Integral Cross Section Measurements Research Articles

A novel activation technique for integrated cross section measurements using accelerator mass spectrometry

41Ca (t1/2 = 9.94 × 104 yrs) is an important stellar radionuclide and its production in the Early Solar System from various irradiation scenarios can help determine the viability of models of early stellar processes. A novel reaction technique has been under development and recently tested at the Nuclear Science Laboratory at the University of Notre Dame. This technique utilizes an “in-cathode” reaction method, where natural CaF2 material is packed into an ion source sample holder (cathode) and then irradiated and subsequently measured using Accelerator Mass Spectrometry (AMS) without the need for chemical processing afterward. The setup for the irradiation was performed using a 3He beam to measure the reaction natCa(3He,x)41Ca. Initial AMS results suggest additional complexity due to ion source sputtering rates and geometry, which will need to be explored further.

Experimental method for determination of the integral cross-section for electron impact ionization of ions with optical control of the target’s initial quantum state

A method for measurement of integral cross-sections for electron impact ionization of ions is proposed. The technique involves the application of a quadrupole ion trap with laser-cooled ions. It allows controlling the initial quantum state of the target ions, measuring the cross-sections separately for such states. The methodology is described in detail, together with a discussion of the reliability of optical selection of the ions’ states. The first results for Ca+ ion ionization from 42S1/2 and 32D3/2 states are presented.

Charm-quark fragmentation fractions and production cross section at midrapidity in pp collisions at the LHC

Recent $p_{\rm T}$-integrated cross section measurements of the ground-state charm mesons and baryons, D$^{\rm 0}$, D$^+$, D$_{\rm s}^{+}$, $\Lambda_{\rm c}^{+}$, and $\Xi_{\rm c}^0$, are used to evaluate the charm fragmentation fractions and production cross section per unit of rapidity at midrapidity ($|y|<0.5$), in pp collisions at $\sqrt{s} = 5.02$ TeV at the LHC. The latter is ${\rm d} \sigma^{\rm c \overline{c}}/{\rm d} y|_{|y| < 0.5}$ =1165 $\pm 44(\rm{stat})^{+134}_{-101}(\rm{syst})$ $\mu b$. These measurements were obtained for the first time in hadronic collisions at the LHC including the charm baryon states, recently measured by ALICE at midrapidity. The charm fragmentation fractions differ significantly from the values measured in e$^+$e$^-$ and ep collisions, providing evidence of the dependence of the parton-to-hadron fragmentation fractions on the collision system, indicating that the assumption of their universality is not supported by the measured cross sections. An increase of a factor of about 3.3 for the fragmentation fraction for the $\Lambda_{\rm c}^{+}$ with a significance of $5\,\sigma$ between the values obtained in pp collisions and those obtained in e$^+$e$^-$ (ep) collisions is reported. The fragmentation fraction for the $\Xi_{\rm c}^0$ was obtained for the first time in any collision system. The measured fragmentation fractions were used to update the $\rm c \overline{c}$ cross sections per unit of rapidity at $|y|<0.5$ at $\sqrt{s} = 2.76$ and 7 TeV, which are about 40% higher than the previously published results. The data were compared with perturbative-QCD calculations and lie at the upper edge of the theoretical bands.

Alternative Approach for the Determination of Mean Free Paths of Electron Scattering in Liquid Water Based on Experimental Data.

Mean free paths of low-energy electrons in liquid water are of importance for modeling many physicochemical processes, but neither theoretical predictions nor experimental results have converged for these parameters. We therefore introduce an approach to determine elastic and inelastic mean free paths (EMFP, IMFP) based on experimental data. We show that ab initio calculations of electron scattering with water clusters converge with cluster size, thus providing access to condensed-phase scattering. The results are used in Monte Carlo simulations to extract EMFP and IMFP from recent liquid-microjet experiments that determined the effective attenuation length (EAL) and the photoelectron angular distribution (PAD) following oxygen 1s-ionization of liquid water. For electron kinetic energies from 10 to 300 eV, we find that the IMFP is noticeably larger than the EAL. The EMFP is longer than that of gas-phase water and the IMFP is longer compared to latest theoretical estimations, but both EMFP and IMFP are much shorter than suggested by experimental measurements of integral cross sections for amorphous ice.

Experimental study of the proton-transfer reaction C + H2+ → CH+ + H and its isotopic variant (D2+).

We report absolute integral cross section (ICS) measurements using a dual-source merged-fast-beams apparatus to study the titular reactions over the relative translational energy range of Er ∼ 0.01-10 eV. We used photodetachment of C- to produce a pure beam of atomic C in the ground electronic 3P term, with statistically populated fine-structure levels. The H2+ and D2+ were formed in an electron impact ionization source, with well known vibrational and rotational distributions. The experimental work is complemented by a theoretical study of the CH2+ electronic system in the reactant and product channels, which helps to clarify the possible reaction mechanisms underlying the ICS measurements. Our measurements provide evidence that the reactions are barrierless and exoergic. They also indicate the apparent absence of an intermolecular isotope effect, to within the total experimental uncertainties. Capture models, taking into account either the charge-induced dipole interaction potential or the combined charge-quadrupole and charge-induced dipole interaction potentials, produce reaction cross sections that lie a factor of ∼4 above the experimental results. Based on our theoretical study, we hypothesize that the reaction is most likely to proceed adiabatically through the 14A' and 14A'' states of CH2+via the reaction C(3P) + H2+(2Σ+g) → CH+(3Π) + H(2S). We also hypothesize that at low collision energies only H2+(v ≤ 2) and D2+(v ≤ 3) contribute to the titular reactions, due to the onset of dissociative charge transfer for higher vibrational v levels. Incorporating these assumptions into the capture models brings them into better agreement with the experimental results. Still, for energies ⪅0.1 eV where capture models are most relevant, the modified charge-induced dipole model yields reaction cross sections with an incorrect energy dependence and lying ∼10% below the experimental results. The capture cross section obtained from the combined charge-quadrupole and charge-induced dipole model better matches the measured energy dependence but lies ∼30-50% above the experimental results. These findings provide important guidance for future quasiclassical trajectory and quantum mechanical treatments of this reaction.

Integral cross section measurements and product recoil velocity distributions of Xe(2+) + N2 hyperthermal charge-transfer collisions.

Charge exchange from doubly charged rare gas cations to simple diatomics proceeds with a large cross section and results in populations of many vibrational and electronic product states. The charge exchange between Xe(2+) and N2, in particular, is known to create N2 (+) in both the A and B electronic states. In this work, we present integral charge exchange cross section measurements of the Xe(2+) + N2 reaction as well as axial recoil velocity distributions of the Xe(+) and N2 (+) product ions for collision energies between 0.3 and 100 eV in the center-of-mass (COM) frame. Total charge-exchange cross sections decrease from 70 Å(2) to about 40 Å(2) with increasing collision energy through this range. Analysis of the axial velocity distributions indicates that a Xe(2+) - N2 complex exists at low collision energies but is absent by 17.6 eV COM. Analysis of the axial velocity distributions reveals evidence for complexes with lifetimes comparable to the rotational period at low collision energies. The velocity distributions are consistent with quasi-resonant single charge transfer at high collision energies.

R-matrix analysis of reactions in the 9B compound system applied to the 7Li problem in BBN

Recent activity in solving the ‘lithium problem’ in big bang nucleosynthesis has focused on the role that putative resonances may play in resonance-enhanced destruction of 7Li. Particular attention has been paid to the reactions involving the 9B compound nuclear system, d+7Be → 9B. These reactions are analyzed via the multichannel, two-body unitary R-matrix method using the code EDA developed by Hale and collaborators. We employ much of the known elastic and reaction data, in a four-channel treatment. The data include elastic 3He +6Li differential cross sections from 0.7 to 2.0 MeV, integrated reaction cross sections for energies from 0.7 to 5.0 MeV for 6Li(3He,p)8Be* and from 0.4 to 5.0 MeV for the 6Li(3He,d)7Be reaction. Capture data have been added to an earlier analysis with integrated cross section measurements from 0.7 to 0.825 MeV for 6Li(3He,γ)9B. The resulting resonance parameters are compared with tabulated values, and previously unidentified resonances are noted. Our results show that there are no near d+7Be threshold resonances with widths that are 10’s of keV and reduce the likelihood that a resonance-enhanced mass-7 destruction mechanism, as suggested in recently published work, can explain the 7Li problem.

Integral cross sections for electron impact excitation of vibrational and electronic states in phenol.

We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of composite vibrational modes and electronic-states in phenol, where the energy range of those experiments was 15-250 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely, for the inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. In addition, for the relevant dipole-allowed excited electronic states, we also report f-scaled Born-level and energy-corrected and f-scaled Born-level (BEf-scaled) ICS. Where possible, our measured and calculated ICSs are compared against one another with the general level of accord between them being satisfactory to within the measurement uncertainties.

Integral cross section measurements of a few threshold reactions induced by Am/Be neutrons

Abstract Integral cross sections of the reactions 46Ti(n, p)46Sc, 47Ti(n, p)47Sc, 48Ti(n, p)48Sc, 60Ni(n, p)60Co and 64Zn(n, p)64Cu were measured with fast neutrons (E n &gt; 1.5MeV) from an Am/Be source. The results were compared with data calculated using the neutron spectral distribution and the excitation function of each reaction given in the data libraries ENDF/B-VII.0, IRDF-2002, JEFF-3.2 and JENDL-4.0. In general, the integral measurement and the integrated value agreed within ±4%, except for the 46Ti(n, p)46Sc reaction where JEFF-3.2 shows a deviation of 7% and the 60Ni(n, p)60Co reaction where ENDF/B-VII.0 and IRDF-2002 exhibit deviations upto 8%.

Cross sections for electron scattering from [formula omitted]-tetrahydrofurfuryl alcohol

We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol. The energy range of these experiments was 20–50eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely for the total cross section, elastic ICS, inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. Where possible, our calculated cross sections are compared to the limited available data of each scattering process.

Intermediate-energy differential and integral cross sections for vibrational excitation in α-tetrahydrofurfuryl alcohol.

Differential and integral cross section measurements, for incident electron energies in the 20-50 eV range, are reported for excitation of several composite vibrational modes in α-tetrahydrofurfuryl alcohol (THFA). Optimisation and frequency calculations, using GAUSSIAN 09 at the B3LYP/aug-cc-pVDZ level, were also undertaken for the two most abundant conformers of THFA, with results being reported for their respective mode classifications and excitation energies. Those calculations assisted us in the experimental assignments of the composite features observed in our measured energy loss spectra. There are, to the best of our knowledge, no other experimental or theoretical data currently available in the literature against which we can compare the present results.

R-matrix Analysis of Reactions in the 9B Compound System

Recent activity in solving the ‘lithium problem’ in big bang nucleosynthesis has focused on the role that putative resonances may play in resonance-enhanced destruction of 7Li. Particular attention has been paid to the reactions involving the 9B compound nuclear system, d+7Be→9B. These reactions are analyzed via the multichannel, two-body unitary R-matrix method using the code EDA developed by Hale and collaborators. We employ much of the known elastic and reaction data, in a four-channel treatment. The data include elastic 3He+6Li differential cross sections from 0.7 to 2.0 MeV, integrated reaction cross sections for energies from 0.7 to 5.0 MeV for 6Li(3He,p)8Be* and from 0.4 to 5.0 MeV for the 6Li(3He,d)7Be reaction. Capture data have been added to an earlier analysis with integrated cross section measurements from 0.7 to 0.825 MeV for 6Li(3He,γ)9B. The resulting resonance parameters are compared with tabulated values, and previously unidentified resonances are noted. Our results show that there are no near d+7Be threshold resonances with widths that are 10's of keV and reduce the likelihood that a resonance-enhanced mass-7 destruction mechanism, as suggested in recently published work, can explain the 7Li problem.

Integral Cross Section Measurements Around 14 MeV for Validation of Activation Libraries

This paper presents preliminary integral cross section data recently measured at the ASP 14 MeV neutron irradiation facility. Reaction cross sections were derived from neutron activated elemental foils following measurement of resulting activation product gamma emissions as a function of time and energy using a HPGe detector, with associated signal processing and data post processing tools. Selected measurements are compared with facility spectrum-averaged cross sections, calculated using the latest release of the FISPACT-II inventory code and TENDL-2011 groupwise cross section data. Examples are shown as plots of the C/E ratio. Measurements are compared with integral data derived from other neutron irradiation facilities. Together, with differential cross section measurements taken from the EXFOR database maintained by the IAEA, we briefly highlight how C/E plots contribute to validation and improvement of activation libraries.

Characterization of neutrons from a thick target 9Be(p, n) reaction by multiple foil activation technique for practical applications: measurement of integral cross sections and their comparison with integrated data from data files

Abstract The neutron spectrum in the energy range of 0.1 to 5.85 MeV in the 0○ direction with respect to the incident proton beam accelerated in a Tandem Accelerator of the Wakasa Wan Energy Research Center (WERC), Japan, has been characterized using the multiple foil activation technique. Flux mapping of thermal and epithermal neutrons at 0○, 20○, 40○ and 60○ at downstream of the beam has also been carried out. The fast neutron spectrum averaged cross sections of several threshold reactions were measured. Two monitor reactions, 58Ni(n, p)58Co and 115In(n, n′, γ)115mIn, were used to determine the fast neutron flux. The use of fast neutron flux in validating some excitation functions is described.

Toward a self-consistent and unitary reaction network for big-bang nucleosynthesis

Author(s): Paris, MW; Brown, LS; Hale, GM; Hayes-Sterbenz, AC; Jungman, G; Kawano, T; Fuller, GM; Grohs, EB; Kunieda, S | Abstract: Unitarity, the mathematical expression of the conservation of probability in multichannel reactions, is an essential ingredient in the development of accurate nuclear reaction networks appropriate for nucleosynthesis in a variety of environments. We describe our ongoing program to develop a reaction for the big-bang nucleosynthesis environment and look at an example of the need and power of unitary parametrizations of nuclear scattering and reaction data. Recent attention has been focused on the possible role of the 9B compound nuclear system in the resonant destruction of 7Li during primordial nucleosynthesis. We have studied reactions in the 9B compound system with a multichannel, two-body unitary R-matrix code (EDA) using the known elastic and reaction data, in a four-channel treatment. The data include elastic 6Li(3He, 3He)6Li differential cross sections from 0.7 to 2.0 MeV, integrated reaction cross sections for energies from 0.7 to 5.0 MeV for 6Li(3He,p)8Be* and from 0.4 to 5.0 MeV for the 6Li(3He,d)7Be reaction. Capture data have been added to the previous analysis with integrated cross section measurements from 0.7 to 0.825 MeV for 6Li(3He,γ) 9B. The resulting resonance parameters are compared with tabulated values from TUNL Nuclear Data Group analyses. Previously unidentified resonances are noted and the relevance of this analysis and a unitary reaction network for big-bang nucleosynthesis are emphasized. © Owned by the authors, published by EDP Sciences, 2014.

The translational, rotational, and vibrational energy effects on the chemical reactivity of water cation H2O+(X 2B1) in the collision with deuterium molecule D2

By employing the newly established vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) double quadrupole-double octopole ion guide apparatus, we have examined the translational, rotational, and vibrational energy effects on the chemical reactivity of water cation H2O(+)(X(2)B1) in the collision with deuterium molecule D2. The application of a novel electric-field pulsing scheme to the VUV laser PFI-PI ion source has enabled the preparation of a rovibrationally selected H2O(+)(X(2)B1; v1 (+)v2 (+)v3 (+); N(+) K a+Kc+) ion beam with not only high internal-state selectivity and high intensity but also high translational energy resolution. Despite the unfavorable Franck-Condon factors, we are able to prepare the excited vibrational states (v1 (+)v2 (+)v3 (+))=(100) and (020) along with the (000) ground vibrational state, for collisional studies, where v1 (+), v2 (+), and v3 (+) represent the symmetric stretching, bending, and asymmetric stretching modes of H2O(+)(X(2)B1). We show that a range of rotational levels from N(+) K a+Kc+ = 000 to 322, covering a rotational energy range of 0-200 cm(-1) of these vibrational states, can also be generated for absolute integral cross section (σ) measurements at center-of-mass collision energies (Ecms) from thermal energies to 10.00 eV. The Ecm dependences of the σ values are consistent with the prediction of the orbiting model, indicating that translational energy significantly hinders the chemical reactivity of H2O(+)(X(2)B1). Rotational enhancements are observed at Ecm < 0.30 eV for all the three vibrational states, (000), (100), and (020). While the σ values for (100) are found to be only slightly below those for (000), the σ values for (020) are lower than those for (000) and (100) by up to 20% at Ecm ≤ 0.20 eV, indicative of vibrational inhibition at low Ecm by excitation of the (020) mode. Rationalizations are proposed for the observed rotational enhancements and the bending vibrational inhibition. Rigorous theoretical calculations are needed to interpret the wealth of rovibrationally selected cross sections obtained in the present study.

ABSOLUTE INTEGRAL CROSS SECTIONS AND PRODUCT BRANCHING RATIOS FOR THE VIBRATIONALLY SELECTED ION-MOLECULE REACTIONS: N$_{2}^{+}$(X2Σ$_{\rm g}^{+}$;v+= 0-2) + CH4

Absolute vibrationally selected integral cross sections (σ v +'s) for the ion-molecule reaction N(X 2Σ; v + = 0-2) + CH4 have been measured by using the newly developed vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) double-quadrupole-double-octopole ion guide apparatus. By employing a novel electric field pulsing scheme to the VUV laser PFI-PI source, we have been able to prepare reactant N ions in single-vibrational quantum states with not only high intensity and high purity but also high kinetic energy resolution, allowing integral cross section measurements to be conducted in the center-of-mass kinetic energies (E cm's) from 0.05 to 10.00 eV. Three primary product channels corresponding to the formations of CH, CH, and N2H+ were identified. After correcting for the secondary reactions involving CH and CH, we have determined the σ v + values of the formation of these primary product ions, σv+(CH), σv+(CH), and σv+(N2H+), and their branching ratios, [σv+(CH): σv+(CH): σv+(N2H+)]/σv+(CH + CH + N2H+), v + = 0-2, in the E cm range of 0.05-10.00 eV, where σv+(CH + CH + N2H+) = σv+(CH) + σv+(CH) + σv+(N2H+). The branching ratios are found to be nearly independent of the v + state and E cm. Complex v +-state and E cm dependences for σv+(CH), σv+(CH), and σv+(N2H+) along with vibrational inhibition for the formation of these product ions are observed. The vibrational effects on the σv+ values are sufficiently large to warrant the inclusion of the vibrationally excited reactions N(X 2Σ; v + ≥ 1) + CH4 for a more realistic modeling of the ion and neutral densities observed in the atmosphere of Titan. The cross-sectional data obtained in the present study are also useful for benchmarking theoretical calculations on ion-neutral collision dynamics.

Prompt charm production in pp collisions at [formula omitted

Charm production at the LHC in pp collisions at s=7 TeV is studied with the LHCb detector. The decays D0→K−π+, D+→K−π+π+, D⁎+→D0(K−π+)π+, Ds+→ϕ(K−K+)π+, Λc+→pK−π+, and their charge conjugates are analysed in a data set corresponding to an integrated luminosity of 15 nb−1. Differential cross-sections dσ/dpT are measured for prompt production of the five charmed hadron species in bins of transverse momentum and rapidity in the region 0<pT<8 GeV/c and 2.0<y<4.5. Theoretical predictions are compared to the measured differential cross-sections. The integrated cross-sections of the charm hadrons are computed in the above pT-y range, and their ratios are reported. A combination of the five integrated cross-section measurements givesσ(cc¯)pT<8 GeV/c,2.0<y<4.5=1419±12(stat)±116(syst)±65(frag) μb, where the uncertainties are statistical, systematic, and due to the fragmentation functions.

A facility for fast-neutron irradiations at Jyväskylä and its use for nuclide cross-section measurements in fission

An efficient and reliable transport system for fast-neutron irradiations has been built at the Physics Department, Jyväskylä, Finland. It is constructed from commercial bicycle components and is driven by a computer-controlled stepping motor. It can be operated in single or cyclic mode. The neutron irradiated targets are moved within 1.2s (full stop to full stop) to a well-shielded position 3m away where they can be removed or directly investigated by γ spectroscopy. The system has been built with the aim to experimentally verify the calculated production rates of neutron-rich nuclei in the SPIRAL2 uranium target. However, the facility can be used for various kinds of fast-neutron irradiations, with a neutron spectrum up to 60MeV produced by stopping a deuteron beam of several μA in a thick target. Examples of applications are activation and integral cross-section measurements, evaluation of damages in materials and biological cells.

Cross section measurements at neutron energies 71 and 112 MeV and energy integrated cross section measurements (0.1 < En < 750 MeV) for the neutron induced reactions O(n,x)10Be, Si(n,x)10Be, and Si(n,x)26Al

The cross sections for the reactions O(n,x)10Be, Si(n,x)10Be, and Si(n,x)26Al were measured at neutron energies 71 and 112MeV. The neutron cross sections for O(n,x)10Be are higher than the corresponding proton cross sections at 70–110MeV and the neutron induced cross section for Si(n,x)10Be at 112MeV is slightly higher than the corresponding proton cross section. Cross sections for the production of 26Al from Si are similar to those from protons at low energies (<40MeV) while at higher energies the measured neutron cross sections for Si(n,x)26Al are lower than the corresponding proton cross sections. Energy integrated (average) cross sections for these reactions were measured using ‘white’ neutron beams (0.1<En<750MeV). The 26Al/10Be production rate ratio from SiO2 measured using ‘white’ neutrons is considerably lower than that observed in terrestrial quartz (SiO2).