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M. G. Procter,
D. M. Cullen,
C. Scholey,
P. Ruotsalainen,
L. Angus,
T. Bäck,
B. Cederwall, A. Dewald,
C. Fransen,
T. Grahn, [......],
S. V. Rigby,
W. Rother,
M. Sandzelius,
J. Sarén,
J. Sorri, M. J. Taylor,
J. Uusitalo,
P. Wady,
C. Qi,
F. R. Xu
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M G Procter,
D M Cullen, M J Taylor,
J Pakarinen,
K Auranen,
T Back,
T Braunroth,
B Cederwall, A Dewald,
T Grahn, [......],
P Peura,
P Rahkila,
P Ruotsalainen,
M Sandelius,
J Saren,
C Scholey,
J Sorri,
S Stolze,
J Uusitalo,
C Qi
Physical Review C. 01/2013; 87(1).
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M. G. Procter,
D. M. Cullen,
C. Scholey,
P. Ruotsalainen,
L. Angus,
T. Bäck,
B. Cederwall, A. Dewald,
C. Fransen,
T. Grahn, [......],
S. V. Rigby,
W. Rother,
M. Sandzelius,
J. Sarén,
J. Sorri, M. J. Taylor,
J. Uusitalo,
P. Wady,
C. Qi,
F. R. Xu
[show abstract]
[hide abstract]
ABSTRACT: Lifetime measurements have been made in the neutron-deficient nucleus 109Te using the coincident recoil distance Doppler-shift method. The experimental B(E2) values have been compared with state-of-the-art shell-model calculations using the monopole-corrected realistic charge-dependent Bonn nucleon-nucleon potential. Lifetimes in the νh11/2 band are consistent with an interpretation based on the deformation driving properties of a single valence neutron outside of the even-even tellurium core and highlight the unexpected presence of collective behavior as the N=50 shell closure is approached. Lifetime measurements for the low-lying positive-parity states also appear to correlate well with shell-model calculations. In addition, a comparison with the proton-unbound nucleus 109I suggests that the presence of a single decoupled valence proton affects the total measured B(E2) strengths in a manner that is not currently well understood.
Phys. Rev. C. 09/2012; 86(3).
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[show abstract]
[hide abstract]
ABSTRACT: The lifetimes of excited states in neutron-rich nuclei around the doubly-magic nucleus 48Ca have been measured using a novel technique that combines the Recoil Distance Doppler Shift method with the CLARA-PRISMA
spectrometers. This is the first time such a method is applied to measure lifetimes of neutron-rich nuclei populated via a
multinucleon transfer reaction. The experimental method will be discussed and the results for Ca nuclei will be compared with
realistic simulations of the CLARA and PRISMA spectrometers.
European Physical Journal A 04/2012; 42(3):387-391. · 2.19 Impact Factor
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Zs. Podolyák,
P. G. Bizzeti,
A. M. Bizzeti-Sona,
S. Lunardi,
D. Bazzacco, A. Dewald,
A. Algora,
G. de Angelis,
M. De Poli,
E. Farnea, [......],
D. R. Kasemann,
T. Klug,
Th. Kröll,
S. Lenzi,
D. R. Napoli,
C. M. Petrache,
R. Peusquens,
C. Rossi Alvarez,
T. Martinez,
C. A. Ur
[show abstract]
[hide abstract]
ABSTRACT: The lifetime andthe γ-decay to the 0+ groundstate of the lowest 3− state in 148Gd has been determined. The reduced strength B(E3, 3− → 0+)=41 (6) W.u. agrees well with the theoretical value from empirical shell model calculations and can be directly compared
with the 12+ → 9− two-octupole-phonon → one-octupole-phonon strength obtained in the same Recoil Distance Method lifetime measurement. The
results of our search for a three octupole-phonon state built on the (νf
7/2)6+2 state is also reported.
European Physical Journal A 04/2012; 8(2):147-151. · 2.19 Impact Factor
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A Lemasson,
H Iwasaki,
C Morse,
D Bazin,
T Baugher,
J S Berryman, A Dewald,
C Fransen,
A Gade,
S Mcdaniel,
A Nichols,
A Ratkiewicz,
S Stroberg,
P Voss,
R Wadsworth,
D Weisshaar,
K Wimmer,
R Winkler
[show abstract]
[hide abstract]
ABSTRACT: The lifetimes of the first 2+ states in the neutron-deficient 76,78 Sr isotopes were measured using a unique combination of the γ -ray line-shape method and two-step nucleon exchange reactions at intermediate energies. The transition rates for the 2 + states were determined to be B(E2; 2 + → 0 +) = 2220(270) e2fm4 for 76 Sr and 1800(250) e2fm4 for 78 Sr, corresponding to large deformation of β 2 = 0.45(3) for 76 Sr and 0.40(3) for 78 Sr. The present data provide experimental evidence for mutually enhanced collectivity that occurs at N = Z = 38. The systematic behavior of the excitation energies and B(E2) values indicates a signature of shape coexistence in 76 Sr, characterizing 76 Sr as one of most deformed nuclei with an unusually reduced E(4 +)/E(2 +) ratio.
Physical Review C 04/2012; 85:041303. · 3.31 Impact Factor
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A. Lemasson,
H. Iwasaki,
C. Morse,
D. Bazin,
T. Baugher,
J. S. Berryman, A. Dewald,
C. Fransen,
A. Gade,
S. McDaniel,
A. Nichols,
A. Ratkiewicz,
S. Stroberg,
P. Voss,
R. Wadsworth,
D. Weisshaar,
K. Wimmer,
R. Winkler
[show abstract]
[hide abstract]
ABSTRACT: The lifetimes of the first 2$^{+}$ states in the neutron-deficient
$^{76,78}$Sr isotopes were measured using a unique combination of the
$\gamma$-ray line-shape method and two-step nucleon exchange reactions at
intermediate energies. The transition rates for the 2$^{+}$ states were
determined to be $B$(E2;2$^{+}$$\to 0^{+}$) = 2220(270) e$^{2}$fm$^{4}$ for
$^{76}$Sr and 1800(250) e$^{2}$fm$^{4}$ for $^{78}$Sr, corresponding to large
deformation of $\beta_2$ = 0.45(3) for $^{76}$Sr and 0.40(3) for $^{78}$Sr. The
present data provide experimental evidence for mutually enhanced collectivity
that occurs at $N$ = $Z$ = 38. The systematic behavior of the excitation
energies and $B$(E2) values indicates a signature of shape coexistence in
$^{76}$Sr, characterizing $^{76}$Sr as one of most deformed nuclei with an
unusually reduced $E$(4$^{+}$)/$E$(2$^{+}$) ratio.
04/2012;
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C Fransen,
W Rother,
H Iwasaki, A Dewald,
T Baugher,
D Bazin,
B A Brown,
H L Crawford,
A Gade,
T N Ginter, [......],
D Miller,
P Petkov,
T Pissulla,
A Ratkiewicz,
K Starosta,
C A Ur,
P Voss,
K A Walsh,
D Weisshaar,
K O Zell
[show abstract]
[hide abstract]
ABSTRACT: The properties of exotic neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 are of particular interest for the understanding of the shell structure for large neutron excess. Effects related to the energy gap between the neutron fp and 1g9/2 shells lead to a strong variation of collectivity for nuclei around N = 40. Whereas 68Ni was found to have doubly magic properties, this was not observed in neighbouring nuclei. Recent shell model calculations for the neutron rich iron isotopes clearly reveal the difficulty to describe nuclei in this mass region and resulted in large deviations of the predicted collectivity depending on the valence space. However, no experimental data on the transition strength existed for the very exotic nucleus 66Fe at N = 40. Here we present the newest results on absolute transition strengths of the lowest excited states in 62,64,66Fe measured model independently using the recoil distance Doppler-shift (RDDS) method. The experiments were performed at NSCL at Michigan State University with the Cologne/NSCL plunger device using Coulomb excitation in inverse kinematics at energies of 80 MeV/u. Our results yield a much higher collectivity for 64,66Fe than expected and allow tests of new calculations.
Journal of Physics Conference Series 09/2011; 312(9):092025.
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M Petri,
P Fallon,
A O Macchiavelli,
S Paschalis,
K Starosta,
T Baugher,
D Bazin,
L Cartegni,
R M Clark,
H L Crawford, [......],
S McDaniel,
D Miller,
M M Rajabali,
A Ratkiewicz,
W Rother,
P Voss,
K A Walsh,
D Weisshaar,
M Wiedeking,
B A Brown
[show abstract]
[hide abstract]
ABSTRACT: Establishing how and when large N/Z values require modified or new theoretical tools is a major quest in nuclear physics. Here we report the first measurement of the lifetime of the 2(1)+ state in the near-dripline nucleus 20C. The deduced value of τ(2(1)+)=9.8±2.8(stat)(-1.1)(+0.5)(syst) ps gives a reduced transition probability of B(E2; 2(1)+→0(g.s.)+)=7.5(-1.7)(+3.0)(stat)(-0.4)(+1.0)(syst) e2 fm4 in good agreement with a shell model calculation using isospin-dependent effective charges.
Physical Review Letters 09/2011; 107(10):102501. · 7.37 Impact Factor
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M. G. Procter,
D. M. Cullen,
P. Ruotsalainen,
T. Braunroth, A. Dewald,
C. Fransen,
T. Grahn,
P. T. Greenlees,
M. Hackstein,
K. Hauschild, [......],
W. Rother,
M. Sandzelius,
J. Sarén,
C. Scholey,
J. Sorri, M. J. Taylor,
J. Uusitalo,
A. Vitturi,
Y. Shi,
F. R. Xu
[show abstract]
[hide abstract]
ABSTRACT: Lifetime measurements have been made in the ground-state band of the transitional nucleus 138Gd from coincidence recoil-distance Doppler-shift data. 138Gd nuclei were produced using the 106Cd (36Ar, 2p2n) reaction with a beam energy of 190 MeV. Reduced transition probabilities have been extracted from the lifetime data collected with the Köln plunger placed at the target position of the JUROGAM-II array. The B(E2) values have been compared with predictions from X(5) critical-point calculations, which describe the phase transition between vibrational and axially symmetric nuclear shapes, as well as with IBM-1 calculations at the critical point. While the excitation energies in 138Gd are consistent with X(5) predictions, the large uncertainties associated with the measured B(E2) values cannot preclude vibrational and rotational contributions to the low-lying structure of 138Gd. Although experimental knowledge for the low-lying γ and β-vibrational bands in 138Gd is limited, potential-energy surface calculations suggest an increase in γ softness in the ground-state band. In order to more fully account for the effects of γ softness, the X(5) and IBM-1 calculations need to be extended to include the γ degree of freedom for 138Gd.
Phys. Rev. C. 08/2011; 84(2).
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M. Niikura,
B. Mouginot,
S. Franchoo,
I. Matea,
I. Stefan,
D. Verney,
F. Azaiez,
M. Assie,
P. Bednarczyk,
C. Borcea, [......],
F. Negoita,
D. Pantelica,
L. Perrot,
Th. Pissulla,
F. Rotaru,
W. Rother,
J. A. Scarpaci,
C. Stodel,
J. C. Thomas,
P. Ujic
[show abstract]
[hide abstract]
ABSTRACT: We report here the first direct lifetime measurement of the 21+ state in 72,74Zn. The neutron-rich beam was produced by in-flight fragmentation of 76Ge at the Grand Accélérateur National d'Ions Lourds and separated with the LISE spectrometer. The 21+ state was excited by inelastic scattering and knock-out reaction on a CD2 target and its lifetime was measured by the recoil-distance Doppler-shift method with the Köln plunger device combined with the EXOGAM detectors. The lifetimes of the 21+ states in 72,74Zn were determined to be 17.9(18) and 27.0(24) ps, which correspond to reduced transition probabilities B(E2;21+→0+)=385(39) and 370(33) e2 fm4, respectively. These values support the idea of a systematic maximum of collectivity at N=42 for Zn, Ge, and Se nuclei. In addition, the available systematics in the neighboring nuclei point toward a transition from a spherical oscillator at N=40 to complete γ-softness at N=42.
Phys. Rev. C. 05/2011; 85(5).
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M Niikura,
B Mouginot,
F Azaiez,
S Franchoo,
I Matea,
I Stefan,
D Verney,
M Assie,
P Bednarczyk,
C Borcea, [......],
F Negoita,
D Pantelica,
L Perrot,
Th Pissulla,
F Rotaru,
W Rother,
J A Scarpaci,
C Stodel,
J C Thomas,
P Ujic
[show abstract]
[hide abstract]
ABSTRACT: We report here the first direct lifetime measurement of the 2 + 1 state in 74 Zn. The neutron-rich 74 Zn beam was produced by in-flight fragmentation of 76 Ge at the Grand Accélérateur National d'Ions Lourds and separated with the LISE spectrometer. The 2 + 1 state was excited by inelastic scattering on a CD2 target and the lifetime was measured by the recoil distance Doppler-shift method with the Köln plunger device combined with the EXOGAM detectors. The lifetime of the 2 + 1 state in 74 Zn was determined to be 27.0(24) ps, which corresponds to a reduced transition probability B(E2; 2 + 1 → 0 +) = 370(33) e 2 fm 4 .
04/2011;
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A Gadea,
E Farnea,
J J Valiente-Dobón,
B Million,
D Mengoni,
D Bazzacco,
F Recchia, A Dewald,
Th. Pissulla,
W Rother, [......],
C A Ur,
V Vandone,
R Venturelli,
F Veronese,
C Veyssiere,
E Viscione,
O Wieland,
A Wiens,
F Zocca,
A Zucchiatti
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; 654(1):88 - 96. · 1.21 Impact Factor
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M G Procter,
D M Cullen,
C Scholey,
P Ruotsalainen,
L Angus,
T Back,
B Cederwall, A Dewald,
C Fransen,
T Grahn, [......],
S V Rigby,
W Rother,
M Sandzelius,
J Saren,
J Sorri, M J Taylor,
J Uusitalo,
P Wady,
C Qi,
F R Xu
Physics Letters B. 01/2011; 704(3):118-122.
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W Rother, A Dewald,
H Iwasaki,
S M Lenzi,
K Starosta,
D Bazin,
T Baugher,
B A Brown,
H L Crawford,
C Fransen, [......],
S McDaniel,
D Miller,
P Petkov,
Th Pissulla,
A Ratkiewicz,
C A Ur,
P Voss,
K A Walsh,
D Weisshaar,
K-O Zell
[show abstract]
[hide abstract]
ABSTRACT: The transition rates for the 2(1)+ states in (62,64,66)Fe were studied using the recoil distance Doppler-shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N = 40. The results are interpreted using the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N = 40 as governed by the number of valence protons with respect to Z ≈ 30. The trend of collectivity suggested by the experimental data is described by state-of-the-art shell-model calculations with a new effective interaction developed for the fpgd valence space.
Physical Review Letters 01/2011; 106(2):022502. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Conversion electron spectroscopy represents an important tool for nuclear structure analysis of medium and heavy nuclei. Two iron-free magnetic electron spectrometers of the orange type have been installed at the Institute for Nuclear Physics of the University of Cologne. The very large transmission of 15% and the very good energy resolution of 1% makes the iron-free orange spectrometer a powerful instrument. By means of fast timing techniques, lifetimes of nuclear excited states can be measured with an accuracy better than 20 ps. For the first time, the energy dependent centroid position of prompt events yielding the time-walk characteristics (the prompt curve) of the orange spectrometer fast timing setup has been measured using prompt secondary δ-electrons generated in a pulsed beam experiment. The prompt curve calibrated as a function of energy allows precise lifetime determination down to a few tens of picoseconds by the use of the centroid shift method.
The Review of scientific instruments 11/2010; 81(11):113505. · 1.52 Impact Factor
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P. G. Bizzeti,
A. M. Bizzeti-Sona,
D. Tonev,
A. Giannatiempo,
C. A. Ur, A. Dewald,
B. Melon,
C. Michelagnoli,
P. Petkov,
D. Bazzacco, [......],
O. Möller,
A. Nannini,
D. R. Napoli,
M. Nespolo,
P. Pavan,
A. Perego,
C. M. Petrache,
N. Pietralla,
C. Rossi Alvarez,
P. Sona
[show abstract]
[hide abstract]
ABSTRACT: To investigate the possible X(5) character of 122Ba, suggested by the ground-state band energy pattern, the lifetimes of the lowest yrast states of 122Ba have been measured, via the recoil distance Doppler-shift method. The relevant levels have been populated by using the 108Cd(16O,2n)122Ba and the 112Sn(13C,3n)122Ba reactions. The B(E2) values deduced in the present work are compared to the predictions of the X(5) model and to calculations performed in the framework of the IBA-1 and IBA-2 models.
Phys. Rev. C. 10/2010; 82(5).
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K. A. Gladnishki,
G. Rainovski,
P. Petkov,
J. Jolie,
N. Pietralla,
A. Blazhev,
A. Damyanova,
M. Danchev, A. Dewald,
C. Fransen,
M. Hackstein,
D. Karagyozov,
O. Möller,
T. Pissulla,
M. Reese,
W. Rother,
R. Topchiyska
[show abstract]
[hide abstract]
ABSTRACT: Low-spin excited states of 140Nd have been studied via the 140Ce(3He,3n)140Nd reaction. The data show that one of the candidates for the one-phonon mixed-symmetry state (MSS) of 140Nd, namely, the 23+ state at 2140 keV with an effective lifetime of 220(90) fs, exhibits a fast M1 decay to the 21+ state. Thus, this state can be considered, at least, as a fragment of the one-phonon MSS of 140Nd. This is the first example where mixed symmetry character is tentatively assigned to a state of an unstable nucleus from the mass A≈140 region based on the data on absolute M1 transition rates. However, the data are not conclusive on whether this decay exhausts the total M1 strength or whether the one-phonon MSS of 140Nd is fragmented.
Phys. Rev. C. 09/2010; 82(3).
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W. Rother, A. Dewald,
H Iwasaki,
S. M. Lenzi,
K. Starosta,
D. Bazin,
T. Baugher,
B A Brown,
H. L. Crawford,
C. Fransen, [......],
S McDaniel,
D Miller,
P Petkov,
Th. Pissulla,
A Ratkiewicz,
C. A. Ur,
P Voss,
K. A. Walsh,
D. Weisshaar,
K O Zell
[show abstract]
[hide abstract]
ABSTRACT: The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied
using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb
excitation reactions. The deduced E2 strengths illustrate the enhanced
collectivity of the neutron-rich Fe isotopes up to N=40. The results are
interpreted by the generalized concept of valence proton symmetry which
describes the evolution of nuclear structure around N=40 as governed by the
number of valence protons with respect to Z~30. The deformation suggested by
the experimental data is reproduced by state-of-the-art shell calculations with
a new effective interaction developed for the fpgd valence space.
06/2010;
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M. G. Procter,
D. M. Cullen,
C. Scholey,
B. Niclasen,
P. J. R. Mason,
S. V. Rigby,
J. A. Dare, A. Dewald,
P. T. Greenlees,
H. Iwasaki, [......],
M. Nyman,
P. Peura,
T. Pissulla,
A. Puurunen,
P. Rahkila,
W. Rother,
P. Ruotsalainen,
J. Sarén,
J. Sorri,
J. Uusitalo
[show abstract]
[hide abstract]
ABSTRACT: The known level scheme of 144Dy has been extended and lifetime measurements have been made with the recoil-distance Doppler-shift method. Reduced transition probabilities and deformations have been determined for four low-lying transitions. These states form part of the first observed band crossing, giving information on the change in nuclear deformation resulting from the rearrangement of h11/2 protons in the nucleus. Two bands built upon excited 10+ states have been assigned π(h11/2)2 prolate and ν(h11/2)-2 oblate configurations with τ=12(2)ps and 0.01<τ≲16ns, respectively. These long lifetimes are reasoned to be a result of shape coexistence at low energy and moderate spin. A known four-quasiparticle dipole band has been extended to higher spin and lifetime measurements suggest a long-lived bandhead state. In this case, the excited states in the band may be consistent with a shears model interpretation of a magnetic dipole rotor. However, the measured B(M1)/B(E2) branching ratios reveal a larger than expected deformed rotational component compared with that in the analogous band in the lower mass isotone 142Gd.
Phys. Rev. C. 05/2010; 81(5).
