Measurement of nuclear transparency from A(e,e'[pi]⁺) reactions

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.In title on t.p., "[pi]" appears as the lower-case Greek letter.Includes bibliographical references (p. 161-165).The color transparency phenomenon refers to the suppression of final-state interactions of a hadron propagating through the nuclear medium at large momentum transfer when the hadron is produced with small transverse size. The pion electroproduction cross section from 1H, 2H,12C, 63Cu and 197Au targets from Q2 = 1.1 to 4.8 (GeV/c)2 was measured in Jefferson Laboratory Experiment E01-107. The nuclear transparency was formed by the ratio of ([sigma]A/[sigma]H) from the data and ([sigma]A/[sigma]H) from a model of electroproduction from nuclei that does not include [pi]-N final state interactions. A signature of color transparency is the enhancement of the nuclear transparency at large Q2 compared with predictions based on Glauber multiple scattering theory. This experiment represents the first nuclear transparency data from (e,e'[pi]+) reactions.by Benjamin Michael Patrick Clasie.Ph.D

Monte Carlo study of the potential reduction in out-of-field dose using a patient-specific aperture in pencil beam scanning proton therapy

This study is aimed at identifying the potential benefits of using a patientspecific aperture in proton beam scanning. For this purpose, an accurate Monte Carlo model of the pencil beam scanning (PBS) proton therapy (PT) treatment head at Massachusetts General Hospital (MGH) was developed based on an existing model of the passive double-scattering (DS) system. The Monte Carlo code specifies the treatment head at MGH with sub-millimeter accuracy. The code was configured based on the results of experimental measurements performed at MGH. This model was then used to compare out-of-field doses in simulated DS treatments and PBS treatments. For the conditions explored, the penumbra in PBS is wider than in DS, leading to higher absorbed doses and equivalent doses adjacent to the primary field edge. For lateral distances greater than 10 cm from the field edge, the doses in PBS appear to be lower than those observed for DS. We found that placing a patient-specific aperture at nozzle exit during PBS treatments can potentially reduce doses lateral to the primary radiation field by over an order of magnitude. In conclusion, using a patient-specific aperture has the potential to further improve the normal tissue sparing capabilities of PBS

Scaling of the F-2 [F subscript 2] Structure Function in Nuclei and Quark Distributions at x > 1

We present new data on electron scattering from a range of nuclei taken in Hall C at Jefferson Lab. For heavy nuclei, we observe a rapid falloff in the cross section for x>1, which is sensitive to short-range contributions to the nuclear wave function, and in deep inelastic scattering corresponds to probing extremely high momentum quarks. This result agrees with higher energy muon scattering measurements, but is in sharp contrast to neutrino scattering measurements which suggested a dramatic enhancement in the distribution of the “superfast” quarks probed at x>1. The falloff at x>1 is noticeably stronger in 2H ]superscript 2 H] and 3He [superscript 3 He], but nearly identical for all heavier nuclei.United States. Dept. of Energy (Contract No. DE-FG02-96ER40950)United States. Dept. of Energy (Contract no. DE-AC05-06OR23177)United States. Dept. of Energy (Contract no. DE-AC02-06CH11357)National Science Foundation (U.S.) (Grant No. NSF-0244899)National Research Foundation (South Africa

Search for sub-threshold photoproduction of J/ψ [J/psi] mesons

A search was made for sub-threshold J/ψ [J / psi] production from a carbon target by using a mixed real and quasireal Bremsstrahlung photon beam with an endpoint energy of 5.76 GeV. No events were observed, which is consistent with predictions under the assumption of quasifree production. The results place limits on exotic mechanisms that strongly enhance quasifree production.United States. Dept. of Energy (Contract No. DEAC05-84ER40150)United States. Dept. of EnergyNational Science Foundation (U.S.)National Research Foundation (South Africa

New Measurements of the European Muon Collaboration Effect in Very Light Nuclei

New Jefferson Lab data are presented on the nuclear dependence of the inclusive cross section from [superscript 2]H, [superscript 3]He, [superscript 4]He, [superscript 9]Be and [superscript 12]C for 0.3<x<0.9, Q[superscript 2]≈3–6  GeV[superscript 2]. These data represent the first measurement of the EMC effect for 3He at large x and a significant improvement for 4He. The data do not support previous A-dependent or density-dependent fits to the EMC effect and suggest that the nuclear dependence of the quark distributions may depend on the local nuclear environment.U.S. Department of Energy (Contract No. DE-AC02-06CH11357, Contract No. DE-AC05-06OR23177)National Science Foundatio

Measurement of the Vector and Tensor Asymmetries at Large Missing Momentum in Quasielastic ([→ over e],e′p) Electron Scattering from Deuterium

We report the measurement of the beam-vector and tensor asymmetries A[subscript ed][superscript V] and A[subscript d][superscript T] in quasielastic ([→ over e],e′p) electrodisintegration of the deuteron at the MIT-Bates Linear Accelerator Center up to missing momentum of 500  MeV/c. Data were collected simultaneously over a momentum transfer range 0.1<Q[superscript 2]<0.5  (GeV/c)[superscript 2] with the Bates Large Acceptance Spectrometer Toroid using an internal deuterium gas target polarized sequentially in both vector and tensor states. The data are compared with calculations. The beam-vector asymmetry A[subscript ed][superscript V] is found to be directly sensitive to the D-wave component of the deuteron and has a zero crossing at a missing momentum of about 320  MeV/c, as predicted. The tensor asymmetry A[subscript d][superscript T] at large missing momentum is found to be dominated by the influence of the tensor force in the neutron-proton final-state interaction. The new data provide a strong constraint on theoretical models