Precise aK measurement of
a test of internal conversion theory
197Pt:
Mark Hernberg, University of Iowa
J.C. Hardy, N. Nica Cyclotron Institute, Texas A&M University
Introduction
Source Preparation
•Radioactive nuclei decay in numerous ways: emitting
electrons, protons, neutrons, alpha particles, gamma
rays, x-rays, or some combination thereof.
In preparation for irradiation, a sample of 197Pt (0.7 mg)
was mixed with aqua-regia and spread manually over a
thin strip of Mylar tape to create a homogeneous film.
•During Internal Conversion nuclear de-excitation
energy is transferred directly to an atomic electron
which is then ejected from the atom. This is followed
by a characteristic x-ray emission as the ‘hole’ left by
the electron is filled. (pictured below on left)
This source was irradiated by thermal neutron
activation at the TRIGA nuclear reactor at Texas A&M
University Nuclear Science Center.
196Pt(n, g) --> 197mPt
Spectrum Analysis
Results
a K  4.24 13
Counts
Data Collection
•This process competes with gamma ray emission.
(pictured in green above)
•The Internal Conversion Coefficient (ICC) is the
calculated ratio between internal conversion and g-ray
emission.
•X and g rays emitted from
the source were measured
with an HPGe detector
Relative photopeak
efficiencies were
calibrated to 0.15%
•17 spectra recorded ~3
hours to 9 days after
activation.
Conclusions
191m Hg
191m Hg
•The clear, distinct gamma ray peak shows no sign of
interfering radiation. However, major impurities plague the
X-ray region: by the 17th spectrum there are over 10 different
instances of interfering radiation. Each impurities’
contribution to the peaks must be carefully analyzed and
subtracted from the total peak area to ensure precise results.
Why Study Internal Conversion?
Until recently ICC measurements rarely had an
uncertainty under 1%. Furthermore, various theoretical
calculations differed with experiment and each other by
a few percent, and in some cases 10% or more.
One important uncertainty in current ICC theories is
deciding the fate of the ‘hole’ left behind by the ejected
electron: is it filled immediately, or does it stay empty
throughout the conversion process? Recent experiments
have also pointed to a possible unknown factor missing
from both theories.
Precise ICC measurements (<1%) can provide a
clear verdict on the correct approach and furthermore
are useful for:
•Nuclear decay schemes
-Spin and parity assignments,
-Transition rates,
-Branching ratios
•Detector calibration
197 Au
Calculations
197mPt
nucleus decays isomerically,
conserving its atomic and mass number, to a
ground state of 197Pt. This nuclear deexcitation yields two distinct decay energies.
The relative intensities of these decays are
used to calculate the ICC.
1 NK eg
aK 
wK Ng e K
Though these results are very preliminary, the data
clearly disagree with previous experimental results
and are now consistent with theoretical calculations.
However, the data lacks the high precision shown
in measurements previously acquired with the HPGe
detector at the Cyclotron Institute. Inspection of the
spectra show that this is due to the high levels of
impurities in the source. An additional experiment
with a new 197Pt source is planned to reduce the
levels of interfering radiation.
Acknowledgements
wK = K-shell fluorescence yield, 0.959(4)*
Thanks to Dr. John C. Hardy and Dr. Ninel Nica for
their support and guidance during the project.
NK, Ng = total number of Kx or g-rays found by
integration of spectra
To the Texas A&M Cyclotron for giving access to a
challenging and exciting research program.
eK, eg = known detector efficiency at peak
*E. Schönfeld, H. Jaben, NIM A 369 (1996) 527.
energies
And to the National Science Foundation for its
continued support of the REU program.