Amplitude Mixing Ratio Research Articles

Negative parity bands in 100Ru observed in the 100Mo(α, 4n)100Ru reaction

In the study of the 100Mo(α, 4n)100Ru reaction at Eα = 45 MeV the ground state band of 100Ru was excited up to Jπ = 10+ and a negative parity band up to Jπ = (15)−. In addition, two negative parity bands were observed, one of which probably has even and the other odd spin states. The experiments encompassed γ-ray angular distribution, coincidence, linear polarization and conversion electron measurements. New levels are reported at Ex = 5130, 5165 (Jπ = (13)−), 5280, 5717 and at 6201 keV (Jπ = (15)−). In addition spin or parity assignments were made for the Ex = 2529, 2953, 2965, 3141, 3356, 3505 and 4233 keV levels as Jπ = 5−, 7−, (6)−, 7−, (8)−, 9− and (11)−, respectively. A 3− state is for the first time observed at Ex = 2180 ± 20 keV in the 100Ru(α, α') reaction at Eα = 104 MeV. Multipolarities, conversion coefficients, branching and quadrupole/dipole amplitude mixing ratios have been determined for many transitions in 100Ru. From a detailed comparison of excitation energies and of the properties of many, even weak, transitions with the results of the interacting boson approximation model, it appears that this simple model provides a good overall parametrization. This supports the description of 100Ru as an anharmonic vibrator with quadrupole and octupole bosons as independent but interacting basic excitation modes. A negative parity band in 101Ru, of which a new level at Ex = 3474 keV is a candidate for the 272− member, is well described by coupling the h112 single particle to the 100Ru quadrupole excitation.

Measurement of the 89-keV-state-to-ground-state quadrupole-moment ratio inRu99

The ratio of nuclear quadrupole moments of the first excited state with respect to the ground state in $^{99}\mathrm{Ru}$ has been determined from M\ossbauer effect measurements with single crystal absorbers of ruthenocene. The result, $\frac{{Q}_{1}}{{Q}_{0}}=2.93\ifmmode\pm\else\textpm\fi{}0.07$, when combined with a recent measurement of ${Q}_{0}$, gives the value ${Q}_{1}=0.23\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ ${\mathrm{cm}}_{2}$. An improved value for the $\frac{E2}{M1}$ amplitude mixing ratio $\ensuremath{\delta}=\ensuremath{-}1.56\ifmmode\pm\else\textpm\fi{}0.02$ is determined from magnetic hyperfine spectra obtained with an absorber of ruthenium dissolved in iron. A determination of the angle between the axis of the electric field gradient and each of the three crystal axes of ruthenocene is in good agreement with the crystal structure reported for this compound. The recoil-free fraction was found to vary with respect to orientation of the crystal axes by a factor of greater than 2.NUCLEAR REACTIONS $^{99}\mathrm{Ru}(\ensuremath{\gamma},\ensuremath{\gamma})$, $E=89.4$ keV; measured M\ossbauer effect ruthenium iron, single crystal ruthenocene. Deduced $\ensuremath{\delta}$, $\frac{{q}_{1}}{{q}_{0}}$, EFG axis, recoilless fraction anisotropy.

Gamma-ray decay scheme of 89Sr from the 88Sr(d, pγ) 89Sr reaction

Gamma-ray decay modes for ten low lying excited states in 89Sr up to E x = 3.76 MeV have been determined. Those for the E x = 2.67, 3.13, 3.25, 3.39 and 3.76 MeV levels are previously unreported. Angular correlation experiments were performed to determine the spins J = 3 2 for the E x = 2.45 and J = 7 2 for the 2.67 MeV levels. Several quadrupole/dipole amplitude mixing ratios are also reported. Electromagnetic decay properties of 89Sr levels up to E x = 2.67 MeV are calculated with previously reported particle-core coupling wave functions. Agreement with experimental data is good for the E x = 2.00 and 2.67 MeV levels, but generally is not satisfactory for the other levels.

Directional Correlations of Gamma Rays inBr79

The $\ensuremath{\gamma}$ radiation following the decay of $^{79}\mathrm{Kr}$ to levels in $^{79}\mathrm{Br}$ has been studied with Ge(Li) detectors. 40 transitions were observed, including 4 which were previously unreported. $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ directional-correlation measurements have been made using two Ge(Li) detectors. The $\frac{E 2}{M 1}$ amplitude mixing ratios for several transitions in $^{79}\mathrm{Br}$ have been determined from these directional-correlation measurements. The results of these measurements together with conversion coefficients and $log\mathrm{ft}$ values have made it possible to assign spins and parities to some of the excited levels.

Rotational states and coriolis interaction in 171Yb

The 170Er(α, 3n) 171Yb reaction is used to populate rotational states built on the 7 2 +[633], 1 2 −[521], 5 2 −[512] and 11 2 −[505] intrinsic states. Particular attention is paid to the positiveparity band. The rotational energies within this band are successfully explained within the unified model with pairing and Coriolis interactions included, provided the theoretical Coriolis matrix elements are reduced. With the wave functions obtained from this energy fit the experimental E2/M1 amplitude mixing ratios are well reproduced. These wave functions also reproduce the cross-section pattern obtained in transfer-reaction experiments very well.

Circular polarization of neutron capture γ-rays from Al, Ar and Ca

Measurements of the circular polarization of γ-rays from the capture of polarized thermal neutrons in natural Al, Ar and Ca result in new spin assignments to the following bound states: 28Al(3.47 MeV), J π = 4 -; 28Al(3.59), J π = 4 −(2) −; 41Ar(2.95), J π = 3 2 − J π = 3 2 − . The 41Ca levels at 3.61 and 4.75 MeV, for which conflicting spin values have been reported previously, both have J π = 1 2 − . The spins of 10 other bound states are confirmed. The M1 + E2 ground state transition from the capturing state in 28Al has an amplitude mixing ratio of δ = +1.00±0.14.

The reaction 23Na(α, γ)27Al

Angular distribution and Doppler-shift attenuation measurements in the reaction 23Na(α,γ)27Al lead to the spin and parity assignments Jπ = 72+ to the 27AlEx = 4.58 MeV level, Jπ = 92+ to the levels at Ex = 5.43, 5.67 and 7.17 MeV, Jπ = 112+ to the 6.51 MeV level and Jπ = 92(+) to the 7.81 MeV level. The Eα = 2.69, 2.79 and 2.81 MeV resonance levels have Jπ = 112(+), 92 and 112+, respectively. Several quadrupole/dipole amplitude mixing ratios and γ-ray transition strengths are also reported. The combined evidence of the decay of the resonance levels and bound states leads to lower limits of 72, 32, 52, 52 and 72 for the spins of the 5.50, 5.96, 6.95, 7.44 and 7.66 MeV levels, respectively, and to similar spin limitations for seventeen resonances.

Sign of 'δ', the Amplitude Mixing Ratio of Gamma Transitions, and Gamma–Gamma–Gamma Angular Correlation Studies in 160Dy

The importance of gamma–gamma–gamma angular correlation in order to study the absolute sign of 'δ', the amplitude mixing ratio of gamma transitions, independent of phase convention is given. A study of the triple gamma-rays cascade of 298 keV → 879 keV → 87 keV in 160Dy from the decay of 160Tb has been done.

Resonance fluorescence studies of levels in 23Na at about 7 MeV

Abstract The Doppler-broadened 6.92 and 7.12 MeV radiation from the 19 F(p, αγ) 16 O reaction has been used to resonantly excite levels in 23Na in 6.923, 6.953, 7.075, 7.086 and 7.138 MeV. From observed branchings and angular distribution measurements of the scattered radiation, spin and parity probable assignments of 5 2 + and 3 2 + have been made for the 7.075 and 7.086 MeV levels, respectively, and the corresponding widths for the ground state transitions were calculated to be 0.68±0.14 and 1.10±0.22 eV. Only limits could be placed on the spins and parities for the other levels. Possible values for the amplitude mixing ratios are also given.

Monopole mixing ratio of the 793 keV 2 + → 2 + transition in 184W

The amplitude mixing ratios of the E2 to M1 and E0 to E2 components of the 2 +(793 keV) 2 + transition in 184W were obtained from γγ, and gamma-conversion electron angular correlation measurements. The γγ measurements used a Ge(Li) detector in some cases; the eγ correlations were performed using a magnetic lens spectrometer. The results obtained are δ(E2:M1) = + 18.7 +4.6 −3.1 + 0.38 ≧ q( E0: E2) ≧ − 0.28 for + 53 ≧ λ ≧ − 113 . Agreement with Kumar's theoretical values for δ and q is contradictory: the former favours a 2″ assignment, the latter a 2prime; assignment to the 904 keV level.

Properties of low-lying 53Mn levels from the 52Cr(p, γ) 53Mn reaction; decay of the [formula omitted] analogue state

The 52Cr(p, γ) 53Mn reaction has been used to obtain excitation energies, γ-ray branching ratios, amplitude mixing ratios, spins, parities and mean lives of 53Mn levels up to 3.5 MeV. The E p = 1006 keV resonance is probably the analogue of the E x = 0.56 MeV, J π = 1 2 − level in 53Cr. Its strength, spin and γ-ray branching have been determined.

Etude des niveaux de 57Co jusqu'à 1.90 MeV

The 57Co levels are excited through the reaction 54Fe(α, p) 57Co at 10.23 MeV and 10.30 MeV incident energies. The coincidence gamma-ray spectra are observed with a Ge(Li) detector and the angular correlations (αp, γ) are measured in the Litherland-Ferguson geometry for the 1.22, 1.68 and 1.75 MeV levels. The following results are obtained: 1.22 MeV level J π = 9 2 −, 1.68 MeV level J π = 11 2 −( 9 2 −) . The corresponding E2/M1 amplitude mixing ratio for the transition 1.22 MeV → 0 is −0.22, and for the transition 1.68 MeV → 1.22 MeV it is 0.00 (0.9). A transition 1.90 MeV → 1.22 MeV is obtained in addition to the transition 1.90 MeV → 0. It is concluded that the levels at 1.75 MeV and 1.90 MeV are doublets.

The reaction 26Mg(p,γ) 27Al (II). Spins of 27Al levels

Measurements of double and triple angular correlations and gamma-ray polarizations at twenty resonances in the reaction 26Mg(p, γ) 27Al, lead to the unambiguous spin and parity assignments Jπ = 7 2 +, 5 2 +, 3 2 +, 9 2 + and 5 2 to the bound states of 27Al at 2.21, 2.73, 2.98, 3.00 and 4.81 MeV, respectively. The 6.48 MeV level has J = 7 2 ( 5 2 ) . The quadrupole/dipole amplitude mixing ratios of the gamma rays de-exciting these levels are given. The spins of 15 resonance levels and the mixing ratios of the main branches in the resonance decay also follow from this experiment. The combined evidence of the decay of the resonance levels and bound states leads to suggested spin values J = ( 1 2 , 3 2 ), 3 2 , ( 1 2 , 3 2 ), 5 2 , 5 2 , ( 3 2 , 5 2 , ( 3 2 , 5 2 ), 3 2 , 3 2 , 3 2 and 3 2 for 27 Al ∗ = 3.68, 3.96, 4.05, 4.41 , 5.25, 6.11, 6.16, 6.61, 6.65 and 6.78 MeV, respectively.

The low-lying levels of Al 27: (II). The 3 MeV doublet levels

The decay of the 2.976 and 3.000 MeV levels in Al 27 has been observed. The only significant branching, apart from ground state transitions, is the (20±10)% cascade 3.000→2.212→0. The E2/M1 amplitude mixing ratio of the 3.000 → 2.212 transitions is −0.03±0.03. The presently known properties of the Al 27 levels are discussed in terms of the two extreme coupled collective models.

THE SPIN OF THE 3.70-MEV LEVEL IN Al25

The 3.70-Mev level in Al25 has been studied by means of the reaction Mg24(p, γ)Al25 at the 1.49-Mev resonance. Direct angular distribution measurements of the de-excitation gamma radiation support the spin assignment of 7/2− for this level. An E2/M1 amplitude mixing ratio of −0.55 ± 0.2 is found for the 1.79-Mev de-excitation radiation from the fourth excited state to the ground state of Al25. The ratio of the reduced transition probability of the E2 radiation from the 1.79-Mev level to the first excited state is shown to be ~30 times that to the ground state. This result provides further confirmation of rotational band structure in Al25 since the collective model predicts such an enhancement of E2 transitions between rotational bands whereas cross-band transitions are not expected to be enhanced.

Identification of a spin 5 state in Cr 52

The state at 3.614-MeV in Cr 52 was found to have a spin of 5 by low temperature nuclear orientation techniques. It is thus reasonable to identify this state with the spin 5 seniority-four state predicted by Edmonds and Flowers for an ( f 7 2 ) 4 configuration. The angular distribution parameters for the 1.246-MeV γ-ray, connecting this state with the 4+ state at 2.369-MeV, require that the amplitude mixing ratio δ( E2 M1 ) be negative. It is probable that this transition is 3–23% quadrupole.

AN ILLUSTRATION OF A TYPE OF TRIPLE CORRELATION MEASUREMENT WHICH CAN BE EASILY INTERPRETED

The Mg26(He4, nγ)Si29 reaction has been used to illustrate the simplifications introduced in the interpretation of triple angular correlations by choosing a target and bombarding particles of zero spin and by observing the emitted particles, in this case neutrons, in a counter fixed at 0° to the beam. The angular correlations of the gamma rays with respect to the incident beam then depend only upon the properties of the final states in the residual nucleus. The angular correlation of the electric quadrupole 2.03-Mev gamma ray is predicted uniquely by theory and this prediction has been verified experimentally. The angular correlations of the 1.28-Mev and 2.43-Mev gamma rays have yielded for the E2/M1 amplitude mixing ratios +0.25 ± 0.05 or −3.4 ± 0.5 and −0.26 ± 0.08 or −1.10 ± 0.16 respectively. In addition, the experiment provides an illustration of the value of the recently discovered technique of neutron – gamma-ray discrimination in an organic scintillator.

Nuclear polarization of Co 55

The angular distribution and linear polarization of the gamma rays emitted from 18-h Co 55, polarized at low temperatures in cerium-magnesium nitrate crystals, have been measured. The amplitude mixing ratios δ(E2/M1) of mixed multipole gamma transitions in Fees have been determined. With a spin of 7 2 for Co 55, we find a spin sequence of 7 2 → 5 2 → 3 2 in the main decay in Fe66, and for the 0.93S MeV gamma ray a δ of + 0.36±0.11. A possible spin sequence 5 2 → 7 2 → 3 2 in Fe 55 has been eliminated by our linear polarization measurements. The ratio of the nuclear g-values of Co 58 and Co 55 has been found from a simultaneous measurement of the angular distribution of the gamma rays from the two isotopes grown into the same crystals. The magnetic moment of Co65 is 6.3±0.4 n.m., if the 1.03 MeV beta branch is predominantly a G.T. transition, or 4.6±0.4 n.m., if a pure Fermi transition.

Nuclear Orientation ofMn56

The angular distribution and circular polarization of the gamma rays emitted from 2.6-hr ${\mathrm{Mn}}^{56}$, polarized at low temperatures in cerium magnesium nitrate, have been measured. Comparing the angular distribution results with angular correlation data it is possible to establish the spins of the 2.65- and 2.98-Mev excited states of ${\mathrm{Fe}}^{56}$ as 2 uniquely. The amplitude mixing ratios $\ensuremath{\delta}(\frac{E2}{M1})$ for the 1.81- and 2.13-Mev $\ensuremath{\gamma}$-rays are shown to be +0.11\ifmmode\pm\else\textpm\fi{}0.06 and -0.27\ifmmode\pm\else\textpm\fi{}0.03, respectively. Gamma anisotropies from aligned ${\mathrm{Mn}}^{56}$ in the same cooling salt have been studied; the results are compared with other Mn alignment experiments. From a simultaneous measurement of the angular distribution of the $\ensuremath{\gamma}$-rays from polarized ${\mathrm{Mn}}^{52}$ and ${\mathrm{Mn}}^{56}$, the ratio of the nuclear $g$-values $(\frac{{g}_{52}}{{g}_{56}})=0.47\ifmmode\pm\else\textpm\fi{}0.05$ has been determined, giving ${\ensuremath{\mu}}_{56}=3.35\ifmmode\pm\else\textpm\fi{}0.35$ nm. The results of the circular polarization experiment determine ${\ensuremath{\mu}}_{56}$ to be positive.