Heavy Ion Discussion Group

Conference Room R-150, Building 203, Argonne National Laboratory

Fridays at 3:30 PM

2015-2016 Program

24 Aug 2015 Special Day: Monday
Sean Kuvin, Florida State University,
"Measurement of the 17F (d, n)18Ne reaction using RESONEUT"

The 17F(p, γ)18Ne reaction of astrophysical importance has been studied using the surrogate reaction 17F(d, n)18Ne in inverse kinematics. The usefulness of this type of approach has been demonstrated in previous experiments at the RESOLUT facility[1]. In this work we have developed a compact neutron detector array, RESONEUT, which is specialized for (d, n) reactions in inverse kinematics. The threshold and efficiency properties of the neutron detectors were characterized using the 12C(d, n)13N reaction. Spectroscopy of the 18Ne nucleus was accomplished using two methods. The first was by neutron time of flight spectroscopy and the second was by kinematic reconstruction of the unbound compound nucleus by detecting the emitted proton and heavy ion. We compared our results with those obtained from 17F+p elastic scattering measurements and from the direct 17F(p, γ) measurement conducted at Oak Ridge[2,3]. Our results provide additional confirmation that the state at ~600 keV is the 3+ state. No other resonances directly above the proton threshold were detected. However, using NaI(T1) detectors detecting gammas in coincidence with the neutrons in RESONEUT, we have placed upper limits on the possibility of having a low-lying proton resonance with a significant Γγ > Γp branching ratio.
[1] Peplowski et al, PRC 79, 032801 (2009)
[2] Bardayan et al, PRL 83, 45(1999)
[3] Chipps et al, PRL 102, 152502 (2009)

27 Aug 2015 Special Day: Thursday
Ran Hong, University of Washington,
High-Precision Measurement of the β-ν Correlation in the 6He Decay

High-precision measurements of β-decays are sensitive probes of new physics beyond the Standard Model (SM). Particularly, the β-ν correlation of Gamow-Teller decays is sensitive to the exotic tensor type weak current which is predicted by the leptoquark model and some super symmetric models. A new experiment that measures the β-ν correlation coefficient αβν of the 6He decay is being developed at the Center of Experimental Nuclear Physics and Astrophysics (CENPA), University of Washington. In this experiment, the 6He atoms are laser-trapped while both the β-particle and the recoil ion are detected. The αβν is extracted by fitting the time-of-flight (TOF) spectrum of the recoil ions. The ultimate goal of this experiment is a 0.1% determination of αβν and the short-term goal is to determine αβν at or lower than 1% and pave the way to the 0.1% level measurement.
In this talk, the construction of the 6He production system, atomic trapping system, β-particle detectors and recoil ion detectors are presented. The 6He are produced through reaction 7Li + 2H -> 6He + 3He. Deuterons are accelerated to 18 MeV by the Van De Graaff accelerator at CENPA, and then hit the molten lithium target. 6He atoms diffuse out from the target and then are slowed down and trapped in the magneto-optical trap (MOT). A multi-wire proportional chamber (MWPC) and a plastic scintillator are put above the MOT for β-particle detection, while a micro-channel plate (MCP) is placed below the MOT for recoil ion detection. A uniform electric field is applied in order to increase the ion detection solid angle. The detail design and construction of the detector system are discussed. The Monte Carlo simulation and data analysis software developments are also presented. The sensitivities of systematic effects are studied and the detectors are calibrated to the desired precision and accuracy. Particularly, the position accuracy of the MCP is calibrated below 10 μm and the resolution is improved to 85 μm FWHM. A total systematic uncertainty of the αβν is expected to be around 0.6% with the present setup.

This work is supported by DOE, Office of Nuclear Physics, under contract nos. DE-AC02-06CH11357 and DE-FG02-97ER41020.

31 Aug 2015 Special Day: Monday
Kenneth Whitmore, Michigan State University,
New Experimental Probes of the Halo Nucleus 19C

Halo nuclei occur at the limits of stability, where a low binding energy allows valence nucleons to tunnel beyond the nuclear core to form a diffuse nuclear cloud. Several experimental probes have been used to identify and characterize halo nuclei, including interaction cross section measurements, momentum distributions following knockout reactions, and Coulomb dissociation reactions. In particular, an enhanced electric dipole (E1) response at low energy has become a unique signature of halo nuclei. Despite numerous investigations into the E1 response, there is very little information on the magnetic dipole (M1) response of halo nuclei.
In this talk, I will present results of a lifetime measurement of the 3/2+ -> 1/2+ transition in 19C. This represents the first measurement of an M1 transition in a halo nucleus. The measurement utilized the line-shape and recoil-distance methods. In the line-shape method, the lifetime is determined based on a distortion of the Doppler-corrected gamma spectrum. With the recoil-distance method, the radioactive beam passes through a degrader downstream of the target, creating fast and slow peaks in the Doppler-corrected gamma spectrum. Both techniques exploited the excellent energy and position resolution of the tracking array GRETINA to identify peak shapes. The results are compared to advanced shell-model calculations in order to understand the microscopic features that allow such an M1 transition. In addition, preliminary results from a one-proton knockout reaction from 20N measured at 70 MeV/nucleon will be presented, and the implications for the structure of 19C will be compared with the lifetime measurement.

3 Sep 2015 Special Day: Thursday
Michael Jones, Michigan State University,
Two-neutron Sequential Decay of 24O
17 Sep 2015 Special Day: Thursday
Kalle Auranen, University of Jyvaskyla,
Spectroscopy of 199,201At

The excited states of 199At and 201At were studied using fusion evaporation reactions, a gas-filled recoil separator and various tagging methods. The level scheme of 201At was extended a lot including a cascade of magnetic dipole transitions, that is suggested to form a shears band. In addition, a 29/2+ [T1/2 = 3.39(9) ms] isomeric state was observed. The 29/2+ state is suggested to originate from the π(h9/2)X|200Po; 11- > configuration, and it depopulates through 269-keV E2 and 339-keV E3 transitions. In both nuclei 199,201At we have observed also the isomeric 1/2+ [T1/2 = 273(9), 45(3) ms, respectively] intruder state, that is suggested to originate from the π(s1/2)-1 configuration. The 1/2+ state decays through 103-keV and 269-keV E3 transitions in 199,201At, respectively. In both nuclei the 1/2+ state is fed from 3/2+ and 5/2+ states, which are suggested to originate from the π(d3/2)-1 and π(d5/2)-1 configurations, respectively.
The text above is the abstract of my doctoral thesis. In this talk I will give an introduction to its topics. The used experimental devices and methods will be presented together with the three mentioned main results.

25 Sep 2015 S&T review,
2 Oct 2015 Torben Lauritsen,Physics Division, Argonne National Laboratory
9 Oct 2015 Andrei Andreyev, University of York, UK/JAEA, Tokai, Japan
on behalf of Leuven-Gatchina-ISOLDE-Mainz-Manchester-York and Windmill-ISOLTRAP-RILIS collaboration
Shape coexistence and charge radii in the long chains of gold, mercury and astatine isotopes studied by in-source laser spectroscopy at RILIS-ISOLDE

The competition between spherical and deformed configurations gives rise to shape coexistence in the neutron-deficient isotopes around Z~82 and N~104 [1] while on the neutron-rich side, effects due to octupole deformation in the vicinity of N~133 could be expected [2]. In order to determine to which extent the ground and isomeric states of these nuclides are affected by these phenomena, an extensive campaign of investigation of changes in the mean-square charge radii and electromagnetic moments is being conducted by our collaboration at the mass-separator ISOLDE (CERN). The measurements rely on the high sensitivity provided by the in-source laser spectroscopy technique [3, 4].
In this contribution, we will present the extended systematics of charge radii and magnetic moments recently obtained for the mercury (April 2015), gold (May 2015) and astatine (September 2014) isotopic chains at ISOLDE. In all three cases, the Windmill decay spectroscopy setup [5] and the Multi-Reflection Time-of-Flight (MR-TOF) mass separation technique [6] were used.

[1] K. Heyde and J. Wood, Rev. Mod. Phys. 83, 1467 (2011)
[2] L.P. Gaffney et al., Nature, 497, 199 (2013)
[3] B.A. Marsh et al., NIM B 317, 550 (2013)
[4] A. E. Barzakh et al., Rev. Sci. Instr. 83, 02B306 (2012)
[5] A.N. Andreyev et al,, Phys. Rev. Lett. 105, 252502 (2010)
[6] R. N. Wolf et al., NIM A 686, 82-90 (2012)

15 Oct 2015 Special Day: Thursday
Sandrine Courtin,IPHC, CNRS/IN2P3, and Universite de Strasbourg, France
Low energy heavy-ion fusion reactions : tunneling through multidimentional barriers

Fusion-evaporation is the dominant reaction mechanism in medium-mass heavy-ion collisions around the Coulomb barrier. At these energies and at moderate sub-barrier energies, enhancement of the fusion cross-sections was observed whereas hindrance of the fusion cross- section has been identified in many systems at deep sub-barrier energies. Fusion cross-sections around the Coulomb barrier have been discussed extensively to be driven by couplings of the relative motion of the colliding nuclei to their low energy surface vibrations and/or stable deformations. The corresponding coupled-channel calculations and the distributions of barriers have revealed to be a powerful tool to better understand the role of couplings to collective degrees of freedom of the target and projectile.
The strong sensitivity of the sub-barrier fusion probability to the structure of the colliding nuclei will be presented as well as recent results on the influence of particle transfer channels on the fusion cross-sections in medium mass systems like Ca+Ca and Ca+Ni.
For lighter systems like C+C and C+O, nuclear fusion is strongly connected to astrophysics, as it is an essential step in the synthesis of the chemical elements in stars. Experimental work on resonances observed in these systems will be discussed.

23 Oct 2015 Daniel Santiago-Gonzalez, Louisiana State University/Argonne National Laboratory
An update on the HELIOS gas target and ionization chamber
30 Oct 2015 DNP meeting,
5 Nov 2015 Special Day: Thursday, 10 am
Rene Reifarth, Goethe Universitaet, Frankfurt
Radioactive isotopes - in stars and laboratories

Most of the time, stars gain their energy from fusion of the very light left-overs of the Big Bang into heavier elements over long periods of time. The observation of radioactive isotopes in different regions of the Universe is an indicator of this ongoing nucleosynthesis. In addition, short-lived nuclei are often intermediate steps during the nucleosynthesis in stars.
A quantitative analysis of these relations requires a precise knowledge of reaction cross sections involving unstable nuclei. The corresponding measurements are very demanding and the applied techniques therefore manifold. The reward however is surprisingly huge. It is possible to constrain basic parameters as the age of the Universe, temperature and convection times in stars, or neutron densities during explosions.
I will present selected recent experiments, which helped to improve the understanding of the corresponding astrophysical scenarios. The experiments cover neutron-, proton-, and gamma-induced reactions. The astrophysical scenarios range from small, compact objects like neutron stars to huge Red Giants.

13 Nov 2015 Melina Avila Coronado, Physics Division, Argonne National Laboratory
Understanding stellar processes through nucler reactions

The understanding of stellar nucleosynthesis is one of the driving forces of nuclear astrophysics. Nuclear reactions provide an essential input for models of stellar evolution, energy generation in stars and stellar explosions. For instance, a large number of proton and α induced reactions such as (p,γ), (α,γ), (α,p) and (α,n) are known to play an important role in different astrophysical scenarios. In general, direct measurements are preferred. However, many of these reactions cannot be measured directly at relevant astrophysical energies because of their small cross section and it becomes crucial to have a reliable indirect technique to evaluate them. Extracting the Asymptotic Normalization Coefficients (ANCs) using sub-Coulomb transfer reactions can be used as an effective method to determine properties of near-threshold resonances, thus constraining key astrophysical reaction rates. In this talk, I will discuss different α induced reaction measurements using both direct and indirect techniques for nuclear astrophysics studies. Results on α-transfer reactions using the ANC technique at sub-Coulomb energies will be presented. In addition, I will also discuss results on direct measurements of (α,p) and (α,n) reactions using the active target system MUSIC.

20 Nov 2015 Michael Carpenter, Physics Division, Argonne National Laboratory
27 Nov 2015 Thanksgiving,
1 Dec 2015 Special Day: Tuesday, 10 am
Brian Bucher, LLNL
3 Dec 2015 Special Day: Thursday, 10 am
Farheen Naqvi, Michigan state University
8 Dec 2015 Special Day: Tuesday, 1:30 pm
Marina Petri, Technical University, Darmstadt
10 Dec 2015 Special Day: Thursday, 10 am
Daniel Santiago, Luisiana State University
17 Dec 2015 Special Day: Thursday
Simone Bottoni, Physics Division, Argonne National Laboratory
25 Dec 2015 Christmas,
1 Jan 2016 New Year's Day,

Dariusz Seweryniak, Chair, (630) 252-1514 mail

Jeannie Glover, Secretary, (630) 252-4020 mail

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