C. A. Velsko

A membrane inlet mass spectrometry system for noble gases at natural abundances in gas and water samples

RATIONALE Noble gases dissolved in groundwater can reveal paleotemperatures, recharge conditions, and precise travel times. The collection and analysis of noble gas samples are cumbersome, involving noble gas purification, cryogenic separation and static mass spectrometry. A quicker and more efficient sample analysis method is required for introduced tracer studies and laboratory experiments. METHODS A Noble Gas Membrane Inlet Mass Spectrometry (NG-MIMS) system was developed to measure noble gases at natural abundances in gas and water samples. The NG-MIMS system consists of a membrane inlet, a dry-ice water trap, a carbon-dioxide trap, two getters, a gate valve, a turbomolecular pump and a quadrupole mass spectrometer equipped with an electron multiplier. Noble gases isotopes (4)He, (22)Ne, (38)Ar, (84)Kr and (132)Xe are measured every 10 s. RESULTS The NG-MIMS system can reproduce measurements made on a traditional noble gas mass spectrometer system with precisions of 2%, 8%, 1%, 1% and 3% for He, Ne, Ar, Kr and Xe, respectively. Noble gas concentrations measured in an artificial recharge pond were used to monitor an introduced xenon tracer and to reconstruct temperature variations to within 2 °C. Additional experiments demonstrated the capability to measure noble gases in gas and in water samples, in real time. CONCLUSIONS The NG-MIMS system is capable of providing analyses sufficiently accurate and precise for introduced noble gas tracers at managed aquifer recharge facilities, groundwater fingerprinting based on excess air and noble gas recharge temperature, and field and laboratory studies investigating ebullition and diffusive exchange.

The Radiochemical Analysis of Gaseous Samples (RAGS) apparatus for nuclear diagnostics at the National Ignition Facility (invited).

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.

A recoverable gas-cell diagnostic for the National Ignition Facility

The high-fluence neutron spectrum produced by the National Ignition Facility (NIF) provides an opportunity to measure the activation of materials by fast-spectrum neutrons. A new large-volume gas-cell diagnostic has been designed and qualified to measure the activation of gaseous substances at the NIF. This in-chamber diagnostic is recoverable, reusable and has been successfully fielded. Data from the qualification of the diagnostic have been used to benchmark an Monte Carlo N-Particle Transport Code simulation describing the downscattered neutron spectrum seen by the gas cell. We present early results from the use of this diagnostic to measure the activation of natXe and discuss future work to study the strength of interactions between plasma and nuclei.

Activation of enriched environmental xenon by 14-MeV neutrons

The international monitoring system exists to verify compliance with the terms of the comprehensive test ban treaty. About 10% of the member stations will be capable of detecting radioxenon, which can be produced in nuclear detonations or through civilian processes. We have studied the activation of radioxenon by the prompt, intense spectrum of 14-MeV neutrons produced at the National Ignition Facility. While 14-MeV neutrons are not currently a significant contributor to the production of radioxenon, we find that radioxenon produced through activation of environmental xenon by 14-MeV neutrons would be distinguishable from activation by nuclear tests.

Determination of relative krypton fission product yields from 14 MeV neutron induced fission of 238U at the National Ignition Facility

Precisely-known fission yield distributions are needed to determine a fissioning isotope and the incident neutron energy in nuclear security applications. 14 MeV neutrons from DT fusion at the National Ignition Facility induce fission in depleted uranium contained in the target assembly hohlraum. The fission yields of Kr isotopes (85m, 87, 88, and 89) are measured relative to the cumulative yield of 88Kr and compared to previously tabulated values. The results from this experiment and England and Rider are in agreement, except for the 85mKr/88Kr ratio, which may be the result of incorrect nuclear data.

Upgrades to the Radiochemistry Analysis of Gas Samples (RAGS) Diagnostic at the National Ignition Facility

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, used 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 target 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.

The Radiochemical Analysis of Gaseous Samples (RAGS) apparatus for nuclear diagnostics at the national ignition facility

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.

Gaseous sample collection 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 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.