165 research outputs found
The first direct measurement of ¹²C (¹²C,n) ²³Mg at stellar energies
Neutrons produced by the carbon fusion reaction ¹²C(¹²C,n)²³Mg play an important role in stellar nucleosynthesis. However, past studies have shown large discrepancies between experimental data and theory, leading to an uncertain cross section extrapolation at astrophysical energies. We present the first direct measurement that extends deep into the astrophysical energy range along with a new and improved extrapolation technique based on experimental data from the mirror reaction ¹²C(¹²C,p)²³Na. The new reaction rate has been determined with a well-defined uncertainty that exceeds the precision required by astrophysics models. Using our constrained rate, we find that ¹²C(¹²C,n)²³Mg is crucial to the production of Na and Al in Pop-III Pair Instability Supernovae. It also plays a non-negligible role in the production of weak s-process elements as well as in the production of the important galacti
Probing the single-particle character of rotational states in F using a short-lived isomeric beam
A beam containing a substantial component of both the ,
ns isomeric state of F and its , 109.77-min ground
state has been utilized to study members of the ground-state rotational band in
F through the neutron transfer reaction , in inverse kinematics.
The resulting spectroscopic strengths confirm the single-particle nature of the
13/2 band-terminating state. The agreement between shell-model
calculations, using an interaction constructed within the shell, and our
experimental results reinforces the idea of a single-particle/collective
duality in the descriptions of the structure of atomic nuclei
In-beam spectroscopy of medium- and high-spin states in Ce
Medium and high-spin states in Ce were investigated using the
Cd(Ne, ) reaction and the Gammasphere array. The level
scheme was extended up to an excitation energy of MeV and spin 93/2
. Eleven bands of quadrupole transitions and two new dipole bands are
identified. The connections to low-lying states of the previously known,
high-spin triaxial bands were firmly established, thus fixing the excitation
energy and, in many cases, the spin parity of the levels. Based on comparisons
with cranked Nilsson-Strutinsky calculations and tilted axis cranking covariant
density functional theory, it is shown that all observed bands are
characterized by pronounced triaxiality. Competing multiquasiparticle
configurations are found to contribute to a rich variety of collective
phenomena in this nucleus.Comment: 20 pages, 11 figure
The role of the g9/2 orbital in the development of collectivity in the A = 60 region: The case of 61Co
An extensive study of the level structure of 61Co has been performed
following the complex 26Mg(48Ca, 2a4npg)61Co reaction at beam energies of 275,
290 and 320 MeV using Gammasphere and the Fragment Mass Analyzer (FMA). The
low-spin structure is discussed within the framework of shell-model
calculations using the GXPF1A effective interaction. Two quasi-rotational bands
consisting of stretched-E2 transitions have been established up to spins I =
41/2 and (43/2), and excitation energies of 17 and 20 MeV, respectively. These
are interpreted as signature partners built on a neutron {\nu}(g9/2)2
configuration coupled to a proton {\pi}p3/2 state, based on Cranked Shell Model
(CSM) calculations and comparisons with observations in neighboring nuclei. In
addition, four I = 1 bands were populated to high spin, with the yrast dipole
band interpreted as a possible candidate for the shears mechanism, a process
seldom observed thus far in this mass region
Fast-timing measurements in the ground-state band of 114Pd
Using a hybrid Gammasphere array coupled to 25 LaBr3(Ce) detectors, the lifetimes of the first three levels
of the yrast band in 114Pd, populated via 252Cf decay, have been measured. The measured lifetimes are Ï„2+ =
103(10) ps, Ï„4+ = 22(13) ps, and Ï„6+ 10 ps for the 2+
1 , 4+
1 , and 6+
1 levels, respectively. Palladium-114 was
predicted to be the most deformed isotope of its isotopic chain, and spectroscopic studies have suggested it
might also be a candidate nucleus for low-spin stable triaxiality. From the lifetimes measured in this work,
reduced transition probabilities B(E2; J → J − 2) are calculated and compared with interacting boson model,
projected shell model, and collective model calculations from the literature. The experimental ratio RB(E2) =
B(E2; 4+
1 → 2+
1 )/B(E2; 2+
1 → 0+
1 ) = 0.80(42) is measured for the first time in 114Pd and compared with the
known values RB(E2) in the palladium isotopic chain: the systematics suggest that, for N = 68, a transition from
γ -unstable to a more rigid γ -deformed nuclear shape occurs.This work was financially supported by the Science
and Technology Facility Council (STFC) Grants
No. ST/L005840/1, No. ST/L005743/1, and No.
ST/G000751/1. This work has also been partially supported
by the U.S. Department of Energy, Office of Science, Office of
Nuclear Physics under Contract No. DE-AC02-06CH11357
(ANL). E.R.G. would like to acknowledge the STFC for
funding via his Ph.D. studentship. D.J.H. acknowledges
the National Science Foundation, Grant No. PHY-1502092.
E.A.S. and O.Y. would like to acknowledge the project
DFNI-E02/6
Evidence for Multiple Chiral Doublet Bands in Ce
Two distinct sets of chiral-partner bands have been identified in the nucleus
Ce. They constitute a multiple chiral doublet (MD), a phenomenon
predicted by relativistic mean field (RMF) calculations and observed
experimentally here for the first time. The properties of these chiral bands
are in good agreement with results of calculations based on a combination of
the constrained triaxial RMF theory and the particle-rotor model.Comment: Minor changes based on referee reviews and corrections of some typo
Key Ne states identified affecting -ray emission from F in novae
Detection of nuclear-decay rays provides a sensitive thermometer of
nova nucleosynthesis. The most intense -ray flux is thought to be
annihilation radiation from the decay of F, which is destroyed
prior to decay by the F(,)O reaction. Estimates of
F production had been uncertain, however, because key near-threshold
levels in the compound nucleus, Ne, had yet to be identified. This
Letter reports the first measurement of the
F(He,)Ne reaction, in which the placement of two
long-sought 3/2 levels is suggested via triton--
coincidences. The precise determination of their resonance energies reduces the
upper limit of the rate by a factor of at nova temperatures and
reduces the average uncertainty on the nova detection probability by a factor
of 2.1.Comment: 6 pages, 4 figure
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