Notes

Outline

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. 87Sr was chosen as benchmark. All nuclear transition data  for theoretical comparisons were taken from literature.

SIER – First Experiment

The First Achievement - 1988

180mTa Cross Sections

1995 NATO - ARW

Isomer systematics at the NATO ARW

An experimental proof was proposed

1996 - SIER proven with 178m2Hf

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. Students revolted.

Proving what

Status of SIER - 1997 Proven with X-rays for 180mTa at NATO-ARW. Unprecedented cross sections. 100 X interaction rates for GS nuclei with X-rays. Demonstrated with a-particles for 178m2Hf. 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.

Slide 16

Performance

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.