Search for the Exotic Wobbling Mode in 171Re

MIDN 1/C Eowyn Pedicini, USN

Advisers: Professor Daryl Hartley

LT Brian Cummings, USN

OutlineOutline

MotivationMotivation Experimental DetailsExperimental Details Data Preparation/AnalysisData Preparation/Analysis ResultsResults Conclusion and Future WorkConclusion and Future Work

Symmetry in NucleiSymmetry in Nuclei

Most nuclei have at least one axis of symmetryMost nuclei have at least one axis of symmetry

Five nuclei have been found to be Five nuclei have been found to be asymmetricasymmetric

(Doorknob)(Football)

EXPERIMENTAL DETAILSEXPERIMENTAL DETAILS

Rotating Compound Nucleus (175Re)

Heavy Ion Reaction

Beam Nucleus (55Mn) Target Nucleus (120Sn)

4 neutrons boil off

Nucleus emits γ rays to slow spin

120Sn + 55Mn 175Re 171Re + 4n + γ

GammasphereGammasphere Germanium detectors Germanium detectors

detect detect γγ rays in rays in coincidence (120 ns)coincidence (120 ns)Coincidence event is Coincidence event is

where multiple where multiple detectors fire at oncedetectors fire at once

100 detectors to get 100 detectors to get full coveragefull coverage

TARGETBEAM

LIN

E

Data PreparationData Preparation Detectors must be checked against each other Detectors must be checked against each other

to ensure accuracy and consistencyto ensure accuracy and consistency Calibrate the detectors with standard Calibrate the detectors with standard γγ-ray -ray

sourcessources Sort into Blue databaseSort into Blue database

3-fold up to 15-fold events saved in files3-fold up to 15-fold events saved in files

Detector CalibrationDetector Calibration

y = -3.307x10-7*x2 + 6.675x10-1*x - 2.851x10-1

Data PreparationData Preparation Detectors must be checked against each other Detectors must be checked against each other

to ensure accuracy and consistencyto ensure accuracy and consistency Calibrate the detectors with standard Calibrate the detectors with standard γγ-ray -ray

sourcessources Sort into Blue databaseSort into Blue database

3-fold up to 15-fold events saved in files3-fold up to 15-fold events saved in files

Data Preparation (cont.)Data Preparation (cont.)

Determine efficiency of detectorsDetermine efficiency of detectorsNot constant for all energiesNot constant for all energies

Energy (keV)Energy (keV)

Rel

ativ

e E

ffic

ienc

yR

elat

ive

Eff

icie

ncy

Correction for Doppler ShiftsCorrection for Doppler Shifts

E (E (θθ) =E) =Eoo(1+(1+ββcos(cos(θθ))))

ββ = (speed of nucleus)/(speed of light) = (speed of nucleus)/(speed of light)

θθ = Angle at which detectors were relative = Angle at which detectors were relative to targetto target

E (E (θθ) = hf) = hf

Doppler Shift Corrections

y = 29.567x + 1024.1

R2 = 0.9993

y = 26.663x + 924.8

R2 = 0.9998

y = 23.193x + 802.92

R2 = 0.9998

y = 15.355x + 532.06

R2 = 0.9998500

600

700

800

900

1000

1100

-1 -0.5 0 0.5 1

cos(θ)

En

erg

y (k

eV)

1

2

3

4

v = 0.0289 c

Band ConstructionBand Construction

As nucleus slows, it As nucleus slows, it emits discrete sequence emits discrete sequence of γ raysof γ rays

Which sequence do the Which sequence do the γ rays go in? In what γ rays go in? In what order?order?

Coincidence matrix Coincidence matrix created from the Blue created from the Blue database database

GatingGating

Level scheme Level scheme was built using was built using “gates” in the “gates” in the coincidence coincidence matrixmatrix

Construction of Construction of 171171Re Level SchemeRe Level Scheme

Shell ModelShell Model

Nucleons are arranged in shells (sNucleons are arranged in shells (s1/21/2, d, d3/23/2, , etc.etc.))

Nucleons paired in time-reversed orbitsNucleons paired in time-reversed orbitsAngular momentum sums to zeroAngular momentum sums to zero

171171Re has 96 neutrons and 75 protonsRe has 96 neutrons and 75 protons Different protons can be unpairedDifferent protons can be unpaired

Different protons give rise to different sequencesDifferent protons give rise to different sequences

Configuration AssignmentsConfiguration Assignments

Alignment (Alignment (iixx)), is the amount of angular , is the amount of angular

momentum of unpaired particle about the momentum of unpaired particle about the rotation axisrotation axis

ix

Alignment PlotsAlignment Plots

ShellShelliixx

Expected Expected (ħ)(ħ)

Type of Type of BandBand

hh11/211/2 11Strongly Strongly CoupledCoupled

dd5/25/2 00Strongly Strongly CoupledCoupled

hh9/29/2 3-43-4 Weakly Weakly CoupledCoupled

dd3/23/2 00 DecoupledDecoupled

dd3/23/2

(AB)(AB)1010

DecoupledDecoupled

ii13/213/2 66 DecoupledDecoupled

h9/2 d3/2 i13/2 d3/2 (AB) d5/2 h11/2

Configuration AssignmentsConfiguration AssignmentsWobbling band?

• Based on i13/2 proton

• Angular momentum off-axis• Nucleus “wobbles” like an

asymmetric top

What is wobbling?i13/2 band

Wobbling band

S. W. Ødegård et al., Physical Review Letters 86, 5866 (2001).

163Lu

History of WobblingHistory of Wobbling First found in First found in 163163LuLu Subsequently found in Subsequently found in 161,165,167161,165,167Lu (N~94)Lu (N~94) Not found in several Ta, Hf, Tm isotopesNot found in several Ta, Hf, Tm isotopes Recently found in Recently found in 167167Ta (N=94)Ta (N=94)

Is Band 6 a Wobbling Band?Is Band 6 a Wobbling Band?

Alignment tracks that of Alignment tracks that of the ithe i13/213/2 band, but does band, but does

not match exactlynot match exactly Moment of inertia also Moment of inertia also

follows the ifollows the i13/213/2 band band

Not likely that Band 6 is Not likely that Band 6 is a wobbler, but if it is, it a wobbler, but if it is, it is different from all is different from all other observed wobblersother observed wobblers

i13/2 bandwobbling band?

163Lu171Re

Future WorkFuture Work

Questions still remain as to whether Questions still remain as to whether 171171Re has Re has an asymmetric nucleusan asymmetric nucleus

Need another experiment (run for several Need another experiment (run for several days) to gather enough datadays) to gather enough data

AcknowledgmentsAcknowledgments

Professor HartleyProfessor Hartley LT CummingsLT Cummings NSFNSF

Questions?Questions?

PACE Calculations

55Mn + 120Sn

0

20

40

60

80

100

120

140

230 240 250 260 270 280

Beam Energy (MeV)

Cro

ss S

ecti

on

(m

b)

172Re (3n)

171Re (4n)

170Re (5n)

169Re (6n)

172W (p2n)

171W (p3n)

170W (p4n)

169W (p5n)

Gain Shifts

Angular Correlation Ratios

Time-reversed OrbitsTime-reversed Orbits

Shell ModelShell Model

Previous Level Scheme for Previous Level Scheme for 171171ReRe

Spectra for Bands 4 and 5Spectra for Bands 4 and 5

Configuration AssignmentsConfiguration Assignments

ix(ω) = Ix(ω) – )(refxI

222

1 )()( KII x

Ixref(ω) = ωJ0 + ω3J1

Band CrossingsBand Crossings

Band Crossings (cont.)Band Crossings (cont.)

Band Signature Band Crossing β2

    (MeV)  

h9/2

+1/2 0.277 0.294

-1/2 0.241 0.294

i13/2 +1/2 0.307 0.333

h11/2

+1/2 0.234 0.270

-1/2 0.234 0.270

d5/2

+1/2 0.202 0.210

-1/2 0.200 0.210

Identifying a Wobbling BandIdentifying a Wobbling Band

Similar moment of inertia (J) as iSimilar moment of inertia (J) as i13/213/2 band band

Hundreds, if not thousands of gates will be Hundreds, if not thousands of gates will be takentaken

165Lui13/2

Wobbling band