Bremsstrahlung Beam Research Articles

Reliability of Cross Sections of the Photoneutron Reactions on 51V and 59Co Nuclei in the Bremsstrahlung Beam Experiments

Reliability of Cross Sections of the Photoneutron Reactions on 51V and 59Co Nuclei in the Bremsstrahlung Beam Experiments

Evaluation of 180mTa formation cross-sections in photoneutron reactions

Determining the relative production cross-sections of the short-lived (ground) and long- lived (metastable) states of 180Ta is integral in nuclear physics research. However, direct measurement of these cross-sections is challenging. In this study, we proposed a method for estimating the total flux-weighted average formation cross-section of 180m+gTa based on GEANT4 modeling to evaluate the short-lived (ground) and long-lived (metastable) states of 180Ta. A Ta target was irradiated by a bremsstrahlung photon beam (maximum electron energy: 20 MeV) obtained from the linear electron accelerator LUE-75 at the A.I. Alikhanyan National Science Laboratory (AANL), Armenia. The experiment was performed using the activation technique, and the proposed GEANT4 simulation-based method was employed to evaluate the flux-weighted average formation cross-section of 180mTa. In addition, the isomeric cross-section ratio for the 180m,gTa isomeric pair was calculated. The theoretical results obtained using the TALYS 1.96 and EMPIRE 3.2 codes were consistent with the experimental ones. To the best of the authors’ knowledge, this paper reports the estimated flux-weighted average formation cross-section of 180mTa and isomer ratio for the 180m,gTa isomeric pair, induced by the irradiation of a bremsstrahlung beam with an end-point energy of 20 MeV, for the first time. This study opens new avenues for determining the relative production cross-sections of the ground and metastable states of 180Ta, which is widely studied as a natural isomeric target in various fields, including nuclear transformation reactions, fission dynamics, etc.

Fundamental limitations of dual energy X-ray scanners for cargo content atomic number discrimination

To combat the risk of nuclear smuggling, radiography systems are deployed at ports to scan cargo containers for concealed illicit materials. Dual energy radiography systems enable a rough elemental analysis of cargo containers due to the Z-dependence of photon attenuation, allowing for improved material detection. This work studies the capabilities for atomic number discrimination using dual energy MeV systems by considering dual energy {6,4}MeV, {10,6}MeV, and {10,4}MeV bremsstrahlung beams. Results of this analysis show that two different pure materials can sometimes produce identical transparency measurements, leading to a fundamental ambiguity when differentiating between materials of different atomic numbers. Previous literature has observed this property, but the extent of the limitation is poorly understood and the cause of the degeneracy is generally inadequately explained. This non-uniqueness property stems from competition between photoelectric absorption and pair production and is present even in systems with perfect resolution and zero statistical noise. These findings are validated through Monte Carlo transparency simulations. Results of this study show that currently deployed commercial radiographic systems are fundamentally incapable of distinguishing between high-Z nuclear materials and miscellaneous mid-Z cargo contents.

Determination of the bremsstrahlung spectra by unfolding technique based on [formula omitted]Bi([formula omitted], xn) reactions

This work explores and describes the possibility of assessment of high energy bremsstrahlung spectrum, through the use of photonuclear reactions. Experimentally obtained values of saturation activities of various Bi isotopes, created by 209Bi(γ, xn) reactions in the 100 MeV bremsstrahlung beam were used in calculations. The photon spectrum is obtained by utilizing the unfolding techniques and cross sections data calculated by the TALYS 1.96 code. The experimental results were compared with the results obtained by Geant4 Monte Carlo simulation.

The fission fragment rocket engine for Mars fast transit

In this paper we discuss the advantages and challenges of utilizing Fission Fragment Rocket Engines (FFREs) to dramatically reduce transit time in space travel, for example, traveling to Mars. We discuss methods to decrease the size and weight of FFREs. These include utilizing metallic deuterides as moderators, driving the engines with electron beam bremsstrahlung, and operating the FFREs as subcritical assemblies, not as nuclear reactors. We discuss these and other new innovations based upon improved materials and technology that may be integrated into a revolutionary nuclear rocket technology.

Measurements of photoneutron dose rate for 15 MV photon beam from medical linear accelerator using neutron survey meter

High-energy medical linear accelerators (>10MV) are increasingly used in the medical field to treat cancer patients depending on the treatment organ and patient physic. Medical linear accelerators (Linacs) operating above 10 MV photon beam produce unwanted neutrons (photoneutron) by means of photonuclear reaction (γ, n) between bremsstrahlung photon beams and constituent materials of Linac head. This study involved the measurement of the neutron dose rate from photon beam of medical linear accelerator (Elekta Synergy) operated at 15 MV photon. For the measurement of dose rate, a neutron survey meter LB 6411 probe was used. Neutron dose rate was obtained as a function of delivered dose, field size and detector position. In the study neutron dose rate was found 13.14 mSv/h at a field size of 10 × 10 cm2 at position (0,90,0) cm for 350 cGy and 9.26 mSv/h at 5 × 5 cm2 field size at position (0,80,0) cm for 200 cGy photon dose delivery. The dose rate varied with respect to detector position in an irregular manner; 2.95 mSv/h at position (-100,0,0) cm -on the side of maze entrance and 4.85 mSv/h at position (100,0,0) cm -off side of maze entrance.

Spatial profiles of collimated laser Compton-scattering γ-ray beams

The intensity and energy spatial distributions of collimated laser Compton scattering (LCS) γ-ray beams and of the associated bremsstrahlung beams have been investigated as functions of the electron beam energy, electron beam phase space distribution, laser optics conditions and laser polarization. We show that the beam halo is affected to different extents by variations in the above listed parameters. In the present work, we have used laser Compton scattering simulations performed with the eliLaBr code (https://github.com/dan-mihai-filipescu/eliLaBr) and real LCS and bremsstrahlung γ-ray beams produced at the NewSUBARU synchrotron radiation facility. A 500 μm MiniPIX X-ray camera was used as beamspot monitor in a wide γ-ray beam energy range between 1.73 MeV and 38.1 MeV.

Optimal scheme for stimulating photofission of shielded nuclear materials on the Microtron M-30: a combination of theoretical and experimental studies

Relevance. The photofission of shielded nuclear materials is widely used to develop methods for non-destructive analysis of their isotopic composition. To stimulate the photofission reaction, bremsstrahlung beams obtained on electronic accelerators are used. Their parameters significantly depend on the design features of accelerators and sample activation schemes. Purpose. Theoretical modelling of parameters of an optimal scheme for stimulating the photofission of shielded nuclear materials on an electronic accelerator – Microtron M-30 for the analysis of their isotopic composition, considering its technical characteristics, and experimental verification of its parameters. Methodology. Theoretical calculations of the parameters of bremsstrahlung beams for the Microtron M-30 were carried out using the GEANT4 toolkit. For experimental studies of the influence of structural elements of the optimal stimulation scheme on the integral characteristics of inhibitory photons, secondary photoneutrons, the method of activation of detectors made of gold was used; for residual electrons – the transmission method based on a passage chamber and a Faraday cylinder. Results. As a result of the combination of theoretical and experimental studies, optimal parameters of the activation scheme of nuclear materials on the Microtron M-30 have been established. The scheme provides experimental conditions under which the losses of bremsstrahlung photon beams interacting with the test samples (with energies ≥6 MeV) do not exceed 35% of their initial values, with the practical absence of residual electrons (98% of electrons are absorbed) and secondary photoneutrons (no more than 1E-9 n/e). Conclusions. The parameters of the developed stimulation scheme for the Microtron M-30 can be applied to various types of accelerators, considering their design features, characteristics of the samples, and implemented activation schemes

High-fidelity photoneutron detection via neutron activation analysis

To interdict illicit radioactive sources and prevent nuclear terror, governments have deployed portal monitor systems at ports of entry. Such portal monitors rely upon the detection of spontaneously-emitted radiation signatures, however, detection scenarios become more challenging for highly enriched uranium, which emits relatively few spontaneous radiation signatures. Photon active interrogation techniques can augment current cargo inspection scenarios and improve detection capabilities for illicit nuclear material. A high-energy photon interrogation source can induce photofission in nuclear material, producing strong radiation signatures for detection. Prompt fission signals are of specific interest because prompt neutrons are greater than 99% of the fission signal. When using detectors capable of spectroscopy, e.g., pulse shape discrimination-capable organic scintillators, the intense interrogating source often will cause pulse pile-up, degrading particle classification. In this work, we demonstrate photoneutron detection via neutron activation of aluminum and iron. The experiments rely upon nuclear reactions that can only be induced by neutrons, and are robust against pile-up, thereby providing high-confidence neutron rates. In this work, we apply neutron activation analysis for the detection of high-energy neutrons produced by high-energy photon irradiation; the depleted uranium sample was irradiated with a 9-MeV bremsstrahlung beam. We find that the irradiated depleted uranium produced an aluminum activation flux of 1.77 × 105 n cm −2 s−1 and an iron-56 activation flux of 1.05 × 105 n cm −2 s−1. The ability to detect radioactivity induced by neutrons created in (γ, n) and photofission reactions demonstrates a new approach for photon active interrogation to identify nuclear materials.

Calculation of a System for Forming a Bremsstrahlung Beam in Discretely Falling Magnetic Field

Calculation of a System for Forming a Bremsstrahlung Beam in Discretely Falling Magnetic Field

Perspectives of the study of fission fragments structure on the Bremsstrahlung beams in project DRIBs (Dubna)

Fission fragments of heavy nuclei (Z > 90) are neutron-rich isotopes of the elements from Zn (Z = 30) to Nd (Z = 60) with a neutron number of 45 - 90. The large neutron excess in the fission fragments under study (in some cases there are 10 - 15 more neutrons, than in the nuclei situated in the -β stability valley) could lead to an essential change in their structure and radioactive decay characteristics.

Features of Distributions Created in a Water Phantom by Narrow Bremsstrahlung Radiation Beams from 10 to 20 MV

The paper analyzes the features of the spatial and energy distributions of photons in depth, in radius
 and in energy for small fields created in water by narrow beams of high-energy bremsstrahlung radiation from medical accelerators and mono-directional, monoenergetic beams of photons. In particular,
 the relationship between the spatial dependences of the absorbed dose, total kerma, and ionization
 kerma is discussed. Using numerical simulation, the features of photon spectra in small fields at a
 depth of 10 cm in a water phantom for bremsstrahlung beams with maximum energies of 10, 15, 18
 and 20 MeV were determined as applied to the design of Varian accelerator heads. It is shown that, in
 contrast to wide fields, the energy distribution of photons in these fields practically does not change
 within the central region of the field and strongly softens when leaving this region. With a decrease in
 the size of small fields from 4.04.0 to 0.50.5 cm, a certain hardening of the spectra is observed in the
 central region (the average energy increases by 2–4 %) and is much more significant outside this region.
 The work also determined the values of the clinical dimensions of small fields generated by high-energy
 beams of Varian accelerators of different energies in a water phantom at a depth of 10 cm, depending on
 the settings of the collimation system.
 This work was carried out with the financial support of the Russian Foundation for Basic Research and
 SITMA within the framework of scientific project No. 18-52-34008.

OPTIMIZATION OF "GLUCOSE 11C" PHARMACEUTICAL PRODUCTION ON THE BEAM OF ELECTRON ACCELERATOR

The process of "Glucose 11C" pharmaceutical production by means of a photonuclear reaction 12C(γ, n) 11C is considered. The parameters of bremsstrahlung and electron beam scattered in the converter are investigated and optimized. It is proposed to use a constant-field magnet to remove electrons from the photon beam. A magnet de-sign is proposed that allows obtaining a field of 0.5 T in a gap of 25 mm. The production of the 11C isotope in the glucose target was estimated.

Specular reflection of hard gamma-quanta from surfaces with different roughness

A model on the structure of a thin, weakly diverging beam of hard electron bremsstrahlung and its transformation during its reflection from a microscopically smooth surface at small angles had been developed, which makes it possible to establish dependences of the specular reflection coefficients on the angular and energy distributions. Experimentally, the reflection of a bremsstrahlung beam with the boundary energy Ee = 6.25 MeV formed at a sliding angle α = 40 μrad with an angular divergence δγ = 27 μrad from the surface of mercury (surfaces with various roughness) was investigated on a 120-meter base. The dependences of the specular reflection coefficients on the sliding angles, the energy of the reflected γ-radiation, and the surface roughness found in this experiment correspond to theoretical predictions.

Miniaturized scintillator dosimeter for small field radiation therapy

The concept of a miniaturized inorganic scintillator detector is demonstrated in the analysis of the small static photon fields used in external radiation therapy. Such a detector is constituted by a 0.25 mm diameter and 0.48 mm long inorganic scintillating cell (1.6 × 10−5 cm3 detection volume) efficiently coupled to a narrow 125 μm diameter silica optical fiber using a tiny photonic interface (an optical antenna). The response of our miniaturized scintillator detector (MSD) under 6 MV bremsstrahlung beam of various sizes (from 1 × 1 cm2 to 4 × 4 cm2) is compared to that of two high resolution reference probes, namely, a micro-diamond detector and a dedicated silicon diode. The spurious Cerenkov signal transmitted through our bare detector is rejected with a basic spectral filtering. The MSD shows a linear response regarding the dose, a repeatability within 0.1% and a radial directional dependence of 0.36% (standard deviations). Beam profiling at 5 cm depth with the MSD and the micro-diamond detector shows a mismatch in the measurement of the full widths at 80% and 50% of the maximum which does not exceed 0.25 mm. The same difference range is found between the micro-diamond detector and a silicon diode. The deviation of the percentage depth dose between the MSD and micro-diamond detector remains below 2.3% within the first fifteen centimeters of the decay region for field sizes of 1 × 1 cm2, 2 × 2 cm2 and 3 × 3 cm2 (0.76% between the silicon diode and the micro-diamond in the same field range). The 2D dose mapping of a 0.6 × 0.6 cm2 photon field evidences the strong 3D character of the radiation-matter interaction in small photon field regime. From a beam-probe convolution theory, we predict that our probe overestimates the beam width by 0.06%, making our detector a right compromise between high resolution, compactness, flexibility and ease of use. The MSD overcomes problem of volume averaging, stem effects, and despite its water non-equivalence it is expected to minimize electron fluence perturbation due to its extreme compactness. Such a detector thus has the potential to become a valuable dose verification tool in small field radiation therapy, and by extension in Brachytherapy, FLASH-radiotherapy and microbeam radiation therapy.

Measurements of Short-Lived Isomers from Photofission as a Method of Active Interrogation for Special Nuclear Materials

Isomeric fission products, such as ${}^{134m}\mathrm{Te}$ (${T}_{1/2}=164$ ns) and ${}^{136m}\mathrm{Xe}$ (${T}_{1/2}=2.95\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{s}$), are proposed as a signature of special nuclear materials in active interrogation applications. To test this conjecture, monoenergetic 9, 11, and 13 MeV photons from the $\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$ facility are used to induce fission of ${}^{235}\mathrm{U}$, ${}^{238}\mathrm{U}$, and ${}^{239}\mathrm{Pu}$ targets. The de-excitation $\ensuremath{\gamma}$ rays of the isomers are measured using time-gated spectroscopy with high-purity germanium detectors. The ${}^{134m}\mathrm{Te}$ and ${}^{136m}\mathrm{Xe}$ isomers are detected and identified by the energy and decay half-life of their characteristic $\ensuremath{\gamma}$-ray transitions. The ratio of yields for these two signature $\ensuremath{\gamma}$ rays, corresponding to ${}^{134m}\mathrm{Te}/{(}^{136m}\mathrm{Xe}{+}^{136}\mathrm{I})$, is found to be strongly correlated with the identity of the fissioning nuclei. These results show that fission-product isomers may be used in active interrogation to detect and identify special nuclear materials, even providing information on the isotopic enrichment. The feasibility of an active interrogation scenario using a bremsstrahlung beam is discussed.

Localization of nuclear materials in large concrete radioactive waste packages using photofission delayed gamma rays

The characterization of radioactive waste packages is mandatory for their transport, interim storage and final disposal. In this framework, the Nuclear Measurement Laboratory of CEA DES IRESNE Institute, at Cadarache, France, uses a high-energy electron linear accelerator (LINAC) to produce an interrogating bremsstrahlung beam with endpoint energies ranging from 9 to 21 MeV to perform X-ray imaging and high-energy photon interrogation on large concrete packages. In particular, highenergy photon beam induces photofission reactions in both fissile (235U, 239Pu, 241Pu) and fertile (238U, 240Pu, 232Th, etc.) actinides possibly present in the radioactive waste. In order to assess their mass, we use delayed gamma rays emitted by their photofission products, which are measured with a 50 % relative efficiency High-Purity Germanium (HPGe) detector. Actinide differentiation, which is important for the fissile mass estimation, is based on the ratios of gamma rays emitted by different photofission products and requires appropriate corrections for the gamma attenuation in concrete. To this aim, we report here a localization method of point-like nuclear materials in the concrete matrix, based on the differential attenuation of several gamma rays emitted by a same photofission product. We use here the 1435.9 and 2639.6 keV lines of 138Cs, with both experimental data and MCNP numerical simulations to determine the (r,θ) coordinates of nuclear materials. Then, the depth inside the concrete matrix, which is determined with a precision of a few percent, mainly depending on counting statistics on 1435.9 and 2639.6 keV net peak areas, is used to correct for the different gamma ratios used in the actinide identification method. Experimental tests with uranium samples have been performed to validate the localization method.

Determination of the long-lived 10Be in construction materials of nuclear power plants using photoactivation method

The problem of handling nuclear power plant irradiated structural materials holds one of the central places in the nuclear power industry. High toxic 10Be with a half-life of T1/2 = 1.6 × 106 years is discovered in NPP structural materials after reactor operating. 10Be decays through only electrons' emission. Pure beta emitters are extremely difficult to determine in irradiated structural materials and radioactive waste. We proposed a photoactivation approach for determining the 10Be activity in NPP samples. The proposed method involves determining 9Be and 10B concentrations and subsequent recalculation of 10Be activity formed in 9Be(n, γ)10Be and 10B(n, p)10Be reactions. The amount of 9Be and 10B is determined by samples' photoactivation using an electron accelerator and 9Be(γ, 2n)7Be-, 10B(γ, p2n)7Be-reactions. These reactions' experimental yields were measured for 20, 40, and 55 MeV boundary energies of the bremsstrahlung beam. The proposed technique was tested on samples of ChNPP 2nd unit irradiated structural materials. The technique's calculated error is about 15–20%; the sensitivity is 1 Bq × g−1.

Estudio de la emisión de radiación de frenado mediante simulaciones mixtas con el código Monte Carlo PENELOPE

El método Monte Carlo permite la descripción precisa de las propiedades de la radiación de frenado, la cual se emplea en medicina para radiodiagnóstico o radioterapia. El código PENELOPE descansa en la implementación de historias condensadas para el transporte de partículas cargadas y permite al usuario adaptar el grado de detalle de las simulaciones mediante los parámetros de simulación. La variación de estos parámetros puede afectar a las distribuciones de partículas obtenidas al simular radiación de frenado producida en blancos gruesos. En este trabajo se analizan las diferencias entre simulaciones con distinto grado de detalle mediante la reproducción con PENELOPE de experimentos publicados de producción de radiación de frenado con electrones de alta y baja energía. Para ello se varían los parámetros de simulación C1 y C2 hasta alcanzar un valor a partir del cual los resultados de las simulaciones son estadísticamente equivalentes. Se ha observado que una inadecuada elección de los parámetros de simulación conlleva una reproducción inexacta de las características del haz de frenado. Se necesita mayor grado de detalle para simular electrones de alta energía en un material de alto número atómico que para electrones de baja energía en un material de bajo número atómico.

12C(p,p′)12CReaction (Ep=19.5–30MeV) for Active Interrogation of Special Nuclear Material

Passive detection of special nuclear material (SNM) is challenging due to its inherently low rate of spontaneous emission of penetrating radiation, the relative ease of shielding, and the fluctuating and frequently overwhelming background. Active interrogation (AI), the use of external radiation to increase the emission rate of characteristic radiation from SNM, has long been considered to be a promising method to overcome those challenges. Current AI systems that incorporate radiography tend to use bremsstrahlung beams, which can deliver high radiation doses. Low-energy ion-driven nuclear reactions that produce multiple monoenergetic photons may be used as an alternative. The $^{12}$C(p,p')$^{12}$C is one such reaction that could produce large gamma-ray yields of highly penetrating 4.4- and 15.1-MeV gamma rays. This reaction does not directly produce neutrons below the $\sim$19.7-MeV threshold, and the 15.1-MeV gamma-ray line is well matched to the photofission cross-section of $^{235}$U and $^{238}$U. We report the measurements of thick-target gamma-ray yields at 4.4 and 15.1 MeV from the $^{12}$C(p,p')$^{12}$C at proton energies of 19.5, 25, and 30 MeV. Measurements were made with two 3'' EJ309 cylindrical liquid scintillation detectors and thermoluminescent dosimeters placed at 0 and 90 degrees. We estimate the highest yields of the 4.4- and 15.1-MeV gamma rays of 1.65$\times10^{10}$ sr$^{-1}\mu$ C$^{-1}$ and 4.47$\times10^8$ sr$^{-1}\mu$ C$^{-1}$ at a proton energy of 30 MeV, respectively. The yield of 4.4 and 15.1 MeV gamma rays in all experimental configurations is greater than a comparable deuteron-driven reaction that produces the same gamma-ray energies- $^{11}$B(d,n$\gamma$)$^{12}$C. However, a two orders of magnitude increase of the neutron radiation dose is observed when the proton energy increases from 19.5 to 30 MeV.