The highly transient nature of shock loading and pronounced microstructure effects on dynamic materials response call for in situ, temporally and spatially resolved, x-ray-based diagnostics. Third-generation synchrotron x-ray sources are advantageous for x-ray phase contrast imaging (PCI) and diffraction under dynamic loading, due to their high photon fluxes, high coherency, and high pulse repetition rates. The feasibility of bulk-scale gas gun shock experiments with dynamic x-ray PCI and diffraction measurements was investigated at the beamline 32ID-B of the Advanced Photon Source. The x-ray beam characteristics, experimental setup, x-ray diagnostics, and static and dynamic test results are described. We demonstrate ultrafast, multiframe, single-pulse PCI measurements with unprecedented temporal (<100 ps) and spatial (∼2 μm) resolutions for bulk-scale shock experiments, as well as single-pulse dynamic Laue diffraction. The results not only substantiate the potential of synchrotron-based experiments for addressing a variety of shock physics problems, but also allow us to identify the technical challenges related to image detection, x-ray source, and dynamic loading.

Excitation-energy-gated two-fragment correlation functions have been studied between E(*)/A = (2-9)A MeV for equilibriumlike sources formed in 8-10 GeV/c pi(-) and p+197Au reactions. Comparison with an N-body Coulomb-trajectory code shows an order of magnitude decrease in the fragment emission time in the interval E(*)/A = (2-5)A MeV, followed by a nearly constant breakup time at higher excitation energy. The decrease in emission time is strongly correlated with the onset of multifragmentation and thermally induced radial expansion, consistent with a transition from surface-dominated to bulk emission expected for spinodal decomposition.

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Understanding the dynamic response of materials at extreme conditions requires diagnostics that can provide real-time, in situ, spatially resolved measurements on the nanosecond timescale. The development of methods such as phase contrast imaging (PCI) typically used at synchrotron sources offer unique opportunities to examine dynamic material response. In this work, we report ultrafast, high-resolution, dynamic PCI measurements of shock compressed materials with 3 μm spatial resolution using a single 60 ps synchrotron X-ray bunch. These results firmly establish the use of PCI to examine dynamic phenomena at ns to μs timescales

Two-proton correlation functions have been measured at 0] b 25 for the "forward kinematics" reactions ' N+ Al, ' N+ ' Au at E/A = 75 MeV, for the "inverse kinematics" reaction Xe+ Al at E/3 =31 MeV, and for the nearly symmetric reaction ' Xe+' Sn at E/3 =31 MeV. For the reactions at 75 MeV per nucleon, the correlation functions exhibit pronounced maxima at relative proton momenta, q =20 MeV/c, and minima at q =0 MeV/c. These correlations indicate emission from fast, nonequilibrium processes. They are analyzed in terms of standard Gaussian source parametrizations and compared to microscopic simulations performed with the Boltzmann-Uehling-Uhlenbeck equation. For the reactions at 31 MeV per nucleon, the two-proton correlation functions do not exhibit maxima at q =20 MeV/c, but only minima at q=0 MeV/c. These correlations indicate emission on a slower time scale. They can be reproduced by calculations based on the Weisskopf . ";ormula for evaporative emission from fully equilibrated compound nuclei. For all reactions, the measured longitudinal and transverse correlation functions are very similar, in agreement with theoretical predictions.

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Two-proton correlation functions measured for the 14 N + 27 A1 reaction at E/A~15 MeV are compared to correlation functions predicted for collision geometries obtained from numerical solutions of the Boltzmann-Uehling-Uhlenbeck (BUU) equation. The calculations are in rather good agreement with the experimental correlation function, indicating that the BUU equation gives a reasonable description of the space-time evolution of the reaction. PACS numbers: 25.70.Np Microscopic models of intermediate-energy nucleusnucleus collisions have been successfully based on the semiclassicalBoltzmann-Uehling-Uhlenbeck (BUU) equation' which describes the temporal evolution of the one-body density under the influence of the nuclear mean field and individual nucleon-nucleon collisions. In this paper we report the first quantitative test of the spacetime geometry predicted by solutions of the BUU equation by using the technique of two-proton intensity interferometry 2 which utilizes the space-time sensitivity of the two-proton correlation function at small relative momenta. 2 " 11 For this purpose, we have measured twoproton correlation functions with high statistical accuracy for the relatively light projectile-target combination ,4 N+ 27 A1, at El A = 75 MeV. For such a light system, numerical calculations can be performed with good accuracy and modest amounts of CPU time.The experiment was performed with a 14 N beam of E/A=15MeV extracted from the K1200 cyclotron of the National Superconducting Cyclotron Laboratory at Michigan State University. An 27 A1 target of 15 mg/ cm 2 areal density was used. Protons were detected with two AE-E detector arrays consisting of 300-400-jumthick silicon AE detectors and 10-cm-long CsI(Tl) or Nal(Tl) E detectors. An array consisting of 37 SiCsI(Tl) telescopes 12 was centered at the polar and azimuthal angles of 0 = 25° and 0=0°; each of its detectors had a solid angle of Aft =0.37 msr and a nearestneighbor spacing of A0 = 2.6°. Another array consisting of 13 Si-Nal(Tl) telescopes was centered at 0 = 25° and 0=90°; each of its detectors had a solid angle of AH =0.5 msr and a nearest-neighbor spacing of A0=4.4°. Coincidence and downscaled singles data were taken simultaneously. Energy calibrations are accurate to better than 2%. Typical detector energy resolutions were of the order of 2% and 1% for protons of 40 and 100 MeV, respectively. All the data were corrected for random coincidences and had a software energy threshold of 10 MeV.The experimental two-proton correlation function R(q) is defined in terms of the coincidence yield F(pi, P2) and the single-proton yields Y(p\) and F(p2): ZK(pi,p 2 )-C[l+/?(?)]£ K(p,)K(p 2 ).(0Here, pi and P2 are the laboratory momenta of the two protons, and q = j \p\ -P2I is the relative momentum of the proton pair. For each experimental gating condition, the sums on both sides of Eq. (l) are extended over all energy and detector combinations corresponding to specific relative momentum bins. The normalization constant C is determined from the requirement R(q)=0 at...