共查询到20条相似文献,搜索用时 31 毫秒
1.
M.S. Basunia R.M. Clark L.A. Bernstein J.T. Burke D.L. Bleuel F.S. Dietrich P. Fallon R. Hatarik S.R. Lesher M.A. McMahan M. Wiedeking 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(11):1899-1903
The surrogate reaction 238U(3He, tf) is used to determine the 237Np(n, f) cross section indirectly over an equivalent neutron energy range from 10 to 20 MeV. A self-supporting ∼761 μg/cm2 metallic 238U foil was bombarded with a 42 MeV 3He2+ beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory (LBNL). Outgoing charged particles and fission fragments were identified using the Silicon Telescope Array for Reaction Studies (STARS) consisted of two 140 μm and one 1000 μm Micron S2 type silicon detectors. The 237Np(n, f) cross sections, determined indirectly, were compared with the 237Np(n, f) cross section data from direct measurements, the Evaluated Nuclear Data File (ENDF/B-VII.0), and the Japanese Evaluated Nuclear Data Library (JENDL 3.3) and found to closely follow those datasets. Use of the (3He, tf) reaction as a surrogate to extract (n, f) cross sections in the 10-20 MeV equivalent neutron energy range is found to be suitable. 相似文献
2.
M. Abdesselam J.P. StoquertM. Djebara C. CerrutiA.C. Chami P. Montgomery 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(2):140-144
A 3.7 MeV He+ ion beam was simultaneously used for Polyethylene Terephtalate (PET) film degradation and characterization. To enhance the potentialities of the characterization method, a multi-detector Ion Beam Analysis (IBA) technique was used. The stoichiometry change of the PET target following the irradiation is quantified at a beam fluence varying between 7 × 1013 and 1.8 × 1016 He+ cm−2. The damage induced in PET films by He+ bombarding was analyzed in-situ simultaneously through Rutherford Backscattering Spectrometry (RBS), Particle Elastic scattering Spectrometry (PES) and Hydrogen Elastic Recoil Detection (ERD).Appropriate experimental conditions for the observation of absolute changes in composition and thickness during irradiation were determined. The oxygen and carbon content evolution as a function of the ion fluence was monitored by He+ backscattering whereas the hydrogen content was measured by H(α, H)α collisions in which both the scattered He+ ions and the recoiling H could be observed. The present study reveals that, at the highest fluence 1.8 × 1016 He+ cm−2, the PET films have lost approximately 15% of the carbon, more than 45% of the hydrogen and 85% of the oxygen of the amount contained in the pristine sample. The energy shift of recoiling H+ ions at a forward angle 45° was followed in order to study the mass loss effect.The experimental results are consistent with the bulk molecular recombination model. Based on the results, hydrogen, oxygen and carbon release cross sections are determined. For hydrogen, comparison with deuteron irradiation indicates a cross section linear dependence on the stopping power. 相似文献
3.
K. Yasuda C. BatchuluunR. Ishigami S. Hibi 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(9):1019-1022
Depth resolution of time-of-flight ERDA using a 4He beam (He TOF-ERDA) has been studied. The measurement system consists of a time detector of the ion transmission type and a silicon surface-barrier detector. Depth resolution was measured using samples of carbon layers on silicon wafers and 4He beams with energies between 3.5 and 10.1 MeV. The depth resolution of 6.0 ± 1.6 nm (FWHM) was obtained with a 3.5 MeV 4He incident beam. The measured depth resolution agreed with that evaluated by a calculation. Comparison with other methods such as heavy ion (HI) TOF-ERDA, resonant elastic scattering and nuclear reaction analysis (NRA) was performed. Depth resolution obtained by He TOF-ERDA is superior to that by NRA or resonant elastic scattering, and comparable to that by HI TOF-ERDA. 相似文献
4.
A. Hermanne R. Adam RebelesF. Tárkányi S. TakácsB. Kiraly A.V. Ignatyuk 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(7):695-699
Reliable assessment of proton induced production of the long lived radionuclide 170Tm (T1/2 = 128.6 d) on natEr requires optimized irradiation and measurement conditions as only a weak 84.2 keV signal is emitted in its decay. Additional detector shielding helps reducing the contaminating Pb-X rays at that energy. Measuring the excitation function up to 16 MeV, normalized to standard monitor cross sections, and comparison with earlier measured data for 167,168Tm results in new cross section data with reduced uncertainty. Comparison with values predicted by ALICE-IPPE, EMPIRE II and different versions of TALYS (EAF2007 and TENDL2010) shows rather good agreement for these simple (p,xn) reactions. 相似文献
5.
T. Schulze-König M. SeilerM. Suter L. WackerH.-A. Synal 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(1):34-39
Isotopic ratios of 14C at natural levels can be efficiently measured with accelerator mass spectrometry (AMS). In compact AMS systems, 13CH and 12CH2 molecular interferences are destroyed in collisions with the stripper gas, a process which can be described by dissociation cross sections. These dissociation cross sections determine the gas areal density required for sufficient attenuation of the interfering molecular beams, and are therefore key parameters in the effort to further reduce the terminal voltage and thus the size of the AMS system. We measured the dissociation cross sections of 13CH and 12CH2 in N2 and He in the energy range of 80-250 keV. In N2, cross sections were constant for energies above 100 keV with average values per molecule of (8.1 ± 0.4) × 10−16 cm2 for 13CH and (9.5 ± 0.5) × 10−16 cm2 for 12CH2. In He, cross sections were constant over the full measured range of 80-150 keV with average values of (4.2 ± 0.3) × 10− 16 cm2 and (4.8 ± 0.4) × 10−16 cm2, respectively. A considerable reduction of the terminal voltage from the currently used 200 kV while using N2 for 13CH and 12CH2 molecule dissociation is not possible: the required N2 areal densities of ∼1.4 μg/cm2, consequential angular straggling and a decreasing 1+ charge state fraction would reduce the ion beam transmission too much. This is not the case for He: sufficient molecule dissociation can be obtained with gas densities of ∼0.4 μg/cm2, for which angular straggling is relatively small. In addition, the 1+ charge state fraction still increases at lower stripping energies. Thus, the usage of He for stripping and molecule dissociation might allow the development of even smaller 14C-AMS systems than available today. 相似文献
6.
We have performed ab initio total energy calculations to investigate the behavior of helium and its diffusion properties in uranium dioxide (UO2). Our investigations are based on the density functional theory within the generalized gradient approximation (GGA). The trapping behavior of He in UO2 has been modeled with a supercell containing 96-atoms as well as uranium and oxygen vacancy trapping sites. The calculated incorporation energies show that for He a uranium vacancy is more stable than an oxygen vacancy or an octahedral interstitial site (OIS). Interstitial site hopping is found to be the rate-determining mechanism of the He diffusion process and the corresponding migration energy is computed as 2.79 eV at 0 K (with the spin-orbit coupling (SOC) included), and as 2.09 eV by using the thermally expanded lattice parameter of UO2 at 1200 K, which is relatively close to the experimental value of 2.0 eV. The lattice expansion coefficient of He-induced swelling of UO2 is calculated as 9 × 10−2. For two He atoms, we have found that they form a dumbbell configuration if they are close enough to each other, and that the lattice expansion induced by a dumbbell is larger than by two distant interstitial He atoms. The clustering tendency of He has been studied for small clusters of up to six He atoms. We find that He strongly tends to cluster in the vicinity of an OIS, and that the collective action of the He atoms is sufficient to spontaneously create additional point defects around the He cluster in the UO2 lattice. 相似文献
7.
K. Khalal-Kouache D. PrimetzhoferP. Bauer 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(12):1425-1427
Scattering of low energy (2 keV) He+ ions from a polycrystalline copper surface is studied. Experimental Time-Of-Flight (TOF) spectra are presented for different values of the angle of incidence α and a fixed scattering angle θ = 129°. Using Monte Carlo simulation, based on the TRIM (TRansport of Ions in Matter [6]) code, energy spectra are calculated and compared to experimental data. The influence of different combinations of interaction potential and inelastic energy loss on the spectrum shape and on the angular distribution of the scattering yield is considered in the simulation. Simulations show very good agreement with the experiment for all investigated geometries. An analysis of the experimental yield of scattered particles in different parts of the spectrum is performed to gain information on the relative contributions of surface single scattering and multiple scattering. 相似文献
8.
9.
Z. Felfli A.Z. MsezaneD. Sokolovski 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(10):1046-1052
Low-energy 0 ? E ? 1.0 eV electron elastic scattering from ground and excited Tm, Lu and Hf atoms has been investigated. Both total and differential cross sections have been calculated; the latter at the scattering angles θ = 0°, 90° and 180°. The recent Regge-pole methodology has been used for the calculations. In the method the crucial electron-electron correlation effects are accounted for through the Mulholland formula. We find that the total cross sections are characterized generally by shape resonances, Ramsauer-Townsend minima and dramatically sharp long-lived resonances from which we extract the binding energies of the negative ions. Our extracted binding energy of the Hf− negative ion from the total cross section is compared with that of Pan and Beck [14]. 相似文献
10.
K. Kawatsura K. Takahiro M. Imai K. Ozaki K. Komaki 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(6):901-904
Energy spectra of electrons ejected through autoionization decay of high-Rydberg states in high-energy collisions of Nq+ (q = 1-3) with He have been measured with high-resolution by using zero-degree electron spectroscopy. Several series of autoionizing lines were observed, corresponding to decays from N3+ 1s22p(2P)nl Rydberg states produced in N3+ + He collisions, from N2+ 1s22s2p(3P)nl Rydberg states produced in N2+ + He and from N+ 1s22s2p2(4P)nl Rydberg states produced in N+ + He, respectively. Angular momentum distributions for the first or second peak of three series of Coster-Kronig electron transitions for Nq+ (q = 1-3) projectiles are also discussed, where the highly excited states are formed by electron excitation. 相似文献
11.
S.E. Agbemava B.J.B. Nyarko J.J. Fletcher R.B.M. Sogbadji E. Mensimah M. Asamoah 《Annals of Nuclear Energy》2011
The thermal neutron capture cross section (σo) and the resonance integral (Io) of the 51V(n,γ)52V reaction were measured with an activation method to provide fundamental data for reactor calculation, activation analysis, and other theoretical and experimental uses concerning the interaction of neutron with matter. The vanadium and manganese samples were irradiated within and without a Cd shield case using a 20 Ci Am–Be neutron source. The activities of the samples were measured using gamma-ray spectroscopy. The thermal neutron capture cross section and the resonance integral were determined relative to the reference reaction 55Mn(n,γ)56Mn and the values obtained are 5.16 ± 0.19 barns and 2.53 ± 0.1 barns respectively. The previous measurements of the σo and Io of the reaction 51V(n,γ)52V were reviewed and the difference between the present values and the previous results were discussed. 相似文献
12.
T. Cai 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(21):3373-3376
The cross sections for the elastic scattering of protons from tritium at 151° and from helium at 155° angles in the laboratory frame, over the energy range of 1.2-3.4 MeV, have been measured in the present work, as a supplement to previous cross section measurements determined at different scattering angles recently. The currently measured cross section data are compared to data available in literature. The cross section enhancement was also investigated for both reactions. It was found that over the whole measured energy range, the elastic cross section for protons on tritium increases linearly with energy and is about 1000 times greater than the Rutherford cross section at 3.4 MeV. On the other hand, in the case of the elastic scattering of protons from helium, the cross section below 2.3 MeV increases almost linearly, and reaches a maximum of about 300 mb/str at the energy of 2.4 MeV for the scattering angle of 165°, and then, after this energy, it keeps oscillating around the maximum. 相似文献
13.
This study implies that 55Mn(n,γ)55Mn monitor reaction may be a convenient alternative comparator for the activation method and thus, it was used for the determination of thermal neutron cross section (TNX) and the resonance integral (RI) of the reaction 152Sm(n,γ)153Sm. The samples of MnO2 and Sm2O3 diluted with Al2O3 powder were irradiated within and without a cylindrical 1 mm-Cd shield case in an isotropic neutron field obtained from the 241Am–Be neutron sources. The γ-ray spectra from the irradiated samples were measured by high resolution γ-ray spectrometry with a calibrated n-type Ge detector. The correction factors for γ-ray attenuation, thermal neutron and resonance neutron self-shielding effects and epithermal neutron spectrum shape factor (α) were taken into account in the determinations. The thermal neutron cross section for 152Sm(n,γ)153Sm reaction has been determined to be 204.8 ± 7.9 b at 0.025 eV. This result has been obtained relative to the reference thermal neutron cross section value of 13.3 ± 0.1 b for the 55Mn(n,γ)56Mn reaction. For the TNX, most of the experimental data and evaluated one in JEFF-3.1, ENDF/B-VI, JENDL 3.3 and BROND 2.0, in general, agree well with the present result. The RI value for 152Sm(n,γ)153Sm reaction has also been determined to be 3038 ± 214 b, relative to the reference value of 14.0 ± 0.3 b for the 55Mn(n,γ)56Mn monitor reaction, using a 1/E1+α epithermal neutron spectrum and assuming Cd cut-off energy of 0.55 eV. In surveying literature, the existing experimental and evaluated data for the RI values are distributed from 1715 to 3462 b. However, when the Cd cut-off energy is defined as 0.55 eV, the present RI value agrees with some previously reported RI values, 3020 ± 163 b by Simonits et al., 3141 ± 157 by Van Der Linden et al., and 2962 ± 54 b by Kafala et al., within the limits of error. 相似文献
14.
D. PrimetzhoferS.N. Markin D.V. EfrosininE. Steinbauer R. Andrzejewski P. Bauer 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(11):1292-1295
Scattering cross sections for He+ ions in the energy range of 100 eV to 100 keV and for Al, Cu and Au target atoms were calculated. Employing the Thomas-Fermi-Molière model the potential strength was tuned by variation of the screening length. The resulting change in scattering cross section was analyzed and the absolute value is compared to cross sections obtained from potentials commonly employed in the medium-energy ion scattering (MEIS) regime. A large influence on the scattering cross section is observed for targets with large atomic number in the very low energy range. For instance, the scattering cross section for 100 eV He+-ions scattered from Au by 129° changes by a factor of 2.5 between different potential strengths claimed in the literature to be suitable for low-energy ion scattering (LEIS) energies. An experiment to determine electronic energy loss of very slow ions in metals is presented. It shows how uncertainties in the scattering potential strength can lead to systematically wrong results, although perfect agreement between experimental data and simulations is found. The impact of these results on quantitative surface structure and composition analysis is discussed. 相似文献
15.
The cross sections for the 175Lu(n, α)172Tm, 176Lu(n, α)173Tm and 175Lu(n, p)175m+gYb reactions have been measured in the neutron energy range of 13.5–14.8 MeV using the activation technique. The first data for 175Lu(n, α)172Tm reaction cross sections are presented. In our experiment, the fast neutrons were produced via the 3H(d, n)4He reaction on K-400 Neutron Generator at Chinese Academy of Engineering Physics (CAEP). Induced gamma activities were measured by a high-resolution (1.69 keV at 1332 keV for 60Co) gamma-ray spectrometer with high-purity germanium (HPGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The neutron fluences were determined by the cross section of 93Nb(n, 2n)92mNb or 27Al(n, α)24Na reactions. The neutron energy in the measurement was by the cross section ratios of 90Zr(n, 2n)89m+gZr and 93Nb(n, 2n)92mNb reactions. The results were discussed and compared with experimental data found in the literature and with results of published empirical formulae. 相似文献
16.
M.S. Rabasovi? S.D. Toši? V. Pej?ev D.M. Filipovi? B.P. Marinkovi? 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(2):279-282
We measured the differential cross sections (DCSs) for the electron-impact excitation of the resonance transition 5p2P1/2-6s2S1/2 of In atom at small scattering angles using a crossed electron-atom beam technique. The incident electron energies were E0 = 10, 20, 40, 60, 80 and 100 eV, while the small scattering angles ranged from 1° to 10° in steps of 1°. The forward scattering function method has been used for normalizing the generalized oscillator strengths (GOS) to the known optical oscillator strength and obtaining the absolute DCS values. 相似文献
17.
M.P. Ray 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(4):615-619
We have investigated the scattering of K+ and Cs+ ions from a single crystal Ag(0 0 1) surface and from a Ag-Si(1 0 0) Schottky diode structure. For the K+ ions, incident energies of 25 eV to 1 keV were used to obtain energy-resolved spectra of scattered ions at θi = θf = 45°. These results are compared to the classical trajectory simulation safari and show features indicative of light atom-surface scattering where sequential binary collisions can describe the observed energy loss spectra. Energy-resolved spectra obtained for Cs+ ions at incident energies of 75 eV and 200 eV also show features consistent with binary collisions. However, for this heavy atom-surface scattering system, the dominant trajectory type involves at least two surface atoms, as large angular deflections are not classically allowed for any single scattering event. In addition, a significant deviation from the classical double-collision prediction is observed for incident energies around 100 eV, and molecular dynamics studies are proposed to investigate the role of collective lattice effects. Data are also presented for the scattering of K+ ions from a Schottky diode structure, which is a prototype device for the development of active targets to probe energy loss at a surface. 相似文献
18.
M. Busch 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(16):2625-2629
The formation of doubly excited states of He atoms during impact of He2+ ions with projectile energies of 60-1000 eV under near-grazing angles of incidence of 5°-20° on clean and adsorbate-covered Ni(1 1 0) surfaces is studied by means of Auger electron spectroscopy. Pronounced dependencies of electron spectra from autoionization of atoms in doubly excited 2s2, 2s2p and 2p2 configurations on the coverage of the target surface with adsorbates are observed. These are directly related to work function changes, which are studied for the controlled adsorption of oxygen. Changes of the electron spectra on the target temperature are found for adsorbate-covered surfaces only, which puts into question recent interpretations of similar electron spectra in terms of a high local electron spin polarization of Ni(1 1 0) by an alternative interpretation based on thermal desorption or dissolution into bulk of surface contaminations. The formation of doubly excited states is studied for the oxygen p(2 × l) and p(3 × l) superstructures on Ni(1 1 0) in order to provide well-defined experimental data for theoretical investigations. 相似文献
19.
M. Abdesselam S. Chami A.C. Chami 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(1):108-112
Matter losses of polyethylene terephthalate (PET, Mylar) films induced by 1600 keV deuteron beams have been investigated in situ simultaneously by nuclear reaction analysis (NRA), deuteron forward elastic scattering (DFES) and hydrogen elastic recoil detection (HERD) in the fluence range from 1 × 1014 to 9 × 1016 cm−2. Volatile degradation products escape from the polymeric film, mostly as hydrogen-, oxygen- and carbon-containing molecules. Appropriate experimental conditions for observing the composition and thickness changes during irradiation are determined. 16O(d,p0)17O, 16O(d,p1)17O and 12C(d,p0)13C nuclear reactions were used to monitor the oxygen and carbon content as a function of deuteron fluence. Hydrogen release was determined simultaneously by H(d,d)H DFES and H(d,H)d HERD. Comparisons between NRA, DFES and HERD measurements show that the polymer carbonizes at high fluences because most of the oxygen and hydrogen depletion has already occured below a fluence of 3 × 1016 cm−2. Release curves for each element are determined. Experimental results are consistent with the bulk molecular recombination (BMR) model. 相似文献
20.
X.M. Chen Z.M. Gao Y. Cui Y.W. Liu J. Du 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,262(2):161-164
Pure target ionization was investigated for 0.4-6.4 MeV Cq+(q = 1-4) + He and Oq+(q = 1-4) + He collisions. The double-to-single target ionization ratios R21 were measured using coincidence techniques. We compare our results with existing experimental results and find they are in good agreement. The ratio R21 is nearly independent of projectile charge state. The relation of R21 ∼ V is analyzed using the over barrier model (OBM) and ionization probability, which is described in our extended over barrier model. Our calculation agrees well with the experimental results. 相似文献