empirical predictions as well as theoretical calculations regarding this problem given by different authors. Some of the models are presented in this section.
One of the first empirical formula was given by Salzborn and Müller . They investigated electron capturecross sections for Ne, Ar, Kr and Xe ions collisions with rare gas atoms and molecular gases (H 2 , O 2 , N 2 , CH 4 , CO 2 ) in the energy range from few keV to 100 keV. Following Olson and Salop they assumed that electron capturecross sections in lowenergy regime do not depend significantly on the projectile energy and for ion charges q>4 do not depend on ion species and should depend only on the initial ion charge state.
235 U evaluation. The benchmarks have been selected by privileging the experiments showing small experimental uncertainties and a significant sensitivity to 235 U capturecross-section. The k eff calculations were performed with both the MCNP 6 code and the 5.C.1 release of the MORET 5 code, using the ENDF/B-VII.1 library for all isotopes except 235 U, for which both the ENDF/B-VII.1 and the new 235 U evaluation was used. The benchmark selection allowed highlighting a significant effect on k eff of the new 235 U capturecross-section. The results of this data testing, provided as input for the evaluators, are presented here.
5 Dipartimento di Scienza e Alta Tecnologia, Università degli Studi dell’Insubria, I-22100 Como, Italy
6 Istituto Nazionale di Fisica Nucleare - Milano Bicocca, I-20126 Milano, Italy
7 Istituto Nazionale di Fisica Nucleare - Trieste, I-34127 Trieste, Italy
Abstract. The antinucleon-nuclei annihilation cross sections at low energies were sys- tematically measured at CERN in the 80’s and 90’s with the LEAR facility and later with the Antiproton Decelerator. Unfortunately only few data exist for very lowenergy antiprotons (p<500 MeV/c) on medium and heavy nuclei. A deeper knowledge is re- quired by fundamental physics and can have consequence also in cosmology and medical physics. In order to fill the gap, the ASACUSA Collaboration has very recently measured the annihilation crosssection of 100 MeV/c antiprotons on carbon. In the present work the experimental result is presented together with a comparison both with the antineutron data on the same target at the same energies and with the other existing antiproton data at higher energies.
The ASACUSA collaboration recently measured the antiproton-carbon annihilation crosssection at 5.3 MeV of kinetic energy of the incoming antiproton. The experimental appa- ratus consisted in a vacuum chamber containing thin foils (∼0.7–1 µm) of carbon crossed by a bunched beam of antiprotons from the CERN Antiproton Decelerator (AD). The fraction of antiprotons annihilating on the target nucleons gives origin to charged pions which can be detected and counted by segmented scintillators placed outside the cham- ber. This work describes the experimental details of the apparatus and the technique to perform the crosssection measurements.
outgoing electrons (e 1 and e 2 ) and the recoil ion is recorded.
From the positions of the hits and the times of flight (TOF), the vector momenta of the detected particles can be calculated.
Note that the projectile beam axis (defining the longitudinal direction) is adjusted exactly parallel to the electric and magnetic extraction fields. Therefore, after passing the target gas jet, the beam arrives at the center of the electron detector, where a central bore in the multichannel plates allows for the undeflected electrons to pass without inducing a hit. In this way, a large part of the full solid angle is covered while there are acceptance holes for electron emission under small forward and backward angles. The cross sections presented here cover the full azimuthal angular range and polar angular ranges of 30 ◦ θ 2 150 ◦ for E 2 = 3 eV, 30 ◦ θ 2 160 ◦ for E 2 = 5 eV, and 40 ◦ θ 2 170 ◦ for E 2 = 15 eV. The momentum resolution for the detected electrons is about 0.05 a.u. This translates into angular resolutions of θ = 5 ◦ for a slow final-state electron with 5 eV kinetic energy and θ = 2 ◦ for the forward-scattered projectile electron with about 50 eV energy.
CO + 2
Figure 2: Recorded time of flight mass spectra identifying all of the detected ions.
Figure 2, shows an example of a recorded time of flight mass spectra identifying the ionization and the dissociative ionic fragments. The areas under the various peaks, after removing the background, were normalized to the same proton current and target gas pressure for all the collisional energies. Our measured relative cross sections for ionization and all of the dissociation fragments are presented in figure 3 within the energy range of 2-9.5 keV. It can be seen that is the dominant fragment, followed by , , and . Besides the statistical uncertainties as shown in figure 3 that are involved, there are additional systematic uncertainties that are mainly due to pressure measurements as well as to the proton beam intensity. The errors in the target gas pressures are identified by the pressure gauge manufacturers to be of ± 5 % and the variations of the gas pressure during each measurement.
A trajectory is generated by selecting an initial point on the section and using the constraints p x = 0 and y > ˙ 0 along with the energy integral to calculate the initial momenta of the orbit. The initial state is then propagated forwards in time using the symplectic integration scheme described above. Intersections of the trajectory with the SOS are checked for after each timestep by looking for a change in sign of p x to detect the crossing of p x = 0. If a crossing is detected the exact location of the intersection is then interpolated. With a small enough timestep this provides an accurate calculation of the SOS. The integration length was chosen to be sufficient to fully populate the KAM tori. For the results presented here a timestep of 0.005 in dimensionless units is used (approximately 6 hours) and the integration length is approximately 0.8 MYr. The method was tested by computing specific sections that could be compared to results in the literature.
In this chapter, the effect of geometry of confining electric potential on centered donor-related PCS in spherical quantum dots is investigated. The electric potentials considered are the parabolic, shifted parabolic, cup-like, and the hill-like potentials, all of which have a parabolic dependence on the radial distance of the spherical quantum dot. To start with, the Schrödinger equation is solved for the electron’s eigenfunctions and energy eigenvalues within the effective mass approximation. It is emphasized that the treatment of photoionization process given here is limited only to isotropic media.
Associate Professor, Department of Physics, Shri M. M. Science College, Morbi, Gujarat, India 1
ABSTRACT: In this paper we calculated differential scattering crosssection for lowenergy electron collision interaction with polyatomic Trifluoromethane (CHF 3 ). The electron collision processes will be helpful to understanding the behaviour of CHF 3 in its use in manufacturing semiconductor devices and other application. CHF 3 is used for plasma etching of silicon compounds for microelectronics fabrication, and so there is interest in developing computer models for plasmas sustained in CHF 3 . Recent measured data have provided a sufficient basis to develop the electron impact differential crosssection set for CHF 3 . The rotational excitation electron impact differential cross sections (DCS) for polyatomic CHF 3 molecule are calculated, at lowenergy 1.5eV, 5.0eV and 7.0eV. The Born Eikonal Series Approximation method and the hard sphere dipole interaction potential model are employed in the present investigation. The present DCS results obtained in angular range (0 to180) . are compared with experimental and other theoretically calculated results. The present results are found better than as compared results.
The experimental data at the lower energies can be de- scribed reasonably well with the theoretical predictions based on a meson-exchange model @ 62–71 # and a hybrid- quark model @ 72 # . The meson-exchange model has one to two meson exchanges between a parity-conserving, strong interaction vertex and a parity-nonconserving, weak interac- tion vertex. At energies below a few hundred MeV in p-p elastic scattering, the parity-conserving interaction is de- scribed by meson-exchange potentials, while the parity- nonconserving interaction is described by several meson- nucleon coupling constants. The predictions give A L ; 10 2 7 . Other theoretical calculations are based on the multiperipheral model @ 73 # , and heavy-boson exchange @ 74 # . At higher energies, a quark-model calculation @ 75,76 # of A L shows that the dominant contribution comes from the parity-nonconserving interaction of two quarks from the same beam proton that may be described as a mixing of the beam protons into intermediate states of negative parity. This higher-twist subprocess dominating the high-energy asym- metry can be approximated in the parton model as quark- vector diquark scattering. A vector diquark from the polar- ized proton ~ unpolarized target ! interacts strongly with a quark from the unpolarized target ~ polarized beam ! with the parity-nonconserving weak interaction occurring only be- tween the quarks of the vector diquark. The asymmetry con- tains soft processes with poorly-known individual param- eters, so the normalization needs to be fixed by experimental data. Once this is fixed, all of the uncertainty in the asym- metry is due to a parameter b, which effectively represents the rate of scale variation of the strength of the QCD cou- pling. By fixing the normalization to the 5.1-GeV data point, the theoretical prediction at 800 MeV matches the experi- mental value fairly well. This calculation predicts a value of A L ; 10 2 4 at a laboratory momentum of 200 GeV/c for b 5 1.4.
When nuclear PDF parameterisations allow for more significant x dependence, the di ff erent sen- sitivity of given probes to specific x-ranges become more important. In this context, it is interesting to compare the sensitivity of different probes - this has been done in Fig. 5. The left panel shows the distributions for different probes of similar p T as obtained from PYTHIA simulations. All probes are sensitive to values of x < 10 −5 , but the distributions have significant tails towards very large x. For measurements possible within LHCb, DY pairs would have a strong advantage from their x-sensitivity, however, they are sensitive to gluons only at next-to-leading order, and, likely more important, their crosssection is extremely small making a measurement very challenging. A measurement of real pho- tons, as it should become possible with the proposed forward calorimeter (FoCal) in ALICE [6, 7], would have an x-sensitivity similar to DY, but would not suffer from those disadvantages.
KEYWORDS: Ccomet’s molecules, Dipole potential, Momentum transfer crosssection I. I NTRODUCTION
Comets contain some of the oldest and most pristine materials in our Solar System. Understanding their unique chemistry could reveal much about the birth of our planet and the origin of organic compounds that are the building blocks of life. ALMA's high-resolution observations provided a tantalizing 3D perspective of the distribution of the molecules within comets and their atmospheres.
Abstract. Neutron capturecross sections and covariances on radioactive 99 Tc and 129 I have been required for developing environmental load-reducing technology. Their eval- uation was performed by using nuclear reaction calculation code CCONE and Baysian code KALMAN with data assumed on the basis of measured data. The obtained total and capturecross sections are in good agreement with the measured data. The result- ing uncertainties of capturecrosssection were 12-18% and 20-29% for 99 Tc and 129 I, respectively, in the keV energy region.
Jayantilal G. Raiyani 1
Associate Professor, Dept. of Physics, Shri M. M. Science College, Morbi, Gujarat, India 1
ABSTRACT: In this paper, we calculated differential scattering crosssection for lowenergy electron collision interaction with polyatomic Nitrogen oxide (N 2 O) and Ozone (O 3 ) molecules. The rotational excitation electron impact differential cross sections (DCS) for polyatomic N 2 O and O 3 molecules are calculated, at lowenergy 5.0 eV, 7.5 eV and 10 eV. respectively. The Born Eikonal Series Approximation method and the hard sphere dipole interaction potential model are employed in the present investigation. The present DCS results obtained in angular range (0 ° to180 ° ) . are compared with experimental and other theoretically calculated results. The present results are found better than as compared results.
2 CEA, DAM, DIF, F-91297 Arpajon, France
Abstract. Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we extend our large-scale calculations of the E1 and M1 absorption γ-ray strength function obtained in the framework of the axially- symmetric deformed quasiparticle random phase approximation (QRPA) based on the finite-range D1M Gogny force to the determination of the de-excitation strength function. To do so, shell-model calculations of the de-excitation dipole strength function as well as experimental data are considered to provide insight in the low-energy limit and to complement the QRPA estimate phenomenologically. We compare our final prediction of the E1 and M1 strengths with available experimental data at low energies and show that a relatively good agreement can be obtained. Its impact on the average radiative width as well as radiative neutron capturecrosssection is discussed.
The calculation of the E1-strength function necessi- tates the knowledge of the low-energy tail of the GDR, governed by the ( γ, γ ) crosssection below the neutron separation energy . Figure 1 shows the main modes of excitations which take place below the GDR. As can be seen, the Pygmy Dipole Resonance (PDR) defines a specific relief of the nuclear dipole response at the tail of the GDR. Measurements at the High Intensity Gamma- Ray Source (HIγ S) facility using monoenergetic and 100% polarized photon beams confirmed the theoretical predictions that the PDR is dominated by E1 excitations [3,4]. Recent experimental and advanced microscopic theoretical studies of the low-energy dipole response of N = 82 and N = 50 isotopes indicate the existence of M1 dipole strength below and closely above the neutron threshold which is related to the excitation of the isovector spin-flip giant resonance [4,5]. However, the determination of neutron-capture reaction rates is based on ‘pure’ statistical HF codes which do not account for M1 contributions. Furthermore, higher-order multipole admixtures e.g., E2 strengths, should be also included to the total photon-transmission coefficient, even though they are expected to have a minuscule amount of the total γ SF.
Fig. 4. Nuclear reaction cross-section sum variation over tungsten sample depth for 10 MeV deuteron, 30 and 45 MeV protons.
protons. It is clearly seen that, as the proton energy increases from 16 to 30 and 45 MeV, there is Bragg peak shift from ∼360 μm to higher depths of ∼1.03 mm and ∼2.06 mm respectively. In view of the higher penetration range of protons and rapid rise of stop- ping power close to the Bragg peak, the plateau region prior to the Bragg peak, which is devoid of rapid drop in proton energy, is considered in this work as applicable irradiation range. This results in an applicable initial sample thickness of 30 0 μm, 50 0 μm and 1 mm for 16, 30 and 45 MeV protons respectively. This strategy is important for all irradiation damage types as it considers vari- ations of nuclear reaction probabilities and PKA distribution, both closely related to the beam energy.