A study of (n,nα) reaction cross sections at 14.7 MeV

Cross sections for (n, nα) reactions induced by 14.7 ± 0.3 MeV neutrons on ⁵¹V, ⁹²Mo, ¹¹⁵In, ¹⁶⁵Ho and ¹⁷⁶Yb have been measured by the activation technique using radiochemical separations and high resolution γ-ray spectroscopy or low-level β⁻counting. A brief summary of the activation data reported in the literature is given and a tentative trend in the data is suggested. The contribution of the (n, nα) process generally amounts to between 10 and 15% of the (n, α) cross section; in some cases, however, it is as low as 0.5%. The summed (n, α) and (n, nα) reaction cross sections obtained by the activation technique are generally in agreement with those deduced from emitted α-particle characterisation as well as mass spectrometry. Detailed Hauser-Feshbach calculations show that the statistical model can describe the (n, nα) cross section only with partial success.     

Total spin-dependent p̄d cross sections at low and intermediate energies

There may be unique (“smoking-gun”) signatures of the breakdown of CPT symmetry, induced in some models of Quantum Gravity entailing decoherence for quantum matter. Such effects can be observed in entangled states of neutral mesons via modifications of the respective Einstein-Podolsky-Rosen (EPR) correlators (“ω-effect”). In the talk I discuss experimental signatures and bounds of the ω-effect in Φ- and B-factories, and argue that the effect might be falsifiable at the next generation facilities.     

Systematical law of (n, γ) reaction cross sections of even-even nuclei

We have derived a formula for the neutron radiative capture cross section in the framework of a statistical model approach to nuclear reactions. Based on this formula, new systematics are established between the (n, γ) reaction cross section and the energy level density of a compound nucleus or a relative neutron excess of an even-even target nucleus for neutron incident energy above the resonance region to MeV. Good agreement with experimental data suggests that this new systematical law is helpful to analyze the experimental data.     

The 7Li(p, α)4 He cross section at low energies

The reaction cross section for ⁷Li(p, α)⁴He was obtained from E_c.m. = 25 to 873 keV corresponding to the temperature range T = (0.033 to 6.8) × 10⁹ K. The data are in fair agreement with R-matrix calculations. Constraints drawn on the universal baryon density from the abundance of ⁷Li remain essentially unchanged by the present data.     

The 12C(α, γ)16O cross section at stellar energies

The capture reaction ¹²C(α, γ)¹⁶O has been investigated at E = 0.94 to 2.84 MeV with the use of an intense α beam and implanted ¹²C targets of high isotopic purity. The studies involved NaI(Tl) crystals and, for the first time, germanium detectors. The measurement of absolute cross sections, γ-ray angular distributions and excitation functions is reported. A cross section of 48 pb is found at E = 0.94 MeV. The data provide information on the E1 and E2 capture amplitudes involved in the transition to the ground state as well as to excited states. The S-factor at stellar energies has been determined by means of theoretical fits. The results verify the previous report of a substantial higher S-value compared to the value recommended in 1975. The present uncertainty in the S-value as well as possible improvements are discussed. This S-value is of crucial importance to nuclear astrophysics.     

Sensitivity of cross section andT 20 to secondary interactions in the reaction indp → ppn at medium energies

Secondary effects in deuteron breakup reactions are reexamined for the process¹ H(d, p) pn with a proton detected at 0° and for the process¹ H (d, pp)n with two fast forward moving protons fixed at the beam line. Sensitivity of the cross section and the tensor asymmetryT ₂₀ to the double-scattering and final-state-interaction corrections is demonstrated. The nonrelativistic method used here incorporates both the energy-conserving and the principal-value part of the free nucleon propagator. The calculations are compared with the inclusive experimental data¹ H(d, p)X at the 1.25 and 2.1 GeV deuteron kinetic energy.The author would like to express his thanks to Prof. B. Tecoult for valuable ideas stimulating this work and Yu.Panebratsev and A. Litvinenko for many helpful discussions. For ideas and advice concerning Sect. 4, I thank to G. Lykasov and S. Shimansky.     

Measurement of the 6Li(e,e′p) reaction cross sections at low momentum transfer

The triple differential cross sections for the ⁶Li(e,e′p) reaction have been measured in the excitation energy range from 27 to 46 MeV in a search for evidence of the giant dipole resonance (GDR) in ⁶Li. The cross sections have no distinct structures in this energy region, and decrease smoothly with the energy transfer. Angular distributions are different from those expected with the GDR. Protons are emitted strongly in the momentum-transfer direction. The data are well reproduced by a DWIA calculation assuming a direct proton knockout process.     

Measurement of e~+e~-→D■ cross sections at the ψ(3770) resonance

We report new measurements of the cross sections for the production of DD final states at theψ(3770)resonance.Our data sample consists of an integrated luminosity of 2.93 fb~(-1)of e~+e~-annihilation data produced by the BEPCⅡ collider and collected and analyzed with the BESⅢ detector.We exclusively reconstruct three D~0and six D~+hadronic decay modes and use the ratio of the yield of fully reconstructed DD events(double tags)to the yield of all reconstructed D or D mesons(single tags)to determine the number of D~0 D~0and D~+D~-events,benefiting from the cancellation of many systematic uncertainties.Combining these yields with an independent determination of the integrated luminosity of the data sample,we find the cross sections to beσ(e~+e~-→D~0D~0)=(3.615±0.010±0.038)nb andσ(e~+e~-→D~+D~-)=(2.830±0.011±0.026)nb,where the uncertainties are statistical and systematic,respectively.     

Calculations on (γ, p) and (γ, n) reactions at photon energies between 40 and 100 MeV

Shell-model calculations with and without short-range correlations have been carried out for the reactions (γ, p) and (γ, n) in the energy region from 40 to 100 MeV. The cross sections for the ¹⁶O(γ, p)¹⁵N process have been investigated in the single-particle model. The results strongly depend on the initial state wave functions especially at high energies. There are large effects on the cross sections if orthogonality between bound and continuum states is violated. For the reaction ¹⁶O(γ, n)¹⁵O it is shown that short-range correlations in the ground state of ¹⁶O do not contribute appreciably to the cross sections, at least up to a photon energy of 100 MeV.     

Scaling law of single ion–atom impact ionization cross sections of noble gases from He to Xe at strong perturbative energies

We extend our previous work of a classical over-barrier ionization(COBI) model to calculate the single ionization cross sections of noble gases ranging from He to Xe at strong perturbative energies.The calculation results are in good agreement with extensive experimental data.The scaling law of single ion–atom impact ionization cross sections of noble gases on projectile charge q and energy E,also on target ionization energy I is drawn from the model.     

Microscopic calculation of the 3He(α,γ)7Be and 3H(α,γ)7Li capture cross sections using realistic interactions

The radiative capture cross sections for the 3He(α,γ)7Be and 3H(α,γ)7Li reactions are calculated in the fully microscopic fermionic molecular dynamics approach using a realistic effective interaction that reproduces the nucleon-nucleon scattering data. At large distances bound and scattering states are described by antisymmetrized products of 4He and 3He/3H ground states. At short distances the many-body Hilbert space is extended with additional many-body wave functions needed to represent polarized clusters and shell-model-like configurations. Properties of the bound states are described well, as are the scattering phase shifts. The calculated S factor for the 3He(α,γ)7Be reaction agrees very well with recent experimental data in both absolute normalization and energy dependence. In the case of the 3H(α,γ)7Li reaction the calculated S factor is larger than available experimental data by about 15%.     

Measurements of natCd(γ, x) reaction cross sections and isomer ratio of 115m,gCd with the bremsstrahlung end-point energies of 50 and 60 MeV

The flux-weighted average cross sections of ^natCd(γ, xn)^{115g,m,111m,109,107,105,104}Cd and ^natCd(γ, x)^{113g,112,111g,110m}Ag reactions were measured at the bremsstrahlung end-point energies of 50 and 60 MeV. The activation and off-line γ-ray spectrometric technique was carried out using the 100 MeV electron linear accelerator at the Pohang Accelerator Laboratory, Korea. The ^natCd(γ, xn) reaction cross sections as a function of photon energy were theoretically calculated using the TALYS-1.95 and the EMPIRE-3.2 Malta codes. Then, the flux-weighted average cross sections were obtained from the theoretical values of mono-energetic photons. These values were compared with the flux-weighted values from the present study and were found to be in general agreement. The measured experimental reaction cross-sections and integral yields were described for cadmium and silver isotopes in the ^natCd(γ, xn)^{115g,m,111m,109,107,105,104}Cd and ^natCd(γ, x)^{113g,112,111g,110m}Ag reactions. The isomeric yield ratio (IR) of ^115g,mCd in the ^natCd(γ, xn) reaction was determined for the two bremsstrahlung end-point energies. The measured isomeric yield ratios of ^115g,mCd in the ^natCd(γ, xn) reaction were also compared with the theoretical values of the nuclear model codes and previously published literature data of the ¹¹⁶Cd(γ, n) and ¹¹⁶Cd(n, 2n) reactions. It was found that the IR value increases with increasing projectile energy, which demonstrates the characteristic of excitation energy. However, the higher IR value of ^115g,mCd in the ¹¹⁶Cd(n, 2n) reaction compared to that in the ¹¹⁶Cd(γ, n) reaction indicates the role of compound nuclear spin alongside excitation energy.     

The insentivity of the γ (d,n)p cross sections to realistic potentials

Employing the Yale and Hamada-Johnston potentials the bremsstrahlung-weighted and integrated cross sections have been evaluated for the photodisintegration of the deuteron and the results are found to be quite insensitive to the details of these potentials.     

Model-independent analysis of the differential cross section for the reaction n+d→π0+t at medium energies

Experimental values of the differential cross section for the reactionn+d→π ⁰+t at large angles (θ?50°) in the neutron energy range 460–560 MeV and the known values of the coupling constants \(G_{nn\pi ^O }^2 \) andG _tdn ² are used to predictdσ/dΩ at smaller angles. The method is based on the use of general analytic properties of the differential cross section in the cosgq-plane.     

A study of (α, n) reactions on 9Be and 13C at low energies

Described in this work are measurements of the thick target neutron yield from reaction¹³C(α, n)¹⁶O. The yield was determined for laboratory bombarding energies between 0.475 MeV and 0.700 MeV using a stilbene scintillator neutron detector and pulse-shape discrimination to eliminate gamma rays. Stellar temperatures between 2.5 and 4.5 × 10⁸ °K are involved in this energy region. The neutron yield was used to determine the astrophysical cross-section factor S(E), which was found to fit a linear function in the interaction energy E; S(E) = [(5.48±1.77)+(12.05±3.91)E] × 10⁵ MeV · b, center-of-momentum system. The rate of the¹³C(α, n)¹⁶O reaction is discussed with reference to neutron production in the helium-burning region of a star.Results are also presented of measurements carried out on the reaction ⁹Be(α, n)¹²C taken with a thin Be target. The bombarding energy range covered was from 0.340 to 0.680 MeV with excitation curves for the ground and first excited state neutrons being reported. Resonances were found at bombarding energies of E_lab = 0.520 MeV(Γ≈55 keV c.m., ωγ = 3.79 eV c.m.) and E_lab = 0.600 MeV(Γ < 4keV c.m., ωγ = 0.88 eV c.m.).     

Analysis of average primary gamma-transition intensities and cross sections of the113Cd(n, γ) reaction

A combined analysis of the available data on the primaryγ-ray intensities from the¹¹³Cd(n, γ) reaction atE _n=1.9 and 24.3 keV neutron energies together with the data on¹¹³Cd neutron capture cross sections in theE _n=3–200 keV energy region was carried out. The neutron strength functions were determined asS _n0=(0.260±0.073) 10^?4 and S_n1=(5.06±0.67) 10^?4. No spin-orbit splitting of thep-wave neutron strength function was found. The energy dependence of theE 1 radiative strength function {ie147-01} was fitted by the Kadmenski-Furman model somewhat better than by a standard Lorentzian. TheM 1 giant resonance parameters were obtained as E _G ^{M 1} =8.8±1.6 MeV and Γ _G ^{M 1} = 4.7±2.6 MeV. The neutron capture cross section of¹¹³Cd from its isomeric state ({ie147-02}=11/2^?, E ₁ ^m =263.7 keV) was calculated.