SIER, Stimulated Isomer Energy Release
The history, 1939-2000
Center for Quantum Electronics
The University of Texas at Dallas
Roots of SIER - 1939
Before 1939 there was a simple model for electromagnetic excitation of charges in a nucleus.
Absorption of an X-ray photon would promote a charge up a ladder of excited states of a “band”.
Spontaneous emission of g-photons would immediately relax it back to the ground state.
Roots of SIER - 1939
In 1939 Bremsstrahlung X-rays were used to excite a “gateway” (intermediate) level “between” bands.
It decayed immediately to a level in an isomeric band.
g – photons were detected from transitions in the GSB after a statistical time lag.
Measurements could be made free from noise and scattered X-rays.
50 Years of “Progress”
In the next 50 years about 50 papers were published extending the original discovery.
We did a significant fraction of that 50 in the last 2-3 yrs of the period.
It was a difficult experiment.
Particle beams could be focused, X-ray photons could not be focused on a target.
Induced g Fluorescence
From 1987 to 1991 we focused upon absolute calibration of g fluorescence.
No fitted parameters.
Four Bremsstrahlung sources in 4 labs in 2 countries were used.
Sr was chosen as benchmark.
All nuclear transition data
for theoretical comparisons were taken from literature.
SIER – First Experiment
The First Achievement - 1988
Ta Cross Sections
1995 NATO - ARW
Isomer systematics at the NATO ARW
An experimental proof was proposed
1996 - SIER proven with
Design Estimates – a triggering
Using recommended upper limits (RUL’s) for nuclear processes, the Orsay
experimental design team estimated that in the 3 days the best case would yield ~50 events.
Orsay students agreed to analyze 50 coincident events aside from regular duties.
Figure shows 16,593 events.
Status of SIER - 1997
Proven with X-rays for
Ta at NATO-ARW.
Unprecedented cross sections.
100 X interaction rates for GS nuclei with X-rays.
Demonstrated with a-particles for
Cross sections larger by ~16593/50 than accepted maxima.
SIER requires only 0-300 keV from a-particles.
SIER is immediate and bypasses 4 s time lag found in spontaneous decay.
“New” lines must be expected in the g-spectra of SIER.
Dental X-ray Results, Evaluation
As expected from the Orsay results, evidence of SIER included:
A new line at ~130 keV not found in spontaneous decay.
Coincidence in prompt emission of the 130 keV photons and those at 213 keV that otherwise are delayed about 4 s when emitted spontaneously.
Results from attenuation of X-rays with high-pass filters (Al foil) proved that the part of the Bremsstrahlung for E< 20 keV was necessary for SIER.
A next phase was planned to use tunable, monochromatic X-rays from SR sources to measure the excitation function for SIER.