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Preparation of thin targets with the isotope separator Paris
Nuclear Instruments and Methods 186 (1981) 7-11 North-Holland Publishing Company
PREPARATION OF THIN TARGETS WITH THE ISOTOPE SEPARATOR PARIS R. M E U N I E R , J.L. D A B A N - H A U R O U , M. S A L O M ~ Laboratmre Rer~ Bernas du Centre de Spectrom~tne NuclJmre et de Spectrom~tne de Masse, B P No I, 91406 Orsay, France
and F. N I C K E L GSI Darmstadt, Postfach 110541, 6100 Darmstadt, F R G
A short review Is given of recent ISOtope separations at the separator pARIS for the preparation of thin target layers of highly ennched isotopes of thicknesses up to the region of mg cm-2 The preparation technique makes use of a special collecting system located behind the separahon magnet By use of electrostatic devices the separated beam is focused and permanently deflected in order to avoid contamination by neutrals. It is fast-scanned over two dimensions for the production of homogeneous layers on large surfaces The beam ts decelerated to 70 eV before striking the thin backing foil This system was improved to obtain an increased target yield by producing a smaller beam spot m the target region.
1. Introduction For many experiments in the field of nuclear and atomic physics with heavy-ion accelerators there is a d e m a n d for thin targets with high isotopic enrichment. These targets have thicknesses in the region of mg cm -2 with surface areas of approximately I cm 2 and isotopic puffties above 99%. In the case of low natural isotope abundance of the required target nuclei, it is useful to prepare the target directly with an electromagnetic separator. Using the latter method, the usual technique of evaporation (or others) using expensive enriched isotope material can be avoided. Thus a source of material loss and target impurity is suppressed. When the desired highly enriched isotope material is expensive or not commercially available, direct target production with a separator is especially attractive.
2. The isotope beam produced by the separator PARIS
respect to contaminations by neighbouring isotopes. This requires a sufficiently large dispersion. The separator P A R I S [1] has a dispersion of 1500 mm A M / M and provides, in the focal plane, isotope beams with an energy of 40 keV. The cross contamination by neighbouring isotopes is very small as was indicated by measurements [1] of an 4°At beam profile: at a distance of 5 mm from the beam center the relative current density drops below 10-3. The obtained isotope beam current depends on the chemical properties of the element and on the isotope abundance. The classical ion source [2] used at the P A R I S separator for example produces an isotope beam current of approximately 0 . 5 m A . This value is normally obtained for isotopes with initial abundances larger than 50%. In the focal plane the beam current distribution has horizontal and vertical half widths of approximately 0.5 x 5 mm 2.
3. The collecting system
To be effective in the preparation of thin targets with an electromagnetic separator, a sufficient isotope beam current is required. Further the beam should be pure especially with
For target preparations a collecting system behind the focal plane of the separator magnet is useful in order to obtain a proper deposit of the isotopes on thin backing foils (see e.g. ref. [3]). The system we used is shown schematically in fig.
0029-554X/81/0000-0000/$2.50 O North-Holland
I. STABLE ISOTOPE SEPARATION
8
R Meunler et al / Preparation of thm targets
i
q
I
I
i
t I ~,,
i i i
q
t__l i
I
:--) U R
separated
" .
+"=
~,0 keY beam
defining
L 2
.
.
.
/ .
.
.
.
.
.
.
.
.
.
.
.
.
+
.
"'--..~.
' ii
]!
/
quadrupote
~r~
(/
target
slit
doublet
ro+.atab,e
,! L'--._~" target holder
deflecting condensor
"'J"l scanning condensors
- 1 kV retardation system
F i g 1. S c h e m a t t c d r a w i n g o f t h e c o l l e c t i n g s y s t e m or 670 ram.
The distances are
1. Behind a defining slit with dimensions adjusted to the beam extension in the focal plane, two electrostatic quadrupoles provide beam focusing. Following the quadrupoles, an electrostatic condenser permanently deflects the beam so that neutrals created before the condenser cannot reach the target position. With two additional condensers a horizontal and vertical fast electric beam scanning can be utilized to prepare homogeneous target layers with large surfaces. At the end of the collecting system, target backing foils are placed on a rotatable target holder with 6 target positions. Just in front of the target, the 40 keV beam is decelerated to 70 eV. Thus self-sputtering of the growing target layer in the beam is strongly reduced as well as the energy dissipation of the beam in the normally very thin backing foils. The deceleration is provided by a grounded circular diaphragm placed 27 mm in front of the target, which has a potential of 70 V below the source potential. Between the grounded diaphragm and the target another diaphragm at -1000 V repels electrons coming from the beam. Thus the measured integrated target current corresponds within a sufficient accuracy to the amount of
L~ = 4 0 7 r a m , It = 12 = 130 m m , D = 15 m r n , L2 = 1200 r n m ,
isotopes deposited. The geometry of this retarding system corresponds to that described by Freeman et al. [4]. As the system is compact and as the beam divergence in the target region is small (approximately 0.5°), the widening of the beam cross section by the decelerating field remains small. For normally obtained beams, the increase of the beam diameter with deceleration is approximately 25% compared with the unaffected beam. Thus the system reduces the energy of the beam from 4 0 k e V to 70eV, changes the spot size from l x 10mm 2 to approximately 13x 6 m m 2 (value for lower currents) and allows scanning over the target surface. This low energy beam is also free of neutrals and electrons.
4. Improvement of the collecting system An extended series of thin targets has already been produced at the separator P A R I S with the collecting system described above. Nevertheless an improvement of the system seemed to be necessary in order to produce a smaller beam spot at the target. The cheap and easily con-
R. Meunier et al /Preparatton of thin targets
structed system of electric fields has the disadvantage of considerably increasing the beam size in the target region for higher beam currents. This increase in size is due to the destruction of space charge neutralization in the electric fields, where the electrons necessary for charge compensation are soon extracted from the ion beam. In fig. 2 the smallest beam cross section at the target obtainable by varying the voltages at the two quadrupoles is shown as a function of a xenon beam current. Considering preparations of targets with surfaces of approximately 1 cm 2, it can be seen from curve (a) in fig. 2 that the useful beam current decreases rapidly for total currents larger than 100 ~tA. In order to decrease the spot size at the target, a simple alteration was made to the collecting system. From the ion optical point of view the lay-out of the system was not optimized for target preparation purposes, as it was constructed and used for other reasons. Thus the distance L2 between the end of the quadrupoles and the target was larger than desirable. So we reduced this length as much as possible. Ion optical calculations of the system were made using the formalism of Brown [5]: the beam waist at the target was determined from the two dimensional o'(1) matrix given by the equation o-(1)= Rcr(0)R T. H e r e o-(1) is the trmatrix at the target (for the definition of or see ref. [5]). tr(0) is the corresponding matrix at the
9
entrance of the system containing the starting conditions of the beam. R is the conventional overall transfer matrix of the system, which is simply obtained by multiplying step-by-step the single transfer matrices of the components: drift length L~, first quadrupole with effective length 1~, drift length D between the quadrupoles, second quadrupole with effective length 12, and drift length L2. In the former system with L2 = 1200 mm the calculations of the beam waist at the target gave a result of 10.2 x 5.4 mm 2. This is in good agreement with the measured value of 1 0 x 4 . 5 m m 2 for low beam currents without retardation and space charge effects (see fig. 2a). The calculations with L2 = 670 mm (new shorter system) showed that it was possible to obtain a spot size of 6.5 x 2.1 mm 2. The measurements of the beam cross section at the target with the shorter L2 are represented for xenon beams by the curve (b) in fig. 2. For low currents the beam spot size without retardation system was 4.3 x 2.5 mm 2, that is somewhat smaller than the calculated value. Besides the approximately 5 times smaller beam spot for very low currents below 30/zA, the major advantage of the L2-modification is the relatively slow increase of the spot size with increasing total beam current. Thus the target preparation time is now considerably reduced. For instance for total beam currents in the region of 300/,tA and target areas of approximately 1 cm 2 the preparation time has been divided by almost a factor of 4.
(
[ram~] 5. Examples for the production and use of enriched targets
300 200 100 ~ a ~ 0
100
200 IkA]"-"
Fig 2 M e a s u r e d (full c u r v e ) a n d c a l c u l a t e d ( b r o k e n line) b e a m cross s e c t i o n S.~. at t h e t a r g e t as a f u n c t i o n of the b e a m c u r r e n t I for X e b e a m s . T h e c u r v e (a) c o r r e s p o n d s t o L2 = 1200 m m , the c u r v e (b) to L2 = 670 m m (see t e x t )
There is a variety of motivations underlying the need for isotopically pure target material used in experiments with heavy ions. The Coulomb excitation experiment performed by B o k e m e y e r et al. [6] may serve as an example. 5.1 MeV/u 2°spb projectiles were used with ~ D y targets produced at K F A Jiilich with the electromagnetic isotope separator S I D O N I E II [7] by sputtering techniques. An enrichment larger than 98% was reached for the lSaDy targets, the natural abundance being 0.1%. The observation of Yrast states up to I ~ = 20 + through the detection of low-intensity gamma rays was posI STABLE ISOTOPE SEPARATION
R Meunier et al / Preparatton of thin targets
10 Table 1 Isotope
Thickness (mg cm -2)
Backing
Enrichment of charge material
Comment
(%) 12C 34S ~S 58N1 6aN1 7°Ge ~Mo 14°Ce x48Sm l~Dy 162'164Dy t76 ~77.17s.179Hf 238U
0 08 0 1 0 001 0 1-0 0 1-0 1 02 0 1 0 2-0 0 1 0 1 0 2-0 1
4 4
4
4
1 mm Ta 30 ~g cm -2 C 30 #g cm 2 C 50/.tg cm 2 C 50 g g cm -2 C t 0 1 mg cm 2 C 33 ~tg cm -2 C 30 ~g cm -2 C Au fod 5 mg cm -2 Fe 5 mg cm 2 Fe 33 /~g cm -2 C 4 0 1 mg cm -2 C
Nat Nat Nat Nat 96 5 Nat Nat Nat 99.81 10 Nat Nat >99 3
sible by reducing the admixture of heavier dysprosium isotopes in the targets. More recently, a rising demand for directly deposited target layers with high isotope enrichment has been made, because a reduction of the admixed carbon in the target, caused by the sputtering technique mentioned above, was preferred. A large number of isotopically enriched targets were prepared by the direct deposition method at the separator P A R I S during 1979/80. Table 1 gives a list of the targets produced. Normally the targets have surface areas of about 1 cm 2 and an isotopic enrichment larger than 99%. As indicated in table 1, for 148Sm a higher enrichment was demanded and obtained. It should be mentioned that the enrichment of 99.987% for 148Sm means only that the contamination by 147Sm is less than 0.013%, as measured at one samarium target with a mass spectrometer. The overall contamination of the samarium targets by numerous other isotopes as for instance IH, 14N, 160 could be larger than this. The example of 58Ni shows that there is frequently a danger of target contamination by isobaric isotopes or compounds, here for instance SSFe. Thus often a specific ion source chemistry is needed to get a relatively clean beam of only one element. For some elements there are difficulties in producing larger target thicknesses on very thin carbon backing foils. For example it was a prob-
Reduction of 13C
Impurity of SSFe
>99 987% ~48Sm
Targets > 0 4 mg cm 2 deform 60 targets
lem to produce targets with more than 0 . 4 m g c m -2 of hafnium on 33/xgcm -2 carbon backings. Due to internal stress in the freshly built-up hafnium layers, the foil bent when this critical thickness was reached, and often broke afterwards. The use of thicker carbon foils or other more stable backing foils seems to be necessary for a simple solution to this problem. The enriched 176Hf target was used in a recent experiment by Schmidt et al. [8] investigating 4°Ar induced fusion reactions and the behaviour of the fission barrier in the region of the closed neutron shell N = 126. Here as in other fusion cross-section measurements with heavy ions, high isotopic enrichment is an important prerequisite in view of the strongly competing evaporation channels from heavier compound nuclei formed due to heavier isotopic contaminants in the target. One of us (FN) acknowledges with pleasure the kind hospitality of the Laboratoire Ren6 Bernas, Orsay. This work was performed in part within a contract between IN2P3 Paris and GSI Darmstadt.
References [1] J. Camplan, R Meumer and C Fatu, Proc 8th EMIS Conf., Skovde (1973) p 186. [2] J L Sarrouy et al., Nucl Instr and Meth 38 (1965) 29
R Meumer et al / Preparation of thin targets [3] E Hechtl, Nucl Instr and Meth 139 (1976) 79, K Freltag et al, Nucl. Instr and Meth 139 (1976) 83 [4] J H. Freeman et al, Nucl Instr and Meth 135 (1976) 1 [5] K L. Brown, Stanford Linear Accelerator Center, Stanford, CA, SLAC-Report no 91 (1973)
11
[6] H Bokemeyer et al, J Phys Soc Jap. 44 (1978) 610 [7] H Ihle, U Kurz and R Wagner, Internal Report, Institut fur Nuklearchemle der K F A Juhch (January 1974) [8] K.H Schmtdt, GSI Darmstadt, pnvate commumcanon (1980)
I. STABLE ISOTOPE S E P A R A T I O N
PREPARATION OF THIN TARGETS WITH THE ISOTOPE SEPARATOR PARIS R. M E U N I E R , J.L. D A B A N - H A U R O U , M. S A L O M ~ Laboratmre Rer~ Bernas du Centre de Spectrom~tne NuclJmre et de Spectrom~tne de Masse, B P No I, 91406 Orsay, France
and F. N I C K E L GSI Darmstadt, Postfach 110541, 6100 Darmstadt, F R G
A short review Is given of recent ISOtope separations at the separator pARIS for the preparation of thin target layers of highly ennched isotopes of thicknesses up to the region of mg cm-2 The preparation technique makes use of a special collecting system located behind the separahon magnet By use of electrostatic devices the separated beam is focused and permanently deflected in order to avoid contamination by neutrals. It is fast-scanned over two dimensions for the production of homogeneous layers on large surfaces The beam ts decelerated to 70 eV before striking the thin backing foil This system was improved to obtain an increased target yield by producing a smaller beam spot m the target region.
1. Introduction For many experiments in the field of nuclear and atomic physics with heavy-ion accelerators there is a d e m a n d for thin targets with high isotopic enrichment. These targets have thicknesses in the region of mg cm -2 with surface areas of approximately I cm 2 and isotopic puffties above 99%. In the case of low natural isotope abundance of the required target nuclei, it is useful to prepare the target directly with an electromagnetic separator. Using the latter method, the usual technique of evaporation (or others) using expensive enriched isotope material can be avoided. Thus a source of material loss and target impurity is suppressed. When the desired highly enriched isotope material is expensive or not commercially available, direct target production with a separator is especially attractive.
2. The isotope beam produced by the separator PARIS
respect to contaminations by neighbouring isotopes. This requires a sufficiently large dispersion. The separator P A R I S [1] has a dispersion of 1500 mm A M / M and provides, in the focal plane, isotope beams with an energy of 40 keV. The cross contamination by neighbouring isotopes is very small as was indicated by measurements [1] of an 4°At beam profile: at a distance of 5 mm from the beam center the relative current density drops below 10-3. The obtained isotope beam current depends on the chemical properties of the element and on the isotope abundance. The classical ion source [2] used at the P A R I S separator for example produces an isotope beam current of approximately 0 . 5 m A . This value is normally obtained for isotopes with initial abundances larger than 50%. In the focal plane the beam current distribution has horizontal and vertical half widths of approximately 0.5 x 5 mm 2.
3. The collecting system
To be effective in the preparation of thin targets with an electromagnetic separator, a sufficient isotope beam current is required. Further the beam should be pure especially with
For target preparations a collecting system behind the focal plane of the separator magnet is useful in order to obtain a proper deposit of the isotopes on thin backing foils (see e.g. ref. [3]). The system we used is shown schematically in fig.
0029-554X/81/0000-0000/$2.50 O North-Holland
I. STABLE ISOTOPE SEPARATION
8
R Meunler et al / Preparation of thm targets
i
q
I
I
i
t I ~,,
i i i
q
t__l i
I
:--) U R
separated
" .
+"=
~,0 keY beam
defining
L 2
.
.
.
/ .
.
.
.
.
.
.
.
.
.
.
.
.
+
.
"'--..~.
' ii
]!
/
quadrupote
~r~
(/
target
slit
doublet
ro+.atab,e
,! L'--._~" target holder
deflecting condensor
"'J"l scanning condensors
- 1 kV retardation system
F i g 1. S c h e m a t t c d r a w i n g o f t h e c o l l e c t i n g s y s t e m or 670 ram.
The distances are
1. Behind a defining slit with dimensions adjusted to the beam extension in the focal plane, two electrostatic quadrupoles provide beam focusing. Following the quadrupoles, an electrostatic condenser permanently deflects the beam so that neutrals created before the condenser cannot reach the target position. With two additional condensers a horizontal and vertical fast electric beam scanning can be utilized to prepare homogeneous target layers with large surfaces. At the end of the collecting system, target backing foils are placed on a rotatable target holder with 6 target positions. Just in front of the target, the 40 keV beam is decelerated to 70 eV. Thus self-sputtering of the growing target layer in the beam is strongly reduced as well as the energy dissipation of the beam in the normally very thin backing foils. The deceleration is provided by a grounded circular diaphragm placed 27 mm in front of the target, which has a potential of 70 V below the source potential. Between the grounded diaphragm and the target another diaphragm at -1000 V repels electrons coming from the beam. Thus the measured integrated target current corresponds within a sufficient accuracy to the amount of
L~ = 4 0 7 r a m , It = 12 = 130 m m , D = 15 m r n , L2 = 1200 r n m ,
isotopes deposited. The geometry of this retarding system corresponds to that described by Freeman et al. [4]. As the system is compact and as the beam divergence in the target region is small (approximately 0.5°), the widening of the beam cross section by the decelerating field remains small. For normally obtained beams, the increase of the beam diameter with deceleration is approximately 25% compared with the unaffected beam. Thus the system reduces the energy of the beam from 4 0 k e V to 70eV, changes the spot size from l x 10mm 2 to approximately 13x 6 m m 2 (value for lower currents) and allows scanning over the target surface. This low energy beam is also free of neutrals and electrons.
4. Improvement of the collecting system An extended series of thin targets has already been produced at the separator P A R I S with the collecting system described above. Nevertheless an improvement of the system seemed to be necessary in order to produce a smaller beam spot at the target. The cheap and easily con-
R. Meunier et al /Preparatton of thin targets
structed system of electric fields has the disadvantage of considerably increasing the beam size in the target region for higher beam currents. This increase in size is due to the destruction of space charge neutralization in the electric fields, where the electrons necessary for charge compensation are soon extracted from the ion beam. In fig. 2 the smallest beam cross section at the target obtainable by varying the voltages at the two quadrupoles is shown as a function of a xenon beam current. Considering preparations of targets with surfaces of approximately 1 cm 2, it can be seen from curve (a) in fig. 2 that the useful beam current decreases rapidly for total currents larger than 100 ~tA. In order to decrease the spot size at the target, a simple alteration was made to the collecting system. From the ion optical point of view the lay-out of the system was not optimized for target preparation purposes, as it was constructed and used for other reasons. Thus the distance L2 between the end of the quadrupoles and the target was larger than desirable. So we reduced this length as much as possible. Ion optical calculations of the system were made using the formalism of Brown [5]: the beam waist at the target was determined from the two dimensional o'(1) matrix given by the equation o-(1)= Rcr(0)R T. H e r e o-(1) is the trmatrix at the target (for the definition of or see ref. [5]). tr(0) is the corresponding matrix at the
9
entrance of the system containing the starting conditions of the beam. R is the conventional overall transfer matrix of the system, which is simply obtained by multiplying step-by-step the single transfer matrices of the components: drift length L~, first quadrupole with effective length 1~, drift length D between the quadrupoles, second quadrupole with effective length 12, and drift length L2. In the former system with L2 = 1200 mm the calculations of the beam waist at the target gave a result of 10.2 x 5.4 mm 2. This is in good agreement with the measured value of 1 0 x 4 . 5 m m 2 for low beam currents without retardation and space charge effects (see fig. 2a). The calculations with L2 = 670 mm (new shorter system) showed that it was possible to obtain a spot size of 6.5 x 2.1 mm 2. The measurements of the beam cross section at the target with the shorter L2 are represented for xenon beams by the curve (b) in fig. 2. For low currents the beam spot size without retardation system was 4.3 x 2.5 mm 2, that is somewhat smaller than the calculated value. Besides the approximately 5 times smaller beam spot for very low currents below 30/zA, the major advantage of the L2-modification is the relatively slow increase of the spot size with increasing total beam current. Thus the target preparation time is now considerably reduced. For instance for total beam currents in the region of 300/,tA and target areas of approximately 1 cm 2 the preparation time has been divided by almost a factor of 4.
(
[ram~] 5. Examples for the production and use of enriched targets
300 200 100 ~ a ~ 0
100
200 IkA]"-"
Fig 2 M e a s u r e d (full c u r v e ) a n d c a l c u l a t e d ( b r o k e n line) b e a m cross s e c t i o n S.~. at t h e t a r g e t as a f u n c t i o n of the b e a m c u r r e n t I for X e b e a m s . T h e c u r v e (a) c o r r e s p o n d s t o L2 = 1200 m m , the c u r v e (b) to L2 = 670 m m (see t e x t )
There is a variety of motivations underlying the need for isotopically pure target material used in experiments with heavy ions. The Coulomb excitation experiment performed by B o k e m e y e r et al. [6] may serve as an example. 5.1 MeV/u 2°spb projectiles were used with ~ D y targets produced at K F A Jiilich with the electromagnetic isotope separator S I D O N I E II [7] by sputtering techniques. An enrichment larger than 98% was reached for the lSaDy targets, the natural abundance being 0.1%. The observation of Yrast states up to I ~ = 20 + through the detection of low-intensity gamma rays was posI STABLE ISOTOPE SEPARATION
R Meunier et al / Preparatton of thin targets
10 Table 1 Isotope
Thickness (mg cm -2)
Backing
Enrichment of charge material
Comment
(%) 12C 34S ~S 58N1 6aN1 7°Ge ~Mo 14°Ce x48Sm l~Dy 162'164Dy t76 ~77.17s.179Hf 238U
0 08 0 1 0 001 0 1-0 0 1-0 1 02 0 1 0 2-0 0 1 0 1 0 2-0 1
4 4
4
4
1 mm Ta 30 ~g cm -2 C 30 #g cm 2 C 50/.tg cm 2 C 50 g g cm -2 C t 0 1 mg cm 2 C 33 ~tg cm -2 C 30 ~g cm -2 C Au fod 5 mg cm -2 Fe 5 mg cm 2 Fe 33 /~g cm -2 C 4 0 1 mg cm -2 C
Nat Nat Nat Nat 96 5 Nat Nat Nat 99.81 10 Nat Nat >99 3
sible by reducing the admixture of heavier dysprosium isotopes in the targets. More recently, a rising demand for directly deposited target layers with high isotope enrichment has been made, because a reduction of the admixed carbon in the target, caused by the sputtering technique mentioned above, was preferred. A large number of isotopically enriched targets were prepared by the direct deposition method at the separator P A R I S during 1979/80. Table 1 gives a list of the targets produced. Normally the targets have surface areas of about 1 cm 2 and an isotopic enrichment larger than 99%. As indicated in table 1, for 148Sm a higher enrichment was demanded and obtained. It should be mentioned that the enrichment of 99.987% for 148Sm means only that the contamination by 147Sm is less than 0.013%, as measured at one samarium target with a mass spectrometer. The overall contamination of the samarium targets by numerous other isotopes as for instance IH, 14N, 160 could be larger than this. The example of 58Ni shows that there is frequently a danger of target contamination by isobaric isotopes or compounds, here for instance SSFe. Thus often a specific ion source chemistry is needed to get a relatively clean beam of only one element. For some elements there are difficulties in producing larger target thicknesses on very thin carbon backing foils. For example it was a prob-
Reduction of 13C
Impurity of SSFe
>99 987% ~48Sm
Targets > 0 4 mg cm 2 deform 60 targets
lem to produce targets with more than 0 . 4 m g c m -2 of hafnium on 33/xgcm -2 carbon backings. Due to internal stress in the freshly built-up hafnium layers, the foil bent when this critical thickness was reached, and often broke afterwards. The use of thicker carbon foils or other more stable backing foils seems to be necessary for a simple solution to this problem. The enriched 176Hf target was used in a recent experiment by Schmidt et al. [8] investigating 4°Ar induced fusion reactions and the behaviour of the fission barrier in the region of the closed neutron shell N = 126. Here as in other fusion cross-section measurements with heavy ions, high isotopic enrichment is an important prerequisite in view of the strongly competing evaporation channels from heavier compound nuclei formed due to heavier isotopic contaminants in the target. One of us (FN) acknowledges with pleasure the kind hospitality of the Laboratoire Ren6 Bernas, Orsay. This work was performed in part within a contract between IN2P3 Paris and GSI Darmstadt.
References [1] J. Camplan, R Meumer and C Fatu, Proc 8th EMIS Conf., Skovde (1973) p 186. [2] J L Sarrouy et al., Nucl Instr and Meth 38 (1965) 29
R Meumer et al / Preparation of thin targets [3] E Hechtl, Nucl Instr and Meth 139 (1976) 79, K Freltag et al, Nucl. Instr and Meth 139 (1976) 83 [4] J H. Freeman et al, Nucl Instr and Meth 135 (1976) 1 [5] K L. Brown, Stanford Linear Accelerator Center, Stanford, CA, SLAC-Report no 91 (1973)
11
[6] H Bokemeyer et al, J Phys Soc Jap. 44 (1978) 610 [7] H Ihle, U Kurz and R Wagner, Internal Report, Institut fur Nuklearchemle der K F A Juhch (January 1974) [8] K.H Schmtdt, GSI Darmstadt, pnvate commumcanon (1980)
I. STABLE ISOTOPE S E P A R A T I O N