Duke Free Electron Laser Laboratory Research Articles

Model independent approach to photodisintegration of 7 Li at the range of energies of interest to BBN

One of the elements that was synthesized primordially in the standard Big Bang Nucleosynthesis is lithium. Lithium, being fragile gets easily destroyed at relatively low temperatures in the mixing process between stellar surface and hot internal layers. So that, at the end of the stellar lifetime the lithium content is believed to be depleted. Series of experimental measurements on lithium isotopes were carried out at High Intensity Gamma Ray Source (HIGS) at Duke Free Electron Laser Laboratory. More recently experiments [1]-[2] were performed, to measure the differential cross section of the photo-neutron reaction channel in photodisintegration of 7 Li, where the progeny nuclei is in the ground state as well as in excited states. The purpose of present contribution is to study the reaction channel 7 Li + γ → 6 Li + n using linearly polarized photons. The model independent irreducible tensor formalism [3]-[5] will be used to study the differential cross section of the reaction. We study the angular dependence of differential cross section by expressing differential cross section in terms of legendre polynomials. In view of the several theoretical and ongoing experimental studies, a detailed theoretical study of the spin structure of the amplitudes in 7 Li + γ → 6 Li + n and their expansion in terms of ’electric’ and ‘magnetic’ amplitudes is needed to analyze the measurements of spin observables as well as differential cross section, which leads to a better understanding of the problem at astrophysical energies

Relative spectral response measurement of spectrometers using undulator radiation

Undulator radiation with known spectral characteristics is recognized as an excellent light source that can be used to measure the spectral response of a variety of spectral measurement devices in a wide range from infrared to x-ray. This technique has been developed at Duke Free-Electron Laser (FEL) Laboratory to successfully measure the spectral response of several spectrometers in the near-infrared, visible, and ultraviolet regions. In this paper, we present both simulation and experimental results of the spectral response measurement, with a focus on high-accuracy spectral response reconstruction. Using simulation studies, we have tested and confirmed the validity of the spectral response measurement method while taking into account major sources of errors. Especially, it shows that the spectral response reconstruction technique developed in this work is rather robust against the spectral broadening of undulator radiation. The usefulness of this spectral response measurement method is also confirmed with the experimental study on a spectrometer in the visible region. Overall, we have achieved good results with the measured spectral response, with an RMS uncertainty of about 2.7% in the range from 414 to 591 nm. Using multiple measurements, the reproducibility of this method has also been tested with a relative difference of about 2.3% (RMS in the range from 415 to 590 nm). For high-accuracy measurements of a broad radiation spectrum, the knowledge of the spectral response of the spectrometer is critical. In this paper, we will show that the details of the measured undulator radiation spectra can be properly restored by correcting the raw spectrum using the measured spectral response. The method of spectral response measurement using undulator radiation is also useful to calibrate spectral devices in extreme spectral ranges such as VUV and x-ray.

A high-pressure polarized 3He gas target for nuclear-physics experiments using a polarized photon beam

Following the first experiment on three-body photodisintegration of polarized $^3$He utilizing circularly polarized photons from High Intensity Gamma Source (HI$\gamma$S) at Duke Free Electron Laser Laboratory (DFELL), a new high-pressure polarized $^3$He target cell made of pyrex glass coated with a thin layer of sol-gel doped with aluminum nitrate nonahydrate has been built in order to reduce the photon beam induced background. The target is based on the technique of spin-exchange optical pumping of hybrid rubidium and potassium and the highest polarization achieved is $\sim$62% determined from both NMR-AFP and EPR polarimetry. The $X$ parameter is estimated to be $\sim0.06$ and the performance of the target is in good agreement with theoretical predictions. We also present beam test results from this new target cell and the comparison with the GE180 $^3$He target cell used previously at HI$\gamma$S. This is the first time that sol-gel coating technique has been used in a polarized $^3$He target for nuclear physics experiments.

A high-pressure polarized 3He gas target for the High Intensity Gamma Source (HI [formula omitted]S) facility at Duke Free Electron Laser Laboratory

A new polarized 3He target has been developed for nuclear physics experiments utilizing the High Intensity Gamma Source (HI γ S) at the Duke Free Electron Laser Laboratory (DFELL). This target is designed for a broad program of physics employing high intensity polarized photons and a polarized 3He target as an effective polarized neutron target. We report the performance of this target based on the technique of spin-exchange optical pumping (SEOP). Due to the significantly larger photon beam size at the HI γ S facility than that of a typical electron beam at electron accelerator laboratories, the HI γ S 3He target contains a larger number of 3He nuclei than any polarized 3He targets reported previously. A target polarization on the order of 33–46% has been achieved from both a regular 3He–Rubidium (Rb) target and a hybrid target which contains a mixture of Rb and potassium. The target polarization has been determined within 3 % using both the Electron Paramagnetic Resonance (EPR) technique and the NMR–AFP (Adiabatic Fast Passage) technique.

Deuteron photodisintegration with polarized photons at astrophysical energies

Following precise experimental studies at the Duke Free-Electron Laser Laboratory, we discuss the photodisintegration of deuterons with 100% linearly polarized photons using a model independent theoretical approach taking together M1 and E1 amplitudes simultaneously. The isoscalar M1{sub s} contribution is also taken exactly into account. From the existing experimental measurement on doubly polarized thermal neutron capture, it is seen that the isoscalar M1{sub s} contribution could be of the same order of magnitude as the experimentally measured cross sections at energies relevant to Big Bang Nucleosynthesis (BBN). Therefore appropriate measurements on deuteron photodisintegration are suggested to empirically determine the M1{sub s} contribution at astrophysical energies.

Shielding for the upgraded duke free electron laser laboratory

The Duke FEL Laboratory is undergoing a series of upgrades staggered over time that will greatly increase the capabilities of the machines and by the same token the importance of radiation safety issues. In this paper, we present the scope of the planned upgrades and provide several specific examples of shielding calculations. We also present our effort to correlate calculations with experimental measurements.

Low-energy photodisintegration of the deuteron and Big-Bang nucleosynthesis

The photon analyzing power for the photodisintegration of the deuteron was measured for seven gamma-ray energies between 2.39 and 4.05 MeV using the linearly polarized gamma-ray beam of the high-intensity gamma-ray source at the Duke Free-Electron Laser Laboratory. The data provide a stringent test of theoretical calculations for the inverse reaction, the neutron–proton radiative capture reaction at energies important for Big-Bang nucleosynthesis. Our data are in excellent agreement with potential model and effective field theory calculations. Therefore, the uncertainty in the baryon density ΩBh2 obtained from Big-Bang Nucleosynthesis can be reduced at least by 20%.

The HIγS Facility: A Free-Electron Laser Generated Gamma-Ray Beam for Research in Nuclear Physics

The High Intensity Gamma-ray Source (HIγS) is a joint project between Triangle Universities Nuclear Laboratory (TUNL) and the Duke Free Electron Laser Laboratory (DFELL). This facility utilizes intra-cavity back-scattering of the FEL photons in order to produce a γ-flux enhancement of approximately 103 over the existing sources. At present, gamma-ray beams with energies ranging from 2 to 50 MeV are available with intensities of 105–107 γ/ s , energy spreads of 1% or better (with lower intensities), and 100% linear polarization. An upgrade is presently underway which will allow for the production of γ rays up to an energy of about 225 MeV having intensities in excess of 108 γ/ sec . The primary component of the upgrade is a 1.2 GeV booster-injector which will provide for efficient injection at any chosen operating energy of the storage ring from 300 MeV to 1.2 GeV. In addition, an upgrade of the present OK-4 FEL to a helical undulator system (OK-5) is underway. This new system has many advantages over the present one, including making switchable linear and circularly polarized beams available, an increase in power and a decrease in mirror-damaging radiation. The full system, including the booster injector, is expected to be ready for use by 2006. TUNL researchers, in collaboration with outside theoretical and experimental colleagues, have proposed a broad based research program in nuclear physics which is designed to exploit the unique flux, energy resolution and polarization of the HIγS beams. A description of the presently available facility and the anticipated facility following the present upgrades will be given in this review, along with a description of recent and planned experiments.

ANALYZING POWER FOR THE PHOTODISINTEGRATION OF THE DEUTERON BETWEEN Eγ = 2.4 AND 4.0 MEV

The photon analyzing power for the photodisintegration of the deuteron was measured for seven gamma-ray energies between 2.39 and 4.05 MeV using the linearly polarized gamma-ray beam of the High-Intensity Gamma-ray Source at the Duke Free-Electron Laser Laboratory. The data provide a stringent test of theoretical calculations for the inverse reaction, the neutron-proton radiative capture reaction at energies important for Big-Bang nucleosynthesis. Our data are in excellent agreement with potential model and effective field theory calculations.

Commissioning of a UV/time-resolved-FTIR beamline at the Duke FEL laboratory

We describe the commissioning of a novel two-color beamline at the Duke Free Electron Laser Laboratory, designed to perform time-resolved FTIR spectroscopy in a pump-probe scheme with sub-nanosecond resolution to measure dynamical processes with durations as long as 10 ns. The UV pump pulses are produced by the tunable (193–700 nm) output of the OK-4 Storage-Ring FEL. The broadband, infrared probe pulses are generated as synchrotron radiation in a bending magnet downstream of the OK-4 wiggler. The repetition rate of the light source (2.79 MHz) is ideal for operating the interferometer in the rapid-scan, asynchronous sampling mode. An investigation of DNA photolyase is proposed.

A Free-Electron Laser Generated Gamma-Ray Beam for Nuclear Physics

The High Intensity Gamma Ray Source (HIγS), a collaborative project between TUNL and the Duke Free Electron Laser Laboratory, is described. An initial experiment and plans for a future research program are discussed briefly.

First measurement of the near-threshold2H(γ→,n)panalyzing power using a free-electron laser basedγ-ray source

The first measurement of the ${}^{2}\mathrm{H}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},n)p$ analyzing power near threshold has been performed using the High-Intensity Gamma-ray Source (HIGS) at the Duke Free-Electron Laser Laboratory. A 3.58 MeV $\ensuremath{\gamma}$-ray beam having an energy resolution of $2.5%$ and $100%$ linear polarization was incident on an active ${\mathrm{C}}_{6}{\mathrm{D}}_{12}$ target. Outgoing neutrons were detected parallel and perpendicular to the plane of $\ensuremath{\gamma}$-ray polarization at a lab angle of 150\ifmmode^\circ\else\textdegree\fi{}. The experimentally determined analyzing power provides a sensitive measurement of the relative $E1$ and $M1$ contributions to the total cross section.

Nuclear Research at Duke

In the News & Comment article “Physicist sues Duke over control of lab” by Eliot Marshall (21 Nov., [p. 1393][1]), a claim in the legal brief of John Madey is summarized as follows: “nuclear physicists on Duke [University's] faculty who are short of funds are scheming to ‘take control of the MFEL [Medical Free Electron Lasar] project and to remove Dr. Madey from his position of authority in order to facilitate their nuclear research plans.’” Madey's claim has no basis in fact. It was Madey who encouraged his colleagues at the Duke Free-Electron Laser Laboratory (DFELL) and nuclear physicists from Duke's faculty to work together in order to produce high-intensity gamma-ray beams through Compton backscattering of FEL photons from high-energy electrons using the facilities at the DFELL and using detection systems provided by the Duke faculty. Madey was part of the collaboration and helped spread the news of the first successful gamma-ray production at the DFELL around the world. He was a co-author of the article in Physical Review Letters ([1][2]) which reported this result. Madey also encouraged his colleagues at the DFELL and nuclear physicists at the Triangle Universities Nuclear Laboratory (TUNL) to write a proposal with the aim of seeking funds from the Department of Energy (DOE) to support an upgrade of the existing electron storage ring and the existing accelerator at the DFELL to make it possible to produce gamma-ray beams of higher energy than currently possible with the existing equipment. Such a proposal has recently been submitted to the DOE. Madey, through his former Associate Director, requested that the TUNL physicists define the space needed in the planned new addition to the DFELL in order to carry out the proposed nuclear research program. Based on mutual agreement with Madey, a “gamma vault” was made part of the new building design. The Duke University nuclear physicists conduct their research as part of TUNL's basic research program in nuclear physics. TUNL is jointly staffed by nuclear physicists from Duke University, the University of North Carolina at Chapel Hill, and North Carolina State University at Raleigh. The TUNL program has been well funded for more than 25 years by DOE and its predecessors; this funding was recently extended for 3 years at the requested level. 1. [↵][3]1. V. N. Litvinenko 2. et al. , Phys. Rev. Lett. 78, 4569 (1997). [OpenUrl][4][CrossRef][5][Web of Science][6] [1]: /lookup/doi/10.1126/science.278.5342.1393a [2]: #ref-1 [3]: #xref-ref-1-1 View reference 1 in text [4]: {openurl}?query=rft.jtitle%253DPhys.%2BRev.%2BLett.%26rft.volume%253D78%26rft.spage%253D4569%26rft.atitle%253DPHYS%2BREV%2BLETT%26rft_id%253Dinfo%253Adoi%252F10.1103%252FPhysRevLett.78.4569%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [5]: /lookup/external-ref?access_num=10.1103/PhysRevLett.78.4569&link_type=DOI [6]: /lookup/external-ref?access_num=A1997XE57100010&link_type=ISI

The TUNL-FELL inverse Compton γ-ray source as a nuclear physics facility

A new technique for producing an intense beam of polarized γ-rays is presented. This High-Intensity Gamma-ray Source (HIGS) will utilize the facilities of the new Duke Free Electron Laser Laboratory. This system includes the LINAC injector, the 1.3 GeV electron storage ring, and the OK-4 undulator.It will be shown that it is possible to tune the electron beam in a manner which allows the FEL photons to backscatter from an electron bunch, all within the ring. This leads to an intense beam of almost 100% linearly polarized γ-rays whose energy can be readily tuned from about 5 to greater than 200 MeV. Furthermore, beam energy spreads of less than 1% can be obtained by pure geometrical collimation. Details of the beam properties and background sources will be presented. It will be shown that this is an ideal beam for nuclear physics and nuclear astrophysics studies. One example of this which takes advantage of the flux, energy resolution and polarization of the beam, is the study of Δ 33 excitations in finite nuclei. These intense polarized beams will also make it possible to perform precision measurements of the nucleon polarizabilities. And we will see that studies in the vicinity of the photo-pion production threshold can provide crucial tests of many of the recent predictions (Low Energy Theorems) of Chiral Perturbation Theory. Our final example will show how the very intense beams available at low energies can be used to determine astrophysically important capture cross sections by measurements of the inverse reactions.

Duke storage ring UV/VUV FEL: status and prospects

Abstract A 1.1 GeV electron storage ring dedicated for UV-VUV FEL operation was commissioned last year at the Duke University Free Electron Laser Laboratory [V.N. Litvinenko et al., Commissioning of the Duke storage ring, Proc. 1995 Particle Accelerator Conf., Dallas, TX, May 1–5, 1995]. The XUV FEL project, based on the collaboration of the Duke FEL Laboratory and Budker Institute for Nuclear Physics (Novosibirsk, Russia) is described. The OK-4 UV FEL has arrived from Novosibirsk at the Duke FEL laboratory and is in the process of installation. The main parameters of the Duke Free Electron Laser Laboratory (DFELL) storage ring, the OK-4 optical klystron, and the experimental set-up are presented. The parameters of the UV-VUV FEL are given and possible future upgrades to this system are discussed. We have developed a new macro-particle code for storage ring simulation including all known mechanisms of storage ring FEL interaction. We confirm our expectations on the average and peak power for the OK-4. In addition we have studied a giant pulse mode of operation. A new mechanism of “super-pulse” generation was discovered during these studies. It allows the generation of peak power up to 10 GW using “phase-space” refreshment of the electron beam caused by synchrotron motion [V.N. Litvinenko, B. Burnham, J.M.J. Madey and Y. Wu, Nucl. Instr. and Meth. A 358 (1995) 334].