Search for the Exotic Wobbling Mode in 171 Re MIDN 1/C Eowyn Pedicini, USN Advisers: Professor Daryl...
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Transcript of Search for the Exotic Wobbling Mode in 171 Re MIDN 1/C Eowyn Pedicini, USN Advisers: Professor Daryl...
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