## Curriculum Vita

Education B.S. 1975, Appalachian State University M.S. 1978, Purdue University Ph.D. 1982,Purdue University Postdoctoral Research Associate,North Carolina State University, 1982-1983 Postdoctoral Research Associate,University of South Carolina, 1983-1991 Assistant Professor,University of South Carolina, 1992-1995 Associate Professor,University of South Carolina, 1995-2001 Professor and Department Head, James Madison University, 2001 - Visiting Scientist, Los Alamos National Laboratory, 1983-1988 Guest Scientist,Brookhaven National Laboratory, 1987-2007 Guest Physicist, Thomas Jefferson National Accelerator Facility 1987-2001 Member of the LEGS collaboration, 1987-2007 $HI\gamma S$ collaboration at the Triangle Universities Nuclear Laboratory (TUNL) 2004 - Experiment E06-101 in Hall-B at Jefferson Lab 2006 -

## Research

### Overview

I and my students study nuclei with light. $\gamma$-rays,light with very short wavelengths are well suited for the study of protons and neutrons (nucleons) and other, more complex nuclei. Although nucleons and nuclei have been studied with $\gamma$-rays for many decades, it has only become possible in the last 20 years or so to produce very high quality polarized $\gamma$-ray beams and polarized nucleon targets. With the introduction of these two technologies, we can probe the inner structure of nucleons and nuclei with a precision that was previously impossible. This is the focus of my research.

Sources of polarized $\gamma$-rays suitable for this experimental program are found at the $HI\gamma S$ facility at the Duke Free Electron Laser Laboratory (DFELL) on the campus of Duke University in Durham, NC and in Hall-B at Jefferson Lab.

### Frozen-Spin Polarized $HD$ Ice Target

A new polarized target technology was constructed for the study of polarized nucleons using polarize gamma-rays. This technology uses molecular $HD$ in the solid phase. These targets are polarized at low temperature (10 mK) and high field (15 T) in a large dilution refrigerator (DF). The spin-lattice coupling which permits polarization (and depolarization) of these targets is effected by a small (~$10^{-4}$) concentration of ortho-$H_2$ (molecular angular momentum, $J=1$). Since these molecules decay at low temperature to the magnetically inert $J=0$ para-$H_2$ with a time constant of approximately 6 days, the relaxation time of the $HD$ target increases as a function of the time the target is held in the polarizing conditions. The protons are polarized by equilibrating the target at low temperature and high field. The short initial relaxation time makes it possible to transfer the proton polarization to the deuteron using rf techniques.

By holding the target in the low temperature/high field conditions for approximately three months (depending on initial conditions and whether $H$ or $D$ or both at to be polarized), the polarization relaxation time increases sufficiently to permit the target extraction using a specially designed transfer cryostat (TC). These frozen spin targets are stored or transported in a storage dewar (2 K/8 T) or inserted directly into the in-beam cryostat (IBC) (0.3 K/0.9 T). The in-beam relaxation time for hydrogen and deuterium in-beam has been measured to be approximately 1 year.

This target provides a unique opportunity to study polarized nucleons, in particular the neutron, in detail. Using deuterium as a neutron target, we are be able to make simultaneous measurements on polarized protons and neutrons with a polarized photon beam.

The polarized $HD$ target was developed by the LEGS collaboration, of which I was a member. Now that LEGS has ended data taking, a proposal was submitted and approved to use this target to study excited nucleon states produce by polarized photons on polarized neutrons at Jefferson Lab.

Here at James Madison University, we are operating the hydrogen distillery that we use to purify the $HD$ gas used in the targets. The spin-lattice relaxation time (the decay time for the polarization) depend critically on the impurity levels in the target material. In particular, we must have only a small, controlled amount of $H_2$ and as little $D_2$ as possible. To do this we begin target production with $HD$ gas that is 99.999% pure. Gas with this purity is not commercially available, so we must produce it ourselves. Starting from commercial grade gas (~2% $H_2$ , 0.5% $D_2$), we take advantage of the small (~10%) difference between the vapor pressures of the $H_2$, $HD$, and $D_2$ to make the separation. A specially designed gas chromotography system, developed by JMU undergraduates, is used to measure the relative concentrations of the isotopic components.

### HIGS

In 2004 I joined the High Intensity Gamma Source ($HI\gamma S$) collaboration to use the Compton backscattered photon beam at the Duke Free Electron Laser Laboratory (DFELL) on the campus of Duke University in Durham, NC to continue my work in photonuclear physics with polarized beams and targets. The $HI\gamma S$ program is supported by the Department of Energy and funded through the Triangle Universities Nuclear Laboratory (TUNL). These experiments will focus on Compton scattering from protons and neutrons to extract a series of fundamental response parameters. These polarizabilities measure the response of the nucleon to the applied electric and magneitc fields of the incident photons.

Here at JMU we are pursuing the $HI\gamma S$ program on two fronts, both basic and applied. The basic research program involves the study the proton and neutron (nucleons) using Compton Scattering (see also here). By scattering linearly and circularly polarized photons from polarized nucleons we can make detailed tests of models of the internal quark structure of the nucleon. Instead of obtaining results which average over the internal details, using polarized beams and targets allows us to reveal a much more complete set of information with which to compare current theories.

In a more applied approach, we are also engaged in the study of photon induced fission. When a fissile nucleus is bombarded with photons ($\gamma$-rays) of the right energies, fission can be induced. When this occurs, along with the fission fragments, there are also neutrons emitted. At $HI\gamma S$, we have found that if the incoming light is linearly polarized then the there is a prefered plane of emission for these neutrons. The energy dependence of this preference is different for each nucleus. This means that with a database of these reactions, it is possible to develop a 'signature' for each nuclide permitting them to be identified by scanning a closed container with a polarized photon beam. Thus, using new photon beam technology in combination with this information, it is possible to device improved methods for querying shipping containers for nuclear material.

As an additional benefit, photofission with polarized photons has never been studied before. Thus, it is possible to also shed light on the fundamental fission process itself.

In support of the $HI\gamma S$ research program, a major component of this program is the development of a detector development lab. A large solid angle detector system is being built at $HI\gamma S$ for the experiments we plan. The completed HINDA ($HI\gamma S$ NaI Detector Array) system will contain 8 large NaI detectors each with a NaI annular shield around it to allow rejection of photons that scatter out (This improves the resolution greatly). A NSF grant was funded to purchase eight of these compton shields. These were tested here on campus by Sean O'Brien and Gregory Maust before sending them to $HI\gamma S$ for installation.

## Selected Recent Publications

• C. Steven Whisnant, Patrick A. Hansen and Travis D. Kelly Measuring the Relative Concentration of $H_2$ and $D_2$ In $HD$ Gas with Gas Chromatography,'' Rev. Sci. Inst. 82, 024101 (2011).
• S. Hoblit, A. M. Sandorfi, K. Ardashev, C. Bade, O. Bartalini, M. Blecher, A. Caracappa, A. D'Angelo, A. d'Angelo, R. Di Salvo, A. Fantini, C. Gibson, H. Glueckler, K. Hicks, A. Honig, T. Kageya, M. Khandaker, O. C. Kistner, S. Kizilgul, S. Kucuker, A. Lehmann, M. Lowry, M. Lucas, J. Mahon, L. Miceli, D. Moricciani, B. Norum, M. Pap, B. Preedom, H. Seyfarth, C. Schaerf, H. Stroeher, C. E. Thorn, C. S. Whisnant, K. Wang, and X. Wei. "Measurements of $\vec{H}\vec{D}\left(\vec{\gamma},\pi\right)$ and Implications for the Convergence of the Gerasimov-Drell-Hern Integral," Phys. Rev. Lett. 102, 172002 (2009)
• C. Steven Whisnant, "Parameterization of the $^2H\left(\gamma,p\right)n$ reaction between 185 and 420 MeV," Phys. Rev. C73, 044005 (2006).
• Xiangdong Wei, Christopher M. Bade, Anthony Caracappaa, Tsuneo Kageya, Frank C. Lincoln, Micheal M. Lowry, John C. Mahon, Andrew M. Sandorfi, Craig E. Thorn, C. Steven Whisnant, "New improvements leading to higher polarization frozen spin $HD$ targets at the LEGS facility." Nucl. Inst. and Meth. A526, 157 (2004).
• G. Blanpied, M. Blecher, A. Caracappa, R. Deininger, C. Djalali, G. Giordano, K. Hicks, S. Hoblit, M. Khandaker, O. C. Kistner, A. Kuczewski, F. Lincoln, M. Lowry, M. Lucas, G. Matone, L. Miceli, B. M. Preedom, D. Rebreyend, A. M. Sandorfi, C. Schaerf, R. M. Sealock, H. Stroeher, C.E. Thorn, S.T. Thornton, J. Tonnison, C. S. Whisnant, H. Zhang, and X. Zhao, (The LEGS Collaboration) "The $N \rightarrow \Delta$ Transition and Proton Polarizabilities from Measurements of $p\left(\vec{\gamma},\gamma \right)$, $p\left(\vec{\gamma}, \pi^0 \right)$, and $p\left(\vec{\gamma}, \pi^+ \right)$," Phys. Rev. C64, 025203 (2001); 029902(E).
• G. Blanpied, M. Blecher, A. Caracappa, C. Djalali, G. Giordano, K. Hicks, S. Hoblit, M. Khandaker, O.C. Kistner, G. Matone, L. Miceli, C. Molinari, B. Preedom, A.M. Sandorfi, C. Schaerf, R.M. Sealock, H. Stroeher, D. Rebreyend, C.E. Thorn, S.T.Thornton, C.S. Whisnant, H. Zhang and X. Zhao, "Polarized Compton scattering from the Proton", Phys. Rev. Lett. 76, 1023 (1996).