Transcript New precise aK measurement as a test of electronic

New precise aK measurement as a
test of internal conversion theory
166 keV transition in 139La
Christine Balonek
Dr. John C. Hardy, Advisor
Dr. Ninel Nica, Deputy Advisor
August 3, 2006
Overview
• Internal Conversion
• 139La Decay Scheme
• 139Ba Source
• Data Collection
• Spectral Analysis
• Impurity Analysis
• K X-Ray Analysis
• aK Calculations
• Preliminary Results
• Summary
• Acknowledgements
Internal Conversion
• Nuclear de-excitation energy transferred to an electron
– Electron is emitted and followed by an x-ray
– In competition with g-ray emission
• Internal Conversion Coefficient
e
a

–
g
L shell
e-
K shell
~10-18 s
• Impact
– Nuclear decay schemes
• Spin and parity assignments
• Transition rates
• Branching ratios
– Detector calibration
Hole
x-ray
e~10-17 s
g-ray
139La
Decay Scheme
Lanthanum
Energy
(keV)
Intensity
a1
33.442
46.8 11
a2
33.034
25.7 6
b1
37.801
8.7 19
b2
38.726
2.81 6
b3
37.72
4.51 10
K x-rays
139Ba
Source
• Source design
• Layer Effects
– Determine number of atoms
(mass of sample) required to
produce desired g-ray counts
– Attenuation calculations
– Back scattering
• Preparation of sources
– Obtain enriched barium
– Dilute Ba(NO3)2 in water
– Two sources, A and B
Trim excess tape to
minimize impurities
Adhesive Mylar tape, 3.81 mm
Ba++(aq) + 2NO3-(aq)
7.0 mm
0.5 in
Insulin
Mylar tape, 12.7 mm
Source ready to be irradiated
Data collection
•
Neutron irradiation of source
– Texas A&M Nuclear Science Center
•
g and x-ray detection
– Germanium detector, Cyclotron Institute,
Texas A&M University
• Relative photopeak efficiencies calibrated
to 0.15%
– 17 spectra recorded between ~1 and
24 hours after activation
g and x-rays
151. mm
Spectral Analysis
• Source A, Sept. 2005 irradiation, spectrum 1
– 52.7 min elapsed time / 46.9 min live time (~0.6 half lives)
Impurity Analysis
x-ray impurities
29.623 keV to 42.290 keV
g-ray impurities
163.138 keV to 168.638 keV
g-ray
Ka
Kb
x-rays
K X-Ray Analysis
Spectrum 1, 0.88 hr
- largely 139La x-rays
Spectrum 9, 15.87 hr
- source impurity x-rays
K X-Ray Analysis
spectrum 1
spectrum 9, scaled
Lanthanum K x-ray region
Impurities:
152Eum
 152Sm
152Eu
 152Sm
152Eum
 152Eu
153Sm
 153Eu
aK Calculation
• K-shell internal conversion coefficient, aK
1 NK eg
aK 
w K Ng e K
•
wK = K-shell fluorescence yield
– 0.905(4)*
•
NK, Ng = total number of K x or g-rays
– Integration of spectra after removal of impurities
•
eK, eg = detector efficiency for K x or g-rays
– Known detector efficiencies at energies of interest
*E. Schönfeld, H. Jaben, NIM A 369 (1996) 527.
Preliminary Results
1 NK eg
aK 
w K Ng e K
Source A, Sept. 2005 Irradiation
 1  770291 0.8387



 0.905 3117232 1.002 
aK  
Source B, July 2006 Irradiation
 1  437196 0.8387



0
.
905
1752099
1
.
002




aK  
a K  0.228527
a K  0.230828
Theoretical Calculations
With hole : a K  0.2231
Without hole : a K  0.2225
Summary
• Successfully prepared and irradiated two enriched
139Ba sources
• Analyzed 17 spectra for impurities based on g-ray
energies and parent nuclei properties
• Performed quantitative x-ray analysis to subtract
impurities
• Calculated preliminary values for aK of 139La
• More detailed analysis of x-rays needed
– Analysis is ongoing
• Next:
196Pt
irradiation
– aK measurement for 197Au
Acknowledgements
• Dr. John C. Hardy, Advisor
• Dr. Ninel Nica, Deputy Advisor
• Hardy Research Group
– Victor Golovko, John Goodwin, Victor Iacob, Hyo In Park
• Texas A&M Cyclotron Institute REU Program
– Dr. Sherry Yennello
– Mary Ann Batson