National Aeronautics and Space Administration

Disclosure of Invention and New Technology (Including Software)

JDATE

I CONTRACTOR CASE NO.

This is an important legal document. Carefully complete and forward to the Patent Representative (NASA in- NASA CASE NO. (OFFICIAL USE ONLY) house innovation) or New Technology Representative (contractor/grantee innovation) at NASA. Use of this NONE report form by contractor/grantee is optional; however, an alternative format must at a minimum contain the information required herein. NASA in-house disclosures should be read, understood and signed by a technically competent witness in the witness signature block at the end of this form. In completing each section, use whatever detail deemed appropriate fora "full and complete disclosure." Contractors/Grantees please refer to the New Technology or Patent Rights - Retention by the Contractor clauses. When necessary, attach additional documentation to provide a full, detailed description.

1. DESCRIPTIVE TITLE lVh:.ltl·lay<er(:d Hadio·!,;oliJp<e [or' Fnhanc(:d P,lolGckUron Avalallche ProCClS

2. INNOV ATOR(S) (For each innovator provide: Name, Title, Work Address, Work Phone Number, and Work E-mail Address. If multiple innovators, number each to match Box 5.)

Smlg Choi RSCH AST. BAS1C PHOPEHTIES OF CiASES

Demns Elu;;hnelJ Rober! Hen.dri.cks

3 . INNOVATOR'S EMPLOYER WHEN INNOVATION WAS MADE (For each innovator provide: Name, Division and Address of Employer, Organizational Codellvfail Code, and Contract/Grant Number if applicable. Ifmultiple innovators, number each to match Box 5.) NASA i\IaU SlOp NASA L~nglcy Hesearch C::nler N-A.SA. (}k:nn Research C~ntt:r NASA L;3.ugIey Re::;earch C(~l.ner 4. PLACE OF PERFORMANCE (Address(es) where innovation made)

5. EMPLOYER STATUS (choose one for each innovator)

6. ORIGIN (Check all that apply and provide all applicable numbers. If multiple Contracts/Grants, etc., list Contract/Grant Numbers in Box 3 with applicable employer information.)

GE Innovator # 1

Innovator #3

GE = Govermnent

Innovator #2 . G):~

Innovator #4

CU = College or University NP = Non-Profit Organization SB = Small Business Firm LE = Large Entity

[ 1 NASA In-house Org. Mail Code [1 Grant/Cooperative Agreement No . [1 Prime Contract No.

Task No. Report No. [ 1 Subcontractor: Subcontract Tier [1 Joint Effort (contract, subcontractor and/or grantee

contributions(s), and NASA in-house contribution) [ 1 Multiple Effort (multiple contractor, subcontractor

and/or grantee contributions, no NASA in-house contribution)

[1 Other (e.g., Space Act Agreement, MOA) No.

7. NASA CONTRACTORING OFFICER'S TECHNICAL 8. CONTRACTOR/GRANTEE NEW TECHNOLOGY REPRESENTATIVE (COTR) REPRESENTATIVE (pO C)

9. BRIEF ABSTRACT (A general description of the innovation which describes its capabilities, but does not reveal details that would enable duplication or imitation of the innovation.) A ne},," deslgn c:oncep! of::\1:l.dti~·NTAC Iayers is presented here ;35 ;3. l.k~\ii inV-(~ntlon Ne\:vty desigxK~d Iayer(~d jsotoP(~ sou:rce~) cotnbined ~:vJth xuuIt3··NTAC layers gi\"e rise to seyeral adYanla.geous f"ajmes for \ 1) capturing the most of ltiglJ. energy photons that greatly reduces the resldmtl radi.ation, requiring rnir:l;n~:J ntdiation prGk:ctioIl, (2) effec1i,"e eIl~ission of ;I\ra;anche electrons in;o ,"aClunn gap by ~tJ;/oiding or redr:.cing pote;ltia] scattering or collision !i-equency <Nithin int:::H::otmc struc,m;:: of emit[;::r materi"J.. (3) ;::s:;entiaJu:ing ,he high order ml;::tactHms within intet~atomic stn.lCtlUe wi,hin (w,ol'e jtself and (~!nJ.tlers of J'}TA.C for Uberating tHOre elecrrons, and (4) xuaklug a djstrjbuted llK~!rHaJ load on (~ach layer. This in\/(~unon descnl:,e~) abo~3t a ne~y 'way to capiialize iSOlope's illternal mubpk interactions in order to build a n"w configuration NTAC filed as an. im·enti.on

NASA FORM PREVIOUS EDITION IS OBSOLETE Page 1 of 4

SECTION I - DESCRIPTION OF THE PROBLEM OR OBJECTIVE THAT MOTIVATED THE INNOVATION'S DEVELOPMENT (Enter as appropriate: A. - General description ofproblemJobjective; B. - Key or unique problem characteristics; C. - Prior art, i.e., prior teclmiques, methods, materials, or devices performing function of the innovation, or previous means for performing function of software; and D. - Disadvantages or limitation of prior art.) A. - (Jenera] desc:lp1l0n of problem!obJective: The de~!gJl cUllce:;:H for efkctive us::: of isotope ',; Jru:Jtlpl::: internal mlet;:ctwllS by the isotop:::-emitted beta pmticle~ and high metgy phutons was Hev;::r beeu j a consideration or i:npternented for 13an3e~)sing such additjonaJ (~nergy as an ad-"\/antage ;3.t an e,?er before.

B.- K;::y or mU(]lle problem charhct;::ristics; The :::ftecllve ;Jbso:ption Ot captme rat;:: of high elletgy photons det:::tmines the pow:::t dellsity of en::::gy conversi()H sy,;t;::ms. But th::::'e at;:: no n:::w ldea Ot UG e:,;:mpks.

C.-PtlW htl, i.e, prior tcctllliqlles. metll()ds, mhterials. or dn ices p;::rformillg i'!Ulctt()n of the im1ov<ltion. or pr;::v iGUS m;::ans for performing fllnctio:l of :soft",~:,~r:::: : The c:onf3guraboa o:£1'-rr./\.( structure ofNTAC

D.- Di,,;:dviHli;lges or htmt;:tlollS OfptlOl' art A ~)j:ngJe el.nitter JnateriaJ \N3th a reasonal:.Je t13jckne::;~) cart captt:re 13jg13 energy photon::;. But the Hberated ek~ctroas ,vithia Ihe eJnili:(~r luaterj;3.t urtdergo nluJhple sc~~tterjng that causes ~~ Joss of eLectron ':) k~llet~c energy bj'- the CouLornb colhs~ons ~Tjth rteighborirtg eJectrons or recolt~binatioll process tluough a free-to-bmwd transition.

SECTION II - TECHNICALLY COMPLETE AND EASILY UNDERSTANDABLE DESCRIPTION OF INNOVATION DEVELOPED TO SOLVE THE PROBLEM OR MEET THE OBJECTIVE (Enter as appropriate; existing reports, if available, may form a part of the disclosure, and reference thereto can be made to complete this description: A. - Purpose and description of innovation/software; B. - Identification of component parts or steps, and explanation of mode of operation of innovation/software preferably referring to drawings, sketches, photographs, graphs, flow charts, and/or parts or ingredient lists illustrating the components; C. - Functional operation; D. - Alternate embodiments of the innovation/software; E. - Supportive theory; F. - Engineering specifications; G. - Peripheral equipment; and H. - Maintenance, reliability, safety factors.) See the attac lK~d fDe

NASA FORM PREVIOUS EDITION IS OBSOLETE Page 2 of 4

SECTION III - UNIQUE OR NOVEL FEATURES OF THE INNOVATION AND THE RESULTS OR BENEFITS OF ITS APPLICATION (Enter as appropriate: A. - Novel or unique features; B. - Advantages of innovation/software; C. - Development or new conceptual problems; D. - Test data and source of error; E. - Analysis of capabilities; and F. - For software, any re-use or re-engineering of existing code, use of shareware, or use of code owned by a non-federal entity.) • More distributed etlll&sicms of high e:lergy photons WH.1 high energy beta p,~rlleles from ,~ tlu:mber of thin i"oiope layer,: th,~t red,JCes the collpiillg probablhty wiHtilltnteHU()mic stnKnm; oi'lso[()pe ,;oU(ce mateti;;:t '" Capture and ccrtf\;erSton of the I.Host of high euergy photons ;3.t~d/or l:,eln parbcIes l:,y u3u.hj,·NTA.C h1y(~r::; \vi!ho~3t !eakage of residua] radiadou, thus

requiring mini,ma). radiation protection. • EffeetiYe emission of avalhtlche electrom: fmm 111e comlntled &truetnre of thin layered radiall0l1 &OllIee alld emders imo </aC11:1;)1 gap by red:1cing jmemal sCht:ering walun ;JtOlntC :srnlcture (;f i,;otope SOl,J'C::: ,md Untrtel rm:1etials, ,;. E::;~)entiahzing the 133gh order unerachons ~vithin interLO(HOtUJC stru(:nxre of thinly layered 1S0!Ope jtself and ::'~l.nit!ers of NTA.C j~)!, Hberating tHOre

ekctrons. and • Makillg a disml:mted thermal load on each layer.

SECTION IV - SPECULATION REGARDING POTENTIAL COMMERCIAL APPLICATIONS AND POINTS OF CONTACT (Including uames of companies producing or using similar products.) Numerous ':-9plicaricms in comme:'C1al sector is ellvi"ioned , Aut()nmmms v:::hicitf; ,md ships • Dro!l;~" ... Renlo1e "e

Tl11ages and to\Vll

• Si!telHres • :Vl<!im power plan1 s

NASA FORM PREVIOUS EDITION IS OBSOLETE Page 3 of 4

· ADDITIONAL DOCUMENTATION (Include copies or list below any pertinent documentation which aids in the understanding or application of innovation (e.g., articles, contractor reports, engineering specs, assembly/manufacturing drawings, parts or ingredients list, operating manuals, test

assembly/manufacturing procedures, etc.).)

TITLE PAGE DATE

1. DEGREE OF TECHNOLOGY SIGNIFICANCE (Which best expresses the degree of technological significance of this innovation?) [ ] Modification to Existing Technology [ ] Substantial Advancement in the Art [X] Major Breakthrough

[ ] Modification [ ] Production Model [ ] Used in Current World

OR CONTEMPLATED PUBLICATION OR PUBLIC DISCLOSURE INCLUDING DATES (Provide as applicable: A. - Type of hl"Y"',nn or disclosure, e.g. report, conference or seminar, oral presentation; B. - Disclosure by NASA or Contractor/Grantee; and C. - Title, volumne

page no., and date ofpublication

Using non-NASA employees to beta-test the program? []YES []NO If Yes, done under a beta-test agreement? []YES []NO Modification of this program continued by civil servant and/or contractual agreement? []YES [ ]NO Copyrighted registered? []YES []NO []UNKNOWN If Yes, then by whom? Has the lastest version been distributed outside of NASA or contractor? []YES [ ]NO []UNKNOWN Were prior version distributed outside of NASA or Contractor? []YES []NO [ ]UNKNOWN If Yes, supply NASA or contractor contact Contains or based on code not owned by U.S. Govermnent or its contractors? []YES []NO []UNKNOWN If Yes, name of code and codes' owner Has a license for use been obtained?

NASA FORM PREVIOUS EDITION IS OBSOLETE Page 4 of 4

Multi-layered Radio-Isotope for Enhanced Photoelectron Avalanche Process

Inventors: Sang H. Choi, Dennis M. Bushnell, Robert C. Hendricks, David Komar,

Brief Abstract:

A new design concept of Multi-NTAC layers is presented here as a new invention. Newly designed layered isotope sources combined with multi-NTAC layers give rise to several advantageous features for (1) capturing the most of high energy photons that greatly reduces the residual radiation, requiring minimal radiation protection, (2) effective emission of avalanche electrons into vacuum gap by avoiding or reducing potential scattering or collision frequency within inter-atomic structure of emitter material, (3) essentializing the high order interactions within inter-atomic structure within isotope itself and emitters ofNTAC for liberating more electrons, and (4) making a distributed thermal load on each layer.

This invention describes about a new way to capitalize isotope's internal multiple interactions in order to build a new configuration NTAC filed as an invention (LAR 17981-1, August 26, 2010).

Description of the Problem or Objective That Motivated the Innovation's Development

(Enter as appropriate: A.- General description of problem/objective; B.- Key or unique problem characteristics; C.-Prior art, i.e., prior techniques, methods, materials, or devices performing function of the innovation, or previous meansfor performingfunction ofsoftware; and D.­Disadvantages or limitations of prior art.)

A.- General description of problem/objective; The design concept for effective use of isotope's multiple internal interactions by the isotope­emitted beta particles and high energy photons was never been in consideration or implemented for harnessing such additional energy as an advantage at all ever before.

B.- Key or unique problem characteristics; The effective absorption or capture rate of high energy photons determines the power density of energy conversion systems. But there are no new idea or no examples.

C.-Prior art, i.e., prior techniques, methods, materials, or devices performing function of the innovation, or previous means for performingfunction ofsoftware; The configuration ofNTAC (LAR 17981-1, August 26,2010) do not show the use of isotope's multiple internal interactions through multiple layer structure ofNTAC.

D. - Disadvantages or limitations of prior art. A single emitter material with a reasonable thickness can capture high energy photons. But the liberated electrons within the emitter material undergo multiple scattering that causes a loss of

electron's kinetic energy by the Coulomb collisions with neighboring electrons or recombination process through a free-to-bound transition.

Technically Complete and Easily Understandable Description of Innovation Developed to Solve the Problem or Meet the Objective

A new design concept of multi -thin-layers of isotope integrated with multi -NTAC layers is presented here as a new invention.

A combination of distributed thin isotope layers and multi-NTAC layers gives rise to several advantageous features: (1) more distributed emissions of high energy photons and high energy beta particles from a number of thin isotope layers that reduces the coupling probability within inter-atomic structure of isotope source material, (2) capture and conversion of the most of high energy photons and/or beta particles by multi-NTAC layers without leakage of residual radiation, thus requiring minimal radiation protection, (3) effective emission of avalanche electrons from the combined structure of thin layered radiation source and emitters into vacuum gap by reducing internal scattering within atomic structure of isotope source and emitter materials, (4) essentializing the high order interactions within inter-atomic structure of thinly layered isotope itself and emitters ofNTAC for liberating more electrons, and (5) making a distributed thermal load on each layer.

The configuration of invention shown in Fig. 1 describes about a new way to capitalize thin multi-layered isotope for the enhancement of electron liberation through higher order interactions. The isotope body and emitter ofNTAC have a similar tendency to scatter and absorb its own emitted radiation and/or beta particles. Such scattering and absorption of high energy photons and beta particles through its own body reduce the intensity of emission spectra. The reduced portion of emission spectra by scattering and absorption turns out as a liberated electrons, including Auger electrons, X-ray fluorescence, and thermal energy. If the radiation isotope and emitter materials are thick, the scattering and absorption of emitted y-rays and high energy beta particles within the isotope and emitter materials become dominant and spread the original intensity of emission spectra into the emissions of lower energetic electrons (Compton edge electrons and Auger electrons), X-ray fluorescence, and increased thermal loading. New configuration ofNTAC shown in Fig. 1 offers a great improvement in performance by adopting a distributed thin multi-layer radioisotope sources as compared to the invention

filed earlier.

The internal thermal loading by scattering and absorption becomes more significant when the decay process of radioisotope creates very high energy photons and/or high energy beta particles and the body mass increases. Such a photon and/or a beta particle initially interacts with the intra-band electrons and nucleus of atom to generate a number of energetic electrons, y-ray remainder, and X-ray fluorescence by energy and momentum splitting. These energetic electrons, y-ray remainder, and X-ray fluorescence from the primary interaction undergo the secondary mode of interaction with neighboring atoms to populate further liberated electrons, but at the same time increase thermal loading if material scattering thickness is too thick.

Such phenomena can be described well by photoelectric (pe), photonuclear (po), Compton scattering (Cs), and electron/positron pair production (pp). A huge number of electrons in the intra-band of atom can be liberated through a bound-to-free transition when coupled with either

high energy photons or high energy beta particles or both together. In the pe process, an electron coupled and liberated by incident high energy photon or by energetic beta particle gains a portion of photon energy or beta particle energy. In such a case, the portion of energy gained by a liberated electron is substantially high up to several hundreds ofkeV level. This electron is energetic and may have an increased collision probability as a sequential Coulomb collision to the shell electrons of neighboring atom as the secondary interaction. The liberated emission of energetic electron from an inner-shell structure of an atom almost instantaneously induces the bound-to-free transition of another neighboring electron while the filling of an inner-shell vacancy of an atom. This phenomenon is known as Auger effect. In this process, the filling of an inner-shell vacancy of an atom also emanates a few keV level X-rays which is generally known as X-ray fluorescence or Bremsstrahlung. Energetic beta particle has almost the same effect to an atom as high energy photon does. Even a beta particle with MeV level energy (i.e. Strontium-90) is able to shake up the nucleus of an atom by collision. In such a case, an emission of y-ray is anticipated and also has a subsequent interactive phenomenon with neighboring atoms. The pn process is also complex as the pe process is. High energy photon can directly couple with a nucleus. In such a coupling case, nucleus can undergo a level reordering process under unstable resonant mode if the photon energy is lower than the binding energy of nucleus. Unstable resonant mode of nucleus generates a variation in centroid energy of nuclei that affects the

Multi-Layered NTAC Radioisotope Core

MJTE Layer

Radiation Shielding

Figure 1. New NTAC device concept with distributed thin radioisotope layers. Thin layers of radioisotope and emitters reduce thermal loading due to multiple scattering of high energy photons and/or energetic beta particles in higher order interactions.

stability of shell electrons. In some case oflevel reordering process, it causes the majority portion of photon energy to turn into creating a pair production near a nucleus, such as an electron and a positron, a muon and an anti-muon, or a proton and an antiproton.

The photon energy of the interaction must be above a threshold to create the pair which is at least the total rest rnass energy of the two particles. To conserve both energy and rnornentum, the photon energy is converted to particle's mass or vice versa. The rest mass energies of electron and positron are 1.022 MeV. Therefore, the minimum photon energy to create an electron­positron pair is 1.022 MeV.

Any photon energy higher than 1.022 MeV can increase the rate of pair production. As mentioned above, when pair production occurs, the nucleus undergoes a mode change with recoiling process. Accordingly, the annihilation process of electron/positron generates a y-ray at L022MeV. This y-ray at L022 MeV has a significant effect on subsequent interactions with shell-electrons of its own or neighboring atom.

The Compton scattering (Cs) is a physical phenomenon that describes the scattering of a photon with a charged particle, just like an electron. When a charged particle is coupled with high energy photon, a charged particle gains energy from the incident photon while the photon energy after scattering is reduced by the same amount of energy gained by a charged particle. When an electron is under Compton scattering with y-ray, the energy level gained by an electron is substantial and accelerates electron with the kinetic energy in keY level. The rest of energy is still carried by photon. The energies carried by an electron and photon after scattering are remained so high that they have consequential effects on higher order interaction.

The coupling processes, such as pe, pn, Cs, and pp, happen when an emitter material receives high energy photons and high energy beta particles. But these coupling processes also take place within its own emitting body structure of radio-isotope that emits gamma rays and/or beta particles. A certain radioisotope, such as Co-60 (see Fig. 2), has not only the emission spectra of beta decays and high energy photons, but also these beta particles and high energy photons are actively coupled with their own isotopic atoms within body material to further yield the Compton-edge electrons, Bremsstrahlung, Auger electrons, and pair production through the primary, secondary, tertiary, ... interactions. In Figure 2, the spectral distribution of emission, except for the two major peaks at 1173.24 keY and 1332.5 keY, is attributed to the complex internal interaction processes identified as the Compton-edge electrons, Bremsstrahlung, Auger electrons, and pair production. Such an emission pattern from an isotope itself can be also beneficial and used for power generation if a different design ofNTAC is introduced to subsidize such an additional photon energy.

With a lengthy explanation above, we see why NTAC would perform better with the distributed radioisotope in thin layers.

Bin ~ 1290 Energy/(keV) ~ 2828 586 Frequsm::". ~ 1 ReldllveFreq/[%) ~ 0

F:uorescence at 75 ke\l to 8D keV Back Scatter Feat\ at 209 _ 8 ke V

Back Scatter Peak at :214.4 keV

Compton Edce at 963.4 l-;eV

Compto" Edge at i 118.1 kel,\ //

CoBO at 1173.24 keV

coeo at 1332.5 keV

Figure 2. Emission spectra from Co-60 [1 J.

Shape and Structure ofNTAC

Cobalt 60 Radiatioc Ser.so;s SPD 38 Nai(TI)

GSll00A MeA Gamma Spec,acuiar 2-10-13. Anti-Proton. com

The attenuation of high energy photons through a material usually follows the Beer-Lambert law. The transmittance of photons through a medium is described by

T = e- rr ·p ·z

where Ci is the attenuation cross-section of a medium, p the density of a medium, and z the path length of the beam of light through a medium. The transmittance of high energy photons can be lowered as the cross section is large, or density is high or the path length is long, or by all work together. However, the cross section and density are pretty much determined by morphological formation of material. The only control parameter for the absorption of high energy photon is the thickness of material. Specifically, for the NTAC applications, the thickness of selected material cannot be increased only to improve the absorption of high energy photons. If the thickness of material is made too thick in order to absorb more high energy photons, the electrons liberated from the intra-band of atoms located deep inside material by high energy photons cannot be readily emitted out of the domain of material due to the loss of energy through multiple scatterings through the Coulomb collisions. The distance of electron passage without scattering is determined by the mean-free path. If the passage length becomes too thick, the photoionic process is pretty much quenched and the liberated energetic electrons are thermalized and eventually undergo their recombination process. Figure 3 shows that when Fayalite is

illuminated by 15 keY electron beam [2], the back-scattered electrons (in red) are emitted from the domain of material. And the multiply scattered electrons (in blue) are stayed within the

Optimum Thickness

Fayalite 15 keV

, ' , -- -- . _.- _ ............ -- ..... _ ... -- .... _ .. _.- _ ........ _ .. -, .. _ ... _ .. -- ..... _ ... -- .. "' _ .. _ .. _ ........ _ .. _. _." "T 1~3B9~:f;~t~1

Figure 3. Simulation model of back-scattered electrons (in red) and multiplication of scattered electrons (in blue) while 15 ke V X-ray is incident on F ayalite. [2 J

domain, and lose their kinetic energy by sequential Coulomb collisions, and are eventually recombined into the atomic structure. To maximize the photo-ionic emission process through which a number of photo-excited electrons are released and emitted from emitter material, an optimal thickness of material can be estimated using a simulation model. For Fayalite shown in Figure 3, the optimum thickness for the maximum emission ofliberated electrons seems to be at a thickness of 463.1 nm under the impingement of 15 keY electron beam. A huge number of electrons can be emitted out from the back surface of Fayalite if 15 keY electron beam is incident on a 463.1 nm thick Fayalite. The estimation of optimum thickness can be made with Monte Carlo simulation code whose open source code is available in public domain.

Even if a flux of high energy photons (keV to MeV level) is incident on a material, there will be emissions of Auger and Compton electrons after the primary interaction of high energy photons with the inter-atomic structure. Such Auger and Compton electrons carry several tens to hundreds ofkeV energy and eventually interact with and liberate much more additional number of multiple electrons as seen in Fig. 3. Accordingly, it is beneficial to keep the thickness of emitter to be thin in order to have additional avalanche emission of electrons tossed off after Coulomb collision with high energy Auger and Compton electrons.

Figure 4 shows a cross-section of newly invented version of Nuclear Thermionic Avalanche Cells (NTAC) as shown in Fig. 1 to maximize the liberation of electrons from emitters by adopting distributed thin isotope layers along with NTAC layers. The left hand side of Fig. 4 shows the portion of the right hand side, but actually it is the axi-symmetry. The core element and thin layers of radioisotope that emit y-rays and/or beta particles are co-axially arranged with radial increments. Both sides of each radioisotope source are wrapped by thin emitter layers that capture high energy photon fluxes from a radioisotope layer for the liberation of intra-band

Radiation Source Emitter

~ Radiation Shielding

Collector Insulator NTAC Layers

f::i'.:~ Metallic Junction TE

Figure 4. Cross section view of new NT A C concept with distributed thin radioisotope layers. The number of layers can be determined by the requirement of power output.

electrons. There are collectors positioned between two thin radioisotope layers wrapped with the emitters on both sides. These collectors receive electrons released from emitters. The collector itself also receives and couples with incident y-ray radiation and energetic electrons that might cause the electrons to be liberated from collector material too. A high Z-material which has a large number of electrons within the shell structure of atom is selected for emitter, while the collector material can be selected from a low or mid Z materials. Therefore, the number of liberated electrons from the emitter arriving at the collector overwhelms the liberated electrons from collector. This phenomenon is well explained by the description shown in Fig. 5. A large number of electrons liberated from emitter materials is emitted from the surface of emitter and cross over the vacuum gap and arrive at the collector surface. By the direct impingement of high energy photons, such as y-ray transmitted through the emitter, X-ray fluorescence and the residue y-ray as a remainder of Compton scattering, the collector itself also undergoes liberating inner­shell electrons from the collector material. However, the number of energetic electrons arriving from the emitter at collector overwhelms the number of liberated electrons from collector. By forming a closed circuit between the emitter and the collector, the power circuit harnesses these supplant electrons from the collector to a load. Within the description of components in Figure 5, the lightning symbol ~ indicates the emission of y-ray and/or high energy beta particles from the core and layers of radioisotope. The symboL,."",,: indicates the emission streams of y-ray, X­ray, and energetic electrons from the emitter materials after the high order interactions and also partially from the core and layers of radioisotope. This emission stream will interact with the material in the next layer. The details of interaction is shown in the inset of which a pattern of electron transition from bound to free is described with the incident photon energy. What is shown in Fig. 5 also describes about how a power circuit is formed between the emitter and collector.

NTAC Layer Power Circuit Load

Electric Current

.... Visible~VUV

y+~ Radioisotope Layers Core Radioisotope Collectors

Figure 5. A large number of electrons liberated from emitter materials cross over the vacuum gap and arrive at the collector surface. By the direct impingement of high energy photons, the collector itself also undergoes generating a liberation of inner-shell electrons. However, a number of energetic electrons arriving from the emitter overwhelms the number of liberated electrons from collector. The power circuit harnesses these supplant electrons from the collector to a load.

:.: . ..-::~ ~>

.... ,~

Figure 6 shows a cross section ofa model for simulation study of the newly invented NTAC concept. This model was used to simulate the system performance for 20 kW or higher power output. This model includes an extra radiation shielding layer and a layer for thermal energy conversion using the metallic junction thermoelectric (MJTE) device in radial direction. The top and bottom caps ofNTAC have radiation shielding layers and metallic junction thermoelectric (MJTE) devices. The radiation source comprises the core and two layers separately. And this system uses gadolinium (Gd) as an emitter material, copper as a collector, and quartz as an insulator as indicated by the red arrows on both sides of Table I. Based on the results of theoretical study shown in Table I, the system needs only 5 layers ofNTAC to absorb and convert the photon power delivered from the radioisotope core and two layers. What it means is after the 5 layers ofNTAC, all radiation is absorbed and converted into useful power and thermal loading. After all, there won't be any residue radiation that will escape the system. As an additional radiation protection, the system has a blanket of lead with 1 cm thickness. A metallic junction with 1.5 cm thickness as an additional layer can also playa role of radiation shielding. There are vacuum gaps between layers where the liberated electrons cross over. Some of initial photon energy can be converted as thermal energy after photon-scattering through materials of layers. A part of this thermal loading on each layer is conducted out through the materials in axial direction. The rest crosses over the vacuum gap by radiative transfer. Because of cylindrical formation ofNTAC layers with narrow vacuum gaps and good view factors, a good portion of

Table L A NTAC configuration with selections of emitter, collector, and insulator.

~ Emitter: 10 cm ID, 2 mm thick

Collector: 16 cm ID, 1 mm thick

Vacuum Gap: 5 , Radiation Source: 5 mm thick mm ---).-"'i ,

;;:

t~I~~il ~~~~~ ~'~]!! ~8]§! "'~~ ~n~l'@ !lm im~ t":·'B ~mi im~ II !~I!m! ~mi im~

r~lmti ~mi im~ !!nll ~mi im~ r~~mti ~mi im~ II r~limi ~mi im~ r~~mti ~mi im~ r~limi ~mi im~ !!nll r~~mti ~mi im~ II r~limi ~mi im~ r~~mti ~mi im~ r~limi ~mi im~ !!nll r~~mti ~mi im~ II r~limi ~mi im~ r~~mti ~mi im~ r~limi ~mi im~ !!nll r~~mti ~mi im~ II r~limi ~mi im~ r~~mti ~mi im~ r~limi ~mi im~ !!nll r~~mti ~mi im~ II r~limi ~mi im~ r~~mti ~mi im~ r~limi ~mi im~ !!nll r~~mti ~mi im~ II r~limi ~mi im~ r~~mti ~mi im~ tin~-:.~ r~limi ~mi im~ tinm r~~mti ~mi im~ l!nIM r~li::m ~mi im~ ~~~ m~ ~:.::~ ~~~ :..~t::..~ ~dt~,§:

... ,~< !.~-.:: ...

10 cm0

~ Radiation Source »»»»> Collector, 1 mm thick

= Emitter, 2 mm thick ,WNN' Insulator, 3 mm thick

• Radiation Shielding, 20 mm fu.~ Metallic Junction TE, 20 mm

Figure 6. Cross section view of new NTAC concept usedfor simulation study. There are two distributed thin radioisotope layers and 7 NTAC layers.

thermal energy can be transmitted in radial direction through the layers of vacuum gaps and

NTAC and eventually arrives at the metallic junction layer. Thermal energy transferred through both in axial and radial direction is converted by MJTE device. In the simulation, only 10% of MJTE efficiency was used to capture and convert thermal energy. Based on the simulation study made for the MJTE device with the 10 layers (108 junctions/layer, 50~m layer thickness) for the temperature difference between 273°K and 1273°K, the efficiency turns out to be 20%. Including the spacer and crossbeam for 10 layers, the actual thickness ofMJTE simulation model was 0.7mm. If we increase the thickness ofMJTE device for the same temperature difference, the efficiency will be much higher than 20%. The efficiency of 10% selected for NTAC simulation is a conservative value.

Figure 7 shows the simulation results ofNTAC which was made with the fixed volume, o. 00217m3, of radioactive materials. The total number ofNTAC layers used for this model was 7

Co-GO 47.40 kg Tolal Weighl 314.90 kg Co-GO 94.80 kg Total Weight 600.27 kg Na-22 5.18 kg Total Weight 272.68 kg Na-22 10.36 kg Total Weight 515.83 kg

7 6,----------------------------,

6

S -'" 0, 5 -'"

'" J:: Q. 4 « E Q)

3 ti >-II)

2

Core1 O-MJ1 O-HO.5

10% Na-22

15%

20%

25%

20 40 60 80 100 120 140 160 180 200 220 240

System Power, kW

S 5 ='!: Cl

.lI::

ci 4 ..c:::: Co.

< E 3

.2! ~

C/) 2

10%

25%

o 100 200

Core1 O-MJ1 O-H1.0

20% 25%

Co-GO

30% 35% 45% ' 40% 45%

300 400

System Power, kW

Figure 7. Simulation results ofNTACwith theflXedvolume (O.00217m3) of radiation source. This model has 7 NTAC layers.

500

layers. Actual need ofNTAC layers to absorb and convert the incident y-ray radiation is only 5 as indicated in the line of Table I with red arrows. Based on the theoretical calculation made for the 1.25 MeV y-ray radiation, the 5 layers of Cu-quartz-Gd set completely absorb the radiation with no remaining radiation leak. The graph on the left of Fig. 7 shows the specific weights of Na-22 and Co-60 cases for the radiation core diameter of 10 cm and the height of 50 cm along with system power. The graph on the right of Fig. 7 is for the radiation core diameter of 10 cm and the height of 100 cm along with system power. The Na-22 seems better for the issue on specific weight than Co-60. It seems that the system power output by Co-60 exceeds that ofNa-22. But it is because the calculation was done by the same volume of radioisotopes. Because of the low density of Na-22, the actual mass ofNa-22 used for calculation is only 5.18 kg vs. 47.4 kg ofCo-60.

Figure 8 shows the power output ofNTAC based on the weight of radioisotope used. The plots were made for the photon power conversion efficiencies, 10% and 20%, for Co-60 and Na-22 while keeping 10% for MJTE efficiency. It is quite noticeable that 40kg ofNa-22 NTAC system has a 400kW power potential which is a 4 times more than that of Co-60 with the same fuel mass.

Photon Power 500

• Co-60 Photon 10% 400 0 Na-22 Photon 10% ... - Co-60 Photon 20%

~ .6. Na-22 Photon 20%

300 -~ ::::J a. -::::J 200 0 0 s... 0 Q)

3: 100 .6. 0 0 ... a.. ...

0 -"f" • I • • 0

5 10 15 20 25 30 35 40 45

Fuel M ass, kg

Figure 8. Power output based on the radioisotope weight. The plots were made for the photon power conversion efficiencies, 10% and 20%, for Co-60 and Na-22 while keeping 10% for MJTE efficiency.

Figure 9 shows the specific weight for the fixed fuel mass. The left graph of Fig. 9 shows the specific weights ofNTAC with the fuel weights of30.5 kg ofCo-60 and 22.56 kg ofNa-22,

Co.,so Na-22

30.59 kg

22.56 kg

Total Weight

Total Weight1 309.41 kg

504.21 kg Co-60

Na-22

53.21 kg

43.42 kg Total Weight

Total Weight

371.38 kg

663.72 kg

6,--------------------------------, 5.--------------------------------, 10% Fuel Vol: D-O.Sm, H-O.Sm

5

s: =l!: 01 ... ci J:: Co

<C

10% E .l2 II)

>-Vl

4

3

2

Fuel Mass 40kg; D-O.Sm, H-O.Sm

10"A~Na-22 15%

20% 25%

30% 35% 40% 45%

o+---_.-----.----~----._--_.,_--~ 0

o 100 200 300 400 500 600 0 200 400 600 800

Power, kW Power Output, kW

Figure 9. Simulation results ofNTACwith theflXedfuel masses (approx. 20kg and 40 kg) of radiation source. This model has 7 NTAC layers.

1000 1200

respectively. The right graph of Fig. 9 shows the specific weights for the fuel weights of 53.21 kg ofCo-60 and 43.42 kg ofNa-22, respectively.

References [1] Rapach, T.A. and Pelcher, M.A., "Gamma Ray

Spectroscopy", http:!h,x/'vv\v. pas .[Och ester. edu/-~adv 1 ab/ reports/ pekher rapac:h gammas nee. pd

f [2] Dapor, M. "Application of the Monte Carlo Method to Electron Scattering Problems: 15 keY

Electrons in fayalite (Fe2Si04)", Casino

software. http://\vw\v.gel.usherbrooke.caicaslno!What.html

Unique or Novel Features

(Enter as appropriate: A.- novel or unique features; B.- Advantages of Innovation/software; c.­Development or new conceptual problems; D.- Test data and source of error; E.-Analysis of capabilities; and F. - For software, any re-use or re-engineering of existing code, use of shareware, or use of code owned by a non-federal entity.)

• More distributed emissions of high energy photons and high energy beta particles from a number of thin isotope layers that reduces the coupling probability within inter-atomic

structure of isotope source material,

• Capture and conversion of the most of high energy photons and/or beta particles by multi-NTAC layers without leakage of residual radiation, thus requiring minimal

radiation protection,

• Effective emission of avalanche electrons from the combined structure of thin layered radiation source and emitters into vacuum gap by reducing internal scattering within

atomic structure of isotope source and emitter materials,

• Essentializing the high order interactions within inter-atomic structure of thinly layered isotope itself and emitters ofNTAC for liberating more electrons, and

• Making a distributed thermal load on each layer.

Commercialization Potential:

Numerous applications in commercial sector is envisioned: • Autonomous vehicles and ships

• Drones

• Remote villages and town

• Satellites

• Major power plants