Note: Descriptions are shown in the official language in which they were submitted.
L7'.SER URANIVM ISOTOPE SEPARATION
. . .
This inven-tion relates to isotope separation pro-
cesses, and to apparatus useful in such processes. ~lore
particularly, the invention is directed to methods and appara-
tus for more efficient separation of U235 and U238 isotopes
S by convertincJ a mlxture of these isotopes to organic com-
pounds or to silicon compounds and then irradiating the
isotope compounds selectively to change their chemical (and/or
ph~sical) properties, thereby to facilitate separation. In
a preferred emhodiment of the invention the uranium com-
pounds are selected from the group having a chemical moiety R
bonded directly to the U atom, the U-R bond having a fundamental,
overtone, or cor~ination vibrational absorption frequency
between 900 and 1100 cm . The selected U mixture is then
~ irradiated ~lith afrequency-selective CO2 laser.
BACXGROUND OF THE INVENTION
Isotope separation is an area of profound importance
not only to chemists and physicists but to the ~ntire populace
a~ well~ The use of infra ~d lasers to separate isotopic
species is suggested in the prior art~ Described techni~ues
involve selectively exciting gaseous molecules of a given
iso~pe with in~ense, highly monochromatic laser radiation.
It is required -that the frequency of the radiation be coin-
cident with a ~undamental, combination, or overtone in the vi-
brational spectrum of the molecule. The vibrational excitement
of the molecules may lead to spontaneous decomposition, or
it may be necessary to introduce a second agentt which xeactsselectively with the excited species. In some cases, simul-
SO
taneous laser and ultraviolet or visible radiation have beenemployed In all ~ases, the objective is selectively to
transform the molecules of a single isotope into an enriched
material which can be separated (on the basis of solubility,
volatility, electrical charge,etc.) from the molecules con-
taininc3 the other iso-tope(s). To prevent energy transfer
between isotopically different molecules, it may be desirable
to operate at low pressures and/or to add an inert diluent.
The above concepts have been proposed for the photo-
excitation separation of the uranium isotopes U and URobieux, U. S. Patent No~ 3,443,087, describes the selective
ionization of UF6 by a combination ofinfra-red tIR) and ultra
~iole~ (UV) laser irradiation to facilitate electrostatic
separation of U235 in the vapor phase, and Belgian Patent No.
821,823 describes selective dissociation of UF6 by a combination
o~ and UV, facilitatiny chemical sepa~ation of U235
However, the fundamental vibrational resonance fre-
quencies of UF6 are 624 cm , and 186 cm , values which are
not presently available from electxically pumped transitions
20 in gas lasers. Semiconductor lasers are available which
can be tuned to this frequency, but their output power is
limited to fractions of a watt. This low power results in an
intensity that is insufficient for multiphoton absorption to ca-ise
dissociation. Any reactions induc~d would occur at low rates
which are impractical for production processes. Other prior
art separation processes such as those in UK Patent No~1,284,6~0
describe the method of isotope separation by selectively stim-
ulating chemical reactions effected by irradiating an isotope
mixture with ~ laser frequency corresponding to the vibrational
absorption frequency. Specifically, it is there disclosed to
use a CO2 laser in combination with the molecules UF6, UFnC16_m,
UC16, or ~(B~14)~ . However, none of these molecules is known
t~o have Eundamental vibration frequencies in the CO2 laser out-
put range' Since the most stable and reliable, and the most
economical source of infra-red laser radiation is a carbon
dioxide gas laser, the most effective range of which'9.2-11.0~,
1086-909 cm , the above molecules would not absorb sufficient
radiation for usable excitation. None is reported to have
fundamental or overtone metal-ligand vibrations in the appro-
pria~e region of ~he spectrum.
It is an important feature of the present invention
that it teaches the use, in laser induced separations of
uranium isotopes, of compounds having vibrational sensitivities
accessible to a CO2 laser.
In achieving the aims of the present invention, two
properties are most desirable as initial criteria for the
suitability of uranium compounds. In one embodiment,the com-
pounds must be sufficiently volatile to be irra~iated in theyas phase~ ~n the second embodiment the compounds may be
condensed from the yas phase in a matrix or applied as a
solution. The molecules must have metal-ligand fundamental
or overtone (preferably the former) vibrations in the region
accessible to a CO2 laser, i.e. 900-1100 cm 1 in the preferred
mode of irradiation. These criteria encompass a surprisingly
wide range oE compounds.
Coordination number and coordinative saturation ap-
pear to play a major role in determining the volatility of
s~
neutrally charged uranium compounds. In low oxidation states,
e.y. -~4 a uranium complex with non-bulky ligands will attempt
to expand its coordination number beyond 4 by coordinating
additional ligands, orJ when these are unavailable, by forming
liyancl briding bonds to neighboring uranium ions. This leads
- to polymeric s-truc-ture, high lattice energies, and low vola-
tility. Two approaches can be used to circumvent this pro-
blem. In ~ligher oxidation states, the uranium will have a
smaller ionic radius, hence a smaller desired coordination
lQ number, ~nd generally more ligands per metal ion. This usually
lea~s to higher volatility. Another way to reduce intermolecular
interactions is by employing sterically bulky ligands.
,
15 U' ~ ,U
~F C > F- F
20~J~ ~ "U F ~¦ ~ F
, '
U
UF4 6
25(distorted square antiprism) (octahedral)
For example, in the alkoxide series, U~OCH3)4 is essentially
non-volatile, insoluble, and is probably extensively as-
sociated in the solid state. In contrast, U[i~OC3H7~ is
more soluble and c~n be sublimed. Further confirmation of
these concepts is found in IJ(OC2H5)s which is dimeric and
rather volatile (boiling point 123 /0.001 mm pressure~ and
in U(OC2~l5~6which is monomeric and even more volatile (boiling
point 72~74/ 0.001 mm pressure). Thus, maY.imizing the oxi-
dation sta-te and the coordinative saturation are feasible
approaches to increased volatility. Also important, but
apparently less critical, is keeping the molecular weight
as 10~7 as possible.
The foregoing discussion is believed to be relevant
- to reaction design for uranium isotope separation. One
attrac~ive s-trateyy is to employ those laser-induced reactions
which disassociate a ligand (or ligands) from the uranium, or
which promote the substitution of a less bulky ligand. Start-
iny with, for example, a U(VI) compound, laser promoted homolytic
6 > UL5 L
UL5 ~ UL4+L
cleavacJes would reduce the uranium to the accessible +5 then ~
oxidation states. The UL5 and UL4 species are entities markedly
less volatile than UL6 and are separable. Alternatively, re-
actions such as
UL~ L4 L ~ UL3L' +L
produce a U(~V) complex with different properties ~e.g.
~olatility, solubility) than UL4, since the Ll is less bulky
and may also form intermolecular bridges.
The compoullds selected for use in the first emhodi-
ment must be stable to the ~ermal conditions necessary to
volatali e them. In the Pearson terminolo~y, uranium is a "hard"
acid. It will have the ~reatest affinity for negative]y
so
charged, non-polarizable ligands. Such ~ualitative rules are relevant in
developing syntheses and also in promoting, via laser irradiation, ligancl
substitution reactions. Fortunately, many of the properties which impart
volatility afford, in addition, some resistance to thermal degradation.
Studies of the mechanism of thermal decomposition of several classes of
uranium organometallics indicate that coordinative saturation of the uranium
ion can greatly retard thermal clecomposition. This presumably arises
because immobilization of t}-le coordination sphere blocks the lo~er energy
pathways for thermolysis. ~lUS, the approaches which should foster higher
volatility are~ in addition, reasonable initial approaches to enhance
thermal stability. Such concel~ts clearly illustrate that decomposition of
the desired molecules by energetic photons facilitates separation from un-
decomposed molecules by the resulting differences in chemical and physical
properties.
BRIEF DESCRIPTION
In accordance with this invention there is provided a process for
separating isotopes of a metallic element, said process comprising the steps
of preparing a compound M-T of said metallic element in which ~1 is a mi.~ture
of isotopes of said metallic element and T is a chemical moiety selected
from the group consisting of organic derivatives, silicon derivatives and
deuterated derivatives, said compound being further characterized in exhibit-
,p.. ,~
ing for at least one isotopic s~e~e thereof a funclamental, overtone, orcombination vibrational absorption e~citation energy level at a frequellcy
~; between 900 and 1100 cm ~, irradiating said compound with energy emitted by
a radiation source at a frequency between 900 and 1100 cm 1 to modify
differentially properties of at least one isotopic specie of said compound,
thereby to establish differences in properties of the irradiated isotopic
species, said differences in properties being relevant to facil:itating a
separation of isotopic species through physical and chemical procedllres
applied to the irracliated compound and co products derived therefrom,
utilizin~ the established diflerences iTI properties SO as selectively to
. ~, .., ~,
recover an isotopic ~p~ie of sail metallic elerrlent from the lrradiated com-
--6-
~ tl~O 3632-1227
pound.
In accordance with another aspec. of this invention
there is provided apparatus for facilitating the separation of
isotopes of a meta]lic element to provide an isotopically-
enriched product, said apparatus comprising: reaction chamber
means for retaining a chemical composition including a plurality
of isotopic species of the metallic element, valve means for
controlling introduction of the chemical composition into said
reaction chamber means, means for controllir.g atmospheric com-
position within said reaction chamber means, temperature controlmeans to regulate the temperature interiorly of said reaction
chamber means, generator means including power supply means for
producing a beam of radiated energy, means including electrode
means to direct said beam to impinge upon said chemical com-
position contained in said chamber means to interact with and
to modify properties of said chemical composition so as to
facilitate the separation of isotopic components thereof.
In accordance with the present invention there is
provided apparatus for separating isotopes of a metallic element
to provide an isotopically-enriched product, said apparatus
comprising: generator means to produce a beam of radiated
energy, irradiation chamber means disposed to receive a beam of
radiated energy from said generator means, movable substrate
means for supporting a composition to be irradiated, means for
supporting and mvving said substrate means and a composition
including a plurality of i~otopic species carried thereon
through said irradiation chamber means, reaction charnber means
and means communicatillg with said irradiation chamber means to
permit passage of said substrate means therethrough rom saLd
irradiation chamber means to said ri:action chamber means, drlve
means for propellillg saicl substrate me.lns through said reaction
chamber mealls to ~~acili~.lte interaction between the substrate-
,~
~ s ~ 3632-1227
earried composition and a reactant contained in said reaction
chamber means.
In accordance with the present invention there is
further provided a process for the separation of the isotopes
of uranium, said process comprising preparing a volatile U02-
eompound by eomhining a ~2 radieal with an organie moi.ety so
as to produee a U02- eontaining eompound havi.ng an isotopically
shifted infrared absorption spectrum associated with saicl
uranium, vaporizing said U02- containing compound, and irradl-
ating said volatile U02- containing eompound with infrared
radiation which is preferentially absorbed by a molecular
vibration of molecules of said volatile U02- containing compound
containing a predetermined isotope of said uranium so as to
provide excited molecules of said compound enriched in said
moleeules of said eompound eontaining said predetermined iso-
tope, enabling separation of said exeited moleeules.
In aeeordanee with the present invention there is
further provided a proeess for the separation of the isotopes of
uranium, said proeess eomprising vaporizing a volatile ~2-
eontaining eompound, said eompound having an isotopieally shi.fted
infrared absorption speetrum assoeiated with said uranium, and
irradiating sai.d volatile ~2- eontaining eompound with .in~rareci
radiation whieh is preferentially absorbed by a moleeular
vibration of molecules of said volatile ~2- eontaining compound
containing a predetermined isotope of said uranium so as to
provide excited molecules of said compound enriehed in said
moleeules of said compound containing said predetermined isotope,
enabling separation of said excited molecules.
DE_~RIP~ION OF_PREFERRED EMBOi~I~FNTS
The follo~incJ is a p.3rtial en~meration of useful
elasses c,f comE~ounds, for th. I~urposes of the present in;ertic)n.
The frequeTley o~ t~c metc3~ and stre-~tching resonance mo(ie
fi~
3 6 3 2 - l 2 2 7
(and to a lesser extent, bending deformation) fund~mental is
important in the practice of the invention. The magnitude of
the frequency difference in ~-' 238U_X versus ~~' 235U X will
depend on the particular molecular system. For uranyl complexes
(0=~-0) the difference should be ca. 0.7 cm 1 for the anti-
symmetric O=U=O stretch. Application of the Teller-Redlich
product rule yields a value
- 6c -
~.Z~( `'S(l~
for the TlU U-O stretching mode of ca. 1.5 cm 1 in U(OCH3)6,
treating the methoxy ligands as point masses ~a crude quali~
tative approximation). The most accurate analysis of metal
lic3and fundarnentals is through high resolution metal isotopic
substitition studies, an area which has recently seen xapid
developmen~.
A nur~er of known volatile uranium complexes, not
s~lggested for such use in the literature, are, in accordance
with the invention, empl~ye~ for the laser-induced separation
of uranium isotopes. These compounds have metal-ligand
undamental ox o-vertone vibrations in the spectral region
accessible to a CO2 laser, and, as herein disclosed, are
susceptible to isotope-selective excitation and interception.
Arran~ed by class, compounds useful in the practice of the
invention include the following:
A. Borohydride-Organo C_mplexes
These complexes of the BH4 ligand have been found
to have a tridentate metal-ligand geometry. Under C3V local
symmetry, -the A1 and E bri~gmg- modes, which are believed to
have considerclble M-H character, occur in the region ca.
1100-1230 crn 1 All have sufficient volatility to make them
.
~ ~\ H -B X or - ~ D ~B--X X-D~H~
attractive. Examples are given below.
--7--
3( ~S()
U (BY~1 3 4
C (Cs~) 2U (E3Ya~? 2
(CsHs)3 U(B~f4) (Y=H~D)
(C5E15) 3 U ~BY3C2 5)
S ~C~ l`l) 3 U (BY4)
Most of these cornplexes can be prepared by displacing halide
ith BH4 or BD4 in an ethereal solvent. Indeed, we have
founa borohydride derivatives to be some of the most accessible
for a n~ er of organoactinide systems studied. Additional
~U-Cl ~ NaBY4 ~ ~ BY4 f NaCl
(or ~iBY4 )
volatile derivatives are prepared by sequences such as,
n ~ U(OR)n lCl NaBH4 > U(O~)
In several of the compounds, for example U(BH~)4,
the desired normal mode is above the frequency accessible
to the CO2 laser ~for U~BH4)4 = 1230 cm ). Deuteration
shifts this absorption to ca. 92~ cm~l, Deuterated rompounds
are accessible via commercially ~Yailable NaBD4 or LiBD4.
B. uranyl Complexes _
. These are complexes which incorporate the O=U=O
r2l5 functionality, usually in a p~n~a~n~l ~A)or hexagonal (B~
bipyramidal arranyement (a few octahedral examples are also
known). The antisymmetrically coupled~ O=U=O stretching
vibration usually occurs in the region 910-940 cm
--8--
so
o o
<~>
o o
. n.
A coml?oun(] for la~c;er irra(liation i~ uranyl
crE~ ;l.lo(,y~ in~, preyar~d in a templa~:e reac~i.oll ~s .~,howr
~e ]. o~
N ~O~N
5 (~C~J + M Z --~ - ? ~ ~ I ~N-O
M = uO~2 ~O,l~ ~
'J.'l~; ~; c,om~o~ d 1l~l5 v~ry higl) ch~mical and therm~l stal~iliLy an~l
L5 ~;ublim~ n va~ uo at: l100". Still otller oryallic "monom~rs"
~rov i ~l ia~tJ m;~c):o~ l.ic uranyl compl~xes oE lowcr molcc~J.~r
ei.cJi~ n(l qrcator volal~ iJlclude:
3 ~ CN ~2N ~CN F
CH3/ \ CN 1I N / \CN F~N
U~ ny l alko;ci(.lcs, U2 (01~) 2, al~;o report:cd in t:he
.I .i t~r~tllrc~ ;~rc q~ncra].ly of low volatility, and ar~ paxl:.icul;ll-ly
Z5 ~uilnl~le coml)lexe~; ror u~e in tlle practice or tlle present invenl ion.
Complexe.c wiLh l~ulky rluorinaLed alcohols are al80 useful in Lhe
pr~qcL ice Or the invention. While known uranyl ~-(liketonaLe~ are nol
_9_
S~)
appreciably volatile, very bulky ligands such as fod, sh~wn
belo~, complexed to uranium are of interest.
~U~
CF2- CF2 - CF - C ~ _ ~ C ~ C/ CH3
H CH3
Also, alumin~n alkoxide ligands impart volatility. A possible
route to such complexes for U(VI) is,
~ 0~
UO~C'12 -t 2NaAl(OR~ RO~ ,O~ ",O~ OR
RO ~ ` O o O ~ `OR
C. Uranium Alkoxides and Siloxiaes
Complexes with OR lig~nds may be prepared for
uranium on ~ large scale and in a variety of oxidation states.
Many are ~uite volatile; some are distillable lî~uids. The
known analo~ous silicon compounds are also appreciably volatile.
Representative species are shown below, and it is apparent
that they offer a wide 1exibility in terms of possible vari-
ation of oxidation state, symmetry, and volatility.
U(OR~4 U~OSiR3)4
U(OR~5 U(oSiR3)5
U(VR)5 U(oSiR3)6
R = variety of organic groups
A U-O fundamental (except possibly for uranium in the +6
vxidation state) will not absorb in the desir~ frequency re-
yion. For example, the Ti-O stretches in Ti(OCH3)4 have been
-10~
assigned at 588 and 553 cm , those in Ti(oC2H5)4 at 625
and 500 cm 1, and those ln Nb(OEt)5 at 571 cm 1 Though
the fundamental U-O stretches in the aforementioned alkoxides
may not be in the CO2 laser range, overtones are. The ~unda-
men-tal U-O stre-tch occurs in the region 460-550 cm 1 Hence,
the first overtone is in the region 920-1100 cm 1 By ap-
propriate selection of ligands to "tune" the symmetry and
various force constants, it is possible to brin~ a U-O over-
tone or combination band into Fermi resonance with another
fundamental (e.g.~ C-O ~ 1000 cm~l), thereby increasing the
excitation cross section. In addition, high power lasers
operative a-t the U-O fundamental frequencies are expected
to be available in the near future.
The uxanium alkoxides also appear to be excellent
precursors to other derivatives. Typic~l reaction schemes to
introduce a variety o~ new ligands are shown below.
O OH
Il I ~OR)n-l
n R'~ ~C// ~R' ~~- ~ O~O ~ROH
,C '- ~,&
H
U(OR)n HCl > U(OR)n-lC~ U(R)n-lBH4
~ U(OR~n-lC5HS
¦ RLi ~ U(OR)n_lR
R = alkyl group
--11--
5(JI
Mixed complexes in which one or more of the OR or
OSiR3 cJroups is replaced by a ~-diketonate, a borodeuteride,
or an alkyl group are within the concept of the present in-
vention.
D. Uranium ~lkyl Compounds
. .
These compounds include complexes of the for~ula Ln
URn_4 where L=C5H5, ~n alkoxide or siloxide, or borodeuteride
and R is an alkyl (e.g. methyl, ethyl, isopropyl, t-butyl,
benzyl, neopentyl)or aryl (e.g. phenyl) group. The U-C
stretching - vibration occurs in the region of 500 cm 1~
Thus, the first overtone is in the region of 1000 cm~l. Urani-
um alkyl compounds are thermally stable only if sufficient
coordinative saturation is present to hinder various intra-
molecular decomposition processes. Thus (C5H5)3 UR compounds
(with ~ -bonded C5H5 ligands) possess rather high thermal
stability. Por R- methyl or vinyl, the complexes are sublimable
X-ray structure of(~5-C5Hs)9U(-C--CC6H5~
Sys-tems such as ~C5H5)3UR offer the attractive feature that
products o~ a homolytic laser-induced cleavage would be
(C5}15)3U, which is nonvolatile, and R-radicals, which could
be scavenged. Other attractive uranium alkyl systems are pre-
~ented below.
-12-
(3S()
CH2 (CsH4) 2UC12 RLl ~, CH2 (CsH4~ 2UR2
U2C12 RI,i ~, U02R2
(C5H5) UC13 2THF RL~3 ( 5 5) UR3
THF = tetrahydrofuran
S Particularly interesting, in terms of imparting thermal
stability, are bulky R groups (e.g. t-butyl), those without
~-hydrogen atoms (e.q. tri-methylsilylmethyl) and chelating
alkyls te.g. those derived from 1, 4-dilithiohutane).
The stability of ~CH3) 6 suggests the utilization
of U(CH3~6, which is expected to be quite volatile.
U~16 ~ U(C~I3)6
E. Uranlum Amides
The diethylamide of uranium U[N(C2R5)2]4 is volatile
enough to be distilled or sublimed. Until recently, it was
the only known uranium dialkylamide. Since the U-N stretch
falls in the 500 cm~l region, the first overtone is in the
xegion of 1000 cm 1. The amido complexes o~ uranium contain
the U-NR2 functionality; examples include U(NR2~4, Ln U~NR~)n 4
where L = B diketonate, alkoxide or siloxide, alkyl group, or
borodeuterid~ Some approaches to a variety o~ compounds are
proposed below.
U(NR2)4 5 6 ~ (C5H5~2V(~R~)2
\~ > U(NR2)4_n(0R)n
The existence of ~[N~CH332~ is impetus to investi~ate uranium
oxidation s-tates higher than +4.
In the above cases, the cornplexes may be irradiated
in the gas phase or in the frozen solid phase at the funda-
mental,combinationr or overtone metal (either U238 or U235) -
liyand frequency, with a high power CO2 ~as laser. This is
carried out both with and without simultaneous ultraviolet or
visible irradiation. Reactive agents such as methanol, styrene,
thiols, etc. can also be added to trap the excited m~lecules.
~n the first el~diment, the reactions are conduct~d preferably
at low pressures, and it is possible to add an inert Ailuent
such as methane~ neon, argon, etc. In all cases r the selective-
ly excited molecules react to form an isotopically enriched
(in U23~ or U235 depending on the irradiation frequency) product
which is chemically different froln the starting material.
The product is then isolated from the starting materials on
the basis of volatilityr solubilityr and/or electrical charge.
It is also possible, in accordance with the second
em~odiment of the present invention, to effect isotopic
substitu-tion by condensing or spraying the proposed compounds
in ari appropriate matrix at cryogenic temperatures. Selective
excitationr as proposed for the gas phase procedures, is
preferably carried out with a CO2 laser r but other tunable,
stable infra-red lasers may be used. The matrix is designed
to react with the selectively excited uraniuM compounds.
Suita~le matrix components include alcohols, Xetones, thiols,
styrene, oryanic nitroxides, etc. Again, the reaction products
differ sufficiently from the starting materials to allow
separati~n when the matrix is warmed to ar~ient temperature.
BRIEF D SCRIPTION GF THE ~RA~ING_
The presen-t invention will be more fully described
with reEerence to the drawinys depicting suitable apparatus
for effectuating the method of the invention and in which
EIGURE 1 illustrates one embodiment of the invention
in which a pulsed CO2 laser, controlled in frequency and in-
tensi~y, is used to irradiate a gaseous U-organic i.sotope
mixture;
F~GUR~: 2 illustrates a second embodiment in ~hich
-the radiation from a CO2 laser is combined with a UV source to
irradi~te a yaseous U-organic isotope mixture; and
FIGURE 3 illustrates a third embodiment in which
laser5 irradiate a solid-state U-organic isotope mixture fro2en
in a glass~ matrix.
DESCRIPTION OF THE APPARATUS AND TEC~INIQUES
ReEerring now more particularly to ~IGURE 1 of the
drawing, a c3aseous mixture o~ U 35 and U incorporatea in
a U-organic compound, ~or example, a uranium alkoxide U(OEt)6
is irradiated in a reactor 10 by a laser beam 12 fxom a pulsed
~2 laser source 16. The reactor includes a one meter long
monel reaction tube 18 having an entry windo~J 20 for entry
of the laser beam 12 and an exit ~lindow 24 for exit of the heam
12. The beam entry and exit windows 20l 2~ may be o NaCl or
other sui-table materials such as Znge that transmit the 9-11
micron CO2 laser radi-aticjn. The ~indo~Js 20, 24 are positioned
at the Brewster angle to the beam 12 to minimize loss of beam
er~ercJy. ~ photo~detector ~6 monitors tlle unabsorbed portion
-15--
f the bealn 12~ and a monitor ~indo~ 28 o~ quar-~z, connected
by a side tube 32 to th~ reactiOn tllbe 18, may l~e used to
monitor the visible a~d ~v f]uorescence ~rom the reac~ion.
The U-orcJanic composition is stored in a reservoir 3~, ~ittea
with a heat exchange coil 34a, and a reactive or bu~er ~as
may be stored in a second r~servoir 36.
The U-oryanic composition, ~or the U-silicon com2osi-
tion) iS introduced into the reaction tube 18 throuc~h ~
me-terin~ valve 38 which may incorporate a conver~ing-diver~ing
nozzle 40 for expansion cooling, designed as i,s we],], kno~n i.n
the art to provide a velocity of app~oxiTnately Mach 1 or la~cJer.
A reaction or buffer gas in reservoir 36 is introduced (~hen
desired) into the reaction tube 18 throu~h a second metering
valve ~2. A heating coil 44 adjusts the temperature in the
reactor 18 for the desired vapor pressure~ ~ vacuum pump ~6
exhausts the yases in the reaction tube 18 througll an apertlire
4g, to a second chamber,or zone 54 the tempera~ure of which
is controlled b~ a heat exchanger S6. A thi~d cham~er or ~one
5~a may be used to condense unreacted components as tJell as
volatile by-produc-ts. Pump 46 exhausts i.nto a storage t,ank 58.
The tetra alkoxide, U(OEt~4 is a principal xeaction product,
together with organ~.c fragments. The less vola~ tetra alk-
oxide is then separated from the more volatile constituents
of the mixture -to achieve the desired isotope enri.chment. 7
focusing lens 60 focuses the laser beam 12 through the entry
window 20 -to a spot on the optical axis of the reaction tube
18 to position the reaction above nozzle 40 o~ the valve 38.
-16-
The laser source 16 uses ~ pulsed electrical dis-
charge be-tween a pair of bronze electrodes 62, 64 to attain
output power bet~een the limits of :Lo4 and 101 watts per cm2
The upper value ~E beam intensi~y is limited in some cases
by breakdown of -the gases and formation of a plasma. The
electrodes 62, 64, in a preferred emb~diment of the invention,
are 50 cm. lony x 2 cm wide and are separated by 1 cm.
The lasing gas, which may be a 1,1,~ molar mixture of CO2
N2,He stored in a pressurized tank 68 is introduced through
a reducing valve 70 into the circulating and cooling system 72
of laser source 16 The electrodes 62/ 64 are symmetrically
positioned above and below the axis of an acryli.c laser tube 76.
The tube ends are sealed by Brewster angle, NaCl end windows
78, B0. An optical resonator is formed between an adjustable
gra~ing 84 and a 95~ reflecting germanium (Ge) mirror 88 which
are centered about the optical axis ~hich is slightly off-set
frorn the center axis of the electrodes 62, 64 when the beam
passes throuyh .the end windows 78,80). Depending on whether
a stable or unstable resonator is desired, the Ge mirror 88
may be con~ex, flat~ or concave, as presented to the grating
~4. The grating ~4 acts as a plane, frequency-selective mirror
which is acljusted for the particular U-organic used. The
grating 84 and the Ge mirror 88 may be positioned insi2e the
laser tube 7~ eliminating the end windows 78, 80. However
wide mirror spacing is desired to improve frequency character-
istics.
Electrical power to the electrodes 62, 64 is sup-
plied by a power supply 92, 94, through suitahle leads 96,98.
-17-
5 ~:)
The electrical pulse from supply 92, 94 is a fast rise-time
pulse of ~ypical. magnitude 47 KV per cm of spacing bet~.leen
the electrodes 62,64 and per atmosphere of lasing gases. The
pot~er supplies 92, 9~ may be a Blumlein or equivalent design
S with low-inductance circuit elements. Alternatively a commer-
cial, trigyered spark-gap may be usecl for the pot~er supply 92,
in whic}l case -the lead ~6 is connected directly to ground
elimina-ting supply 94.
To facilitate a uniform glow discharge at high lasing
gas pressures in the laser tube 76, a thin ~.007") tungsten
wire 102 is positioned at mid-plane but outside the edges of
the elec-trodes 62, 64 and connected througn a small capacitor
10~ (typically 50 pF or less) to the lead 98. Thus, the rising
voltage ~rorn the power supply 92, which increases the potential
di.fference bet~/een the electrodes 62, 64, also increases the
potential difference between the wire 102 and the electrode 62.
Ilo~lever, the To~msend breakdown voltage between the wire 102
and the electrode 62 is adjusted to be lower than ~etween
the electrodes 62,64 ~hereby causing limited breakdown and pre-
ioni~a~ion of the lasiny gas prior to breakdown between theelec-trodes 62,6~. Othex pre-ionization c.ircuits may he used
such as naked spark-gaps positioned outside the electrodes
62,6~ along the mid-plane to W-irradiate the gap hetween
the electrodes 62,64. Also, a low ionization~potential liquid
sucll as tri-butylamine may be applied to the electrodes 62,64
to reduce sparkin~.
~ lot lasin~ gases from the gap bet~ieen the electrodes
62,6~ are recirculated and cooled through a cooling tube 106 of
the refrigerator 72 by clucts 110,112 by means of a pump ~not
-18-
Js~ ~
shown~. A cooling coil 116 extracts the heat, from the lasing
gases, added by po~7er absorbed from the power supply 92 during
t~le electrical discharge. ~he ducts 110, 112 are ideally
located to circul~te lasing gases direct]y through the space
between the electrodes and may use a diEfuser if turbulence
is required to stabilize the discharge.
The llOS t convenient operating pressure of lasing
gases in the laser -tube 76 is atmospheric. However, the value
can be above or belo~ one atmosphere, depending on desired
output characteristics. In some cases it may be necessary
to raise the pressure to attain tunability above the natural
transitions as broadening of the CO~ l~nes increases 3GHz per
atmosphere up to 10 atmospheres where CO2 laser lines overlap.
- Thus in operation, the laser source 16 is switched
on the alicJned wi-th the optical axis of the reaction tube 18
of the reactor 10. To obtain the proper output frequency
selection of the laser source 16, the reaction tube 18 is
evacuated and backfilled with U-organic compound enriches in
U235. Absorption is noted while laser lines are selected with
the yra~ g 8~. The U-organic feedstock in reservoir 34 is
then admitted through the reducing nozzle 40 and irradiated.
Non-volatile reac-tion products are condensed in Chamber 54
and non-volatile products as well as reacted U-organic are
condensed in a second cold zone 54a.
Of course, other U-organics may be used with the
laser source 16 tuned by the grating 84 to the desired fre-
quency and ~Jith -the intensity selected to the proper value.
In each case the reaction proceeds from the focal spot back
up-stream to~Jard the laser source 16 until the intensity falls
below the minimum value.
su
The apparatus of FIGUI~ 2 differs from that of
FIGUE~ 1 primarily in the arrangement of the "laser source",
two sources being us~d in the ~IGURE 2 embodiment For
the most part, -the reactor of ~IGURE 2 is the same as for
5 FIGU~E~ 1 ana, therefore, the corresponding mechanical com-
- po~ents o~ ~:[GU~ 2 are designated by "primes" (')
Referri.ng now to FIGUE~ 2, tunab].e C02 infra-red
laser source 120 and tunahle ar40n io~ laser source 13Q direc-t
laser beams 134 and 136 through Brewster angle input ~Jindo~7s
140 and 142 to a common focal spot. The second input ~indow
142 is made from a s:ilica or~Vycor plate, transparent to UV
and visib:Le radiation while the remaining parts, desiyn~ted
with .subscrip-ts "a" and "b", of the two laser apparati are
similar to those described ~Jith reference to FIGUE~ 1. ~owev~r,
since Eewer IR pho-tons are required, sufficient interl.si.t:~ rflay
be obtained from the laser source 120 without use of a ~ocu.sin~
lens, ~hich is omit-ted, or by means of a CW C0~ laser witl
suEficient output intensity ~power per unit area).
~n operatio~, on proper frequency tuning, the las~r
source 120 excites the ~ibrational states in the U-organic
~ompound and the laser source 130 raises the electronic stat:e.s
sufEiciently -to dissociate the desired chemical bond attached
~lirectly to the U atom or to stimulate a chemical reaction.
Laser 130 may be replaced with a filtered H~ lamp or other
UV source oE su-fficient intensity to dissociate tlle desired
~ond in the cases that sufficient isotope selectivity is ob-
-tained through vibrational e~citati.on by irradiating ~ith
laser 120. ~ frcquency doubler (not shown~ may be used JitJ)
the tunab]e laser 130, depending upon the particular U--or~anic
Referring to FIGUE~, 3, laser sources 150 and 160
provide 1aSer beams 16~ and 16G to irradiate U-organics in th~
--~0--
frozen solicl state transported on a rihbon-like substrate
1-lO throu~}l a reaction chamber 172 bet~Jeen two adjacent ir-
radiation sectio}ls 174, 176 in ~Jnich the atmosphere may be
controlled. Laser 160 may be replacecl with a filtered Hg
lamp or o-ther UV source of sufficien-t intensity to dissociate
the de~ired bo~c~ in the cases that sufficient isotope selec:-
ti~Jity is o~tained through vibrational excitation by irradiatinc3
with laser 1~0. In the irradiation section 174, the sub-
strate 170, which may be thin stainless steel foil, i5 moved
from a take-off spool 180 onto a hollow, rotating first drum
1~2 ~hich is cvoled by liquid N~ injected -through a hollo~
jourrlal 186. ~ no~zle 1~8 sprays on U-organic such as LnUO2
where L is a rnacrocyclic lig~d such as superphthalocyanine mixed
with ~ mat~:ix such as 3 methylpentane in the molar ratio of
1/lO0. Al-ternati~Jely, the matrix may be selected from several
ases or oryanic liquids or gases which do not absorb photons
clt the laser frequencies used and which do not broaden the
U-or~anic vibrational absorption substantially. The fro~en
U-organi~ and matrix on the substrate 170 is irradiated by a
~0 beam 1~, from a CO~ laser source 150 transmitted throug}l a
Na~l window 19~ ~or ZnSe2) and a beam 16~ from a~ ar~on iorl
laser source 160 tnrouc~h a silica ~indow 202. An auxiliary
l~ns 20~ may be used to focus the beam 16~ onto the substrate
170 to :;rlcrease its intensity. The CO~ laser sourcc 150 is
tulled to the vibrational absorption frequency of the V-oryanic
and the arc3on laser source 160 is tuned to -the electronic ab-
sorption freqclency to ef~ect dissociation of the U-bond or to
ir!cluce a reartion .:ith a reactall~ such as C12 incorporated in
--2~-
v
the matrix. Other reactan-ts may be ~ICl, HI, etc. Alternative]y,
as in FIGURE 1, the CO2 laser source 150 may supply photons
of s~lfficient intensity to cause dissociation of a U-bond.
The limits oE such intensity are between 104 watts/cm2 and
5 11 watts/cm2. In this case the argon laser source is not
used. Subse~uently, the substrate 170 containing ~he reaction
products from irradiation and unreacted feedstock is moved
through a slit 208 in a section-separating partition 212 of
the chamber 172 over a second hollow drum 214 and onto a take-
up spool 216. The temperature of the drum 214 is controlled
by introducirlg a fluid from a heat exchanger, (not shown) through
a hollow journal 220. The temperature of the second drum 21
is adjusted -to raise the temperature of reaction products o
the U-organic on substrate 170 to cause a reaction with the
reac-tLve material to facilitate separation. This temperature
may be as low as a few degrees above the temperature of the
~irst drum 182 or may be higher to facilitate separation of
reaction products by their resulting volatility differences.
The atmosphere in the chamber sections 174, 176 may he con-
-trolled by evacua-tion through pipes 224, 226 and backfilling
throuyh tubes 22~, 230. Reac-tive material may be introduced
throuyh a tube 234 directly onto the moving substrate 170.
The substrate 170 is then removed from the take up spool 21
and modified U235- Grganic adhered thereto is chemically
separatea. Other U~organics may be used in all embodiments,
provided a furldarnental overtone or conbination vibrational ab-
sorption occurs in the 900-1100 cm CO2 laser output ran~3e.
Also, tunable laser sources 130 and 150 may be tunable dye
lasers with suitable frequency doublers (not shown), depending
on the electronic energy levels of the U-L bond.
--~2-
