Unfolding Code Research Articles

No evidence that visual impulses enhance the readout of retrieved long-term memory contents from EEG activity

Abstract The application of multivariate pattern analysis (MVPA) to electroencephalography (EEG) data allows neuroscientists to track neural representations at temporally fine-grained scales. This approach has been leveraged to study the locus and evolution of long-term memory contents in the brain, but a limiting factor is that decoding performance remains low. A key reason for this is that processes such as encoding and retrieval are intrinsically dynamic across trials and participants, and this runs in tension with MVPA and other techniques that rely on consistently unfolding neural codes to generate predictions about memory contents. The presentation of visually perturbing stimuli may experimentally regularize brain dynamics, making neural codes more stable across measurements to enhance representational readouts. Such enhancements, which have repeatedly been demonstrated in working memory contexts, could offer a tool to improve decoding in long-term memory tasks. In this study, we evaluated whether visual perturbations—or pings—improve our ability to predict the category of retrieved images from EEG activity during cued recall. Overall, our findings suggest that while pings evoked a prominent neural response, they did not reliably produce improvements in MVPA-based classification across several analyses. We discuss possibilities that could explain these results, including the role of experimental and analysis parameter choices and mechanistic differences between working and long-term memory.

Bonner sphere measurements of high-energy neutron spectra from a 1 GeV/u 56Fe ion beam on an aluminum target and comparison to spectra obtained by Monte Carlo simulations

The goal of this work is to characterize the secondary neutron spectra produced by 1 GeV/u56Fe beam colliding with a thick cylindric aluminum target and to perform a quantitative comparison with simulated results obtained with Monte Carlo codes. The measurements were performed using extended-range Bonner sphere spectrometers at two positions (15° and 40°) with respect to the beam direction. The secondary radiation field was simulated using four Monte Carlo codes (FLUKA, MCNP6, Geant4 and PHITS) and several physical models of nuclei transport and interaction. Neutron and proton energy distributions were simulated for the experimental measurement positions. The simulated neutron spectra, together with data measured with Bonner sphere spectrometers, after carrying out the correction of the contributions induced by the secondary protons, were used as input for the MAXED spectrum unfolding code to obtain the measured neutron spectra. Unfolded neutron spectra were compared with simulated ones to carry out a quantitative analysis of the performance of the chosen Monte Carlo codes and their corresponding physical models. This comparison showed that, because of experimental uncertainties and physical models, there are no unique solutions for each measurement location, but a range of solutions where the true experimental neutron spectra probably lie. The results showed deviations between 4.23% and 8.42% for some simulated spectra. Regarding the total integral values of neutron fluence and ambient equivalent dose, the unfolded neutron spectra showed deviations lower than 2%.

Development and validation of a Bayesian unfolding program using OpenBUGS open-source software for Bonner spheres neutron spectrometry

This study presents the development of a novel unfolding program based on a Bayesian method for Bonner spheres spectrometry. The program incorporates a priori information on the neutron spectrum, employing a linear superposition of three non-negative parametric functions: thermal-Maxwellian distribution, an intermediate region represented by a straight line in lethargy space (1/E behavior), and the Watt fission distribution for the fast region. The effectiveness of the developed program was validated through its application to two reference cases from the EURADOS 2018 exercise (LINAC and Skyshine), followed by its implementation in characterizing the neutron field around an OB26 neutron irradiator at the Secondary Standards Dosimetry Laboratory (SSDL) of the Nuclear Research Center of Algiers (CRNA), Algeria. While validation results for the LINAC case were promising, achieving comparable neutron spectrum shape and integral quantities to the reference, challenges were encountered with the Skyshine case. However, these challenges were partially addressed through sensitivity analysis, resulting in slightly improved outcomes compared to the previous participation and to the reference. Application of the program to characterize the neutron field around the OB26 irradiator yielded satisfactory results when compared to reference data. A two-step sensitivity analysis further enhanced the outcomes, initially substituting the Watt fission distribution with the evaporation distribution, thereby improving spectrum shape and integral quantities. Subsequently, utilizing the obtained neutron spectra as prior information for unfolding codes MAXED and GRAVEL ensured stability and agreement with reference data and preliminary results.

239Pu[sbnd]Be neutron reference field: Physical and dosimetric parameters

This paper presents the establishment of a 239PuBe neutron reference field at the Military Institute for Chemical and Environmental Engineering, Hanoi, Viet Nam. The evaluation of the field parameters due to neutrons of the total component was performed using an in-house developed Bonner sphere spectrometer in combination with the output data from the FRUIT unfolding code. As results, these following field parameters were obtained for neutrons of the total component, at several points of interest: (i) neutron fluence spectrum; (ii) integral neutron fluence rate - ϕ, unit in cm−2s−1; (iii) neutron ambient dose rate (a new operational quantity) - Ḣ∗, unit in μSvh−1; (iv) neutron ambient dose equivalent rate (an old operational quantity) - Ḣ∗(10), unit in μSvh−1; (v) neutron fluence-to-ambient dose conversion coefficient - h∗, unit in pSvcm2; (vi) fluence-averaged neutron energy - E¯, unit in MeV; and (vii) ambient dose-averaged neutron energy - E˜, unit in MeV. The standard combined uncertainties of Ḣ∗ and Ḣ∗(10) due to the total neutron component were estimated within 10%, considered as acceptable for measurements of Ḣ∗ and/or Ḣ∗(10) less than 50 μSvh−1. In addition, the fluence-to-ambient dose equivalent conversion coefficient (h) for the direct neutron component was also deduced. The standard deviation of h between those obtained from this work and from published data was calculated as within 5.7%, acceptable for radiation protection purpose.

Measurement of secondary neutron spectra induced by 480 MeV proton and 430 MeV/u 4He beams with a thick aluminum target

Knowledge of the characteristics of secondary neutrons produced by the interaction of Galactic Cosmic Radiation with spacecraft shielding materials is becoming increasingly important for predicting and mitigating biological risks of space explorers during deep-space travel. Hadron accelerators for medical applications are well suited to reproduce part of the conditions found in deep-space in terms of ion species and energies. The objectives of this work are to measure the secondary neutron spectra produced by proton and helium ion beams hitting an aluminum target with energies that correspond to the Galactic Cosmic Radiation peak during solar minimal activity and to validate and compare physical models of Monte Carlo simulations. Neutron spectra were measured with the extended-range Bonner sphere system NEMUS at two positions, 0° and 90° relative to the direction of the primary ion beam. The experimental setup consisted of 480 MeV proton and 430 MeV/u 4He beams colliding with a 30×30×63.5 cm3 aluminum target. The experimental neutron spectra were analyzed using the MAXED unfolding code and compared to several Monte Carlo simulation codes. The results show deviations in terms of the shape of the neutron energy distributions ranging between 1% and 14% and of the integral quantities of fluence and ambient dose equivalent ranging between 1% and 5.2%.

Neutron spectrum unfolding code based on iterative method combined with artificial neural networks for bonner sphere spectrometer

Neutron spectrum unfolding code based on iterative method combined with artificial neural networks for bonner sphere spectrometer

Chameleon: a cloud computing Industry 4.0 neutron spectrum unfolding code.

This work presents Chameleon, a cloud computing (CC) Industry 4.0 (I4) neutron spectrum unfolding code. The code was designed under the Python programming language, using Streamlit framework®, and it is executed on the cloud, as I4 CC technology through internet, by using mobile devices with internet connectivity and a web navigator. In its first version, as a proof of concept, the SPUNIT algorithm was implemented. The main functionalities and the preliminary tests performed to validate the code are presented. Chameleon solves the neutron spectrum unfolding problem and it is easy, friendly and intuitive. It can be applied with success in various workplaces. More validation tests are in progress. Future implementations will include improving the graphical user interface, inserting other algorithms, such as GRAVEL, MAXED and neural networks, and implementing an algorithm to estimate uncertainties in the calculated integral quantities.

GRAVEL unfolding of gamma-ray spectra of CeBr3 detectors and related uncertainties

Unfolded spectra are needed for the application of some spectrum analysis methods. Frequently, iterative deconvolution methods are used, especially if the spectra have a high resolution. However, the uncertainties on the obtained results are difficult to judge. In general, the user of an unfolding code gets no information on the influence of chosen parameters, especially the choice of the first estimate of the unfolded spectrum. General studies regarding the uncertainties of unfolding algorithms are difficult to perform, if not impossible, and therefore not available. In this work, uncertainties of the results on the iterative GRAVEL algorithm, which is based on SAND II, are closely investigated by using medium resolution spectra recorded by using a CeBr3 detector. Relevant parameters are varied systematically to gain some information on the associated uncertainties on the basis of examples. The uncertainty budget of the calculation of total fluences and doses of unfolded spectra is compared with the uncertainty budget of the results obtained by applying the conversion method. The results allow, at least, the estimation of the magnitude of typical uncertainties.

Neutron Flux Determination for the NEAR Station at the CERN n_TOF Facility Using the SAND II Unfolding Code

The NEAR station, a new experimental area of the n_TOF facility, was established after the second long shut down of CERN in 2020. This new area was created in order to exploit in situ the high instantaneous neutron flux (originating from proton spallation into a lead target in bunches with momenta reaching up to 20 GeV/c). The reason for the creation of the NEAR station is to utilize the neutrons for experiments related to radiation damage on materials and nuclear astrophysics and the corresponding neutron flux was characterized via extensive neutron multiple foil activation measurements. The irradiated foils were subsequently measured using high purity germanium detectors (HPGe) to determine their induced activities. Finally, the widely used SAND II unfolding code was implemented for the characterization of the neutron flux, using the evaluated cross sections from the IRDFF library, along with the experimentally derived activities. The preliminary results concerning the neutron flux determined in the present work are compared with the corresponding FLUKA simulated ones.

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.

Comparison of extended-range and conventional Bonner Sphere Spectrometers (BSS) in an AmBe neutron field – Applicability of the ReBUNKI unfolding code for extended-range BSS

In proton therapy facilities, high-energy neutron fields are generated as a consequence of (p,Xn) nuclear interactions. UPM has designed and tested its own extended-range Bonner Spheres Spectrometer (BSS) to support the development of this technology in Spain. This work shows the results obtained in the first experimental testing of this new BSS, using for the first time the ReBUNKI unfolding code in this kind of BSS. An intercomparison exercise with several unfolding codes has been carried out to validate ReBUNKI results and the new extended-range BSS response matrix.

Measuring the near-target neutron field of a D–D fusion facility with the novel NCT-WES spectrometer

A new directional neutron spectrometer called NCT-WES (Neutron Capture Therapy Wide Energy Spectrometer) was recently developed within the INFN ENTER_BNCT project. This device constitutes a more compact and portable alternative to state-of-the-art directional neutron spectrometers. The device was used for the first time to characterise the near-target field produced by an accelerator-driven D–D fusion neutron source. NCT-WES operates as a “parallelised” Bonner spheres spectrometer, embedding six semiconductor-based thermal neutron detectors in a cylindrical moderator. Owing on a cylindrical collimating aperture, the device exhibits sharply directional response. To account for the non-uniform irradiation condition experienced in the near-target field, a dedicated NCT-WES response matrix was developed. The neutron spectrum at 0^{circ } from the D–D neutron target, determined by means of the FRUIT unfolding code, is coherent with that previously derived with Bonner spheres. NCT-WES proved to be a promising device for angular spectrometric characterisation of neutron-emitting targets.

Spectrometry of leakage photoneutrons of 18 MV medical accelerator head by Sohrabi passive multi-directional spherical neutron spectrometry system

PurposeSpectrometry of leakage photoneutrons (PN) of a Siemens ONCOR medical linear accelerator head by applying recently invented Sohrabi passive multi-directional multi-detector neutron spherical spectrometry system; measurements of scientific interest and of importance for meeting the regulatory and safety standards. MethodsThe neutron spectrometry system applied consists of 6 polycarbonate/10B detectors mounted on 6 sides of a polyethylene cube used as bare and also embedded at center of 8 PE spheres of different diameters. Multi-directional and mean PN spectra at isocenter as well as at the left and right sides of head at 100 cm distance from the X-ray target on its plane of 10x10 cm2 18-MV X-ray beams were determined applying Multisphere Neutron Spectrometry Unfolding Code (MNSU + ). ResultsThe well-resolved unfolded directional leakage PN spectra obtained at the 3 positions showed a thermal PN peak of lower intensityfollowed by a tail of epithermal PNs before reaching a fast PN higher peak.“ The mean PN energy are 0.47 ± 0.03 MeV and 0.48 ± 0.02 MeV respectively for the left and right sides of the head and 0.48 ± 0.02 MeV at the isocenter. ConclusionsDue to importance of leakage PN spectra of an accelerator head being of scientific interest and for meeting regulatory and safety standards, well-resolved leakage PN spectra of 3 locations of the medical accelerator head were determined using Sohrabi passive multi-directional neutron spectrometry system. It is a novel learning that the mean PN spectra and mean PN energy of the 3 locations are quite similar within statistical variations.

Gamma-response characterization of a solution-grown stilbene based detector assembly in the 59 keV–4.44 MeV energy range; an alternative low-resolution gamma spectrometer

The photon response characterization of a Ø 25.4 mm × 25.4 mm solution-grown stilbene based detector assembly was performed in the 59 keV–4.44 MeV energy range. Energy calibration was carried out using not only direct measurements but also via coincidence measurements in order to obtain more reliable results. Both methods gave consistent results. To establish an accurate model of the detector, its energy resolution was determined and included in MCNPX-PoliMi simulations. This model served to compute the gamma-response matrix in the 0.1–7.3 MeV energy range. This matrix was used as an input of the GRAVEL spectrum unfolding code when attempting to unfold the measured spectra of well-known sources. Despite a few discrepancies concerning peak intensities, the main gamma peaks were successfully identified in the 0.059–4.4 MeV energy range, thus confirming the utility of solution-grown stilbene as a low-resolution gamma spectrometer, especially for identifying the gamma component in neutron fields.

Neutron spectrum determination of accelerator-driven d(10)+Be neutron source using the multi-foil activation technique

New neutron field of the compact accelerator-driven fast neutron source based on the cyclotron and beryllium target station was studied and developed at the NPI CAS. Neutrons were generated using the deuteron bombardment on 8 mm thick beryllium layer by the 10.3 MeV deuteron beam. Broad neutron energy spectra of the d(10)+Be source reaction at two source-to-sample distances (14 mm and 154 mm) were determined for the first time at the NPI. Sets of eight activation materials comprising Au, Co, Ti, In, Al, Fe, Ni, and Nb were irradiated in the d(10)+Be neutron field, and activated dosimetry foils were analysed using the nuclear gamma-spectroscopy technique (HPGe detector) and reaction rates were measured. Neutron energy spectra of the d + Be source reaction for 10.3 MeV deuterons were reconstructed employing the modified version of the SAND-II unfolding code. For 9.7 μA deuteron beam, the fast neutron flux of developed d(10)+Be neutron field reached the value of 1.4 × 1010 cm−2s−1 at a distance of 14 mm from the source target and 4.1 × 108 cm−2s−1 at a distance of 154 mm. The novel d(10)+Be neutron field with energy range up to 15 MeV is convenient for neutron cross-section data validation, experimental simulation of the fast neutron spectrum of experimental nuclear reactors, applications of neutron activation analysis, and radiation hardness tests of materials important for nuclear energetics.

Monte Carlo simulation of NaI(Tl) detector and GRAVEL deconvolution for biological, geological samples and their dosimetry evaluation

A new approach for natural radioactivity evaluation in environmental samples was presented. The method was based on the combination of GRAVEL unfolding code and Monte Carlo simulation. The NaI(Tl) detector model was validated by comparing the simulated data with the experiment using a calibration point source. Then, the response matrixes at 1.46 and 1.76 MeV corresponding to 40K and 238U respectively, was used to restore the incident γ spectra. The measured activities were used to estimate the biological activities and the annual absorbed doses. The annual absorbed doses are lower than the worldwide reference value of 1 mSv·y-1.

Cosmic ray neutron spectrometry and dosimetry at High Altitude Research Laboratory, Gulmarg, Kashmir, India

Cosmic ray neutrons are produced by the interaction of primary cosmic rays with the air molecules present in the atmosphere. At the ground level, these secondary neutrons are one of the important contributors of natural cosmic ray radiation background dose. With two major peaks around 1 MeV and 100 MeV, the neutron energies can extend up to 10 GeV. At the ground level, considerable presence of thermal neutrons can also be observed due to collisions and moderation of fast neutrons with the soil and other surrounding materials. A study on the evaluation of cosmic ray neutron spectra, and the resulting ambient dose equivalents was carried out at High Altitude Research Laboratory, Gulmarg, India (altitude 2650 m, N34.0484°, E74.3805°) considering the enhanced contribution of cosmic ray background in the region. Extended energy Bonner Sphere Spectrometer (BSS) was used for the continuous measurement of cosmic ray neutrons during the period of October 2018 to June 2019. Neutron spectra and ambient dose equivalents were unfolded from the BSS counts with the Monte Carlo generated response matrix and the FRUIT unfolding code. Along with Bonner sphere spectrometer, Tissue Equivalent Proportional Counter (TEPC) was also used for a limited period for independent measurement of cosmic ray dose equivalents and Linear Energy Transfer (LET) distribution. For comparison, neutron spectra and dose equivalent rates were also calculated using Monte Carlo code FLUKA and EXPACS software program. The ambient dose equivalent rates were found to vary in the range of 24–34 nSv. h−1 during the entire observation period of 9 months. No considerable seasonal variations were observed during the course of the study. Dose equivalent rates, estimated by the TEPC were slightly higher than the neutron dose equivalent rates measured by BSS. Experimentally measured values match reasonably well with theoretically simulated results.

NEUTRON SPECTRUM UNFOLDING USING VARIOUS COMPUTER CODES: A COMPARISON

Dosimetric quantities at various distances from a 30 cm diameter polyethylene sphere moderated 241Am-Be source were investigated using the Bonner sphere spectrometer system. The different international commercial unfolding codes were applied to unfold the neutron spectrum, and their shapes were compared to each other. Additionally, the integrated neutron fluence rates overall spectrum and fractional neutron fluence rates were deduced and compared between the results obtained from different unfolding codes. As an important quantity applying in radiation safety assessment, the neutron ambient dose equivalent rates were also calculated and compared to each other to verify the utility feasibilities of the codes.

Beam loss monitoring with unfolding techniques

Since the first particle accelerator’s construction in 1931, an exponential spread of these machines occurred worldwide, in different kinds of applications. Nowadays, these are mainly used for industrial (60%) and medical (35%) purposes and for scientific research (5%). High energy secondary mixed fields produced by the particle beams interaction with matter imply a complex environmental dosimetry and special radiation protection regulations able to guarantee workers and population safety. In the medical field, this aspect is particularly emphasized in hadrontherapy centres, where high energy charged particles such as protons and carbon ions modify environmental doses, with a significant increase in the neutron contribution. This work proposes a technique to identify points of losses of the primary particle beam around an acceleration ring and has been developed within the radiation protection section at the National Centre for Oncological Hadrontherapy situated in Pavia. In the first part, the radiation field produced by protons and carbon ions interactions with structural materials at different energies was investigated. The main instrument of analysis is the Monte Carlo code for particle transport FLUKA, supported by experimental measurements in the treatment room carried out with the rem counter LUPIN, designed for pulsed neutron fields dosimetry. This first step allowed an analysis of both the angular and energetic instrumental response and a comparison of experimental results with simulations. The second part proposes a description of the technique for beam loss positions reconstruction around the acceleration ring at CNAO based on the application of unfolding codes.

The p(20)+Be reaction as a source of fusion relevant neutrons

The p(20)+Be neutron source reaction was investigated at the Nuclear Physics Institute of the Czech Academy of Sciences using the 20 MeV proton beam on thick beryllium target (thickness of 8 mm). Neutron field in close source-to-sample distances was determined by means of the activation foils technique; set of ten activation foils (Al, Ti, Co, Fe, Ni, Y, In, Nb, Lu, Au) was utilized. Neutron spectrum reconstruction from reaction rates obtained using the gamma-spectroscopy method (semiconductor HPGe detectors) was performed utilizing the modified version of SAND-II unfolding code and relevant activation cross-sections from the EAF-2010 nuclear database. Determined neutron energy spectra were validated against the MCNPX calculations. Developed p(20)+Be neutron field with broad spectrum represents a useful tool for the cross-section data validation within the ITER and IFMIF-DONES research programs (≥ 12 MeV), neutron-hardness tests of microelectronics, study of material damage, and calibration of new detection systems.