... 1 * I OFT ORNLP 2260 02 - IN TFF1 no E MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS -1963 ORNL-P. Bar 206 To be cubmitted for publication in the August issue of the IEEE's Transactions on Nuclear Science, Proceedings of the International Conference on Isochronous Cyc'strong, Gatlinburg, Tennessee, May 2-5, 1966. Cont_660510-8 CIE? c.. 27 958 w HC. $ 1.00: MN,50 THE ORIC HIGH-RESOLUTION SPECTROGRAPH FACILITY* J. B. Ball Oak Ridge National Laboratory Oak Ridge, Tennessee Summary The beam analyzer is an n = 1/2, double focussing magnet with a 72 inch radius of curva- ture. The entrance and exit slits are equidistant from the field boundary so that the magnet oper- . ates with unity radial magnification. If both entrance aad exit slits are set to the same open- ing, then a slit width of 0.072" corresponds to an energy resolution of 1 part in 1000. This has been the slit setting for all of the preliminary work described here. The installation of a broad range spectro- graph system at ORIC has now been completed. The system consists of a beam analyzing magnet, two triplet quadrupole magnets, and the spectro- graph magnet. These magnets are operated as a compound system to obtain optimuin energy resolution. The quadrupole pair gives the system a unique flexibility in roatching the pro · perties of the beam preparation and the spectro- graph magnets. Preliminary results of the operation of the system show the importance of this compound operation with obtained resolutions approaching 1 part in 2000. Y os'.'VE! With the proper setting of Qi and Q2 it is possible to get 50% of the extracted beam through the 0.072" entrance slit of the 153 degree magnet. Transmission through this slit is somewhat aided by the relative orientation of the cyclotron and the analyzer bending plane. The narrow dimen- sion of the entrance slit corresponds to the axial co-ordinate of the cyclotron. The axial diver- gence of the extracted beam is significantly less than the radial divergence. Di The last of the major pieces of equipment to be itstalled at the ORIC was the broad-range spectrograph. This magnor and its associated components were received and assembled, in the larger of the two experimental areas, during the last half of 1965. Calibration and preliminary runs were made during January and February of 1966. It is the purpose of this paper to discuss some of the unique features of this system and to report some preliminary results. The exit slit of the 153 degree magnet serves as the object for the two triplet quadrupole mag- nets Q3 and Q5. This quadrupole pair transports the analyzed beam to the spectrograph target chamber at station 4. AE The layout of the spectrograph system, with respect to the ORIC cyclotron, is shown in Figure 1. This figure indicates the elements which are active in the operation of the system. The Epectrograph magnet is a uniform field, single wedge magnet of the type described by Elbek and co-workers.' The magnet covers a range of radii of curvature from 30" to 63" and operates at fields up to 13.5 kGauss. The mag- net sits on a cradle which rotates about the scattering chamber with an angular coverage of -10 to +160 degrees. The spectrograph gap is two inches and lies in the same plane as the gap of thie. 153 degree magnet. Both magnets Geflect particles in the same direction. The solid angle of the spectrograph is of order 4 x 10-4. The external beam from the cyclotron is passed through quadrupole Qi. This doublet quadrupole is adjusted to provide a paralicl beam in both the radial and axial directions. This parallel beam is then focussed by quadrupole Q2 onto the entrance slit of the 153 degree analyzing magnet. Research sponsored by the U. S. Atomic Energy Commission under contract with Union Carbide Corporation The importance of the pair of quadrupoles between the beam analyzing magnet and the spectrograph can be qualitatively explained using the schematic representation of the optics shown in Figure 2. LEGAL NOTICE The report m. propred N D account of Government sponsored work. Noltber Who Valind Haldı, sor the Commission, por kay person acting on behall of the Commission. A. Makes day warranty or reprenouatioa, expruund o: implied, with respect to the accu- racy, completeness, or unatalness of the laformativo contained to the rooort, or want the wo of way Information, apparatus, method, or procene disclosedla do report may not lalringe printoly owned righus; or B, ASMA.Lay liabilities with respect to the use of, or for damages rosulun from the un of way Information, appunttus, method, or proceus discloud in this report. As cand la Obe abon, "portou acttag on behalf of the Commission" includes may sa- ployee or contractor of the Coaniosion, or employee of much contractor, to the meat that such employme or contractor of the Commission, or employna of euch contractor preparer, dioxminates, or provides accu., say lolormation purnuant to his employmat or contract wu the Conmussloa, or wo employment with much contractor. RELEASED FOP. ANNOUNCEMENT IN NUCLEAR SCIENCE ABSTRACTS is changed simply by adjusting the two quadrupole currents and hence shifting the position of the intermediate image. Since the energy spread in the cyclotron beam passing through the entrance slit S2 is greater than the spread defined by the width of the exit slit S3, the particles will be distributed across the opening of S3 with a definite energy gradient. Particles with lower energies will have smaller radii of curvature in the analyzer and will be focussed closer to the lower slit than those particles having higher enermy. There is one additional advantage to the ORIC system. At large angles it becomes neces- sary to take reflection data rather than traus- mission data. As the situation is drawn in Figure 2, it is apparent that this would result in an energy gradient across the target in the wrong directio: The recessary "flipping' of the gradient is accomplished by making the beam parallel be- tween the two quadrupoles. This feature is not available with the simpler systems. The purpose of the quadrupole pair is to: transmit the beam to the spectrograph target while maintaining the directional sonse of this energy graäient. We thua cbtain an image on the target with an energy gradient as indicated in Figure 2. The effect of this gradient is most easily seen by imagining a point source of particles on the focal plane at point FP. If these particles travel backwards through the spectro- graph they will be dispersed across the target with an energy gradient having the same sense as the gradient in the beam. Now, if the two gradients are matched, the particles coming from the target will tend to focus to a point image at the focal plane. (It must be remembered that there is an incoherent energy spread introduced by the finite width of $2.) The effect of this careful dispersion match- ing is to remove the offect of the target spot size on the final line width. Another way of stating this is that ty operation of the magnets as a com- pound system, the final line width is determined by the width of slit S2 and not by the combination of S2 and S3. For a beam preparation magnet with unit magnification the energy spread in the prepared beam is proportional to the sum of entrance anci exit slits. This means that for cyclotron systems where we have the condition of the energy spread in the raw beam exceeding the spread deiined by an analysis magnet, spectrograph magacts are intrinsically better than other types of detectors by a factor of two in energy resolution. The importance of this dispersion matching has been discussed by Cohen2, 3 for a system of two wedge magnets without quadrupoles. In that case the dispersion matching was accomplished by appropriate choice of target angle. However, it is also important to choose the target angle to riinimize the spread in particle energy 1088. In the system described by Cohen the target angle is chosen as a compromise between dispersiori matching and energy spread. The relative independence of overall reso- lution on target spot size for the compound system is illustrated in Figure 3. This shows the line width for 31 MeV protons elastically scattered from a 0.5 mg/cm2 target of 60 Ni. A slit placed in front of the target was respectively opened to allow the natural inage widt'n on the target (about 0.060"), closed to 0.040", and finally closed to 0.020". The observed line width varies only slightly with the reducing target spot size. With an incident beam having an energy resolution of 0.1%, the observed line width is about 0.06%. In the ORIC system described here, the dispersion matching is accomplislied by choice of appropriate magnification of the two quadru. pole system. This leaves the target angle a free parameter. Since a real image is inverted, we must run the quadrupole system with an inter- mediate image to obtain the propex gradient. It would have been possible to partially satisfy these requirements by using only one quadrupole and installing the spectrograph magnet to deflect particles in the other direction. This would have che difficulty that the magnification is fixed and can be changed only by physically moving the quadrupole. In the ORIC system the magnification One of the first spectra taken with the mag- net during its initial operation is shown in Figure 4. These are deuterons resulting from the re- action of 31 MeV protons with ". The incident protons have an energy spread of about 31 keV. The deuterons have an energy of about 21 MeV with an observed line width of 17 keV. It is expected that after some experience has been gained in the operation of this system, decreases in the energy spread of the prepared beam ard in target thicknesses will allow im- provements over the present resolution of the spectrograph system. References 1. J. Bor green, B. Elbek, and L. Perch Nielson, Nucl. Instr. and Mechode, 24, 1 (1963). 2. B. L. Cohen, Rev. Sci. Inst. 30, 415, 195?. 3. B. L. Cohen, Rev. Sci. Inst. 33, 85, 1962. ومهما م نعنعنمننسننهسنننننننننننننننننننننننننننننننننننننننننننننننننننننننننننننننننننننننممننننننننننننننننننننننننننننننننننمعلمغسلت . ". . •• - : : د ننن،ننهننهننننهسعنننننننننننن مننننننننننننلبسهننننننننم نندا نے تمام ن وم ... ....... م ن تن . / T = ع نان منشفة •رور EXIT نننننننننننن ANALYZING MAGNET عه ۲۰۰۲ COLLIMATOR SLITS FOR ANALYZING MAGNET نننننننننننننننننننننن . نننننننن العين STATION 4 نننننننننننننننننننننننننننننننننننننننننننننننننننلنين:: ... ...... •• ENTRANCE نننننننننننننننننننننننننننننننتتتننننننغن ... BROAD - RANGE SPECTROGRAPH : تنس نننننننننننن . ننننننننننننننننننننننننمننننقشت - VERTICAL POSITIONING MAGNET تن :: نننعنننننمنننسمسم - سيبن ببینینتني -CYCLOTRON Fig. 1 Beam optics layout at ORIC show- ing components use 1 in the spectrograph system. ORNS-DUG 66-3995 BROAD – RANGE SPECTROGRAPH 153° MAGNET TARGET S3 S2 - BEAM Fig. 2 Schematic representation of spectrograph system to illustrate disper- sion matching. - - - - - - - - -zat * iki * iaw n : : : :- ORNL-DWG 66-3879 .. . . - . . . - . anaka ke r ini . .:. . ORNL-DWG 66-3879 800 700 600 tracks/V4 mm TTTTTTT +0.796 TTTT +0.77| | | -0.75 | I 300 T TT 200 100 ! S= AE=19.4 ke TF S-4.0 AE= 18.9 keV S=0.5 SE=18.4 kev L ! 1 . 2 1 3 1 2 3 DISTANCE ALONG PLATE (mm) 2 3 .." Fig. 3 Observed line width as a function of tar- get spot size. N ' ORNL-DWG 66-3878 DEUTERON ENERGY (MeV). 20.0 20.5 21.0 21.5 500 19.5 T 400 89710, d) 88Y 8 = 30° E. =31 MeV tracks /mm STT 100 olamente 20 40 60 160 480 200 o Fig. 4 Spectrum of deuterons from 89Y(p, d) 88Y reaction. 80 100 120 140 DISTANCE ALONG PLATE (mm) - 1. 4.. W .. ... - - - - - - * - - - - M " • ARSELVA . AI 1. , . TV KW "O CUM is LY! VARIOUS * ARKUS MSW M . O : 'si hy Why L IN ! 411 S 6 AL Mar 17 . . lay, .. END - - - - - - - - . .. . ... -- _ DATE FILMED 7 / 27 / 66 . U