[en] One- and two-photon detachment of electrons from the negative hydrogen ion are observed with 1.17 eV laser pulses from a Nd:YAG laser. To the authors knowledge, the 2-photon detachment is the first experimental observation of non-resonant excess photon detachment (EPD) from the negative hydrogen ion. This apparatus was previously used to perform the first resonant multiphoton detachment of the ¹D^e resonance of H^- just below the n=2 threshold. A Penning ion source produces an 8μA, 35 keV H^- beam in 500 ns pulses at a 5 Hz repetition rate. The laser beam consists of pulse energies of up to 1 J cylindrically focused down to a 13 μm waist in the ion beam direction, creating an interaction region with laser intensities of up to 10¹¹ W/cm². The resulting photoelectrons are detected by a microchannel plate (MCP) at the end of a 1 m time-of-flight drift tube. The outer electron of H^- has a binding energy of 0.75 eV, thus one 1.17 eV photon provides an excess energy of 0.42 eV. By rotating the linear polarization angle the authors studied the angular distribution of the electrons for both 1 - and 2-photon detachments. The spectra were compared to a model based on a Legendre polynomial expansion of the time differential photo-ionization cross section. Studies of the peak size vs the laser intensity were also performed

[en] Recently broadly tunable, coherent VUV radiation down to 111 nm has become available. An experiment is underway using a VUV light source capable of a few μJ per 10 ns pulse to study the spectrum of H in the region of 113 nm. The photon energy of the VUV can be easily tuned and may determine whether the shape resonance has a Fano profile as predicted. A non-relativistic (35 keV), low-emittance H^- beam from the GTA injector at LANL will be used as the ion source. The electrons ejected from the intersecting beams will be analyzed using an electron time-of-flight (TOF) spectrometer. A narrow VUV linewidth allows the width of the Feshbach and shape resonances to be measured to high resolution (∼1 cm^-1). The branching ratios of neutral hydrogen states H(1s), H(2s), H(2p) for each resonance will be calculated by measuring the TOF of the ejected electrons. Of particular interest is the differential of the H(2s) and H(2p) branching ratios, since the product states are nearly degenerate in energy. Simulation of TOF data allows determination of both energy and the angular distribution of the electrons, thus permitting the authors to distinguish all three product states

[en] Experiments were conducted to determine the effects on the distribution of H^o Stark states produced in the interaction of an 800 MeV H^- ion beam with a thin Al₂O₃ foil in a 0.16 T magnetic field. The foil was upstream of a second magnet with a constant field gradient along the beam direction resulting in a motional electric field strong enough to ionize H^o states if n ≥ 3. The individual Stark states stripped at different field strengths and the remaining protons were dispersed in the field. The transverse distribution of protons was determined 5.5 m downstream using a scanning scintillator. The distributions of individual Stark states within the n = 3 and 4 levels were measured for the field-on and field-off cases. The authors observed significant differences between the field-on and field-off spectra. Compared with a statistical distribution, a greater fraction of the distribution arises from states with m = 0, and a smaller contribution is from states with m ≠ 0. This departure from a statistical distribution was present even when the foil was not placed in a field, and was further enhanced when the foil was placed in the field. In lieu of a quantitative theory, a simple qualitative model is presented to explain the major trends

[en] The lifetime of 800-MeV H^- 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 H^- ions. The unstripped H^- ions, neutral H⁰ atoms, and protons were detected 5.5 m from the magnet. This spectrum was analyzed to determine the lifetime of the H^- 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 H^- is briefly discussed

[en] As part of our systematic study of the stripping of H^- ions passing through thin foils at near the speed of light, we have made some preliminary measurements of the effect of a magnetic field in the foil on the stripping efficiency. In addition to its intrinsic physical interest, if synergistic magnetic field effects on stripping are present, there may be consequences for the technique for proton injection into future storage rings. The preliminary results of our first measurements on an Al₂O₃ foil some 156 μg/cm² thick are not dramatically conclusive, but there is evidence that the simultaneous action of a motional electric field as an H^- ion interacts with a matter field is different from the action of these two agents separately. (author)

[en] Cross sections for ^223,225Ra, ²²⁵Ac and ²²⁷Th production by the proton bombardment of natural thorium targets were measured at proton energies below 200 MeV. Our measurements are in good agreement with previously published data and offer a complete excitation function for ^223,225Ra in the energy range above 90 MeV. Comparison of theoretical predictions with the experimental data shows reasonable-to-good agreement. Results indicate that accelerator-based production of ²²⁵Ac and ²²³Ra below 200 MeV is a viable production method. - Highlights: ► Natural thorium targets were irradiated with protons up to a nominal 200 MeV. ► ²²⁵Ac, ^223,225Ra, and ²²⁷Th production cross sections were measured. ► Multi-curie quantities of ²²⁵Ac and ²²³Ra can likely be produced at Los Alamos and Brookhaven. ► Accelerator-based production of ²²⁵Ac and ²²³Ra is a viable production method

[en] Terbium foils were irradiated with 800 MeV protons to ascertain the potential for production of lanthanide isotopes of interest in medical, astrophysical, and basic science research and to contribute to nuclear data repositories. Isotopes produced in the foil were quantified by gamma spectroscopy. Cross sections for 35 isotopes produced in the irradiation are reported and compared with predictions by the MCNP6 transport code using the CEM03.03, Bertini and INCL + ABLA event generators. Our results indicate the need to accurately consider fission and fragmentation of relatively light target nuclei like terbium in the modeling of nuclear reactions at 800 MeV. The predictive power of the code was found to be different for each event generator tested but was satisfactory for most of the product yields in the mass region where spallation reactions dominate. However, none of the event generators' results are in complete agreement with measured data.

[en] Measurements of H^- stripping and H⁰ excited-state production for a wide range of foil thicknesses and experimental conditions are reported. An 800-MeV H^- beam was passed through carbon or aluminum oxide foils of thicknesses ranging from 10 to 550 μg/cm² and the excited states produced were analyzed by field stripping in a special magnet downstream of the foil. The foil thicknesses were independently determined. The H⁰ atoms emerging in excited states with n approx-gt 2 can be stripped to protons in fields of up to 1.3 T. The yield of excited states as a function of foil thickness and the cross sections for the various interactions are presented. The cross-section ratio of double to single ionization of H^- in carbon is found to be (1.8±0.9)%. copyright 1996 The American Physical Society

[en] We have measured the cross section for the detachment of three electrons from the Cl^- ion following the absorption of a single photon. The triple-photodetachment cross section is compared to our earlier measurement of the cross section for double photodetachment from the same ion. Possible direct and indirect mechanisms responsible for multiple-electron detachment are discussed. The direct process of ejection of three valence electrons seems to be the most likely process. This conjecture needs theoretical verification

[en] The recently completed 100-MeV H⁺ Isotope Production Facility (IPF) at the LANSCE will provide radioisotopes for medical research and diagnosis, for basic research and for commercial use. A change to the LANSCE accelerator facility allowed for the installation of the IPF. Three components make up the LANSCE accelerator: an injector that accelerates the H⁺ beam to 750-KeV, a drift-tube linac (DTL) that increases the beam energy to 100-MeV, and a side-coupled cavity linac (SCCL) that accelerates the beam to 800-MeV. The transition region, a space between the DTL and the SCCL, was modified to permit the insertion of a kicker magnet (23^o kick angle) for the purpose of extracting a portion of the 100-MeV H⁺ beam. A new beam line was installed to transport the extracted H⁺ beam to the radioisotope production target chamber. This paper will describe the commissioning and initial operating experiences of IPF.