R. E. Lanou

Rayleigh scattering in rare-gas liquids

Abstract The Rayleigh scattering length has been calculated for rare-gas liquids in the ultraviolet for the frequencies at which they luminesce. The calculations are based on the measured dielectric constants in the UV in the gas phase, in some cases extrapolated to the wavelength of luminescence. The scattering length may place constraints on the design of some large-scale detectors, using UV luminescence, being proposed to observe solar neutrinos and dark matter. Rayleigh scattering in mixtures of rare-gas liquids is also discussed.

A study of the axial-vector form factor and second-class currents in antineutrino quasielastic scattering

Abstract The antineutrino quasielastic reaction ν μm p →μ + n has been studied in the Q 2 range up to 1.0 (GeV/ c ) 2 at the Brookhaven AGS. The value of the axial vector mass M A in the dipole parametrization of the from factor was determined from the shape of the Q 2 distribution to be 1.09±0.03±0.02 GeV/ c 2 . A search for second-class currents was also conducted. No significant effect was found.

Neutron background for a dark matter experiment at a shallow depth site

Abstract The neutron flux in the Stanford Underground Facility, a shallow depth site with an overburden of 17 ± 1 m.w.e., has been measured using a moderated BF 3 proportional counter. This counter has also been used to measure the neutron flux inside various shielding configurations required for a dark matter search at this site. These measurements demonstrate that lead shielding, used for photon attenuation, acts as a strong neutron source, with the neutrons being produced primarily by cosmic ray muon interactions within the lead. We have determined the production rate of cosmic ray induced neutrons in lead at this depth. Fortunately, these measurements also demonstrate that it is possible to moderate and capture these neutrons so that the resulting neutron flux is no longer sensitive to the presence of the lead shielding. For a dark matter search, however, care still has to be taken to minimize the inactive mass near the detector.

Enhancement of radiation effect on cancer cells by gold-pHLIP

Significance Nanometer-sized gold particles are shown to increase the effectiveness of radiation in killing cancer cells. Improved radiation effectiveness allows less radiation to be used, reducing adverse effects to patients. Alternatively, more cancer killing could be possible while using current radiation doses. Here we used pH Low-Insertion Peptide (pHLIP) to tether gold nanoparticles to membranes of cancer cells. This increases their effectiveness because the radiation/particle effect is very localized. We find that pHLIP significantly increases the amount of gold particles in cancer cells, as well as the amount of cancer cell death from radiation. This methodology is promising for clinical research, as previous results show efficient targeting of gold nanoparticles to tumors by pHLIP. Previous research has shown that gold nanoparticles can increase the effectiveness of radiation on cancer cells. Improved radiation effectiveness would allow lower radiation doses given to patients, reducing adverse effects; alternatively, it would provide more cancer killing at current radiation doses. Damage from radiation and gold nanoparticles depends in part on the Auger effect, which is very localized; thus, it is important to place the gold nanoparticles on or in the cancer cells. In this work, we use the pH-sensitive, tumor-targeting agent, pH Low-Insertion Peptide (pHLIP), to tether 1.4-nm gold nanoparticles to cancer cells. We find that the conjugation of pHLIP to gold nanoparticles increases gold uptake in cells compared with gold nanoparticles without pHLIP, with the nanoparticles distributed mostly on the cellular membranes. We further find that gold nanoparticles conjugated to pHLIP produce a statistically significant decrease in cell survival with radiation compared with cells without gold nanoparticles and cells with gold alone. In the context of our previous findings demonstrating efficient pHLIP-mediated delivery of gold nanoparticles to tumors, the obtained results serve as a foundation for further preclinical evaluation of dose enhancement.

A test of transition radiation detectors for a colliding beam experiment

Abstract We have tested transition radiation detectors (TRDs) to separate electrons from pions in the momentum range between 2.0 GeV/c and 7.5 GeV/c. The radiator materials used in this experiment were polypropylene (CH2) fibers and lithium (Li) foils. A Xe filled longitudinal drift chamber of 3 cm depth was used for detecting transition radiation photons. We compared the methods of truncated mean of the total charge measurements and of maximum likelihood as well as cluster counting methods. We obtained 2% electron/pion separation for the CH2 fibers in the configuration of four modules with total length of 32 cm for a typical geometry of a collider experiment.

Simultaneous calorimetric detection of rotons and photons generated by particles in superfluid helium

Abstract A charged particle stopped in superfluid helium produces both excitations in the liquid (phonons and rotons) and photons by fluorescence. Using a calorimeter with a response time of 50 μs we are able to time-resolve in a single detector signals from the photons and from the excitations of the liquid at 25 mK. The implications of this observation for the detection of low energy solar neutrinos are discussed.

Scintillation and quantum evaporation generated by single monoenergetic electrons stopped in superfluid helium

An electron stopped in superfluid helium generates phonons and rotons in the liquid as well as uv photons via scintillation. We report recent measurements with single 364 ke V electrons. A sapphire wafer with a superconducting transition-edge sensor is mounted above the liquid and can measure energy and timing information of individual events. We observe both uv photons and the quantum evaporation of helium atoms resulting from phonons and rotons generated by the ionizing particle in the liquid. The production of photons and rotons is strikingly different for an electron and for an alpha particle. The origin of the differences is associated with the different density of excitations along the tracks of an alpha particle and an electron.

Drosophila melanogaster show a threshold effect in response to radiation.

We investigate the biological effects of radiation using adult Drosophila melanogaster as a model organism, focusing on gene expression and lifespan analysis to determine the effect of different radiation doses. Our results support a threshold effect in response to radiation: no effect on lifespan and no permanent effect on gene expression is seen at incident radiation levels below 100 J/kg. We also find that it is more appropriate to compare radiation effects in flies using the absorbed energy rather than incident radiation levels.

Precise Determination of Sin**2-

Measurements of the semileptonic weak neutral-current reactions ..nu../sub ..mu../p..--> nu../sub ..mu../p and nu-bar/sub ..mu../p..-->..nu-bar/sub ..mu../p which yield the absolute differential cross sections dsigma(..nu../sub ..mu../p)/dQ/sup 2/ and dsigma(nu-bar/sub ..mu../p)/dQ/sup 2/ described. The weak-neutral-current parameter, sin/sup 2/theta/sub W/, is determined to be sin/sup 2/theta/sub W/ = 0.220 +- 0.016 (stat)/sub -0.031//sup +0.023/(syst).

\theta^-

Alpha particles stopped in a 3 liter volume of liquid helium at 30 mK are observed by the calorimetric detection of helium atoms evaporated from the free surface of the liquid. Quantum evaporation of the helium is produced by the rotons that are created by the α particle. While the energy spectrum of the 5.5 MeV αs from the241Am source has a width of less than 0.5%, the energy distribution of the observed evaporation signals extends from the low energy threshold of several keV up to a maximum of several 100 keV, depending on geometrical factors and the collection area of the calorimeter. The origin of the observed distribution may result in part from the presence of the substrate and a dependence on the direction of the track of the α particle. A simple model of the generation of rotons by the α particle will be discussed.