R.E. Welsh

SPECT-CT system for small animal imaging

The Detector Group at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) and the Biology, Physics, and Applied Sciences Departments at the College of William and Mary are collaborating on the development of a miniature dual modality SPECT-CT system for mouse imaging. The detector heads of the SPECT sub-system are designed to be capable of imaging the gamma- and X-ray emissions (28-35 keV) of the radioactive isotope iodine-125 (I-125). Two different sets of I-125 imaging detectors are configured on a gantry that has an open-barrel type design. One set of detector heads is based on the 1-in square Hamamatsu R5900-M64 position sensitive photomultiplier tube coupled to crystal scintillator arrays. The other detector heads configured on the gantry are two 5-in diameter Hamamatsu R3292-based compact gamma cameras. The X-ray radiographic projections are obtained using a LIXI Inc. model LF-85-503-OS X-ray imaging system that has an active area of 5.5 cm in diameter. The open-barrel shaped gantry facilitates the positioning of various mini gamma-ray imaging detectors and the X-ray system. The data acquisition and gantry control is interfaced through a Macintosh G3 workstation. Preliminary SPECT reconstruction results using the R5900 based detector are presented.

The time-of-flight system for CLAS

The time-of-flight system for the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility is described. The system, covering an area of 206-square-meters, is composed of scintillation counters 5.08 cm thick, 15 and 22 cm wide, and lengths which vary from 32 cm at the most forward angle to 450 cm at larger angles. All of the components of the system have been designed to optimize the time resolution. Event timing, achieved by leading-edge discrimination with time-walk correction, has been measured with cosmic rays, a laser pulser, and known particle interactions. The intrinsic time resolution varies from about 80 ps for the short counters to 160 ps for the longer counters. Reconstruction of interacting particles during the first period of operation yields an average time resolution for electrons of 163 ps.

An experimental study of muonic X-ray transitions in mercury isotopes☆

Abstract Muonic X-ray spectra have been measured for 198–202, 204Hg. These data have been interpreted in terms of a two parameter Fermi distribution for the charge density. We have interred the spectroscopic quadrupole moments (Qs) of some of the 2+ nuclear states. For 199Hg we have determined the spectroscopic quadrupole moments of the first two excited states and the B(E2) connecting these states to the ground state. For 201Hg the ground state quadrupole moment has been obtained as well as several other E2 moments but the interpretation of the data has been hampered by a possible incomplete knowledge of the nuclear scheme of this nucleus. The muonic isotope shifts have been measured and interpreted in terms of σRk and are compared to electronic X-ray and optical isotope shift measurements.

Measurement of X-rays from anti-protonic hydrogen and deuterium

Abstract The yields of K and L series X-rays from pp atoms and of the L series X-rays from pd atoms have been measured at gas densities of 0.25, 0.92, 2.0 and 10.0ρ STP . For pp atoms the strong interaction shift and width for the 1s state and the width of the 2p state have been measured. The results are in good agreement with the predictions of potential models.

Muonic 197Au: A test of the weak-coupling model☆

Abstract We report the measurement of the energies of various muonic atomic transitions above 500 keV in 197Au. We have used the weak-coupling model in order to analyze the hyperfine structure of 197Au. Using transitions to and from the 1s, 2s 2p and 3p levels as well as the fine structure of the 2p states and hyperfine splittings of the 2p, 3p and 3d states we have fitted our data to two deformed Fermi distributions: one with a constant skin thickness, the other with a skin thickness which varies. Both yield equally good fits. We have determined the quadrupole moment of 197Au to be 0.547±0.016 b. The model dependence of our results is discussed. The weak coupling parameters of de-Shalit Ω p , Ω 22 , Ω 20 and A 2 have been determined and are in fair agreement with Coulomb excitation results. There is also good agreement between our results and those of electron scattering.

Negative muon capture in carbon leading to specific final states

Abstract The yields of γ rays from specific final nuclear states excited following negative muon capture in 12 C have been measured. Using the values for the capture rates to excited states in 12 B and the result of an earlier experiment for the total capture to all bound states in 12 B, we obtain for the durect capture rate to the ground state of 12 B, λ( 12 B gs ) = (6.0 ± 0.4) × 10 3 s −1 . This value is in agreement with theoretical predictions, but the theoretical and experimental uncertainties permit extraction of only a rather imprecise value for the weak-magnetism coupling constant in the muon capture Hamiltonian.

K-series X-rays from anti-protonic hydrogen and deuterium

Abstract Energies and yields of K-series X-rays from pp atoms have been measured with two gas scintillation proportional detectors at target gas densities of 0.25 and 0.92 ρ STP . Values for the strong interaction shift and width of the 1s state obtained from the X-ray spectra are compared with the predictions of a variety of theoretical models. Upper limits for the yield of K-series X-rays from pd atoms have also been obtained.

New limit on muon and electron lepton number violation from K0(L) ---> mu+- e-+ decay

The most sensitive experiment to date to search for the muon and electron lepton number violating decay

X-rays from anti-protonic hydrogen and deuterium

K^0_L \to \mu^\pm e^\mp

Muonic X-ray study of the charge distribution of 165Ho

has detected no events consistent with this process. Based on this result, the 90% confidence level upper limit on the branching fraction is