Los Alamos Meson Physics Facility Research Articles

Electric-field-induced electron detachment of 800-MeV H- ions.

The lifetime of 800-MeV ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ions against electron detachment in a static electric field was measured over a range of eight orders of magnitude in experiments at the High Resolution Atomic Beam Facility of the Los Alamos Meson Physics Facility. The ions traversed a linear gradient magnetic field of 1.3-T peak strength resulting in a 6-MV/cm peak rest-frame electric field capable of stripping a large fraction of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ions. The unstripped ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ions, neutral ${\mathrm{H}}^{0}$ atoms, and protons were detected 5.5 m from the magnet. This spectrum was analyzed to determine the lifetime of the ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ion versus electric-field strength and the results were compared with previous studies. Three parametrizations of the lifetime formula based on an existing theory were used to calculate the stripping probability. The data were fit to the lifetime formula and good agreement with theoretical predictions was found. Finally, a possible experiment for observing excited states of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ is briefly discussed.

An alternative analysis of the LSND neutrino oscillation search data on nu -bar micro--> nu -bare.

This analysis of data from the Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos Meson Physics Facility (LAMPF) sets bounds on neutrino oscillations in the appearance channel ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{e}$ by searching for the signature of the reaction ${\overline{\ensuremath{\nu}}}_{e}p\ensuremath{\rightarrow}{e}^{+}n$: an ${e}^{+}$ followed by a 2.2 MeV $\ensuremath{\gamma}$ ray from neutron capture. Five ${e}^{\ifmmode\pm\else\textpm\fi{}}$- $\ensuremath{\gamma}$ coincidences are observed in time with the LAMPF beam, with an estimated background of 6.2 events. The 90% confidence limits obtained in this analysis are $\ensuremath{\Delta}{m}^{2}<0.07{\mathrm{eV}}^{2}$ for ${sin}^{2}2\ensuremath{\theta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$, and ${sin}^{2}2\ensuremath{\theta}<6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ for $\ensuremath{\Delta}{m}^{2}\ensuremath{\gtrsim}20{\mathrm{eV}}^{2}$. The possible signal at the edge of the detector's sensitivity is mentioned.

Recent developments in zinc oxide target chemistry

Zinc oxide targets irradiated with high energy protons at the Los Alamos Meson Physics Facility (LAMPF) contain a number of radioactive spallation products in quantities large enough to warrant recovery. This paper describes methods for recovering7Be,46Sc, and48V from such targets and offers suggestions on possible ways to recover additional isotopes. The proposed methods are based on traditional precipitation and ion exchange techniques, are readily adaptable to hot cell use, and produce no hazardous waste components. The products are obtained in moderate to high yields and have excellent radionuclidic purity.

Thermal hydraulic study of the neutron production target at the Los Alamos Neutron Scattering Center

The Los Alamos Neutron Scattering Center (LANSCE) operates a pulsed neutron source for materials science research. The neutrons are produced by bombarding a tungsten target with the 800 MeV proton beam from the Los Alamos Meson Physics Facility (LAMPF). In an attempt to clarify the thermal hydraulics of the neutron production target, we performed a sequence of experiments aimed at determining temperature distributions in the target, as well as various heat transfer parameters. The results of these measurements were compared, and shown to agree, with radiation transport and heat transfer calculations. The information obtained from these tests was then used to determine other target properties, such as thermal stress, that are very difficult to measure directly.

Measurement of the reaction 12C( nu micro, micro-)X near threshold.

The reaction C12(νμ,μ−)X has been measured near threshold using a π+ decay-in-flight νμ beam from the Los Alamos Meson Physics Facility and a massive liquid scintillator neutrino detector (LSND). In the energy region 123.7<Eν<280 MeV, the measured spectral shape is consistent with that expected from the Fermi-gas model (FGM). However, the measured flux-averaged inclusive cross section {[8.3±0.7(stat)±1.6(syst)]×10−40 cm2} is more than a factor of 2 lower than that predicted by the Fermi-gas model and by a recent random phase approximation calculation.Received 28 September 1994DOI:https://doi.org/10.1103/PhysRevC.51.R1065©1995 American Physical Society

A LAMPF controls retrospective: the good, the bad, and “it seemed like a good idea at the time”

LAMPF (Los Alamos Meson Physics Facility) was the first large particle accelerator to require the use of a computerized control system as part of its design. Over the past 25 years, the LAMPF control system has evolved from a single mini-computer system using home-built data acquisition hardware to a complex network of VAX and micro-VAX computers using CAMAC and other data acquisition protocols. On the occasion of LAMPF's possible closing, this paper provides a look back at how the LAMPF control system got to where it is today. After a brief historical introduction, we will discuss aspects of control system design and implementation including, the impact of technology on decision making and topics from the LAMPF operational experience.

Long-Term Tracer Study at Los Alamos, New Mexico. Part I: Wind, Turbulence, and Tracer Patterns

An array of three portable, pressurized ionization chambers (PICs) measured external radiation levels during 1986 and 1987 caused by radionuclides emitted from a 30-m stack of the Los Alamos Meson Physics Facility (LAMPF). Three PICs were located from 700 to 900 m north to northeast of the release stack, across a 120-m-deep canyon, and at the closest off-site location. Four additional PICs were deployed during 1987 at various sites and directions, at distances varying from 550 to 2700 m downwind of the stack. Winds were measured near the source and 700 m downwind, across a deep canyon. Analysis of monitoring data confirmed that a predominant mountain-valley wind up the Rio Grande Valley during the evening and early morning transported the emissions to the north-northeast and northeast of LAMPF, causing the highest external atmospheric radiation levels there. Daytime winds are southerly and southeasterly, transporting more radionuclides to the north and northwest. Because of increased turbulence, external radiation levels were generally lower during the day.

A position-sensitive proton telescope

The Medium Resolution Proton Spectrometer (MRS) at the Los Alamos Meson Physics Facility (LAMPF) was used to develop a position-sensitive proton telescope with CsI(pure) crystals. Photomultiplier tubes were mounted at both ends of a 7.5 × 15 × 30 cm long proton telescope and position measurements using the difference of the time signals were performed. The position resolution was measured to be 2.5 cm FWHM. An energy resolution ΔE/ E = 3 to 4% was measured.

Neutron-proton bremsstrahlung experiments

It is well known that charged particles emit bremsstrahlung radiation when they are accelerated. Classical electron bremsstrahlung occurs when a proton is emitted by an electron accelerated in the field of a nucleus. The bremsstrahlung process also occurs in the scattering of nucleons, for which it is the lowest energy inelastic process that can occur. Like electron bremsstrahlung, nucleon-nucleon bremsstrahlung also requires the exchange of a virtual particle to conserve energy and momentum. In electron bremsstrahlung a virtual photon is exchanged but with two nucleons a meson can be exchanged. Unlike electron bremsstrahlung, in nucleon-nucleon bremsstrahlung the photon can originate from the exchanged meson. This exchange contribution has been shown in calculations to be a significant fraction of bremsstrahlung events. Thus bremsstrahlung serves as a probe of exchange currents in the nucleon-nucleon interaction. Because of a lack of a free neutron target or an intense neutron beam, few measurements of neutron-proton bremsstrahlung exist, each having poor statistical accuracy and poor energy resolution. The white neutron source at the Weapons Neutron Research (WNR) target area at the Los Alamos Meson Physics Facility (LAMPF) produces neutrons with energies from below 50 to above 400 MeV. Using time-of-flight techniques and a liquid hydrogen target, we are measuring the outgoing photons of energies up to 250 MeV at gamma ray angles of around 90° relative to the incident beam. Protons scattered at very forward angles are also detected in coincidence with the gamma rays.

Monte Carlo simulation of the response of NaI scintillator to medium energy neutrons

A layered NaI scintillation detector (total thickness = 30.6 cm) was exposed to tagged neutrons at the Los Alamos Meson Physics Facility. The neutrons were approximately monoenergetic at ten energies in the range 36–709 MeV. The energy loss of the neutrons in the detector was subsequently simulated using a Monte Carlo program, which incorporated the HETC, EGS, and MORSE computer codes. The agreement between the experiment and the simulation for the detection efficiency was within 35%. A comparison of the measured and calculated energy-loss spectra showed differences generally within 50%. Details of the detector geometry, the Monte Carlo simulation, and the comparison of the data and the simulation are presented.

Limits on neutrino oscillations from nu -bare appearance.

A 20-ton neutrino detector located near the Los Alamos Meson Physics Facility beam stop is used to search for [bar [nu]][sub [ital e]] generated via neutrino oscillations from any of the three neutrino types, [nu][sub [mu]], [bar [nu]][sub [mu]], and [nu][sub [ital e]], which radiate from the beam stop. The analysis of three years of data provides limits on the oscillation modes [bar [nu]][sub [mu]][r arrow][bar [nu]][sub [ital e]], [nu][sub [ital e]][r arrow][bar [nu]][sub [ital e]], and [nu][sub [mu]][r arrow][bar [nu]][sub [ital e]], and the lepton-number-violating decay process [mu][sup +][r arrow][ital e][sup +]+[bar [nu]][sub [ital e]]+[nu][sub [mu]]. The 90%-confidence-level limits for [bar [nu]][sub [mu]][r arrow][bar [nu]][sub [ital e]] oscillations are [delta][ital m][sup 2][le]0.14 eV[sup 2] for maximal mixing, and sin[sup 2]2[theta][le]0.024 for large [delta][ital m][sup 2].

Neutron total cross sections at intermediate energies.

Pulsed-beam time-of-flight techniques are used in a transmission measurement with a continuous spectrum of neutrons to determine neutron total cross sections with good precision up to 600 MeV. Neutrons are produced by spallation of the 800 MeV proton beam from the Los Alamos Meson Physics Facility accelerator incident on a thick, heavily shielded tungsten target at the Weapons Neutron Research facility at Los Alamos National Laboratory. Transmission measurements were completed for fifteen elements with 9\ensuremath{\le}A\ensuremath{\le}209 and three isotopically enriched samples of $^{40}\mathrm{Ca}$, $^{90}\mathrm{Zr}$, and $^{208}\mathrm{Pb}$. Principal features of the experiment are the intensity and time structure of the neutron source, tight collimation of the neutron beam line, good geometry, rapid cycling of the samples, stable electronics, and a small, fast neutron detector. Errors due to counting statistics were generally less than 1% for each of several hundred energy bins for each target. The measurements represent steps in the development of a neutron-nucleus optical potential at intermediate energy and important input for the clarification of isovector effects in the nucleon-nucleus interaction. The data also provide insight into the long-standing discussion of mean free paths of the nucleon in the nucleus.

Neutron flux enhancement at LASREF

The accelerator at the Los Alamos Meson Physics Facility produces a 1 mA beam of protons at an energy of 800 MeV. Since 1985, the Los Alamos Spallation Radiation Effects Facility (LASREF) has made use of the neutron flux that is generated as the incident protons interact with the nuclei in targets and a copper beam stop. A variety of basic and applied experiments in radiation damage and radiation effects have been completed. Recent studies indicate that the flux at LASREF can be increased by at least a factor of 10 from the present level of about 5 E + 17 m −2 s −1. This requires changing the beam stop material from Cu to W and optimizing the geometry of the beam-target interaction region. These studies are motivated by the need for a large volume, high energy, and high intensity neutron source in the development of materials for advanced energy concepts such as fusion reactors.

A simple three-dimensional magnetic field interpolation technique

A simple technique based on the least-squares method for interpolating a magnetic field in three-dimensions is discussed. The technique has been used successfully in a Monte Carlo model for a neutron-proton elastic scattering experiment performed at the Los Alamos meson physics facility. Results from this model are given as an example. Some of the methods should be useful in other applications in which it is necessary to generate a smooth function that is constrained to pass through a set of measured points.

Determination of the level density of 29Si from Ericson fluctuations.

Neutron total cross-section measurements for $^{28}\mathrm{Si}$ have been made with the white neutron source at Los Alamos Meson Physics Facility for neutron energies between 4 and 600 MeV. Very good resolution (\ensuremath{\approxeq}0.2 ns/m) was obtained. The detailed structure at low energies is found to be different than obtained in previous measurements, although at energies 7${\mathit{E}}_{\mathit{n}}$15 MeV the agreement is quite good. The cross section becomes quite smooth above 15 MeV. An Ericson analysis is performed to yield values for the level density of $^{29}\mathrm{Si}$ between 13 and 22 MeV.

High energy proton SEU test results for the commercially available MIPS R3000 microprocessor and R3010 floating point unit

Proton single event upset (SEU) cross sections and proton total dose hardness of commercially available MIPS R3000 microprocessors (CPU) and R3010 floating point units (FPU) were obtained by exposing these parts to 256 MeV protons from the linear accelerator (LINAC) at the Los Alamos Meson Physics Facility (LAMPF). Parts from several manufacturers were tested. The CPUs and FPUs were tested dynamically during radiation exposure with specially designed assembly language codes which exercised a subset of the available instructions. Cross sections derived from the SEU data were used to calculate expected upset rates for a 500-km, 60-degree inclination orbit during quiet solar conditions and during the August 4. 1972, King solar fire event modeled by J.H. Adams et al. (1981).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Production of mono-isotopic 88Y from the decay of 88Zr

Mono-isotopic 88Y was recovered from the decay of 88Zr. The 88Zr was produced with other spallation products, by irradiating natural molybdenum metal with 800-MeV protons at the Los Alamos Meson Physics Facility. The 88Zr was separated from the molybdenum target material and other spallation produced-isotopes by ion-exchange procedures. After the 88Zr had decayed to 88Y, a second ion-exchange separation was performed to isolate the 88Y.

Spectra from multiphoton electron detachment of H^−

New data are reported on the multiphoton detachment process in a fast beam of H− ions. The angle-tuned relativistic Doppler shift is used to vary the photon energy of a focused (~10 GW/cm2) 10.6-μm CO2 laser beam from ~0.05 to ~0.4 eV in the rest frame (CM frame) of the fast ions. The ions are produced at 800 MeV (β = v/c = 0.84) by the Los Alamos Meson Physics Facility linear accelerator at Los Alamos and experience ~1-psec pulses in the CM frame as they cross the laser beam focus. Peaks in the detachment signal corresponding to each order for two- to six-photon processes are observed. At modest laser intensity in the gigawatt-per-square-centimeter range, observed shifts of the apparent two-photon threshold are found to be not more than 30–50% of the expected maximum shift, based on the value of the ponderomotive potential. Experimental uncertainties are due mainly to imprecise knowledge of the maximum laser intensity. The data analysis and modeling of the expected threshold shape experiments are continuing.

The Los Alamos National Laboratory Spallation Neutron Sources

Two neutron sources used for nuclear physics research at Los Alamos National Laboratory are described. Both are driven by the 800-MeV proton beam from the Los Alamos Meson Physics Facility. The Los...

Providing common data access for the LAMPF and PSR control systems

The merging of the Los Alamos Meson Physics Facility (LAMPF) and the Los Alamos Proton Storage Ring (PSR) controls and operations groups in early 1988 motivated planning for a common, probably workstation-based, operator interface. Application programs driving this interface must be able to communicate with both LAMPF and PSR devices in a uniform manner. We would like this communication to be implemented with minimal changes to the current LAMPF and PSR control systems. A common device-naming scheme has made it possible for remote systems to acquire both LAMPF and PSR data through the use of server processes residing in the appropriate network nodes. Remote supervisory control of LAMPF devices has been provided in a similar manner. Incompatibilities between information in the LAMPF and PSR database has made remote supervisory control of PSR devices somewhat more difficult. This paper discusses our experience providing this common access and plans for providing future common communications.