Construction and Commissioning of a Micro-Mott Polarimeter
for Photocathode Research and Development. APRIL
COOK (Monmouth College, Monmouth, IL, 61462) MARCY STUTZMAN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Thomas Jefferson
National Accelerator Facility uses polarized electrons to further
the understanding of the atomic nucleus. The polarized source produces
electrons by directing laser light onto a specially prepared gallium
arsenide (GaAs) photocathode. During the course of this project,
an off-beamline micro-Mott polarimeter has been built and commissioned
within the Source Lab for photocathode research and development.
A polarimeter measures the polarization, or spin direction, of
electrons. The micro-Mott runs at 30 keV and can be used directly
in the Source Lab, off of the main accelerator beamline. Construction
of the Mott system began with a polarized source, which consists
of a vacuum chamber complete with a cesiator and nitrogen triflouride
(NF3) to activate the photocathode, residual gas analyzer (RGA),
ultra-high vacuum pumps, an electrostatic deflector to bend the
electron beam 90 degrees, and electrostatic lenses. The polarimeter
is housed in an adjacent vacuum chamber. The circularly polarized
laser light enters the polarized source, hits the GaAs photocathode,
and liberates polarized electrons. The original longitudinally-polarized
electrons are transformed into transversely-polarized electrons
by the electrostatic bend. They are then directed onto a gold target
inside the Mott and scattered for data analysis. The polarized
source has been commissioned, achieving photoemission from the
activated GaAs crystal, and the electrostatic optics have been
tuned to direct the electrons onto the gold target. Nearly ten
percent of the electrons from the photocathode reach the target,
giving adequate current for polarization measurement. The micro-Mott
polarimeter will aid in photocathode research and pre-qualification
of material for use in the injector.
Digital Voltage Controller for the Field Emission Microscope at Jefferson Lab. BRENDAN MATHEWS (West Virginia University, Morgantown,
WV, 26506) JOHN MUSSON (Thomas Jefferson National Accelerator Facility,
Newport News, VA, 23606)
Jefferson Lab
(JLab) uses refined niobium to create superconducting cavities
for the electron beam. Several polishing procedures are used on
the niobium to ensure that arcing does not occur inside these cavities
due to inconsistencies on the surface of the cavities. The metal
is examined under a field emission microscope to detect any remaining
flaws on the surface. This microscope runs a steady current between
the niobium and a phosphorous screen and measures the voltage changes
in order to detect and stalagmites that may appear on the metal.
This device requires that the voltage in the system be regulated
in order to maintain a steady current. Until recently this device
was manually controlled, but the ultimate goal of this project
was to create a device that would eliminate this unnecessary human
error. This new device would require analog inputs so an analog
to digital converter (ADC) was necessary to allow manipulation
of the inputs. After the data comes in through the ADC, it was
processed by an infinite impulse response filter in an attempt
to eliminate any noise. After this process is completed, the date
is fed into a proportional integral derivative controller in order
to bring the output to the desired level. Finally, after all of
this is completed the signal is fed back out into the system by
way of a digital to analog converter (DAC). Testing has shown that
the controller is able to maintain a steady voltage level within
10% of the desired value. Automating this process will allow JLab
to have a more efficient procedure, as well as provide for more
accurate mapping of the niobium used in the beam cavities.
Effect of Acid Agitation on Buffered Chemical Polishing
of Niobium for Radiofrequency Cavities. SARA
MOHON (The College of William and Mary, Williamsburg, VA, 23186) ANDY WU (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
The performance
of niobium superconducting radiofrequency (SRF) cavities can be
affected by the smoothness of their inner surfaces. Smoother inner
surfaces tend to result in better performance. Normally, smooth
niobium surfaces are obtained by buffered chemical polish (BCP).
BCP is necessary to remove the damaged layer created during fabrication
and machining of the cavities. Previous experiments conducted in
the Surface Science Lab at Thomas Jefferson National Accelerator
Facility have shown that the morphology of niobium surfaces may
be altered via different agitation constraints during BCP. The
focus of this research is a systematic study of the effect of agitation
on the BCP treatment of niobium. Six samples of niobium, each one
square centimeter in size, were prepared using a 1:1:2 BCP mixture
for 75 minutes. A control sample was also analyzed with no BCP
treatment. Each BCP treated sample was agitated after a certain
amount of time, varying from 0 to 75 minutes. After this treatment,
the samples were examined by a 3D profilometer, where quantitative
information about surface morphology was extracted. Qualitative
inspection of the surface of each sample was performed a metallographic
optical microscope (MOM). It was found that the surface roughness
increased up to a certain asymptotic limit as the time interval
between agitations increased, and that a green unidentified cloud-like
material appeared above the inner surface area of niobium samples
when there was no agitation. The MOM photographs show evidence
that the BCP mixture attacked the grain boundaries and defect locations
more than it did elsewhere, making a BCP treated surface rougher
in comparison to some other polishing methods. The treated samples
became smoother as the time interval between agitations decreased
although they never become as smooth as the control sample. Smoother
surfaces were also found in areas where the green cloud formed
than in areas where it was absent. A model is proposed to qualitatively
explain the experimental results. Further investigation is warranted
for different BCP ratios to see if a smoother surface finish is
possible and what agitation it requires. In addition, a BCP study
of how larger grain samples affect niobium surface morphology is
promising to the improvement of SRF cavities. These endeavors and
the experimental results are useful for the BCP treatment of niobium
SRF cavities to be used in particle accelerators.
Error Reduction in Polarization Measurement. DONALD JONES (Acadia University, Wolfville, NS,
0) ROBERT MICHAELS (Thomas Jefferson National Accelerator Facility, Newport
News, VA, 23606)
One of the greatest
barriers to definitive conclusions in any scientific experiment
is the accumulation of errors. Due to the precision required in
parity-violation experiments, an effort has been made in Hall A
at Jefferson Lab (JLab) to reduce the cumulative error by targeting
specific sources. A particular focus has been placed on reduction
of error in beam polarization measurements. Compton polarimetry
is utilized at JLab because of its unique advantage of allowing
polarization to be determined while an experiment is running, without
interrupting the beam. Electrical signals produced by scattered
photons and electrons are used to determine beam polarization.
The helicity of the beam is reversed every 33 milliseconds (ms)
and the asymmetry that arises from pulse measurements during consecutive
33 ms intervals, is used to calculate beam polarization. While
this asymmetry has been created in the past by counting photons,
electrons or electron-photon coincidences, this method gives rise
to many systematic errors. New methods are being sought to more
accurately calculate polarization. The focus of this research has
been to determine whether signal integration can be used to effectively
reduce the error to under the 1% level within a feasible time frame.
Extensive tests have been done to determine the reliability of
signal integration across the full 33ms gate, in order to determine
if the background noise is too great to make this technique useful.
Because of difficulties encountered, and the lack of beam operation
during the time this research was done, a pulse generator was used
to simulate the electrical pulses that arise from electron scattering
in the Compton polarimeter. The data from the pulse-generated asymmetry
indicates that polarization can be accurately determined within
three hours of beam operation. Because experiments can last for
days, this is a reasonable length of time. To ensure the reliability
of this technique, the results were then verified using Monte Carlo
simulations. The results of this research show that this method
of beam polarization measurement has great promise of being able
to reduce the measurement error from the present 3%, to below 1%.
This method has yet to be tested during beam operation, but its
success would enhance future parity violation experiments.
GEANT Simulations of the Preshower Calorimeter for CLAS12 Upgrade of the Forward
Electromagnetic Calorimeter. KRISTIN WHITLOW (University
of Florida, Gainesville, FL, 32612) STEPAN STEPANYAN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Hall B at the
Thomas Jefferson National Accelerator Facility uses the CEBAF (Continuous
Electron Beam Accelerator Facility) Large Acceptance Spectrometer
(CLAS) to study the structure of the nucleon. The accelerator is
currently planning to upgrade from using a 6 GeV beam to a 12 GeV
beam. With the beam upgrade, more high-energy pions will be created
from the interaction of the beam and the target. Above 6 GeV, the
angle between the two-decay photons of high-energy pions becomes
too small for the current electromagnetic calorimeter (EC) of CLAS
to differentiate between two photon clusters and single photon
events. Thus, a preshower calorimeter will be added in front of
the EC to enable finer granularity and ensure better cluster separation
for all CLAS experiments at higher energies. In order to optimize
cost without compromising the calorimeter’s performance, three
versions of the preshower varying in number of scintillator and
lead layers were compared by their resolution and efficiency. Through
the use of GSIM, a GEANT detector simulation program for CLAS,
po’s and single photons were passed through the CLAS detector with
the added preshower calorimeter (CLAS12 EC). The resolution of
the CLAS12 EC was calculated from the Gaussian fit of the sampling
fraction, the energy CLAS12 EC detected over the Monte Carlo simulated
momentum. The single photon detection efficiency was determined
from the energy and position of the photon hits. The resolution
measured in the five-modules version was 0.0972, the four-modules
version was 0.111, and three-modules version was 0.149. Both the
five- and four-modules versions had 99% efficiency above 0.5 GeV
while the 3 module version had 99% efficiency above 1.5 GeV. Based
on these results, the suggested preshower configuration is the
four-modules version containing twelve layers of scintillator and
fifteen layers of lead because it is the most realistic choice
to construct in resolution, efficiency and cost. The next step
will be to do additional GSIM simulations to verify that the four-modules
version has acceptable po mass
reconstruction and continue Research and Development (R&D)
analysis on the preshower calorimeter.
G0++: Creating a User Interface
for Fastbus Data. JONATHAN HOOD (University
of Maryland, College
Park, MD, 20742) TANJA HORN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
The G0 collaboration
at Thomas Jefferson National Accelerator Facility (Jefferson Lab)
investigates the contribution of strange quarks to the fundamental
properties of the nucleon. To do this, the G0 experiment sends
a highly energized electron beam into a target, such as liquid
hydrogen. When the electrons in the beam collide with nucleons
in the target, a spray of particles radiates from the collision
point. This spray of particles travels across a magnetic field
into a variety of particle detectors, resulting in large amounts
of unanalyzed data. Data taken during the G0 experiment pertaining
to the time of flight and amplitudes of particle trajectories is
referred to as Fastbus data, which is organized by Root, a C++
interpreter designed for manipulating large number of data points.
For the G0 experiment, Fastbus data provide a general evaluation
of the performance of the detector and electronic systems. Therefore,
an efficient analysis of these data is essential at the startup
and during the running of an experiment. The goal of this project
was to make the Fastbus data more accessible, especially to people
who are not familiar with the Root language. To do this, a good
understanding of the data acquisition and its analysis was required.
By collaborating with scientists at the National Jefferson Laboratory,
a design was constructed and implemented. Scientists need to look
at the data in many different ways, and the program was designed
to include a variety of tools that allows them to do so. In order
to analyze the data quickly and effectively, a Graphical User Interface
(GUI) was programmed to give users a convenient way to create,
display, and manipulate graphs. The interface has been constructed
with many useful tools that aid scientists in the G0 experiment,
including such features as the ability to add cuts to remove unwanted
data points and the ability to fit the data with numerical equations.
The program, titled “G0++: GoFast Goes Fast” will be used by G0
scientists, and eventually the program could be used for general
Hall C data analysis in a C++ framework.
Investigating the Polarization Effects of Free Electrons
Through a Longitudinal Stern-Gerlach Apparatus. RACHEL
SPARKS (Old Dominion University, Norfolk, VA, 23517) DR. DOUGLAS W. HIGINBOTHAM (Thomas Jefferson National Accelerator
Facility, Newport
News, VA, 23606)
Otto Stern and
Walther Gerlach completed an experiment in 1922 that opened many
important questions and discoveries about the quantum mechanical
world. Known as the Stern-Gerlach experiment, a beam of neutral
silver atoms was passed through an inhomogeneous transverse magnetic
field and then projected onto a screen. Classically, one would
expect the screen to display a single blob of silver atoms; however,
two blobs appeared. The breakthrough from this experiment was that
the electron has an intrinsic spin, similar to a rotating top.
Attempts have been made to conduct the Stern-Gerlach experiment
with a beam of free electrons; but the Lorentz force, along with
the Heisenberg uncertainty principle, blurs the splitting of the
beam. In 1928, Brillouin suggested that a longitudinal Stern-Gerlach
apparatus would minimize the effect of the Lorentz force. While
this idea was dismissed in 1930 by Wolfgang Pauli, recent papers
have shown that Brillouin's idea may have been valid. A computer
simulation for an experiment to use the longitudinal Stern-Gerlach
was completed this summer by analyzing the effect of different
spin separations of the beam. Enhancement of the polarization was
seen even using a realistic spread in the electron's momentum.
Thus, it appears feasible to conduct an experiment that will investigate
Brillouin's idea. In the future, this could be done in the Jefferson
Lab test cave with equipment that is readily available.
Optical and Mechanical Design Features of the Qweak
Main Detector. ELLIOTT JOHNSON (North Dakota State University, Fargo, ND, 58105)
DAVE MACK (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Cerenkov radiation
is emitted when charged particles exceed the local speed of light
within a transparent medium. In experimental particle physics,
this radiation can be used to detect high-energy particles. The
Cerenkov radiation detector being used in the Qweak experiment
at Thomas Jefferson National Accelerator Facility (Jefferson Lab)
has unique design features compared with previous detectors, imposing
more specific requirements on the detector’s radiator components.
The new design includes a glue joint in the beam pathway, and side-mounting
Photomultiplier Tubes (PMT’s) instead of the traditional end-on
layout, a change that allows increased detector mobility during
beam operation. The system implements aluminum trays to support
the glue joints and terminal cap pieces that hold the ends of the
quartz bars. Ultra-pure artificial quartz (Spectrosil 2000) bars
with a large resistance to radiation damage are needed for a high
transmission of UV photons. Dimensional and optical specifications
of these bars were assessed with the use of a Coordinate Measuring
Machine (CMM) and a traveling microscope. Presented here is a synopsis
of the high-precision measurements performed on the radiator bars,
as well as a summary of the R&D conducted to develop a usable
detector integrating the new design features. The quality assurance
procedures developed will be essential for future detector projects
involving quartz detectors.
Properties of Light Vector mesons in Dense Nuclei. SCARLET NORBERG (Kent State University, Kent,
OH, 44243) DENNIS WEYGAND (Thomas Jefferson National Accelerator
Facility, Newport News, VA, 23606)
The strong force
is a fundamental force, which describes the forces in the nucleus,
and is expressed by Quantum Chromodynamics (QCD). In dense and
hot matter, masses may change while the underlying symmetries remain
intact. In addition, coupling constants may change. Thus properties
of vector mesons, such as their masses and widths, may change in
dense or hot matter. These modifications are related to the partial
restoration of chiral symmetry at high density and/or temperature.
The g7 experiment was performed using the Large Acceptance Spectrometer
(CLAS) at Jefferson Lab using a tagged photon beam of energies
up to 4 GeV on various nuclear targets. Because the photon can
penetrate the nuclear volume, the interaction occurs approximately
uniformly throughout the nuclear medium. The properties of the
lightest vector mesons, rho, omega, and phi are investigated through
their rare leptonic decay to e+e-. This decay channel is preferred
over hadronic modes in order to eliminate the final state interactions
of the decay products in the nuclear matter. The goal of this study
is to examine any changes in the mass and/or width of rho, omega
and phi produced in the nuclear medium. In this study, the mass
and width of the rho meson have been measured in both a light nuclear
target, deuterium, an intermediate target, carbon, and a heavy
target, iron. The spectral function of the rho meson was compared
to the correct resonance form, a Breit-Wigner function modified
by an electromagnetic propagator (1/m3) required by the e+e- decay.
It was found that the mass and width of the rho meson does not
change in carbon nor deuterium. In iron, while the mass of the
meson is stable, there is an indication that the width changes
by about 2 sigma, consistent with collisional broadening effects.
Implications of the results of g7 will have a major impact on the
interpretation of experiments of the low mass e+e- pairs currently
being performed in high-energy heavy ion collisions at the Relativistic
Heavy Ion Collider (RHIC) at Brookhaven.
Rehabilitation and Implementation of Scintimammography Gamma Camera Integrated
into a Stereotactic Core Biopsy Digital X-ray System. CLARISSA
FREEMAN (Hampton University, Hampton, VA, 23606) STAN MAJEWSKI
(Thomas Jefferson National Accelerator Facility, Newport News,
VA, 23606)
Biopsies are
used to accurately confirm the presence of breast cancer when suspicious
lesions are found. A biopsy is a small sampling of tissue that
can be tested to determine whether there is malignancy. Approximately
three out of every four women still have unnecessary biopsies.
A scintimmamography gamma camera integrated into a stereotactic
core biopsy digital x-ray system may be used to reduce unnecessary
biopsies. The scintimmamography gamma camera is a custom-built
mini gamma camera with an active area of 5.3 cm by 5.3 cm. It is
based upon a 2 by 2 array of position-sensitive photomultiplier
tubes made by Hamamatsu. The system obtains dynamic scintimammographic
data by performing dynamic radiopharmaceutical uptake studies;
these images can confirm or negate the need for a biopsy, leading
to fewer unnecessary procedures. The objective of the project was
to remove the system out of its clinical setting for repair and
calibration. It has a primary detector head for most clinical settings,
as well as a second detector to be used as an auxiliary. A new
crystal map was created for the system, detector head energies
were calibrated, and corrected images were taken. In addition,
electrical components were replaced and appropriately labeled.
For optimal stability, calibrations were performed using Kmax Sparrows
NT development package. A dynamic energy range for detector head
one was found to be 540 volts, and the second detector range was
found to be 580 volts. The system was tested once all repairs were
complete and calibrations were finalized. In the coming months,
the system will be put into a clinical environment so that its
performance can be tested against traditional detector systems.
RF TE011 Cavity Prototyping and Characterization for
Surface Science Studies. JARED
NANCE (Beloit College, Beloit, WI, 53511)
HAIPENG WANG (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Understanding
the properties of superconducting materials is crucial to the future
development of accelerating structures. According to BCS theory,
superconductors possess a very small surface impedance at RF frequencies.
For superconducting particle accelerators operating at RF frequencies
such as the Continuous Electron Beam Accelerator Facility (CEBAF),
this means that there is some mechanism by which the energy stored
in the RF fields can be dissipated, and the accelerator's performance
degraded. The SRF (Superconducting RF) group at Thomas Jefferson
National Accelerator Facility has developed a cavity which will
be used for testing the surface impedance of flat superconducting
samples. The cavity is optimized for operation at superconducting
temperatures of 2K. The intent of the design is to store energy
in the form of a dominant TE011 mode
resonance at 7.5GHz. The TE011 mode is well suited for surface science studies because of its
inherently high ratio of power stored to power dissipated (the
Quality (Q) factor), as well as its simple and well understood
cylindrical symmetry. The complex geometry of the cavity itself
is not, however, exclusive to the TE011 mode;
a large number of resonances are permitted, all with varying characteristics
and symmetries. Without conclusive knowledge of which resonant
mode the samples are exposed to, the field at the surface of the
sample cannot be known exactly. Therefore, correct identification
and characterization of the TE011 mode
is critical for the experiment. Vector Network Analysis techniques
were used to characterize the fields by monitoring the response
of the Scattering (S) Parameters to perturbations of the cavity
geometry. The S-Parameters of a network (the cavity) are a measure
of the reflectance and transmittance of that network. Resonance
conditions in the cavity can therefore be detected by interpreting
peaks in the S-Parameter spectra as stored or dissipated energy
in the cavity. The results of the analysis indicate that the TE011 mode
is in fact the dominant main cavity mode at 7.5GHz, in agreement
with theory.
Study of Beam Spin Asymmetry in Exclusive πo
Production. IAN HOWLEY (The College of William
and Mary, Williamsburg, VA, 23186) HARUT AVAKIAN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Describing and
understanding atomic nuclei is a puzzle that has intrigued scientists
for decades. Approximately ten years ago, a way to describe nucleon
structure, referred to as Generalized Parton Distribution (GPD),
was introduced. GPDs are a way of describing scattering and production
processes in a single framework. Deeply Virtual Compton Scattering
(DVCS) is a process that scatters a photon from a proton and detects
a scattered electron, a proton, and one photon in the final state.
From DVCS, GPDs can be extracted in order to lead us to a more
complete picture of nucleon structure. The focus of this study
is to understand the beam spin asymmetry (BSA) of the neutral πo meson,
a main source of background during the DVCS process. To calculate
the BSA, the number of πo events
with positive helicity (spin) and negative helicity were counted
by integrating histograms with Gaussians fits. It is shown that
there is a significant non-zero BSA in production of exclusive πo,
namely 0.0655 ± 0.0022. In the analysis of previous experiments,
the BSA of πo was
assumed to be zero and therefore ignored. Now, since it is proven
to exist, it can be taken into account in future DVCS studies.
A deeper understanding of background processes (πo) in the DVCS will allow precision measurements of GPDs, providing
new insight concerning the structure of nucleons.
Study of the Effect on Larger Wire Diameter on Drift
Chamber Performa. NATALIE HANSEN (Brigham Young University, Provo, UT, 84606) MAC MESTAYER (Thomas Jefferson National Accelerator
Facility, Newport News, VA, 23606)
A wire chamber
is essentially a gas-filled box traversed by anode (sense) and
cathode (field) wires held at a high electric potential difference
that is used to detect charged particles. Electrons are freed as
a particle ionizes gas atoms in its path. These electrons travel
along field lines and register as a current when reaching the sense
wires. The distance between wires, the gas composition and the
voltage difference between wires all determine the detection efficiency.
The drift chambers for the Continuous Electron Beam Accelerator
Facility (CEBAF) Large Acceptance Spectrometer (CLAS) detector
at Jefferson Lab use a 90% argon and 10% CO2 gas
mixture and sense wires of 20 µm diameter. Proposed changes for
a planned upgrade include increasing the sense wire diameter to
30 µm, which, however, may lead to increased levels of noise. This
project focused on assembling a prototype chamber to test the effect
of changing the sense wire diameter. A previously built chamber
was restrung with 30 µm wire, leaving one 20 µm wire for comparison.
The associated electronic equipment and gas system were set up
and the chamber is operational. The experimental results were plots
of count rate versus voltage for different discriminator settings.
Individual plots show a hint of a high voltage plateau around 1500
- 1525 V, despite the fact that much of the data were inconsistent,
presumably due to bursts of external, electronic noise. When the
hit rate was plotted versus gas gain rather than voltage, the individual
graphs for different discriminator settings came very close to
a universal curve. Any slight deviations from that curve may be
due to the increased probability of spontaneous electron emission
(noise) from the field wire. Increasing the sense wire radius and
the voltage seems to yield only a modest increase of noise levels.
Suitability of a New Calorimeter for Identifying Exotic Meson Candidates. CRAIG
BOOKWALTER (Florida State University, Tallahassee, FL, 32306) PAUL EUGENIO (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Exotic mesons,
particles that have quantum numbers that are inaccessible to conventional
quark-model mesons, are predicted by quantum chromodynamics (QCD),
but past experiments seeking to identify exotic candidates have
produced controversial results. The HyCLAS experiment (E04005)
at Thomas Jefferson National Accelerator Facility (TJNAF) proposes
the use of the Continuous Electron Beam Accelerator Facility (CEBAF)
Large Acceptance Spectrometer (CLAS) in Hall B to study the photoproduction
of exotic mesons. However, the base detector package at CLAS is
not ideal for observing and measuring neutral particles, particularly
at forward angles. The Deeply Virtual Compton Scattering (DVCS)
experiment at TJNAF has commissioned a new calorimeter for detecting
small-angle photons, but studies must be performed to determine
its suitability for a meson spectroscopy experiment. The ηπ system
has been under especial scrutiny in the community as a source for
potential exotics, so the new calorimeter's ability at reconstructing
these resonances must be evaluated. To achieve this, the invariant
mass of showers in the calorimeter are reconstructed. Also, two
electroproduction reaction channels analogous to photoproduction
channels of interest to HyCLAS are examined in DVCS data. It is
found that, while not ideal, the new calorimeter will allow access
to additional reaction channels, and its inclusion in HyCLAS is
warranted. Results in basic shower reconstruction show that the
calorimeter has good efficiency in resolving π0 decays, but its η reconstruction is not as strong. When
examining ep epπ0η, preliminary reconstruction of the ηπ0 system
shows faint signals in the a0(980) region. In the ep e n π+ η channel, preliminary reconstruction of the ηπ+ system
gave good signals in the a0(980) and a2(1320) regions, but statistics were poor. While more analyses
are necessary to improve statistics and remove background, these
preliminary results support the claim that the DVCS calorimeter
will be a valuable addition to CLAS for upcoming exotic meson searches
in photoproduction.
Testing and Development of Neutron Bubble Dosimeters for Upgrading Radiation
Monitors. PHILLIP ZELLNER (Virginia Polytechnic Institute and
State University, Blacksburg, VA, 24060) ERIK ABKEMEIER (Thomas
Jefferson National Accelerator Facility, Newport News, VA, 23606)
Jefferson Lab
is upgrading its particle accelerator from 6 GeV to 12 GeV to give
physicists greater insight in the experiments they run. An unfortunate
side effect of the upgrade, is that the experiments performed by
Jefferson Lab will generate neutron radiation with much higher
energy (up to 20 MeV). The ion chambers that the Lab uses to monitor
the radiation dose given to the public, will not be able to detect
the higher energy neutrons. In order to solve this problem, neutron
bubble dosimeters are being developed to detect the higher energy
neutrons. These dosimeters are the first instruments to put superheated
bubbles. The ability of the neutron bubble dosimeters to detect
20 MeV neutrons has already been proven. However, this project
tested the feasibility of using the neutron bubble dosimeters.
The detectors were tested on Jefferson Lab’s radiation range and
calibrated. Then the neutron bubble dosimeters were tested side-by-side
with the ion chamber dosimeters in the existing radiation monitoring
stations. It was shown that the neutron bubble dosimeters could
detect the higher energy neutrons. The test results from the comparison
of the two types of dosimeters showed that the neutron bubble dosimeters
were at least as reliable as the ion chambers in detecting the
neutrons that are currently produced by the accelerator. This success
ensures that a reliable radiation detection system will be in place
well before the 12 GeV upgrade is complete, thereby ensuring the
safety of Jefferson Lab’s employees and the public.
