materials exhibit the most effective shielding performance.

Using the gamma-index analysis for inter-fractional comparison of in-beam PET images for head-and-neck treatment monitoring in proton therapy: A Monte Carlo simulation study

Goal:In-beam Positron Emission Tomography (PET) is a technique for in-vivo non-invasive treatment monitoring for proton therapy. To detect anatomical changes in patients with PET, various analysis methods exist, but their clinical interpretation is problematic. The goal of this work is to investigate whether the gamma-index analysis, widely used for dose comparisons, is an appropriate tool for comparing in-beam PET distributions. Focusing on a head-and-neck patient, we investigate whether the gamma-index map and the passing rate are sensitive to progressive anatomical changes. Methods/materials:We simulated a treatment course of a proton therapy patient using FLUKA Monte Carlo simulations. Gradual emptying of the sinonasal cavity was modeled through a series of artificially modified CT scans. The in-beam PET activity distributions from three fields were evaluated, simulating a planar dual head geometry. We applied the 3D-gamma evaluation method to compare the PET images with a reference image without changes. Various tolerance criteria and parameters were tested, and results were compared to the CT-scans. Results:Based on 210 MC simulations we identified appropriate parameters for the gamma-index analysis. Tolerance values of 3 mm/3% and 2 mm/2% were suited for comparison of simulated in-beam PET distributions. The gamma passing rate decreased with increasing volume change for all fields. Conclusion:The gamma-index analysis was found to be a useful tool for comparing simulated in-beam PET images, sensitive to sinonasal cavity emptying. Monitoring the gamma passing rate behavior over the treatment course is useful to detect anatomical changes occurring during the treatment course.

Towards a Timepix3 Radiation Monitor for the Accelerator Mixed Radiation Field: Characterisation with Protons and Alphas from 0.6 MeV to 5.6 MeV

A Timepix3 detector with a 300 μm silicon sensor has been studied as a novel radiation monitor for the mixed radiation field at the Large Hadron Collider at CERN. This work describes a test campaign carried out at Centro Nacional de Aceleradores with quasi-mono energetic protons (alphas) from 0.6 (1) to 5 (5.6) MeV, where orthogonal irradiations are used to obtain an energy calibration, and a low-energy angular scan to estimate the front dead layer thickness of the sensor. The detector is operated in hole collection mode and at a partial bias of 250 μm at 50 V, which increases the charge sharing among pixels to mitigate the signal saturation at high energy depositions. The data, supported by FLUKA Monte Carlo simulations of energy losses in the sensor, show that the Timepix3 monitor operates in a linear regime up to energy depositions of around 600 keV per pixel and 2 MeV per cluster. As a result, the detector has been found to be suitable for measuring charged particle fluxes in the LHC mixed radiation field within the linear calibration regime, with the partial exception of inelastic nuclear reaction hits (mostly from neutrons).

Development and evaluation of boron carbide-modified unsaturated polyester resin for use as neutron radiation Protection

Neutrons are electrically neutral particles that can penetrate through various materials and interact with atomic nuclei. Neutrons can emit radiation with varying degrees of energy, which can be harmful to both living organisms and the environment. The objective of this study is to evaluate the thermal neutron (0.025 eV) shielding properties of unsaturated polyester resin with boron carbide content ranging from 0 to 20 wt% for use as neutron shielding materials. The FLUKA Monte Carlo simulation was utilized to evaluate the interactions between thermal neutrons and materials with a thickness of 5 cm. The total cross-section, mean free path, and half-value thickness were calculated to assess the shielding properties of materials. The results indicated that as the boron carbide content increased, the total cross-section increased while the mean free path and half-value thickness decreased. In addition, the polyester resin with 20 wt% of boron carbide exhibited the best properties for shielding thermal neutrons. Thus, this study suggests that unsaturated polyester resin containing boron carbide can be used as an effective material for shielding thermal neutrons.

Study of the radionuclide deposition in the radioactive ion line of the Selective Production of Exotic Species (SPES) facility

SPES (Selective Production of Exotic Species) is a second generation facility for the production of radioactive ion beams that is going to be commissioned at the Laboratori Nazionali di Legnaro of INFN at Legnaro, Padua, Italy. Radioactive neutron-rich isotopes are expected to be produced by nuclear fission induced by a 40 MeV, 200 μA primary proton beam impinging on a 238UCx target. The expected reaction rate is about 1013 fission/s. Radioactive ion beams are produced using the isotope separation on-line technique. The production of such an amount of radioactive species raises radiological issues throughout the life cycle of the facility. A study of the radioactive contamination of the components of the radioactive ion beam line is performed with the FLUKA Monte Carlo simulation code, under realistic hypotheses for the produced isobaric beams. The present results complete previous studies focused on the radiological impact of the production target irradiation, the residual activation of the primary proton beam line and the radioactive contamination of the ion source complex. The overall ambient dose equivalent rate due to the different radiation sources is calculated at several positions inside the production bunker and at different times after a typical one-year operating period of the facility with the 238UCx target at full power. The obtained results and the developed methodology provide the guidelines and the needed tools to plan ordinary and extraordinary interventions as well as final decommissioning of the SPES facility.

Radiation attenuation and optical properties of P2O5-based glass system

This research paper aims to investigate the optical characteristics and the radiation attenuation ability of a newly developed glass system with the composition of 10CaO – 10CaF2 – 10B2O3 ‒ (60-x) P2O5 – 10SrO – xNb2O5 (x = 0, 2.0, 4.0 and 5.0 mol%). We reported several optical characteristics such as refractive index, transparency, bandgap, and more. For radiation attenuation, the FLUKA Monte Carlo simulation package is utilized to model the interactions between particles and photons within the glass system accurately. Furthermore, the XCOM software is employed to calculate the macroscopic cross-sections based on the elemental composition of the glass system. We found that the LAC, at 15 keV, increased from 22.057 cm to 1 to 27.911 cm-1 as the Nb2O5 content increased from 0 to 5 mol%. Moreover, CCBPSN4 glass system possesses the lowest HVL with the value of 0.02483 cm at the energy of 15 keV. This research contributes to the development of efficient radiation shielding glasses, aiding in the design of safer and more effective shielding solutions for radiation-intensive industries and applications. Therefore, the continuous refinement of radiation shielding glasses illuminate a path toward enhanced safety, precision, and progress, especially in an age where radiation continues to play a pivotal role across various sectors.

Synthesis and optimization of B2O3-based glass: Influence of MgO on hardness, structure properties, and radiation shielding performance

This study investigates the structural, mechanical, and gamma shielding features of glass samples with the composition 9Na2O-5BaO-Fe2O3-25Bi2O3-40B2O3 -(20-x)SiO2-xMgO (where x = 0 (G), 4 (GMgO4), 8 (GMgO8) and 12 (GMgO12) mol%). The glasses were prepared using the melt-and-quench method with the aim of characterizing them for radiation shielding and other relevant applications. The influence of MgO on the structure, density, hardness, and brittleness of the glass system was also investigated. The glassy nature of the prepared glasses was confirmed with the aid of a X-ray diffractometer. The mass attenuation coefficients (MACs) of the investigated glass samples were computed from data from FLUKA Monte Carlo simulations and XCOM datasets. The densities of the glasses varied from 2.98 gcm−3 (for G) to 3.18 gcm−3 for (GMgO12). The values of the hardness for the G, GMgO4, GMgO8, and GMgO12 samples are 4.28, 5.13, 5.51, and 5.79 GPa, respectively. The corresponding values of the brittleness are 2.81, 3.46, 3.76, and 4.10 (µ.m)−0.5. In addition, the fracture toughness declined from 1.66 MPa.m−0.5 for G to 1.39 MPa.m−0.5 for GMgO12. The values of the MAC for G, GMgO4, GMgO8, and GMgO12 vary from 0.0374 to 74.4652 cm2/g, 0.0375–74.9213 cm2/g, 0.0375–75.2458 cm2/g, 0.0376–75.5835 cm2/g, respectively. Also, the half-value layers ranging from 0.0031 to 6.2169 cm, 0.0031–6.1428 cm, 0.0030–5.9968 cm, and 0.0030–5.8017 cm were obtained for G, GMgO4, GMgO8, and GMgO12, respectively. The photon shielding abilities of the glasses trended in the following order: G < GMgO4 < GMgO8 < GMgO12. The GMgO12 glass showed a better gamma photon absorption capacity in contrast to conventional and nontraditional shielding materials. The optical transparency of the investigated glasses makes them more versatile in radiation shielding applications.

Response function and photon interaction of LaBr3:Ce and BGO scintillation detectors by Monte Carlo simulation

This work aims to investigate the response function and photon interaction of the LaBr3:Ce and BGO scintillation detectors using the FLUKA Monte Carlo simulation software. To improve the realism of detectors, the DETGEB card was used to activate the gaussian energy broadening (GEB) function. The GEB parameters of both detectors were obtained by fitting a nonlinear curve to the relation between FWHM and gamma-ray energy. The energy resolution (R), peak-to-Compton ratio (PCR), peak-to-total ratio (PTR), and full-energy peak efficiency (FEPE) of both detectors were investigated by simulation and experiment at different gamma-ray energy obtained from 133Ba, 137Cs, and 60Co sources. The simulated spectra of those radioisotopes were found to agree with the actual spectra. The results found that the R, PCR, and FEPE values of the LaBr3:Ce and BGO detectors tend to decrease as energy increases. Moreover, the total atomic cross-section (σt,a), effective atomic number (Zeff) and effective electron density (Neff) of both crystals was investigated by FLUKA and compared with the XCOM theoretical program covering an energy range of 15 keV to 15 MeV. The simulated results of the σt,a, Zeff, and Neff are in excellent agreement with the theoretical ones. The GEB parameters obtained from this study will improve the simulation performance of LaBr3:Ce and BGO detectors in investigating the gamma-ray response and shielding properties of materials.

METU-DBL: a cost effective proton irradiation facility

The Middle East Technical University Defocusing Beamline (METU-DBL) is designed to deliver protons with selectable kinetic energies between 15–30 MeV, and proton flux between 106–1010 protons/cm2/s, on a maximum 21.55 to 15.40 cm target region with a beam uniformity within ±6%, in accordance with the ESA ESCC No. 25100 specification for single event effects (SEEs) tests in the low energy range. The achieved high proton fluences, allow users to test space-grade materials; electronic circuits, ASICs, FPGAs, optical lenses, structural elements, and coating layers for LEO, GEO, and interplanetary missions.The total received dose on the Device-Under-Test (DUT) from secondary particles created during proton-material interactions at the first beam collimator and the beam dump never exceed 0.1% of the dose from primary protons. The METU-DBL is equiped with several measurement stations and services to the user teams. A secondary measurement station in a rotating drum that can hold multiple samples has been constructed next to the first collimator which provides neutrons for transmission experiments. At the target region, a robotic table is located, which provides mechanical and electrical mounting points to the samples and allows multiple samples to be tested in a row. A modular vacuum box can also be attached on the robotic table for any test that may require a vacuum environment. Power rails on the robotic table provide various outputs for the DUT. For the data acquisition, high-speed networking and a modular industrial PC are available at the target station. The design of the METU-DBL control software enables test users to integrate and optimize the data acquisition and controlling of the DUT.The beam properties at the target region are measured with the diamond, Timepix3, and fiber scintillator detectors mounted on the robotic table. With diamond and Timepix3 detectors, measurements are taken from the five different points (center and the four corners) of the test area to measure the proton flux and ensure that it is uniform across the full test area. Fiber scintillators on both axes (X and Y) scan the target area to cross-check the beam profile's uniformity. Secondary doses during the irradiation are measured by a Geiger-Müller tube sensitive to electrons and gammas above 0.1 MeV and by a neutron detector located at the entrance of the R&D room. The room cools down relatively fast after any irradiation (<1 hour).Accurate linear energy deposition rates and absorbed doses on the samples are calculated using MCNP6, FLUKA and Geant4 Monte Carlo simulations. Alanine dosimetry measurements that are calibrated against these simulations are also used to estimate the absorbed dose on the sample.

2D mapping of radiation dose and clonogenic survival for accurate assessment of in vitro X-ray GRID irradiation effects

Spatially fractionated radiation therapy (SFRT or GRID) is an approach to deliver high local radiation doses in an ‘on-off’ pattern. To better appraise the radiobiological effects from GRID, a framework to link local radiation dose to clonogenic survival needs to be developed. A549 lung cancer cells were irradiated in T25 cm2 flasks using 220 kV x-rays with an open field or through a tungsten GRID collimator with periodical 5 mm openings and 10 mm blockings. Delivered nominal doses were 2, 5, and 10 Gy. A novel approach for image segmentation was used to locate the centroid of surviving colonies in scanned images of the cell flasks. GafchromicTM film dosimetry (GFD) and FLUKA Monte Carlo (MC) simulations were employed to map the dose at each surviving colony centroid. Fitting the linear-quadratic (LQ) function to clonogenic survival data for open field irradiation, the expected survival level at a given dose level was calculated. The expected survival levels were then mapped together with the observed levels in the GRID-irradiated flasks. GFD and FLUKA MC gave similar dose distributions, with a mean peak-to-valley dose ratio of about 5. LQ-parameters for open field irradiation gave Gy−1 and Gy−2. The mean relative percentage deviation between observed and predicted survival in the (peak; valley) dose regions was (4.6; 3.1) %, (26.6; −1.0) %, and (129.8; −2.3) % for 2, 5 and 10 Gy, respectively. In conclusion, a framework for mapping of surviving colonies following GRID irradiation together with predicted survival levels from homogeneous irradiation was presented. For the given cell line, our findings indicate that GRID irradiation causes reduced survival in the peak regions compared to an open field configuration.

3D range-modulators for proton therapy: near field simulations with FLUKA and comparison with film measurements

The 3D range-modulator is a device used in particle delivery systems that can create a highly conformal and homogeneous dose distribution in the target volume with mono-energetic beams, providing an option for high dose-rate FLASH therapy. In the normal case, the modulators are positioned at a typical distance of 30-50 cm in front of the target in order to avoid the fluence ripples resulting from the periodic structure of the modulators. FLUKA Monte Carlo simulation package was used to investigate the fluence distributions of protons penetrating through the 2D range-modulator, the simplified version of the 3D range-modulator, and to determine the minimum distance at which the fluence is homogeneous enough for the treatment. To implement the complex geometry of the modulator in FLUKA, a dedicated FLUKA user routine was developed for the simulation of the periodic pin structures. The highest fluence ripple occurred at a few centimetres behind the modulators and then faded away as the distance increased, which can be described by the edge-scattering effect and later by the blur-out of the overlapping contributions from the pins. Moreover, the dose distribution in water was investigated, particularly for small distances between the modulators and the water phantom. Furthermore, the Monte Carlo results were compared with radiochromic film measurements irradiated with a 3D-printed range modulator and showed a good qualitative agreement. Prospectively, for low modulator-to-target distances, the strong dose inhomogeneities which appear in the proximal part of the target, could introduce additionally a kind of ‘mini beam’ normal-tissue sparing by the 3D range-modulators.

LET spectrometry for p+nat(Li+C) system at different proton energies using CR-39: Development of autoLET code for automated generation of LET spectra and dose values

The present work describes measurement of LET (linear energy transfer) spectra due to neutrons generated from the p+nat(Li+C) system at 4 different proton energies (8, 12, 16 and 20 MeV) using CR-39 detector. A computer program (autoLET) was developed to process the track and the etching parameters for automated generation of the LET spectra and the corresponding dosimetric quantities. After chemical etching of irradiated CR-39 detectors, the track parameters were fed as inputs to the autoLET code to generate the LET spectra as well as to determine the track density and dosimetric quantities. FLUKA Monte Carlo simulations were performed to estimate the neutron fluence, energy spectrum and ambient dose equivalent for the same p+nat(Li+C) system. The measured track density and the dose equivalent were found to decrease initially from 8 to 12 MeV and further increased with increase in proton energy. Similar estimations for neutron fluence and ambient dose equivalent were also observed from the FLUKA simulations. The relative response of CR-39 in terms of track and dose equivalent determined for this radiation environment was found to be 1.60 × 10−4±3.85×10−5 track/n and 0.394 ± 0.054 respectively. The dose equivalent response (HLET/H*(10)) obtained in this study was compared with the data available in literature. The present study would be useful in estimating the neutron field around particle accelerator environment and for the radiation protection purposes in neutron generating facilities.

Development of a single sphere neutron spectrometer using α-Al2O3:C based optically stimulated luminescence detectors

A multi-shell single sphere moderating assembly has been designed and developed to measure the neutron spectra in which the optically stimulated luminescence (OSL) detector pairs (Al2O3:C + 6, 7LiF) were used. The response matrix of OSL detectors, covering 11 energy decades (from thermal to 100 MeV neutrons) at different depths of the sphere, was generated using FLUKA-Monte Carlo simulation. The testing and validation of the spectrometer was performed using 3 standard neutron sources, viz. 241AmBe, 252Cf and DT. Neutron spectra were generated using 2 different unfolding codes. The design of the moderating assembly has the flexibility of selecting the desired sphere size as per the end point energy of the neutron spectrum. This can be conveniently employed in the complex radiation environment around particle accelerators, where the time and the space for irradiations have limitations. The details of the spectrometer design, response matrix generation and unfolding results are presented here.

Na22 activation level measurements of fused silica rods in the LHC target absorber for neutrals compared to simulations

The Target Absorbers for Neutrals (TANs) are located in a high-intensity radiation environment inside the tunnel of the Large Hadron Collider (LHC). TANs are positioned about $140$ m downstream from the beam interaction points. Seven $40$ cm long fused silica rods with different dopant specifications were irradiated in the TAN by the Beam RAte of Neutrals (BRAN) detector group during $p$+$p$ data taking from 2016 to 2018 at the LHC. The peak dose delivered to the fused silica rods was $18$ MGy. We report measurements of the $^{22}$Na activation of the fused silica rods carried out at the University of Illinois at Urbana-Champaign and Argonne National Laboratory. At the end of the irradiation campaign, the maximum $^{22}$Na activity observed was $A=21$ kBq$/{\rm cm^3}$ corresponding to a density, $\rho= 2.5\times 10^{12} /{\rm cm^3}$, of $^{22}$Na nuclei. FLUKA Monte Carlo simulations have been performed by the CERN FLUKA team to estimate $^{22}$Na activities for the irradiated BRAN rod samples. The simulations reproduce the $^{22}$Na activity profile measured along the rods, with a 35% underestimation of the experimental measurement results.