Excitation of the analogue of the T> giant dipole resonance of90Zr via the (n,p) reaction

Proton spectra have been measured at lab angles ofθ=0° to 100° for the reaction Zr(n, p)Y at 21.8 MeV incident neutron energy. Spectra over an angular spread of 80° were accumulated simultaneously using a detection system consisting of proportional counterΔE detectors and a curved plastic scintillator as energy detector. Resonant behaviour is observed in the proton spectra for the Zr(n, p)Y reaction but not for the Fe(n, p)Mn reaction. The resonant structure is attributed to the excitation of the analogues ofT _> giant dipole states of Zr. The resonant structure is shown to correspond in position, gross and fine structure, and, in strength and angular dependence of the cross sections, with expectations for the⁹⁰Zr(n, p)⁹⁰Y reaction. DWBA cross sections are derived and fitted to the experimental data with a Lane potential of 150 MeV.     

Isobaric spin mixing in the analog states of 90Zr

A 90° photoproton energy spectrum has been obtained from the reaction ⁹⁰Zr(γ, p)⁸⁹Y using an isotopically enriched target foil. Previously unreported proton groups are observed at E_p = 6.95, 9.55, 10.68 and 11.03 MeV. A total photoneutron cross section and a low-energy neutron energy spectrum are also presented, and isospin mixing is demonstrated by comparison with the photoproton data. The possibility of T_> strength in the region 23–24 MeV excitation is noted.     

Partial width fluctuation method of determining nuclear level density

A new method of determining the nuclear level density is presented. This method is based on the statistical analysis of the partial width fluctuations appearing in an excitation function of the radiative proton capture. The method was applied in the case of the ⁸⁸Sr(p, γ₀)⁸⁹Y and⁸⁹Y(p, γ₀)⁹⁰Zr reactions. The density of levels with spin 1^? in ⁹⁰Zr and the densities of levels with spins $\text{1}\text{2}{}^{\mathrm{+}}$ and $\text{3}\text{2}{}^{\mathrm{+}}$ in ⁸⁹Y at excitation energies from 10.9 to 11.6 MeV and from 9.3 to 10.8 MeV respectively, were determined with an uncertainty of about 35%.     

Neutron-hole strengths and isobaric analog states in 95Zr

The ⁹⁶Zr(τ, α)⁹⁵Zr reaction at 39 MeV incident energy was used to populate both the low-lying and highly excited (up to an excitation energy of 18 MeV) analog states in ⁹⁵Zr and some low-lying levels in other Zr isotopes. The main components of the 2d_{$\text{5}\text{2}$}. and 1g_{$\text{9}\text{2}$}. hole strengths and the analogs of the 2p_{$\text{1}\text{2}$}., 2p_{$\text{3}\text{2}$}. and 1f_{$\text{3}\text{2}$}. proton hole states in ⁹⁵Y have been observed in this work. Angular distributions of transitions to 27 levels in ⁹⁵Zr have been extracted and analysed with DWBA calculations to yield spectroscopic factors. Between the excitation energies of 1 and 3 MeV in ⁹⁵Zr a number of levels with l = 2, 4 and 5 angular distributions have been identified. These are associated with the 2d_{$\text{3}\text{2}$}, 1g_{$\text{7}\text{2}$} and 1h_{$\text{11}\text{2}$} components already observed in the previous study of the ⁹⁴Zr(d, p) and (α, τ) reactions. The total strength and center of gravity for levels assigned to the (1g_{$\text{9}\text{2}$})^?1 configurations in ⁹⁵Zr are presented and compared to the results obtained from the studies of neutron pick-up reaction on ⁹¹Zr and ⁹⁸Mo. For the isobaric analog states observed between the excitation energies of 15 and 17 MeV, total widths, Coulomb displacement energies and spectroscopic factors are also determined from this experiment and the results compared with the properties of the low-lying proton hole states in the ⁹⁵Y parent nucleus.     

The decays of the Tz = 32 β-delayed proton precursors 83Zr, 87Mo and 91mRu

The decays of the nuclides ⁸³Zr,⁸⁷Mo and ^91mRu have been studied with singles proton counting as well as with pX and pγ coincidences. The half-lives for the three nuclides were measured to be 37.8 ± 1.1 s, 13.3 ± 0.4 s and 7.6 ± 0.8 s, respectively. The proton branch in the decay of ⁸³Zr that populates the first excited state in ⁸²Sr was measured to be (6 ± 4) % of the total delayed proton decay. The corresponding branch in the decay of ⁸⁷Mo, populating the first excited state in ⁸⁶Zr was measured to be (15 ± 8) %. Restrictions to the possible spin and parity assignments of ⁸³Zr and ⁸⁷Mo were deduced from comparisons between the experimental excited-state branches, and those predicted from a statistical model of delayed particle decay. Fits to the endpoints of the delayed proton spectra from ⁸³Zr and ⁸⁷Mo yielded values of the energy available for delayed proton decay (Q_e.c.?B_p) of 2.75 ± 0.10 MeV and 3.7 ± 0.3 MeV, respectively. Comparison between calculated and experimental proton spectra was used as an argument that the source of ⁹¹Ru activity is actually a $\text{1}\text{2}{}^{\mathrm{?}}$ isomer.     

Experimental and shell-model studies of the reactions 91Zr(d,p)92Zr and 90Zr(t,p)92Zr

The results of high-resolution studies of the ⁹¹Zr(d, p) reaction at E_d = 12 MeV and the ⁹⁰Zr(t, p) reaction at E_t = 11.85 MeV are presented. Absolute cross sections have been measured for both reactions and (d, p) spectroscopic factors determined. A comparison of these results with earlier data has been made, and although many of the previous assignments have been confirmed, many new features concerning the structure of ⁹²Zr have been discovered. Shell-model calculations have been performed for ⁹¹Zr and ⁹²Zr using a neutron space which includes the $\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$, $\text{3}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, $\text{2}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, $\text{1}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and $\text{1}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ orbits and a proton space comprising the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ and $\text{2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ orbits. Realistic proton-neutron and neutron-neutron interactions based on the Sussex matrix elements were used in the calculations. Spectroscopic factors have been calculated for the ⁹⁰Zr(d, p) and ⁹¹Zr(d, p) reactions and cross sections calculated for the ⁹⁰Zr(t, p) reaction. In general, good agreement between the theoretical and the experimental results has been obtained.     

Scattering and transfer reactions for 6, 7Li + 90, 91Zr

Elastic scattering data have been measured for the ⁷Li + ⁹⁰Zr, ⁶Li + ⁹⁰Zr, and ⁶Li + ⁹¹Zr systems at E(Li) = 34 MeV. Inelastic scattering data for the ⁷Li + ⁹⁰Zr and ⁶Li + ⁹⁰Zr systems were also measured for the 2⁺(2.18 MeV) and 3^?(2.75 MeV) states in ⁹⁰Zr and the $\text{1}\text{2}{}^{\mathrm{?}}\text{(0.48}\text{MeV}\text{)}$ state in ⁷Li. Optical model analyses of the elastic scattering data and DWBA analyses for the states in ⁹⁰Zr were performed. The deduced deformation lengths for the 2⁺ state agreed with those extracted in other studies but the deformation length for the 3^? state was smaller. The ⁹⁰Zr(⁷Li, ⁶Li)⁹¹Zr angular distributions were measured for the 1.21 and 2.03 MeV states and the 2.19 MeV doublet in ⁹¹Zr. Also, ⁹⁰Zr(⁷Li, ⁶He)⁹¹Nb angular distributions were measured for the ground states, 0.10, 3.41 and 4.82 MeV states in ⁹¹Nb. The transitions well matched in angular momentum were described by finite-range DWBA calculations, while other transitions displayed the same phase problems seen with heavier ions. The extracted spectroscopic information was consistent with the results of other reaction studies. At the present energy, it was not possible to determine whether the l = 1 phase problem that occurs for heavy-ion single-nucleon transfer reactions on 2s-1d shell nuclei occurs in ⁹¹Zr also.     

Relaxation of the analyzing power of the (p, τX) and (p, αX) reactions in the continuum

The observed continuous decrease of the analyzing power for the reactions ($\text{p}$, τX) and ($\text{p}$, αX) on ⁹⁰Zr and ²⁰⁹Bi at E_p = 72 MeV as a function of the excitation energy of the final nucleus is described by a phenomenological relaxation process.     

Quantum-mechanical treatment of diabatic neutron emission in heavy-ion collisions

The diabatic precompound emission of neutrons is studied in a finite time-dependent two-center shell model for central collisions of ⁹⁰Zr + ⁹⁰Zr and ⁹⁶Zr + ⁹⁶Zr. For laboratory energies between 8 $\text{MeV}\text{u}$ and 20 $\text{MeV}\text{u}$ the neutron multiplicity is found to be significantly enhanced for ⁹⁶Zr + ⁹⁶Zr as compared to ⁹⁰Zr + ⁹⁰Zr. The angular distribution of the emitted neutrons is forward-backward peaked in the center-of-mass system, while the energy spectra show an exponential tail, with a slope parameter T₀ roughly independent of the scattering angle. A close relation between the diabatic emission process, the Fermi-jet mechanism and the exiton model is established.     

Alpha decay of neutron-deficient isotopes of tungsten

Three neutron-deficient isotopes of tungsten have been produced by the reactions of ²⁴Mg on targets of ¹⁴⁷Sm and ¹⁴⁴Sm. They are ¹⁶⁴W, E_α = 5.153 MeV, $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 6.3 s}$; ¹⁶³W, E_α = 5.385 MeV, $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 2.5}\text{s}$; and ¹⁶²W, E_α = 5.53 MeV, $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{< 0.25}\text{s}$.     

Resonant photon scattering on the semi-magic nucleus 89Y up to 7 MeV

The semi-magic nucleus ⁸⁹Y has been investigated in a (γ,γ′) experiment at an endpoint energy of the bremsstrahlung of E₀ = 7 MeV. The scattered photons have been detected with a EUROBALL Cluster detector. The observed excitations are discussed in the framework of the shell model and a coupling of the unpaired proton to multi-phonon structures in the doubly even neighbours. Transitions above 4.7 MeV are considered to have E1 character. Around 6.3 MeV an unusually large concentration of E1 strength is found. Its origin is likely to correspond to similar structures in the ⁸⁸Sr and ⁹⁰Zr isotones which can be interpreted to result from the constructive interference of strong two-phonon amplitudes with weak admixtures from the low-energy tail of the giant dipole resonance.     

Fragment angular distributions in electron-induced fission of 232Th

Fission fragment angular distributions have been observed in electron-induced fission of ²³²Th for electron energies 8.7 MeV ≦ E_e ≦ 30 MeV. For low energies (though above the fission threshold) the angular distributions contain both a dipole and a quadrupole component. The (90°/0°) anisotropy decreases rapidly for higher electron energies but reveals smaller peaks after the onset of second-, third- and fourth-chance fission suggesting that the effective fission barriers for ²³¹Th and ²²⁹Th in second- and fourth-chance fission, respectively, are both characterized by $\text{K =}\text{1}\text{2}$.     

Proton spectra from the 6,7Li(γ,p) 5,6He reactions at Eγ = 60 MeV

The ${}^{\mathrm{6,7}}\text{Li}\text{(γ,}\text{p}\text{)}$ reactions have been investigated for E_γ = 60 MeV. Excitation of residual (1p)^?1 and (1s)^?1 hole states is evident from the proton spectra measured at ?_p = 45°. The data are compared with a theoretical calculation which includes short-range correlations.     

Deuteron d-state effects for the reactions 117Sn(d, p)118Sn and 119Sn(d, p)120Sn

Angular distributions of the differential cross section and the three tensor analyzing powers were measured for the reactions ¹¹⁷Sn($\text{d}$, p)¹¹⁸Sn and ¹¹⁹Sn($\text{d}$, p)¹²⁰Sn at E_d = 12 MeV. In addition, excitation functions of the tensor analyzing power T₂₀ were measured at proton lab angles of 0° and 5° for energies ranging from 10 to 12 MeV. At forward angles, the tensor analyzing powers for the ground state (l_n = 0) transitions are more than an order of magnitude larger than the predictions of distorted-wave calculations which neglect the deuteron D-state. Qualitative agreement with the measurements is obtained when the D-state is included.     

Evidence for assignment of 14.0 MeV state in 11B from 10B(n,n)10B

The differential cross section and polarization for neutrons scattered from ¹⁰B have been measured at E_n = 2.63 MeV (E_x = 13.85 MeV). The results of this experiment and other available neutron scattering data in the range 1 < E_n < 4 MeV are interpreted through a single-level R-matrix calculation over the region 12 < E_x < 15 MeV. Based on this analysis the most probable J^π assignment for the 14.0 MeV level in ¹¹B is $\text{11}\text{2}{}^{\mathrm{+}}$. The anomaly near E_x = 13.1 MeV can only be explained in terms of two overlapping levels having assignments of ($\text{5}\text{2}$, $\text{7}\text{2}$)^? and ($\text{3}\text{2}$, $\text{5}\text{2}$, $\text{7}\text{2}$)⁺.     

Study of 11B at high excitations with the 9Be(3He,p)11B and 9Be(α, d)11B reactions

The nucleus ¹¹B has been studied over the excitation energy range from 8.5 MeV to 21.5 MeV with the ⁹Be(³He, p)¹¹B / reaction at / E_{³He = 38 MeV}. The analogs of the parent states in ¹¹Be have been located at 12.56, 12.92, 14.40, 16.44, 17.69, 18.0, 19.15 and 21.27 MeV. A complementary measurement with the ⁹Be(α, d)¹¹B reaction at E_α = 48 MeV demonstrates that the 16.44, 17.69, 18.0 and 19.15 MeV resonances have rather pure isospin $\text{T}{}_{\mathrm{f}}\text{=}\text{3}\text{2}$. The 14.40 MeV state is a strongly isospin-mixed analog of the $\text{5}\text{2}{}^{\mathrm{+}}\text{1.78}\text{MeV}$ state in ¹¹Be. It is argued that spin S = 1 transfer is involved in the excitation of the 16.44 MeV state and its 3.887 MeV parent in ¹¹Be in a two-step stripping process. The $\text{T}{}_{\mathrm{f}}\text{=}\text{1}\text{2}$ states and the lowest three $\text{T}{}_{\mathrm{f}}\text{=}\text{3}\text{2}$ states are compared with the predictions of DWBA utilizing shell-model form factors. It is concluded that the $\text{T}{}_{\mathrm{f}}\text{=}\text{1}\text{2}$ strength is more strongly fragmented than is implied by the calculations of Teeters and Kurath.     

Elastic and inelastic scattering of 15 MeV polarized deuterons from isotopes of Ca,Cu, Sr,Zr, and Mo

The elastic and inelastic scattering of 15 MeV polarized deuterons from ⁴⁸Ca, ⁶³Cu, ⁸⁸Sr, ⁹⁰Zr, ⁹²Zr, and ⁹²Mo has been investigated. Angular distributions of the cross section and vector analyzing power iT₁₁ have been measured for all these nuclei; the tensor analyzing powers T₂₀ and T₂₂ have been studied for ⁹²Zr. Cross sections and vector analyzing powers are generally well explained by the optical model for elastic scattering and by the DWBA with a macroscopic form factor for the inelastic scattering; this is consistent with previous work. Distributions for ⁴⁸Ca, however, are poorly fitted. Anomalous behavior of the N = 50 nuclei found in the inelastic scattering of polarized protons is not present for deuterons. Tensor analyzing powers are not well explained by standard procedures: use of approximate folding model optical parameters did not improve the fits. The distribution of iT₁₁ for the $\text{1}\text{2}$^? state in ⁶³Cu is significantly different from the distributions for the $\text{5}\text{2}$^? and $\text{7}\text{2}$^? states.     

A study of the 91Zr(d,p)92Zr reaction using vector-polarized deuterons

Differential cross sections and vector analyzing powers were measured for the ⁹¹Zr($\text{d}$, d)⁹¹Zr and ⁹¹Zr($\text{d}$, p)⁹²Zr reactions at an incident deuteron energy of 12 MeV. Deuteron optical-model parameters were determined from an analysis of the elastic data. Comparison of the proton data to DWBA predictions showed that the DWBA does not quantitatively reproduce the measured analyzing powers, hence empirical analyzing power calibration curves were required to analyze the data. New spectroscopic information about the configurations of the excited states in ⁹²Zr has been determined and is compared to the results of previous experiments as well as a shell-model calculation. The results of this experiment are in quantitative agreement with the predictions of the shell-model calculation for most of the transitions although some discrepancies do exist.     

Tensor analysing powers of (d,p) reactions on 28Si, 67Zn, 90Zr and 208Pb at 12.3 MeV

The tensor analysing powers T₂₀ and T₂₂ of(d, p) reactions leading to several states of the final nuclei ²⁹Si, ⁶⁸Zn, ⁹¹Zr and ²⁰⁹Pb were measured at 12.3 MeV deuteron beam energy. The measured tensor analysing powers together with the vector analysing power and cross-section data are compared with DWBA calculations with and without the deuteron D-state. The D-state effects and j-dependence of the tensor analysing powers are discussed. The spin transfers involved in populating the 1.08, 1.88 and 3.30 MeV states in ⁶⁸Zn in the ⁶⁷Zn(d, p)⁶⁸Zn reaction are deduced to be predominantly $\text{1}\text{2}{}^{\mathrm{?}}$. This implies an assignment for the 3.287 MeV level of ⁶⁸Zn of J^π = 2⁺.     

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.