Γγ Coincidence Research Articles

Excited-State Half-Lives in ^{130}Cd and the Isospin Dependence of Effective Charges.

The known I^{π}=8_{1}^{+}, E_{x}=2129-keV isomer in the semimagic nucleus ^{130}Cd_{82} was populated in the projectile fission of a ^{238}U beam at the Radioactive Isotope Beam Factory at RIKEN. The high counting statistics of the accumulated data allowed us to determine the excitation energy, E_{x}=2001.2(7) keV, and half-life, T_{1/2}=57(3) ns, of the I^{π}=6_{1}^{+} state based on γγ coincidence information. Furthermore, the half-life of the 8_{1}^{+} state, T_{1/2}=224(4) ns, was remeasured with high precision. The new experimental information, combined with available data for ^{134}Sn and large-scale shell model calculations, allowed us to extract proton and neutron effective charges for ^{132}Sn, a doubly magic nucleus far-off stability. A comparison to analogous information for ^{100}Sn provides first reliable information regarding the isospin dependence of the isoscalar and isovector effective charges in heavy nuclei.

Three-phonon multiplets in 116Sn

Low-lying states in the even-even 116Sn nucleus have been studied by populating them using the 114Cd(α, 2n)116Sn reaction at the beam energy of 34 MeV. γγ coincidences, directional correlation ratio, and polarization asymmetry measurements were performed using the Indian National Gamma Array (INGA) with a digital data acquisition system. Three-phonon multiplets in the 116Sn nucleus have been investigated. The experimental energy levels are analyzed using theoretical approaches of the interacting boson model (IBM) in the U(5) limit and large-scale shell-model calculations using two different model spaces.

Low-spin states in Ge80 populated in the β decay of the Ga80 3− isomer

The structure of Ge80 has been investigated at the ISOLDE facility at CERN. A previous study reported for the first time a low-lying 02+ intruder state at 639 keV, based on the coincidence with a previously unobserved 1764-keV γ ray, and suggested it as evidence for shape coexistence in Ge80. We used the β decay from the 3− 22.4-keV state in Ga80 to enhance the population of low-spin states in Ge80, including any excited 0+ level, and γγ coincidences to investigate it. We observed a 1764-keV γ ray in coincidence with strong transitions in Ge80, thus not feeding the proposed 639-keV 02+. No connecting transitions from previously known levels to the 639-keV and 2403-keV 23+ states could be established either. Shell-model calculations for Ge isotopes and N=48 isotones were performed. They succeed to explain most of the experimental levels, but fail to reproduce the presence of a 02+ state below ≈1200 keV in Ge80. Our experimental findings and shell-model calculations are difficult to reconcile with a very low-lying 02+ state in Ge80.1 MoreReceived 20 October 2020Revised 23 July 2021Accepted 27 July 2021DOI:https://doi.org/10.1103/PhysRevC.104.024317Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasIsomer decaysNuclear structure & decaysProperties59 ≤ A ≤ 89TechniquesRadiation detectorsRadioactive beamsSpectrometers & spectroscopic techniquesNuclear Physics

Measuring Low Neutron Fluxes at the Modane Underground Laboratory Using Iodine-Containing Scintillators

The first results of neutron-flux measurements at the LSM underground laboratory (Modane, France) using a new sensitive method are presented. Neutrons are detected by counting delayed γγ coincidences in the 127I(n, γ)128I reaction. It is shown that this approach makes it possible to measure thermal-neutron fluxes at a level of 10–6 neutron cm–2 s–1.

Lifetime Measurements and Triple Coexisting Band Structure in ^{43}S.

Lifetime measurements of excited states in the neutron-rich nucleus ^{43}S were performed by applying the recoil-distance method on fast rare-isotope beams in conjunction with the Gamma-Ray Energy Tracking In-beam Nuclear Array. The new data based on γγ coincidences and lifetime measurements resolve a doublet of (3/2^{-}) and (5/2^{-}) states at low excitation energies. Results were compared to the π(sd)-ν(pf) shell model and antisymmetrized molecular dynamics calculations. The consistency with the theoretical calculations identifies a possible appearance of three coexisting bands near the ground state of ^{43}S: the K^{π}=1/2^{-} band built on a prolate-deformed ground state, a band built on an isomer with a 1f_{7/2}^{-1} character, and a suggested excited band built on a newly discovered doublet state. The latter further confirms the collapse of the N=28 shell closure in the neutron-rich region.

New low-spin states of 122Xe observed via high-statistics β-decay of 122Cs

Excited states of 122Xe were studied via the β+/EC decay of 122Cs with the 8π γ-ray spectrometer at the TRIUMF-ISAC facility. Compton-suppressed HPGe detectors were used for measurements of γ-ray intensities, γγ coincidences, and γ-γ angular correlations. Two sets of data were collected to optimize the decays of the ground (21.2 s) and isomeric (3.7 min) states of 122Cs. The data collected have enabled the observation of about 505 new transitions and about 250 new levels, including 51 new low-spin states. Spin assignments have been made for 58 low-spin states based on the deduced β-decay feeding and γ-γ angular correlation analyses.

On neutron activation analysis with γγ coincidence spectrometry.

A new γγ coincidence system has been set up at NIST. It is operated with a digital data finder supported by new software developed at NIST. The system is used to explore possible enhancements in instrumental neutron activation analysis (INAA) and study applicability to neutron capture prompt gamma activation analysis (PGAA). The performance of the system is tested with certified reference materials for efficiency calibration and quantitative performance. Comparisons of INAA results based on conventional gamma-ray spectrometry data with INAA results based on coincidence data obtained from the same samples show improvements in the counting uncertainties and demonstrates the quantitative accuracy of the new system.

Study of vibrational signatures in 102Ru

Abstract A Mo 100 ( α , 2 n ) Ru 102 fusion evaporation experiment, performed at the HORUS cube spectrometer at the Cologne FN-Tandem accelerator, is presented and discussed. Via the analysis of γγ coincidences, it was possible to extend the level scheme with 40 new levels and 81 decays. Several new spins and multipole mixing ratios were determined using the γγ angular correlation technique. In addition, a DSAM analysis was performed and 14 new effective lifetimes were determined in the femtosecond range. Thus, several effective transition strengths were determined. Investigating the phononic structure, candidates for the quadrupole–octupole phonon multiplet 2 1 + ⊗ 3 1 − were found. The data is compared to calculations within the Interacting Boson Model (IBM-1) in the U(5) limit, the O(6) limit as well as a transitional class U(5)–O(6). The low spin level energies show characteristics of multiphonon excitations and point towards 102Ru resembling an anharmonic vibrational nucleus. The B ( E 2 ) transition strengths do not exactly match this picture, and are described in a better way using the U(5)–O(6) calculation.

Observation of new microsecond isomers among fission products from in-flight fission of 345 MeV/nucleon238U

A search for isomeric γ decays among fission fragments from 345 MeV/nucleon 238U has been performed at the RIKEN Nishina Center RI Beam Factory. Fission fragments were selected and identified using the superconducting in-flight separator BigRIPS and were implanted in an aluminum stopper. Delayed γ rays were detected using three clover-type high-purity germanium detectors located at the focal plane within a time window of 20 μs following the implantation. We identified a total of 54 microsecond isomers with half-lives of ∼0.1–10 μs, including the discovery of 18 new isomers in very neutron-rich nuclei: 59Tim, 90Asm, 92Sem, 93Sem, 94Brm, 95Brm, 96Brm, 97Rbm, 108Nbm, 109Mom, 117Rum, 119Rum, 120Rhm, 122Rhm, 121Pdm, 124Pdm, 124Agm, and 126Agm, and obtained a wealth of spectroscopic information such as half-lives, γ-ray energies, γ-ray relative intensities, and γγ coincidences over a wide range of neutron-rich exotic nuclei. Proposed level schemes are presented for 59Tim, 82Gam, 92Brm, 94Brm, 95Brm, 97Rbm, 98Rbm, 108Nbm, 108Zrm, 109Mom, 117Rum, 119Rum, 120Rhm, 122Rhm, 121Pdm, 124Agm, and 125Agm, based on the obtained spectroscopic information and the systematics in neighboring nuclei. The nature of the nuclear isomerism is discussed in relation to the evolution of nuclear structure.13 MoreReceived 10 August 2012DOI:https://doi.org/10.1103/PhysRevC.86.054319©2012 American Physical Society

Nuclear structure of 216 Ra at high spin

High-spin states of 216Ra (\(\emph{Z}=88\), \(\emph{N}=128\)) have been investigated through 209Bi(10B, 3n) reaction at an incident beam energy of 55 MeV and 209Bi(11B, 4n) reaction at incident beam energies ranging from 65 to 78 MeV. Based on γγ coincidence data, the level scheme for 216Ra has been considerably extended up to ~ 33\(\hbar\) spin and 7.2 MeV excitation energy in the present experiment with placement of 28 new γ-transitions over what has been reported earlier. Tentative spin-parity assignments are done for the newly proposed levels on the basis of the DCO ratios corresponding to strong gates. Empirical shell model calculations were carried out to provide an understanding of the underlying nuclear structure.

Improvements in determinations using the Cu-64 annihilation gamma rays

The method of γγ coincidence counting has been applied to the determination of Cu via the 64Cu annihilation gamma rays. Preliminary experiments show that at least an order of magnitude reduction in 24Na interference may be obtained by employing the 511–511 keV coincidence peak rather than the singles 511-keV peak. The effect of the sample matrix on the yield of 24Na pair-production events was investigated by a combination of experimental measurements and Monte Carlo calculations.

Spherical proton-neutron structure of isomeric states inCd128

The γ-ray decay of isomeric states in the even-even nucleus Cd128 has been observed. The nucleus of interest was produced both by the fragmentation of Xe136 and the fission of U238 primary beams. The level scheme was unambiguously constructed based on γγ coincidence relations in conjunction with detailed lifetime analysis employed for the first time on this nucleus. Large-scale shell-model calculations, without consideration of excitations across the N=82 shell closure, were performed and provide a consistent description of the experimental level scheme. The structure of the isomeric states and their decays exhibit coexistence of proton, neutron, and strongly mixed configurations due to πν interaction in overlapping orbitals for both proton and neutron holes.Received 24 September 2008DOI:https://doi.org/10.1103/PhysRevC.79.011301©2009 American Physical Society

Formula omitted] coincidence spectrometer for instrumental neutron-activation analysis

Neutron-activation analysis (NAA) is an important technique for the accurate and precise determination of trace and ultra-trace elemental compositions. The application of γγ coincidence counting to NAA in order to enhance specificity was first explored over 40 years ago but has not evolved into a regularly used technique. A γγ coincidence spectrometer has been constructed at the National Institute of Standards and Technology, using two HPGe γ-ray detectors and an all-digital data-acquisition system, for the purpose of exploring coincidence NAA and its value in characterizing reference materials. This paper describes the initial evaluation of the quantitative precision of coincidence counting versus singles spectrometry, based upon a sample of neutron-irradiated bovine liver material.

High spin states of 141Pm

The high spin states in the N=80 odd- A 141Pm nucleus have been investigated by in-beam γ-spectroscopic techniques following the reaction 133Cs( 12C, 4n) 141Pm at E=65 MeV using a modest γ detector array, consisting of seven Compton-suppressed high purity germanium detectors and a multiplicity ball of 14 bismuth germanate elements. Thirty new γ rays have been assigned to 141Pm on the basis of γ-ray singles and γγ-coincidence data. The level scheme of 141Pm has been extended upto an excitation energy of 5.2 MeV and spin 35 2 ℏ and 16 new levels have been proposed. Spin-parity assignments for most of the newly proposed levels have been made on the basis of the deduced directional correlation orientation ratios for strong transitions. The meanlives of a few excited states have been determined from the pulsed beam- γγ coincidence data using the generalised centroid-shift method. The level structure is discussed in the light of known systematics of neighbouring N=80 isotonic nuclei.

Search for particle–hole excitations across the N=28 shell gap in 45,46Ar nuclei

The structure of the N≃28 45,46 18Ar 27,28 nuclei has been investigated through in-beam γ-ray spectroscopy using the fragmentation reaction of a 60 A MeV 48Ca beam on a thin Be target. γ-ray energies, intensities, γγ coincidences and γ-ray angular anisotropies have been measured. The level scheme of 45Ar is proposed for the first time, while that of 46Ar has been extended to states above the previously known 2 + first excited state. An isomeric state at 537 keV of 0.34 +0.32 −0.15 ns lifetime has been found in 45Ar from the line-shape analysis of the γ ray connecting the first excited state to the ground state. The experimental results are interpreted using shell-model calculations.

Excited levels in 149Pm from the decay of 149Nd

The level structure of 149Pm has been investigated by studying the gamma rays emitted following the β − decay of 149Nd (T 1/2=1.7 h). The singles and the γγ coincidence spectra were taken using HPGe detectors with high energy resolution. The energy and relative intensities of 198 gamma rays have been determined, 45 for the first time and several multiplets were resolved using bidimensional data analysis. A decay scheme with 51 levels has been proposed. This includes 6 new levels, at 1407, 1368, 1364, 1329, 1293 and 1181 keV. The present results permitted assignments of spin and parity for a number of these levels.

Decay properties of low-lying collective states in 132Ba

The decay properties of low-lying collective states in 132Ba were studied by means of γ spectroscopy following the β-decay of the 2 − ground state ( T 1/2=4.8 h) and a 6 − isomer ( T 1/2=24.3 min) of 132La. The lanthanum nuclei were produced at the Cologne fn tandem accelerator using the reaction 122Sn( 14N, 4n) 132La. The γγ coincidences and singles spectra were measured with the osiris-cube spectrometer. Beside ground and quasi-gamma band many other low-lying states were observed. The γγ angular correlations were analyzed to assign spins to the excited states, and to determine the multipolarities of the depopulating the γ transitions. We also confirmed the expected dominant E2 character of transitions in the quasi-gamma band and from the quasi-gamma to the ground band but with a certain deviation: the decay 6 + 2→6 + 1 shows an unexpected large M1 fraction. Also the decays of the third, fourth and fifth 2 + states are dominated by M1 radiation. A level at 1660 keV could be identified as the 0 + 3 state in 132Ba. The experimental data are compared with calculations using the proton–neutron interacting boson model (IBM-2). Good agreement is reached in the vicinity of the O(6) limit.

Energy levels in [formula omitted] from the decay of [formula omitted

The γ-ray spectrum of 139La following the β− decay of 139Ba has been studied using both singles and γγ coincidence spectroscopy techniques. The energies and intensities of 30 γ-transitions have been determined, which include three new transitions placed in the level scheme. Two new levels at 1524.6 and 1900.3keV excitation energies are proposed and a number of γ-transitions have been confirmed. On the basis of these results a precise decay scheme is proposed.

102Ag: In-beam gamma-ray spectroscopy

Gamma-rays associated with the decay of states in the 102Ag nucleus have been identified, sixty-four of them for the first time following the reaction 50Cr(56Fe, 3pn)102Ag at a mean energy of 195 MeV. Identification was made using an array of nine escape-suppressed Ge detectors coupled to the Daresbury Recoil Separator. Excited states in 102Ag were identified using recoil-gamma and γγ coincidences. From the intensity balance and the coincidence data, a new set of levels was identified which may be interpreted as reminiscent of “three-quasiparticle” bands in neighboring odd-mass nuclei and similar to a four-quasi-particle band observed in 106Ag.

Depopulation of the Jπ = 9- isomer in 180Ta to the Jπ = 1+ ground state by Coulomb excitation

In-beam Coulomb excitation of the exotic odd-odd nucleus 180Ta has been studied by using a 136Xe beam and a setup consisting of five EUROBALL CLUSTER detectors and the Darmstadt-Heidelberg Crystal Ball array. Spectroscopic information on the extremely rare 180Ta is obtained from the comparison between an enriched (3.6±0.3% 180Ta) and a natural tantalum target. Possible evidence for a depopulation from the long-lived high-spin Jπ = 9- isomer to the short-lived Jπ = 1+ ground state is searched for by different methods. The decay of low-K bandheads, which are nanosecond isomers, towards the ground-state band can be demonstrated in delayed spectroscopy. A γγ coincidence analysis provides indications of K = 5 in-band transitions. Finally, when the Crystal Ball is used as an energy and γ multiplicity filter, signals of decay into the K = 0 band are observed.