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New precise a K measurement as a test of internal conversion theory

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### 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

L shell

e-

~10-18 s

K shell

g-ray

Hole

x-ray

e-

~10-17 s

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
- Impact
- Nuclear decay schemes
- Spin and parity assignments
- Transition rates
- Branching ratios
- Detector calibration

Trim excess tape to minimize impurities

Adhesive Mylar tape, 3.81 mm

Ba++(aq) + 2NO3-(aq)

Insulin

Mylar tape, 12.7 mm

139Ba Source- Layer Effects
- Attenuation calculations
- Back scattering

- Source design
- Determine number of atoms (mass of sample) required to produce desired g-ray counts
- Preparation of sources
- Obtain enriched barium
- Dilute Ba(NO3)2 in water
- Two sources, A and B

7.0 mm

0.5 in

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)

g-ray

Ka

Kb

x-rays

Impurity Analysis

x-ray impurities

29.623 keV to 42.290 keV

g-ray impurities

163.138 keV to 168.638 keV

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

Lanthanum K x-ray region

spectrum 9, scaled

Impurities:

152Eum152Sm

152Eu 152Sm

152Eum 152Eu

153Sm 153Eu

aK Calculation

- K-shell internal conversion coefficient, aK
- 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

Source A, Sept. 2005 Irradiation

Source B, July 2006 Irradiation

Theoretical Calculations

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

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