Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Precision measurement of relative γ-ray intensities from the decay of 61Cu.

A discrepancy, well outside reported uncertainties, has been observed between the accepted and measured values of the intensity ratio of the two strongest γ rays following 61Cu β+ decay. This discrepancy has significant impact since the natNi(d,x)61Cu reaction has historically been one of only a few IAEA recommendations for use as a deuteron flux monitor and a considerable number of published cross sections measured in ratio to that beam monitor cross section may depend on the choice of either the first or second strongest γ ray in those calculations. To determine the magnitude of this error most precisely, over a hundred separate measurements of the 283 keV to 656 keV γ-ray emission ratio were collected from seven experiments and a variety of detectors and detection geometries. A weighted average of all these measurements indicates an error in the value listed in the Nuclear Data Sheets of 11% in either the primary or second-highest intensity γ ray of 61Cu, potentially introducing an 11% error in 61Cu production cross section measurements, cross sections using nickel activation as a deuteron beam current monitor, or in dose rates when 61Cu is used in nuclear medicine. General agreement with the Data Sheets with ten other intensity ratios suggests the most probable error is in the secondary (656 keV) emission, which accordingly should be updated from 10.8% to 9.69%

Precision measurement of relative γ-ray intensities from the decay of 61Cu.

A discrepancy, well outside reported uncertainties, has been observed between the accepted and measured values of the intensity ratio of the two strongest γ rays following 61Cu β+ decay. This discrepancy has significant impact since the natNi(d,x)61Cu reaction has historically been one of only a few IAEA recommendations for use as a deuteron flux monitor and a considerable number of published cross sections measured in ratio to that beam monitor cross section may depend on the choice of either the first or second strongest γ ray in those calculations. To determine the magnitude of this error most precisely, over a hundred separate measurements of the 283 keV to 656 keV γ-ray emission ratio were collected from seven experiments and a variety of detectors and detection geometries. A weighted average of all these measurements indicates an error in the value listed in the Nuclear Data Sheets of 11% in either the primary or second-highest intensity γ ray of 61Cu, potentially introducing an 11% error in 61Cu production cross section measurements, cross sections using nickel activation as a deuteron beam current monitor, or in dose rates when 61Cu is used in nuclear medicine. General agreement with the Data Sheets with ten other intensity ratios suggests the most probable error is in the secondary (656 keV) emission, which accordingly should be updated from 10.8% to 9.69%

Performance evaluation of an energy tuning assembly for neutron spectral shaping

An energy tuning assembly (ETA) was designed to be fielded at the National Ignition Facility (NIF) to modify the characteristic D-T fusion spectrum to include a prompt fission neutron spectral component. The ETA was characterized at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory to measure the shaped spectrum from an incident deuteron breakup neutron source, test the proposed neutron spectroscopy techniques used to inform the flux measurements at NIF, and validate the ability to predict ETA performance using a Monte Carlo Neutral Particle (MCNP) simulation. Activation foils (i.e., Ni, In, Au, Al) were exposed to a collimated 33-MeV deuteron-breakup beam originating from a tantalum breakup target. The source spectrum absent the ETA was characterized using a set of activation foils and the STAYSL unfolding code. Finally, the ETA-modified spectrum was obtained using activation foil unfolding with a [Formula presented]=1.32. The ETA-modified unfolded spectrum agreed with the MCNP-simulated prediction in the energy range of 0.1–14 MeV, but exhibited disagreements in the 10 eV–100 keV region. This work demonstrates shaping of the NIF neutron spectrum via the ETA to be a viable path forward for tailored neutron beams at NIF

Neutron Spectroscopy for pulsed beams with frame overlap using a double time-of-flight technique

A new double time-of-flight (dTOF) neutron spectroscopy technique has been developed for pulsed broad spectrum sources with a duty cycle that results in frame overlap, where fast neutrons from a given pulse overtake slower neutrons from previous pulses. Using a tunable beam at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory, neutrons were produced via thick-target breakup of 16 MeV deuterons on a beryllium target in the cyclotron vault. The breakup spectral shape was deduced from a dTOF measurement using an array of EJ-309 organic liquid scintillators. Simulation of the neutron detection efficiency of the scintillator array was performed using both GEANT4 and MCNP6. The efficiency-corrected spectral shape was normalized using a foil activation technique to obtain the energy-dependent flux of the neutron beam at zero degrees with respect to the incoming deuteron beam. The dTOF neutron spectrum was compared to spectra obtained using HEPROW and GRAVEL pulse height spectrum unfolding techniques. While the unfolding and dTOF results exhibit some discrepancies in shape, the integrated flux values agree within two standard deviations. This method obviates neutron time-of-flight spectroscopy challenges posed by pulsed beams with frame overlap and opens new opportunities for pulsed white neutron source facilities

Simultaneous measurement of organic scintillator response to carbon and proton recoils

Background: Organic scintillators are widely used for neutron detection in both basic nuclear physics and applications. While the proton light yield of organic scintillators has been extensively studied, measurements of the light yield from neutron interactions with carbon nuclei are scarce. Purpose: Demonstrate a new approach for the simultaneous measurement of the proton and carbon light yield of organic scintillators. Provide new carbon light yield data for the EJ-309 liquid and EJ-204 plastic organic scintillators. Method: A 33-MeV H+2 beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory was impinged upon a 3-mm-thick Be target to produce a high-flux, broad-spectrum neutron beam. The double time-of-flight technique was extended to simultaneously measure the proton and carbon light yields of the organic scintillators, wherein the light output associated with the recoil particle was determined using np and nC elastic scattering kinematics. Results: The proton and carbon light yield relations of the EJ-309 liquid and EJ-204 plastic organic scintillators were measured over a recoil energy range of approximately 0.3 to 1 MeV and 2 to 5 MeV, respectively, for EJ-309, and 0.2 to 0.5 MeV and 1 to 4 MeV, respectively, for EJ-204. Conclusions: These data provide new insight into the ionization quenching effect in organic scintillators and key input for simulation of the response of organic scintillators for both basic science and a broad range of applications

Simultaneous measurement of organic scintillator response to carbon and proton recoils

Background: Organic scintillators are widely used for neutron detection in both basic nuclear physics and applications. While the proton light yield of organic scintillators has been extensively studied, measurements of the light yield from neutron interactions with carbon nuclei are scarce. Purpose: Demonstrate a new approach for the simultaneous measurement of the proton and carbon light yield of organic scintillators. Provide new carbon light yield data for the EJ-309 liquid and EJ-204 plastic organic scintillators. Method: A 33-MeV H+2 beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory was impinged upon a 3-mm-thick Be target to produce a high-flux, broad-spectrum neutron beam. The double time-of-flight technique was extended to simultaneously measure the proton and carbon light yields of the organic scintillators, wherein the light output associated with the recoil particle was determined using np and nC elastic scattering kinematics. Results: The proton and carbon light yield relations of the EJ-309 liquid and EJ-204 plastic organic scintillators were measured over a recoil energy range of approximately 0.3 to 1 MeV and 2 to 5 MeV, respectively, for EJ-309, and 0.2 to 0.5 MeV and 1 to 4 MeV, respectively, for EJ-204. Conclusions: These data provide new insight into the ionization quenching effect in organic scintillators and key input for simulation of the response of organic scintillators for both basic science and a broad range of applications

GENESIS: Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering

Improved neutron inelastic scattering cross section data are needed to inform integral benchmark studies and advance applications in a wide variety of areas including nuclear energy, stockpile stewardship, nonproliferation, and space exploration. Neutron inelastic scattering also serves as a non-selective probe of low-lying nuclear structure. To help meet these needs, the Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS) was constructed at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. This array couples high-resolution γ-ray detectors and fast neutron detectors to achieve single and coincident n/γ detection over a broad energy range. The current configuration of the array includes 26 organic liquid scintillators and four high-purity germanium detectors (two single-crystal and two four-crystal CLOVER detectors with two-fold segmentation). The array was constructed with minimal supporting material and designed to cover a wide range of secondary particle angles and energies with limited inter-element scattering. Data acquisition is accomplished using Mesytec MDPP-16 multi-channel high-resolution digital pulse processing modules. The array characteristics, including γ-ray and neutron energy resolution, timing resolution, and detection efficiency were measured and used to validate a GEANT4 model of the array. The primary sources of neutron background and the uncertainties in the determination of incident and secondary neutron energy were assessed. GENESIS provides a new capability to address nuclear data needs and facilitates the advancement of a wide range of nuclear applications

Proton light yield in organic scintillators using a double time-of-flight technique

Recent progress in the development of novel organic scintillators necessitates modern characterization capabilities. As the primary means of energy deposition by neutrons in these materials is n-p elastic scattering, knowledge of the proton light yield is paramount. This work establishes a new model-independent method to continuously measure the proton light yield in organic scintillators over a broad energy range. Using a deuteron breakup neutron source at the 88-in. Cyclotron at Lawrence Berkeley National Laboratory and an array of organic scintillators, the proton light yield of EJ-301 and EJ-309, commercially available organic liquid scintillators from Eljen Technology, was measured via a double time-of-flight technique. The light yield was determined using a kinematically over-constrained system in the proton energy range of 1-20 MeV. The effect of the pulse integration length on the magnitude and shape of the proton light yield relation was also explored. This work enables accurate simulation of the performance of advanced neutron detectors and supports the development of next-generation neutron imaging systems