D. E. Gonzalez Trotter

New Measurement of the {sup 1}S {sub 0} Neutron-Neutron Scattering Length Using the Neutron-Proton Scattering Length as a Standard

The present paper reports high-accuracy cross-section data for the 2 H(n,nnp) reaction in the neutron-proton (np) and neutron-neutron (nn) final-state-interaction (FSI) regions at an incident mean neutron energy of 13.0 MeV. These data were analyzed with rigorous three-nucleon calculations to determine the 1 S0 np and nn scattering lengths, anp and ann. Our results are ann = -18.7±0.6 fm and anp = -23.5 ±0.8 fm. Since our value for anp obtained from neutron-deuteron (nd) breakup agrees with that from free np scattering, we conclude that our investigation of the nn FSI done simultaneously and under identical conditions gives the correct value for ann. Our value for ann is in agreement with that obtained in � − d measurements but disagrees with values obtained from earlier nd breakup studies.

Verification of the space-star anomaly in nd breakup

Abstract Cross-section measurements of a collinear configuration, the space-star and the coplanar-star configurations in nd breakup at E n = 13.0 MeV are reported. The present measurements for the collinear configuration are in good agreement with pd and nd data. Our coplanar-star data are consistent with theoretical predictions and resolve the reported problem with this configuration. The previously observed large discrepancy between theory and nd cross-section data for the space-star configuration is confirmed in the present work.

Modeling the axial extension of a transmission line source within iterative reconstruction via multiple transmission sources

Reconstruction algorithms for transmission tomography have generally assumed that the photons reaching a particular detector bin at a particular angle originate from a single point source. In this paper, we highlight several cases of extended transmission sources, in which it may be useful to approach the estimation of attenuation coefficients as a problem involving multiple transmission point sources. Examined in detail is the case of a fixed transmission line source with a fan-beam collimator. This geometry can result in attenuation images that have significant axial blur. Herein it is also shown, empirically, that extended transmission sources can result in biased estimates of the average attenuation, and an explanation is proposed. The finite axial resolution of the transmission line source configuration is modeled within iterative reconstruction using an expectation-maximization algorithm that was previously derived for estimating attenuation coefficients from single photon emission computed tomography (SPECT) emission data. The same algorithm is applicable to both problems because both can be thought of as involving multiple transmission sources. It is shown that modeling axial blur within reconstruction removes the bias in the average estimated attenuation and substantially improves the axial resolution of attenuation images.

Implications of the space-star anomaly in nd breakup

Abstract Cross-section measurements of six exit-channel configurations in nd breakup at 13.0 MeV are reported and compared to rigorous calculations. Except for the coplanar-star configuration, our data are consistent with previous data. The present data for all configurations, with the exception of the space star, are in good agreement with theoretical predictions. The previously observed large discrepancy between theory and data for the space-star configuration is confirmed in the present work. The inclusion of the Tucson-Melbourne 2π exchange three-nucleon force with a cutoff parameter that correctly binds the triton only changes the predicted cross section by 2%, a factor of 10 smaller than the amount needed to bring theory into agreement with data.

Resolution of discrepancy between backward angle cross-section data for neutron-deuteron elastic scattering

High-accuracy differential cross-section data for neutron-deuteron elastic scattering at centre-of-mass backward angles in the range from 140° to 178° have been measured to accuracies better than ±3% for incident neutron energies of 8.0, 10.0, and 14.0 MeV. The measurements were made by detection of the recoil deuterons and protons from a mixed CD2-CH2 foil. The new data are compared to existing data and to three-nucleon calculations with the Bonn-B nucleon-nucleon potential. We conclude that the present measurements unambiguously resolve the discrepancies among previously reported data of the same type.

Neutron–proton analyzing power at 12 MeV and inconsistencies in parametrizations of nucleon–nucleon data

Abstract We present the most accurate and complete data set for the analyzing power A y ( θ ) in neutron–proton scattering. The experimental data were corrected for the effects of multiple scattering, both in the center detector and in the neutron detectors. The final data at E n = 12.0 MeV deviate considerably from the predictions of nucleon–nucleon phase-shift analyses and potential models. The impact of the new data on the value of the charged pion–nucleon coupling constant is discussed in a model study.

Scattering length measurements from radiative pion capture and neutron-deuteron breakup

The neutron-neutron and neutron-proton {sup 1}S{sub 0} scattering lengths a{sub nn} and a{sub np}, respectively, were determined simultaneously from the neutron-deuteron breakup reaction. Their comparison with the recommended values obtained from two body reactions gives a measure of the importance of three-nucleon force effects in the three-nucleon continuum. In order to check on the result obtained for a{sub nn} from the two-body {pi}{sup {minus}}-d capture reaction, a new measurement was performed at LANL. Preliminary results of the three experiments are given.

Absolute quantitation of I-131 activity distributions using a high-resolution rotating collimator: a phantom study

The authors acquired SPECT data using a high-resolution rotating parallel-hole collimator especially designed for imaging of medium-energy radionuclides. They reconstructed images of I-131 activity distributions for a sphere inside a water-filled cylinder. Reconstructions were performed using FBP and iterative MAP/ICD methods. The MAP/ICD reconstructions with an edge-preserving convex prior provided the more accurate absolute activity distributions with better resolution (FWHM of 0.5 cm). The spheres activity and activity density were reproduced to within 5% of their known values.

Cross-section measurements of the space-star configuration in N-D breakup at 13.0 MeV

In this paper we present results for kinematically complete cross‐section measurements of the space‐star configuration in neutron‐deuteron breakup for an incident neutron energy of 13.0 MeV. These data are a subset of the results obtained in a recent experiment in which cross sections for 46 configurations were measured simultaneously. The experimental techniques are described. These new data are in good agreement with previous n‐d data but differ significantly from both rigorous n‐d calculations and proton‐deuteron breakup data.

ELECTROMAGNETIC EFFECTS AND THE LONG-STANDING THREE-NUCLEON ANALYZING POWER PUZZLE

New results for the neutron-deuteron analyzing power Ay(θ) at En = 1.2 and 1.9 MeV and their comparison to proton-deuteron data reveal a sizeable and unexpected difference which increases with decreasing center-of-mass energy. This finding calls for the theoretical treatment of a subtle electromagnetic effect presently not incorporated in rigorous three-nucleon scattering calculations, before it is justified to invoke charge-dependent three-nucleon forces and/or other new physics.