Stopping power of low-energy deuterons in 3He gas

The stopping power of atomic and molecular deuterons in ³He gas was measured over the range E _d = 10 to 100 keV using the ³He pressure dependence of the ³He(d,p) ⁴He reaction yield. At energies above 30 keV, the observed stopping power values are in good agreement with a standard compilation. However, near 18 keV the experimental values drop by a factor 50 below the extrapolated values of the compilation. In a simple model, the behavior is due to the minimum 1s↦2s electron excitation of the He target atoms (= 19.8 eV, corresponding to E _d = 18.2 keV), i.e. it is a quantum effect, by which the atoms become nearly transparent for the ions.     

Preliminary results of the study of the d(d,n)3He reaction in the astrophysical energy range with the use of a Hall plasma accelerator

The possibility of using a plasma accelerator based on a pulsed Hall ion source to study the characteristics of pd, dd, d³He, ³He, and⁴He reactions in the astrophysical energy range (2–12 keV) has been considered. The preliminary experimental data on measurement of the astrophysical S factor for the dd reaction (dd → ³He + n (2.5 MeV)) at average deuteron collision energies E _col = 4.5 and 4.95 keV and the deuteron beam energy spread FWHM = 18% are reported. The found value of the S factor is in agreement with the results of the experiments carried out by us previously using linear plasma in the inverse Z-pinch configuration.     

Low-energy behavior of the 3He(α, γ)7Be cross section

Cross sections for the ³He(α, γ)⁷Be reaction have been measured at several energies from E_c.m. = 165 to 1169 keV by counting prompt γ-rays from a windowless, differentially pumped, recirculating, ³He gas target. The cross-section factor S₃₄(E_c.m.) and branching ratio γ₁/γ₀ were determined at each energy. Cross sections were also measured at E_c.m. = 947 and 1255 keV by counting the γ-rays from the ⁷Be produced in a ³He gas cell with a Ni entrance foil. Combining the results of these two independent experiments yields a zero-energy intercept for the cross-section factor of S₃₄(0) = 0.53 ± 0.03 keV · b. The relationship between these measurements and several theoretical calculations, and the import of the extrapolated cross section for the solar-neutrino problem are discussed.     

A search for deeply bound pionic states of xenon produced in the 136Xe(d, 3He)135Xeπ-bound reaction

A search for deeply bound pionic states of xenon produced in the ¹³⁶Xe(d, ³He)¹³⁵Xe_π-bound reaction at E _d = 500 MeV is reported. The population of the 1s pionic-atom state of ¹³⁵Xe is observed on the predicted level of the cross section ～ 40 μb/sr. The binding energy of the 1s state, B = 2.9 ± 0.5 MeV, however, is lower than theoretically predicted.     

The structure of27Al

Gamma decay modes and spin assignments of levels in²⁷Al have been investigated by proton-γ-ray angular correlation measurements in the²⁴Mg(α, pγ) reaction at 14.2, 15 and 15.6 MeV bombarding energy and byγ-ray angular distribution measurements on the E_p=1820, 2114, 2293 and 2574 keV resonances of the²⁶Mg(p, γ) reaction. Unique spin assignments were obtained as follows: I=3/2 for the 5827 keV state, I=5/2 for the 6115, 6465, 6765, 7577, 7721, 8097, 8136, 8324 keV states, I=7/2 for the 5433, 6533, 7413, 8037, 8442, 8586 keV states, I=9/2 for the 5418, 6512, 6713, 7997 keV states, I=11/2 for the 5500, 6948, 7400, 8396 keV states. The level scheme and electromagnetic properties of levels are compared with the results of shell model calculations which use the complete configuration space of the 0d_5/2-1s_1/2-0d_3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent and extends into the region of high level density above 7 MeV excitation energy. The total B(M1↑) below 8.5 MeV excitation energy is evaluated, using published resonance fluorescence and (e, e′) data, and quenching relative to the free-nucleon predictions is reexamined. Evidence in favour of a prolate ground state deformation of²⁷Al and implications of this work for the astrophysically interesting²⁶Al(p, γ) reaction are discussed.     

Absolute cross sections for the 6Li(p, 3He)4He reaction at energies below 1 MeV

Total cross sections and angular distributions in the ⁶Li(p,³He)⁴He reaction have been measured over the energy range E_p = 100?700 keV. The extrapolation of the cross section to the energy region which is of interest in controlled thermonuclear reactors is given. The values of the “astrophysical S-function” are deduced from the cross sections.     

DD reaction enhancement and X-ray generation in a high-current pulsed glow discharge in deuterium with titanium cathode at 0.8–2.45 kV

The DD reaction yield (3-MeV protons) and the soft X-ray emission from a titanium (Ti) cathode surface in a periodic pulsed glow discharge in deuterium were studied at a discharge voltage of 0.8–2.45 kV and a discharge current density of 300–600 mA/cm². The electron screening potential U_e = 610 ± 150 eV was estimated in the range of deuteron energies 0.8 keV < E_d < 2.45 keV from an analysis of the DD reaction yield as a function of the accelerating voltage. The obtained data show evidence for a significant enhancement of the DD reaction yield in Ti in comparison to both theoretical estimates (based on the extrapolation of the known DD reaction cross section for E_d ≥ 5 keV to low deuteron energies in the Bosch-Halle approximation) and the results of experiments using accelerators at the deuteron energies E_lab ≥ 2.5 keV and current densities 50–500 μ A/cm². Intense emission of soft X-ray quanta (10¹³–10¹⁴ s^?1 cm^?2) was observed at an average energy of 1.2–1.5 keV. The X-ray emission intensity and the DD reaction yield enhancement strongly depend on the rate of deuterium diffusion in a thin subsurface layer of Ti cathode.     

Low-energy fusion cross sections of D + D and D + 3He reactions

The D(d, n)³He and D(d, p)T reactions have been investigated at E_c.m = 2.98 to 162.5 keV and the ³He(d, p)⁴He reaction at E_c.m. = 6.95 to 141.8 keV. The studies involved high-current accelerators with well-known beam characteristics and windowless gas target systems of the extended and quasi-point supersonic jet type. The measurement of absolute cross sections, angular distributions and excitation functions is reported. The data extend into the thermal energy region of future fusion reactors. The results for the D(d, n)³He and D(d, p)T reactions are in good agreement with previous work, while substantial differences are found for ³He(d, p)⁴He.     

A molecular beam study on the interaction of NO with a Pt(111) surface

NO adsorbs on Pt(111) with a (temperature independent) initial sticking coefficient S₀=0.88. The fraction of molecules not being chemisorbed is directly inelastically scattered back due to failure of translational energy accommodation. The nonlinear variation of s with coverage can well be described by a precursor-state model, the precursor state being formed by NO molecules translationally and rotationally accommodated in a physisorbed second layer. Dissociation is essentially restricted to defect sites and is negligible on perfect (111) planes. These defect sites (present in small concentration) are first populated and are also sampled by the modulated beam technique yielding an activation energy for desorption E_d = 33.1 kcal/mole and preexponential factor v_d = 10^15.5s^?1. Isothermal desorption measurements yielded E_d and v_d as a function of coverage: E_d rapidly drops from its initial value (at defect sites) to about 27 kcal/mole — which value is considered as representing the adsorption energy on a perfect (111) plane — and then decreases continuously due to effective repulsive interactions. Simultaneously v_d is decreasing to about 10¹² s^?1 at θ = 0.25 which marks the equilibrium coverage to be reached at 300 K. If the surface is precovered with oxygen atoms the NO sticking coefficient is reduced to 0.6, and the desorption parameters are lowered to E_d = 17.1 kcal/mole and v_d= 10^12.6s^?1 (at zero NO coverage).     

Investigation of the D(<Superscript>3</Superscript>He, <Emphasis Type="Italic">p</Emphasis>)<Superscript>4</Superscript>He Reaction in the Astrophysical Energy Region of 18–30 keV

The D(³He, p)⁴He reaction is first investigated in a solid target of deuterated zirconium (ZrD) in the ³He⁺ ion energy range E_He = 18–30 (E = 7.2?12.0keV keV in the center-of-mass system) with a step of 2 keV. The electron screening potential U_e = (617.8 ± 154.7) eV and the D(³He, p)⁴He reaction enhancement factors are experimentally determined in the given energy range. The measured electron screening potential is six times higher than in gaseous targets. This can be due to the ZrD lattice effects, which have not been studied either theoretically or experimentally so far. The D(³He, p)⁴He reaction has been investigated at the pulsed plasma Hall accelerator (Tomsk).     

Calculation of the nuclear vertex constant (asymptotic normalization coefficient) for the virtual decay 6Li → α + d on the basis of the three-body model and application of the result in describing the astrophysical nuclear reaction d(α, γ)6Li at ultralow energies

Within the (α, n, p) three-body model, the s-wave ⁶Li → α + d vertex constant G ₀₁ and the asymptotic normalization coefficient C ₀₁ (these two quantities are proportional to each other) for the wave function describing the ⁶Li nucleus in the α + d channel are calculated by solving Faddeev equations for various sets of nucleon-nucleon and α N potentials. The resulting values of G ₀₁ and C ₀₁ are used to calculate the astrophysical factor S(E) for the radiative-capture reaction d(α, γ)⁶Li at energies in the range E = 0–600 keV. The calculated values of G ₀₁ and C ₀₁ appear to be sensitive to the form of the pair potentials used. It is shown that, upon correctly taking into account the contributions of the E2 and E1 multipolarities, the values of S(E) in the region E < 150 keV are determined primarily by the values of C ₀₁ and of the ⁶Li binding energy in the α + d channel.     

Elastic scattering of deuterons by 14C from Ed = 4 to 10 MeV

Angular distributions for the elastic scattering of deuterons by ¹⁴C were measured at nine energies between E_d = 4.2 and 10 MeV. Excitation functions were taken in 50 keV steps from E_d = 4 to 10 MeV. A resonance was observed at E_d = 4.5 MeV, which corresponds to an excitation energy of 14.41 MeV in ¹⁶N. An analysis using an optical model plus a single-level formula derived from the R-matrix formalism yields an l-value assignment of l = 4 for this resonance. Of the three J^π values allowed for l = 4 (J^π = 3⁺, 4⁺, 5⁺), the value of J_π = 3⁺ is found to be slightly preferred. Possible identification of this resonance with an analog in ¹⁶O is discussed. The angular distributions measured at off-resonance energies were analyzed with an optical-model potential which has a surface-peaked imaginary well. The energy dependence of the real and imaginary well depths are explicitly determined in the present work for E_d = 4 to 10 MeV. The best-fit optical-model parameters obtained from the present study are compared to those from the ¹⁴N(d, d)¹⁴N work.     

A study of the121,123Sb(p,d) reactions

Levels of^120,122Sb have been observed using the^121,123Sb(p, d) reactions atE _p = 26.2 MeV. Thirty-two levels of¹²⁰Sb and thirty-four levels of¹²²Sb are observed below 2.0 MeV excitation with an energy resolution better than 25 keV FWHM. Experimental angular distributions were compared to DWBA calculations in order to extractl-transfers and spectroscopic factors. Strong mixing between the 3s _1/2, 2d _3/2, 2d _5/2, and 1g _7/2 neutron orbitals is observed in both nuclei. Nuclear Reactions:^121,123Sb(p, d),E=26.2 MeV; measuredσ(E _d ,θ).^120,122Sb deduced levels,l,J,π, spectroscopic factors. Enriched targets, magnetic spectrometer.     

Threshold states in 26Al revisited

Threshold states in ²⁶Al have been re-examined using the ²⁷Al(³He, α)²⁶Al and ²⁵Mg(³He, dγ)²⁶Al reactions in order to resolve apparent ambiguities in some of the previously reported properties of these states. In particular, the s-wave resonance strength reported at E_c.m. = 37 keV is now found to be located at E_c.m. = 57.54 keV, and the proton width for the 374 keV resonance has been revised to Γ_p = 0.82 eV. These results have been used to calculate a new resonance strength of ωγ = 1.6 × 10⁻¹³ eV for the 57.54 keV resonance. As a result, the stellar production rate for ²⁶Al is increased by a factor ∼- 3–38 for temperatures T₉ = 0.05–0.1.     

3s- and 3p-core level excitations in 3d-transition metal oxides from electron-energy-loss spectroscopy

3s- and 3p-core level excitations for a large number of 3d-transition metal oxides, with a formal 3d occupation from 3d⁰ to 3d¹⁰, have been measured by electron energy loss spectroscopy in reflection geometry (REELS) with primary energies 200 eV≤E ₀≤1600 eV. Their intensities decrease systematically with the formal 3d-count, classifying them as transitions to empty 3d-states. The structure of the 3s excitations is analysed in detail and is compared to the 3s-XPS photoemission spectra of the samples. This 3s-REELS structure and its change with the 3d occupation can be explained by the assumption that the excitation arises mainly from a 3s²3dⁿ→3s¹3dⁿ⁺¹ quadrupole transition.     

Astrophysical <Emphasis Type="Italic">S</Emphasis>-factor of T(<Superscript>4</Superscript>He, γ)<Superscript>7</Superscript>Li reaction at <Emphasis Type="Italic">E</Emphasis><Subscript>cm</Subscript> = 15.7 keV

The astrophysical S-factor of the reaction T(⁴He, γ)⁷Li is measured for the first time at the center of mass energy E _cm = 15.7 keV, lower than the energy range of the Standard Big Bang Nucleosynthesis (SBBN) model. The experiment is performed on a Hall pulsed accelerator (TPU, Tomsk). An acceleration pulse length of 10 μs allows one to suppress the background of cosmic radiation and the ambient medium by five orders of magnitude. A beam intensity of ~ 5 × 10^{14 4}He⁺ ions per pulse allows one to measure an extremely low reaction yield. The yield of γ-quanta with the energies E _γ ⁰ = 2483.7 keV and E _γ ¹ = 2006.1 keV is registered by NaI(Tl) detectors with the efficiency ε = 0.331 ± 0.026. A method for direct measurement of the background from the chain of reactions T(⁴He, ⁴He)T→T(T, 2n)X→(n, γ) and/or (n, n′γ) which ends by neutron activation of materials surrounding the target is proposed and implemented in this study. The value of the astrophysical S-factor of the reaction T(⁴He, γ)⁷Li S _αt (E _cm = 15.7 keV) = 0.091 ± 0.032 keV b provides the choice from the set of experimental data for the astrophysical S _αt -factor in favor of experimental data [4] with S _αt (E _cm = 0) = 0.1067 ± 0.0064 keV b.     

Mass spectrometry study of the kinetics of CdTe molecular-beam epitaxy: Part I. Cd, Te2, and CdTe

Surface processes in CdTe molecular-beam epitaxy were studied using in situ mass spectrometry. Modulated molecular Cd and Te₂ beams were used for measuring kinetic parameters. The experiments were performed at crystal temperatures of 600–730 K. The results were processed within a model in which condensation and evaporation occur through adsorption and desorption stages. The desorption rate was 2–10 s^?1 for Te₂ and more than 30 s^?1 for Cd. The CdTe evaporation activation energy and desorption energies were determined as E _ev = 1.1 eV, E _d (Cd) = 1.0 eV, and E _d (Te) = 0.6 eV. The adsorbate coverage was estimated as n(Cd) < 0.01 and n(Te) = 0.1–1 Te.     

The tensor analyzing power AzzATθ = 0° for the 3He(d, p)4He reaction

The tensor analyzing power f_zz has been measured for the ³He($\text{d}$, p)⁴He reaction at 0 = 0° over an incident deuteron energy range E_d = 6.6–15.8 MeV in steps of 0.5 MeV. The present results agree with and extend the previous measurements of Grüebler et al. The present results indicate that this reaction is a very good tensor analyzer for polarized deuteron beams with energies up to 15.8 MeV.     

Experimental determination of the electron screening potential energy for the d(d, n)3He Reaction in ZrD2 and D2O in the ultralow energy region

This work is devoted to measuring of the values of the astrophysical S-factors and electron screening potential energy for a d(d,n)³He reaction occurring at ultralow energies in zirconium deuteride ZrD₂ (3.5–7.0 keV) and heavy water D₂O (2.2–6.0 keV). The experiment was performed on the Hall pulsed plasma accelerator at the TPU Nuclear Physics Institute (Tomsk) with ZrD₂ and D₂O targets produced by the magnetron sputtering of zirconium in a deuterium environment and heavy water freezing-out on a copper support, respectively. A χ ² analysis of the dependence of the neutron yields and astrophysical S-factors for the dd reaction on the deuteron collision energy E revealed that the upper bounds of the electron screening potential energy for interacting deuterons in ZrD₂ and D₂O and of the astrophysical S-factors at the deuteron collision energy E = 0 were U _e (ZrD₂) < 30 eV, U _e (D₂O) < 25 eV, S(0) = (57.2 ± 3.9) keV · b (ZrD₂), S(0) = (58.6 ± 3.6) keV · b (D₂O) at the 90% confidence level.