AECL-5503 ATOMIC ENERGY WS& L'ENERGIE ATGMIQUE OF CANADA LIMITED •Ajf DU CANADA LIM1TEE PROCEEDINGS OF THE 1S74 ANNUAL CONFERENCE OF THE NUCLEAR TARGET DEVELOPMENT SOCIETY held at CHALK RIVER NUCLEAR LABORATORIES CHALK RIVER, ONTARIO 1-3 OCTOBER, 1974 Printed by Atomic Energy of Canada Limited Chalk River, Ontario January 1975 Reprinted April 1976 NUCLEAR TARGET DEVELOPMENT SOCIETY PROCEEDINGS OF THE 1974 ANNUAL CONFERENCE K.L. Perry - Conference Chairman J.L. Gallant - Co-Chairinan Texts of the 2; papers that were presented at the 1974 N'TDS Annual Conference held at CHALK RIVER NUCLEAR LABORATORIES CHALK RIVER, ONTARIO, CANADA 1-3 OCTOBER, Printed by Atomic Energy of Canada Limited Chalk River, Ontario January, 1975 Reprinted April 1976 AECL-5503 NUCLEAR TARGET DEVELOPMENT SOCIETY Compte rendu des travaux du Congres annuel de 1974 Resume Cette publication comprend le compte rendu d' UP. Congres international dont les travaux se sont deroules dans le doir.aine general de la preparation des cibles pour les accelerateurs de particules. Le compte rendu ccncerne les 21 communications presentees au Congres. Les questions a 1'ordre du jour etaient les suivantes: 1. preparation de films minces (solides) par diverses methodes: evaporation sous vide; roulage, precipitation chimique, implantation d'ions, electrodeposition, electropulverisation; 2. cibles liquides; 3. cibles gazeuses; 4. substrats et agents de separation; 5. preparation de matieres destinees a former des cibles; 6. mesure de l'epaisseur, de 1'uniformite et de la purete. Tenu du ler au 3 octobre 1974 dans les Laboratoires Nucleaires de Chalk River en Ontario, ce Congres etait parraine par Nuclear Target Development Society en cooperation avec l'Energie Atomique du Canada, Limitee. imprime par L'Energie Atomique du Canada, Limitee Laboratoires Nucleaires de Chalk River Chalk River, Ontario Janvier 1975 Reimprime en avril 197b AECL-55 03 NUCLEAR TARGET DEVELOPMENT SOCIETY PROCEECINGS OF THE 1974 ANNUAL CONFERENCE ABSTRACT This publication Incorporates the proceedings of an international conference concentrating on the general field of target preparation for use with particle accelerators. The proceedings include the 21 papers that were presented at the meeting dealing with the following topics: 1. preparation of thin (solid) films by vacuum evaporation, rolling, chemical deposition, ion implantation, electro- deposition and electrospraying, 2. liquid targets, 3. gas targets, 4. substrates and parting agents, 5. preparation of target materials, 6. measurement of thickness, uniformity and purity. The conference was held at the Chalk River Nuclear Laboratories, Chalk River, Ontario, from 1-3 October, 1974. It was sponsored by the Nuclear Target Development Society in co-operation with Atomic Energy of Canada Limited. Printed by Atomic Energy of Canada Limited Chalk River, Ontario January 1975 Reprinted April 1976 AECL-55C3 (i) CONTENTS pAGE TUESDAY, 1 OCTOBER SESSION A D.C. SANTRY H.I.. ADAIR à E.H. KOBTSK L.0. LOVE 29 A. LOUGHEiiD & E.K. HLH.FT 39 SESSION B G. SLETTEN W.V. CONNER 59 VuLti'.-lc :.'ir,k ll..n\ ;;• T-iP.jci Material P. miER-KOMOE 70 '/upep i'l'esciu'a on VI'Ï'J .:>•. B'takiu ;a by ':i>:-j 1 F.o 1.1 ;;•: Cia\ C-A. BOUCHARD 74 K.W. ALLEN et al. 76 i:.ïdi-?.ti>Ju Caviure WEDNESDAY, 2 OCTOBER SESSION C I.V. MITCHELL .--. L'<:Ï'.V'ITi.O:: !-!ethod for DeteP'r.ininc A.H. CHUNG, W.T. DIAMOND 84 & A.E. LITHERLAND :.•: ïualc'M' jar jets i.':;";t .'A;.,v Measurements Problems J.S. MERRITT 86 (ii) J. KW1NTA & F. AMOL'URY 95 J.D. S1INSCN 100 N. BUR.N & L.B. BENDER 105 SESSION D i're: 'rali :••' ait.i ,'.. J. VAN A'JDCNHOVE, 119 V. VERDINGH, H. ESCHBACH & P. DE BIEVRE :'.-. of Substrates I, D. RAMSAY 151 E.W. McDANIEL, L.O. LOVE 159 W.K. PRATER & R.L. BAILEY Palladium, and Platinw ]'.'!'• iiescarak Use W.D. RIEL 167 Enriched Iron from Ike I>i-Situ Ru da avion of Fe .•• 0., Sy.Z'-ti.ai Tocjet Preparation 7cciv:~'.. J.L. GA!.LANT 169 for Chalk River Unclear Pays'C-L SESSION E : 'ike lsc of Lasers for the o<:;;ar>al-: R.D. McALPINE 179 PREPARATION OF TARGETS BY ION IMPLANTATION D.C. Santry Chalk River Nuclear Laboratories Atomic Energy of Canada Limited Chalk River, Ontario [INTRODUCTION The technique of using an energetic irir. beam to introduce ions into a substance is called ion iniplantatxr.n. .Although the method is usod extensively for the doping of cemiroiic.ao-or materials for the preparation of commercial semiconductor devices, ion implantation has not gained wide acceptance in target preparation for nuclear measurements. In this paper I propose to describe various factors which are involved in target preparation by direct ion implantation and will emphasize the limitations and pitfalls of the method. Examples will be given of experiments for which ion implanted targets are well suited. Since the central theme of the conference is target preparation for use with accelerators, I intend to say very little about implan- ter machines other than to mention that they too are accelerators, usually laboratory size electromagnetic isotope separators. The topic of target preparation therefore becomes one of the chemistry and physics of accelerated beams stopping in solids. ION RANGES One of the main differences between targets prepared by ion implantation and the various deposition methods is that the former introduces a specific material into a substrate rather than on top of it. When an ion beam of low energy hits the surface of a target material, most of the ions are stopped and trapped in a thin layer just below the surface. The thickness of the layer depends on the ion. energy, mass of the ion, and the nature of the stopping material. The distribution of the implanted ions is expected to be approxi- mately Gaussian in shape and the thickness penetrated by 50% of the ions is referred to as the median rango. For many experiments ion implantation can be regarded as pro- ducing very thin targets. However, for high precision work such as particle spectrometry, the energy spreac introduced by an effective thickness of any .source can be important. It therefore becomes de- sirable to know the range of implanted ions in solids. Unfortuna- tely, this information is still sadly lacking. There is available the semi-empirical tabulation of heavy ion ranges by Northcliffe and Schilling (1) which covers the energy range 10 keV/AMU to 12 Mev/AMU, energies too high for most ion implantations, Johnson and Gibbons (2) have provided calculated range data for various projectiles into selected targets, covering a more useful energy range of 10 to 1000 keV. The calculations are based on the L.S.S. (3) theoretical treatment of ion ranges. I would now like to show that the only certain way of knowing the range of a specific ion is to actually measure it for the material to be used. Figure 1A shows an integral range distribution l0 °\ l34 40 keV Cs i\ 40 keV IONS IN TUNGSTEN ",'0r Q ; \ \- 'N TUNGSTEN \ IN GOLC; 50 100 150 200 250 300 25 50 75 100 125 150 175 DEPTH (ug/cmZ) DEPTH (ug/cm2) Figure 1 measured by ion implanting at 40 keV a radioactive tracer into polycrystalline gold and tungsten. The residual activity was measured as thin layers were removed from ti.e surface (4). As was expected from theory, the median range was identical in Au and W. Figure IB confirms that different elements with similar masses when implanted at a given energy will have the same median range. Range measurements were made using many radioactive nuclides and the median range values obtEiined are plotted in Figure 2. The relationship MEDIAN RANGE OF 40 keV ions O IN WCJ D fiO 80 I0D !?D 140 1 ED !8D ilJD ;20 Figure 2 between ion range and ion energy is shown in Figure 3. Note that for high Z stopping media, measured ranges are greater than that calculated by the L.S.S. theory. In Figure 4 are shown a series of 50- 10 60 K e V Figure 3 Figure 4 range measurements made with a W single crystal. The median range for implanting along the 111 direction was 247 ...g/cm , the en- hanced penetration being due to the ion channe1ing effect. Implant- ing at an angle of 8° from the 111 direction decreased the range distribution only slightly. An analysis of the crystal structure of W indicated that a tilt of 24° would produce the most random arrange- ment of atoms for this crystal. Implants made under these conditions gave a median range of 27 -cj/cm which is close to the value of 24 ..g/cm obtained with polycrystalline material. However, the range distribution for the random direction indicated chat many ions are still able to travel great distances into the crystal. The polycrystalline W metal used for range measurements shown in Figure 2 was prepared by pressing and sintering very fine grained W powder. Range measurements made using rolled W foil are shown in 2 Figure 5. The median range value was 40 u.g/cm and the range t'\ H 1 - - \ \ - 1 1 1 Figure 5 distribution showed large penetration depths for a small fraction of the implanted ions. The sintered W when annealed at 2250°C gave a 2 median range of 33 ug/cm and also exhibited the enhanced penetration of ions. Thus it has been observed that the depth of an implant can also be influenced by crystal structure and the metallurgical process used to prepare the stopping media. Perhaps it should be pointed out that such effects may also be important for other measurements in- volving ions or particles moving through matter, i.e.