System and method for generating ion emission from tidx via low-energy ion beams

Abstract

A method for generating energetic particles includes generating a first ion beam comprising a first group of atomic nuclei. Next, providing a condensed matter medium comprising a second group of atomic nuclei and then interacting the first ion beam with the condensed matter medium so that some atomic nuclei of the first group of atomic nuclei are implanted into the condensed matter medium and generate a loaded region in the condensed matter medium. Subsequently inducing phonons in the loaded region in the condensed matter medium, and then the induced phonons interact with the first group of atomic nuclei and the second group of atomic nuclei in the loaded region and enable nonradiative transfer of excitation energy from nuclear states of the first group of atomic nuclei to nuclear states of the second group of atomic nuclei. Finally, emitting energetic particles stemming from deexcitation processes of exited nuclear states of the second group of atomic nuclei in the loaded region.

Description

[0001] SYSTEM AND METHOD FOR GENERATING ION EMISSION FROM TIDx VIA LOW-ENERGY ION BEAMS

[0002] Cross Reference to related Co-Pending Applications

[0003] This application claims the benefit of U.S. provisional application Serial No.

[0004] 63 / 770,678 filed March 12th, 2025 and entitled “SYSTEM AND METHOD FOR GENERATING ION EMISSION FROM TIDx VIA LOW-ENERGY ION BEAMS”, the contents of which are expressly incorporated herein by reference.

[0005] This application is a continuation-in-part and claims the benefit of U.S. non-provisional application Serial No. 15 / 733,950 filed Dec. 1st, 2020 and entitled “System and method for phonon-mediated excitation and de-excitation of nuclear states”, the contents of which are expressly incorporated herein by reference.

[0006] Field of the Invention

[0007] The present invention relates to a system and method for generating ion emission from TiDx, and in particular to a system and method for generating ion emission from TiDx using low energy ion beams.

[0008] Background of the Invention

[0009] Charged particles, such as alpha particles at MeV energies, represent a highly ionizing radiation with low penetration depth (a few centimeters of air or skin) and have many applications. Energetic alpha particles have an energy of about 16MeV or higher and are used for targeted cancer treatment due to their high linear energy transfer. Because alpha particles have high energy but low penetration, they can kill cancer cells precisely without damaging surrounding healthy tissue.

[0010] Energetic alpha particles are usually produced from the uncontrolled decay of radioactive isotopes, whose production in turn requires large scale nuclear reactors, or particle accelerators. There is a need for small scale devices that can generate energetic alpha particles and other energetic particles that can be used for medical and industrial applications.

[0011] Summary of the InventionThe present invention relates to a system and method for generating ion emission from TiDx, and in particular to a system and method for generating ion emission from TiDx using low energy ion beams.

[0012] In general, in one aspect, the invention features a method for generating energetic particles including the following. First generating a first ion beam comprising a first group of atomic nuclei. Next, providing a condensed matter medium comprising a second group of atomic nuclei and then interacting the first ion beam with the condensed matter medium so that some atomic nuclei of the first group of atomic nuclei are implanted into the condensed matter medium and generate a loaded region in the condensed matter medium. Subsequently inducing phonons in the loaded region in the condensed matter medium, and then the induced phonons interact with the first group of atomic nuclei and the second group of atomic nuclei in the loaded region and enable nonradiative transfer of excitation energy from nuclear states of the first group of atomic nuclei to nuclear states of the second group of atomic nuclei. Finally, emitting energetic particles stemming from deexcitation processes of exited nuclear states of the second group of atomic nuclei in the loaded region.

[0013] Implementations of this aspect of the invention may include one or more of the following features. The first ion beam comprises ions with energies in the range of lOOeV to 2000 eV. The method further includes providing a particle detector for detecting the emitted energetic particles. The condensed matter medium is contained within a vacuum chamber. The condensed matter medium comprises a Titanium foil and the second group of atomic nuclei comprises Ti-nuclei. The first group of atomic nuclei comprises deuterium (H-2) and optionally protium (H-l) nuclei. The emitted charged particles comprise tritium (H-3) and Helium-4 (He-4) nuclei resulting from deexcitation processes of exited nuclear states of the Ti-nuclei. The loaded region comprises vacancies and / or open-volume defects and the first group of atomic nuclei is implanted in said vacancies and / or open-volume defects. The phonons are induced in the loaded region of the condensed matter medium via bombardment by a second ion beam and the second ion beam comprises non-hydrogen inert-gas ions. The nonhydrogen inert-gas ions comprise Argon ions.In general, in another aspect the invention features a system for generating energetic particles including a device for generating a first ion beam comprising a first group of atomic nuclei, and a condensed matter medium comprising a second group of atomic nuclei. The first ion beam is configured to interact with the condensed matter medium so that some atomic nuclei of the first group of atomic nuclei are implanted into the condensed matter medium and generate a loaded region in the condensed matter medium. The device further includes a device for inducing phonons in the loaded region in the condensed matter medium. The induced phonons are configured to interact with the first group of atomic nuclei and the second group of atomic nuclei in the loaded region and enable nonradiative transfer of excitation energy from nuclear states of the first group of atomic nuclei to nuclear states of the second group of atomic nuclei. Energetic particles are emitted stemming from deexcitation processes of exited nuclear states of the second group of atomic nuclei in the loaded region.

[0014] Brief Description of the Drawings

[0015] Referring to the figures, wherein like numerals represent like parts throughout the several views:

[0016] FIG. 1A depicts a schematic illustration of one class of excitation-transfer dynamics according to this invention;

[0017] FIG. IB depicts candidate acceptor-side state energies for titanium isotopes together with a donor-side excitation energy associated with the D2 / He-4 system near 23.85 MeV;

[0018] FIG. 2 depicts a schematic diagram of a first embodiment of a system for obtaining the first group of data, according to this invention;

[0019] FIG. 3 depicts a photograph of the vacuum chamber and ion gun in the embodiment of FIG. 2;

[0020] FIG. 4 depicts a calibration spectrum in 1 atm helium from241Am calibration source, wherein the counts at the peak correspond to alpha particles with energies of about 5.5 MeV;FIG. 5 depicts graphs of range versus energy for alpha and proton particles in silicon, based on the SRIM code ( J. F. Ziegler, “SRIM-2003,” Nuclear instruments and methods in physics research section B: Beam interactions with materials and atoms 219 (2004) 1027-1036);

[0021] FIG. 6 depicts a graph of the ion beam current as a function of time (left y-axis), a graph of the gas flow out of the chamber as a function of time (right y-axis), and charged particle counts (circles) as a function of time (inset y-axis), wherein the charged particle energies are estimated based on the described calibration;

[0022] FIG. 7 depicts calibration data of a 3.38 mm lithium drifted silicon detector, wherein the triangles represent data for Th-228 alphas , the circles represent data for energetic deuterons, and the squares represent data for energetic alphas (J. H. Elliot, “Thick junction radiation detectors made by ion drift,” Nuclear Instruments and Methods 12 (1961) 60-66);

[0023] FIG. 8 depicts results of SRIM calculations for incomplete energy deposition for alphas at normal incidence on a 500 pm thick silicon detector (R-series detector), and for complete energy deposition ( A-series detector);

[0024] FIG. 9 depicts neutron counts (vertical lines) correlated in time with charged particle counts (circles);

[0025] FIG. 10 depicts a graph of the ion beam current as a function of time (left y-axis), a graph of the gas flow out of the chamber as a function of time (right y-axis), and charged particle count (circle) as a function of time (inset y-axis), wherein the charged particle energies are estimated based on the described calibration;

[0026] FIG. 11 depicts a schematic cross-sectional diagram of an arrangement of a sample holder, a charged particle detector and a sample in a second embodiment of the system of FIG. 2;FIG. 12 depicts counts as a function of channel from the A-series detector (Experiment 5j ), showing the uppermost channels with low-channel noise and the charged particle counts (circles);

[0027] FIG. 13 depicts a graph of energy loss for an alpha particle normal through 5 pm of Ti as a function of energy;

[0028] FIG. 14 depicts a graph of energy of a 6.6 MeV alpha particle passing through 5 urn of Ti as a function of angle;

[0029] FIG. 15 depicts counts as a function of channel from the A-series detector (Experiment 5k);

[0030] FIG. 16 depicts a graph of the energy of a 35 MeV alpha particle after transit at normal incidence through a Ti foil as a function of Ti foil thickness;

[0031] FIG. 17 depicts nuclear molecule state energies as a function of decay rate for the stable Ti isotopes46Ti,47Ti,48Ti,49Ti, and50Ti;

[0032] FIG. 18 depicts candidates for low-level energetic particle emission from Ti nuclear molecules near 23.86 MeV;

[0033] FIG. 19 depicts an idealized schematic for excitation transfer to nuclear molecule states and highly asymmetric decay pathways under consideration, where AE is the D2 / 4He transition energy of 23.86 MeV; and

[0034] FIG. 20 depicts a cumulative background spectrum recorded with the charged-particle detector over three weeks with the vacuum system running, showing absence of high-energy counts above the low-channel noise cutoff.

[0035] Detailed Description of the Invention

[0036] The systems and methods described herein generate energetic particles from a condensed-matter medium by implanting nuclei into the medium and then operating the medium under conditions associated with phonon generation. In one example, anion beam comprising a first group of atomic nuclei is directed toward a condensed-matter medium comprising a second group of atomic nuclei such that at least some atomic nuclei of the first group are implanted into the condensed-matter medium. In some implementations, the implanted nuclei comprise hydrogen-isotope nuclei, including deuterium nuclei and, in some cases, protium nuclei. The condensed-matter medium may comprise a metal, alloy, metal hydride, metal deuteride, foil, film, coating, layered structure, or other solid-state medium. In one example, the condensed-matter medium comprises titanium or a titanium-containing material.

[0037] Implantation of the first group of atomic nuclei establishes a region in the condensed-matter medium that is referred to herein as a loaded region and, in some implementations, also as an implanted region. Unless the context indicates otherwise, the terms “loaded region” and “implanted region” refer to the same region of the condensed-matter medium in which implanted nuclei of the first group are present and in which the disclosed excitation transfer dynamics may occur. In some implementations, the loaded region is near a surface of the condensed-matter medium. In some implementations, the loaded region is associated with hydrogen-isotope loading, defect formation, vacancy formation, open-volume defects, or combinations thereof. In some implementations, at least a portion of the implanted nuclei of the first group occupy, are localized in, or are otherwise associated with such vacancies and / or open-volume defects. In some implementations, such defect-localized loading contributes to local environments favorable for close hydrogen-isotope pair configurations.

[0038] After implantation, the condensed-matter medium is operated under conditions associated with induction of phonons in the medium. In one example, such conditions comprise continued ion-beam interaction or later ion bombardment. In other examples, such conditions comprise outgassing, deuterium flux, heating, electrical current, acoustic or vibrational excitation, mechanical relaxation, or combinations thereof. In some implementations, more than one such process is present at the same time. In some implementations, implantation and later phonon-inducing operation are carried out in distinct stages. In other implementations, the two overlap partially or fully in time.At sub-keV beam energies, the kinetic energy of the incident projectiles is not treated as the primary driver of the disclosed energetic-particle emission. Instead, ion bombardment may contribute through secondary effects including implantation / loading of hydrogen-isotope nuclei, creation of defects or vacancies, and incidental excitation of phonon modes in the loaded region.

[0039] In some implementations, phonon mode excitation also arises indirectly from subsequent sample processes including diffusion, lattice deformation, cracking, release, outgassing, or combinations thereof. In some implementations, such processes occur during or after loading of the condensed-matter medium and contribute to the later conditions under which energetic-particle emission is observed.

[0040] In one class of implementations, the phonons are induced in the loaded region by bombardment with a second ion beam after implantation of the first group of atomic nuclei. In some implementations, the second ion beam comprises non-hydrogen inertgas ions. In one example, the non-hydrogen inert-gas ions comprise argon ions. In some implementations, the second ion beam is applied after a hydrogen-isotope implantation step. In other implementations, interaction of the second ion beam with the loaded region overlaps in time with outgassing or other phonon-enhancing processes.

[0041] During operation, the induced phonons interact with nuclear states associated with the implanted nuclei and with nuclear states associated with nuclei of the condensed-matter medium. In some implementations, such interaction enables nonradiative transfer of excitation energy from nuclear states of the implanted nuclei to nuclear states of the condensed-matter medium. In some implementations, energetic particles are emitted through decay, disintegration, or other emission processes associated with the nuclear states of the condensed-matter medium after such transfer. In some implementations, the energetic particles comprise charged particles. In some implementations, neutrons are emitted.

[0042] In one class of implementations, implantation of the first group of atomic nuclei and subsequent phonon induction are carried out as conceptually distinct functions. The implantation step provides loading of the condensed-matter medium and may establish a loaded region containing implanted nuclei together with vacancies, open-volumedefects, or other defect-rich local structure. A later triggering condition is then applied or allowed to develop, the triggering condition being associated with induction or enhancement of phonons in the loaded region. Such a triggering condition may comprise later ion bombardment, outgassing, heating, electrical current, deuterium flux, acoustic stimulation, mechanical relaxation, or combinations thereof. In some implementations, the loading function and the triggering function are temporally distinct. In other implementations, they overlap partially or fully in time.

[0043] The disclosed systems and methods may be practiced in a vacuum chamber at a pressure suitable for ion-source operation and particle detection. In some implementations, one or more detectors are positioned to detect energetic charged particles, neutrons, gamma rays, or combinations thereof emitted during operation of the system. Specific exemplary apparatus configurations and representative observed results are described below.

[0044] Without wishing to be bound by theory, the inventors believe that the energetic-particle emission described herein is associated with interaction between implanted nuclei, nuclei of the condensed-matter medium, and lattice modes in the medium, resulting in lattice-mediated excitation transfer dynamics. In one class of implementations, excitation energy associated with implanted nuclei is transferred nonradiatively to nuclear states of the condensed-matter medium, and energetic particles are then emitted through decay, disintegration, or other deexcitation processes associated with those nuclear states.

[0045] A useful starting point is the local structure of the implanted region. In some implementations, implanted hydrogen-isotope nuclei are located in vacancies, openvolume defects, vacancy-hydrogen complexes, defect-rich regions, or combinations thereof. Such environments can support unusually small inter-nuclear separation and, in some cases, close hydrogen-isotope pair configurations, including close deuteron pairs at unusually small separations (in solids), in some implementations below about 100 pm. In these implementations, the density of close hydrogen-isotope pairs is more relevant to the disclosed dynamics than bulk loading alone.

[0046] Electron screening and related local electronic-structure effects may also contribute. In some implementations, defect structure, impurity content, microstructure, dynamiclattice conditions, or combinations thereof increase an effective local screening value beyond that expected for an ideal lattice. Such screening can reduce effective Coulomb repulsion, reduce effective separation of hydrogen-isotope nuclei, increase tunneling probability, or contribute in other ways to the conditions under which excitation-transfer dynamics become significant. In the implementations of interest here, screening is not the only relevant effect, but acts together with local proximity and lattice-mediated dynamics.

[0047] The disclosed process is not limited to isolated two-body dynamics. In some implementations, nuclear states associated with implanted nuclei and nuclear states associated with nuclei of the condensed-matter medium are coupled through one or more shared modes of the medium. Such shared modes may include phonons and, in some cases, other collective or quasiparticle modes. In some implementations, donor-like nuclear states associated with implanted nuclei couple to resonant or near-resonant acceptor-like nuclear states associated with nuclei of the condensed-matter medium through these shared modes, enabling nonradiative transfer of excitation energy.

[0048] In some implementations, the disclosed transfer process is not described as two isolated and independent nuclear reactions occurring in sequence, but as coupled excitationtransfer dynamics involving donor-like nuclear states, acceptor-like nuclear states, and one or more shared modes of the condensed-matter medium. In some implementations, these coupled dynamics are analogous in certain respects to resonance energy transfer processes known in other physical domains. In such implementations, the donor-side and acceptor-side dynamics are treated as part of a coupled many-body process rather than as wholly separable reaction steps. Observability may then arise when the coupled dynamics become open through decay, disintegration, or other emission processes associated with one or more acceptor-side nuclear states.

[0049] In implementations involving deuterium implantation, close deuteron-pair configurations may function as donor-like states. Nuclei of the condensed-matter medium may provide acceptor-like states, including excited states of lattice nuclei. A relatively large density of available acceptor-side states, together with exchange of energy between nuclear states and oscillator modes, may broaden or increase the number of accessible pathways for transfer. In some implementations, multiple donor-like states, multiple acceptor-likestates, or both participate in the process, so that the relevant dynamics are many-body and may be collectively enhanced.

[0050] Referring to FIG. 1A, a lattice of nuclei 10, includes a close hydrogen-isotope donor pair 11 (i.e., a close deuteron pair) having donor-side states 19, acceptor nuclei 13 having a density of available acceptor-side states 17 associated with nonradiative transfer and energetic-particle emission, and an excited shared mode 14 that mediates indirect coupling between donor-side nuclear states and acceptor-side nuclear states. Reference numeral 12 denotes a coupling region, including in one implementation a coherence domain, across which coupling between nuclear states and one or more excited modes is substantially uniform. Reference numeral 15 denotes an exemplary acceptorside excited state, and reference numeral 16 denotes an exemplary acceptor-side lower-energy state, including in one implementation a ground state. Reference numeral 18 denotes a combined acceptor-side state candidate that is resonant or near-resonant with a donor-side transition, and reference numeral 19 denotes an excited state on the donor side.

[0051] FIG. IB depicts candidate acceptor-side state energies for titanium isotopes together with a donor-side excitation energy associated with the D2 / He-4 system near 23.85 MeV, illustrating one class of candidate energetic alignments in which combinations of multiple acceptor-side states can satisfy or approach resonance conditions relevant to excitation-transfer dynamics under consideration. In FIG. IB, the donor-side excitation energy associated with the D2 / He-4 system near 23.85 MeV provides a reference energy for resonance or near-resonance. In this example, candidate acceptor-side state energies for stable titanium isotopes are shown. The figure illustrates that, even among documented bound excited states of stable titanium isotopes and even if such states are filtered or weighted, there are many candidate acceptor-side states whose combinations can satisfy or approach the donor-side resonance condition. In some implementations, this combinatorial availability of acceptor-side states contributes to the density-of-states picture illustrated schematically in FIG. 1A. In some implementations, such candidate energetic alignments are relevant to assessing receiver-state availability and possible emission pathways after nonradiative transfer of excitation energy. In some implementations, the states shown in FIG. IB are treated as illustrative candidate acceptor-side states, while the actual subset of states most relevant to excitation transfermay depend on transition multipolarity, coupling strength, and the availability of additional documented or undocumented states.

[0052] Phonons relevant to the disclosed dynamics may be induced, enhanced, or brought into a favorable regime by one or more processes occurring during or after implantation. Examples include ion bombardment, outgassing, heating, electrical current, deuterium flux, acoustic drive, mechanical shock, phase change, internal lattice dynamics, or combinations thereof. In some implementations, these processes increase mode occupancy, increase mode amplitude, increase effective coupling, or otherwise move the system into a regime in which energetic-particle emission becomes observable.

[0053] In one class of implementations, the coupling that facilitates the disclosed excitationtransfer dynamics includes a relativistic phonon-nuclear coupling between lattice motion and internal nuclear degrees of freedom. In some implementations, the lowest-order interaction has E1 / M2 multipolarity. Accordingly, candidate acceptor-side transitions may be weighted toward transitions having suitable El and / or M2 character, including in some implementations M2 transitions that are comparatively long-lived. The candidate state alignments shown in FIG. IB are illustrative and are not limited to fully characterized or exhaustively documented excited states.

[0054] In some implementations, phonon modes of interest are acoustic modes in the MHz range. In some implementations, effective mode power is at least on the order of tens of microwatts. In some implementations, time-averaged mode power is on the order of about 100 pW or greater. In some implementations involving deliberate stimulation, effective mode power exceeds about 10 mW. Such mode excitations may be produced deliberately or incidentally, including through ion bombardment, loading, diffusion, outgassing, cracking, direct driving or combinations thereof. In some implementations, the relatively long wavelengths of MHz-range modes permit coupling of many donorlike and acceptor-like nuclear states to shared modes of the condensed-matter medium.

[0055] The coupled dynamics may be difficult to observe if excitation remains confined to a closed donor-receiver system. In one class of implementations, observability arises when the coupled dynamics become open through decay, disintegration, or other emission processes associated with one or more excited nuclear states of the condensed-mattermedium. Such processes may result in emission of charged particles, neutrons, gamma rays, or combinations thereof.

[0056] In some implementations, exchange of energy between nuclear states and lattice modes also produces smaller quanta in the medium and populates lattice modes. Energetic-particle emission and related exothermic effects may therefore represent different manifestations of related excitation-transfer dynamics.

[0057] In some implementations, the energetic charged particles emitted from the condensed-matter medium comprise helium-4 nuclei, tritium nuclei, or both. In one class of implementations involving titanium-containing media, such energetic charged particles are associated with decay, disintegration, or other deexcitation processes of excited nuclear states of titanium nuclei after nonradiative transfer of excitation energy to those states.

[0058] In implementations employing argon-ion bombardment at sub-keV energies, the argon projectiles are not expected to directly drive conventional nuclear reactions through binary collision energy. For example, at about 950 eV, direct Ar-to-D knock-on energies are far below energies conventionally associated with dd-fusion. Accordingly, in such implementations the argon bombardment is treated as contributing through secondary effects including defect or vacancy creation, loading-related effects, outgassing-associated dynamics, and incidental excitation of phonons in the loaded region.

[0059] The foregoing theoretical considerations are provided to illustrate mechanisms that may be associated with the disclosed systems and methods. The invention is not limited to any particular microscopic theory except as expressly recited in a claim.

[0060] SYSTEM EMBODIMENTS

[0061] A first system embodiment 100 is illustrated in FIG. 2. In one example, operation of the first system embodiment 100 with a deuterium-loaded titanium sample produced charged-particle counts of interest together with neutron counts of interest (“first set of data”). A second system embodiment, described further below, produced a second set of charged-particle counts of interest in a deuterium-loaded titanium configuration (“second set of data”).The first system embodiment 100 includes a vacuum chamber 102, one or more chamber ports 103, an ion source 104 configured to generate an ion beam 105, a sample 106 supported in the vacuum chamber 102, a charged-particle detector 108, a neutron detector 109, apump system 111, and a vacuum pressure gauge 112. In one example, the vacuum chamber 102 is an 18-inch outer-diameter Lesker SP1800SEP spherical vacuum chamber made of 304 stainless steel and having multiple flanged ports 103. During operation, the chamber pressure is maintained sufficiently low to permit stable operation of the ion source 104. A suitable pressure is about 10'7torr with the ion beam off and up to about 10'5torr with the ion beam on. In one example, the chamber is evacuated by the pump system 111, which includes a primary 400 L / s turbo-molecular pump and a scroll pump, and the pressure is monitored with the vacuum pressure gauge 112 mounted in a chamber port.

[0062] In one example, the sample 106 is mounted on a sample holder extending inward from one of the chamber ports 103 so that the sample is positioned near the geometric center of the vacuum chamber 102. The sample holder may include a rigid support rod and a plate configured to secure the sample mechanically. In one example, the plate measures about 50 mm * 50 mm x 5 mm. The sample 106 may comprise a metal foil and, in one example, comprises a titanium foil. In one example, the sample measures about 50 mm x 50 mm x 0.1 mm and is attached to the sample holder by metal clips or other mechanical retention structures. In one class of implementations, the titanium foil comprises commercially pure grade 2 titanium conforming to ASTM B625, obtained from McMaster-Carr.

[0063] The ion source 104 is mounted to a chamber port 103 and directed toward the sample 106. In one example, the sample surface is oriented at an angle of about 45 degrees relative to the ion beam 105. In one example, the beam diameter is about 25 mm at an invacuum length of about 100 mm. A suitable ion source is aDC25 ion source from Oxford Applied Research mounted via an accessory flange to the vacuum chamber 102. The ion source 104 may be operated with deuterium gas, hydrogen gas, argon gas, or combinations thereof. In one example, the ion source is operated with a hydrogen / deuterium mixture. In another example, the ion source is operated with substantially pure deuterium. In another example, the gas ratio is adjusted duringoperation. The system may be operated such that the ion beam reaches the sample 106 at energies ranging from about 500 eV to about 1000 eV. In one example, the beam current is about 0.1 mA. In other implementations, the beam current is varied over a broader range, including from about 0.01 mA to about 40 mA. The ion-gun specifications indicate a beam current up to about 40 mA, although in one example the collected current on target is lower by about an order of magnitude. In one example, the deuterium gas is 99.8% pure deuterium from Sigma- Aldrich, product number 361860. In one example, the argon gas is ultra-high-purity grade 5.0 argon from Airgas.

[0064] Charged particles emitted during operation of the first system embodiment 100 are detected with the charged-particle detector 108. In one example, the charged-particle detector 108 is a silicon-based surface-barrier detector. A suitable detector is an R-series detector from Ortec and, in one example, comprises an Ortec BR-015-050-500 detector having an active area of about 50 mm2and a thickness of about 500 pm. In one example, the R-series detector used for the first set of data is operated at a bias voltage of about -180 V. In one example, the detector 108 is mounted inside the vacuum chamber 102 on a detector holder attached to a port flange and arranged so that the detector faces the sample 106. In one example, the detector is offset from the ion source by about 45 degrees around the chamber circumference and is positioned at approximately the same polar angle as the ion source. In this configuration, the detector surface is substantially parallel to the sample surface. In one example, the distance between the detector surface and the sample surface is about 50 mm. Other detector positions may also be used.

[0065] The charged-particle detector 108 is connected through a chamber feedthrough to signalprocessing electronics outside the vacuum chamber 102. In one example, the electronics include a preamplifier, a spectroscopy amplifier, a bias supply, and a multichannel analyzer. In one example, the detector 108 is connected to an Ortec 142 preamplifier, an Ortec 672 spectroscopy amplifier, an Ortec 428 bias supply, and an Ortec EASY-MCA multichannel analyzer. Spectra may be accumulated over one-minute intervals and then summed over longer operating periods. In one example, one-minute spectra acquired over about 12 hours are summed to form a cumulative spectrum. In one example, the charged-particle detection subsystem is calibrated with an Am-241 source, with the 5.486 MeV peak centered near channel 1730 of a 16000-channel scale. In one example, the calibration follows the procedure outlined in Experiment 4.1 of the Ortec / Ametekdocumentation for the detector system. In one example, a calibration spectrum is obtained in 1 atm He at a distance of about 2 mm from the Am-241 source. Expected ranges of charged particles in silicon may be estimated using SRIM calculations.

[0066] The neutron detector 109 is positioned outside the vacuum chamber 102 near the sample location. In one example, the neutron detector is placed within about 50 cm of the sample. A suitable detector is a Wendi-2 wide-energy neutron detector from Thermo Fisher Scientific (formerly Thermo Eberline), model FHT 762, including a 2 bar He-3 counter tube and FHT 642 P preamplifier.

[0067] During operation of the first system embodiment 100, the ion beam 105 is directed toward the sample 106 such that hydrogen-isotope nuclei are implanted into the sample and establish a loaded region therein. In examples where the sample 106 comprises titanium, the implanted nuclei may comprise deuterium nuclei or deuterium nuclei together with hydrogen nuclei. In some implementations, continued operation of the system after implantation is associated with induction of phonons in the sample 106. In some implementations, energetic charged particles and neutrons are detected during operation of the system.

[0068] Specific operating conditions and observed results for thick-foil and thin-foil configurations are described below. In one implementation, the sample remains in the vacuum chamber over multiple loading and bombardment cycles without breaking vacuum.

[0069] EXEMPLARY THICK-FOIL EMBODIMENT AND OBSERVED RESULTS

[0070] In one example, the first system embodiment 100 was operated using a Ti foil sample having a thickness of about 1.59 mm, the foil comprising commercially pure grade 2 titanium in accordance with ASTM B625 and obtained from McMaster-Carr. The foil was retained in the vacuum chamber and used for multiple deuterium-loading and argon-bombardment cycles. Charged-particle counts of interest were recorded with the R-series detector described above, and a temporally correlated burst of neutron counts was also observed. FIGS. 6-10 illustrate representative results from this thick-foil configuration.In one example corresponding to FIG. 6, deuterium ions were implanted into the Ti foil at about 950 eV. The deuterium implantation was carried out at a beam current near 0.5 mA for about 1.7 hours and then near 0.63 mA for about 2.75 hours. After this loading step, argon-ion bombardment at about 950 eV was applied for about 0.25 hours. In the data of FIG. 6, an initial argon current spike up to about 1.5 mA is observed, after which the current on target decreases to below about 0.5 mA. Gas flow out of the chamber is also shown in FIG. 6.

[0071] In these thick-foil runs, argon-ion bombardment and gas flow out of the chamber were both present during the later operating interval associated with the counts of interest. In some implementations, that later interval is characterized not solely by application of argon ions, but also by outgassing and related lattice dynamics occurring contemporaneously with argon bombardment. Accordingly, the later interval may be viewed as a triggering interval in which one or more phonon-inducing or phononenhancing processes are present together.

[0072] In this example, four very energetic charged-particle counts were observed on the R-series detector beginning about five minutes after the argon bombardment started and extending over a period of about nine minutes. Outside this short interval, no comparable cluster of counts was observed in the same high-energy channel range.

[0073] The charged-particle detector was positioned on the front side of the Ti target and about 80 mm from the center of the beam spot on the sample. In this configuration, the detector was positioned on the same side of the target as the ion source and outside the direct ionbeam path. Assuming unit detection efficiency for particles that strike the detector, this geometry corresponds to a solid-angle detection efficiency of about 6.2 x IO'4

[0074] The charged-particle detector used in this configuration was not calibrated with a dedicated source in the 30 MeV range (and no calibration sources in that energy range are readily available). However, the detector response for low-Z charged particles is expected to be reasonably linear over a substantial range, as shown by the calibration data of FIG. 7. Based on the low-energy calibration and the observed detector channels, the detected particles in this run are inferred to have high energies, and in one interpretation have energies greater than about 25 MeV. In some implementations, the inferred energiesfall in a range of about 32 MeV to about 40 MeV, subject to uncertainty associated with extrapolating the low-energy calibration into the higher-energy regime.

[0075] The observed high-energy counts are not readily attributable to protons, deuterons, or tritons because the stopping range of such particles near 30 MeV is substantially greater than the 500 pm detector thickness. By contrast, according to SRIM calculations, an alpha particle at about 32.5 MeV has a range in silicon of about 500 pm at normal incidence. At higher alpha energies, incomplete energy deposition is expected, as illustrated in FIG. 8. In one interpretation, if the observed counts correspond to alpha particles, the actual alpha energy may be somewhat higher than the calibrated deposited-energy estimate.

[0076] A burst of neutron counts was recorded on the Wendi-2 neutron detector starting shortly before the first energetic charged particle was registered, as shown in FIG. 9. The temporal proximity of the neutron burst and the charged-particle counts - two spatially and electronically separated detectors based on different operating principles - is one feature of interest in this run.

[0077] In another run carried out two days later, a single count was observed in a high-energy channel during argon bombardment following loading via deuterium bombardment, as shown in FIG. 10. The protocol used in that run was similar, except that less deuterium implantation was applied because the sample remained loaded from previous cycles without breaking vacuum. In that run, a single very energetic charged particle was observed during the argon bombardment.

[0078] No pretreatment beyond ordinary cleaning was applied to the Ti targets used in these thick-foil runs. In some implementations, the Ti foil remains in the chamber over multiple loading and bombardment cycles without breaking vacuum between cycles.

[0079] These thick-foil runs provide one example of operation in which a deuterium-loaded Ti foil, followed by argon bombardment, was associated with observation of energetic charged particles in high-energy detector channels and with temporally correlated neutron counts. Additional thin-foil results are described below.EXEMPLARY THIN-FOIL EMBODIMENT AND OBSERVED RESULTS

[0080] In another example, the system was operated using free-standing thin Ti foil samples having a thickness of about 5 pm and an area of about 25 mm x 25 mm. In one implementation, the thin Ti foil has a purity of about 99.6+% and is obtained from Millipore / Sigma (part number GF16653696). In this configuration, a charged-particle detector was positioned behind the foil rather than on the front side. FIGS. 11-16 and 20 illustrate representative configurations and results for this thin-foil embodiment. FIGS.

[0081] 17-19 illustrate additional theoretical considerations relevant to certain implementations of the disclosed systems and methods.

[0082] FIG. 11 shows a cross-sectional schematic of one such thin-foil configuration. In this embodiment, a a thin-foil sample 106 comprising a thin Ti foil is supported by a holder 113, thermally coupled through a heat-transfer layer 114 to a heat sink 115, and a charged-particle detector 108 is positioned behind the foil. In one example, the detector comprises an A-series silicon surface-barrier detector having an active area of about 50 mm2and a thickness of about 2000 pm. This detector thickness is sufficient to stop alpha particles with energies up to about 60 MeV at normal incidence.

[0083] In one example corresponding to FIG. 12, the thin Ti foil was subjected to deuterium implantation followed by argon bombardment. In that run, the sample was loaded with deuterium for about two hours at a beam current of about 0.20 mA and a beam energy of about 950 eV. The argon beam was then run at up to about 1.5 mA and about 950 eV for about 10 minutes, after which the beam was turned off. FIG. 12 shows one example of detector output under these conditions, with a short time window focusing on the Ar bombardment and a much longer time window focusing on the subsequent absence of counts. In this configuration, the sample and detector are water-cooled. During the Ar bombardment, detector temperature increases can shift the low-channel noise cutoff upward. In one example, the higher cutoff corresponds to a charged-particle energy near about 1 MeV and the lower cutoff corresponds to about 0.36 MeV. The resulting detector data include charged-particle counts of interest in higher-energy channels, well above the noise cutoff. For comparison, FIG. 20 shows a cumulative background spectrum recorded over about three weeks with the vacuum system operating, in which no comparable high-energy counts are observed.According to SRIM calculations, an alpha particle with an energy of about 6 MeV has a range in Ti of about 20 pm, which motivates the use of a thin 5 pm free-standing Ti foil in this configuration. FIG. 13 depicts a calculated energy loss for an alpha particle passing at normal incidence through a 5 pm Ti foil as a function of the alpha-particle energy. In one implementation, this calculation indicates that if an alpha particle is generated near the front surface of the foil, it loses at least about 1 MeV while traversing the Ti foil. FIG.

[0084] 14 depicts the energy of a 6.6 MeV alpha particle after passage through a 5 pm Ti foil as a function of angle. Together, these calculations provide a basis for interpreting charged-particle energies in the thin-foil detector configuration.

[0085] In another example corresponding to FIG. 15, data from a later loading / bombardment cycle on the same sample, in the same experimental configuration and without breaking vacuum, were recorded during and after argon bombardment. In that run, a single energetic count appeared near the end of the 10-minute argon bombardment. After the beam was turned off, additional counts were recorded that correspond to charged-particle energies up to about 11 MeV in a burst event extending over about 42 hours. Outside the limited intervals in which counts of interest were observed, no counts above the noise cutoff were observed over extended operating periods.

[0086] FIG. 16 illustrates an example estimate of the energy of a 35 MeV alpha particle after transit at normal incidence through a Ti foil as a function of Ti foil thickness. In one implementation, this calculation indicates that very energetic alpha particles can traverse a thin Ti foil with only limited energy loss over the thickness range of interest. Together with the detector-response considerations discussed above, this geometry provides a useful basis for interpreting charged-particle counts observed in the thin-foil configuration.

[0087] In one implementation, the thin-foil results differed from the thick-foil results in at least two respects. First, the detector was positioned behind the target foil rather than in front of it. Second, the observed counts in the thin-foil configuration were in a lower energy regime than the very high-energy counts inferred in the thick-foil front-side configuration. Even so, both configurations provide examples in which deuterium-loaded Ti, followed by argon bombardment, was associated with charged-particle counts of interest.In some implementations, the thin-foil embodiment is useful for examining, at a large solid angle, charged-particle emission that can traverse a thin Ti target and deposit energy in a detector behind the target. In some implementations, the thin-foil embodiment also facilitates comparison of detector response, particle stopping behavior, and inferred particle energies across different sample thicknesses and geometries.

[0088] Additional embodiments and characterization methods are described below.

[0089] ALTERNATIVE EMBODIMENTS AND CHARACTERIZATION

[0090] The systems and methods described above may be implemented in a variety of related configurations beyond the specific thick-foil and thin-foil examples. Although the examples above use Ti foils and ion-beam operation in a spherical vacuum chamber, other condensed-matter media, sample geometries, detector arrangements, and triggering conditions may also be used.

[0091] In some implementations, the condensed-matter medium comprises a metal, alloy, hydride, deuteride, coating, multilayer, foil, film, or layered structure. In addition to titanium-containing media, suitable media may include palladium-containing media, zirconium-containing media, nickel-containing media, alloys thereof, or combinations thereof. In some implementations, the medium includes a surface layer configured to receive implanted nuclei together with a subsurface hydrogen or deuterium reservoir. In one example, a Ti-containing layer is formed on or coupled to a Pd-containing deuterium reservoir.

[0092] The implanted nuclei need not be limited to the specific hydrogen / deuterium mixtures described above. In some implementations, the implanted nuclei comprise deuterium nuclei. In other implementations, the implanted nuclei comprise hydrogen nuclei, deuterium nuclei, tritium nuclei, or combinations thereof. The condensed-matter medium likewise need not be limited to Ti nuclei, provided the medium contains nuclei capable of participating in the disclosed excitation-transfer dynamics and associated emission processes.The conditions used to induce or enhance phonons in the condensed-matter medium may also vary. In the examples above, one such condition is argon-ion bombardment following hydrogen-isotope implantation. In other implementations, phonons are induced or enhanced by outgassing, heating, electrical current, deuterium flux, acoustic or vibrational drive, mechanical shock, phase change, or combinations thereof. In some implementations, more than one such process is present at the same time. In some implementations, ion bombardment and outgassing occur together during a later stage of operation and are both associated with observation of energetic-particle counts.

[0093] The ion source configuration may also vary. Different ion sources, beam diameters, working gases, beam currents, and operating pressures may be used. In some implementations, the loading step and the later phonon-inducing step are carried out with different gases. In other implementations, one ion source is used for both loading and subsequent operation. In still other implementations, the loading and later phononinducing conditions overlap in time rather than occurring as fully distinct steps.

[0094] In one implementation, the condensed-matter medium comprises a Ti-containing film or layer and the later phonon-inducing condition comprises electrical current through the Ti-containing medium. In another implementation, a Ti-containing implantation layer is used together with a subsurface hydrogen or deuterium reservoir.

[0095] The sample geometry and detector geometry may likewise be varied. In some implementations, the condensed-matter medium is thicker than the thick-foil example described above. In some implementations, the medium is thinner than the 5 pm thin-foil example described above. In some implementations, a detector is positioned on a front side of the sample. In other implementations, a detector is positioned behind the sample. In some implementations, multiple charged-particle detectors are used at different angles relative to the beam direction and sample surface. In some implementations, a larger-area detector is used to increase geometric collection efficiency. In some implementations, separate detectors are used for charged particles, neutrons, gamma rays, or combinations thereof.

[0096] Particle identification may also be carried out with detector arrangements more elaborate than those used in the exemplary runs. In some implementations, energetic chargedparticles are recorded with CR-39. In some implementations, a dE-E detector arrangement is used. In some implementations, charged-particle identification is improved by detector calibration over a broader energy range than the Am-241 calibration discussed above. In some implementations, detector thickness, detector material, detector spacing, and detector angle are selected to improve discrimination among alpha particles, protons, deuterons, tritons, or heavier charged particles.

[0097] In some implementations, characterization of the condensed-matter medium is used to relate sample condition to energetic-particle emission. Such characterization may include one or more of thermal desorption spectroscopy (TDS), positron annihilation spectroscopy (PAS), x-ray diffraction (XRD), laser Doppler vibrometry (LDV), piezoelectric sensing, acoustic-emission sensing, current-spectrum monitoring, or combinations thereof. In some implementations, such measurements are used to characterize hydrogen or deuterium loading, vacancy concentration, defect population, phase, microstructure, outgassing behavior, vibrational mode content, or combinations thereof. In some implementations, such measurements are used to infer the density of vacancy-bound hydrogen-isotope inventory, the presence of vacancy-hydrogen complexes, or the density of close hydrogen-isotope pairs relevant to the disclosed transfer dynamics.

[0098] In some implementations, the systems and methods are operated so as to increase defect formation, vacancy formation, defect activity, or combinations thereof in the condensed-matter medium. In some implementations, defect-rich regions, open-volume defects, or loaded vacancies are intentionally created or preserved before, during, or after implantation. In some implementations, such structures are associated with increased hydrogen-isotope localization and with close-pair configurations relevant to the disclosed transfer dynamics.

[0099] In some implementations, the disclosed systems are configured not only to detect energetic particles, but also to correlate such detection with one or more simultaneously measured variables, including beam current, gas flow, chamber pressure, neutron counts, detector count rate, sample temperature, outgassing rate, and vibrational response. In some implementations, such correlation is used to identify operating conditions associated with enhanced energetic-particle emission.FIGS. 17-19 illustrate additional theoretical considerations relevant to certain implementations of the disclosed systems and methods. FIG. 17 depicts candidate nuclear-molecule state energies as a function of decay rate for stable Ti isotopes. FIG. 18 depicts candidate lower-level energetic-particle-emission pathways in the vicinity of the 23.848109 MeV transition energy associated with the D2 / He-4 system. FIG. 19 depicts an idealized schematic for excitation transfer to nuclear-molecule states and for highly asymmetric decay pathways under consideration.

[0100] Candidate acceptor-side states under consideration include nuclear-molecule states associated with nuclei of the condensed-matter medium, including in some implementations titanium isotopes. In some implementations, such candidate states provide a relatively dense manifold of acceptor-side states in an energy range relevant to excitation transfer from donor-like hydrogen-isotope states. Lower-level energetic-particle-emission channels, including channels associated with low-Z charged-particle emission, are also under consideration. FIGS. 17-19 are provided to illustrate representative candidate receiver-state and candidate emission-pathway considerations and are not intended to limit the invention to any single identified microscopic pathway.

[0101] In some implementations, these figures illustrate candidate acceptor-side nuclear states and candidate emission pathways that may be associated with nonradiative transfer of excitation energy from implanted hydrogen-isotope nuclei to nuclei of the condensed-matter medium. In some implementations, a relatively large density of acceptor-side states, together with mode-mediated coupling and exchange of energy with the medium, contributes to accessible transfer pathways and subsequent emission. These figures are provided as illustrative theoretical considerations and do not limit the invention to any particular microscopic mechanism except as expressly recited in a claim.

[0102] The foregoing examples are intended to illustrate the range of apparatus configurations, material systems, and characterization approaches that may be used in connection with the disclosed systems and methods. The invention is not limited to the specific configurations set forth in the exemplary thick-foil and thin-foil embodiments.

Claims

What is claimed is:

1. A method for generating energetic particles comprising:generating a first ion beam comprising a first group of atomic nuclei; providing a condensed matter medium comprising a second group of atomic nuclei;interacting the first ion beam with the condensed matter medium so that some atomic nuclei of the first group of atomic nuclei are implanted into the condensed matter medium and generate a loaded region in the condensed matter medium;subsequently inducing phonons in the loaded region in the condensed matter medium;wherein the induced phonons interact with the first group of atomic nuclei and the second group of atomic nuclei in the loaded region and enable nonradiative transfer of excitation energy from nuclear states of the first group of atomic nuclei to nuclear states of the second group of atomic nuclei; andemitting energetic particles stemming from deexcitation processes of exited nuclear states of the second group of atomic nuclei in the loaded region.

2. The method of claim 1, wherein the first ion beam comprises ions with energies in the range of 1 OOeV to 2000 eV.

3. The method of claim 1, further comprising providing a particle detector for detecting the emitted energetic particles.

4. The method of claim 1, wherein the condensed matter medium is contained within a vacuum chamber.

5. The method of claim 1, wherein the condensed matter medium comprises a Titanium foil and the second group of atomic nuclei comprises Ti-nuclei.

6. The method of claim 1, wherein the first group of atomic nuclei comprises deuterium (H-2) and optionally protium (H-l) nuclei.

7. The method of claim 1, wherein the emitted charged particles comprise tritium (H-3) and Helium-4 (He-4) nuclei.

8. The method of claim 1, wherein the first group of atomic nuclei comprises deuterium (H-2) and protium (H-l) nuclei, the second group of atomic nuclei comprises Ti-nuclei and the emitted charged particles comprise tritium (H-3) and Helium-4 (He-4) nuclei resulting from deexcitation processes of exited nuclear states of the Ti-nuclei.

9. The method of claim 1, wherein the loaded region comprises vacancies and / or open-volume defects and wherein the first group of atomic nuclei is implanted in said vacancies and / or open-volume defects.

10. The method of claim 1, wherein phonons are induced in the loaded region of the condensed matter medium via bombardment by a second ion beam and wherein said second ion beam comprises non-hydrogen inert-gas ions.

11. The method of claim 10, wherein the non-hydrogen inert-gas ions comprise Argon ions.

12. A system for generating energetic particles comprising:a device for generating a first ion beam comprising a first group of atomic nuclei;a condensed matter medium comprising a second group of atomic nuclei; wherein the first ion beam is configured to interact with the condensed matter medium so that some atomic nuclei of the first group of atomic nuclei are implanted into the condensed matter medium and generate a loaded region in the condensed matter medium;a device for inducing phonons in the loaded region in the condensed matter medium;wherein the induced phonons are configured to interact with the first group of atomic nuclei and the second group of atomic nuclei in the loaded region and enable nonradiative transfer of excitation energy from nuclear states of the first group of atomic nuclei to nuclear states of the second group of atomic nuclei; and wherein energetic particles are emitted stemming from deexcitation processes of exited nuclear states of the second group of atomic nuclei in the loaded region.

13. The system of claim 12, wherein the first ion beam comprises ions with energies in the range of 1 OOeV to 2000 eV.

14. The system of claim 12, further comprising a particle detector for detecting the emitted energetic particles.

15. The system of claim 12, wherein the condensed matter medium is contained within a vacuum chamber.

16. The system of claim 12, wherein the condensed matter medium comprises a Titanium foil and the second group of atomic nuclei comprises Ti-nuclei.

17. The system of claim 12, wherein the first group of atomic nuclei comprises deuterium (H-2) and optionally protium (H-l) nuclei.

18. The system of claim 12, wherein the emitted charged particles comprise tritium (H-3) and Helium-4 (He-4) nuclei.

19. The system of claim 12, wherein the first group of atomic nuclei comprises deuterium (H-2) and protium (H-l) nuclei, the second group of atomic nuclei comprises Ti-nuclei and the emitted charged particles comprise tritium (H-3) and Helium-4 (He-4) nuclei resulting from deexcitation processes of exited nuclear states of the Ti-nuclei.

20. The system of claim 12, wherein the loaded region comprises vacancies and / or open-volume defects and wherein the first group of atomic nuclei is implanted in said vacancies and / or open-volume defects.

21. The system of claim 12, wherein the device for inducing phonons in the loaded region of the condensed matter medium comprises a second ion beam and wherein said second ion beam comprises non-hydrogen inert-gas ions.

22. The system of claim 21, wherein the non-hydrogen inert-gas ions comprise Argon ions.

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