Gamma-gamma Directional Correlations Research Articles

Proton-neutron mixed-symmetry 3(+)(ms) state in 94Mo

We identify a Jpi = 3(+)(ms) state in 94Mo. This identification is based on six M1 and E2 strengths and is the first identification of a 3(+)(ms) state from B(M1) and B(E2) values. The transition strengths were determined from the measurement of Doppler shifts, branching ratios, and E2/M1 mixing ratios, obtained from gammagamma directional correlations following the 91Zr(alpha,n) reaction and the beta(+) decay of (94)Tc(m). The interacting boson model agrees with the observations, which prove the 2(+) mixed-symmetry states to be a building block in nuclear structure.

Investigation of the decay of 211Rn to 211At and the three-particle configuration in 211At

The gamma-gamma directional correlations for ten cascades observed in the decay of 211Rn were measured by means of a multi-detector system (seven Ge(Li) detectors). Together with the experimental data on the internal conversion of electrons this allowed a unique and model-independent assignment of the spin values for eight levels in 211At. Multipole mixing ratios for seven gamma transitions were also derived. The properties of 211At were treated in the framework of the multi-particle shell model using finite-range forces. The influence of core collective vibrations on the electromagnetic properties was taken into account by using the effective electromagnetic operators.

Gamma-gamma directional correlations: Simplifications at high spin

We derive simplified expressions, valid at high spin, for the gamma-gamma directional correlation function. With only four directional distribution coefficients to characterize the coincident transitions, close agreement is obtained with the exact result already at spin 20 h ̵ .

Directional distribution of high-energy gamma rays from hot 125, 127Cs and 171Lu compound nuclei

Gamma-gamma directional correlations have been measured following 12C + 113,115In and 159Tb reactions at 100 MeV. Directional distribution coefficients have been determined for the gamma-ray spectrum between 2 and 16 MeV. For energies above 10 MeV the results for both reactions are in disagreement with interpretations in terms of the decay of the giant dipole resonance statistically excited either in a permanently deformed prolate compound nucleus undergoing collective rotation or an oblate nucleus with the angular momentum along the axis of symmetry. For the reaction on Tb indications of a quadrupole component at energies around 10 MeV are presented.

Gamma-gamma directional correlation measurements in144Nd

Gamma-gamma directional correlations have been measured for cascades in 144Nd following thermal-neutron capture by 143Nd. Unique multipole mixing ratios have been assigned to 12 transitions. Coincidence relations established from 18 coincidence gates have enabled an extensive decay scheme to be constructed. The results are compared with the predictions of the interacting boson approximation and some agreement is found. The 2+ assignment to the 1560 keV state is confirmed, which is in conflict with existing averaged resonance capture data.

Gamma-gamma correlation measurements in114Cd

Gamma-gamma directional correlations have been measured for cascades in 114Cd that follow thermal-neutron capture by 113Cd. In total, 14 correlations have been analysed, allowing spins and multipolarities to be assigned. Using the present E2:M1 mixing ratio and previous internal conversion results, it was found that the 805.9 keV 23+-21+ transition has the value X=B(EO; 23+-21+)/B(E2;23+-21+)>or=53, which is one of the largest ever noted, and occurs in a situation in which the radiative component of the transition is predominantly M1. Coincidences from 12 coincidence gates have allowed new data to be added to the existing level scheme.

Level structure and gamma-gamma directional-correlation studies in147Pm

The level structure of147Pm is studied with a high-efficiency sum coincidence spectrometer. The levels at 182, 320 and 725 keV are confirmed and their decay modes are also proposed. The gamma-gamma directional correlations involving the (194–531) and (595–91) keV cascades in147Pm are studied. The spin of the 725 keV level is established to be 5/2+. The mixing ratios for the 194 and 595 keV gamma transitions are estimated to be δ=−3.65±0.84 and 0.27±0.11, respectively. The half-life of the 686 keV level determined by a slope method employing a delayed-coincidence technique isT1/2=(0.22±0.01) ns. The experimentalM1 andE2 transition probabilities of the gamma-rays following the decay of the 686, 531, 410 and 91 keV levels are compared with the single-particle estimates.

Determination of solid angle corrections for precise gamma-gamma directional correlation experiments with Ge-detectors

An experimental method is described to determine angle dependent attenuation factors due to the finite solid angle in gamma-gamma directional correlations with Ge-detectors. The correction factors have been calculated a.o. for the 622-512 keV (0 +−2 +−0 +) cascade in 106Pd. Data from a correlation experiment on this cascade have been fitted to the factors and produced A 2 and A 4 anisotropy coefficients within 1% of the theoretical values. Angle independent correction factors obtained from Monte-Carlo calculations and from a horizontal scan method have been used in a comparison with the mentioned results. This comparison has shown that differences of more than 10% can arise by using these methods. An extended measurement yielded A 2 and A 4 coefficients for the (0 +−2 +−0 +) cascade in 106Pd. The values are: A 2 = 0.356(2) and A 4 = 1.143(3), very close to the theoretical ones.

Gamma-ray multipolarities in 206Pb studied by gamma-gamma directional correlations

Gamma-gamma directional correlations have been measured in the decay of 206Bi. Using a multichannel goniometer with 2 Ge and 6 NaI detectors the directional correlations have been measured for 17 cascades in 206Pb. From the results, electromagnetic multipole mixing ratios are deduced and limits to transition strengths are estimated.

Gamma-gamma directional correlation measurements in162,164Dy following thermal neutron capture

An on-line angular correlation facility to measure directional correlation coefficients of gamma-ray cascades following thermal neutron capture is described. The apparatus has been used to measure gamma-gamma directional correlations in 162,164Dy and multipolarities of sixteen transitions in 162Dy and nine in 164Dy were determined. In addition, new coincidence relationships were found in both isotopes. The transitions between the gamma and ground bands have been considered theoretically using the symmetric rotor model of Bohr and Mottelson, (1975).

Gamma-gamma directional correlations in 90Zr

Directional correlations of γγ cascades in 90Zr have been measured employing a twelve-channel goniometer. The obtained correlation coefficients are: 141.2–1129.1 keV, A 2 = −0.070(12), A 4 = −0.003(10); 1611.8–1129.1 keV, A 2 = −0.088(20), A 4 = 0.013(18); 1716.4–1129.1 keV, A 2 = −0.011(75), A 4 = 0.041(60); 1984.7–1129.1 keV, A 2 = −0.006(54), A 4 = −0.036(50); 827.7–1913.3 keV, A 2 = 0.164(40), A 4 = 0.062(35); 132.7–2186.4 keV, A 2 = 0.187(38), A 4 = −0.063(36); 890.6−2186.4 keV, A 2 = 0.132(51), A 4 = −0.023(48). The spin and parity 7 + is assigned to the 5060.0 keV level. The multipole mixing ratios of the involved γ-ray transitions have been determined. The γ-ray transition probabilities for some transitions are calculated and compared with predictions of the shell model for the 90Zr nucleus.

Gamma-gamma directional correlations and coincidence studies in154Gd

The intensities, placements andE2/M1 mixing ratios of transitions in the decay of154Eu have been carefully studied to provide accurate data for microscopic calculations. Coincidence relationships in the decay of154Eu have been studied extensively with a multiparameterγ-γ coincidence system with two large volume Ge(Li) detectors. Spectra in coincidence with twenty energy gates were analyzed. Twenty-nine new coincidence relationships were established and confirmed most, but not all, of several levels previously assigned by energy fits only. From an analysis of coincidence spectra and singles spectra with a 18% efficiency Ge(Li) detector new information on the gamma-ray intensities were obtained. Precise values of theE2/M1 mixing ratios of transitions from the gamma- and beta-vibrational bands to the g.s. band have been determined fromγ-γ directional correlation measurements with a NaI(Tl)-Ge(Li) detector coincidence system. Mixing ratios were obtained for a number of other transitions including those fromKπ =0− and 2+ bands from direct and skipped cascade correlations.

Spin of the 1248- and 1958-keV levels inTe124determined from gamma-gamma directional and polarization-directional correlations

Directional correlations and polarization-directional correlations have been measured for the 646-603- and 709-646-keV cascades in $^{124}\mathrm{Te}$ populated from the decay of $^{124}\mathrm{Sb}$. Ge(Li) detectors were used in both spectrometers, one of them, a planar Ge(Li) detector as the linear-polarization analyzer for the $\ensuremath{\gamma}$ radiation. Combination of the results of these measurements gives unique spin assignments of ${4}^{+}$ for the 1248- and 1958-keV levels. The determined $\frac{E2}{M1}$ mixing ratios are: $\ensuremath{\delta}(646)=0.00\ifmmode\pm\else\textpm\fi{}0.01$ and $\ensuremath{\delta}(709)={0.02}_{\ensuremath{-}0.07}^{+0.06}$.RADIOACTIVITY $^{124}\mathrm{Sb}$; measured $\ensuremath{\gamma}\ensuremath{\gamma}(\ensuremath{\theta})$ and $\ensuremath{\gamma}\ensuremath{\gamma}(90\ifmmode^\circ\else\textdegree\fi{} \mathrm{LP})$ (linear-polarization correlation), $^{124}\mathrm{Te}$ deduced $I$ $\ensuremath{\delta}(\frac{E2}{M1})$. Ge(Li) detectors.

Spin values of the low lying nuclear levels of201Hg

Gamma-gamma directional correlations have been investigated for the cascades of 135-30 keV and 135-32 keV in201Hg from the decay of201Tl. A combination of NaI (Tl) and Si (Li) detectors was used for the experiments. Spin values ofI=1/2, 3/2 and 1/2 have been assigned to 1.58, 32.19 and 167.49 keV energy levels. In addition, the relative intensities of theγ rays have been measured with a Ge (Li) detector system. The results are 2.2±0.2, 2.2±0.2, 26.5±1.3, 1.6±0.1 and 100 for theγ rays of 30.60, 32.19, 135.34, 165.88 and 167.43 keV energies, respectively.

Gamma-gamma directional correlations in69Ga

Employing a Ge(Li)-NaI(Tl) detector system, gamma-gamma directional correlations for nine cascades in69Ga have been measured. The result of the present measurements combined with other existing data allowed the adoption of a 5/2− spin and parity for the 1106.4 keV level, and a 7/2− for the 1 336.1 and 1487.5 keV levels. A tentative 7/2− spin and parity has been adopted for 1923.1 keV level. Mixing ratios have been determined for six transitions. The data obtained are utilized to extractM1 andE2 reduced transition probabilities. A comparison of the experimental data is made with the predictions of the one particle-core and three particles-core coupling models.

Levels and transitions in126Te

The decay of126Sb to126Te is studied by use of Ge(Li) detectors in singles and coincidence arrangements. The gamma-gamma directional correlations of six cascades are measured. A level scheme is constructed where all transitions observed are located. The characteristics of several of the levels are assigned, on basis of the logft values deduced and the directional correlation results. Mixing ratios are deduced for three transitions. From the comparison of the relative intensities ofE1 andE2 transitions depopulating the same levels, threeE1 transitions are concluded to be strongly retarded.

Kernspektroskopische Untersuchungen zu den Termschemata der Kerne56Fe und56Co

Gamma-gamma directional correlations have been investigated for several cascades in56Fe formed in the decay of56Mn or56Co. A combination of NaI(Tl) and Ge(Li) detectors was used for the experiments. It was established that a level at 3601 keV is populated in the decay of56Co. Spins given in the paranthesis were assigned to levels at the following energies: 2658(2), 2960(2), 3123(4), 3370(2), 3445(3), 3601(2), 3856(3), 4049(3), 4100(4), 4120(3), 4298(4), 4395(3) and 4459 keV (3,4). Multipole mixing ratios were determined forγ transitions of the following energies: 978, 1038, 1175, 1360, 1772, 1811, 1964, 2015, 2035, 2113, 2213, 2523, 2599, 3010, 3202, 3254, 3273, 3451 and 3548 keV. Theγ-rays from the decay of56Co of energies 674.7 and 2657.4 keV have been observed for the first time, and the presence of several other weakγ-rays in the56Fe decay has been confirmed. Nine angular correlations in the decay of56Ni have been investigated. The spin sequence 4, 3, 2, 0, 1 was unambiguously determined for the levels at 0, 158.2, 970.1, 1450.7 and 1720.0 keV. The multipolarity of theγ-rays of energies 158.2, 749.9 and 811.9 keV was determined as almost pure M1. The results are discussed within the framework of recent shell model calculations.

Gamma-gamma directional-correlation studies in143Pr

The gamma-gamma directional correlations on (293-57), (665-57), (881-57), (231-491) and (587-351) keV cascades in143Pr are studied with high-efficiency sum and sum-peak coincidence spectrometers. The correlation coefficients of the cascades are obtained. The spins of the 351, 491, 722 and 938 keV levels in143Pr are conclusively assigned. The mixing ratios for the 231, 587, 665 and 881 keV transitions are determined.

The analysis of gamma-gamma directional correlations in a triple cascade

If a triple cascade exists among the nuclear levels of an isotope, the (1–3) directional correlation coefficients combined with those of the (1–2) and (2–3) cascades offer an effective way for determining mixing ratios or spin sequences. A formula is given to determine the mixing ratios for the intermediate transition directly, regardless of whether or not the other two transitions are mixed. Graphs are introduced for analyzing triple cascades.

Gamma-gamma Directional Correlations in 103Rh

Gamma-gamma directional correlations in 103Rh were measured in the decay of 103Ru. No dependence on the chemical composition of the source was observed. The following directional correlation coefficients were determined: A2(557 - 53) = -0.064 ± 0.003, A2(444 - 53) = -0.035 ± 0.013. The lifetime of the 93 keV state was measured as T½ = 1.06 ± 0.05 ns. By use of this value for the lifetime and the rotation in an external magnetic field of the directional correlation pattern, the gyromagnetic factor of the 93 keV state is obtained as g = 1.07 ± 0.17. The properties of 103Rh were calculated on basis of the unified vibrational model. The adequacy of this model for describing the positive-parity states studied in this work is discussed.