Browsing by Subject "Nuclear physics"

Experiments at Jefferson Lab have been conducted to extract the nucleon spin-dependent structure functions over a wide kinematic range. Higher moments of these quantities provide tests of QCD sum rules and predictions of chiral perturbation theory ($\chi$PT). While precise measurements of $g_{1}^n$, $g_{2}^n$, and $g_1^p$ have been extensively performed, the data of $g_2^p$ remain scarce. Discrepancies were found between existing data related to $g_2$ and theoretical predictions. Results on the proton at large $Q^2$ show a significant deviation from the Burkhardt-Cottingham sum rule, while results for the neutron generally follow this sum rule. The next-to-leading order $\chi$PT calculations exhibit discrepancy with data on the longitudinal-transverse polarizability $\delta_{LT}^n$. Further measurements of the proton spin structure function $g_2^p$ are desired to understand these discrepancies.

Experiment E08-027 (g2p) was conducted at Jefferson Lab in experimental Hall A in 2012. Inclusive measurements were performed with polarized electron beam and a polarized ammonia target to obtain the proton spin-dependent structure function $g_2^p$ at low Q$^2$ region (0.02$<$Q$^2$$<$0.2 GeV$^2$) for the first time. The results can be used to test the Burkhardt-Cottingham sum rule, and also allow us to extract the longitudinal-transverse spin polarizability of the proton, which will provide a benchmark test of $\chi$PT calculations. This thesis will present and discuss the very preliminary results of the transverse asymmetry and the spin-dependent structure functions $g_1^p$ and $g_2^p$ from the data analysis of the g2p experiment .

The Standard model process of Coherent Elastic Neutrino-Nucleus Scattering (CEvNS), which was first predicted by Freedman in 1974, has recently been observed by the COHERENT collaboration on CsI and liquid argon targets. The result is a new way to build a compact neutrino detector which unlocks new channels to test the Standard Model. A semiconductor germanium detector, a technology that has been developed by many dark matter direct detection experiments due to its excellent energy resolution and low-energy thresholds, will also be deployed to ORNL in order to detect CEvNS as part of the next phase of the COHERENT experiment. One of the challenges is to understand the signature of neutrino-induced low-energy nuclear recoils in germanium. A measurement was carried out at the Triangle Universities Nuclear Laboratory (TUNL) to characterize the it response to low-energy nuclear recoils. A quenching factor of 14-20% for nuclear recoil energies between 0.8-4.9 keV in Ge was established. A long predicted smearing effect due to quenching was observed for the first time and estimated to be 0.024 at ~2 keVnr. Finally, the impact of this effect and the quenching factor on the expected CEvNS spectrum of the future Ge deployment is presented.



Giant multipole resonances are a fundamental property of nuclei and

arise from the collective motion of the nucleons inside

the nucleus. Careful studies of these resonances and their properties provides

insight into the nature of nuclear matter and constraints

which can be used to test our theories.

An investigation of the Isovector Giant Quadrupole Resonance (IVGQR)

in ²⁰⁹Bi has been preformed using the High Intensity γ-ray

Source (HIγS) facility. Intense nearly monochromatic

polarized γ-rays were incident upon a ²⁰⁹Bi target producing

nuclear Compton scattered γ-rays that were detected using the HIγS

NaI(Tl) Detector Array (HINDA). The HINDA array consists of six

large (10''x10'') NaI(Tl) core crystals, each surrounded by an

optically segmented 3'' thick NaI(Tl) annulus. The scattered γ-rays

both parallel and perpendicular to the plane of polarization were

detected at scattering angles of 55° and 125° with

respect to the beam axis. This was motivated by the realization that

the term representing the interference between the electric dipole

(E1) and electric quadrupole (E2) amplitudes, which appears in the

theoretical expression for the ratio of the polarized cross sections,

has a sign difference between the forward and backward angles and also

changes sign as the incident γ-ray energy is scanned over the E2

resonance energy. The ratio of cross sections perpendicular and

parallel to the plane of polarization of the incident γ-ray were

measured for thirteen different incident γ-ray energies between 15 and

26 MeV at these two angles and used to extract the parameters of the

IVGQR in ²⁰⁹Bi.

The polarization ratio was calculated at 55° and

125° using a model consisting of E1 and E2 giant resonances as

well as a modified Thomson scattering amplitude. The parameters of the E1 giant

resonance came from previous measurements of the Giant Dipole

Resonance (GDR)

in ²⁰⁹Bi. The finite size of the nucleus was

accounted for by introducing a charge form factor in the (modified)

Thomson amplitude. This form factor was obtained from

measurements of the charge density in inelastic electron scattering

experiments.

The resulting curves were fit to the data by varying the

E2 parameters until a minimum value of the χ² was found.

The resulting parameters from the fit yield an IVGQR in ²⁰⁹Bi

located at E_res=23.0±0.13(stat)±0.25(sys) MeV

with a width of Γ=3.9±0.7(stat)±1.3(sys) MeV and a

strength of 0.56±0.04(stat)±0.10(sys) Isovector Giant

Quadrupole Energy Weighted Sum Rules (IVQEWSRs).

The ability to make precise measurements of the parameters of the

IVGQR demonstrated by this work opens up new challenges to both

experimental and theoretical work in nuclear structure. A detailed

search for the missing sum rule strength in the case of ²⁰⁹Bi should

be performed. In addition, a systematic study of a number of nuclei

should be studied with this technique in order to carefully examine

the A dependence of the energy, width and sum rule strength of the

IVGQR as a function of the mass number A. The unique properties of

the HIγS facility makes it the ideal laboratory at which to perform

these studies.

Such a data base will provide more stringent tests of nuclear

theory. The effective parameters of collective models can be fine

tuned to account for such precision data. This should lead to new

insights into the underlying interactions responsible for the nature

of the IVGQR. Furthermore, with the recent advances in computational

power and techniques, microscopic shell model based calculations

should be possible and could lead to new insights into the underlying

properties of nuclear matter which are responsible for the collective

behavior evidenced by the existence and properties of the IVGQR.

In order to analyze the strongly interacting quark gluon plasma in heavy ion collisions, we study different probes by applying the gauge/gravity duality to facilitate our qualitative understandings on such a non-perturbative system. In this dissertation, we utilize a variety of holographic models to tackle many problems in heavy ion physics including the rapid thermalization, jet quenching, photon production, and anomalous effects led by external electromagnetic fields. We employ the AdS-Vaidya metric to study the gravitational collapse corresponding to the thermalization of a strongly coupled gauge theory, where we compute the approximated thermalization time and stopping distances of light probes in such a non-equilibrium medium. We further generalize the study to the case with a nonzero chemical potential. We find that the non-equilibrium effect is more influential for the probes with smaller energy. In the presence of a finite chemical potential, the decrease of thermalization times for both the medium and the light probes is observed.

On the other hand, we also investigate the anisotropic effect on the stopping distance related to jet quenching of light probes and thermal-photon production. The stopping distance and photoemission rate in the anisotropic background depend on the moving directions of probes.

The influence from a magnetic field on photoemission is as well investigated in the framework of the D3/D7 system, where the contributions from massive quarks are involved. The enhancement of photon production for photons generated perpendicular to the magnetic field is found. Given that the mass of massive quarks is close to the critical embedding, the meson-photon transition will yield a resonance in the spectrum. We thus evaluate flow coefficient $v_2$ of thermal photons in a 2+1 flavor strongly interacting plasma. The magnetic-field induced photoemission results in large $v_2$ and the resonance from massive quarks gives rise to a mild peak in the spectrum. Moreover, we utilize Sakai-Sugimoto model to analyze the chiral electric separation effect, where an axial current is generated parallel to the applied electric field in the presence of both the vector and axial chemical potentials. Interestingly, the axial conductivity is approximately proportional to the product of the vector chemical potential and the axial chemical potential for arbitrary magnitudes of the chemical potentials.

Over the past 200 years, the Earth's atmospheric carbon dioxide (CO₂) concentration has increased by more than 35%, and climate experts predict that CO₂ levels may double by the end of this century. Understanding the mechanisms of resource management in plants is fundamental for predicting how plants will respond to the increase in atmospheric CO₂. Plant productivity sustains life on Earth and is a principal component of the planet's system that regulates atmospheric CO₂ concentration. As such, one of the central goals of plant science is to understand the regulatory mechanisms of plant growth in a changing environment. Short-lived positron-emitting radiotracer techniques provide time-dependent data that are critical for developing models of metabolite transport and resource distribution in plants and their microenvironments. To better understand the effects of environmental changes on resource transport and allocation in plants, we have developed a system for real-time measurements of metabolite transport in plants using short-lived positron-emitting radiotracers. This thesis project includes the design, construction, and demonstration of the capabilities of this system for performing real-time measurements of metabolite transport in plants.

The short-lived radiotracer system described in this dissertation takes advantage of the combined capabilities and close proximity of two research facilities at Duke University: the Triangle Universities Nuclear Laboratory (TUNL) and the Duke University Phytotron, which are separated by approximately 100 meters. The short-lived positron-emitting radioisotopes are generated using the 10-MV tandem Van de Graaff accelerator located in the main TUNL building, which provides the capability of producing short-lived positron-emitting isotopes such as carbon-11 (¹¹C; 20 minute half-life), nitrogen-13 (¹³N; 10 minute half-life), fluorine-18 (¹⁸F; 110 minute half-life), and oxygen-15 (¹⁵O; 2 minute half-life). The radioisotopes may be introduced to plants as biologically active molecules such as ¹¹CO₂, ¹³NO₃^-, ¹⁸F^--[H₂O], and H₂^{15<\sup>O. Plants for these studies are grown in controlled-environment chambers at the Phytotron. The chambers offer an array of control for temperature, humidity, atmospheric CO₂ concentration, and light intensity. Additionally, the Phytotron houses one large reach-in growth chamber that is dedicated to this project for radioisotope labeling measurements.}

There are several important properties of short-lived positron-emitting radiotracers that make them well suited for use in investigating metabolite transport in plants. First, because the molecular mass of a radioisotope-tagged compound is only minutely different from the corresponding stable compound, radiotracer substances should be metabolized and transported in plants the same as their non-radioactive counterparts. Second, because the relatively high energy gamma rays emitted from electron-positron annihilation are attenuated very little by plant tissue, the real-time distribution of a radiotracer can be measured in vivo in plants. Finally, the short radioactive half-lives of these isotopes allow for repeat measurements on the same plant in a short period of time. For example, in studies of short-term environmental changes on plant metabolite dynamics, a single plant can be labeled multiple times to measure its responses to different environmental conditions. Also, different short-lived radiotracers can be applied to the same plant over a short period of time to investigate the transport and allocation of various metabolites.

This newly developed system provides the capabilities for production of ¹¹CO₂ at TUNL, transfer of the ¹¹CO₂ gas from the target area at TUNL to a radiation-shielded cryogenic trap at the Phytotron, labeling of photoassimilates with ¹¹C, and in vivo gamma-ray detection for real-time measurements of the radiotracer distribution in small plants. The experimental techniques and instrumentation that enabled the quantitative biological studies reported in this thesis were developed through a series of experiments made at TUNL and the Phytotron. Collimated single detectors and coincidence counting techniques were used to monitor the radiotracer distribution on a coarse spatial scale. Additionally, a prototype Versatile Imager for Positron Emitting Radiotracers (VIPER) was built to provide the capability of measuring radiotracer distributions in plants with high spatial resolution (~2.5 mm). This device enables detailed quantification of real-time metabolite dynamics on fine spatial scales.

The full capabilities of this radiotracer system were utilized in an investigation of the effects of elevated atmospheric CO₂ concentration and root nutrient availability on the transport and allocation of recently fixed carbon, including that released from the roots via exudation or respiration, in two grass species. The ¹¹CO₂ gas was introduced to a leaf on the plants grown at either ambient or elevated atmospheric CO₂. Two sequential measurements were performed per day on each plant: a control nutrient solution labeling immediately followed by labeling with a 10-fold increase or decrease in nutrient concentration. The real-time distribution of ¹¹C-labeled photoassimilate was measured in vivo throughout the plant and root environment. This measurement resulted in the first observation of a rapid plant response to short-term changes in nutrient availability via correlated changes in the photoassimilate allocation to root exudates. Our data indicated that root exudation was consistently enhanced at lower nutrient concentrations. Also, we found that elevated atmospheric CO₂ increased the velocity of photoassimilate transport throughout the plant, enhanced root exudation in an annual crop grass, and reduced root exudation in a perennial native grass.

Two separate experimental searches for second-order weak nuclear decays to excited final states were conducted. Both experiments were carried out at the Kimballton Underground Research Facility to provide shielding from cosmic rays. The first search is for the two-neutrino double-beta decay of 96Zr to excited final states of the daughter nucleus, 96Mo. As a by product of this experiment, the beta decay of 96Zr was also investigated. Two coaxial high-purity germanium detectors were used in coincidence to detect gamma rays produced by the daughter nucleus as it de-excited to the ground state. After collecting 1.92 years of data with 17.91 g of enriched 96Zr, half-life limits at the level of 10^20 yr were produced. Measurements of this decay are important to test neutrinoless double-beta decay nuclear matrix element calculations, which are necessary to extract the neutrino mass from a measurement of the neutrinoless double-beta decay half-life.

The second experiment is a search for the resonantly-enhanced neutrinoless double-electron capture decay of 156Dy to excited states in 156Gd. Double-electron capture is a possible experimental alternative to neutrinoless-double beta decay, which could distinguish the Dirac or Majorana nature of the neutrino. Two clover high-purity germanium detectors were used in coincidence to investigate the decay. A 213.5 mg enriched 156Dy sample was observed for 0.635 year, producing half-life limits of 10^17 yr. The limits produced by both of these experiments are currently the most stringent limits available for these decays.

An experimental study of the two-neutrino double-beta (2νββ) decay of 150Nd to various excited final states of 150Sm was performed at Triangle Universities Nuclear Laboratory (TUNL). Such data provide important checks for theoretical models used to predict 0νββ decay half lives.

The measurement was performed at the recently established Kimballton Underground Research Facility (KURF) in Ripplemeade, Virginia using the TUNL-ITEP double-beta decay setup. In this setup, two high-purity germanium detectors were operated in coincidence to detect the deexcitation gamma rays of the daughter nucleus. This coincidence technique, along with the location underground, provides a considerable reduction in background in the regions of interest.

This study yields the first results from KURF and the first detection of the

coincidence gamma rays from the 0+₁ excited state of 150Sm. These gamma rays

have energies of 334.0 keV and 406.5 keV, and are emitted in coincidence through a 0+₁→2+₁→0+_gs transition. The enriched Nd₂O₃ sample obtained from Oak Ridge

National Laboratory consists of 40.13 g 150Nd. This sample was observed for 391 days, producing 29 raw events in the region of interest. This count rate gives a half life of T_1/2 = (0.72+0.36_−0.18 ± 0.04(syst.)) × 1020 years, which agrees within error with

another recent measurement, in which only the single deexcitation gamma rays were detected (i.e., no coincidence was employed). Lower limits were also obtained for decays to higher excited final states.

In this thesis, we study effective field theories for doubly heavy baryons and lattice QCD. We construct a chiral Lagrangian for doubly heavy baryons and heavy mesons that is invariant under heavy quark-diquark symmetry at leading order and includes the leading O(1/m_Q ) symmetry violating operators. The theory is used to predict the electromagnetic decay width of the J = 3/2 member of the ground state doubly heavy baryon doublet. Numerical estimates are provided for doubly charm baryons. We also calculate chiral corrections to doubly heavy baryon masses and strong decay widths of low lying excited doubly heavy baryons. We derive the couplings of heavy diquarks to weak currents in the limit of heavy quark-diquark symmetry, and construct the chiral Lagrangian for doubly heavy baryons coupled to weak currents. Chiral corrections to doubly heavy baryon zero-recoil semileptonic decay for both unquenched and partially quenched QCD are calculated. This theory is used to derive chiral extrapolation formulae for measurements of the doubly heavy baryon zero-recoil semileptonic decay form factors in lattice QCD simulations. Additionally, we study the pion physics on lattice using chiral perturbation theory. For finite volume field theories with discrete translational invariance, conserved currents can obtain additional corrections from infrared effects. We demonstrate this for pions using chiral perturbation theory coupled to electromagnetism in a periodic box. Gauge invariant single particle effective theories are constructed to explain these results. We use chiral perturbation theory to study the extraction of pion electromagnetic polarizabilities from lattice QCD. Chiral extrapolation formulae are derived for partially quenched and quenched QCD simulations. We determine finite volume corrections to the Compton scattering tensor of pions.

It is of great importance to identify new sources of discrete symmetry violations because it can explain the baryon number asymmetry of our universe and also test the validity of various models beyond the standard model. Neutron Electric Dipole Moment (nEDM) and short-range force are such candidates for the new sources of P&T violations. A new generation nEDM experiment was proposed in USA in 2002, aiming at improving the current nEDM upperlimit by two orders of magnitude. Polarized 3He is crucial in this experiment and Duke is responsible for the 3He injection, measurements of 3He nuclear magnetic resonance (NMR) signal and some physics properties related to polarized 3He.

A Monte-Carlo simulation is used to simulate the entire 3He injection process in order to study whether polarized 3He can be successfully delivered to the measurement cell. Our simulation result shows that it is achievable to maintain more than 95% polarization after 3He atoms travel through very complicated paths in the presence of non-uniform magnetic fiels.

We also built an apparatus to demonstrate that the 3He precession signal can be measured under the nEDM experimental conditions using the Superconducting Quantum Interference Device (SQUID). Based on the measurement result in our lab, we project that the signal-to-noise ratio in the nEDM experiment will be at least 10.

During this SQUID test, two interesting phenomena were discovered. One is the pressure dependence of the T₁ of the polarized 3He which has never been reported before. The other is the discrepancy between the theoretically predicted T₂ and the experimentally measured T₂ of the 3He precession signal. To investigate these two interesting phenomena, two dedicated experiments were built, and two papers have been published in Physical Review A.

In addition to the nEDM experiment, polarized 3He is also used in the search for the exotic short-range force. The high pressure 3He cell used in this experiment has a very thin window (~250 μm) to maximize the effect from the force. We demonstrate that our new method could improve the current best experimental limit by two orders of magnitude. A rapid communication demonstrating the technique and the result was published in Physical Review D.

Ultrarelativistic heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) are thought to have produced a state of matter called the Quark-Gluon-Plasma (QGP). The QGP forms when nuclear matter governed by Quantum Chromodynamics (QCD) reaches a temperature and baryochemical potential necessary to achieve the transition of hadrons (bound states of quarks and gluons) to {it deconfined} quarks and gluons. Such conditions have been achieved at RHIC, and the resulting QGP created exhibits properties of a near perfect fluid. In particular, strong evidence shows that the QGP exhibits a very small shear viscosity to entropy density ratio &eta/s, near the lower bound predicted for that quantity by Anti-deSitter space/Conformal Field Theory (AdS/CFT) methods of &eta/s = $hbar$/ 4 &pi $k_B$ where $hbar$ is Planck's constant and $k_B$ is Boltzmann's constant. As the produced matter expands and cools, it evolves through a phase described by a hadron gas with rapidly increasing $eta/s$.

This thesis presents robust calculations of $eta/s$ for hadronic and partonic media as a function of temperature using the Green-Kubo formalism. An analysis is performed for the behavior of $eta/s$ to mimic situations of the hadronic media at RHIC evolving out of chemical equilibrium, and systematic uncertainties are assessed for our method. In addition, preliminary results are presented for the bulk viscosity to entropy density ratio $zeta/s$, whose behavior is not well-known in a relativistic heavy ion collisions. The diffusion coefficient for baryon number is investigated, and an algorithm is presented to improve upon the previous work of investigation of heavy quark diffusion in a thermal QGP.

By combining the results of my investigations for $eta/s$ from our microscopic transport models with what is currently known from the experimental results on elliptic flow from RHIC, I find that the trajectory of $eta/s$ in a heavy ion collision has a rich structure, especially near the deconfinement transition temperature $T_c$. I have helped quantify the viscous hadronic effects to enable investigators to constrain the value of $eta/s$ for the QGP created at RHIC.

This dissertation describes the first study of three-body photodisintegration of polarized 3He (γ3He → npp) with a circularly polarized photon beam.

This measurement was carried out at the High Intensity γ-Ray Source(HIγS) facility located at Duke University Free Electron Laser Laboratory and the incoming photon energy was 11.4 MeV. A high-pressure polarized 3He target based on spin exchange optical pumping (SEOP) of hybrid alkali was employed. Two methods--Nuclear Magnetic Resonance (NMR) and Electron

Paramagnetic Resonance (EPR)--were used to measure the polarization, which was determined to be ∼ 42%.

The data from the experiment were analyzed and a GEANT4 simulation was carried out to determine the corrections for finite geometry, neutron multiple scattering and detector efficiencies used in this experiment. The results are compared to the state-of-the-art three-body calculations and agreements are observed within rather large statistical uncertainties of the measurement. This experiment represents the first measurement of the asymmetry using spin-dependent 3He photodisintegration.

The unpolarized differential cross section and helicity-dependent differential cross-section difference results are also presented and compared to the same theoretical calculations followed by a discussion of the results. Total cross section is also extracted using two different methods and agrees well with the theoretical prediction.

New developments including a Sol-Gel coated pyrex 3He cell since the experiment are then presented. The in-beam test results of the aforementioned target cell from May 2009 test run are included and the prospect of future three-body photodisintegration is discussed in the end.

Heavy flavor hadrons serve as valuable probes of the transport properties of the quark-gluon plasma (QGP) created in relativistic heavy-ion collisions. In this dissertation, we introduce a comprehensive framework that describes the full-time evolution of heavy flavor in heavy-ion collisions, including its initial production, in-medium evolution inside the QGP matter, hadronization process from heavy quarks to their respective mesonic bound states and the subsequent interactions between heavy mesons and the hadron gas.

The in-medium energy loss of heavy quarks is studied within the framework of a Langevin equation coupled to hydrodynamic models that simulate the space-time evolution of the hot and dense QGP matter. We improve the classical Langevin approach such that, apart from quasi-elastic scatterings between heavy quarks and the medium background, radiative energy loss is incorporated as well by treating gluon radiation as a recoil force term. The subsequent hadronization of emitted heavy quarks is simulated via a hybrid fragmentation plus recombination model. The propagation of produced heavy mesons in the hadronic phase is described using the ultra-relativistic quantum molecular dynamics (UrQMD) model. Our calculation shows that while collisional energy loss dominates the heavy quark motion inside the QGP in the low transverse momentum (pT) regime, contributions from gluon radiation are found to be significant at high pT. The recombination mechanism is important for the heavy flavor meson production at intermediate energies. The hadronic final state interactions further enhance the suppression and the collective flow of heavy mesons we observe. Within our newly developed framework, we present numerical results for the nuclear modification and the elliptic flow of D mesons, which are consistent with measurements at both the CERN Large Hadron Collider (LHC) and the BNL Relativistic Heavy-Ion Collider (RHIC); predictions for B mesons are also provided.

In addition, various transport properties of heavy quarks are investigated within our numerical framework, such as the thermalization process of heavy quarks inside the QGP, and how the initial configuration of the QGP as well as its properties affect the final state spectra and the elliptic flow of heavy mesons and their decay electrons. The effects of initial state fluctuations in heavy-ion collisions are also studied and found to enhance the heavy quark energy loss in a (2+1)-dimensional boost invariant scenario. Furthermore, a new set of observables -- heavy-flavor-tagged angular correlation functions -- are explored and found to be potential candidates for distinguishing different energy loss mechanisms of heavy quarks inside the QGP.

The lifetime of $^{19}$Ne is an important parameter in precision tests of the Standard Model. Improvement in the uncertainty of experimental observables of this and other $T=\frac{1}{2}$ mirror isotopes would allow for an extraction of

V$_{ud}$ at a similar precision to that obtained by superallowed $0^+\rightarrow0^+$ Fermi decays. We report on a new high precision measurement of the lifetime of $^{19}$Ne, performed at the Kernfysich Versneller Instituut (KVI) in Groningen, the Netherlands. A 10.5 $\frac{MeV}{A}$ $^{19}$F beam was used to produce $^{19}$Ne using inverse reaction kinematics in a H$_2$ gas target. Contaminant productions were eliminated using the TRI$\mu$P magnetic isotope separator. The $^{19}$Ne beam was implanted into a thick aluminum tape, which was translated to a shielded detection region by a custom tape drive system. Collinear annihilation radiation from the emitted decay positrons were detected by two high purity germanium (HPGe) detectors. Event pulse waveforms were digitized and stored using a CAEN V1724 Digitizer. Systematic studies were performed to characterize rate-dependent data acquisition effects, diffusion, backgrounds, and contamination from the separator. We have obtained the result for the lifetime of $\tau = 24.9344 \pm 0.0073(stat) \pm 0.0083(sys)$ seconds.

Parton distribution functions (PDFs) provide important information about the flavor and spin structure of nucleon, which is one of the most fundamental building blocks of nature. Furthermore, they can also shed light on quantum chromodynamics (QCD) in the confinement region. Inclusive deep inelastic scattering (DIS) has been one of the most common tools in accessing PDFs through the measurement

of structure functions. Moreover, the cross section in semi-inclusive deep inelastic scattering (SIDIS), which is the product of PDFs and fragmentation functions (FF), which describe the parton hadronization process due to the color force, provides additional information about PDFs. With recent theoretical developments in the framework of the transverse momentum dependent parton distribution functions

(TMDs), the importance of SIDIS process have been widely recognized and accepted, since the inclusive DIS will not be able to attain the information of parton transverse momentum.

JLab experiment E06-010 is measuring the target single spin asymmetry (SSA) in SIDIS from the n (e, e′π+,−)X reaction with a transversely polarized 3He (effective polarized neutron) target at JLab Hall A with a 5.89 GeV incident electron beam. The kinematic coverage is 0.13 < x < 0.41 and 1.31 < Q2 < 3.1 (GeV2). This experiment represents the first SSA measurement from the SIDIS n (e, e′π±)X process. One of the main objectives of the experiment is to measure the Collins asymmetry,

which in turn constrains the "transversity", one of the PDFs whose direct physical interpretation is the probability of finding a transversely polarized parton inside a transversely polarized nucleon. The other main objective of the experiment is to measure the Sivers asymmetry which reveals important information about correlations between the parton transverse momentum and the nucleon spin. The Sivers asymmetry is closely linked to the parton's orbital angular momentum, which is one important piece in understanding the nucleon spin in terms of quark and gluon

degrees of freedom.

This dissertation will first give an introduction to QCD, SIDIS and current

theoretical and the experimental status of SSA. Next the experimental setup of E06-010 will be described, followed by the data analysis procedure to extract the Collins/Sivers asymmetries. In the end, the preliminary results from the data analysis will be shown and discussed.

Measurements of the three-body photodisintegration of 3He were performed at the High Intensity &gamma-ray Source (HI&gammaS). Neutrons emitted in this reaction inside a 3He gas target were detected with seven 12.7 cm diameter liquid scintillator detectors. Time-of-flight (TOF) and pulse-shape discrimination (PSD) techniques were used to identify neutron events. The absolute differential cross sections for the 3He(&gamma, n)pp reaction as a function of outgoing neutron scattering angle and energy were determined from the measurements at the incident &gamma-ray energies of 11.4, 12.8, 13.5, and 14.7 MeV to within a precision better than +/- 6 %.

The absolute cross sections at each incident energy are compared to the results of Gorbunov [Gor74], phase space calculations, and state-of-the-art three-body calculations. The inclusion of the Coulomb interaction in the three-body problem has been a long-standing challenge in theoretical nuclear physics. The present experimental data were found to be in good agreement with the state-of-the-art theory, which includes a full treatment of the Coulomb interaction between

the protons in the final state [Del05].

An experiment measuring the analyzing power A_y(θ) for neutron–helium-3 (n-3He) elastic scattering over broad angular distributions for a range of incident neutron energies from 1.60 to 5.54 MeV has been conducted at the Triangle Universities Nuclear Laboratory. These measurements represent an effort to resolve the long-standing discrepancy between experiment and theory in low-energy three-nucleon analyzing powers, through the evaluation of analyzing powers in the four-nucleon systems, which are expected to exhibit sensitivities not accessible with fewer nucleons. The present work is described in terms of the experimental setup and data reduction techniques; a comparison of the results with rigorous calculations using both nucleon-nucleon and, as recently has become available, three-nucleon potential models is presented. While a discrepancy between calculation and measurement was observed, at low energies substantially better agreement was achieved than in related measurements of the proton–helium-3 (p-3He) analyzing power, suggesting a sizeable dependence on isospin in the four-nucleon systems.

In 2009 the researchers at Triangle Universities Nuclear Laboratory (TUNL) participated in a series of experiments with the Radiation Countermeasures Center of Research Excellence (RadCCORE). This thesis project is a component of the research done at TUNL that was partially supported by the RadCCORE collaboration. The primary goals of this work are: (1) to measure the neutron fluence (and hence the dose) from the standard neutron beam source at TUNL delivered to a small animal target to an accuracy of better than ± 10% and (2) to develop techniques for real time monitoring of the absolute dose delivered to small animal targets from neutron beam irradiation. These two projects are interconnected as the development of the real-time monitoring techniques depends on the results of the absolute fluence measurements.

Measuring the absolute neutron beam fluence necessitates the use of a reaction in which the neutron cross section is accurately known over the relevant energy range and a detection technique which is insensitive to gamma-rays or is capable of distinguishing gamma-rays from neutrons. In this work, neutron activation of aluminum and gold foils was used to make absolute measurements of the fast neutron (E_n ~ 10 MeV) fluence. Neutron activation of gold foils was also used to make a relative measurement of the thermal neutron fluence. The neutrons produced nuclear reactions in the foils, converting a small quantity of the stable atoms in the foils into radioactive ones which subsequently generate gamma-rays in their decay process. The activated foils are then removed from the beam and placed in front of a high-purity germanium (HPGe) detector that measures the energy spectrum of the gamma-rays emitted by the foil. By counting the number of gamma-rays detected over a set time, the incident neutron fluence at the foil location was determined using the known reaction cross sections. The measured neutron fluence was used to calculate the imparted dose to live mouse targets via the muscle tissue neutron kerma factors. Liquid and plastic scintillation detectors were also used to monitor the relative neutron flux in real time during the experiments. These relative detectors were subsequently calibrated using flux results obtained from the foil activation measurements and were used for real time dose monitoring.

The neutron beam produced at TUNL also has an intrinsic gamma component that adds to the dose received by a small animal target. The gamma contribution to imparted dose is generally taken to be around 10% or less for neutron beams created by linear accelerators utilizing the 2H(d,n)3He reaction, but no confirming measurements of this type have been performed at TUNL prior to this work. To verify this claim, an experiment was conducted to quantify the gamma-ray contribution to the target dose at several incident neutron energies and gas cell pressures.

The dosage from the mixed beam was measured using two ionization chambers that have different sensitivities to neutron and gamma radiation. The chambers were placed in the neutron beam, and the total charge induced in the ionization chamber by the mixed radiation field was monitored. The percent gamma-ray contribution to total target dose was calculated utilizing the procedures outlined in AAPM Report No. 7 and Attix.

Using the foil activation technique, the neutron fluence incident on target and dose delivered were measured to within ± 10%. The target dose estimated using the scintillation detectors was found to be accurate to within ± 20%. The results of the ion chamber measurements imply the gamma-ray component of the neutron beam at TUNL contributes less than 5% to the total target dose. Given the large difference in quality factors between gamma-rays (=1) and fast neutrons (~10), the contribution by gamma radiation to the total equivalent dose was determined to be negligible.

Precision measurements of 238U(n,n'g) and 235,238U(n,2ng) partial cross sections have been performed at Triangle Universities Nuclear Laboratory (TUNL) to improve crucial data for the National Nuclear Security Administration's (NNSA) Stockpile Stewardship Program. Accurate neutron-induced reaction cross-section data are required for many practical applications, including nuclear energy and reactor technology, nuclear transmutation, and explosive nuclear devices. Due to the cessation of underground nuclear testing in the early 1990s, understanding of the performance of nuclear devices is increasingly dependent on precise model calculations which are, in turn, themselves reliant on accurate reaction data to serve as benchmarks for model codes. Direct measurement of (n,n') and (n,2n) reaction cross sections for uranium is extremely difficult due to large neutron background from fission and very close nuclear level spacing. Previous direct measurements of the cross sections are incomplete and/or discrepant over the energy range of interest. However, the (n,n'g) and (n,2ng) partial gamma-ray cross-section data obtained in the present work can be combined with model calculations to infer total (n,n') and (n,2n) reaction-channel cross sections.

A pulsed and monoenergetic neutron beam was used in combination with high-resolution gamma-ray spectroscopy to measure these partial cross sections for incident neutron energies between 5 and 14 MeV. Gamma-ray yields were measured with high-purity germanium (HPGe) clover and planar detectors. Neutron fluxes were determined from the well-measured 2+ -> 0+ transition in 56Fe to be on the order of 10^4 n/cm^2/s. Detector efficiency and attenuation of gamma rays in the target were simulated using the MCNPX Monte-Carlo radiation transport code.

Measured partial cross sections were compared with previous measurements and calculations from GNASH and TALYS Hauser-Feshbach statistical-model codes. Results are generally in good agreement with existing data and provide cross-section data for transitions in energy regions where none previously existed. Total reaction-channel cross sections are inferred from statistical-model calculations and compared with existing direct measurement data.

The first measurements of the two- and three-body photodisintegration of longitudinally

polarized 3He with a circularly-polarized gamma-ray beam were carried out at the High Intensity gamma-ray Source facility located at Triangle Universities Nuclear Laboratory (TUNL). A high pressure 3He target, polarized via spin exchange optical pumping with alkali metals, was used in the experiments. The protons from the two-body photodisintegration experiment were detected using seventy two silicon surface barrier detectors of various thicknesses while the neutrons from the three-body photodisintegration were detected with sixteen 12.7 cm diameter liquid scintillator detectors. The spin-dependent cross sections and the contributions from the two- and three-body photodisintegration to the 3He Gerasimov-Drell-Hearn sum rule integrand were extracted and compared with state-of-the-art three-body calculations at the incident photon energies of 29.0 MeV (two-body) and 12.8, 14.7, and 16.5 MeV (three-body).

These are the first measurements of the contributions of the two- and three-body photodisintegration of 3He to the GDH integrand. These measurements were found to be in good agreement with the theoretical calculations which include the Coulomb interaction between protons in the final state. They also reveal-for the first time-the importance of the three-nucleon forces and the relativistic single-nucleon charge corrections which are responsible in the calculations for the observed difference

between the spin-dependent cross sections.