Effects of inelastic multistep processes on (p,t) reactions in a transition region between rare-earth nuclei and double-magic 208Pb

Effects of inelastic multistep processes on (p, t) reactions in a transition region between well-deformed rare-earth nuclei and the double-magic ²⁰⁸Pb have been investigated by the ¹⁸⁸Os(p, t) ¹⁸⁶0s, ^{194, 196}Pt(p, t)^{192, 194}Pt and ^{200, 202}Hg(p, t)^{198, 200}Hg reactions at E_p = 51.9 MeV. The observed ground 0⁺, first excited 2⁺ and 4⁺ angular distributions together with those for the ^{206, 208}pb(p, t)^{204, 206}pb reactions have been compared with CCBA and DWBA calculations, using transfer form factors based on the Nilsson, vibrational and shell models. It is found that the inelastic multistep processes play a very important role in reproducing both the shapes and magnitudes of the observed first excited 2⁺ angular distributions, contrasting to small contributions in the ground-state 0⁺ transitions. The effects of the inelastic multistep processes on the first excited 4⁺ transitions are also considered to be important.     

One- and two-step processes in natural- and unnatural-parity 208Pb(p,t)206Pb reaction at Ep = 22 MeV

Reaction mechanism and nuclear-structure dependence of the natural- and unnatural-parity ²⁰⁸Pb(p, t)²⁰⁶Pb(2⁺, 3⁺, 4⁺, 5⁻ and 7⁻) reaction are studied by using a 22 MeV polarized proton beam. Angular distribution of the analyzing power for the second 3⁺(3₂⁺) transition has an opposite sign to that for the 3₁⁺ one and the difference is explained in terms of the j-dependence in the sequential two-step (p, d)(d, t) process. The observed analyzing powers and cross sections for the two 3⁺ transitions are reproduced by the finite-range first- and second-order DWBA calculation. Two-step analysis is necessary to explain the variety of angular distributions of the analyzing powers for the natural-parity transitions. Microscopic analysis in terms of the one- and two-step (p, t) calculation is made for the transitions to the 2_1–5⁺, 4_1–3⁺, 5_{1, 2}⁻ and 7₁⁻ states in ²⁰⁶Pb. The calculation reproduces the absolute values of the observed cross sections within a factor of 2.     

A study of the (3He,n) reaction on isotopes of tin

The (³He, n) reaction has been studied on^{112,116,118,120,124}Sn at 25.4 MeV. Angular distributions were measured over the range 0°–25° and the results compared with predictions of zero-range DWBA calculations. In addition to the around-state transitions, L = 0 transitions were also observed to low-lying states in every case. Simple two component wave functions, as well as those obtained from a more sophisticated pairing model, are compared with the data in order to explain the appearance of the anomalously low-lying excited 0⁺ states observed. L = 2 transitions were observed to low-lying 2⁺ states, but the strength of these transitions was much less than expected from the systematics of (t, p) results for N = 50 nuclei.     

Unnatural parity transitions in (p,t) reactions using realistic triton wavefunctions

The reaction ²⁰⁸Pb(p,t)²⁰⁶Pb leading to the unnatural parity 3⁺ state of ²⁰⁶Pb is analyzed in the framework of finite range DWBA formalism. The main aspect of the present analysis is the use of a realistic triton wavefunction with S, S′ and D state components which permit this transition in DWBA. Excellent agreement between theoretical prediction and experiment is obtained casting serious doubt on the treatment of this reaction as a sequential transfer process.     

Measurement of elastic ω photoproduction at HERA ZEUS Collaboration

The reaction γp →ωp(ω → π⁺π^?π⁰ and π⁰ → γ γ) has been studied in ep interactions using the ZEUS detector at photon-proton centre-of-mass energies between 70 and 90GeV and ∣t∣ < 0.6GeV², where t is the squared four momentum transferred at the proton vertex. The elastic ω photoproduction cross section has been measured to be σ_{γp → ωp} = 1.21 ±0.12 ±0.23 μb. The differential cross section dσ_γp→ωp/d¦t¦ has an exponential shape e^?b∣t∣ with a slope b =10.0 ± 1.2 ± 1.3 GeV^?2. The angular distributions of the decay pions are consistent with s-channel helicity conservation. When compared to low energy data, the features of ω photoproduction as measured at HERA energies are in agreement with those of a soft diffractive process. Previous measurements of the ρ⁰ and ? photoproduction cross sections at HERA show a similar behaviour.     

The theoretical basis and phenomenology of the OZI rule

No reliable theoretical recipe exists for predicting strengths of OZI-forbidden transitions proceeding via two OZI-allowed transitions like φ→K⁺K^?→?π, π^?p→K⁺K^?n→φφn or π^?p→ηn→φφn. Nonet symmetry, exchange degeneracy and duality suppress such transitions by cancellations between different diagrams. Unpredictable OZI violations are introduced by breaking of these symmetries. Phenomenological analyses of charmonium decays and meson photoproduction establish an emperical topological criterion for classifying some processes as less forbidden and suggest that π^?p→φφn should not be suppressed by a factor of more than three in amplitude. Its observation is not conclusive evidence for new exotic particles.     

Investigations with two-neutron transfer reactions on the even isotopes of samarium

The (p, t) reaction on the even isotopes of samarium has been investigated at a proton energy of 25.5 MeV. Angular distributions were obtained in the range 18° ≦ θ ≦ 148° with angular steps between 2° and 5°. The experimental energy resolution varied between 35 keV and 50 keV FWHM. Spin and parity assignments are performed by comparing the measured angular distributions to zero-range DWBA calculations. Some difficulties of DWBA calculations for (p, t) reactions are pointed out. The relative cross sections for transitions to different levels of the final nuclei are compared with other (p, t) and (t, p) measurements in the same region of the rare earth isotopes. The dependence of the (p, t) cross sections for different transitions on the neutron number of the final nuclei is discussed. Some 2⁺ states observed in (p, t) and (t, p) reactions are described in the quadrupole pairing vibrational picture.     

A theoretical study of the beta decay transitions 0− → 2+ and 0− → 0+ of the Ho166 nucleus

The theoretical beta decay observables are compared with the experimental values for the 0^? → 2⁺ and 0^? → 2⁺ transitions. By considering a Ho¹⁶⁶ ground state configuration infered from (d, p) reaction experiments, and using all the matrix elements, satisfactory results are obtained for the 0^? → 2⁺ transition. For the 0^? → 2⁺ transition an important cancellation effect has been found which determines the failure of the ξ approximation and an energy dependent spectrum shape.     

Measurement of the reactions K+d → K+d and K+d → p+pn and an investigation of elastic K+-nucleon scattering at 4.6 GeV/c

The coherent elastic reaction K⁺d → K⁺d and the break-up reaction K⁺d → K⁺pn are studied in a K⁺d experiment at 4.6 GeV/c which the CERN 2 m bubble chamber. Partial and differential cross sections are given and the slopes of the differential cross sections are determined. The results for the reaction K⁺d → K⁺p(n_s), where n_s denotes the spectator neutron, are compared with those of the reaction K⁺p → K⁺p on free protons. Combining our data with existing data on the reactions K⁺d → K⁰pp and K⁺p → K⁺p, parameters of the elastic K⁺-nucleon scattering at 4.6 GeV/c are determined in the framework of the Glauber model. The D-wave of the deuteron and spin-flip effects are taken into account.     

Techniques to Treat the Continuum Applied to Electromagnetic Transitions in 8Be

Bremsstrahlung emission in collisions between charged nuclei is equivalent to nuclear gamma decay between continuum states. The way the continuum spectrum can be treated is not unique, and efficiency and accuracy of cross section calculations depend on the chosen method. In this work we describe, relate, and compare three different methods in practical calculations of inelastic cross sections, that is, by (i) treating the initial and final states as pure continuum states on the real energy axis, (ii) discretizing the continuum states on the real energy axis with a box boundary condition, and (iii) complex rotation of the hamiltonian (complex scaling method). The electric quadrupole transitions, 2⁺ → 0⁺ and 4⁺ → 2⁺, in α + α scattering are taken as an illustration.     

A precision determination of the radial charge parameters and the quadrupole moment of 181Ta using muonic X-rays

We report the measurement of the energies of the 4f → 3d, 3d → 2p and 2p → 1s atomic transitions in muonic ¹⁸¹Ta. Using transitions to and from the 1s and 2p levels, as well as the hyperfine splittings of the 2p and 3d states, we obtained the radial charge parameters assuming deformed Fermi distributions. We found the intrinsic static quadrupole moment Q₀ = 6.82 ± 0.06 e · b, in excellent agreement with Coulomb excitation results. We verified that the dynamic (corresponding to transitions to the first excited state) and the static (ground state) E2 moments were equal to within 1.1 %. The intrinsic hexadecapole moment was determined to be Π₀ = ?0.12 ± 0.40 e · b².     

Vector analysing power and cross section for 90Zr(d, p)91Zr at 11 and 12 MeV

Angular distributions of the vector analysing power and the cross section were measured for ⁹⁰Zr($\text{d}$, p)⁹¹Zr. Measurements were made on two transitions at a deuteron energy of 11 MeV and on 20 transitions at 12 MeV. The observed j-dependence of the vector analysing power provided unambiguous spin assignments for most final states. Measurements of the cross section and vector analysing power were also made for deuteron elastic scattering at 11 MeV in order to determine the potential parameters for DWBA calculations. The DWBA predictions are in good agreement with the measured (d, p) cross sections and in qualitative agreement with the analysing powers. Enriched targets.     

Competition between simultaneous and successive transfer processes in the two-nucleon transfer reactions induced by heavy ions

It is demonstrated that the successive transfer process dominates over the simultaneous transfer in the two-nucleon transfer between heavy ions. We present the results of the DWBA analyses for the case of the ⁶⁴Ni (¹⁶O, ¹⁴C) ⁶⁶Zn reaction.     

Quark-quark spin-isospin-interaction and6Li(p, δ+ +)6He reaction

The elementary reaction pp→nΔ ^{+ +}, through which the⁶Li(p, Δ ^{+ +})⁶He reaction proceeds, is considered as the flip of spins and isospins of two quarks, one in each of the two quark bags of the interacting nucleons. Using the experimental data on the⁶Li(p, Δ ^{+ +})⁶He reaction at 1.04 GeV and the distorted wave Born approximation (DWBA) for the reaction mechanism, the strength of the spin-isospin quark-quark interaction is determined. It is found to be 70 MeV fm³.     

A study of the states of 30Si with the 28Si(t,p)30Si and 29Si(d,p)30Si reactions

The excitation energies of the levels in ³⁰Si have been measured up to an excitation of 9.46 MeV with the ²⁸Si(t, p)³⁰Si reaction at a triton energy of 6.0 MeV. Angular distributions have been measured of proton groups from the ²⁸Si(t, p)³⁰Si and ²⁹Si(d, p)³⁰Si reactions in a multi-angle magnetic spectrograph. Triton bombarding energies of 10.5 and 12.1 MeV were used and the deuteron incident energy was 10.0 MeV. States in ³⁰Si up to an excitation of 8 MeV were observed. Spins and parities of several states have been assigned using an empirical method for the (t, p) results and using a DWBA analysis for the (d, p) distributions. Spectroscopic factors for twelve states were obtained from the latter analysis. Two of these disagree with theoretical predictions. The state previously reported at an excitation of 6.63 MeV in ³⁰Si was observed to be formed by a strong L = 0 transition in the (t, p) reaction and also by a strong l = 1 transition in the (d, p) reaction. We deduce that there are two closely spaced states at about this excitation, one having a spin and parity of 0⁺ and the other 0^?, 1^? or 2^?.