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R. O. Hughes, C. W. Beausang,
T. J. Ross,
J. T. Burke,
N. D. Scielzo,
M. S. Basunia,
C. M. Campbell,
R. J. Casperson,
H. L. Crawford,
J. E. Escher,
J. Munson,
L. W. Phair,
J. J. Ressler
[show abstract]
[hide abstract]
ABSTRACT: The surrogate ratio method has been tested for (p,d) and (p,t) reactions on uranium nuclei. 236U and 238U targets were bombarded with 28-MeV protons and the light ion recoils and fission fragments were detected using the Silicon Telescope Array for Reaction Studies detector array at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. The (p,df) reaction channels on 236U and 238U targets were used as a surrogate to determine the σ[236U(n,f)]/σ[234U(n,f)] cross-section ratio. The (p,tf) reaction channels were also measured with the same targets as a surrogate for the σ[235U(n,f)]/σ[(233U(n,f)] ratio. For the (p,df) and (p,tf) surrogate measurements, there is good agreement with accepted (n,f) values over equivalent neutron energy ranges of En=0–7 MeV and En=0–5.5 MeV, respectively. An internal surrogate ratio method comparing the (p,d) and (p,t) reaction channels on a single target is also discussed. The σ[234U(n,f)]/σ[233U(n,f)] and σ[236U(n,f)]/σ[235U(n,f)] cross-section ratios are extracted using this method for the 236U and 238U targets, respectively. The resulting fission cross-section ratios show relatively good agreement with accepted values up to En∼5 MeV.
Phys. Rev. C. 02/2012; 85(2).
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N D Scielzo,
J E Escher,
J M Allmond,
M S Basunia, C W Beausang,
L A Bernstein,
D L Bleuel,
J T Burke,
R M Clark,
F S Dietrich, [......],
J Gibelin,
B L Goldblum,
S R Lesher,
M A Mcmahan,
E B Norman,
L Phair,
E Rodriguez-Vieitez,
S A Sheets,
I J Thompson,
M Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: The surrogate nuclear reaction method is being applied in many efforts to indirectly determine neutron-induced reaction cross sections on short-lived isotopes. This technique aims to extract accurate (n,γ) cross sections from measured decay properties of the compound nucleus of interest (created using a different reaction). The advantages and limitations of a method that identifies the γ -ray decay channel by detecting any high-energy ("statistical") γ ray emitted during the relaxation of the compound nucleus were investigated. Data collected using the Silicon Telescope Array for Reaction Studies and Livermore-Berkeley Array for Collaborative Experiments silicon and germanium detector arrays were used to study the decay of excited gadolinium nuclei following inelastic proton scattering. In many cases, this method of identifying the γ -ray decay channel can simplify the experimental data collection and greatly improve the detection efficiency for γ -ray cascades. The results show sensitivity to angular-momentum differences between the surrogate reaction and the desired (n,γ) reaction similar to an analysis performed using low-lying discrete transitions even when ratios of cross sections are considered.
Physical Review C 01/2012; 852060(85):054619. · 3.31 Impact Factor
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J. J. Ressler,
J. T. Burke,
J. E. Escher,
C. T. Angell,
M. S. Basunia, C. W. Beausang,
L. A. Bernstein,
D. L. Bleuel,
R. J. Casperson,
B. L. Goldblum, [......],
R. Hatarik,
R. Henderson,
R. O. Hughes,
J. Munson,
L. W. Phair,
T. J. Ross,
N. D. Scielzo,
E. Swanberg,
I. J. Thompson,
M. Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: The neutron-induced fission cross section of 238Pu was determined using the surrogate ratio method. The (n,f) cross section over an equivalent neutron energy range 5–20 MeV was deduced from inelastic α-induced fission reactions on 239Pu, with 235U(α,α′f) and 236U(α,α′f) used as references. These reference reactions reflect 234U(n,f) and 235U(n,f) yields, respectively. The deduced 238Pu(n,f) cross section agrees well with standard data libraries up to ~10 MeV, although larger values are seen at higher energies. The difference at higher energies is less than 20%.
Phys. Rev. C. 05/2011; 83(5).
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J. M. Allmond, C. W. Beausang,
J. O. Rasmussen,
T. J. Ross,
M. S. Basunia,
L. A. Bernstein,
D. L. Bleuel,
W. Brooks,
N. Brown,
J. T. Burke, [......],
P. Fallon,
H. B. Jeppesen,
J. D. LeBlanc,
S. R. Lesher,
M. A. McMahan,
D. A. Meyer,
L. Phair,
N. D. Scielzo,
S. R. Stroberg,
M. Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: A segmented Si telescope and HPGe array is used to study the 156Gd(p,d-γ)155Gd direct reaction by d-γ and d-γ-γ coincidence measurements using 25-MeV protons. The present investigation is the first time that this N=91 nucleus and the N=90 region—which is known for a rapid change from vibrational to rotational character, several low-lying 0+ states in the even-even nuclei, and large Coriolis (ΔΩ=1) plus ΔN=2 mixing in the even-odd nuclei—have been studied by particle-γ coincidence following a direct reaction with light ions. Gamma-ray energies and branches, excitation energies, angular distributions, and cross sections are measured for states directly populated in the (p,d) reaction. A new low-energy doublet state at 592.46 keV (previously associated with the K=0⊗3/2-[521] bandhead) and several new γ-ray transitions (particularly for states with excitation energies >1 MeV) are presented. Most notably, the previous ν 7/2+[404] systematics at and around the N=90 transition region are brought into question and reassigned as ν 5/2+[402]. This reassignment makes the ν 1/2+[400], ν 3/2+[402], and ν 5/2+[402] orbitals, which originate from the 3s1/2, 2d3/2, and 2d5/2 spherical states, respectively, responsible for the three largest cross sections to positive-parity states in the (p,d)155Gd direct reaction. These three steeply upsloping orbitals undergo ΔN=2 mixing with their N=6 orbital partners, which are oppositely sloped with respect to deformation. The presence of these steeply sloped and crossing orbitals near the Fermi surface could weaken the monopole pairing strength and increase the quadrupole pairing strength of neighboring even-even nuclei, which would bring ν 2p-2h 0+ states below 2Δ. Indeed, this could account for a large number of the low-lying 0+ states populated in the (p,t)154Gd direct reaction.
Phys. Rev. C. 06/2010; 81(6).
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N. D. Scielzo,
J. E. Escher,
J. M. Allmond,
M. S. Basunia, C. W. Beausang,
L. A. Bernstein,
D. L. Bleuel,
J. T. Burke,
R. M. Clark,
F. S. Dietrich, [......],
J. Gibelin,
B. L. Goldblum,
S. R. Lesher,
M. A. McMahan,
E. B. Norman,
L. Phair,
E. Rodriquez-Vieitez,
S. A. Sheets,
I. J. Thompson,
M. Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: The surrogate nuclear reaction method can be used to determine neutron-induced reaction cross sections from measured decay properties of a compound nucleus created using a different reaction and calculated formation cross sections. The reliability of (n,γ) cross sections determined using the Weisskopf-Ewing and ratio approximations are explored for the 155,157Gd(n,γ) reactions. Enriched gadolinium targets were bombarded with 22-MeV protons and γ rays were detected in coincidence with scattered protons using the Silicon Telescope Array for Reaction Studies/Livermore-Berkeley Array for Collaborative Experiments (STARS/LiBerACE) silicon and germanium detector arrays. The γ-emission probabilities for the 154,156,158Gd compound nuclei were measured at excitation energies up to 12 MeV. It is found that the approximations yield results that deviate from directly measured 155,157Gd(n,γ) cross sections at low energies. To extract reliable cross sections, a more sophisticated analysis should be developed that takes into account angular-momentum differences between the neutron-induced and surrogate reactions.
Phys. Rev. C. 03/2010; 81(3).
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J. J. Ressler,
J. A. Caggiano,
C. J. Francy,
P. N. Peplowski,
J. M. Allmond, C. W. Beausang,
L. A. Bernstein,
D. L. Bleuel,
J. T. Burke,
P. Fallon,
A. A. Hecht,
D. V. Jordan,
S. R. Lesher,
M. A. McMahan,
T. S. Palmer,
L. Phair,
N. D. Scielzo,
P. G. Swearingen,
G. A. Warren,
M. Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: Short-lived isomers in fission fragments following bombardment of 45-MeV 6Li on 232Th were examined. Isomers in the A~95,122, and 132 mass regions were observed. New isomeric decays were observed in 121In [T1/2=17(2) μs], 123In (T1/2≳100 μs), and 125Sb [T1/2=25(4) μs]. These isomers are suggested to arise from ν(h11/2⊗d3/2)7- and ν(h11/2⊗s1/2)5- neutron core excitations coupling with the valence proton.
Phys. Rev. C. 01/2010; 81(1).
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H. B. Jeppesen,
R. M. Clark,
K. E. Gregorich,
A. V. Afanasjev,
M. N. Ali,
J. M. Allmond, C. W. Beausang,
M. Cromaz,
M. A. Deleplanque,
I. Dragojević, [......],
M. A. Garcia,
J. M. Gates,
S. Gros,
I. Y. Lee,
A. O. Macchiavelli,
S. L. Nelson,
H. Nitsche,
L. Stavsetra,
F. S. Stephens,
M. Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: Two isomeric states have been identified in 255Lr. The decay of the isomers populates rotational structures. Comparison with macroscopic-microscopic calculations suggests that the lowest observed sequence is built upon the [624]9/2+ Nilsson state. However, microscopic cranked relativistic Hartree-Bogoliubov (CRHB) calculations do not reproduce the moment of inertia within typical accuracy. This is a clear challenge to theories describing the heaviest elements.
Phys. Rev. C. 09/2009; 80(3).
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J. M. Allmond,
L. A. Bernstein, C. W. Beausang,
L. Phair,
D. L. Bleuel,
J. T. Burke,
J. E. Escher,
K. E. Evans,
B. L. Goldblum,
R. Hatarik,
H. B. Jeppesen,
S. R. Lesher,
M. A. McMahan,
J. O. Rasmussen,
N. D. Scielzo,
M. Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: The internal surrogate ratio method allows for the determination of an unknown cross section, such as (n,γ), relative to a better-known cross section, such as (n,f), by measuring the relative exit-channel probabilities of a surrogate reaction that proceeds through the same compound nucleus. The validity of the internal surrogate ratio method is tested by comparing the relative γ and fission exit-channel probabilities of a 236U* compound nucleus, formed in the 235U(d,p) reaction, to the known 235U(n,γ) and (n,f) cross sections. A model-independent method for measuring the γ-channel yield is presented and used.
Phys. Rev. C. 05/2009; 79(5).
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H. B. Jeppesen,
I. Dragojević,
R. M. Clark,
K. E. Gregorich,
M. N. Ali,
J. M. Allmond, C. W. Beausang,
D. L. Bleuel,
M. Cromaz,
M. A. Deleplanque, [......],
H. L. Liu,
A. O. Macchiavelli,
S. L. Nelson,
H. Nitsche,
J. R. Pavan,
L. Stavsetra,
F. S. Stephens,
M. Wiedeking,
R. Wyss,
F. R. Xu
[show abstract]
[hide abstract]
ABSTRACT: Excited states in Rf256 were populated via the Pb208(Ti50,2n)
fusion-evaporation reaction. Delayed γ-ray and electron
decay spectroscopy was performed and three isomeric states in Rf256 have
been identified. A fourth low-energy nonyrast state was identified from
the γ-ray decay of one of the higher lying isomers. The states are
interpreted as multi-quasiparticle excitations.
Physical Review C 02/2009; 79(3):31303. · 3.31 Impact Factor
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S R Lesher,
J T Burke,
L A Bernstein,
H Ai, C W Beausang,
D L Bleuel,
R M Clark,
F S Dietrich,
J E Escher,
P Fallon, [......],
B L Goldblum,
I Y Lee,
A O Macchiavelli,
M A Mcmahan,
K J Moody,
E B Norman,
L Phair,
E Rodriguez-Vieitez,
N D Scielzo,
M Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: In the Surrogate Method, the measured decay probability of a compound nucleus formed via a direct reaction is used to extract the cross section for a reaction with a different entrance channel that proceeds through the same compound nucleus. An extension of the Surrogate Method, the Surrogate Ratio Method (SRM), uses a ratio of measured decay probabilities to infer an unknown cross section relative to a known one. To test the SRM we compare the direct-reaction-induced fission probability ratio of 234 U(α, α f) to 236 U(α, α f) with the ratio of cross sections of 233 U(n, f) to 235 U(n, f). These ratios were found to be in agreement over an equivalent neutron energy range of 0.4–18 MeV.
01/2009; 0446097987(25).
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H B Jeppesen,
I Dragojevic,
R M Clark,
K E Gregorich,
M N Ali,
J M Allmond, C W Beausang,
D L Bleuel,
M Cromaz,
M A Deleplanque, [......],
H L Liu,
A O Macchiavelli,
S L Nelson,
H Nitsche,
J R Pavan,
L Stavsetra,
F S Stephens,
M Wiedeking,
R Wyss,
F R Xu
Phys.Rev. C. 01/2009; 79:031303.
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J. T. Burke,
L. A. Bernstein,
N. D. Scielzo,
D. L. Bleuel,
S. R. Lesher,
J. Escher,
L. Ahle,
F. S. Dietrich,
R. D. Hoffman,
E. B. Norman, [......],
E. Rodriguez‐Vieitez,
M. Wiedeking,
B. F. Lyles, C. W. Beausang,
J. M. Allmond,
H. Ai,
J. A. Cizewski,
R. Hatarik,
P. D. O'Malley,
T. Swan
[show abstract]
[hide abstract]
ABSTRACT: Over the past three years we have studied various surrogate reactions (d,p), (3He,t), (α,α′) on several uranium isotopes 234U, 235U, 236U, and 238U. An overview of the STARS∕LIBERACE surrogate research program as it pertains to the actinides is discussed. A summary of results to date will be presented along with a discussion of experimental difficulties encountered in surrogate experiments and future research directions.
AIP Conference Proceedings. 04/2008; 1005(1):96-100.
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S. R. Lesher,
L. A. Bernstein,
H. Ai, C. W. Beausang,
D. Bleuel,
J. T. Burke,
R. M. Clark,
P. Fallon,
J. Gibelin,
I. Y. Lee,
B. F. Lyles,
A. O. Macchiavelli,
M. A. McMahan,
K. J. Moody,
E. B. Norman,
L. Phair,
E. Rodriguez‐Vieitez,
M. Wiedeking
[show abstract]
[hide abstract]
ABSTRACT: We measured the ratio of the fission probabilities of 234U∗ relative to 236U∗ formed via an (α,α′) direct reactions using the STARS array at the 88‐inch cyclotron at the Lawrence Berkeley National Laboratory. This ratio has a shape similar to the ratio of neutron capture probabilities from 233U(n,f) and 235U(n,f), indicating the alpha reactions likely formed a compound nucleus. This result indicates that the ratios of fission exit channel probabilities for two actinide nuclei populated via (α,α′) can be used to determine an unknown fission cross section relative to a known one. The validity of the External Surrogate Ratio Method (ESRM) is tested and the results support the conclusions of Burke et al. [1].
AIP Conference Proceedings. 04/2008; 1005(1):113-115.
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B Fant,
B Cederwall,
J Cederkäll,
L O Norlin,
R Wyss,
P Fallon, C W Beausang,
P A Butler,
J W Roberts,
A M Bruce,
D M Cullen,
S M Mullins,
R J Poynter,
R Wadsworth,
M A Riley,
W Korten,
M J Piiparinen
[show abstract]
[hide abstract]
ABSTRACT: 195Pb was investigated utilizing the reactions 164Dy(36S, 5n)195Pb and 164Dy(34S, 3n)195Pb at beam energies of 170 and 160 MeV respectively. Two new dipole bands which feed into the yrast 25/2+ state, were found in 195Pb. The connection between the bands and the spherical states was established and thus spins and energies of the involved collective states were determined. The deformation is understood as mainly due to excitations of protons across the Z = 82 shell gap. The observed backbends are interpreted as alignment of i13/2 neutrons.
Physica Scripta 01/2007; 1995(T56):245. · 1.20 Impact Factor
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F Azaiez,
J Duprat,
J F Sharpey-Schafer,
M Aïche,
G Bastin, C W Beausang,
C Bourgeois,
R M Clark,
I Deloncle,
R Duffait, [......],
Y Le Coz,
M Meyer,
N Perrin,
N Poffe,
M G Porquet,
N Redon,
H Sergolle,
C Schuck,
J Simpson,
R Wadsworth
[show abstract]
[hide abstract]
ABSTRACT: Recent data from the EUROGAM array have revealed dipole transitions linking signature partner superdeformed bands in 194Tl and 195Tl nuclei. Measurements of the decay branching ratios, taken together with the average quadrupole moment of the neighboring superdeformed nuclei, enable the absolute M1 strengths to be determined. From these data and using the strong coupling model, we find that two SD bands in 195Tl are due to the 81st proton being in the [642]5/2+ orbital and four from the six SD bands in 194Tl correspond to a configuration where the intrinsic spins of the single proton and single neutron are aligned.
Physica Scripta 01/2007; 1995(T56):35. · 1.20 Impact Factor
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Y Le Coz,
A Astier,
R Béraud,
R Duffait,
M Meyer,
N Redon,
G Bastin,
I Deloncle,
B Gall,
F Hannachi, [......],
G Smith,
H Hübel,
P Willsau,
G de France,
I Ahmad,
M Carpenter,
R Henry,
R V F Janssens,
T L Khoo,
T Lauritsen
[show abstract]
[hide abstract]
ABSTRACT: The 192Hg nucleus has been produced via the 36S(160Gd, 4n) reaction at a beam energy of 159 MeV. The γ-rays have been detected with the multi-detector array EUROGAM phase 1. The level scheme has been extended up to 10.4 MeV excitation energy and spin 34. Two new structures, composed of competing ΔI = 1 and ΔI = 2 transitions, have been observed and, for the first time in Mercury isotopes, some links with the previously known low-lying states have been established. These experimental results are discussed in terms of mean-field Hartree-Fock plus BCS calculations and the new bands are proposed to originate from deformation-aligned quasi-proton excitations. π(i13/2 * h9/2)kπ=11 and π(h9/2)2kπ=8+ coupled to rotation-aligned quasi-neutrons v(i13/2)n and quasi-proton π(h11/2)2 excitations.
Physica Scripta 01/2007; 1995(T56):234. · 1.20 Impact Factor
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N. Nica,
G. Duchêne,
V. E. Iacob,
J. Dudek,
F. A. Beck,
Th. Byrski,
D. Curien,
G. de France,
B. Haas,
B. Kharraja, [......],
M. Aïche,
M. M. Aléonard,
J. F. Chemin, C. W. Beausang,
S. Clarke,
P. J. Dagnall,
M. Smith,
P. J. Twin,
J. Simpson,
M. A. Bentley
[show abstract]
[hide abstract]
ABSTRACT: The high-spin decay scheme of 155Er, known previously, has been considerably extended by using the EUROGAM II γ-ray array. The so-called quasi-isotropic gating data-analysis method, capable of providing spin and parity assignments with triple or quadruple coincidence data has been used. With such coincidence information, we have determined γ-ray angular distributions, DCO ratios, and linear polarizations for many of the observed transitions. The level scheme is interpreted by using the particle-hole analysis based on the deformed Woods-Saxon potential and the monopole pairing interaction. The results indicate that at ∼12.3 MeV excitation energy, all nine valence particles around the 64146Gd82 core exhaust the maximum spin of I=79/2ħ. At higher spin, relatively high-energy transitions, of the order of ∼1.5 MeV, related to the breaking of the proton or neutron cores are observed. According to the calculations, this corresponds to an oblate-shape polarization of the nucleus with quadrupole deformation β2∼-0.12.
Phys. Rev. C. 08/2001; 64(3).
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[show abstract]
[hide abstract]
ABSTRACT: High-spin states in neutron-rich nuclei, populated following deep-inelastic multi-nucleon transfer, have been studied using
the GAMMASPHERE array at the LBNL, USA. A 64Ni beam at an energy ∼ 15% above the Coulomb barrier was incident upon a thick 208Pb target, leading to the population of more than 130 different nuclei. The strongest channels correspond to nuclei close
to the projectile and target, although transfer of up to 50 nucleons has been observed. New high-spin states in neutron-rich
60,62Fe and 68,70,72Zn nuclei have been observed. Some limitations of this method of high-spin spectroscopy are discussed, including the apparent
difficulty of populating odd-odd and odd-even isotopes via this type of reaction. The data have been searched for superdeformed
(SD) states in the A = 190-200 region, but no evidence for their presence has been found.
European Physical Journal A 10/2000; 9(2):183-189. · 2.19 Impact Factor
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M A Bentley, C W Beausang,
P J Twin,
P J Dagnall,
A Atac,
F A Beck,
T Byrski,
S Clarke,
D M Curien,
G Duchene, [......],
B Herskind,
B Haas,
J C Lisle,
B M Nyako,
J Nyberg,
E S Paul,
J Simpson,
J Styczen,
J P Vivien,
K Zuber
[show abstract]
[hide abstract]
ABSTRACT: The Eurogam I gamma -ray array has been used to search for the linking transitions between the superdeformed (SD) and normal deformed states in 152Dy. Triple gamma -ray coincidence data were analysed by employing the technique of summation of discrete gamma -rays observed in coincidence with the transitions in the lowest energy (yrast) SD band in 152Dy. Several high energy peaks have been observed in the spectrum of the summed gamma -rays and these are consistent with decay paths between the two structures. Analysis of these data and of single gamma -ray spectra confirm that the decay is highly fragmented and that decays occur through a quasi-continuum of states between the SD and normal deformed minima.
Journal of Physics G Nuclear and Particle Physics 12/1998; 21(4):L21. · 4.18 Impact Factor
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E S Paul,
R Ma, C W Beausang,
S A Forbes,
D B Fossan,
J Gizon,
J R Hughes,
Y Liang,
S M Mullins,
P J Nolan,
W F Piel Jr,
R J Poynter,
P H Regan,
R Wadsworth,
N Xu
[show abstract]
[hide abstract]
ABSTRACT: Electromagnetic properties of the negative-parity yrast bands of the N=75 isotones ranging from barium to gadolinium (56<or=Z<or=64) are summarized. Experimental E2/M1 multipole mixing ratios for inband Delta I=1 transitions have been extracted up through the first band crossing, allowing the evaluation of B(M1; I to I-1)/B(E2; I to I-1), B(M1; I to I-1)/B(E2; I to I-2) and B(E2; I to I-1)/B(E2; I to I-2) ratios of reduced transition probabilities for both the nu h11/2 and nu h11/2(X)( pi h11/2)2 configurations. The results obtained at low spin provide evidence for triaxial nuclear shapes, while at high spin the data are consistent with axially symmetric shapes.
Journal of Physics G Nuclear and Particle Physics 12/1998; 17(5):605. · 4.18 Impact Factor
