Triple Angular Correlation Research Articles

T-odd angular asymmetry in nuclear reactions involving sequential particle emission

A triple T-odd angular correlation is considered in the kinematically similar reactions 10B(n, αγ) and 233U(n, αf) induced by cold polarized neutrons. It is shown that, in the former reaction, this correlation is suppressed by the double parity-conservation selection rule due to the two-step character of the process; however, T invariance does not impose any specific constraints on this correlation. The mechanism through which the T-odd correlation found in ternary-fission reactions is formed seems to be closely related to a nearly simultaneous disintegration of the nucleus involved into two fission fragments and an alpha particle.

Parities and multipolarities of gamma rays in neutron-rich odd-mass Ba nuclei

The nuclei 143,145,147Ba produced in the spontaneous fission of 248Cm have been studied using the EUROGAM phase II array. The parities and multipolarities of γ rays in these nuclei have been assigned from triple angular correlation, directional linear-polarisation correlation and internal conversion coefficient measurements. These data confirm an alternating-parity sequence connected by strong electric dipole transitions in 143Ba. They also reveal a more weakly populated, complementary alternating-parity sequence. The two sequences together exhibit some characteristics of parity-doublet bands. Interpreting the E1 strengths in terms of a rotating intrinsic dipole moment gives a moment similar in size to that observed in 142Ba and 144Ba. No well-developed similar structure is seen in 145Ba, although E1 transitions are observed, from which a value of the dipole moment is obtained. This value is smaller than the moment observed in 143Ba. No features appropriate to strong octupole correlations were observed in 147Ba.

Determination of spins and mixing ratios from directional correlations measured with the OSIRIS array

From the general triple angular correlation of γ-radiations from axially symmetric oriented nuclear states the limit of double correlations with unobserved intermediate transitions is derived. Expressions for DCO ratios are obtained for a detector geometry in which the OSIRIS array is placed perpendicular to the beam direction and an additional Ge detector is positioned close to the beam axis. Spin assignments to high-spin states in 89,90Mo and 90Tc populated in the 58Ni + 36Ar fusion reaction are reported. The relevance and precision of E2/M1 mixing ratios deduced from the DCO ratios is tested against those obtained from angular distributions which were taken for the same transitions, populated in the reaction 58Ni + 35Cl.

Triple angular correlations in the decay of 110Agm.

Double and triple gamma-ray angular correlations are reported for cascades in $^{110}\mathrm{Cd}$ following the decay of $^{110}\mathrm{Ag}$. The 764-1505-658 keV triple correlation helps to resolve a long-standing ambiguity concerning the E2/M1 multipole mixing ratio of the 1505-keV transition. The potential of triple correlations to contribute to nuclear spectroscopy is thereby demonstrated.

Some remarks concerning triple angular correlations

The theory and reported experiments involving triple angular correlations are reviewed. The sensitivity of these experiments to nuclear spectroscopic parameters is discussed.

Cluster structure of 8p-4h states inNe20

The structure of high-lying states in $^{20}\mathrm{Ne}$ has been studied using the $^{12}\mathrm{C}(^{12}\mathrm{C}, \ensuremath{\alpha})^{20}\mathrm{Ne}$ reaction at $E(^{12}\mathrm{C})=64 \mathrm{and} 80$ MeV. The spins and branching ratios to the $\ensuremath{\alpha}$ +$^{16}\mathrm{O}$ channel were determined by measuring double ($\ensuremath{\alpha}\ensuremath{-}\ensuremath{\alpha}$) and triple ($\ensuremath{\alpha}\ensuremath{-}\ensuremath{\alpha}\ensuremath{-}\ensuremath{\gamma}$) angular correlations. The branching ratios for decay to the $^{12}\mathrm{C}$ + $^{8}\mathrm{Be}$ channel were obtained from an $\ensuremath{\alpha}$-$^{12}\mathrm{C}$ coincidence experiment. In addition to confirming the spins of several lower-lying states, we have made a spin assignment of ${8}^{+}$ for the state at 18.538 MeV and also suggest assignments to states at 17.259 MeV (${7}^{\ensuremath{-}}$), 20.478 MeV (${8}^{+}$), and 24.378 MeV (${7}^{\ensuremath{-}}$). The 13.927-MeV (${6}^{+}$) state is assigned to the ${K}^{\ensuremath{\pi}}={0}_{2}^{+}$ band, and it is suggested that this band also includes the ${8}^{+}$ state at 20.478 MeV. The 18.538-MeV (${8}^{+}$) state was found to have a large reduced width for decay into $^{12}\mathrm{C}$ + $^{8}\mathrm{Be}$ which, together with its small reduced width for decay to $\ensuremath{\alpha}$ +$^{16}\mathrm{O}_{\mathrm{g}.\mathrm{s}.}$,suggests that it has a large $^{12}\mathrm{C}$ + $^{8}\mathrm{Be}$ cluster parentage. This state appears to be the ${8}^{+}$ member of a new 8p-4h band which has the 12.436-MeV (${0}_{6}^{+}$) state as its band head and the state at 15.159 MeV as its ${6}^{+}$ member. The discovery of such a rotational band in $^{20}\mathrm{Ne}$ with a large $^{12}\mathrm{C}$ + $^{8}\mathrm{Be}$ cluster parentage and a large moment of inertia provides the first direct indication of correlations between the \ensuremath{\alpha} clusters in 8p-4h states.NUCLEAR STRUCTURE $^{20}\mathrm{Ne}$; measured spins, parities, branches to $\ensuremath{\alpha}$ +$^{16}\mathrm{O}$ and $^{12}\mathrm{C}$ + $^{8}\mathrm{Be}$; deduced reduced widths, cluster structure.

A (p, p? ?) angular correlation study of an intermediate structure in the 3? exit channel of40Ca+p

Excitation functions of the40Ca(p,p 2γ) triple angular correlations have been measured in the region of an intermediate structure centered atE p=6.25 MeV, for 12 pairs of proton and gamma detector positions. The angular correlations are consistent with the spin 5/2 assigned for these resonances and have established thep 1/2 partial wave as the main decay mode of the intermediate structure in the 3− inelastic channel. These results are strongly supporting the description of the structure observed in the 3− exit channel as consisting of 2p-1h doorway states in which a 2p 1/2 single-particle state weakly coupled to 3− excited core is split by residual interactions. An improved dynamical treatment, aimed to obtain the strength function of the 2p 1/2 single-particle state in the 3− channel, is suggested.

Studies of continuum states using angular correlation techniques (II). 24Mg

A study of the region of excitation energy between 17.5 and 22 MeV has been carried out using angular correlation techniques. Alpha decays of continuum levels populated using the 12C( 16O, α) 24Mg reaction were observed to the ground state and first two excited states of 20Ne. Double (α-α) and, in some cases, triple (α-α-γ) angular correlation measurements were carried out for levels at E x = 17.60, 17.86, 18.19, 18.56, 19.14, and 21.3 MeV. Branching ratios were determined for all of the above levels plus additional states at E x = 19.37, 20.57 and 20.90 MeV. In most cases spin assignments could not be made from the angular correlations, either because of a strong continuum background or because the groups turned out to consist of more than one level. A search for a direct γ-decay branch of the E x = 21.3 MeV level was carried out; a limit Γ γ/Γ < 0.013 was obtained, in disagreement with a previously reported experiment. While the present work shows that the observed 21.3 MeV peak does not consist of a single state, the measured triple correlations provide some evidence for a J π = 10 + level at this energy.

Studies of continuum states using angular correlation techniques (I). 20Ne

A study of the region of excitation energy between 14 and 21 MeV in 20Ne has been carried out using angular correlation techniques. Alpha decays of continuum levels populated via the 12C( 12C, α) 20Ne reaction were observed to both the ground and excited states of 16O. Measurement of double (α-α) and triple (α-α-γ) angular correlations have been made for levels at E x = 14.26, 15.16, 15.36, 15.88, 16.52, 16.68, 17.40, 18.06, 18.4, 18.7 and 20.67 MeV. Spin assignments were possible for most of these states, many of which confirmed the results of previous work. New spectroscopic information obtained includes the discovery of a closely spaced doublet of states with J π = 7 − at E x = 16.52 and E x = 16.68 MeV, the demonstration that J π = 8 + for the E x = 15.88 MeV level using the dominant decay branch to the 16O 3 − level, and the demonstration that the E x = 20.67 MeV level strongly populated in the 12C( 12C, α) 20Ne reaction has E π = 9 −. Branching ratios to different 16O final states were determined for all levels studied. In addition, an attempt has been made to probe the limitations of the present angular correlation techniques for spectroscopy in this region of mass and excitation energy.

On the general form of the double and triple angular correlation following the sequential decay of the heavy reaction products

The general form of the double and triple differential cross-sections for the sequential three-body reaction X(a,b) Y(c)Z and four-body reaction X(a,b)Y(c)Z(f)R, respectively, are derived in the one-level excitation hypothesis. The transition amplitudes for the sequential processes are related to the scattering matrixS. Moreover, theoretical expressions for the b-c angular correlation are given under the hypothesis that the excited and partly polarized nucleus Y is produced in heavy-ion deeply inelastic collisions.

A new possibility of identifying high-spin states at high excitation energies

The great amount of theoretical predictions [1 4] on the structure of high lying high-spin states and yrast lines in light nuclei (A 1 0 brought a new impetus to the experimental investigations. However the actual confinement of the experimental knowledge to the region E 10MeV in light nuclei is the use of high-spin selective compound reactions [5, 6]. Together with statistical model calculations the "relative" cross sections yield directly the spins of the high-spin states and the critical angular momentum J~it limiting the formation of the compound nucleus. This method is limited, however, for high spins by the loss of selectivity for spins near J~it [7] and is limited further for high excitation energies (E > 20 MeV) by the high level density of low-spin states [7]. The high level density also affects double and triple angular correlation methods which have a further even lower limitation in excitation energy due to the fact that the sequential decay of these highly excited states cannot be in general expected to proceed via a spin-zero state in the final nucleus. The high level density limits also the accuracy of spin measurements by selective direct transfer reactions [-8, 9]. In the present work a new procedure for identifying highly excited high-spin states will be presented which

États de haut spin dans 53Mn

The 40Ca( 16O, 3pγ) 53Mn reaction has been used at a beam energy of 45 MeV to search for high-spin states in 53Mn. By means of the techniques of in-beam γ-ray spectroscopy, the excitation functions, γ-γ coincidences, angular distributions, linear polarizations and simplified triple angular correlations were measured. A new decay scheme for high-spin states is given. For the following levels (MeV), we deduced spin-parity assignments; 2.56, 13 2 − (confirmed); 3.44, 15 2 −; 4.38, ( 17 2 −); 5.61 ( 19 2 −); 6.53, ( 21 2 −); 7.00, ( 23 2 −). Mixing ratios are also reported. It is only with this spin sequence that the experimental populations of these states are well reproduced by compound nucleus evaporation calculations. High-spin states are successfully interpreted by including neutron excitations out of the f 7 2 shell.

Improved Experimental Test of Time-Reversal Symmetry inNe19βDecay

We report on a new measurement of the time-reversal-violating triple angular correlation between the nuclear spin and the positron and neutrino directions $D\stackrel{^}{J}\ifmmode\cdot\else\textperiodcentered\fi{}({\stackrel{\ensuremath{\rightarrow}}{\mathrm{v}}}_{\ensuremath{\beta}}\ifmmode\times\else\texttimes\fi{}{\stackrel{^}{q}}_{\ensuremath{\nu}})$. Our result for the decay process $^{19}\mathrm{Ne}\ensuremath{\rightarrow}^{19}\mathrm{Fe}^{\ensuremath{-}}+{e}^{+}+\ensuremath{\nu}$ is $D=\ensuremath{-}0.0005\ifmmode\pm\else\textpm\fi{}0.0010$, consistent with time-reversal symmetry.

Spin assignment to the 9.026 MeV resonance level of36Ar using35Cl(p, ?)36Ar triple angular correlation measurements forE p = 533 keV

Triple correlation experiments have been performed to study the35Cl(p, γ)36Ar resonance for a proton energyEp = 533 keV. From the analysis of the measured gamma ray angular distributions, due to the gamma decay of the 9.026 MeV resonance level in36Ar via the 9.026 MeV→1.97 MeV→0 MeV double cascade, a spin value ofJ1 =2+ for the 9.026 MeV level and a mixing ratio of ≪1.97 MeV∥L′1 = 2∥9.026 MeV≫/≪1.97 MeV∥ L1= 1∥9.026 MeV≫ = −0.055 + 0.022 for the 9.026 MeV→ 1.97 MeV transition could be derived.

Spectroscopy ofP29via theSi28(p,p′γ)reaction

Excitation functions have been measured for inelastic proton scattering from the 1.78 MeV, ${2}^{+}$ first excited state of $^{28}\mathrm{Si}$ between 3.1 and 5.7 MeV. Two previously unidentified resonances corresponding to states in $^{29}\mathrm{P}$ with excitation energies of 6.577 and 7.272 MeV have been observed. Triple angular correlations in the Goldfarb-Seyler geometry have been measured as a function of energy over all the resonances observed in the inelastic excitation function. Information obtained from the angular correlation data has been combined with previous information concerning these states to allow ${J}^{\ensuremath{\pi}}$ assignments for 9 of the 11 states observed.NUCLEAR REACTIONS $^{28}\mathrm{Si}(p,{p}_{1})$, measured $\ensuremath{\sigma}(E)$, $E=3.1\ensuremath{-}5.7$ MeV. $^{28}\mathrm{Si}(p,{p}_{1}\ensuremath{\gamma})$, measured $p\ensuremath{-}\ensuremath{\gamma}$ correlations, deduced ${J}^{\ensuremath{\pi}}$ of $^{29}\mathrm{P}$ levels.

Isobaric Analogue State of the 0.211 MeV Level of Mn56 in Fe56

AbstractGamma‐ray spectrum from the reaction Mn55(p, γ) Fe56 at the isobaric analogue resonance at Ep = 1537 ± 4keV has been measured with a 15 cm3 Ge(Li) detector. Double and triple angular correlations at this resonance state have been measured. Proton elastic scattering was studied also at this resonance at the angles 135° and 150°. Analysis of these data yields a spin and parity assignment 2+, proton radiative width 2 ± 0.2 keV and total width 9 keV to this resonance state which is the isobaric analogue of the third excited state of Mn56 at excitation energy 0.211 MeV.

Isobaric Analogue State of the 0.211 MeV Level of Mn56in Fe56

Gamma-ray spectrum from the reaction Mn55(p, γ) Fe56 at the isobaric analogue resonance at Ep = 1537 ± 4keV has been measured with a 15 cm3 Ge(Li) detector. Double and triple angular correlations at this resonance state have been measured. Proton elastic scattering was studied also at this resonance at the angles 135° and 150°. Analysis of these data yields a spin and parity assignment 2+, proton radiative width 2 ± 0.2 keV and total width 9 keV to this resonance state which is the isobaric analogue of the third excited state of Mn56 at excitation energy 0.211 MeV.

Octupole excitation of the 6.88 level of28Si by deuteron inelastic scattering at 29.5 MeV

The experiments have been performed with the Grenoble Isochronous Cyclotron beam, focused on a 4 mg/cm ~ thin foil target of natural silicon. The scattered deuterons are detected by two 3 mm thick Si(Li) detectors, mounted on the two rotable arms of a chamber of 65 cm internal diameter. The positioning accuracy of the arms is 0.05 ~ Each detector has an angular resolution of • ~ delimited by a 4 • 8 mm tanta lum diaphragm. A monitoring detector is fixed at 45 ~ and a Faraday cup collects the beam charge. The detectors are cooled to about 2 0 ~ Each detector is connected to a charge preamplifier which gives rise to an analogue channel and a logic channel. This logic channel used an antipile-eup circuit which eliminates the pile-up effects by cancelling the pulse arriving at interval of t ime less than 30 ~s. The spectra from the multichalmel analyser are stored on magnetic tapes and handled by a PD1)-9 computer. An example of the spectra obtained is given in Fig. I. The overall energy resolution is (I00--150) keV. The beam energy is measured with a (CD2) ~ thin foil target, by crossover techniques. The angular distributions of deuterons scattered from the ground state, the first 2+-state and the 6.88 MeV level are shown in Fig. 2 together with the optical model and DWBA calculations. The first excited level of 2ssi has been well explained by Hartree-Fock and HartreeFoek-Bogoliubov calculations (1) as a rotational state of the ground band. Some recent experiments and calculations suggested an oblate deformation (2.3). :For the 6.88 level, gamma-ray double and triple angular-correlation measurements (4) from the 2:Al(p, T)2sSi reaction let to the spin-3 assignment and suggested the od,t narity, supported by some transfer reactions, particularly the 27 Al(aiie, d)2ssi reaction (a). According to the Blair

The level of 40Ca at 6.75 MeV

The 6.75 MeV level of 40 Ca was populated by means of proton inelastic scattering and the properties accessible to study through its γ-ray decay were determined. This level is found to decay only to the second excited state at 3.74 MeV. The energy of the transition is found to be E = 3013.7±1.5 keV placing the level at an excitation energy of 6750.5±1.5 keV. The mean lifetime of the level as measured by the method of Doppler-shift attenuation is determined to be τ m = 185 ± 65 fs. On the basis of pγ double and pγγ triple angular correlation measurements, a spin J = 2 is assigned to the level and a value of δ = 0.84 ± 0.16 to the mixing ratio of the 3.01 MeV γ-ray. An M1-E2 multipolarity for this transition is inferred from the combined lifetime and correlation results and thus the parity of the level is determined to be odd. Electromagnetic transition strengths computed from these data are B ( M 1) = (0.66 ± 0.26) × 10 −2 μ 0 2 and B ( E 2) = 7.4 ± 3.0 e 2 · fm 4 .

Coulomb excitation of 107, 109Ag

Coulomb excitation effected with 10 MeV alpha particles and with 45.5 MeV oxygen ions has been used to determine the properties of the low-lying 3 2 − and 5 2 − states in 107, 109Ag. The gamma-ray energies and branching ratios, and the B(E2), B(M1) and T 1 2 values were extracted from the gamma-ray yields, angular distributions, triple angular correlations and Doppler shift measurements. The results were compared to the predictions of the single-particle core weak coupling model. It was found that the 3 2 − 786.5 keV and 5 2 − 949.7 keV levels in 107Ag and the analogous states in 109Ag at 702.0 and 862.5 keV are consistent with the interpretation that they are due to coupling of the odd p 1 2 proton to the second 2 + core state. Another state of spin 3 2 was observed at 1464.7 keV in 107Ag and at 1324.2 keV in 109Ag. Still other states were populated via multiple Coulomb excitation, as effected with oxygen ions, at 973.5 and 1146.8 keV in 107Ag and at 912.3 and 1090.6 keV in 109ag.