Laboratory Angles Research Articles

Experimental studies of neutron emission spectra in Li(d,xn) reactions for IFMIF

To improve the accuracy of the neutron emission data in the natLi(d,xn) reaction, which will be used as the neutron source in the International Fusion Materials Irradiation Facility (IFMIF), we measured the double-differential neutron emission cross-sections (DDXs) of the d-Li reaction at 25MeV at the cyclotron facility of Tohoku University. The DDXs were measured at ten laboratory angles between 0° and 110° by the time-of-flight method, using a beam-swinger system and a well-collimated neutron flight channel. We used a two-gain method to obtain over most of the energy range of secondary neutrons and reveal the shape of the overall emission spectra including the breakup peak of incident deuterons near half the incidence energy, and several peaks in the high-energy tail due to stripping reactions. The experimental results compared favorably with those obtained using the extended Serber model.

Investigation of0+states inPt192andPt194isotopes

Excited states in $^{192}\mathrm{Pt}$ and $^{194}\mathrm{Pt}$ have been studied with high-energy resolution, in the ($p,t$) reaction, by using the Q3D magnetic spectrograph at the Munich MP tandem accelerator. Outgoing tritons were recorded at laboratory angles sensitive to the unique shape of the $L=0$ angular distribution. Sets of previously unknown ${0}^{+}$ states were identified up to an energy of $~3 \mathrm{MeV}$. The ${0}^{+}$ states in $^{192,194}\mathrm{Pt}$ are discussed in the context of the evolution of intruder states and shape coexistence in the light Pt isotopes.

Double-differential cross sections and kerma coefficients for light-charged particles produced by 96 MeV neutrons on carbon

Double-differential cross sections of inclusive light-ion (p, d, t, He-3 and alpha) production in carbon induced by 96 MeV neutrons have been measured at eight laboratory angles from 20 to 160 in steps of 20 degrees. Experimental techniques, as well as procedures for data taking and data reduction, are presented. Deduced energy-differential and production cross sections are herewith reported. Experimental cross sections are compared with theoretical reaction model calculations and experimental data in the literature. The measured production cross sections for protons, deuterons, tritons, He-3, and alpha particles support the trends suggested by data at lower energies. Deduced partial kerma coefficients for carbon are also shown.

Study of astrophysically important resonant states in 30S using the 32S(p,t) 30S reaction

The 29P(p, γ) 30S reaction plays an important role in understanding the Si isotopic abundances in presolar grains of nova origin, which in turn provide us with information on the nature of the probable white dwarf progenitor's core, as well as the peak temperatures achieved during nova outbursts. This rate at nova temperatures is determined by two low-lying 3 + and 2 + resonances above the proton threshold at 4399 keV in 30S. We have studied the 30S nuclear structure via the 32S(p,t) 30S reaction at 5 laboratory angles between 9 ° to 62 ° . We have observed 14 states including two levels at 4692.7 ± 4.5 keV and 4813.8 ± 3.4 keV that are candidates for the 3 + and the previously “missing” 2 + state, respectively.

Study of astrophysically important resonant states in 30 S using the 32S(p,t)30 S reaction

A small fraction ( P(p,γ )30 S reaction plays an important role in understanding the Si isotopic abundances in such grains, which in turn provide us with information on the nature of the probable white dwarf progenitor’s core, as well as the peak temperatures achieved during nova outbursts, and thus the nova nucleosynthetic path. The 29 P(p,γ )30 S reaction rate at nova temperatures is determined by two low-lying 3+ and 2+ resonances above the proton threshold at 4399 keV in 30 S. Despite several experimental studies in the past, however, only one of these two states has only been observed very recently. We have studied the 30 S nuclear structure via the 32 S(p,t) 30 S reaction at 5 laboratory angles between 9° to 62°. We have observed 14 states, eleven of which are above the proton threshold, including two levels at 4692.7 ± 4.5 keV and 4813.8 ± 3.4 keV that are candidates for the 3+ and the previously “issing” 2+ state, respectively.

Study of astrophysically important resonant states in 30S using the 32S(p,t)30S reaction

A small fraction (< 1%) of presolar SiC grains is suggested to have been formed in the ejecta of classical novae. The 29P(p,γ)30S reaction plays an important role in understanding the Si isotopic abundances in such grains, which in turn provide us with information on the nature of the probable white dwarf progenitor's core, as well as the peak temperatures achieved during nova outbursts, and thus the nova nucleosynthetic path. This rate at nova temperatures is determined by two low-lying 3+ and 2+ resonances above the proton threshold at 4399 keV in 30S. Despite several experimental studies in the past, however, these two states have only been observed very recently. We have studied the 30S nuclear structure via the 32S(p,t)30S reaction at 5 laboratory angles between 9° to 62°. We have observed 14 states, eleven of which are above the proton threshold, including two levels at 4692.7 ± 4.5 keV and 4813.8 ± 3.4 keV that are candidates for the 3+ and the previously "missing" 2+ state, respectively.

Subthreshold and near-threshold kaon and antikaon production in proton–nucleus reactions

The differential production cross sections of K+ and K− mesons have been measured at the ITEP proton synchrotron in p + Be, p + Cu collisions under a laboratory angle of 10.5°, respectively, at 1.7 and 2.25, 2.4 GeV beam energies. A detailed comparison of these data with the results of calculations within an appropriate folding model for incoherent primary proton–nucleon, secondary pion–nucleon kaon and antikaon production processes and processes associated with the creation of antikaons via the decay of intermediate ϕ mesons is given. We show that the strangeness exchange process YN → NNK− gives a small contribution to the antikaon yield in the kinematics of the performed experiment. We argue that in the case when antikaon production processes are dominated by the channels with KK− in the final state, the cross sections of the corresponding reactions are weakly influenced by the in-medium kaon and antikaon mean fields.

Measurement of the differential cross section for the two-body photodisintegration ofHe3atθLAB=90°using tagged photons in the energy range14−31MeV

The two-body photodisintegration of He-3 has been investigated using tagged photons with energies from 14-31 MeV at MAX-lab in Lund, Sweden. The two-body breakup channel was unambiguously identified by the (nonsimultaneous) detection of both protons and deuterons. This approach was made feasible by the overdetermined kinematic situation afforded by the tagged-photon technique. Proton-and deuteron-energy spectra were measured using four silicon surface-barrier detector telescopes located at a laboratory angle of 90 degrees with respect to the incident photon-beam direction. Average statistical and systematic uncertainties of 5.7% and 6.6% in the differential cross section were obtained for 11 photon-energy bins with an average width of 1.2 MeV. The results are compared to previous experimental data measured at comparable photon energies as well as to the results of two recent Faddeev calculations which employ realistic potential models and take into account three-nucleon forces and final-state interactions. Both the accuracy and precision of the present data are improved over those obtained in the previous measurements. The data are in good agreement with most of the previous results, and favor the inclusion of three-nucleon forces in the calculations. (Less)

Light-ion production in the interaction of 96 MeV neutrons with carbon

Double-differential cross sections for light-ion (p, d, t, 3He and alpha) production in carbon induced by 96 MeV neutrons have been measured at eight laboratory angles from 20 degrees to 160 degrees in steps of 20 degrees. Experimental techniques are presented as well as procedures for data taking and data reduction. Deduced energy-differential, angle-differential and production cross sections are reported. Experimental cross sections are compared with theoretical reaction model calculations and experimental data in the literature. The measured particle data show marked discrepancies from the results of the model calculations in spectral shape and magnitude. The measured production cross sections for protons, deuterons, tritons, 3He, and alpha particles support the trends suggested by data at lower energies.

Cross-section for D(p,p)D elastic scattering from 1.8 to 3.2 MeV at the laboratory angles of 155° and 165°

The D(p,p)D cross-sections for elastic scattering of proton on deuterium over incident proton energy range from 1.8 to 3.2 MeV at both laboratory angles of 155° and 165° were measured. A thin solid state target Ni/TiD x /Ta/Al used for cross-section measurement was fabricated by firstly depositing layers of Ta, Ti and Ni film on the Al foil substrate of about 7 μm in turn using magnetron sputtering and then deuterating under the deuterium atmosphere. The areal density of metal element in each layer of film was measured with RBS analysis by using a 4.0 MeV 4He ion beam, while the areal density of the deuterium absorbed in the Ti film was measured with ERD analysis by using a 6.0 MeV 16O ion beam. The results show that the cross-sections of p-D scattering under this experimental circumstance were much enhanced over the Rutherford cross-section value. It was found that the enhancement increases linearly as the energy of the incident beam increases. The total uncertainty in the measurements was less than 7.5%.

Singularity in the laboratory frame angular distribution derived in two-body scattering theory

The laboratory (lab) frame angular distribution derived in two-body scattering theory exhibits a singularity at the maximum lab scattering angle. The singularity appears in the kinematic factor that transforms the centre of momentum (cm) angular distribution to the lab angular distribution. We show that it is caused in the transformation by the funnelling of a range of cm scattering angles into a much smaller range of lab angles. Correct treatment of this singularity is important when transforming angular distributions from the cm or projectile frame to the lab frame.

Measurement and analysis of the energy–angular distribution of secondary neutrons for 9Be at 5.9 and 6.4 MeV incident neutrons

The energy-angle double-differential neutron emission cross-sections of beryllium have been measured using the time of flight technique for 5.9 and 6.4 MeV incident neutrons, respectively, at 10 laboratory angles between 25° and 150°. The measured results are compared with model calculations based on the LUNF code and those of other authors and the ENDF/B-VII data. The estimation of the inelastic scattering neutron cross-sections leaving 9Be ∗ at the low-lying level states are also theoretically analyzed by the LUNF code. The experimental and calculated results indicated that the lowest (1.68 MeV) level still contributes to the ( n, 2 n) reaction with cross-sections of several 10 mb. The angular distributions and the angle-integrated elastic scattering cross-sections are also presented in comparison with other ones, these being in good agreement with the ENDF/B-VII data.

Exploring the dynamics of reactions of oxygen atoms in states P3 and D1 with ethene at collision energy 3 kcal mol−1

In a crossed molecular-beam apparatus, we reacted atomic O in states (3)P and (1)D with ethene (C(2)H(4)) at collision energy 3 kcal mol(-1). Employing two mixtures, 20% O(2) + 80% He and 3% O(2) + 12.5% Ar + 84.5% He, as discharge media allowed us to generate two sources of oxygen atoms that have the same mean velocity but different ratios of (1)D/(3)P populations, 0.0017 and 0.035. We identified six reactions and recorded time-of-flight spectra of products CH(2)CHO, CH(2)CO, and CH(3) as a function of laboratory angle. Reaction O((3)P) + C(2)H(4) --> CH(2)CHO + H has a fraction f(t) = 0.43 of energy release in translation, and product CH(2)CHO has a maximal probability at scattering angle of 140 degrees. For reaction O((1)D) + C(2)H(4) --> CH(2)CO + 2H, f(t) = 0.26, and the angular distribution of product CH(2)CO shows a backward preference. For reaction O((3)P) + C(2)H(4) --> CH(2)CO + H(2), f(t) = 0.35, and the angular distribution of product CH(2)CO has a slight preference for a sideways direction. In contrast, reaction O((1)D) + C(2)H(4) --> CH(2)CO + H(2) has f(t) = 0.26 and an angular distribution with forward and backward peaking and symmetry. Reactions O((3)P and (1)D) + C(2)H(4) --> CH(3) + HCO have f(t) = 0.09 and 0.08, respectively, and angular distributions with forward and backward peaking and nearly symmetric. The reactivity of O (1)D with ethene is ca. 38 and 90 times that of O (3)P for channels to eliminate H(2) and CH(3), respectively. For reactions of O (1)D, the branching ratio for elimination of 2H is ca. 3.3 times that for elimination of H(2).

Elastic scattering cross-section of proton from helium at the laboratory angle of 165°

The differential He(p,p)He reaction cross-section was determined at a laboratory angle of 165° for proton energies between 1.6 and 3.6 MeV. A new method for preparation of helium–titanium (Ti) targets by direct current (DC) magnetron sputtering was employed for the first time. The currently measured cross-section data are compared with the available literature values. They show a similarly trend in the higher energy range but with a maximum difference of up to 12% in the absolute value. The uncertainty in the present cross-section data is about 7.3%.

Levels in 13N examined by 12C+p elastic resonance scattering with thick target**Supported by National Natural Science Foundation of China (10445004, 10575136, 10735100) and Major State Basic Research Development Program (2007CB815003)

The elastic resonance scattering of 12C+p has been studied in inverse kinematics via a novel thick target method at GIRAFFE facility of HI-13 tandem accelerator laboratory, Beijing. The recoil protons were measured by a ΔE-E counter telescope based on a large area double-sided silicon strip detector at laboratory angles around θ0 = 15°. The excitation function for 12C(p,p) elastic scattering has been obtained over a wide energy range of Ec.m.=0.31–3.45 MeV, which was explained quite well by the R-matrix calculation with known resonance parameters of the first three levels in 13N nucleus. Thus it is demonstrated that the present setup can be directly applied to the study of elastic resonance scattering with secondary radioactive beams.

Exploring the dynamics of reaction N+SiH4 with crossed molecular-beam experiments and quantum-chemical calculations

We investigated the reaction N((4)S,(2)D,(2)P)+SiH(4) in crossed molecular beams at a collision energy of 4.7 kcal mol(-1) with a time-of-flight mass spectrometer and selective photoionization. Ion signals were observed at m/z=42-45, associated with two product channels, HSiNH/SiNH(2)+H+H and HSiN/HNSi+H(2)+H. The species producing the signal at m/z=43 is assigned to product HSiN/HNSi and that at m/z=44 to product HSiNH/SiNH(2). The signal observed at m/z=42 is attributed to daughter ions of those two products and that at m/z=45 to (29)Si and (30)Si isotopic variants. We report time-of-flight spectra as a function of laboratory angle and simulations for the two products, from which both kinetic-energy and angular distributions of products in the center-of-mass (c.m.) frame were derived. The dependence of release of kinetic energy on the c.m. scattering angle is weak. The average translational energy released is 7.7 kcal mol(-1) for product channel HSiNH/SiNH(2)+H+H and 30.3 kcal mol(-1) for product channel HSiN/HNSi+H(2)+H. Through consecutive triple fragmentation, the angular distribution is slightly anisotropic for product HSiNH/SiNH(2) but isotropic for product HSiN/HNSi. Assuming equal efficiencies of detection, we estimate the branching ratios of products HSiNH/SiNH(2) and HSiN/HNSi to be roughly 15:85. To facilitate an understanding of the reaction mechanisms, we calculated the potential-energy surface for reaction N((2)D)+SiH(4) with quantum-chemical methods. Reactions N((2)D)+SiH(4)-->SiNH(2)+H+H and N((2)D)+SiH(4)-->HNSi+H(2)+H account satisfactorily for the present experimental results. Isomeric products HSiNH and HSiN are minor in this work.

Measurement of cumulative-photon spectra at high transverse momenta in 12C9Be interactions at an energy of 3.2 GeV per nucleon

For 12C9Be interactions at a kinetic beam energy of 3.2 GeV per nucleon, the spectra of photons at laboratory angles in the range 55°–73° were measured off the kinematical region available to the interaction of single nucleons within colliding nuclei. The use of a fast trigger for selecting events involving the production of high-transverse-momentum photons made it possible to measure spectra off the kinematical boundary of four-nucleon interaction. It is shown that the proposed procedure is adequate to the problem of searches for and investigation of flucton-flucton interaction. In the kinematical region where flucton-flucton interaction can manifest itself, the cross sections in question are on the same order of magnitude as respective model predictions. In order to draw definitive conclusions on the role of flucton-flucton interaction, it is highly desirable to extend the angular range of the measurements toward smaller angles.

Dynamics of the reaction C(P3)+SiH4: Experiments and calculations

We conducted the reaction C((3)P)+SiH(4) at a collision energy of 4.0 kcal mol(-1) in a crossed molecular-beam apparatus measuring time-of-flight mass spectra and selective photoionization. Product ions with m/z=41-43 are associated with two product channels, H(2)SiCH/HSiCH(2)/SiCH(3)+H and H(2)SiC/HSiCH/SiCH(2)+H(2). Apart from daughter ions and isotopic variants of reaction products, the species observed at m/z=43 is assigned to product H(2)SiCH/HSiCH(2)/SiCH(3) and that at m/z=42 to product H(2)SiC/HSiCH/SiCH(2). The signals observed at m/z=41 are due to dissociative ionization of silicon-carbon hydrides of these two types. We report time-of-flight spectra of products at specific laboratory angles and theoretical simulations, from which both kinetic-energy and angular distributions of products in the center-of-mass frame were derived. The release of kinetic energy is weakly dependent on the scattering angle for these two reactions. The channels for loss of H and H(2) release average translational energies of 10.5 and 16.7 kcal mol(-1), respectively. As hydrogen transfer before decomposition is facile, products H(2)SiCH/HSiCH(2)/SiCH(3) and H(2)SiC/HSiCH/SiCH(2) exhibit mildly forward/backward preferred and isotropic angular distributions, respectively. We estimate the branching ratios of these channels for loss of H and H(2) to be roughly 6:4. The measurements of release of kinetic energy and ionization thresholds of products indicate that SiCH(3)((2)A(")) and SiCH(2)((3)A(2)) are dominant among isomeric products. To explore the reaction mechanism, we computed the potential-energy surfaces for the reaction C((3)P)+SiH(4). The most likely mechanism is that atom C (3)P inserts into bond Si-H of SiH(4) in the entrance channel, and the reaction complex H(3)SiCH subsequently isomerizes to HSiCH(3) followed by decomposition to SiCH(3)((2)A("))+H and SiCH(2)((3)A(2))+H(2). We observed no significant evidence for the reaction C((1)D)+SiH(4).

Measurement of (d,p) and (d,α) differential cross-sections for aluminum

The differential cross-sections for 27Al(d,p 0+1,2+3,4,5+6) 28Al and 27Al(d,α 0,1,2,3,4) 25Mg have been measured in the energy ranges from 1.3 to 2.3 MeV and from 1.5 to 2.4 MeV, respectively at the laboratory angle of 150°. The obtained results are compared with data published in the literature. Discrepancies between new and previously acquired data are discussed. The cross-sections measured in the present work were uploaded to the IBANDL data base ( www-nds.iaea.org/ibandl/).

Photofragment translational spectroscopy of propargyl radicals at 248nm

The photodissociation of propargyl radical, C(3)H(3), and its perdeuterated isotopolog was investigated using photofragment translational spectroscopy. Propargyl radicals were produced by 193 nm photolysis of allene entrained in a molecular beam expansion and then photodissociated at 248 nm. Photofragment time-of-flight spectra were measured at a series of laboratory angles using electron impact ionization coupled to a mass spectrometer. Data for ion masses corresponding to C(3)H(2)(+), C(3)H(+), C(3)(+), and the analogous deuterated species show that both H and H(2) loss occur. The translational energy distributions for these processes have average values E(T)=5.7 and 15.3 kcal/mol, respectively, and are consistent with dissociation on the ground state following internal conversion, with no exit barrier for H loss but a tight transition state for H(2) loss. Our translational energy distribution for H atom loss is similar to that in a previous work on propargyl in which the H atom, rather than the heavy fragment, was detected. The branching ratio for H loss/H(2) loss was determined to be 97.62.4+/-1.2, in good agreement with previous calculations.