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Jones, M. D.

Publications and source records attributed to Jones, M. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Investigation of the \(\gamma \)-ray Properties of the \(2^+\) States in \(^{14}\)C

The properties of the 2$^+_1$ and 2$^+_2$ excited states in 14 C were studied in an experiment conducted at Argonne National Laboratory. A 9 Be( 6 Li,pγ) fusion-evaporation reaction and the GRETINA-ORRUBA setup were employed to populate states of 14 C and detect γ-particle coincidence events. Finally, the precise determination of the 2$^+_1$ level energy, complemented by the estimation of the γ-ray branch of the 2$^+_2$ near-threshold state, will serve as a benchmark to test the Shell Model Embedded in the Continuum calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Core of 25 F studied by the 25 F(–p) proton-removal reaction

The 9 Be( 25 F(5/2 + ), 24 O)X proton-removal reaction was studied at the NSCL using the S800 spectrometer. The experimental spectroscopic factor for the ground-state to ground-state transition indicates a substantial depletion of the proton d 5/2 strength compared to shell-model expectations, similar to the findings of an inverse-kinematics (p,2p) measurement performed at RIBF. The 25 F to 24 O ground-states overlap is considerably less than anticipated if the core nucleons behaved as rigid, doubly-magic 24 O within 25 F. We interpret the new results within the framework of the Particle-Vibration Coupling (PVC) model, of a d 5/2 proton coupled to a quadrupole phonon of an effective core. This approach provides a good description of the experimental data, requiring an effective 24 O* core with a phonon energy of ℏω 2 = 3.2 MeV and a B(E2) ≈ 2.7 W.u. – softer and more collective than a bare 24 O. Here, both the Nilsson deformed mean field and the PVC models appear to capture the properties of the effective core of 25 F, suggesting that the additional proton polarizes 24 O in such a way that it becomes either slightly deformed or a quadrupole vibrator.

20 ≤ A ≤ 38↗
DOE OSTI2022

Model-independent determination of the dipole response of 66 Zn using quasimonoenergetic and linearly polarized photon beams

Background: Photon strength functions are an important ingredient in calculations relevant for the nucleosynthesis of heavy elements. The relation to the photoabsorption cross section allows to experimentally constrain photon strength functions by investigating the photoresponse of atomic nuclei. Purpose: Here, we determine the photoresponse of 66 Zn in the energy region of 5.6 MeV to 9.9 MeV and analyze the contribution of the 'elastic' decay channel back to the ground state. In addition, for the elastic channel electric and magnetic dipole transitions were separated. Methods: Nuclear resonance fluorescence experiments were performed using a linearly polarized quasi-monoenergetic photon beam at the High Intensity γ-ray Source. Photon beam energies from 5.6 to 9.9 MeV with an energy spread of about 3% were selected in steps of 200–300 keV. Two high purity germanium detectors were used for the subsequent γ-ray spectroscopy. Results: Full photoabsorption cross sections are extracted from the data making use of the monoenergetic character of the photon beam. For the ground-state decay channel, the average contribution of electric and magnetic dipole strengths is disentangled. The average branching ratio back to the ground state is determined as well. Conclusions: The new results indicate lower cross sections when compared to the values extracted from a former experiment using bremsstrahlung on 66 Zn. In the latter, the average branching ratio to the ground state is estimated from statistical-model calculations in order to analyze the data. Corresponding estimates from statistical-model calculations underestimate this branching ratio compared to the values extracted from the present analysis, which would partly explain the high cross sections determined from the bremsstrahlung data.

59 ≤ A ≤ 89↗
DOE OSTI2022

Mirror nucleon removal reactions in p-shell nuclei

Nucleon removal reactions have been shown to be an effective tool for studying the single particle structure of nuclei. This work continues efforts to experimentally probe and benchmark the reaction and structure models used to calculate the removal reaction cross sections when using microscopic nuclear structure inputs. Here, three different single nucleon removal reactions were performed, from p -shell nuclei with masses A = 7, 9, and 10. The residual nuclei from the reactions were detected in coincidence with γ rays to determine partial cross sections to individual final states. The eikonal direct-reaction model is combined with overlap functions and residual nucleus densities from microscopic, variational Monte Carlo calculations to provide consistent nuclear structure input to the partial cross section calculations. Comparisons of measured and calculated cross sections, including for mirror reactions, are presented. The analysis of the partial cross sections leading to the ground states shows a similar behavior to the one observed from analyses of inclusive cross sections using shell model nuclear structure input: the theoretical description of the removal process is in better agreement with the data when removing weakly bound nucleons, than when removing well-bound ones. The two mirror reaction pairs presented here show consistent results between the respective members of the pairs. The results obtained for the population of the excited states, however, show a systematically different trend that appears connected to the structure part of the calculation. Additional cases are needed to better understand the respective roles of structure and dynamical effects in the deviations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Search for the 1/2 + intruder state in 35 P

The excitation energy of deformed intruder states (specifically the 2p2h bandhead) as a function of proton number Z along N = 20 is of interest both in terms of better understanding the evolution of nuclear structure between spherical Ca 40 and the Island of Inversion nuclei, and for benchmarking theoretical descriptions in this region. At the center of the N = 20 Island of Inversion, the n p n h (where n = 2 , 4 , 6 ) neutron excitations across a diminished N = 20 gap result in deformed and collective ground states, as observed in Mg 32 . In heavier isotones, n p n h excitations do not dominate in the ground states but are present in the relatively low-lying level schemes. With the aim of identifying the expected 2 p 2 h x s 1 / 2 + state in P 35 , the only N = 20 isotone for which the neutron 2p2h excitation bandhead has not yet been identified, the S 36 ( d , He 3 ) P 35 reaction has been revisited in inverse kinematics with the HELical Orbit Spectrometer (HELIOS) at the Argonne Tandem Linac Accelerator System (ATLAS). While a candidate state has not been located, an upper limit for the transfer reaction cross section to populate such a configuration within a 2.5 to 3.6 MeV energy range provides a stringent constraint on the wave function compositions in both S 36 and P 35 .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Quadrupole and octupole collectivity in 143 Ba

The neutron-rich barium nuclei have been the subject of intense interest due to the enhanced octupole correlations they are predicted to exhibit. The observation of enhanced octupole collectivity in 144,146 Ba as measured in sub-barrier Coulomb excitation, consistent with static octupole deformation, has further heightened this interest. In the present work, these studies are extended to the neighboring odd-mass 143 Ba to investigate the interplay between single-particle and collective octupole degrees of freedom. A new measurement of the first 9/2 – -state lifetime is also presented. Reflection-Asymmetric Triaxial Particle Rotor Model calculations indicate that the negative-parity bands in 143 Ba can be understood as a decoupled structure of νh 9/2 parentage, while the positiveparity bands are built on a decoupled octupole phonon. Here, no evidence for E3 excitation is observed in this work, but an upper limit is placed on the E3 matrix element to the lowest octupole band.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Firm spin and parity assignments for high-lying, low-spin levels in stable Si isotopes

A natural silicon target was investigated in a nat Si(γ,γ') photon-scattering experiment with fully linearly-polarised, quasi-monochromatic γ rays in the entrance channel. The mean photon energies used were < E γ >= 9.33, 9.77, 10.17, 10.55, 10.93, and 11.37 MeV, and the relative energy spread (full width at half maximum) of the incident beam was ΔE γ /< E γ >≈ 3.5–4 %. The observed angular distributions for the ground-state decay allow firm spin and parity assignments for several levels of the stable even-even silicon isotopes.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

First Spectroscopy of the Near Drip-line Nucleus Mg 40

One of the most exotic light neutron-rich nuclei currently accessible for experimental study is 40 Mg , which lies at the intersection of the nucleon magic number N=28 and the neutron drip line. Low-lying excited states of 40 Mg have been studied for the first time following a one-proton removal reaction from 41 Al, performed at the Radioactive Isotope Beam Factory of RIKEN Nishina Center with the DALI2 γ-ray array and the ZeroDegree spectrometer. Two γ-ray transitions were observed, suggesting an excitation spectrum that shows unexpected properties as compared to both the systematics along the Z=12, N ≥ 20 Mg isotopes and available state-of-the-art theoretical model predictions. A possible explanation for the observed structure involves weak-binding effects in the low-lying excitation spectrum.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Examination of the low-energy enhancement of the γ -ray strength function of Fe 56

A model-independent technique was used to determine the gamma-ray strength function (gamma SF) of Fe-56 down to gamma-ray energies less than 1 MeV for the first time with GRETINA using the (p, p') reaction at 16MeV. No difference was observed in the energy dependence of the gamma SF built on 2(+) and 4(+) final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

Jones, M. D.↗
DOE OSTI2017

Search for excited states in O 25

Theoretical calculations suggest the presence of low-lying excited states in 25 O. Previous experimental searches by means of proton knockout on 26 F produced no evidence for such excitations. We search for excited states in 25 O using the 24 O(d,p) 25 O reaction. The theoretical analysis of excited states in unbound 25,27 O is based on the configuration interaction approach that accounts for couplings to the scattering continuum. We use invariant-mass spectroscopy to measure neutron-unbound states in 25 O. For the theoretical approach, we use the complex-energy Gamow Shell Model and Density Matrix Renormalization Group method with a finite-range two-body interaction optimized to the bound states and resonances of 23–26 O, assuming a core of 22 O. Here we predict energies, decay widths, and asymptotic normalization coefficients. Our calculations in a large spdf space predict several low-lying excited states in 25 O of positive and negative parity, and we obtain an experimental limit on the relative cross section of a possible J π = 1/2 + state with respect to the ground state of 25 O at σ 1/2+ /σ g.s. = 0.25$^{+1.0}_{-0.25}$. We also discuss how the observation of negative parity states in 25 O could guide the search for the low-lying negative parity states in 27 O. Previous experiments based on the proton knockout of 26 F suffered from the low cross sections for the population of excited states in 25 O because of low spectroscopic factors. In this respect, neutron transfer reactions carry more promise.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Strongly coupled rotational band in Mg 33

The “island of inversion” at N≈20 for the neon, sodium, and magnesium isotopes has long been an area of interest both experimentally and theoretically due to the subtle competition between 0p-0h and np-nh configurations leading to deformed shapes. However, the presence of rotational band structures, which are fingerprints of deformed shapes, have only recently been observed in this region. In this work, we report on a measurement of the low-lying level structure of Mg33 populated by a two-stage projectile fragmentation reaction and studied with the Gamma Ray Energy Tracking In-Beam Nuclear Array (GRETINA). The experimental level energies, ground-state magnetic moment, intrinsic quadrupole moment, and γ-ray intensities show good agreement with the strong-coupling limit of a rotational model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Energy reconstruction of an n-type segmented inverted coaxial point-contact HPGe detector

We have characterized, for the first time, an n-type segmented Inverted Coaxial Point-Contact detector. This novel detector technology relys on a large variation in drift time of the majority charge carriers, as well as image and net charges observed on the segments, to achieve a potential γ-ray interaction position resolution of better than 1 mm. However, the intrinsic energy resolution in such a detector is poor (more than 20 keV at 1332 keV) because of charge (electron) trapping effects. We propose an algorithm that enables restoration of the resolution to a value of 3.44 0.03 keV at 1332 keV for events with a single interaction. The algorithm is based on a measurement of the azimuthal angle and the electron drift time of a given event; the energy of the event is corrected as a function of these two values.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Neutron-unbound excited states of N 23

Neutron unbound states in 23 N were populated via proton knockout from an 83.4 MeV/nucleon 24 O beam on a liquid deuterium target. The two-body decay energy displays two peaks at E 1 ~ 100 keV and E 2 ~ 1MeV with respect to the neutron separation energy. The data are consistent with shell model calculations predicting resonances at excitation energies of ~3.6MeV and ~4.5MeV. The selectivity of the reaction implies that these states correspond to the first and second 3/2 - states. Furthermore, the energy of the first state is about 1.3 MeV lower than the first excited 2 + in 24 O. This decrease is largely due to coupling with the πp $-1\atop{3/2}$ hole along with a small reduction of the N = 16 shell gap in 2 3N.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

The Mg 30 ( t , p ) Mg 32 “puzzle” reexamined

Background: Competing interpretations of the results of a Mg 30 (t,p)Mg 32 measurement populating the ground state and 0$+\atop{2}$ state in Mg 32 , both limited to a two-state mixing description, have left an open question regarding the nature of the Mg 32 ground state. Purpose: Inspired by recent shell-model calculations, we explore the possibility of a consistent interpretation of the available data for the low-lying 0 + states in Mg 32 by expanding the description from two-level to three-level mixing. Methods: A phenomenological three-level mixing model of unperturbed 0p0h, 2p2h, and 4p4h states is applied to describe both the excitation energies in Mg 32 and the transfer reaction cross sections. Results: Within this approach, self-consistent solutions exist that provide good agreement with the available experimental information obtained from the Mg 30 (t,p)Mg 32 reaction. Conclusion: The inclusion of the third state, namely the 4p4h configuration, resolves the "puzzle" that results from a two-levelmodel interpretation of the same data. In our analysis, the Mg 32 ground state emerges naturally as dominated by intruder (2p2h and 4p4h) configurations, at the 95% level.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗