Search for the Exotic Wobbling Mode in 171 Re MIDN 1/C Eowyn Pedicini, USN Advisers: Professor Daryl Hartley LT Brian Cummings, USN

Outline Motivation Motivation Experimental Details Experimental Details Data Preparation/Analysis Data Preparation/Analysis Results Results Conclusion and Future Work Conclusion and Future Work

Symmetry in Nuclei Most nuclei have at least one axis of symmetry Most nuclei have at least one axis of symmetry Five nuclei have been found to be asymmetric Five nuclei have been found to be asymmetric (Doorknob) (Football)

EXPERIMENTAL DETAILS

Rotating Compound Nucleus ( 175 Re) Heavy Ion Reaction Beam Nucleus ( 55 Mn) Target Nucleus ( 120 Sn) 4 neutrons boil off Nucleus emits γ rays to slow spin 120 Sn + 55 Mn 175 Re 171 Re + 4n + γ

Gammasphere Germanium detectors detect γ rays in coincidence (120 ns) Germanium detectors detect γ rays in coincidence (120 ns) Coincidence event is where multiple detectors fire at once Coincidence event is where multiple detectors fire at once 100 detectors to get full coverage 100 detectors to get full coverage TARGET BEAM LINE

Data Preparation Detectors must be checked against each other to ensure accuracy and consistency Detectors must be checked against each other to ensure accuracy and consistency Calibrate the detectors with standard γ-ray sources Calibrate the detectors with standard γ-ray sources Sort into Blue database Sort into Blue database 3-fold up to 15-fold events saved in files 3-fold up to 15-fold events saved in files

Detector Calibration y = x10 -7 *x x10 -1 *x x10 -1

Data Preparation Detectors must be checked against each other to ensure accuracy and consistency Detectors must be checked against each other to ensure accuracy and consistency Calibrate the detectors with standard γ-ray sources Calibrate the detectors with standard γ-ray sources Sort into Blue database Sort into Blue database 3-fold up to 15-fold events saved in files 3-fold up to 15-fold events saved in files

Data Preparation (cont.) Determine efficiency of detectors Determine efficiency of detectors Not constant for all energies Not constant for all energies Energy (keV) Relative Efficiency

Correction for Doppler Shifts E ( θ ) =E o (1+ β cos( θ )) β = (speed of nucleus)/(speed of light) θ = Angle at which detectors were relative to target E ( θ ) = hf v = c

Band Construction As nucleus slows, it emits discrete sequence of γ rays As nucleus slows, it emits discrete sequence of γ rays Which sequence do the γ rays go in? In what order? Which sequence do the γ rays go in? In what order? Coincidence matrix created from the Blue database Coincidence matrix created from the Blue database

Gating Level scheme was built using “gates” in the coincidence matrix Level scheme was built using “gates” in the coincidence matrix

Construction of 171 Re Level Scheme

Shell Model Nucleons are arranged in shells (s 1/2, d 3/2, etc.) Nucleons are arranged in shells (s 1/2, d 3/2, etc.) Nucleons paired in time-reversed orbits Nucleons paired in time-reversed orbits Angular momentum sums to zero Angular momentum sums to zero 171 Re has 96 neutrons and 75 protons 171 Re has 96 neutrons and 75 protons Different protons can be unpaired Different protons can be unpaired Different protons give rise to different sequences Different protons give rise to different sequences

Configuration Assignments Alignment (i x ), is the amount of angular momentum of unpaired particle about the rotation axis Alignment (i x ), is the amount of angular momentum of unpaired particle about the rotation axis ixix

Alignment Plots Shell i x Expected (ħ) Type of Band h 11/2 1 Strongly Coupled d 5/2 0 Strongly Coupled h 9/2 3-4 Weakly Coupled d 3/2 0Decoupled d 3/2 (AB) 10Decoupled i 13/2 6Decoupled

h 9/2 d 3/2 i 13/2 d 3/2 (AB)d 5/2 h 11/2 Configuration Assignments Wobbling band?

Based on i 13/2 proton Angular momentum off-axis Nucleus “wobbles” like an asymmetric top What is wobbling? i 13/2 band Wobbling band S. W. Ødegård et al., Physical Review Letters 86, 5866 (2001). 163 Lu

History of Wobbling First found in 163 Lu First found in 163 Lu Subsequently found in 161,165,167 Lu (N~94) Subsequently found in 161,165,167 Lu (N~94) Not found in several Ta, Hf, Tm isotopes Not found in several Ta, Hf, Tm isotopes Recently found in 167 Ta (N=94) Recently found in 167 Ta (N=94)

Is Band 6 a Wobbling Band? Alignment tracks that of the i 13/2 band, but does not match exactly Alignment tracks that of the i 13/2 band, but does not match exactly Moment of inertia also follows the i 13/2 band Moment of inertia also follows the i 13/2 band Not likely that Band 6 is a wobbler, but if it is, it is different from all other observed wobblers Not likely that Band 6 is a wobbler, but if it is, it is different from all other observed wobblers i 13/2 band wobbling band?

163 Lu 171 Re

Future Work Questions still remain as to whether 171 Re has an asymmetric nucleus Questions still remain as to whether 171 Re has an asymmetric nucleus Need another experiment (run for several days) to gather enough data Need another experiment (run for several days) to gather enough data

Acknowledgments Professor Hartley Professor Hartley LT Cummings LT Cummings NSF NSF

Questions?

PACE Calculations

Gain Shifts

Angular Correlation Ratios

Time-reversed Orbits

Shell Model

Previous Level Scheme for 171 Re

Spectra for Bands 4 and 5

Configuration Assignments i x (ω) = I x (ω) – I x ref (ω) = ωJ 0 + ω 3 J 1

Band Crossings

Band Crossings (cont.) BandSignatureBand Crossingβ2β2 (MeV) h 9/2 +1/ / i 13/2 +1/ h 11/2 +1/ / d 5/2 +1/ /

Identifying a Wobbling Band Similar moment of inertia (J) as i 13/2 band Similar moment of inertia (J) as i 13/2 band Hundreds, if not thousands of gates will be taken Hundreds, if not thousands of gates will be taken 165 Lu i 13/2 Wobbling band