Note: Descriptions are shown in the official language in which they were submitted.
3~ ~ ~
45,~32
~AC~GROUND OF THE INYENTIOM
Field of the Invention:
.
This invention relates to isotope separation
processes and more particularly to separation processes
based upon selective isotopic excitation.
Descriptîon of the Prior Art:
Selected isotopic species are useful ~or many
purposes including medical apparatus and treatment, tracer
studies of chemical and biological processes, and as target
materials and fuels for nuclear reactor application. Per-
haps the largest present utilization is for nuclear reactors,
which typically require, for example, fuel enriched in
uranium-235.
The system most widely used today for isotopic
separation is gaseous diffusion through a porous barrier,
which requires a large, complex, and costly cascading net-
work. More recently systems are being considered based upon
technologies such as distillation and photo-ionization in
the presence of magnetic and electric fields. Exemplary of
the latter are U.S. Patent No. 3,772,519 in the name of R.
H. Levy et al. and U.S. Patent No. 3,443,o87 in the name of
J. Robieux et al.
While such processes offer much promise for increas-
ing the efficiency of isotopic separation processes, it is
desirable to provide further alternatives, particularly with
a view toward practical application.
SUMMARY OF THE INVENTION
This invention provides additional alternatives to
existing and proposed isotope separation techniques. In
3 each of the preferred embodiments, an atomic or molecular
--2--
~k
r~
45,~32
isotopic mixture is selectively irradiated so as to select-
ively excite an isotopic species, preferably through photo-
excitation by a laser.
In one embodiment a molecular isotopic species is
selectively excited to a preselected internal energy and
exposed to positive ions of a predetermined ionization
energy. The sum of the internal and ionization energies is
sufficiently high to cause a dissociative charge transfer
process to occur, releasing as a fragment a positive ion
form of the desired isotope. The positive ion is then
separated from the balance of the mixture. Preferably, the
sum of the ionization energy and the internal energy of the
unexcited molecular species in the mixture is below the
threshold energy for a dissociative charge transfer process
between these constituents so as to decrease the probability
for competing processes. This method is particularly appli-
cable to the separation of uranium-235 in a mixture of
U 35F6 and U233F6.
In another embodiment the positive ion form of the
desired isotope, as summarized in the above paragraph, is
~,~ reacted with a negative ion form of the desired isotope to
form a neutral species which is separated from the balance
of the mixture. The negative ions are formed by addition-
ally exposing the selectively excited molecular species to
free electrons, thereby causing a dissociative electron
attachment process.
Another embodiment exposes the selectively excited
molecular isotopic species to another excited species such
that the sum of the excitation energies is sufficient to
cause a dissociative ionization process to occur, resulting
--3--
3~
45,832
in release of a positive ion of the selected isotope. The
positive ion form is then separated from the balance of the
constituents subsequent to the excitation transfer process
by conventional magnetic, electrostatic, electromagnetic or
chemical means, in addition to other separation means disclosed.
In other embodiments a near resonance charge
transfer process is utilized to separate isotopes in an
isotopic, preferably atomic mixture by exposing selectively
excited isotopes to positive ions. The sum of the isotope
excitation energy and the ionization energy is substantially
e~ual to the ionization energy of the selected isotope, and
the resulting resonance charge transfer process releases the
selected isotopes as positive ions. The process is advan-
tageously carried out in a discharge tube which creates an
ambipolar diffusion field transverse to the tube axis.
Under the influence of the field, the desired positive
isotope ions drift toward the tube periphery and can there-
fore be separated from other constituents within the dis-
charge tube. Separation can also be accomplished by flowing
the products of the process through a curved passage and a
magnetic field, thereby deflecting the desired ions to a
collection area separate from the collection area for the
balance of constituents.
Separation apparatus is also disclosed which can
advantageously be used for such isotope separation processes
and includes components positioned to enhance the reactions
and efficiency of the processes. A discharge device, such
as a pair of electrodes, acts upon a flowing gaseous species
to form the initial ions and electrons. The isotopic molecu-
lar or atomic species are injected into the flowing afterglow
45,832
region downstream of the discharge, mixing with the flowinggas, and are then selectively lrradiated by a ]aser. The
i flowing products are directed along a curved centrifuge
path, thereby being de~lected to dirfererlt degrees, and are
then collected by segmented areas. In those instances where
the desired isotope is in an ionic form, a magnetic field
directed perpendicular to the flow velocity assists in the
deflection, and hence enhances isotopic separation.
The advantages of the inventive embodiments are
substantial and include alleviation of the need for an
atomic beam as typical in other isotopic separation pro-
cesses and apparatus. The invention further provides a
convenient and practical means~ such as electrical dis-
charge, for provision of atomic or molecular ion species,
n e~a - ~bles
meta stable3 or chemical radicals not otherwise readily
~, available for photochemical or other types of isotopic
separation. Additionally, as a result of the discharge
afterglow, the mean electron energy can be provided over a
broad range, compatible with a large number of reaction
processes, by varying the point of injection of the isotopic
mixture downstream in the afterflow. Further, the energy
spread of the electrons in the discharge afterflow at a
selected downstream distance is smaller than that typically
obtained with an electron beam. Also, the electron density
obtainable is substantially higher than the density obtain-
able with an ordinary electron beam in the same energy
range. Complex electron beam formation apparatus is there-
for alleviated. Additionally, where the discharge may
provide photons of proper energy, a portion of the energy
3 required for the discharge can be extracted as a laser beam
--5--
3 ~ ~
~15,832
to be used for the selective excitation leading to enhance-
ment in the charge and/or mass difference in the selected
isotopic species, thereby increasing the overall system
efficiency for isotopic separation.
It will be apparent to those skilled in the art
that the various processes disclosed herein are not com-
pletely efficient. Accordingly, it is to be understood that
reference to the terms "separating", "collecting" and the
like refer to increasing the concentration or enrichment of
the selected isotopic species relative to the feed concen-
tration. Similarly, reference to phrases such as "the
balance of constituents" and the like refer to the various
fragments, species and reaction products decreased in con-
centration of the selected isotopic species. And, while the
examples provided relate to actions directed primarily
toward the desired isotopic species, it will also be appar-
ent that actions can similarly be directed toward an unde-
sired species and also provide isotopic separation.
BRIEF DESCRIPTION OF THE DRAWINGS
The advantages, nature and additional ~eatures of
the invention will become more apparent from the following
description taken in connection with the accompanying draw-
ings in which:
Figure l is a block diagram of an isotope separa-
tion process;
Figures 2 and 3 are schematic illustrations of
apparatus in accordance with embodiments of this invention;
Figures 4 and 5 are perspective schematics of
further apparatus in accordance with this invention; and
3 Figures 6 and 7 are schematic illustrations of
--6--
7o'~
45,832
additional embodiments of the apparatus of Figures 4 and 5.
DESCRIPTION OF TIIE PREFERRED EMBODIMENTS
According to the quasiequilibrium theory of uni-
molecular decomposition of polyatomic ions, (see, ~or ex-
ample, H. M. Rosenstock, M. B. Wallens~ein, A. L. Wahshaftig,
and H. Eyring, Proc. Natl. Acad. Sci. USA 38, 667 (1952); H.
M. Rosenstock, Adv. Mass Spectrom. 4, 523 (1968); M. L.
Vestal, in "Fundamental Process in Radiation Chemistry",
edited by P. Ansloos (Wiley, New York, 1968), pp. 59-118;
and A. L. Washshaftig, in "Mass Spectrometry", MTP Intnl.
, Review of Science, edited by A. Maccoll (Butterworths,
London, 1972), Physical Chemistry Series One, Vol. 5, pp. 1-
24), the fragmentation of such an ion is a function of its
total internal energy and is independent o~ the means by
which the ion state is arrived at prior to fragmentation.
For example, the dissociative charge transfer process can be
written as ~ollows
A + XY~ A + tXY ) ~ A + X + Y (1)
where A denotes a positive ion, XY is a molecular compound,
and the asterisk (*) denotes an excited state. The positive
ion can also be that of a molecular compound, AB .
The total internal energy of the parent polyatomic
ion (XY ) prior to decomposition consists of two parts: the
thermal or internal energy of the neutral molecule XY and
the ionization energy of A through transfer. The thermal
e-nergy and the transferred energy are equivalent in promot-
ing dissociation, since randomization of internal energy is
assumed to be extremely fast, on the order of a few hundred
vibrational periods, i.e., 10 12 sec., prior to dissociation.
Experimental evidence (W. A. Chupka, J. Chem.
--7--
3t7~4
l~5,832
Phys. 54, 1936, 1971; and C. Lifshitz and T. 0. Tiernan, J.
Chem. Phys. 59, 6143, 1~73) showed that the theory is essen-
tially correct. In particular, Lifshitz and Tiernan have
- found that fragmentation patterns of neopentane, 2-methyl-
pentane, 2,3-dimethyl butane and n-octane all exhibit a
- strong temperature dependence upon charge exchange with
mercury ions ~Ig+. They observed a factor of two or more
increase in the fractional abundance of the dissociated ions
by increasing the temperature of the neutral molecules (XY)
from 28C to 142C. The increase in the degree of fragmen-
tation of XY to form X is believed to be the result of
vibrational excitation of the molecule XY.
Accordingly, isotope separation can be accom-
plished by employing a dissociative charge transfer process
as exemplified in reaction (1) and modifying it so that
positive ions of the desired isotopic species can be created
selectively. This is performed by selective photo-excita-
tion of the desired isotopic species followed by dissocia-
tive charge transfer. Assuming for clarity that there are
only two isotopic species in the target gas, then by virtue
of the isotope shift in the absorption spectrum it is pos-
sible to selectively excite one isotopic species over the
other,
hz~ + lxy + 2xy~ (lxy) + 2XY, (2)
where h~ denotes the selectively exciting narrow band photo-
irradiation of chosen wavelength for isotopic species lXY
and X and X denote different isotopes of an element, and
so on throughout the specification.
Since the dissociative charge transfer process
depends strongly on the internal excitation of the target
--8--
,t$~
4 5 , 8 3 2
molecule, the isotopic ionlc species lX can be created
selectively via the following process
A+ + (lXY)* + 2Xy_~A + (lXY ) + XY
~ ~ + lx+ + y + 2~y (3)
Reaction (3) will occur if the following condition is met:
the sum of the ionization energy of A and the internal
energy of ~lXY) is above the threshold energy needed for
reaction ~1), while the sum of the energies of A and 2XY is
below the threshold.
An example of photon enhancement of reaction (1)
can be found in uranium hexafluoride (UF6) or sulfur hexa-
fluoride (SF6). It is known that the threshold energy for
SF5 from SF6 by electron impact is 15.7 + 3.8 eV, (see V.
H. Dibler and F. L. Mohler, J. Research Natl. Bureau Stand-
ards, 40, 25, 1948) and that the ionization potential for
argon is 15.68 eV, (R. C. Weast edited, "Handbook of Chem-
istry and Physics", The Chemical Rubber Co., Cleveland,
Ohio, 1968 p. E-59). It has also been found that at room
temperature, the ~3 (943 cm 1) mode of vibration of SF6 is
in resonance with the P(20) to P(30) lines, (and preferably
the P(26) to P(30) lines) (~10.6~ m) of the carbon dioxide
laser. It is therefore expected that the following reactions
will occur:
h Y(0.117 eV) + SF6 ~(SF6) (4)
where the SF6 is a gas at room temperature and
Ar (15.68 eV) + (SF6) ~ SF5 (15.7 eV) + F (5)
It will be recognized that reaction (5) is a resonance
process. Since there is an isotope shift in the absorption
spectrum of 32SF6 and 34SF6, then isotope separation of 32S
from 3 S is possible by selective excitation of the desired
_g_
3'~4
1~5, 832
isotopic species. SF5 is a stable ion and can be .separated
and collected by conventional magnetic, electrostatic,
electromagnetic, or chemical means, as well as by apparatus
discussed hereinafter.
A block diagram of the exemplary dissociative
charge transfer process for isotope separation is shown in
Figure 1. Pure argon gas is introduced into the ionization
zone 1 where the argon gas is ionized by either dc or ac
discharge or by other means known in the art. The ionized
argon gas flows into a reaction zone 2 where the isotopic
molecu~Lar mixture of SF6 gas is injected from a gas source 3
at a controlled rate based upon the argon ion concentration,
the gas flow rate and the intensity of a continuous wave
(cw) C02 laser 4. For room temperature SF6 gas, the C02
laser 4 is operated on the P(20) to P(30), and preferably
the P(26) to P(30) transitions of the C02 (001-100) band,
- whereby 32SF6 will be selectively excited. The arrangement
is preferably chosen such that the density ratio of Ar to
34SF6 in the reaction zone 2 is larger than the ratio of the
cross section of excitation transfer (reaction (9)) to that
of dissociative charge transfer (reaction (3)), as shown in
(12). The dissociated ionic species 32SF5 from the reac-
tion zone is then directed through an ion separator 5 where
the positive ions are drawn in a direction different than
the balance of constituents by electrostatic force resulting
in isotope separation. In another mode of separation the
desired isotopic species 32SF5 is neutralized through
volume recombination with either electrons or negative ions.
The neutralized 32SF5 is then condensed out on the walls of
a condenser 6. The temperature of the condenser wall is so
--10--
~3.,~3 ~l~3a~
45,832
adjusted such that 32S~5 is the selectlve condensate.
A relatively si}nple embodiment for utilizing a
selective dissociative-charge-transfer process for isotope
separation is illustrated in ~ig. 2. Neutral gas A is fed
into a flowing afterglow tube 10 fro-rn one end. The tube 10
includes three basic regions. Gaseous discharge is estab-
lished in region "a" where electrons and ions A are pro-
duced. The discharge can be accomplished through any of a
number of means such as by plates 12 which set up an elec-
tric field in region "a". Electromagnetic wave, directcurrent, alternating current and microwave fields, among
others, can also be utilized. The electrons and ions pro-
duced are carried downstream by the flowing gas. At an
appropriate point downstream, region "b", gaseous mixkure
lxy + 2x~ is introduced into the flowing plasma through an
inlet 14 and simultaneously radiation of proper frequency,
for example, P(20) to P(30) lines of the CO2 laser, is used
to selectively irradiate the mixture of S~6. The radiation
is here shown as coming from a laser 16. The stable posi-
tive product ions lX , produced in accordance with reaction(3), can be collected further downstream in region "c",
through mechanical, chemical or the electrical process
shown. The system illustrated has many degrees of freedom
through adjustment of such parameters as the gas pressure
and temperature, flow velocity, discharge intensity, iso-
topic mixture feed density and laser intensity.
Electrons produced in the discharge also appear in
the flowing afterglow. By proper location of the injection
point of the isotopic mixture and hence selecting the proper
energy of the electrons in the flowing afterglow, a selective
--11--
45,832
dissociative electr-on attachment process can also be accom-
plished:
e + (lxy~ + 2xy-~lxy~~* + 2xy
_~lX_ + y + 2xy (6)
The negative product ions lX produced in accordance with
reaction (6) and the positive product ions lX produced in
accordance with reaction (3) will recombine readily. For
example, in the case of sulfur hexafluoride
SF5 + SF5 ~2SF4 + 2F (7)
Accordingly, a simplified separation process can be utilized
in region "c", such as cooling the reaction products to
condense the enriched SF4 onto a removal surface.
For isotope separation of a uranium mixture,
such as U235F6 and U238F6, similar dissociative charge
transfer and dissociative electron attachment processes can
be used. The threshold energy at which UF5 is formed from
UF6 is 15.5 _ 0.7 eV (J. R. White and A. E. Cameron, Phys.
Rev. 71, 907, 1947). The argon ion is a preferred candidate
for the process, although other ions can be utilized. As
potential candidates for the primary positive ions A for
any dissociative charge transfer process for isotope separa-
tion, a whole spectrum of atoms and molecules with ioniza-
tion potential ranging from as low as 3.87 eV (for cesium)
to as high as 24.46 eV ~for helium) exist.
The processes taught can be Eurther extended to
include a selective dissociative excitation transfer process
for isotope separation. In reaction (3? a long-lived meta-
stable excited species A is substituted for the positive
ion A :
A + ( XY) + XY~ A + X + Y + e + XY (8)
l~ere, the sum of the excitation energies of the species A
-12-
~ 3~8~ ~5,832
and (lXY) must be sufficient to cause reaction ~) to
occur.
In any selective photon excitation process for
isotope separation, a competing process to reduce the effect-
iveness and overall efficiency of separation is the unde-
sired excitation transfer, such as
(lxy)~ + 2xy~ lxy + (2XY) (9)
The cross section of this process has been found to be inthe range of 10 14 to 10 15 cm2. However, the dissociative
charge transfer process, reaction (3), is also expected to
be large where near energy resonance occurs, as illustrated
in the example of Ar + (SF6) . In order to achieve a high
separation factor in a practical device such as illustrated
in ~ig. 2, the selective dissociative charge exchange rate
of reaction (3) must be higher than the excitation transfer
rate of reaction (9). This criteria is satisfied if
[A ] ~ XY ] QDCT Vr1~[ XY ] [ XY] QXT Vr2, (10)
where the brackets represent the particle density of the
indicated species within a given reaction volume; QDCT and
QXT are respectively the cross sections of the dissociative
charge transfer process reaction (3), and the excitation
transfer process reaction (9); and vr1 and vr2 are the
relative velocities of the colliding partners in reactions
(3) and (9), respectively.
The velocities are substantially equal,
Vrl ~ Vr2, ( 11 )
and accordingly, a large separation factor can be achieved
if
[A ] > QXT (12)
[ 2XY ] QDCT
--13--
45,832
Accordingly, once the cross sectlons QDCrll and QXT are accur-
ately known, one can control the gas A flow rate, the dis-
charge condition and the neutral lxy + 2XY injection rate so
that reaction (12) is satisfied. Apparatus disclosed here-
inafter, particularly with respect to Fig. 5, can be util-
ized for carrying out the discussed reactions.
It has been found that atoms in an atomic isotopic
mixture, such as U 35 atoms in a mixture including atoms of
U 38, can be selectively ionized by a resonance charge
transfer process following selecti~e excitation. The physi-
cal separation of the ions from the balance of constituents
of the process is preferably achieved by apparatus utilizing
radial ambipolar diffusion techniques (P. C. Stangeby and J.
E. Allen, Nature 233, 472, 1971) or a combination of elec-
trostatic and magnetohydrodynamic effects. This process
advantageously eliminates the need for provision of an
atomic beam of atoms, such as uranium atoms, as typically
required.
It is known (J. B. Hasted, Advances in Atomic and
Molecular Physics, Edited by D. R. Bates and I. Estermann
(Academic Press, New York, 1968), p. 237) that the charge
transfer cross section of
A + B~ A + B +~E, whereQ E is the
energy released (13)
is very large ( 10 13 cm ) if QE~O. The neutral species B
in reaction (13) can be either in the ground state or in the
excited states. For the exemplary separation of isotopes of
uranium, U235 atoms are selectively excited by, for example,
monochromatic light such as dye laser radiation:
3 h~ + U235 + U233_~U235~ + U238 (14)
-14-
45,832
The excited atoms U235 are then ionized by res-
onance charge transfer wlth ions A ,
A+ + U235* + U238-~A + U235+ + U 3 . (15)
As a more specific example,
~ 29 3A~ ~ U235 + U238~ U235 (2.328 eV) + U , ~16)
and
Cs (3.87 e~) + U235 (2.328 eV)~ Cs + U235+ (17)
It is believed that the ionization potential of uranium is
6.22 + 0.5 eV ~see D. W. Steinhaus et al., Present Status of
the Analyses of the First and Second Spectra of Uranium (UI
and UII~ as Derived from Measurements of Optical Spectra,
Los Alamos Scientific Report LA-4501, October 1971) and the
5329.3 A radiation and the Cs ions in reactions (16) and
(17) are chosen for illustration only, many other wave-
lengths and ions being equally applicable. Other wave-
lengths for selective excitation of U235 are well known.
The objective for a workable atomic charge transfer reaction
for uranium is that the sum of the excitation energy of U235
and the ionization energy of A is substantially equal to,
but no less than, the ionization energy of uranium 235. It
is to be understood that while the exemplary reactions
relate to atomic isotopic mixtures, the teaching is appli-
cable to molecular isotopic mixtures.
One embodiment of apparatus for carrying out the
disclosed process is shown in Figure 3, and another in
Figure 4. While the exemplary cesium-uranium reaction is
discussed, the process and apparatus are not to be construed
as so limited.
In Fig. 3, cesium and uranium vapor are caused to
3 flow into a discharge tube 20 through an inlet 22. A few
-15-
7~ ~
45,832
Torr of a noble gas can advantageously be added to act as a
bufrer and maintain a stable glow discharge. Cesiurn atoms
are readily ionized due to their low ionization potential.
At the same time the discharge tube is irradiated with
radiation of a predetermined frequency, such as monochrom-
atic light so that U235 is produced and reacts with Cs to
form U235 according to reaction (15). The U235 ions drift
toward the walls of the discharge tube under the influence
of an ambipolar diffusion field which is formed by the
discharge reaction. The enriched fraction can then be
collected downstream as shown.
Figure 4 shows apparatus particularly useful for
high flow rates. The atomic uranium mixture is injected
through ports 26 which supply the mixture downstream of a
discharge zone 28 into a flowing cesium afterglow. Mono-
chromatic radiation h~ is also introduced into the flowing
medium in the area where uranium is injected. The U 35
ions created by charge transfer are separated from the
mixture by an electrostatic-magnetohydrodynamic enhanced
nozzle technique as shown. This includes flow of the reac-
tion products at a velocity v through a curved centrifuge
passage or zone 30 in the presence of magnetic field B32
acting in the direction perpendicular to the velocity shown.
The various products, under the influence of the curved
passage and the magnetic field, are deflected along differ-
ent flow paths and collected in different segmented areas
34, 36, 38.
As illustrated above, most photon-assisted physi-
cal or chemical processes for isotope separation require, in
addition to the isotopic mixture, electrons, ions or neutrals
-16-
~.Z3~84 ~5,~32
in some preferred state. For exam~le, the photon-enhanced
dissociative electron attachment process
h~ + lX~ + 2xy ~ (lxy~* ~ 2XY (2)
and
e~ + (1XY)* ~ lX- + Y, (1~), (6)
requires a well defined range of electron (e ) energies.
Similarly, the dissociative charge transfer process
h~ + lxy + 2xy ~ (lxy)* ~ 2xy (23
and
A~ + (lxy)* + 2xy ~ lX~ + Y + A 1 2XY (3)
requires an ion (A+) with appropriate ionization energy.
And, the photo-chemical process
h~ + 1X ~ 2X ~ 1X* + 2X(19), (14)
and
AB + 1X* ~ 2X ~ 1XB ~ A + 2X (20)
or
B + lX* + 2X ~ 1XB + 2X (2~)
requires neutrals AB or B which may be chemical radicals
produced in a discharge.
The arrangement disclosed and illustrated in
Figure 5 not only provides the capability to perform all
of these processes, but also provides distinct operational,
cost and efficiency advantages as compared to prior art
arrangements. The present system for isotope separation
combines the principle of aerodynamic mass separation and
v x B drift of a moving charged particle (velocity v) in a
-17-
8 4
45,832
magnetic field, B. In addition, the teaching of the present
invention utilizes flowing afterglow for positive ion pro-
duction for a selective-dissociative charge transfer process
for isotope separation. The electrons produced in the
discharge can be used for space charge neutralization or
negative ion production for further improvement of effi-
ciency of isotope separation. An optical cavity can also be
created in the discharge zone for further improvements in
overall efficiency.
As shown in Figure 5, flowing gas A (or AB~,
enters the passage 40 from an inlet area 42. A glow dis-
- charge is struck in a discharge zone 44, for example, by
discharge means such as a pair of electrodes 46. The elec-
trons for reaction ~18) or A ions for reaction (3) are
carried by the flow downstream where the mixture of isotopes
lXY and 2XY or lX and 2X is injected into the stream. At
the same time, these constituents are irradiated with a
narrow line radiation (h~), such as from a tunable dye
laser~ The selectively created isotopic species X from
reaction (18), or lX+ from reaction (3) then enters an
aerodynamic mass separation or curved centrifuge section 48
of the system with a flowing velocity v.
The aerodynamic mass separator 48 employs the
centrifugal force upon particles traversing a curved path
and takes advantage of the enhanced mass difference between
isotopic species as a result of the effected reaction pro-
cess. The heavier isotopic species 2XY traverses a flow
path to the outer channel 38, formed by fingers 50, while
the lighter species lX , or X , prefers an inner channel 36
3 for exit and collection, resulting in separation.
;: -18-
378~
45,832
The mass separation can be enhanced further by
magnetohydrodynamic means since lX , or X , is a charged
particle for some period of time subsequent to formation.
A dc magnetic field, B, is applied transverse to the con-
stituent flow v such that a Hall field v X B is developed
across the flow passage 40. Thus the charged isotopic
species under the influence of this field are caused to
deflect toward the inner wall 52 of the passage 48, thereby
enhancing the mass separation.
In the limiting case of no collisions, the ion
drift velocity vl across the magnetic field and the drift
distance dl due to the Hall effect at the end of the cen-
trifugal section of length 1 are
vl = MBl in cm/sec (22)
and
d = eBl_ in cm, (23)
respectively. Here Mi is the mass of the ion formed from,
for example, selective dissociative charge transfer, e is
the charge of the ion in esu; 1 is the length of the centri-
fugal section, v is the flowing gas velocity in cm/sec; andB is the transverse magnetic field in gauss. In the event
collision of the ionic species with the buffer gas occurs,
the drift velocity and distance can also be predetermined.
The curvature and length of the centrifugal section together
with other parameters of the arrangement such as exit channel
widths can be tailored to achieve optimum isotope separation.
A practical example of utilization of the present
arrangement is an application to uranium or sulfur isotope
separation using, for example, SF6 (or UF6) gas. Argon gas
3 is introduced into the device at inlet 42. The gas is
--19--
~ A
~-~ ~J ~ 45,832
ionized while passing through the pair of electrodes 46
where an adequate field, either ac or dc, is maintained.
Downstream of the discharge zone about 100 ~sec in the
afterglow region, an isotopic mixture of SF6 gas is injected
into the ionized gas stream. Simultaneously a cw C02 laser
operated on the P(20~ to P(30~ and preferably the P(26) to
P(30) transitions of the C02 (001-100) band is beamed at
the injection zone so that the 32SF6 isotope is selectively
excited. The intensity of the laser beam is such that a
high concentration of 32SF6 is excited to the upper vibra-
tional states where dissociative charge transfer with Ar
ions is effective. The mixture of reaction products then
CUt-";tl ~ear
B flows into the _ region where both centrifugal
force and v X B force act upon the charged particles.
Spatial separation of molecules and other species of dif-
ferent mass is achieved and enrichment of the particular
isotopic species 32S is obtained by proper location of the
exit channel.
It will be apparent to those skilled in the art
that the disclosed arrangement provides a convenient and
practical means, such as electrical discharge, for provision
of atomic or molecular species or chemical radicals not
otherwise readily available for photochemical or other
isotopic separation processes. Additionally, as a result of
the discharge afterglow, the mean electron energy can be
provided over a broad range, compatible with a large number
of species, by varying the point of injection of the iso-
topic mixture downstream in the afterflow. The energy can
range from, for example, 1 eV to 0.03 eV. Further, the
energy spread of the electrons in the afterflow at a selected
-20-
~ 4 45,~32
downstream distance is smaller- than that typically obtained
with an electron beam. Also, the electron density obtain-
able is in the range of 10~ to 1011 cm 3, which is substan-
tially higher than the density obtainable with an ordinary
electron beam in the same energy range. Complex electron
beam formation apparatus is therefor eliminated.
Additional arrangements can also be advantageously
utilized to further benefit the disclosed system and provide
increased system efficiency. Figures 6 and 7 illustrate
arrangements where the energy input to the discharge, typi-
cally electrical energy, can be partially extracted as laser
energy and used, respectively, directly or indirectly for
the separation process. In both of the figures the discharge
area is modified, such as by the addition of mirrors 52, to
form an optical cavity 54. As shown in Figure 6, the result-
ing laser beam can then be directed, through additional
mirrors 56, to perform the irradiating function where proper
photon wavelengths are obtained from the discharge. As
shown in Figure 7, the resulting laser beam can also be
utilized to pump another laser, such as a dye or solid state
unit, which performs the irradiating function.
Further modifications and additions are possible
in view of the above teachings. It therefore is to be
understood that within the scope of the claims, the invent-
ive embodirnents can be practiced other than as specifically
described.
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