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The $R$-matrix analysis of $A=5$ nuclear systems has been partially validated by applying the technique to the $^{5}\mathrm{Li}$ system and comparing the predicted $\ensuremath{\gamma}$-ray spectrum with historical data. $R$-matrix analysis of the similar $^{5}\mathrm{He}$ system was then used to predict the $\ensuremath{\gamma}$-ray spectral shape for the deuterium-tritium (DT) reaction. The resulting spectra have been used in the analysis of DT implosions on the Omega laser where the $\ensuremath{\gamma}$-ray interaction rate was measured by a gas Cherenkov detector. Comparison of predictions to experiment confirmed the presence of both 16.75 and $\ensuremath{\approx}13$ MeV $\ensuremath{\gamma}$-ray contributions; analysis, using $R$-matrix spectra, yielded a ratio of $\ensuremath{\gamma}$-ray emission from a transition to the intermediate excited state to that from a transition to the ground state of $(2.1\ifmmode\pm\else\textpm\fi{}0.4):1$, substantiating the first spectral measurement of the DT fusion $\ensuremath{\gamma}$ ray in an inertial fusion environment.

$\ensuremath{\gamma}$-ray emission from $^{12}\mathrm{C}$ and $^{13}\mathrm{C}$ samples irradiated with deuterium-tritium fusion neutrons was experimentally measured at the Omega Laser Facility and at the Ohio University Edwards Accelerator Laboratory. The intent of these measurements was to determine the feasibility of using $^{13}\mathrm{C}$-based plastic ablators with embedded $^{12}\mathrm{C}$ layers for ``dark mix'' diagnosis of inertial confinement fusion implosions. Spectrally resolved measurements at Ohio University identified significant 4.44-MeV $\ensuremath{\gamma}$-ray emission from the $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 reaction channel. The recorded 4.44-MeV $^{13}\mathrm{C}$ signal was compared against emission from an identically irradiated $^{12}\mathrm{C}$ target with known $^{12}\mathrm{C}$($n,{n}^{\ensuremath{'}}\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section, which resulted in an average $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section of 117 $\ifmmode\pm\else\textpm\fi{}$ 17 mb over the incident neutron energy distribution range from 14.4 to 15.8 MeV. Integrated $^{13}\mathrm{C}$ $\ensuremath{\gamma}$-ray signals above 2.9 MeV recorded with the Gas Cherenkov Detector at Omega exceeded MCNP6.1 predictions by a factor of 3. The additional signal was attributed to 4.44-MeV $\ensuremath{\gamma}\mathrm{s}$ resulting in an inferred $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section of $95\ifmmode\pm\else\textpm\fi{}11$ mb at 14.1-MeV average incident neutron energy. As a result, the $^{13}\mathrm{C}$-based ``dark mix'' diagnostic concept was deemed infeasible.

Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4 keV and particle densities of n≈(12-2)×10^{24} cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data.

A glass Cherenkov detector, called the Diagnostic for Areal Density (DAD), has been built and implemented at the OMEGA laser facility for measuring fusion gammas above 430 keV, from which remaining shell ⟨ρR⟩abl can be determined. A proof-of-principle experiment is discussed, where signals from a surrogate gas Cherenkov detector are compared with reported values from the wedge range filter and charged particle spectrometer and found to correlate strongly. The design of the more compact port–based DAD diagnostic and results from the commissioning shots are then presented. Once absolutely calibrated, the DAD will be capable of reporting remaining shell ⟨ρR⟩abl for plastic and glass capsules within minutes of a shot and with potentially higher precision than existing techniques.

We determined fission yields of xenon (133mXe, 135Xe, 135mXe, 137Xe, 138Xe, and 139Xe) resulting from 14 MeV neutron induced fission of depleted uranium at the National Ignition Facility. Measurements begin approximately 20 s after shot time, and yields have been determined for nuclides with half-lives as short as tens of seconds. We determined the relative independent yields of 133mXe, 135Xe, and 135mXe to significantly higher precision than previously reported. The relative fission yields of all nuclides are statistically indistinguishable from values reported by England and Rider (ENDF-349. LA-UR-94-3106, 1994), with exception of the cumulative yield of 139Xe. Considerable differences exist between our measured yields and the JEFF-3.1 database values.

Indirect drive converts high power laser light into x-rays using small high-Z cavities called hohlraums. X-rays generated at the hohlraum walls drive a capsule filled with deuterium–tritium (DT) fuel to fusion conditions. Recent experiments have produced fusion yields exceeding 50 kJ where alpha heating provides ~3× increase in yield over PdV work. Closing the gaps toward ignition is challenging, requiring optimization of the target/implosions and the laser to extract maximum energy. The US program has a three-pronged approach to maximize target performance, each closing some portion of the gap. The first item is optimizing the hohlraum to couple more energy to the capsule while maintaining symmetry control. Novel hohlraum designs are being pursued that enable a larger capsule to be driven symmetrically to both reduce 3D effects and increase energy coupled to the capsule. The second issue being addressed is capsule stability. Seeding of instabilities by the hardware used to mount the capsule and fill it with DT fuel remains a concern. Work reducing the impact of the DT fill tubes and novel capsule mounts is being pursed to reduce the effect of mix on the capsule implosions. There is also growing evidence native capsule seeds such as a micro-structure may be playing a role on limiting capsule performance and dedicated experiments are being developed to better understand the phenomenon. The last area of emphasis is the laser. As technology progresses and understanding of laser damage/mitigation advances, increasing the laser energy seems possible. This would increase the amount of energy available to couple to the capsule, and allow larger capsules, potentially increasing the hot spot pressure and confinement time. The combination of each of these focus areas has the potential to produce conditions to initiate thermo-nuclear ignition.

Radiochemical diagnostic techniques such as solid- and gas-phase capsule debris analysis may prove to be successful methods for establishing the success or failure of ignition experiments at the National Ignition Facility (NIF). Samples in the gas phase offer the most direct method of collection by simply pumping out the large target chamber following a NIF shot. The target capsules will be prepared with dopants, which will produce radioactive noble-gas isotopes upon activation with neutrons or charged particles. We have designed and constructed the Radchem Apparatus for Gas Sampling (RAGS) in order to collect postshot gaseous samples for NIF capsule diagnostics. The design of RAGS incorporates multiple stages intended to cryogenically purify, transfer, and count the radioactive decays from gaseous products synthesized in NIF experiments. An implementation timeline at NIF is discussed.

We have built a gas-phase argon ionization detector to measure small nuclear recoil energies ( 10 keVee ) . In this paper, we describe the detector response to X-ray and gamma calibration sources, including analysis of pulse shapes, software triggers, optimization of gas content, and energy- and position-dependence of the signal. We compare our experimental results against simulation using a 5.9-keV X-ray source, as well as higher-energy gamma sources up to 1332 keV. We conclude with a description of the detector, DAQ, and software settings optimized for a measurement of the low-energy nuclear quenching factor in gaseous argon. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344. Funded by Lab-wide LDRD. LLNL-JRNL-415990-DRAFT.

This paper highlights some of the current basic nuclear physics research at Lawrence Livermore National Laboratory (LLNL). The work at LLNL concentrates on investigating nuclei at the extremes. The Experimental Nuclear Physics Group performs research to improve our understanding of nuclei, nuclear reactions, nuclear decay processes and nuclear astrophysics; an expertise utilized for important laboratory national security programs and for world-class peer-reviewed basic research.

Efficient, readily-available, low-cost, high-energy neutron detectors can play a central role in detecting illicit nuclear weapons since neutrons are a strong indication for the presence of fissile material such as Plutonium and Highly-Enriched Uranium. The main challenge in detecting fast neutrons consists in the discrimination of the signal from the gamma radiation background. At present, the only well-investigated organic crystal scintillator for fast neutron detection, in a n/gamma mixed field, is stilbene, which while offering good pulse shape discrimination, is not widely used because of its limited availability and high cost.

Active interrogation with low-energy neutrons provides a search technique for highly-enriched uranium concealed in cargo. We describe the technique and show initial results using a low-dose 60-keV neutron beam. This technique produces a clear induced fission signal in the presence of small quantities of 235 U. The technique has been validated with low-Z and high-Z cargo materials. The technique uses a forward-directed beam of 60-keV neutrons to induce fission in 235 U. Detection of the fast fission neutrons with pulse-shape discriminating scintillators is then the signature for 235 U. The beam of neutrons is generated with a 1.93 MeV proton beam impinging on a natural lithium target. The proton beam is produced by a radio-frequency quadrupole LINAC. The 60 keV neutron beam is forward-directed because the 7 Li(p, n) reaction is just above threshold for a proton energy of 1.93 MeV.

The Radiochemical Analysis of Gaseous Samples (RAGS) diagnostic apparatus operates at the National Ignition Facility (NIF). At the NIF, xenon is injected into the target chamber as a tracer, us ed as an analyte in the NIF targets, and generated as a fission product from 14 MeV neutron fission of depleted uranium contained in the NIF hohlraum. Following a NIF shot, the RAGS apparatus used to collect the gas from the NIF targ et chamber and then to cryogenically fractionate xenon gas. Radio-xenon and other activation products are collected and counted via gamma spectrometry, with the results used to determine critical physics parameters including: capsule areal density, fuel-ablator mix, and nuclear cross sections. We will discuss the following performance upgrades to the system: Modification of the xenon fractionator to allow collection of krypton. Krypton is an important target analyte and is also generated as fission gas in NIF shots. We have modified the cryostat to enable fractionation of xenon, krypton, or both. A translatable detector for quantification of the fission gases. An in situ Germanium detector is used to count the radio isotopes collected on the coldhead. NIF shots that incorporate depleted uranium in the hohlraum generate large amounts of fission gas, the radioactivity of which paralyzes the detector. We have designed a system that will adjust the detector-to-coldhead distance based upon either the count rate or the time after the NIF shot. Keywords: krypton, radiochemistry, cryogenic, nuclear diagnostic

Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α ~ 3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8 X 10¹⁵ neutrons, with 20% calculated alpha heating at convergence ~27X.

We are developing a new active interrogation system based on a kinematically focused low energy neutron beam. The key idea is that one of the defining characteristics of special nuclear materials (SNM) is the ability for low energy or thermal neutrons to induce fission. Thus by using low energy neutrons for the interrogation source we can accomplish three goals: (1) energy discrimination allows us to measure the prompt fast fission neutrons produced while the interrogation beam is on; (2) neutrons with an energy of approximately 60–100 keV do not fission 238U and Thorium, but penetrate bulk material nearly as far as high energy neutrons do and (3) below about 100 keV neutrons lose their energy by kinematical collisions rather than via the nuclear (n, 2n) or (n, n′) processes thus further simplifying the prompt neutron induced background. 60 keV neutrons create a low radiation dose and readily thermal capture in normal materials, thus providing a clean spectroscopic signature of the intervening materials. The kinematically beamed source also eliminates the need for heavy backward and sideway neutron shielding. We have designed and built a very compact pulsed neutron source, based on an RFQ proton accelerator and a lithium target. We are developing fast neutron detectors that are nearly insensitive to the ever-present thermal neutron and neutron capture induced gamma ray background. The detection of only a few high energy fission neutrons in time correlation with the linac pulse will be a clear indication of the presence of SNM.

The generation of dynamic high energy density plasmas (HEDP) in the pico- to nano-second time domain at high-energy laser facilities affords unprecedented nuclear science research possibilities. At the National Ignition Facility (NIF), the primary goal of Inertial Confinement Fusion research has led to the synergistic development of a unique high brightness neutron source, sophisticated nuclear diagnostic instrumentation, and versatile experimental platforms. These novel experimental capabilities provide a new path to investigate nuclear processes and structural effects in the time, mass and energy density domains relevant to astrophysical phenomena in a unique terrestrial environment. Some immediate applications include neutron capture cross-section evaluation, fission fragment production, and ion energy loss measurement in electron-degenerate plasmas. More generally, the NIF conditions provide a singular environment to investigate the interplay of atomic and nuclear processes such as plasma screening effects upon thermonuclear reactivity. Achieving enhanced understanding of many of these effects will also significantly advance fusion energy research and challenge existing theoretical models.

An axion detector consisting of a tunable high-Q cavity, a superconducting magnet, and a superheterodyne receiver with an ultra-low noise pre-ampli"er has been built to search for galactic halo axions in the mass range of 1.3}13 leV. The detector instrumentation, search process, and data analysis are described. For the "rst time, this class of detector has reached su$cient sensitivity to detect halo axions with high con"dence. ( 2000 Elsevier Science B.V. All rights reserved.

Fissile materials, e.g., 235U and 239Pu, can be detected non-invasively by active neutron interrogation. A unique characteristic of fissile material exposed to neutrons is the prompt emission of high-energy (E > 1 MeV) fission neutrons. One promising mode of operation subjects the object to a beam of low-energy (E < 1 MeV) neutrons, generated by a proton beam impinging on a Li target. The emergence of high-energy secondary neutrons then clearly indicates the presence of fissile material. Our interrogation system comprises a low-dose 60-keV neutron generator (5 times 106/s ), and a 1 m2 array of scintillators for high-energy neutron detection. Preliminary experimental results demonstrate the detectability of small quantities (376 g) of 235U shielded by steel (200 g/cm2) or plywood (30 g/cm2), with a typical measurement time of 1 min.

The broad spectra of radioactive β-decay energies led to the discovery of the neutrino in the 1930s. There was also speculation that the shape of the spectrum could be used to measure a possible neutrino mass. In 1991, it was predicted that there should be ripples in the spectra called ‘β-environmental fine structure’ or BEFS. These ripples have been measured in a new experiment, which may eventually transcend the massive-neutrino controversy in that BEFS can be used to probe the atomic structure of many solids.

Excited states in ${}^{208}$Pb have been studied by measuring $\ensuremath{\gamma}$ rays in time coincidence with reaction charged particles. ${}^{208}$Pb states were produced with both the ${}^{207}$Pb${(d,p)}^{208}$Pb and ${}^{209}$Bi$(t,\ensuremath{\alpha})$${}^{208}$Pb reactions. The energy resolution of the particle spectra of 100 keV allowed a rough determination of level excitation, which then was determined with high resolution from the coincident $\ensuremath{\gamma}$ decay measured in Ge detectors. Many new $\ensuremath{\gamma}$ transitions have been found and previously unresolved multiplets of states resolved. The data give spectroscopic factors for neutron transfer and proton pickup. Spins and parities of levels could be deduced from their $\ensuremath{\gamma}$ decays. A least squares fit of all $\ensuremath{\gamma}$ energies gave very precise (0.1 keV) level energies. All states predicted by the shell model below 4.6 MeV are now found and their spins determined unambiguously.

The gas Cherenkov detectors at NIF and Omega measure several ICF burn characteristics by detecting multi-MeV nuclear γ emissions from the implosion. Of primary interest are γ bang-time (GBT) and burn width defined as the time between initial laser-plasma interaction and peak in the fusion reaction history and the FWHM of the reaction history respectively. To accurately calculate such parameters the collaboration relies on Monte Carlo codes, such as GEANT4 and ACCEPT, for diagnostic properties that cannot be measured directly. This paper describes a series of experiments performed at the High Intensity γ Source (HIγS) facility at Duke University to validate the geometries and material data used in the Monte Carlo simulations. Results published here show that model-driven parameters such as intensity and temporal response can be used with less than 50% uncertainty for all diagnostics and facilities.

This paper highlights some of the exotic nuclei studies at Lawrence Livermore National Laboratory (LLNL) within the Experimental Nuclear Physics (ENP) group. The work at LLNL concentrates on investigating nuclei at the extremes. The ENP group performs research to improve our understanding of nuclei, nuclear reactions, nuclear decay processes and nuclear astrophysics; an expertise utilized for important laboratory national security programs and for world-class peer-reviewed basic research.

The newest generation of Gas Cherenkov Detector (GCD-3) employed in Inertial Confinement Fusion experiments at the Omega Laser Facility has provided improved performance over previous generations. Comparison of reaction histories measured using two different deuterium-tritium fusion products, namely gamma rays using GCD and neutrons using Neutron Temporal Diagnostic (NTD), have provided added credibility to both techniques. GCD-3 is now being brought to the National Ignition Facility (NIF) to supplement the existing Gamma Reaction History (GRH-6m) located 6 m from target chamber center (TCC). Initially it will be located in a reentrant well located 3.9 m from TCC. Data from GCD-3 will inform the design of a heavily-shielded "Super" GCD to be located as close as 20 cm from TCC. It will also provide a test-bed for faster optical detectors, potentially lowering the temporal resolution from the current ∼100 ps state-of-the-art photomultiplier tubes (PMT) to ∼10 ps Pulse Dilation PMT technology currently under development.

Initial results from the newest Gas Cherenkov Detector (GCD-3) are reported demonstrating improved performance over previous GCD iterations. Increased shielding and lengthening of the Cherenkov photon optical path have resulted in a diminished precursor signal with increased temporal separation between the precursor and the primary DT Cherenkov signal. Design changes resulted in a measured GCD-3 sensitivity comparable to GCD-1 at identical 100 psia CO2 operation. All metal gasket seals and pressure vessel certification to 400 psia operation allow for a GCD-3 lower Cherenkov threshold of 1.8 MeV using the fluorinated gas C2F6 as compared to the 6.3 MeV lower limit of GCD-1 and GCD-2. Calibration data will be used to benchmark GEANT4 and ACCEPT detector models. Lastly, the GCD-3 acts as a prototype for the Super GCD being fielded at the National Ignition Facility (NIF) as part of the National Diagnostics Plan and will be installed at NIF in early 2016.

C.B. Yeamans, W. Cassata, J.A. Church, D.N. Fittinghoff, M. Gatu Johnson, N. Gharibyan, R. Hatarik, D.B. Sayre, H.W. Sio, R.M. Bionta, D.L. Bleuel, J.A. Caggiano, C.J. Cerjan, G.W. Copper, M.J. Eckart, E.R. Edwards, S.A. Faye, C.J. Forrest, J.A. Frenje, V.Yu. Glebov, P.F. Grant, G.P. Grim, E.P. Hartouni, H.W. Herrmann, J.D. Kilkenny, J.P. Knauer, A.J. Mackinnon, F.E. Merrill, K.J. Moody, M.J. Moran, R.D. Petrasso, T.W. Phillips, H.G. Rinderknecht, D. H. G. Schneider, S.M. Sepke, D.A. Shaughnessy, W. Stoeffl, C.A. Velsko, P. Volegov 1 Lawrence Livermore National Laboratory, Livermore, California, USA 2 General Atomics, San Diego, California, USA 3 Los Alamos National Laboratory, Los Alamos, New Mexico, USA 4 Massachusetts Institute of Technology, Cambridge, Massachusetts, USA 5 University of California, Berkeley, Berkeley, California, USA 6 University of New Mexico, Albuquerque, New Mexico, USA 7 University of Rochester, Laboratory for Laser Energetics, Rochester, New York, USA yeamans1@llnl.gov

The Radiochemical Analysis of Gaseous Samples (RAGS) diagnostic apparatus was recently installed at the National Ignition Facility (NIF). Following a NIF shot, RAGS is used to pump the gas load from the NIF chamber for purification and isolation of the noble gases. After collection, the activated gaseous species are counted via gamma spectroscopy for measurement of the capsule areal density and fuel-ablator mix. Collection efficiency was determined by injecting a known amount of (135)Xe into the NIF chamber, which was then collected with RAGS. Commissioning was performed with an exploding pusher capsule filled with isotopically enriched (124)Xe and (126)Xe added to the DT gas fill. Activated xenon species were recovered post-shot and counted via gamma spectroscopy. Results from the collection and commissioning tests are presented. The performance of RAGS allows us to establish a noble gas collection method for measurement of noble gas species produced via neutron and charged particle reactions in a NIF capsule.

The gamma reaction history diagnostic at the National Ignition Facility has the capability to determine a number of important performance metrics for cryogenic deuterium-tritium implosions: the fusion burn width, bang time and yield, as well as the areal density of the compressed ablator. Extracting those values from the measured γ rays of an implosion, requires accounting for a γ-ray background in addition to the impulse response function of the instrument. To address these complications, we have constructed a model of the γ-ray signal, and are developing a simultaneous multi-shot fitting routine to constrain its parameter space.

The gamma-to-electron magnetic spectrometer, having better than 5% energy resolution, is proposed to resolve γ-rays in the range of E(o) ± 20% in single shot, where E(o) is the central energy and is tunable from 2 to 25 MeV. Gamma-rays from inertial confinement fusion implosions interact with a thin Compton converter (e.g., beryllium) located at approximately 300 cm from the target chamber center (TCC). Scattered electrons out of the Compton converter enter an electromagnet placed outside the NIF chamber (approximately 600 cm from TCC) where energy selection takes place. The electromagnet provides tunable E(o) over a broad range in a compact manner. Energy resolved electrons are measured by an array of quartz Cherenkov converters coupled to photomultipliers. Given 100 detectable electrons in the energy bins of interest, 3 × 10(14) minimum deuterium/tritium (DT) neutrons will be required to measure the 4.44 MeV (12)C γ-rays assuming 200 mg/cm(2) plastic ablator areal density and 3 × 10(15) minimum DT neutrons to measure the 16.75 MeV DT γ-ray line.

The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0±0.1 g cm(-2), which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1-1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275-300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25-35 μm. Neutron images of the implosion were used to estimate a fuel density of 500-800 g cm(-3).

Radiochemical diagnostic methods are currently under development for the National Ignition Facility (NIF). Samples in the gas-phase offer a direct method of collection by pumping out the large target chamber following a NIF shot and transporting the gas down-stream for further analysis. Ignition capsules will have a small amount (roughly 1015 atoms) of dopant added to the inner-most layers of the ablator shell. These elements will undergo nuclear activation from neutrons, deuterons, or alpha particles produced via the fusion process. For example, doping 124Xe and 127I in the shell will create activated xenon isotopes that can be correlated to the amount of fuel ρR and long-range mix in the capsule. We are building the Radiochemical Analysis of Gaseous Samples (RAGS) apparatus for collecting and analyzing activated gases produced via the ignition process. Following a shot, gases will be pumped out of the chamber and transported to a two-part system. The first part consists of a pre-filter that will remove particulates and other reactive gases. The second part is a cryogenic xenon collection station where xenon will be isolated, and will then either be removed for mass spectrometric analysis, or counted via gamma spectroscopy. Preliminary results from RAGS commissioning will be presented and future improvements to the apparatus will also be discussed.

Absolute bang time measurements with the gas Cherenkov detector (GCD) and gamma reaction history (GRH) diagnostic have been performed to high precision at the OMEGA laser facility at the University of Rochester with bang time values for the two diagnostics agreeing to within 5 ps on average. X-ray timing measurements of laser-target coupling were used to calibrate a facility-generated laser timing fiducial with rms spreads in the measured coupling times of 9 ps for both GCD and GRH. Increased fusion yields at the National Ignition Facility (NIF) will allow for improved measurement precision with the GRH easily exceeding NIF system design requirements.

The gamma reaction history (GRH) diagnostic is a multichannel, time-resolved, energy-thresholded γ-ray spectrometer that provides a high-bandwidth, direct-measurement of fusion reaction history in inertial confinement fusion implosion experiments. 16.75 MeV deuterium+tritium (DT) fusion γ-rays, with a branching ratio of the order of 10(-5)γ/(14 MeV n), are detected to determine fundamental burn parameters, such as nuclear bang time and burn width, critical to achieving ignition at the National Ignition Facility. During the tritium/hydrogen/deuterium ignition tuning campaign, an additional γ-ray line at 19.8 MeV, produced by hydrogen+tritium fusion with a branching ratio of unity, will increase the available γ-ray signal and may allow measurement of reacting fuel composition or ion temperature. Ablator areal density measurements with the GRH are also made possible by detection of 4.43 MeV γ-rays produced by inelastic scatter of DT fusion neutrons on (12)C nuclei in the ablating plastic capsule material.

The National Ignition Facility (NIF) successfully completed its first inertial confinement fusion (ICF) campaign in 2009. A neutron time-of-flight (nTOF) system was part of the nuclear diagnostics used in this campaign. The nTOF technique has been used for decades on ICF facilities to infer the ion temperature of hot deuterium (D(2)) and deuterium-tritium (DT) plasmas based on the temporal Doppler broadening of the primary neutron peak. Once calibrated for absolute neutron sensitivity, the nTOF detectors can be used to measure the yield with high accuracy. The NIF nTOF system is designed to measure neutron yield and ion temperature over 11 orders of magnitude (from 10(8) to 10(19)), neutron bang time in DT implosions between 10(12) and 10(16), and to infer areal density for DT yields above 10(12). During the 2009 campaign, the three most sensitive neutron time-of-flight detectors were installed and used to measure the primary neutron yield and ion temperature from 25 high-convergence implosions using D(2) fuel. The OMEGA yield calibration of these detectors was successfully transferred to the NIF.

A temporally gated x-ray framing camera based on a proximity focus microchannel plate is one of the most important diagnostic tools of inertial confinement fusion experiments. However, fusion neutrons produced in imploded capsules interact with structures surrounding the camera and produce background to x-ray signals. To understand the mechanisms of this neutron induced background, we tested several gated x-ray cameras in the presence of 14 MeV neutrons produced at the Omega laser facility. Differences between background levels observed with photographic film readout and charge-coupled-device readout have been studied.

This paper compares the results from a GEANT4 simulation of the gas Cherenkov detector 1 (GCD1) with previous simulations and experimental data from the Omega laser facility. The GCD1 collects gammas emitted during a deuterium-tritium capsule implosion and converts them, through several processes, to Cherenkov light. Photon signals are recorded using subnanosecond photomultiplier tubes, producing burn reaction histories. The GEANT4 GCD1 simulation is first benchmarked against ACCEPT, an integrated tiger series code, with good agreement. The simulation is subsequently compared with data from the Omega laser facility, where experiments have been performed to measure the effects of Hohlraum materials on reaction history signals, in preparation for experiments at the National Ignition Facility.

Radiochemical diagnostic techniques such as solid- and gas-phase capsule debris analysis may prove to be successful methods for establishing the success or failure of ignition experiments at the National Ignition Facility (NIF). Samples in the gas phase offer the most direct method of collection by simply pumping out the large target chamber following a NIF shot. The target capsules will be prepared with dopants which will produce radioactive noble gas isotopes upon activation with neutrons. We have designed and constructed the Radchem Apparatus for Gas Sampling (RAGS) in order to collect post-shot gaseous samples for NIF capsule diagnostics. The design of RAGS incorporates multiple stages intended to purify, transfer, and count the radioactive decays from gaseous products synthesized in NIF experiments. We will present preliminary results from the RAGS system's commissioning experiments highlighting collection efficiency and transport times. In addition, future improvements including cryogenic collection and purification of analytes and an implementation timeline at NIF will be discussed.

Detection of high-energy neutrons in the presence of gamma radiation background utilizes pulse-shape discrimination (PSD) phenomena in organics studied previously only with limited number of materials, mostly liquid scintillators and single crystal stilbene. The current paper presents the results obtained with broader varieties of luminescent organic single crystals. The studies involve experimental tools of crystal growth and material characterization in combination with the advanced computer modeling, with the final goal of better understanding the relevance between the nature of the organic materials and their PSD properties. Special consideration is given to the factors that may diminish or even completely obscure the PSD properties in scintillating crystals. Among such factors are molecular and crystallographic structures that determine exchange coupling and exciton mobility in organic materials and the impurity effect discussed on the examples of trans-stilbene, bibenzyl, 9,10-diphenylanthracene and diphenylacetylene.

The National Ignition Facility and the Omega Laser Facility both have a need for measuring prompt gamma radiation as part of a nuclear diagnostic program. A new gamma-detection diagnostic using off-axis-parabolic mirrors has been built. Some new techniques were used in the design, construction, and tolerancing of this gamma ray diagnostic. Because of the wavelength requirement (250 to 700 nm), the optical element surface finishes were a key design consideration. The optical enclosure had to satisfy pressure safety concerns and shielding against electromagnetic interference induced by gammas and neutrons. Structural finite element analysis was needed to meet rigorous optical and safety requirements. The optomechanical design is presented. Alignment issues are also discussed.

Peak core temperature is an important measure of implosion performance, and will be a critical diagnostic of ignition implosion performance at the National Ignition Facility because peak temperatures must attain high values in order to form the hot-spot spark that ignites the main mass of deuterium-tritium fuel. We plan to measure peak core temperatures, resolved in space and time, using a gated pinhole camera that differentially filters the individual images in different continuum x-ray bands. Ross pair analysis allows the temperature profile to be measured directly. We describe the technique, the various challenges that include x-ray scattering, Abel inversion of noisy images that do not have perfect two-dimensional symmetry, calibrations, and background suppression, and we discuss how we expect to meet these challenges.

Gas Cherenkov detectors have been used to convert fusion gammas into photons to achieve gamma reaction history (GRH) measurements. These gas detectors include a converter, pressurized gas volume, relay optics, and a photon detector. A novel design for the National Ignition Facility (NIF) using 90° Off-Axis Parabolic mirrors efficiently collects signal from fusion gammas with 8-ps time dispersion.1 Fusion gammas are converted to Compton electrons, which generate broadband Cherenkov light (our response is from 250 to 700 nm) in a pressurized gas cell. This light is relayed into a high-speed detector using three parabolic mirrors. The detector optics collect light from a 125-mm-diameter by 600-mm-long interchangeable gas (CO 2 or SF 6 ) volume. Because light is collected from source locations throughout the gas volume, the detector is positioned at the stop position rather than at an image position. The stop diameter and its position are independent of the light-generation locations along the gas cell. This design incorporates a fixed time delay that allows the detector to recover from prompt radiation. Optical ray tracings demonstrate how light can be collected from different angled trajectories of the Compton electrons as they traverse the gas volume. A Monte Carlo model of the conversion process from gammas to Cherenkov photons is used to generate photon trajectories. The collection efficiencies for different gamma energies are evaluated. At NIF, a cluster of four channels will allow for increased dynamic range, as well as different gamma energy thresholds. This GRH design is compared to a gas Cherenkov detector that utilizes a Cassegrain reflector now used at the OMEGA laser facility.

In this paper, bang time and gamma reaction history measurements are fundamental components of diagnosing ICF implosions and will be essential contributors to diagnosing attempts at ignition on the National Ignition Facility (NIF). Fusion gammas provide a direct measure of fusion interaction rate without being compromised by Doppler spreading. Gamma based Gas Cherenkov Detectors that convert fusion gamma rays to optical Cherenkov photons for collection by fast recording systems have been developed and fielded at Omega.

We are designing a gas-Cherenkov detector system1 for the NIF THD campaign. A very small fraction of DT fusion reactions produce a 16.7 MeV gamma ray instead of a 14 MeV neutron, the time history of the fusion gammas is an accurate representation of the fusion reaction history. Gas Cherenkov detectors with a gamma-to-electron converter can be tuned to be only sensitive to gamma rays above a certain energy. We will have a cluster of several Cherenkov detectors installed at NIF, just outside the target chamber wall. The multiple detectors will allow us to measure the time history for several different (integral) threshold energies, ranging from 3.5 MeV to 20 MeV. The HT fusion reaction (yielding an alpha particle and a 19.8 MeV gamma ray) is a very rare process in a typical fusion plasma, but the reaction has a 100% branching ratio to gamma rays, unlike the DT fusion reaction. A THD plasma with 0.5% deuterium will have a thermal reaction rate producing mostly 16.7 MeV gammas from the DT fusion, but if the fuel is dense enough to scatter a significant number of 14 MeV neutrons, there will be a high fraction of up-scattered MeV protons and tritons in the plasma. The reaction rate for DT is falling in the MeV energy range, the HT reaction rate is increasing by about 1000 times relative to the DT fusion for MeV ions, considering that most of the fuel is H and T. The energetic up-scattered ions will enhance the 19.8 MeV HT gamma production rate dramatically, making it the dominant gamma rate. Using the energy selective Cherenkov detectors, we can extract a number for the fuel rho-r or neutron down-scatter fraction, which is directly related to the number of up-scattered protons and tritons. A time dependent measurement of the HT to DT fusion gamma rate can be used to measure a time dependent rho-r for the THD fuel. It is a potentially clean measurement of the fuel rho-r, integrated over all angles. The signal is not contaminated by other reactions in the fuel.

A Gas Cherenkov Detector (GCD) which captures 16.75 MeV DT fusion γ-rays has been developed by Los Alamos National Laboratory in collaboration with Lawrence Livermore National Laboratory and Atomic Weapons Establishment. Due to the fast time response (∼ 120 ps), the GCD will be an essential instrument for National Ignition Facility (NIF) fusion reaction history studies. A challenge faced by the GCD is potential interference of primary DT fusion γ-rays (γ p ) with various secondary γ-rays (γ s ). NIF implosions produce 14 MeV DT neutrons (n o ) that induce the production of γ s from reactions on capsule materials (12C, 16O) and hohlraum materials (Au, U, Al). Experimental characterization of the GCD responses to various gamma rays is required for accurate measurements of NIF fusion reaction history. Our primary experimental goal in this work is to simulate the neutron-induced secondary gamma production of a NIF hohlraum.

Radiochemical diagnostic techniques such as solid- and gas-phase capsule debris analysis may prove to be successful methods for establishing the success or failure of ignition experiments at the National Ignition Facility (NIF). Samples in the gas phase offer the most direct method of collection by simply pumping out the large target chamber following a NIF shot. The target capsules will be prepared with dopants which will produce radioactive noble gas isotopes upon activation with neutrons. We have designed the Radchem Apparatus for Gas Sampling (RAGS) in order to collect post-shot gaseous samples for NIF capsule diagnostics. The design of RAGS incorporates multiple stages intended to purify, transfer, and count the radioactive decays from gaseous products synthesized in NIF experiments.

Imaging plate (IP) is a phosphor which has image storage capability. Because of its immunity to electric-magnetic-interference, IP's have been used in various laser-plasma experiments as a detector for x-ray imaging and electron spectroscopy. IP's are sensitive to most of ionizing radiations. Response of IP's to x-ray, gamma-ray, and charged particle exposure has been reported. However its intrinsic response to neutron exposure has not been understood clearly. In order to assess expected performance of IP's in harsh neutron background environment of the National Ignition Facility, it is crucial to understand IP's sensitivity to 14MeV neutrons. We exposed absolutely calibrated IP's to known neutron flux at OMEGA laser facility. Comparison of experimental results and Monte Carlo simulations will be reported.

We present a study of the inclusive production of neutral pions and charged particles from 112 000 hadronic Z 0 decays. The measured inclusive momentum distributions can be reproduced by parton shower Monte Carlo programs and also by an analytical QCD calculation. Comparing our results to e + e − data between √ s = 9 and 91 GeV, we findfind that the evolution of the spectra with center of mass energy is consistent with the QCD predictions.

From 2540 Z0 → τ+τ− events, we determine the inclusive decay branching fractions of the τ-lepton into one and three charged particles to be 0.856 ± 0.006 (stat.) ± 0.003 (syst.) and 0.144 ± 0.006 (stat.) ± 0.003 (syst.), respectively. The leptonic branching fractions are measured to be 0.175 ± 0.008 (stat.) ± 0.005 (syst.) for τ → μνμντ and 0.177 ± 0.007 (stat.) ± 0.006 (syst.) for τ → eνeντ. We determined the τ lifetime both from three-prong decays using the decay length and from one-prong decays using the impact parameter. The results from the two independent methods agree and yield a combined value of [0.309 ± 0.023 (stat.) ± 0.030 (syst.)] × 10−12s.

Understanding mix in inertial confinement fusion (ICF) experiments at the National Ignition Facility requires the diagnosis of charged-particle reactions within an imploded target. Radiochemical diagnostics of these reactions are currently under study by scientists at Los Alamos and Lawrence Livermore National Laboratories. Measurement of these reactions requires assay of activated debris and tracer gases from the target. Presented below is an overview of the prompt radiochemistry diagnostic development efforts, including a discussion of the reactions of interest as well as the progress being made to collect and count activated material.

Bang time and reaction history measurements are fundamental components of diagnosing inertial confinement fusion (ICF) implosions and will be essential contributors to diagnosing attempts at ignition on the National Ignition Facility (NIF). Fusion gammas provide a direct measure of fusion interaction rate without being compromised by Doppler spreading. Gamma-based gas Cherenkov detectors that convert fusion gamma rays to optical Cherenkov photons for collection by fast recording systems have been developed and fielded at Omega. These systems have established their usefulness in illuminating ICF physics in several experimental campaigns. Bang time precision better than 25 ps has been demonstrated, well below the 50 ps accuracy requirement defined by the NIF system design requirements. A comprehensive, validated numerical study of candidate systems is providing essential information needed to make a down selection based on optimization of sensitivity, bandwidth, dynamic range, cost, and NIF logistics. This paper presents basic design considerations arising from the two-step conversion process from gamma rays to relativistic electrons to UV/visible Cherenkov radiation.