US-12625282-B2 - In-situ beta-particle detector for high resolution 234th export measurements

Abstract

A sea going instrument is used to measure the 234 Th activity on settling particles in the ocean as an indicator of carbon sequestration as export from the surface ocean. The instrumentation can be adapted to multiple sampling platforms with the goal of providing high temporal resolution 234 Th flux measurements at multiple locations and depths in the ocean. This proxy of mass flux is used to complement other in situ sensors to provide high resolution data for features such as Chlorophyll-a concentration (Chla), accessory pigments, and PIC normalized to mass flux.

Inventors

• Timothy J. Shaw
• Michael L. Myrick

Assignees

• UNIVERSITY OF SOUTH CAROLINA

Dates

Publication Date

20260512

Application Date

20240517

Claims (20)

1. 1 . A method for in-situ high resolution beta-particle detection for measurements of 234 Th activity on settling particles in the ocean as an indicator of carbon sequestration as export from the surface ocean to the ocean floor, comprising: using a scintillation material sensor to sense the beta decay activity occurring at a sensor placed in a location of the ocean to be assessed and to output responsive beta energy signals from the sensor, and detecting the presence of 234 Th by discriminating relatively higher beta energy signals from the sensor indicating a measurement of the beta decay of an excited state of its daughter 234m Pa.
2. 2 . The method according to claim 1 , wherein the relatively higher beta energy signals comprise about 2.27 MeV beta emissions.
3. 3 . The method according to claim 1 , wherein: the beta energy signals are detected as scintillation generated photon signals; and detecting and discriminating includes using signal pulse height analysis of a spectrum of beta energy signals generated by the scintillation material, for differentiation of photon energies associated with the 234 Th daughter from those comprising ambient background.
4. 4 . The method according to claim 3 , further comprising using a multichannel pulse height analyzer in place of high mass shielding.
5. 5 . The method according to claim 1 , wherein the scintillation materials comprise beta-sensitive plastic scintillation materials that are responsive to beta particles in the energy range of about 2.27 MeV.
6. 6 . The method according to claim 5 , wherein the plastic scintillation materials a planar scintillator comprising a sheet from 1 mm to several cm thick and with an efficiency of at least 10% above the ambient background.
7. 7 . The method according to claim 6 , wherein the plastic scintillation materials include a polymer base comprising polyvinyl toluene.
8. 8 . The method according to claim 1 , wherein detecting and discriminating includes using a photon signal detector, with the detector comprising one of a photomultiplier tube (PMT) or a silicon photomultiplier (SiPM).
9. 9 . The method according to claim 8 , wherein detecting and discriminating includes using a photon signal detector comprising a photomultiplier tube (PMT) placed directly under the plastic scintillation materials and a sample to be assessed.
10. 10 . The method according to claim 9 , wherein the output of the PMT is coupled to a fast preamplifier, with the output of the preamplifier directed to one of: (a) a comparator and pulse counter or (b) to a multichannel analyzer, to count pulses while retaining information about their pulse height.
11. 11 . The method according to claim 10 , further comprising producing a histogram of counts for different pulse heights.
12. 12 . The method according to claim 10 , further comprising collecting and sorting all the pulses observed from the PMT.
13. 13 . The method according to claim 1 , further comprising providing a motor-driver shuttle sample system for selectively providing sequential analysis by movement of samples and standards adjacent to the scintillation material sensor.
14. 14 . The method according to claim 13 , further comprising selectively performing sequential analysis of ambient background counts, sample and background counts, standard counts with ambient background and standard counts over the sample counts.
15. 15 . The method according to claim 14 , wherein the location of the ocean comprises a selected depth from the ocean surface.
16. 16 . The method according to claim 1 , further comprising using a plurality of the scintillation material sensors to respectively sense the beta decay activity occurring at sensors placed in a corresponding plurality of locations of the ocean to be assessed and to output responsive beta energy signals from the respective sensors.
17. 17 . The method according to claim 16 , wherein using a plurality of the scintillation material sensors comprises using at least one of autonomous or moored sediment traps.
18. 18 . The method according to claim 1 , further comprising using a sample collection shutter system associated with an existing floating collection sensor.
19. 19 . The method according to claim 18 , wherein the sample collection shutter system includes two shutters respectively controlled to rotate to collect a sample, isolate the sample for counting, position a standard over an associated photon signal detector for standard evaluation, and move an empty cell with only ambient seawater over the photon signal detector for background counting.
20. 20 . The method according to claim 1 , further comprising adapting the method of associate a plurality of scintillation material sensors to multiple sampling platforms, and providing high temporal resolution 234 Th flux measurements recorded at multiple depths in the ocean.

Description

PRIORITY CLAIM The present application claims the benefit of priority of U.S. Provisional Patent Application No. 63/504,833, titled In-Situ Beta-Particle Detector For High Resolution 234Th Export Measurements, filed May 30, 2023, and which is fully incorporated herein by reference for all purposes. BACKGROUND OF THE PRESENTLY DISCLOSED SUBJECT MATTER Presently disclosed subject matter generally relates to high resolution beta-particle detectors, and more particularly to development of in-situ beta-particle detectors for high resolution 234Th (Thorium-234) export based mass flux measurements on moored and autonomous sediment traps, such as comprising instruments used in oceanography and limnology to measure the quantity of sinking particulate material in aquatic systems, primarily oceans. In some presently disclosed embodiments, a sea going instrument may be used to measure the 234Th activity on settling particles in the ocean as an indicator of carbon sequestration as export from the surface ocean. It is believed there are currently no available technologies that can measure 234Th on sedimenting particulates in-situ in the ocean water column at activities relevant to ongoing climate change research. Global estimates of the transport of phytodetritus to the deep ocean as Particulate Organic Carbon (POC) flux put an upper limit of the impact of the “Carbon Pump” to the deep ocean on the order of 5-15% of global carbon export (Laws et al., 2000; Giering et al., 2014). However, changing climate conditions have led to increased intensity and variability of factors that mediate POC flux, particularly in dynamic coastal systems (Smith et al., 2013; 2018). The resultant episodic productivity events associated with transient physical processes are becoming more significant in their contribution to the net transfer of organic carbon from the upper ocean to abyssal depths (Henson et al., 2019; Smith et al., 2013; 2018, Stukel et al., 2017). Ephemeral oceanographic processes like upwelling events, fronts, eddies and filaments lead to productivity events that export particulate carbon out of surface waters as pulses of highly variable duration (Smith et al., 2018; Bishop et al., 2016). An important factor affecting the efficiency of carbon export to the deep ocean during these events is the particle transit time (Shaw et al., 2019; Smith et al., 2018). The physical dynamics of these systems can enhance both primary production as well as vertical transport of particulate phases by processes such as direct subduction of particles and enhanced aggregation. The organic material carried with rapidly sinking particles is less susceptible to carbon flux attenuation at mid depths and results in observed periods of high carbon-export efficiency to the abyss (Baldwin et al., 1998; Shaw et al., 1998; Buesseler 1998, Riley et al, 2012; Smith et al., 2018). For example, Buesseler and Boyd (2009) found lower attenuation of surface carbon export through the “twilight zone” following diatom bloom events in a mesotrophic location (K2) compared to an oligotrophic site (Aloha). Current methods for estimation of carbon attenuation (e.g. Martin fit versus remineralization length scale) have relatively low sensitivity for short timescale events and are susceptible to location bias (Buesseler and Boyd 2009; de Melo Viríssimo et al., 2022). Remineralization with depth is a key term in global biogeochemical models, and spatiotemporal changes in this term have been shown in model experiments to alter the accumulation of atmospheric CO2 (Kwon et al. 2009). A number of critical factors that affect sinking velocity, and hence carbon flux attenuation, are magnified in association with short timescale physical processes in surface waters (Alldredge et al., 1995; Passow and de la Rocha, 2006; Armstrong et al., 2009). Factors such as aggregation of POC phases and ballasting by biogenic and/or lithogenic phases are consistent with observed episodic flux events (Baldwin et al., 1998; Shaw et al., 1998; Buesseler et al., 1998). These important but ephemeral depositions to the abyss have been shown to occur seasonally and inter-annually over periods of days or weeks at magnitudes equal to or greater than monthly or even annual fluxes at other times. The temporal relationship between dynamic surface processes and their contribution to the net POC flux at abyssal depths requires sampling resolution on timescales of hours to days (Bishop et al., 2016; Stukel et al., 2017; Smith et al., 2018). Carbon Flux Proxy Measurements: Shipboard based depth integrated particle export and remineralization for POC, PIC, nutrient and biogenic phases are often measured using the 234Th/238U disequilibrium method (Rutgers van der Loeff et al., 2006; Waples et al., 2003, Buesseler and Boyd 2009). This approach requires a depth profile of 234Th and 238U activities coupled with particulate phase analyte to 234Th ratios (e.g. POC/234Th, PIC/234Th, Nut/234Th) from one or more depth