A broad spectrum neutron spectrometer utilizing a high energy Bonner sphere extension

A novel broad spectrum neutron spectrometer has been created to extend the useful energy range of existing neutron Bonner Sphere Spectrometers (BSS). Both an active LiI(Eu) scintillator probe and passive gold foil detector were utilized to extend the energy response of the existing BSS. Above 20 MeV the energy structure for the standard polyethylene BSS are poor because the response functions are not unique. MCNPX was used to investigate several modifications to the BSS system which resulted in the Bonner Sphere Extension (BSE). This cost effective extension uses several concentric spheres of copper, lead, and tungsten heavy metal downscatter materials to extend the useful range of the current BSS from 20 MeV to above 1 GeV. Using both a 3" and 5" inner polyethylene spheres, aluminum shell sets were made with a 1" cavity and filled with the high Z materials for six total sets of spheres. a 12" and 8" polyethylene sphere were also milled to accept the heavy metal spheres. The system was validated at the Los Alamos Neutron Science Center (LANSCE) neutron beam. The system was calibrated at LANSCE for neutrons up to 800 MeV on target 4's 15 degree right flightpath (4FP15R) at 90 meters. Detailed models in MCNPX were made of the BSS, BSE and LANSCE facilities. Fine group responses were made and compared to the unfolded data from LANSCE. A vast improvement over the BSS system alone was seen with reasonable agreement with time of flight data measured at LANSCE and MCNPX calculated neutron spectra.M.S.Committee Chair: Hertel, Nolan; Committee Co-Chair: Howell, Rebecca; Committee Member: Wang, Chris C-

Observational and Dynamical Characterization of Main-Belt Comet P/2010 R2 (La Sagra)

We present observations of comet-like main-belt object P/2010 R2 (La Sagra) obtained by Pan-STARRS 1 and the Faulkes Telescope-North on Haleakala in Hawaii, the University of Hawaii 2.2 m, Gemini-North, and Keck I telescopes on Mauna Kea, the Danish 1.54 m telescope at La Silla, and the Isaac Newton Telescope on La Palma. An antisolar dust tail is observed from August 2010 through February 2011, while a dust trail aligned with the object's orbit plane is also observed from December 2010 through August 2011. Assuming typical phase darkening behavior, P/La Sagra is seen to increase in brightness by >1 mag between August 2010 and December 2010, suggesting that dust production is ongoing over this period. These results strongly suggest that the observed activity is cometary in nature (i.e., driven by the sublimation of volatile material), and that P/La Sagra is therefore the most recent main-belt comet to be discovered. We find an approximate absolute magnitude for the nucleus of H_R=17.9+/-0.2 mag, corresponding to a nucleus radius of ~0.7 km, assuming an albedo of p=0.05. Using optical spectroscopy, we find no evidence of sublimation products (i.e., gas emission), finding an upper limit CN production rate of Q_CN<6x10^23 mol/s, from which we infer an H2O production rate of Q_H2O<10^26 mol/s. Numerical simulations indicate that P/La Sagra is dynamically stable for >100 Myr, suggesting that it is likely native to its current location and that its composition is likely representative of other objects in the same region of the main belt, though the relatively close proximity of the 13:6 mean-motion resonance with Jupiter and the (3,-2,-1) three-body mean-motion resonance with Jupiter and Saturn mean that dynamical instability on larger timescales cannot be ruled out.Comment: 23 pages, 13 figures, accepted for publication in A

Lacerta I and Cassiopeia III. Two Luminous and Distant Andromeda Satellite Dwarf Galaxies Found in the 3π Pan-STARRS1 Survey

We report the discovery of two new dwarf galaxies, Lacerta I/Andromeda XXXI (Lac I/And XXXI) and Cassiopeia III/Andromeda XXXII (Cas III/And XXXII), in stacked Pan-STARRS1 r P1- and i P1-band imaging data. Both are luminous systems (MV ~ –12) located at projected distances of 20fdg3 and 10fdg5 from M31. Lac I and Cas III are likely satellites of the Andromeda galaxy with heliocentric distances of $756^{+44}_{-28}{\rm \,kpc}$ and $772^{+61}_{-56}{\rm \,kpc}$, respectively, and corresponding M31-centric distances of 275 ± 7 kpc and $144^{+6}_{-4}{\rm \,kpc}$. The brightest of recent Local Group member discoveries, these two new dwarf galaxies owe their late discovery to their large sizes ($r_h = 4.2^{+0.4}_{-0.5}$ arcmin or $912^{+124}_{-93}{\rm \,pc}$ for Lac I; $r_h = 6.5^{+1.2}_{-1.0}$ arcmin or 1456 ± 267 pc for Cas III) and consequently low surface brightness (μ0 ~ 26.0 mag arcsec–2), as well as to the lack of a systematic survey of regions at large radii from M31, close to the Galactic plane. This latter limitation is now alleviated by the 3π Pan-STARRS1 survey, which could lead to the discovery of other distant Andromeda satellite dwarf galaxies.Astronom

Lacerta i and cassiopeia III. Two luminous and distant andromeda satellite dwarf galaxies found in the 3π pan-starrs1 survey

We report the discovery of two new dwarf galaxies, Lacerta I/Andromeda XXXI (Lac I/And XXXI) and Cassiopeia III/Andromeda XXXII (Cas III/And XXXII), in stacked Pan-STARRS1 r_P1- and i_P1-band imaging data. Both are luminous systems (M_V ~ -12) located at projected distances of 20.3{\deg} and 10.5{\deg} from M31. Lac I and Cas III are likely satellites of the Andromeda galaxy with heliocentric distances of 756^{+44}_{-28} kpc and 772^{+61}_{-56} kpc, respectively, and corresponding M31-centric distances of 275+/-7 kpc and 144^{+6}_{-4} kpc . The brightest of recent Local Group member discoveries, these two new dwarf galaxies owe their late discovery to their large sizes (r_h = 4.2^{+0.4}_{-0.5} arcmin or 912^{+124}_{-93} pc for Lac I; r_h = 6.5^{+1.2}_{-1.0} arcmin or 1456+/-267 pc for Cas III), and consequently low surface brightness (\mu_0 ~ 26.0 mag/arcsec^2), as well as to the lack of a systematic survey of regions at large radii from M31, close to the Galactic plane. This latter limitation is now alleviated by the 3{\pi} Pan-STARRS1 survey, which could lead to the discovery of other distant Andromeda satellite dwarf galaxies.Comment: 7 pages, 5 figures. Accepted for publication in Ap

Measured Neutron Spectra and Dose Equivalents From a Mevion Single-Room, Passively Scattered Proton System Used for Craniospinal Irradiation.

PurposeTo measure, in the setting of typical passively scattered proton craniospinal irradiation (CSI) treatment, the secondary neutron spectra, and use these spectra to calculate dose equivalents for both internal and external neutrons delivered via a Mevion single-room compact proton system.Methods and materialsSecondary neutron spectra were measured using extended-range Bonner spheres for whole brain, upper spine, and lower spine proton fields. The detector used can discriminate neutrons over the entire range of the energy spectrum encountered in proton therapy. To separately assess internally and externally generated neutrons, each of the fields was delivered with and without a phantom. Average neutron energy, total neutron fluence, and ambient dose equivalent [H* (10)] were calculated for each spectrum. Neutron dose equivalents as a function of depth were estimated by applying published neutron depth-dose data to in-air H* (10) values.ResultsFor CSI fields, neutron spectra were similar, with a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate continuum between the evaporation and thermal peaks. Neutrons in the evaporation peak made the largest contribution to dose equivalent. Internal neutrons had a very low to negligible contribution to dose equivalent compared with external neutrons, largely attributed to the measurement location being far outside the primary proton beam. Average energies ranged from 8.6 to 14.5 MeV, whereas fluences ranged from 6.91 × 10(6) to 1.04 × 10(7) n/cm(2)/Gy, and H* (10) ranged from 2.27 to 3.92 mSv/Gy.ConclusionsFor CSI treatments delivered with a Mevion single-gantry proton therapy system, we found measured neutron dose was consistent with dose equivalents reported for CSI with other proton beamlines

Mapping the monoceros ring in 3D with Pan-STARRS1

Using the Pan-STARRS1 survey, we derive limiting magnitude, spatial completeness, and density maps that we use to probe the three-dimensional structure and estimate the stellar mass of the so-called Monoceros Ring. The Monoceros Ring is an enormous and complex stellar sub-structure in the outer Milky Way disk. It is most visible across the large Galactic Anticenter region, 120° < l < 240°, -30° < b < +40°. We estimate its stellar mass density profile along every line of sight in 2° × 2° pixels over the entire 30,000 deg2 Pan-STARRS1 survey using the previously developed MATCH software. By parsing this distribution into a radially smooth component and the Monoceros Ring, we obtain its mass and distance from the Sun along each relevant line of sight. The Monoceros Ring is significantly closer to us in the south (6 kpc) than in the north (9 kpc). We also create 2D cross-sections parallel to the Galactic plane that show 135° of the Monoceros Ring in the south and 170° of the Monoceros Ring in the north. We show that the northern and southern structures are also roughly concentric circles, suggesting that they may be waves rippling from a common origin. Excluding the Galactic plane ∼±4°, we observe an excess mass of 4 × 106M⊙ across 120° < l < 240°. If we interpolate across the Galactic plane, we estimate that this region contains 8×106M⊙. If we assume (somewhat boldly) that the Monoceros Ring is a set of two Galactocentric rings, its total mass is 6×107M⊙. Finally, if we assume that it is a set of two circles centered at a point 4 kpc from the Galactic center in the anti-central direction, as our data suggests, we estimate its mass to be 4 × 107M