G. P. Gilfoyle

The CLAS drift chamber system

Abstract Experimental Hall B at Jefferson Laboratory houses the CEBAF Large Acceptance Spectrometer, the magnetic field of which is produced by a superconducting toroid. The six coils of this toroid divide the detector azimuthally into six sectors, each of which contains three large multi-layer drift chambers for tracking charged particles produced from a fixed target on the toroidal axis. Within the 18 drift chambers are a total of 35,148 individually instrumented hexagonal drift cells. The novel geometry of these chambers provides for good tracking resolution and efficiency, along with large acceptance. The design and construction challenges posed by these large-scale detectors are described, and detailed results are presented from in-beam measurements.

Using Nuclear Materials To Prevent Nuclear Proliferation

Efforts to halt proliferation of nuclear weapons are threatened by vulnerability of weapons‐usable material to smuggling especially in Russia. Mixing 232U into highly‐enriched uranium (HEU) makes it readily observable and harder to steal. Adding a proportion of 233U associated with a specific storage site enables attribution to be performed on stolen HEU that has been recovered. Incorporating 244Pu into plutonium does the same for this material. U.S. programs for radioactive surplus disposition could provide a source for tags. Current U.S.‐Russian efforts to dispose of surplus nuclear weapons open opportunities to incorporate tags into large amounts of weapons‐usable material. The 232U detection tag would also enhance ongoing US‐Russian efforts to detect smuggling of weapons‐usable materials out of Russia.

A new teaching approach to quantum mechanical tunneling

The transfer matrix method has been used to investigate quantum mechanical tunneling in introductory quantum mechanics. The method is applied first to calculate the transmission coefficient for tunneling through a rectangular barrier and is then extended to the problem of potential barriers of arbitrary shape, in particular, to radioactive decay. This approach uses matrix methods that are accessible to a broader range of undergraduates than other numerical techniques, the connection between the rectangular barrier problem and potential barriers of arbitrary shape is transparent, and it can be readily executed by undergraduates. The classroom experience with this approach is discussed.

Small angle neutron-neutron correlation functions for the 16O+27Al reaction at 220 MeV

Abstract Small angle correlations between two neutrons emitted at a laboratory angle near 45° from the 16 O+ 27 Al reaction at 220 MeV have been measured. The results show a positive correlation peak centered near a relative momentum of 7.5 MeV/ c . However, when restrictions are placed on the total momentum of the two-neutron system, the strength of the correlation function is found to be dependent on the total momentum of the two-neutron system. A possible anti-correlation is observed at low relative momentum for low total momentum pairs.

CLARA: A Contemporary Approach to Physics Data Processing

CLARA (CLAS12 Reconstruction and Analysis framework) is CLAS12 physics data processing (PDP) application development framework based on a service oriented architecture (SOA). This framework allows users to design and deploy data processing services as well as dynamically compose PDP applications using available services. Services can be written in Java, C++, and Python languages. The PDP service bus provides a layer on top of a distributed pub-sub middleware implementation. This allows complex service composition and integration without writing a code. We believe that by deviating from the traditional self contained, monolithic PDP application models we can improve maintenance, scalability and quality of physics data analysis. The SOA approach also helps us to separate a specific service programmer from a PDP application designer. Examples of service creation and deployment, along with the CLAS12 track reconstruction application design are presented.

Construction update and drift velocity calibration for the CLAS drift chamber system

Abstract We briefly describe the drift chamber system for the CLAS detector at CEBAF, concentrating on the method which will be used to calibrate the drift velocity function. We identify key features of the function which should apply to any small-cell drift chamber geometry in which the cathode and anode surfaces are wires. Using these ideas, we describe a simple method to compensate for variations in the drift velocity function due to environmental changes.

Effects of non-parallel magnetic fields on hexagonal cell drift chambers

The effect of magnetic field on drift velocity was measured in a wire chamber with an hexagonal cell geometry and an argon-ethane (50:50 by weight) gas mixture. The CLAS (CEBAF large acceptance spectrometer) prototype drift chamber was tested in a magnetic field using cosmic rays. The drift time to distance correlation was studied as a function of magnetic field strength using cosmic ray tracks. Particular attention was paid to the corrections due to differing track entrance angles and differing angles of the magnetic field direction with respect to the wire axis. Spatial resolutions better than 190 mu m were achieved for field strengths up to 1.5 T and angles between wire and field direction ranging from 0 degrees to 30 degrees . An argon-ethane mixture diluted with 60% helium showed less sensitivity to magnetic field effects, and only slightly worse resolution.<<ETX>>

QCD in nuclear processes at Jefferson Lab

The scientific program at Jefferson Lab to probe the properties of QCD in the nuclear environment is outlined. The experimental facilities are described and recent results are presented including measurements of color transparency and medium modifications of vector mesons. The evidence for the onset of color transparency is modest and changes to the mass and width of the ρ meson in heavy nuclei are consistent with zero. Finally, the future prospects for the upgraded laboratory are discussed.

Resonances in C13(13C,)22Ne

Complete angular distributions (theta/sub c.m./ = 9/sup 0/--90/sup 0/) for the reaction /sup 13/C( /sup 13/C,..cap alpha..) /sup 22/ Ne in the energy range E/sub c.m./ = 6.25--13.38 MeV have been measured. The data exhibit significant resonancelike behavior and a portion of it has been fitted to extract the amplitudes and phases of the relevant l values with two methods. The first uses a least-squares procedure to fit the angular distributions to a linear sum of Legendre polynomials while the second makes a grid search to find a best fit to an amplitude squared equation.

Resonances inC13(13C,α)22Ne

Complete angular distributions (theta/sub c.m./ = 9/sup 0/--90/sup 0/) for the reaction /sup 13/C( /sup 13/C,..cap alpha..) /sup 22/ Ne in the energy range E/sub c.m./ = 6.25--13.38 MeV have been measured. The data exhibit significant resonancelike behavior and a portion of it has been fitted to extract the amplitudes and phases of the relevant l values with two methods. The first uses a least-squares procedure to fit the angular distributions to a linear sum of Legendre polynomials while the second makes a grid search to find a best fit to an amplitude squared equation.