scholarly journals Study of the 232Th(n,f) Cross section at NCSR ‘Demokritos’ using Micromegas Detectors

2020 ◽  
Vol 27 ◽  
pp. 106
Author(s):  
Sotirios Chasapoglou ◽  
A. Tsantiri ◽  
A. Kalamara ◽  
M. Kokkoris ◽  
V. Michalopoulou ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Detection Efficiency ◽  
High Energy ◽  
Tandem Accelerator ◽  
Line Detector ◽  
Accelerator Driven Systems ◽  
The Masses

The accurate knowledge of neutron-induced fission cross sections in actinides, is of great importance when it comes to the design of fast nuclear reactors, as well as accelerator driven systems. Specifically for the 232Th(n,f) case, the existing experimental datasets are quite discrepant in both the low and high energy MeV regions, thus leading to poor evaluations, a fact that in turn implies the need for more accurate measurements.In the present work, the total cross section of the 232Th(n,f) reaction has been measured relative to the 235U(n,f) and 238U(n,f) ones, at incident energies of 7.2, 8.4, 9.9 MeV and 14.8, 16.5, 17.8 MeV utilizing the 2H(d,n) and 3H(d,n) reactions respectively, which generally yield quasi-monoenergetic neutron beams. The experiments were performed at the 5.5 MV Tandem accelerator laboratory of N.C.S.R. “Demokritos”, using a Micromegas detector assembly and an ultra thin ThO2 target, especially prepared for fission measurements at n_ToF, CERN during its first phase of operations, using the painting technique. The masses of all actinide samples were determined via α-spectroscopy. The produced fission yields along with the results obtained from activation foils were studied in parallel, using both the NeusDesc [1] and MCNP5 [2] codes, taking into consideration competing nuclear reactions (e.g. deuteron break up), along with neutron elastic and inelastic scattering with the beam line, detector housing and experimental hall materials. Since the 232Th(n,f) reaction has a relatively low energy threshold and can thus be affected by parasitic neutrons originating from a variety of sources, the thorough characterization of the neutron flux impinging on the targets is a prerequisite for accurate cross-section measurements, especially in the absence of time-of-flight capabilities. Additional Monte-Carlo simulations were also performed coupling both GEF [3] and FLUKA [4] codes for the determination of the detection efficiency.

scholarly journals Measurement of the 234U(n,f) cross section in the energy range between 14.8 and 17.8 MeV using Micromegas detectors

2020 ◽  
Vol 27 ◽  
pp. 25
Author(s):  
Antigoni Kalamara ◽  
S. Chasapogloou ◽  
V. Michalopoulou ◽  
A. Stamatopoulos ◽  
Z. Eleme ◽  
...  
Keyword(s):  
Energy Range ◽  
Cross Section ◽  
Cross Sections ◽  
Volume Fraction ◽  
Tandem Accelerator ◽  
Driven Systems ◽  
Accelerator Driven Systems ◽  
New Generation ◽  
Actinide Targets ◽  
Fission Yields

Neutron induced fission cross sections of actinides present special interest, since they lead to the design optimization of new generation reactors (Generation IV) as well as Accelerator Driven Systems (ADS). In the present work, the 234U(n,f) cross section was measured for which only a few available discrepant data exist in literature leading to poor evaluations. More specifically, four irradiations were performed at the 5.5 MV Tandem Accelerator Laboratory of NCSR “Demokritos” using quasi-monoenergetic neutrons produced by the 3H(d,n)4He reaction in the 14.8-19.2 MeV energy range. The 234U(n,f) cross section was measured relatively to the 235U(n,f) and 238U(n,f) reference ones and in order to perform the in-beam measurements for each of the actinide targets (234U, 238U, 235U), a Micromegas detector was used to record the fission fragments. The target-detector pairs were placed in an Al chamber filled with a Ar:CO2 (in 80:20 volume fraction) gas mixture at atmospheric pressure and temperature. The efficiency of the Micromegas detectors was estimated by Monte-Carlo simulations using the GEF and FLUKA codes. In addition, a detailed study of the neutron energy spectra was carried out by coupling both NeuSDesc and MCNP5 codes in order to take into account and correct for the contribution of low energy parasitic neutrons in the fission yields.

Cross-section measurements of 6Li, 7Li, 9Be, 10Be, 10B, 11B formed by spallation reactions induced by protons in the energy range 150 MeV to 19 GeV in oxygen targets

1968 ◽  
Vol 46 (10) ◽  
pp. S557-S560 ◽  
Author(s):  
F. Yiou ◽  
J. Dufaure de Citres ◽  
F. Frehel ◽  
E. Gradsztajn ◽  
R. Bernas
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Cosmic Ray ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Mass Spectrometric ◽  
Spectrometric Method ◽  
Mass Spectrometric Method ◽  
Spallation Reactions

The determination of Li, Be, and B cross sections formed by spallation reactions induced by high-energy protons in C, N, and O targets is of interest for cosmic-ray physics and astrophysics. A mass-spectrometric method has been devised to measure the stable and long-lived isotopes 6Li, 7Li, 9Be, 10Be (τ = 2.5 × 106 yr), 7Be (τ = 54 d), 10B, 11B, formed in oxygen for proton energies of 0.15, 0.60, and 19 GeV. These results have been included in a program of calculations allowing us to determine the quantity of matter traversed by galactic cosmic rays of energy > 1.5 GeV/nucleon; the observed relative abundances are best fitted, in the slab approximation, by passage through 5.4 ± 1 g/cm2 of hydrogen.

A quantitative approach to inner shell losses

1978 ◽  
Vol 36 (1) ◽  
pp. 526-527 ◽  
Author(s):  
R.D. Leapman ◽  
P. Rez ◽  
D.F. Mayers
Keyword(s):  
Energy Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Accurate Determination ◽  
Background Intensity ◽  
Core Excitation ◽  
Quantitative Basis ◽  
Cross Section Differential ◽  
Bound Electrons

Microanalysis by EELS has been developing rapidly and though the general form of the spectrum is now understood there is a need to put the technique on a more quantitative basis (1,2). Certain aspects important for microanalysis include: (i) accurate determination of the partial cross sections, σx(α,ΔE) for core excitation when scattering lies inside collection angle a and energy range ΔE above the edge, (ii) behavior of the background intensity due to excitation of less strongly bound electrons, necessary for extrapolation beneath the signal of interest, (iii) departures from the simple hydrogenic K-edge seen in L and M losses, effecting σx and complicating microanalysis. Such problems might be approached empirically but here we describe how computation can elucidate the spectrum shape.The inelastic cross section differential with respect to energy transfer E and momentum transfer q for electrons of energy E0 and velocity v can be written as

In situ irradiation effects studies in medium- and high-voltage TEM

1995 ◽  
Vol 53 ◽  
pp. 234-235
Author(s):  
Charles W. Allen
Keyword(s):  
Cross Section ◽  
Particle Flux ◽  
Threshold Value ◽  
High Energy ◽  
Irradiation Damage ◽  
Defect Complexes ◽  
Lattice Position ◽  
Electrons And Ions ◽  
The Masses

With respect to structural consequences within a material, energetic electrons, above a threshold value of energy characteristic of a particular material, produce vacancy-interstial pairs (Frenkel pairs) by displacement of individual atoms, as illustrated for several materials in Table 1. Ion projectiles produce cascades of Frenkel pairs. Such displacement cascades result from high energy primary knock-on atoms which produce many secondary defects. These defects rearrange to form a variety of defect complexes on the time scale of tens of picoseconds following the primary displacement. A convenient measure of the extent of irradiation damage, both for electrons and ions, is the number of displacements per atom (dpa). 1 dpa means, on average, each atom in the irradiated region of material has been displaced once from its original lattice position. Displacement rate (dpa/s) is proportional to particle flux (cm-2s-1), the proportionality factor being the “displacement cross-section” σD (cm2). The cross-section σD depends mainly on the masses of target and projectile and on the kinetic energy of the projectile particle.

scholarly journals Total cross sections of eγ → $$ eX\overline{X} $$ processes with X = μ, γ, e via multiloop methods

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Roman N. Lee ◽  
Alexey A. Lyubyakin ◽  
Vyacheslav A. Stotsky
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Elliptic Integral ◽  
High Energy ◽  
Calculation Methods ◽  
Complete Elliptic Integral ◽  
Total Cross Sections ◽  
Multiloop Calculation ◽  
The Cross ◽  
Analytical Expressions

Abstract Using modern multiloop calculation methods, we derive the analytical expressions for the total cross sections of the processes e−γ →$$ {e}^{-}X\overline{X} $$ e − X X ¯ with X = μ, γ or e at arbitrary energies. For the first two processes our results are expressed via classical polylogarithms. The cross section of e−γ → e−e−e+ is represented as a one-fold integral of complete elliptic integral K and logarithms. Using our results, we calculate the threshold and high-energy asymptotics and compare them with available results.

scholarly journals Saturation effects in SIDIS at very forward rapidities

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
E. Iancu ◽  
A. H. Mueller ◽  
D. N. Triantafyllopoulos ◽  
S. Y. Wei
Keyword(s):  
Inelastic Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
Virtual Photon ◽  
Large Fraction ◽  
Quark Distribution ◽  
High Energy ◽  
Longitudinal Momentum ◽  
Black Disk ◽  
Gluon Saturation

Abstract Using the dipole picture for electron-nucleus deep inelastic scattering at small Bjorken x, we study the effects of gluon saturation in the nuclear target on the cross-section for SIDIS (single inclusive hadron, or jet, production). We argue that the sensitivity of this process to gluon saturation can be enhanced by tagging on a hadron (or jet) which carries a large fraction z ≃ 1 of the longitudinal momentum of the virtual photon. This opens the possibility to study gluon saturation in relatively hard processes, where the virtuality Q2 is (much) larger than the target saturation momentum $$ {Q}_s^2 $$ Q s 2 , but such that z(1 − z)Q2 ≲ $$ {Q}_s^2 $$ Q s 2 . Working in the limit z(1 − z)Q2 ≪ $$ {Q}_s^2 $$ Q s 2 , we predict new phenomena which would signal saturation in the SIDIS cross-section. For sufficiently low transverse momenta k⊥ ≪ Qs of the produced particle, the dominant contribution comes from elastic scattering in the black disk limit, which exposes the unintegrated quark distribution in the virtual photon. For larger momenta k⊥ ≳ Qs, inelastic collisions take the leading role. They explore gluon saturation via multiple scattering, leading to a Gaussian distribution in k⊥ centred around Qs. When z(1 − z)Q2 ≪ Q2, this results in a Cronin peak in the nuclear modification factor (the RpA ratio) at moderate values of x. With decreasing x, this peak is washed out by the high-energy evolution and replaced by nuclear suppression (RpA< 1) up to large momenta k⊥ ≫ Qs. Still for z(1 − z)Q2 ≪ $$ {Q}_s^2 $$ Q s 2 , we also compute SIDIS cross-sections integrated over k⊥. We find that both elastic and inelastic scattering are controlled by the black disk limit, so they yield similar contributions, of zeroth order in the QCD coupling.

scholarly journals Measurement of the 241Am(n,2n)240Am cross section at 17.5 MeV

2019 ◽  
Vol 21 ◽  
pp. 160
Author(s):  
A. Kalamara ◽  
R. Vlastou ◽  
M. Diakaki ◽  
M. Kokkoris ◽  
M. Anastasiou ◽  
...  
Keyword(s):  
Cross Section ◽  
Neutron Beam ◽  
Cross Sections ◽  
Reaction Cross ◽  
Activation Technique ◽  
Tandem Accelerator ◽  
Hpge Detectors ◽  
Reaction Cross Sections ◽  
Reference Reaction ◽  
High Radioactivity

The 241Am(n,2n)240Am reaction cross section has been measured at neutron beam energy 17.5 MeV, relative to the 27Al(n,α)24Na, 197Au(n,2n)196Au and 93Nb(n,2n)92mNb reference reaction cross sections, using the activation technique. The irradiation was carried out at the Van der Graaff 5.5 MV Tandem accelerator laboratory of NCSR “Demokritos” with monoenergetic neutron beam provided by means of the 3H(d,n)4He reaction, implementing a new Ti-tritiated target. The high purity Am target has been constructed at IRMM, Geel, Belgium and consisted of 40 mg 241Am in the form of AmO2 pressed into pellet with Al2O3 and encapsulated into Al container. Due to this high radioactivity (5 GBq), the Am target was enclosed in a Pb container for safety reasons. After the end of the irradiation, the activity induced by the neutron beam at the target and reference foils, was measured off-line by two 100%, a 50% and a 16% relative efficiency, HPGe detectors.

scholarly journals Activation cross section of the (n,2n) reaction on Hf isotopes

2019 ◽  
Vol 23 ◽  
pp. 47
Author(s):  
A. Kalamara ◽  
M. Serris ◽  
A. Spiliotis ◽  
D. Sigalos ◽  
N. Patronis ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Reaction Cross Section ◽  
Beam Energy ◽  
Reaction Cross ◽  
Activation Technique ◽  
Incident Neutron ◽  
Activation Cross Section ◽  
Reference Reaction

Cross sections of the 174Hf(n,2n)173Hf and 176Hf(n,2n)175Hf reactions have been experimentally determined relative to the 27Al(n,α)24Na reference reaction at incident neutron energies of 15.3 and 17.1 MeV by means of the activation technique. The irradiations were carried out at the 5 MV tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" with monoenergetic neutron beams provided via the 3H(d,n)4He reaction, using a new Ti-tritiated target of 373 GBq activity. In the determination of the 176Hf(n,2n)175Hf reaction cross section the contamination of the 174Hf(n,γ)175Hf and 177Hf(n,3n)175Hf reactions has been taken into account. Moreover, the neutron beam energy has been studied by means of Monte Carlo simulation codes and the neutron flux has been determined via the 27Al(n,α)24Na reference reaction.

scholarly journals Determination of the absorption cross-sections of higher order iodine oxides at 355 nm and 532 nm

2020 ◽  
Author(s):  
Thomas R. Lewis ◽  
Juan Carlos Gómez Martin ◽  
Mark A. Blitz ◽  
Carlos A. Cuevas ◽  
John M. C. Plane ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Atmospheric Chemistry ◽  
Absorption Cross Section ◽  
Absorption Cross ◽  
Time Resolved ◽  
Flight Mass Spectrometry ◽  
Iodine Oxides ◽  
Photo Ionization

Abstract. Iodine oxides (IxOy) play an important role in the atmospheric chemistry of iodine. They are initiators of new particle formation events in the coastal and polar boundary layer and act as iodine reservoirs in tropospheric ozone-depleting chemical cycles. Despite the importance of the aforementioned processes, the photochemistry of these molecules has not been studied in detail previously. Here, we report the first determination of the absorption cross sections of IxOy, x = 2, 3, 5, y = 1–12 at λ = 355 nm by combining pulsed laser photolysis of I2/O3 gas mixtures in air with time-resolved photo-ionization time-of-flight mass spectrometry, using NO2 actinometry for signal calibration. The oxides selected for absorption cross section determinations are those presenting the strongest signals in the mass spectra, where signals containing 4 iodine atoms are absent. The method is validated by measuring the absorption cross section of IO at 355 nm, σ355 nm, IO = (1.2 ± 0.1) ×  10–18 cm2, which is found to be in good agreement with the most recent literature. The results obtained are: σ355 nm, I2O3 

scholarly journals Quantitative Ausmessung des Brom-Affinitätskontinuums und Bestimmung der Detachment-und Attachment-Querschnitte

1970 ◽  
Vol 25 (11) ◽  
pp. 1617-1626 ◽  
Author(s):  
H. Frank ◽  
M. Neiger ◽  
H.-P. Popp
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Electron Affinity ◽  
Elastic Cross Section ◽  
Electron Atom ◽  
Intensity Measurements ◽  
Long Wave ◽  
The Mean ◽  
Intense Electron

Abstract A wall stabilized low-current cylindric arc was used to produce the radiation of the negative Bromine-ions. The radiation consists of an affinity-continuum with a long-wave threshold of 3682 Å, yielding an electron affinity for Bromine of 3.366 eV, and of an intense electron-atom Bremsstrahlung in the visible. Intensity measurements of the continua allow the determination of the photo-detachment-and attachment-cross-sections of Bromine and also the determination of the mean elastic cross-section of electrons against Bromine atoms.

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