Angular Correlation Of Γ-rays Research Articles

Recent developments in the modeling of (n,γ) reactions with FIFRELIN

Nowadays, the accuracy of experimental results relies more and more on detailed simulations. In the STEREO experiment, the interaction of neutrinos in the liquid scintillator is signed by a n-capture on a Gd atom. The FIFRELIN predictions of the Gd γ-cascades were shown to significantly improve the Data/MC agreement. In the CRAB method, lately proposed to calibrate cryogenic particle detectors at low energy (100 eV), the FIFRELIN cascades of the W and Ge isotopes played a central role in the feasibility study of the method. The FIFRELIN code employs a Monte Carlo Hauser-Feshbach framework based on Bečvár’s algorithm. A sample of nuclear level schemes is generated for a specific isotope of interest, taking into account the uncertainties from nuclear structure. In this work, new improvements on the FIRELIN de-excitation process are reported. Angular correlations of γ-rays in the de-excitation process have been implemented in order to provide a more accurate description of the γ-ray cascades. The anisotropy of the γ-rays with respect to the axis of a previously emitted γ-ray is modeled using the angular correlation formalism, which requires input of the spins and multipolarities of the states involved in the FIFRELIN cascade. Furthermore, the simulation of primary γ-rays emitted from (n,γ) reactions has been updated using the EGAF database.

Spectroscopy of fission fragments using prompt-delayed coincidence technique

The time-stamp structure of the digital data acquisition system of the Indian National Gamma Array (INGA) has been utilized to carry out prompt-delayed coincidence technique for the spectroscopic study of fission fragments. This technique was found to be useful to determine the states above the long-lived isomer (with half-life up to ∼5 μs), present in the fission fragments. The angular correlation of γ-rays, emitted by the fission fragments, has also been used in the present INGA geometry to determine the spins of the de-exciting states.

MULTI-QUASIPARTICLE ISOMERS INVOLVING PROTON-PARTICLE AND NEUTRON-HOLE CONFIGURATIONS IN 131I AND 133I

The nuclei 131 I and 133 I have been populated in multi-nucleon transfer reactions between 136 Xe ions and various targets, and their structure investigated by time-correlated γ-ray coincidence spectroscopy and the measurement of γ-ray angular correlations. A 19/2- isomer at 1918 keV, with a half-life of 24(1) µs, has been identified in 131 I , as well as nanosecond isomers with Jπ = 23/2+ in both isotopes. A T1/2 = 25(3) ns isomer at 4308 keV in 131 I is suggested to have Jπ = (31/2-, 33/2-) and is primarily attributed to the coupling of an odd proton in the d5/2 or g7/2 orbit with the [Formula: see text] configuration in 130 Te , responsible for the 15- isomer in that nucleus. The observed level properties are compared with predictions of a shell-model calculation.

γ-ray angular distributions and correlations after projectile-fragmentation reactions

The formulation required to interpret angular distribution and angular correlation measurements following projectile fragmentation reactions is outlined. Some concepts required to understand the observed fragment spin alignments and polarizations are discussed. Applications to in-beam spectroscopy using fragmentation reactions are considered, particularly in relation to γ-ray multipolarity measurements and spin assignments.

Monte Carlo Simulations of PAC-Spectra as a General Approach to Dynamic Interactions

Time Dependent Perturbed Angular Correlations of γ-rays (PAC) can be used to study hyperfine interactions of a dynamic nature. However, the exact effect of the dynamic interaction on the PAC-spectrum is sometimes difficult to derive analytically. A new approach based on Monte Carlo simulations is therefore suggested, here implemented as a Fortran 90 program for simulating PAC spectra of dynamic electric field gradients of any origin. The program is designed for the most common experimental condition where the intermediate level has spin 5/2, but the approach can equally well be used for other spin states. Codes for 4 different situations have been developed: (1) Rotational diffusion by jumps; used as a test case. (2) Jumps between two states with different electric field gradients, different lifetimes and different orientations of the electric field gradient principal axes. (3) Relaxation of one state to another. (4) Molecules adhering to a surface with random rotational jumps around the axis perpendicular to the surface. To illustrate how this approach can be used to improve data-interpretation, previously published data on 111mCd-plastocyanin and 111Ag-plastocyanin are re-considered. The strength of this novel approach is its simplicity and generality so that other dynamic processes can easily be included by only adding new program units describing the random process behind the dynamics. The program is hereby made publicly available.

Pre-equilibrium dipole excitation and γ-ray fragment angular correlation in the 32S +74Ge reaction

We report on the results obtained from the study of the 32S +74Ge deep inelastic reaction at incident energy E= 320 MeV. High-energy γ-rays were detected in an array of 6 seven-pack BaF2 clusters. Coincidence with complex fragments detected in 12 three-stage telescopes ensured the selection of peripheral reaction events. In order to investigate the pre-equilibrium dipole strength excitation two independent analyses were performed. In the first analysis the energy spectra of the γ-rays were evaluated in the statistical model framework while in the second one the γ-ray fragment angular correlation with respect to the nuclear spin vector of the composite system was studied. Both methods indicate the excitation of dipole strength in the highly deformed dinucleus and provide dipole resonance parameter sets that are in good agreement with each other.

Indium solubility in iron studied with perturbed angular correlations

Segregation of In in Fe-based alloys containing 0.11–2.12 at.% In has been studied by measuring the perturbed angular correlations of γ-rays emitted in the nuclear decay of 111In. The probe atoms were introduced into the alloys by either adding the carrier-free 111In during melting or via ion implantation. Ageing of the samples at elevated temperatures followed by a slow cooling to room temperature allowed us to determine the upper limit of the solubility at room temperature, S(300 K)≤ 30 at. ppm. This value is far below the one reported in the published phase diagram. Quenching of the samples in water from 973–1373 K resulted in the determination of the indium solubility in iron at these elevated temperatures.

Nuclear Quadrupole Interactions Studied by Time Differential Perturbed Angular Correlations of γ-Rays

Abstract This paper gives an elementary introduction to time differential perturbed angular correlation of γ-rays emitted from excited nuclei with particular reference to nuclear quadrupole interactions. We start with a comparison to other techniques such as nuclear quadrupole resonance and the Mössbauer effect, quote all necessary formulae, describe a typical spectrometer, list suitable isotopes, and finally give some examples for modern applications.

Level Structure of177Lu Studied through the Beta Decay of177Yb

The level scheme of 177 Lu following the β-decay of 177 Yb ( T 1/2 =1.9 h) has been constructed from results of γ singles and γ-γ coincidence measurements. Angular correlations of γ-rays were measured with a 4-Ge detector system. Mixing ratios (E2/M1) of seven γ-rays were obtained. The spins and parities of the 1049.4, 1150.0 and 1241.7 keV levels have been assigned to be 9/2 - , 7/2 + and 7/2 + , respectively. These assignments for the 1049.4 and 1241.7 keV levels are consistent with the interpretation that these levels are members of three-quasiparticle multiplets. Energy splittings of three-quasiparticle states were calculated. The calculated 1160 keV 7/2 + level may correspond to the observed 1150.0 keV 7/2 + level. A calculation with a rotation-vibration coupling model was performed. The K -2 γ-vibrational state of the 7/2 + [404] state and the K ±2 γ-vibrational states of the 9/2 - [514] state are expected to exist near 1300 keV.

PAC study of intrinsic defects in germanium: Dependence on doping and defect production

Perturbed angular correlation of γ-rays has been used to study intrinsic defects in Ge. The neutrino-recoil technique in combination with electron-irradiation experiments in highly p-doped Ge shows a defect in close vicinity to the probe atom111In. This defect can definitely be identified as an intrinsic one, very likely a vacancy. Comparing this result to those of electron-irradiation experiments in n- and lower p-doped samples where another defect signal appears, we suggest that due to the different position of the Fermi level another charge state of the probe atom-vacancy complex has also been detected.

Stochastic perturbation of the gamma -ray angular correlation in the case of a quadrupole interaction.

Stochastic perturbation of the gamma -ray angular correlation in the case of a quadrupole interaction.

Collective excitations in 106Cd

High spin states in 106Cd were populated by the reactions 94Zr( 17O, 5n) and 76Ge( 34S, 4n) at 80 MeV and at 148 MeV, respectively. The γ-decay was studied by γ-spectroscopic methods using the Nordball multi-detector array. Protons and α-particles were detected in particle detector system, thus selecting the neutron channel. The experiment included γ-ray yields, γγ-coincidences and γ-ray angular correlation measurements. Collective bands extending up to spin 26 ++, 20 − and 21 −, have been observed in 106Cd. A new lifetime of 11 +6 -3, ns for the 16 + state at 7118.7 keV has been found. Both total Routhian surfaces and spin diabatic surfaces have been calculated and used for assigning quasiparticle configurations to the bands. The (+, 0) band is assigned as a v h 2 11 2 configuration below I = 16 + and at higher spins suggested to be built on a πg 2 9 2 v h 2 11 2 configuration. The large hindrance observed for the decay from the 16 + state supports the latter assignment. With the alignment of the v h 2 11 2 pair the deformation is predicted to change from ( ϵ 2 γ) = (0.13,-2°) to (0.17,4°). The configuration of the negative parity bands is assigned as either a v h 1 11 2 d 1 5 2 or a v h 1 11 2 ( g 7 2 ⊗d 5 2 ) 1 , with ( ϵ 2, γ) = (0.14,9°).

Shapes, electromagnetic properties and enhanced E1 strength in 169Lu

Rotational bands in 169Lu previously observed via (p, 3n) and (α, 4n) reactions were extended by 8–14 units of angular momentum using the 154Sm( 19F, 4n) reaction and the Nordball detector array. By analysis of γγ coincidence relations and γ-ray angular correlations we have established the [541] 1 2 − , α = + 1 2 band to 57 2 h ̵ , the [514] 9 2 − bands to 47 2 > the [404] 7 2 + bands to 53 2 h ̵ and the [411] 1 2 [su+ , α = − 1 2 to 47 2 ( 55 2 ) h ̵ . The bands belonging to the [411] 1 2 + and [402] 5 2 + configurations with α = + 1 2 appear to be rather mixed in the low spin region. One of these bands is established to 45 2 ( 49 2 ) units of spin. The transitions interconnecting the signature partners, in the bands based on the [514] 9 2 − and [404] 7 2 + Nilsson orbitais, as well as in and between the strongly mixed [411] 1 2 + and [402] 5 2 + bands are compared to particle-rotor model calculations. By DSAM analysis, lifetimes and thereby transition quadrupole moments for the band built on the configuration h 9 2 [541] 1 2 − , α = + 1 2 could be extracted. The abnormal alignment pattern at the ν i 13 2 crossing for the h 9 2 [541] 1 2 − ban analysed in terms of a difference in both deformation and neutron pairing compared to the other less polarizing configurations. The influence of octupole modes on the strength of observed [411] 1 2 +⇒[541] 1 2 − E1 transitions as well as on observed spin-flip, [514] 9 2 −⇒[404] 7 2 + , E1 transitions is investigated theoretically and compared to the experimental data.

A “superdeformed” band in 103Pd

A superdeformed (SD) band in 103Pd was studied using the reaction 76Ge(34S,α3n) at 148 MeV. Yields of γ-rays, γ-γ coincidences and γ-ray angular correlation measurements were obtained with the NordBall multi-detector system. The SD band is compared with similar bands in 104,105Pd. Calculations of spin diabatic surfaces have been performed and are used for assigning deformation parameters and quasiparticle configurations to the bands. Additional occupation of intruder orbitals from π or ν h112 and the νi132 [660]12, in combination with band terminations of the normal deformed bands may explain the existence of the SD band in 103Pd.

Hyperfine interaction of 111Cd impurities in Mn 2O 3, Mn 3O 4 and β-Fe 2O 3

The perturbed γ-ray angular correlation (PAC) technique with implanted radioactive 111In tracers has been used to measure the electric field gradients (efg) of 111Cd impurities on various substitutional sites in Mn 2O 3, Mn 3O 4 and β-Fe 2O 3. The oxides Mn 2O 3 and β-Fe 2O 3 have identical lattice structures and in both cases we find two efgs which can be attributed to the substitutional sites with 8 b and 24 d point symmetry. In the spinel oxide Mn 3O 4 two sites are identified, one having a highly asymmetric efg (η = 0.89) and the other one an approximately symmetric efg (η = 0.13). A simple model is used to discuss the influence of covalent bonding on the field gradients in these oxides.

Rotational bands in 107Cd

High-spin states in 107Cd were populated by the reaction 94Zr( 17O, 4n) at 80 MeV and their decay was studied by γ-spectroscopic methods using the NORDBALL multi-detector array. The experiment included γ-ray yields, γ-coincidences and γ-ray angular correlation measurements. Rotational bands were observed up to spin 39 2 and ( 51 2 + ) in the negative- and positive-parity bands, respectively. Calculations of total routhian surfaces and quasi-particle routhians have been performed and are used for assigning quasiparticle configurations to the bands. In the g 7 2 neutron band, a h 11 2 neutron alignment is observed. A large signature spliting is expected in the ν g 7 2 band before the band crossing. For the band built on a single ν h 11 2 quasiparticle, an alignment of either g 7 2 or h 11 2 neutrons is proposed. Shape change effects are discussed.

PAC studies of ion beam induced mixing and phase formation in NiAl multilayers

Abstract The perturbed γ-ray angular correlation (PAC) technique with radioactive tracers is a novel method of investigating early stages of ion beam induced phase transformations, visible as changes in the hyperfine interaction parameters of the probe nuclei. In this study NiAl multilayers of different composition ratios doped with implanted 111 In ions were irradiated with 900 keV Xe 2+ ions and analysed by means of PAC. Room temperature bombardment of samples with the ratio 1:3 or 3:1 produced amorphous or highly disordered phases, while the 3:2 phase was observed to become partly amorphous. Amorphisation was also found for LN irradiation of NiAl in the ratio 1:1, contrary to the formation of the crystalline NiAl phase at RT. These results are discussed in the light of the NiAl bilayer mixing rates and current ion mixing models.

Gamma-ray spectroscopy of 126Ba

States of 126Ba up to spin 36 + were populated in the reaction 96Zr( 34S, 4n) 126Ba at 155 MeV and up to spin 20 + in the reaction 116Sn( 13C, 3n) 126Ba at 56 MeV. Gamma-ray spectroscopy was performed with the 8π spectrometer, an instrument comprising 20 Campton-suppressed HPGe detectors and 71 BGO ball elements. A level scheme organized into fifteen rotational bands is proposed on the basis on the γγ-coincidence and γ-ray angular correlation data. The competing π h 11 2 and v h 11 2 band crossings are investigated and interpreted in terms of cranked shell model and total routhian surface calculations. Amongst the topics discussed are (i) a comparison of DCO and spin orientation techniques for determining spins and multipolarities. (ii) the addivity property of quasiparticle energies or routhians, and (iii) analysis of B(M1)/ B(E2, ratios between signature partner bands. The possibility of couplings between vibrational and aligned quasiparticle structures is explored.

Gyromagnetic ratios of excited states in 150Sm and 152Sm

The gyromagnetic ratios of the 2 1 +, 4 1 +, 6 1 +, 2 2 +, and 2 3 + states in 150Sm and the 2 1 +, 4 1 +, 6 1 +, 8 1 +, 10 1 +, 2 2 +, and 2 3 + levels in 152Sm have been measured using the transient field perturbed γ-ray angular correlation technique. States of interest were populated by multiple Coulomb excitation using 150- and 220-MeV 58Ni beams. The present results display no significant deviation from constancy of the g-factors of all levels investigated in either isotope separately or of corresponding states in 150,152Sm. These findings are compared with available prior measurements and assessed in terms of applicable theoretical model calculations.

Gamma-ray angular correlation in intermediate energy proton-nucleus scattering

The role of γ-ray angular correlation in intermediate energy proton scattering is examined. By using polarized incident proton, detecting the polarization of the scattered particle, and/or the polarization of the emitted γ-ray, information unavailable otherwise can be obtained including a determination of the (8 J f + 3) pieces of independent parameters in the scattering amplitude from a 0 + target.