206324920
New measurement of the charge radius of the neutron.
The neutron transmission through a thorogenic liquid {sup 208}Pb sample 2 in. thick has been measured in the neutron energy range between 0.1 and 360 eV at the ORNL neutron source ORELA. Analyzing the shape of the transmission spectra as a function of neutron energy, agreement was found with the predictions by the atomic form factor. With a sensitivity for the mean squared charge radius of the neutron {l_angle}{ital r}{sup 2}{sub {ital n}}{r_angle} as high as 3%, a very reliable and also accurate result of {l_angle}{ital r}{sup 2}{sub {ital n}}{r_angle}={minus}0.113{plus_minus}0.003{plus_minus}0.004 fm{sup 2} was extracted. For the neutron-electron scattering length we obtained {ital b}{sub {ital ne}}=({minus}1.31{plus_minus}0.03{plus_minus}0.04){times}10{sup {minus}3} fm.
117298547
Neutron widths and level spacings of Zn 64 + n
High resolution neutron total cross-section measurements on the separated isotope /sup 64/Zn have been made in energy range of few eV to about 370 keV using a pulsed neutron time-of-flight technique with a nominal resolution of 0.07 ns/m. We have analyzed the cross section data up to 370 keV using a multilevel multichannel computer code and obtained values of the resonance parameters (E/sub 0/, J/sup ..pi../, gGAMMA/sub n/). From these results we obtain the following values for the average properties of the resonance parameters: /sub l/=03.59=(plus-or-minus0.16) keV, S/sub 0/( x 10/sup 4/)=1.89 +- 0.26, and S/sub 1/( x 10/sup 4/)=0.59 +- 0.06. We have also investigated the neutron width and nearest neighbor spacing distributions for 103 s-wave resonances up to 370 keV. The neutron width distribution follows a chi-squared distribution with ..nu..=1.15 +- 0.30. We have determined values for Dyson-Mehta's ..delta../sub 3/ statistic for s-wave levels up to 300 keV as a function of energy. These are found to be in excellent agreement with the predicted values as explained in Table V. Similarly the linear coefficient of correlation between nearest neighbor spacings gives a value of rho=-0.35 in agreement with the predicted value of the random matrix model. The valuemore » for the mean p-wave level spacing is larger than expected from the (2J+1) density law, indicative of missed p-wave levels.« less
116539030
Neutron research and facility development at the Oak Ridge Electron Linear Accelerator 1970 to 1995
This report reviews the accomplishments of the first decade of operation of the Oak Ridge Electron Linear Accelerator (ORELA) and discusses the plans for the facility in the coming decade. Motivations for scientific and applied research during the next decade are included. In addition, ORELA is compared with competing facilities, and prospects for ORELA's improvement and even replacement are reported. Development efforts for the next few years are outlined that are consistent with the anticipated research goals. Recommendations for hardware development include improving the electron injection system to give much larger short-pulse currents on a reliable basis, constructing an Electron Beam Injector Laboratory to help make this improvement possible, continuing a study of possibly replacing the electron accelerator with a proton machine, and replacing or upgrading the facility's data-acquistion and immediate-analysis computer systems. Increased operating time and more involvement of nuclear theorists are recommended, and an effective staff size for optimum use of this unique facility is discussed. A bibliography of all ORELA-related publications is included.
119253432
Non‐Statistical Effects in Neutron Capture
There have been many reports of non‐statistical effects in neutron‐capture measurements. However, reports of deviations of reduced‐neutron‐width (Γn0) distributions from the expected Porter‐Thomas (PT) shape largely have been ignored. Most of these deviations have been reported for odd‐A nuclides. Because reliable spin (J) assignments have been absent for most resonances for such nuclides, it is possible that reported deviations from PT might be due to incorrect J assignments. We recently developed a new method for measuring spins of neutron resonances by using the DANCE detector at the Los Alamos Neutron Science Center (LANSCE). Measurements made with a 147Sm sample allowed us to determine spins of almost all known resonances below 1 keV. Furthermore, analysis of these data revealed that the Γn0 distribution was in good agreement with PT for resonances below 350 eV, but in disagreement with PT for resonances between 350 and 700 eV. Our previous (n,α) measurements had revealed that the α strength function...
117328580
New Maxwellian averaged neutron capture cross sections for Cl-35,Cl-37
The Oak Ridge Electron Linear Accelerator (ORELA) was used to measure neutron total and capture cross sections of natural chlorine in the energy range from 100 eV to 600 keV. We performed an R-matrix analysis of our new capture and transmission data up to 500 keV. From these resonance parameters new (n, gamma) astrophysical reaction rates were determined over the entire energy range needed by the latest stellar models of the s process.
39396881
Measurement of the electric polarizability of the neutron.
12086987
Geodesics in Kasner universes.
Recently, Kasner model universes of various dimensionalities have been explored to see if they could be used in the manner of Kaluza-Klein models to provide the additional unobservable dimensions called for in current elementary-particle models. These discussions have focused narrowly on the number of dimensions and the manner in which those dimensions in excess of the observable four of spacetime behave. This paper discusses some features of Kasner models which ultimately should be considered if these models are to provide a useful arena for studying elementary particles. In particular, geodesics are examined in detail. It is found that there may be a limit to the distance traveled by timelike particles, that spacelike geodesics are limited in their temporal extent, and that for null geodesics in expanding directions the coordinate speed approaches zero.
42736184
Nonrenormalization of the superstring tension.
It is argued that the superstring tension is not renormalized in perturbation theory for vacua which preserve N= 1 spacetime supersymmetry. Some implications of this result for macroscopic superstrings are discussed, as well as some analogies between macroscopic superstrings and solitons in supersymmetric theories.
37326897
Momentum distribution of projectile fragments and nuclear shape.
When one or two neutrons are lost in a collision between a projectile with a diffuse neutron-rich surface and a target nucleus, the transverse momentum distribution of the fragments thus produced can be fit with a double Gaussian curve in which a narrow component is superimposed on a much broader one. It is shown that this phenomenon is also observed for fragments from the normal'' projectile [sup 12]C. A density-dependent nucleon Fermi momentum and fragment recoil with the momentum of the lost nucleon give good agreement with experiment. The two Gaussian components do not require the presence near the nuclear surface of nucleons with two widely different binding energies, as often supposed.
29173646
Octonionic superstring solitons.
An extended-soliton solution to the low-energy heterotic-field-theory equations of motion is constructed from an eight-dimensional octonionic instanton. The soliton describes a string in ten-dimensional Minkowski space, and preserves only one of the sixteen spacetime supersymmetries.
17319033
Hairy black holes in string theory.
Solutions of bosonic string theory are constructed which correspond to four-dimensional black holes with axionic quantum hair. The basic building blocks are the renormalization group flows of the ${\mathrm{CP}}^{1}$ model with a \ensuremath{\theta} term and the SU(1,1)/U(1) WZW coset conformal field theory. However the solutions are also found to have negative energy excitations, and are accordingly expected to decay to the vacuum.