J. De Raedt

Precise energy determination of the first excited state in 137Cs for absolute energy calibration in muonic atoms

Abstract The energy of the γ-ray de-exciting the 5 2 1 + level of 137 Cs was determined with high accuracy in an isotope separator on-line experiment. The result is (455.490±0.003) keV as referred to the 198 Au energy standard of (411.794±0) keV. Knowledge of this energy is important for the determination of muonic X-ray energies in Ba as a test of the validity of quantum electrodynamics. In addition, the 4 1 + →2 1 + transition in 138 Cs was determined to be (462.785±0.005) keV.

Problems related to the use of annihilation radiation for precision energy calibration of Ge(Li) detectors

Abstract The energy of positron annihilation radiation emanating from several materials was measured, using recently established energies of the 198Au and 192Ir γ-rays for calibration. Corrections for the binding energy of positrons and electrons were applied. A peak fitting routine was used which took into account the background “step” under the peak, and used the possibility that only a part of the detector contains charge-carrier traps. We could reproduce the electron rest mass energy (corrected for binding energies) to within ±10 eV, in some “well-behaved” metals even to within ±5 eV.

A simple algorithm for background corrections to γ-γ angular correlation measurements

Abstract A simple algorithm is proposed for the subtraction of background below peaks in angular correlation measurements.

Spin and parity assignment of the 1924 keV level in 131I

The spin and parity of the 1924 keV level in 131I are determined uniquely by angular correlation measurement of the 1151 keV-774 keV cascade and conversion coefficient measurement of the 278 keV transition to be 11/2-.

A computerized piezoelectric Mössbauer spectrometer

mode. A system ensuring the source motion by a piezoelectric specimen oscillating at its resonance should be less sensitive to external noise because it has a much higher Q-value compared to loudspeaker-type drives. As we could demonstrate that the piezoelectric ceramic still can be used as a MOssbauer spectrometer, even at the temperature of liquid helium, the spectrometer is suitable for low-temperature work and can easily be incorporated into a small cryostat. The maximum velocity, limited by the maximum permissible strain of the piezoceramic, should be about ] m/s. In resonance, voltage and current of the piezoelectric bar and the velocity of the endfaces are sinusoidal, and in phase. From a measurement of the current one can obtain the velocity of the endface4). The velocity-scanning data accumulation acts as follows. The time interval between a gamma ray leaving the source and a time reference point returning periodically with the oscillation period of the transducer is measured. The length of this time interval defines the velocity of the source when the M6ssbauer gamma left and corresponds to an address in the computer memory where one event is added to the contents. The maximum number of addresses can be 256 or 512.

The angular correlation of the 459.7−27.7 kev γ-γ-cascade in129I and its use for a TDPAC

In contrast to earlier measurements, the angular correlation coefficient of the 459.7−27.7 keVγ-γ cascade in129I has been found to be consistent with the mixing ratios of the transitions and equal toA22=−0.0305±0.0037. Further, it is shown that this cascade can be used for time differential hyperfine interaction studies.