Session D4: Nuclear Physics Experiment

Cross Section Measurement of the $^{12}$C($^{6}$Li, d)$^{16}$O Reaction and the $^{12}$C($\alpha $, $\gamma )^{16}$O Reaction

The $^{12}$C($\alpha $, $\gamma )^{16}$O reaction is a very important reaction for the understanding of the helium burning in massive stars. However, despite many experimental studies, the low-energy cross-section of the $^{12}$C($\alpha $, $\gamma )^{16}$O reaction remains highly uncertain. In view of the importance of $^{12}$C($\alpha $, $\gamma )^{16}$O reaction, a new determination of the $^{12}$C($\alpha $, $\gamma )^{16}$O reaction cross-section has been performed via a measurement of the transfer reaction $^{12}$C($^{6}$Li, d)$^{16}$O at the Edwards Accelerator Laboratory at the Ohio University. The differential cross-section of the $^{12}$C($^{6}$Li, d)$^{16}$O reaction has been measured to the 0$^{+}$ (6.05 MeV), 3$^{-}$ (6.13 MeV), 2$^{+}$ (6.92 MeV), and 1$^{-}$ (7.12 MeV) states of $^{16}$O with $^{6}$Li beams of 3-, 4-, and 5-MeV. The cross-section measurements were done by detecting the deuterons. The time of flight method was used to separate the different particles.   

Measurement of D$+$D Neutrons at 5- and 7-MEV Deuteron Beam Energy

The D$+$D reaction can produce neutrons through D(d,n)$^{3}$He as well as D(d,np)D and D(d,np)np reactions. The first reaction gives neutrons of single energy at a fixed angle for constant beam energy while the latter two produce low energy continuous spectrum neutrons. These neutrons from the first two reactions have been measured at different angles for deuteron beam energies of 5- and 7-MeV using a deuterium gas cell target. The D(d,n)$^{3}$He neutrons were measured from 0 to 135 degrees of detection angles and those from D(d,np)D were measured from 0 to 45 degrees. The time of flight technique was used with a 6-meter flight path to find the energy of the neutrons detected by three NE213 detectors. This cross section measurement was done using the 4.5-MV tandem accelerator at Edwards Accelerator Laboratory at Ohio University.   

Measurement of Neutron Knockout Cross Section of 24O to the Groud-State of 23O

This research provides an understanding of the structure of the ground state wave-function of $^{24}$O through measuring the neutron knockout cross section of $^{24}$O to the $\frac{1}{2}$$^{+}$ ground state of $^{23}$O. The experiment was conducted at the National Superconducting Cyclotron Laboratory using the S800 spectrograph and 470 mg/cm$^2$ Be reaction target with 92.3 MeV/u $^{24}$O beam energy. The cross section values to the different final states of $^{23}$O along with the related spectroscopic factors will convey to us information regarding how doubly magic $^{24}$O is. Specific details of this investigation, analysis, and interpretation of resulting cross sections will be discussed.   

Study of nuclear level density and gamma-strength function in 90-Zr, 196-Pt, 197-Pt

The level density of $ ^{90} Zr$ was obtained by measuring neutron evaporation spectra from the $ ^{89} Y(d, n) ^{90} Zr$ reaction at $E_{d} = 7.5 MeV$. The experiment was carried out at the Edwards Accelerator Laboratory. The $\gamma$ -strength functions and level densities of $ ^{196} Pt$ and $ ^{197} Pt$ from $ ^{196} Pt (p, p' \gamma) ^{196} Pt$ and $ ^{196} Pt (d, p \gamma ) ^{197} Pt$ reactions were obtained at the Oslo Cyclotron Laboratory by measuring $ p-\gamma$ coincidences. Level densities were compared to the known discrete levels and neutron resonance spacings at the neutron separation energy. They were also compared with model calculation.   

Photon-Hadron Azimuthal Correlation Measurement in 200GeV d+Au Collisions at RHIC

Deuteron-gold collisions are essential to measure the cold nuclear effects, as well as help to study the quark gluon plasma when compared with the heavy ion collision results. Direct photons are less affected by the nuclear medium, thus, they are able to identify the momentum of the scattered partons and the away-side jets. Also, because of the prevailence of the Compton scattering in the direct photon events, the away-side jets are predominated by quark jets. We analyze the azimuthal correlation between high pT direct photons and hadrons and look for the modification of the away-side jet portion of this correlation. The current status of this gamma-jet correlation analysis in d+Au collisions is presented in this speak. This includes analysis of the $x_{E}$ distribution which is related to the fragmentation function D(z). We will also present the status of a new analysis in d+Au of the asymmetry between positive and negtive charged hadrons in the away-side quark jets due to the cross-section dominace of up vs down quarks, which can be compared to Au+Au.   

Direct Photon - Hadron Pair Correlations Measurement in Au+Au Collision at PHENIX

The direct photon - hadron pair correlations serve as an excellent probe of the hot and dense medium created in the heavy ion collision at RHIC. The unmodified photon is used as a reference for the modification of the jet energy by the medium. The low cross section of QCD Compton scattering that produces direct photon - quark pairs added with the enormous production of the background photons requires large amount of Au+Au events to allow a measurement with convincing statistical certainty. In 2010 (Run 10) PHENIX has collected 8.2 billion events of Au+Au collision with 200 GeV of center-of-mass energy per nucleon, a factor of 1.5 times larger than the same collision system collected in 2007 (Run 7). Improvement can also be achieved by event-by-event based methods that would reject large number of the background photons and thus increase the signal-to-background ratio. We will present a feasibility status of the event-by-event isolation cut application in Au+Au collisions and give a status report on the measurement of direct photon - hadron pair correlations.   

Nuclear level densities of 64,66Zn from the analysis of neutron evaporation spectra

The neutron spectra from the reactions $^{63}$Cu(d,n)$^{64}$Zn and $^{65}$Cu(d,n)$^{66}$Zn have been measured using deuteron energies 6 and 7.5 MeV. These results have been compared with the cross sections obtained from the Hauser-Feshbach calculations using the EMPIRE code. Different level density models have been tested, which include three phenomenological (Gilbert-Cameron model, generalized superfluid model and enhanced generalized superfluid model) and one microscopic (Hartree-Fock-Bogoliubov microscopic model), and it was found that by using the Gilbert-Cameron model the calculated cross section closely agrees with the experimental results. We have also studied the non-compound component of the reactions by analyzing the neutron angular distributions. The non-compound component has been shown to be forward-peaked and is more pronounced at high neutron emission energies. We have also observed a slight enhancement of the non-compound contribution as the incident deuteron energy is increased.   

Two-Neutron Decay from the Ground State of 26O

Recent experiments have indicated that $^{24}$O is bound and the tests have failed to find bound states of $^{25}$O and $^{26}$O. So to further understand the behavior and properties of neutron-rich heavy oxygen isotopes the study of $^{26}$O is important. Unstable $^{26}$O decays to stable $^{24}$O by emitting two neutrons rather than decaying via $^{25}$O, which has an unbound ground state energy of 770keV. An investigation of $^{26}$O was conducted at the National Superconducting Cyclotron Laboratory, which possesses the capability to produce rare isotope beams and detect neutrons with an efficiency of about 70$\%$ with the MoNA detector. The reaction of interest being $^{26}$O$\rightarrow^{24}$O + 2n, production of $^{26}$O was done by one-proton removal from a $^{27}$F beam with an energy of 82 MeV/u impending on a 705 mg/cm$^2$ Be target. Coincidence of two neutrons with $^{24}$O was measured for four-vector momentum event reconstruction. The analysis of this experiment will determine the invariant mass of $^{26}$O and the status of the analysis will be presented.