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Precise aK measurement of 197Pt a test of
internal conversion theoryMark Hernberg,
University of Iowa J.C. Hardy, N. Nica Cyclotron
Institute, Texas AM University
Spectrum Analysis

• Introduction
• Radioactive nuclei decay in numerous ways
  emitting electrons, protons, neutrons, alpha
  particles, gamma rays, x-rays, or some
  combination thereof.
• 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)

Source Preparation 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.
This source was irradiated by thermal neutron
activation at the TRIGA nuclear reactor at Texas
AM University Nuclear Science Center. 196Pt(n,
g) --gt 197mPt
Results
Counts

• Data Collection

• 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.

• 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.

197 Au
Conclusions 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.
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 (lt1) 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

Calculations wK K-shell fluorescence
yield, 0.959(4) NK, Ng total number of Kx or
g-rays found by integration of spectra eK, eg
known detector efficiency at peak energies
346.5 M4
53.1 E2
Acknowledgements Thanks to Dr. John C. Hardy and
Dr. Ninel Nica for their support and guidance
during the project. To the Texas AM Cyclotron
for giving access to a challenging and exciting
research program. And to the National Science
Foundation for its continued support of the REU
program.
197mPt nucleus decays isomerically, conserving
its atomic and mass number, to a ground state of
197Pt. This nuclear de-excitation yields two
distinct decay energies. The relative intensities
of these decays are used to calculate the ICC.
E. Schönfeld, H. Jaben, NIM A 369 (1996) 527.