Quantitative analysis of aluminium by prompt nuclear reactions

Journal of Radioanalytical Chemistry, Vol. 12 (1972) 189--208 QUANTITATIVE ANALYSIS OF ALUMINIUM BY P R O M P T N U C L E A R R E A C T I O N S G. DECONNINCK, G. DEMORTIER Facult~s Universitaires de Namur, L . A . R . N . , Namur (Belyiam) A new physical method of analysis of samples containing small quantities of aluminium is described. The sample is bombarded with fast protons and the resulting 7;-rays are analysed by the Ge(Li) technique. The high selectivity of these detectors allows identification of the nuclei responsible for the ;;-ray emission. A careful analysis has been made of the different nuclear reactions involved in the production of).-rays in the bombardment of aluminium. Four y-rays have been observed with sufficient intensities for rapid determination: 843 keV, 1 013 keV, 1 368 keV and 1 778 keV. Thick-target excitation yields are presented and discussed in view of their use in analysis. A complete tabulation of these reactions is also presented. The method allows the determination of the aluminium concentration in every solid matrix in the 100 ppm range. In some cases concentrations as low as I0 ppm can be observed. All these determinations are quantitative. Lower concentrations can be detected qualitatively. Examples of the application of the method to different substances are the following: stainless steel, inorganic compounds, crystals, evaporated layers, etc. The resonance pattern observed in the intensity curves can be used to measure the homogeneity and the thickness of thin layers containing aluminium (0.2 to 4/xm). In most cases the method can be considered non-destructive and there is no residual radioactivity. Analysis of a sample of a total weight not exceeding 0.1 mg can be achieved. Introduction The aim of the present project is to apply some p a r t i c u l a r types of n o n - d e s t r u c tive m e t h o d s to the analysis of a l u m i n i u m , using the k n o w n f u n c t i o n a l dependence of the intensity o f ~-rays o n the energy of p r o t o n s p r o d u c i n g these r a d i a t i o n s d u r i n g the b o m b a r d m e n t of AI. T o determine the best a p p r o a c h to this analysis, we i n t e n d to study the n u c l e a r reactions induced by the b o m b a r d m e n t of AI by protons, select the useful reactions, a n d t a b u l a t e the values measured. This is the aim of the first part. I n the second p a r t we establish the m e a s u r i n g procedure. I n order that a d v a n t a g e m a y be t a k e n of this research, practical i n s t r u c t i o n s are formulated, a n d the region of applicability a n d the limits of the m e t h o d are clearly stated. The third part will be devoted to the applications. J. Radioanal. Chem. 12 (1972) G. DECONNINCK, G. DEMORTIER: ANALYSIS OF ALUMINIUM 190 Physical aspects of the analytical problem, production and selection of the ~,-radiation Production of ?-radiation by the bombardment of AI with protons In order to determine the most appropriate measuring conditions in each instance, a systematic study of the reactions leading to the emission of ),-radiation and a measurement of the intensities as a function of the energy of acceleration of the protons have been made. Ge(LI) c.,. i ,C..~.il" ~ ~D.C. ! ~JJJJJRH~II Ref. purser ~//c/r ~ 9" ~'/,-'(/~';'/; ~ p. I ~ i. -I1 ,o I I_C~'l IH~''- . r..O.r Monitor ~ I DisPta~ i [ HP 5430A I I = H.P 2114A --- [, I , , / / I 2L Fig. 1. Sketch of the experimental set-up A target of pure aluminium of 1 mm thickness was bombarded by protons from the AN-2500 Van de Graaff accelerator of L A R N . 1 The emitted ]:-radiation was detected by a calibrated and standardized Ge(Li) detector. 2 3". Radioanal. Chem. 12 (1972) G. D E C O N N I N C K , G. D E M O R T I E R : ANALYSIS OF ALUMINIUM 191 The spectra of the radiations emitted by the pure AI target bombarded with protons of energy varying between 500 and 2 500 keV were recorded by the experimental apparatus described elsewhere I and are shown schematically in Fig. 1. Fig. 2 gives the spectra generated by 1 000, 1 700 and 1 950 keV protons, for the same number of/~C incident on the target (note the difference in scale along the ordinate). 5 r z Ep= 1000 key 300 el 13o00 ! A ~ Ep=1700 keY A Fig. 2. Typical spectra of emitted 7-rays under bombardment with 1 000, 1700 and 1950 keV protons of a thick target of pure aluminium The analysis permits the identification of the characteristic ),-rays of the reactions of protons on AI. Only the most intense characteristic peaks will be considered. The numbering of the 7-rays together with their identified origins and their intensities as measured by a Ge(Li) detector" of 26 cm :~ are given in Table 1. The symbol (n) indicates that the ),-rays cannot be distinguished from the background noise. J. Radioanal. Chem. 12 (1972) 192 G. DECO1NNINCK, G. DEMORTIER: ANALYSIS OF ALUMINIUM Table 1 Characteristic 7-rays from the reactions of proton on aluminium E? (observed), keV E.f (emitted), keV Reaction 170 170 27Al(p, p'7)27A1 1 043 --~ 643 511 511 annihilation 756 (2esc) 1 778 843 1 013 1 ~TAl(p, 7)2sSi 1 778--~ 0 Relative intensities at Ep, keV 1 000 1 700 1 950 0 0 5 000 600 3 000 3 500 80 450 (n) 843 27Al(p, p'7)27Al 843 --~ 0 0 8 000 28 000 013 ~TAl(p, p'7)27A1 0 700 23 000 (n) (n) 1 013 ~ 0 1 267 (lesc) 1 778 ~TAl(p, 7)28Si 1 778 ~ 0 1 368 1 368 "7Al(p, ~)~4Mg 1 368 ~ 0 1 778 1 778 'zrAl(p, ~)28Si 1 778--* 0 1 815 (2esc) 2 835 2 835 3 470 (2esc) 60 0 300 4 900 510 3 000 3 500 ~TAl(p, 7)28Si 4 610 ~ 1 778 25 150 (n) 2 835 "rAl(p, 7)2ssi 4 610--~ 1 778 30 180 (n) 4 490 27Al(p, 7)'~ssi 6 270 ~ 1 778 20 80 (n) T h e intensities o f the f o l l o w i n g y-rays w e r e m e a s u r e d s y s t e m a t i c a l l y : 1 778 k e Y for t h e r e a c t i o n 27Al(p, ?)28Si; 843 a n d 1 013 k e V f o r t h e r e a c t i o n ZTAl(p, p'?)ZTA1; a n d 1 368 k e V f o r the r e a c t i o n 27Ai(p, ct?)24Mg. A c r i t i c a l a n a l y s i s o f t h e results w i t h a v i e w to a b e t t e r c h o i c e o f t h e p r o t o n a c c e l e r a t i o n e n e r g y a n d t h e e n e r g y o f t h e ? - r a y is c o n t a i n e d in t h e f o l l o w i n g f o u r sections. The reaction 27Al(p, ?)2ssi ( E r = 1 778 k e V ) T h e i n t e n s i t y o f the ? - r a y s f o r this r e a c t i o n w a s m e a s u r e d a b s o l u t e l y 500 a n d 1 800 k e V in steps o f 1.5 k e V , a n d b e t w e e n 1 800 a n d 2 500 k e V o f 20 k e V f o r O r = 0 ~ a n d O r = 90 ~. F o r the m e a s u r e m e n t s m a d e at ?-rays c r o s s t h e s a m p l e b e f o r e r e a c h i n g t h e d e t e c t o r ; a f r a c t i o n o f the r a y s J. Radioanal. Cheat. 12 (1972) between in steps 0 ~ the is t h e r e - (,;. D E C O N N I N C K , G. D E M O R T I E R : ANALYSIS OF A L U M I N I U M 193 t~. 104 z" 27 2B AI (p,]) Si E 1 = 1778keV 0 =90 ~ _/- tO ~ p, 5.10 ~ T z 103 5.10 2 8 / _rr7 o~ 0.7 0'.8 I ~9 ~o IF 1.~ Ep.MeV (~ i 12 i 1.4 I 1.6 I 1.8 20 I 22 .J ~.. 2.4 Ep.MeV Fig. 3. Absolute intensities of the 1 778 kcV ;)-rays from the reaction 2~Al(p, 7)"8Si. The photons are detected at 90 '~ with respect to the direction of the incident proton beam fore autoabsorbed. Measurements performed at 90 ~ will be most often used in analysis, since in this case the flux o f v-rays resulting f r o m the surface b o m b a r d ment is detected w i t h o u t first being attenuated by the sample. The intensity curve N~(Ev) o f the emitted y-rays as a function o f the p r o t o n energy expresses an intensity increase by a factor l 200 between 500 and 2 500 keY. The intensity increases in the beginning in a stepwise manner. A j u m p in the intensity corresponds every time to the appearance o f a resonance in the reaction 27Al(p, 7)28Si. Tile presence o f these level stretches indicates that y-rays are not emitted except at the resonance energies (cf. Ref. 1 p. 8). Beyond 2 MeV the intensity increases monotonically (Fig. 3). The y-ray intensities measured at O r = 90 ~ are summarized in Table 2. The most outstanding and ofte'n used regions for the analysis o f Al in the sample surface are situated at resonance energies o f 632 and 991.82 keV. 13 J. Radioanal. Chem. 12 (1972) 194 G. DECONNINCK, G. DEMORTIER: ANALYSIS OF ALUMINIUM Table 2 Absolute intensities of the 1 778 keV y-rays emitted u n d e r b o m b a r d m e n t by p r o t o n s f r o m in the relative i n t e n ~ t ~ s are less t h a n 5 ~ . Intermediate values can be obtained Ep, keV 500 504 *504.8 505 *506.9 508 510 520 530 540 550 560 570 580 590 600 605 610 611 "612.1 613 615 620 625 630 632 632.6 633 635 640 645 650 654 *654.9 656 660 665 670 675 678 *678.6 679 680 685 690 J. RadioanaL N~ ~ 7 7 11 14 17 19 19 19 19 19 19 19 19 19 19 19 19 19 19 22 28 28 28 28 28 28 60 93 93 93 93 93 93 117 142 142 142 142 142 142 157 170 170 170 170 Ep, keV 695 700 705 710 715 720 725 730 731 "731.3 732 735 736 *736.3 737 740 742 *742.3 743 745 750 755 759 *760 761 764 767 *767.9 769 770 773 *773.7 774 775 780 785 790 795 800 805 810 815 820 825 830 Chem. 12 (1972) N~ ~ 17C 17C 17C 17G 170 170 170 170 170 176 182 182 182 193 204 204 204 237 265 ~65 265 265 ~65 ~75 ~86 ~86 ~86 300 314 314 314 344 375 375 375 375 375 375 375 375 375 375 375 375 375 Ep, keV 835 840 845 850 855 860 865 870 875 880 *885 890 895 900 905 910 915 920 922 *922.6 923 925 930 935 937 *937.2 938 940 945 950 955 960 965 970 975 980 985 990 991 "991.822 992 995 1 000 1 001 *1 002.1 N~ #C ' s t 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 396 418 418 418 418 418 452 485 485 485 485 485 485 485 485 485 485 485 485 485 670 904 904 904 904 1 020 Ep, keV 1 003 1 005 1 010 1 015 1 020 1 024 *1 025 1 026 1 030 1 035 1 040 1 045 1 050 1 055 1 060 1 065 1 070 1 075 1 080 1 085 1 089 *1 089.8 1 091 1 095 1 097 *1 097.6 1 098 1 099 1 100 1 105 1 110 1 115 1 117 *1 118.4 1 120 1 125 1 130 1 135 1 140 1 145 1 150 1 155 1 160 1 165 1 170 N~, #C "st 1 130 1 130 1 130 1 130 1 130 1 130 1 185 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 245 1 280 1 310 1 310 1 310 1 310 1 310 1 310 1 310 1 310 1 310 1 310 1 310 G. DECO NNINCK, G. DEMORTIER: ANALYSIS OF ALUMIN!UM 195 a t h i c k target o f p u r e AI. T h e errors in t h e a b s o l u t e v a l u e s are less t h a n 15 %, a n d t h c e r r o r s by l i n e a r i n t e r p o l a t i o n ; * indicates t h e p o s i t i o n s o f t h e expected r e s o n a n c e s Ep, keV 1 171 *1 171.9 1 173 1 175 1 180 1 181 *1 183.3 1 185 1 190 1 195 *1 199.4 1 201 1 205 1 210 1 212 *1 213 1 214 1 215 1 220 1 225 1 230 1 235 1 240 1 245 1 250 1 255 1 260 1 261 *1 262.2 1 263 1 265 1 270 1 275 *1 276 1 277 1 280 1 285 1 290 1 295 1 300 1 305 1 310 1 315 1 316 *1 316.8 13 N~ 1 3113 1 395 1 475 1 475 1 475 1 475 1 475 1 475 1 475 1 475 1 490 1 510 1 510 1 510 1 510 1 595 1 675 1 675 1 675 1 675 1 675 1 675 1 675 1 675 1 675 1 675 1 675 1 675 1 770 1 885 1 885 1 885 1 885 1 950 2 015 2 015 2 015 2 015 2 015 2 015 2 015 2 015 2 015 2 015 2 050 N~, Ela, 9 keV 1 317 1 320 ! 325 1 327 "1 328.1 1 329 1 330 1 335 1 340 1 345 1 350 1 355 1 360 1 363 *1 363.7 1 365 1 370 I 375 1 380 *1 381.3 1 382 1 385 1 388 * 1 388.4 1 389 l 390 1 392 *1 392 1 393 1 395 1 400 1 405 1 410 1 415 *1 416.8 1 420 1 425 1 430 1 435 1 440 1 445 1 450 1 455 *1 457.3 1 460 keV 2 080 2 080 2 080 2 080 2 195 2310 2 310 2 310 2 310 2 310 2 310 2 310 2 310 2 310 2 445 2 590 2 590 2 590 2 590 2 900 3 215 3 215 3 215 3.510 3 800 3 800 3 800 4 180 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 1 465 1 475 1 475 1 480 1 485 1 490 1 500 1 502.3 1 510 1 5t8 * 1519.6 1 521 1 530 1 540 1 550 1 560 *1 565.5 1 570 *1 577.9 1 580 *1 588.2 1 590 1 600 1 610 1 620 1 630 1 640 *1 647.4 1 650 1 660 *1 662.2 *1 663 1 670 1 680 *1 683.9 1 690 1 700 *1 705.6 1 710 1 720 *1 724.4 1 730 1 740 *1 749 1 750 4 56O 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 560 4 920 5 120 5 150 5 175 5 195 5 220 5 225 5 230 5 235 5 240 5 250 5 250 5 260 5 275 5 285 5 300 5 315 5 325 5 330 5 340 5 345 5 345 5 350 5 360 5 365 5 375 5 395 5 400 5 405 5 415 5 420 5 425 5 435 5 445 5 445 J. Radioanal. Ep, keV 1 760 1 770 1 780 1 790 1 797 1 799.9 1 800 1 802 i 810 1 820 1 830 *1 841.5 1 850 7.860 1 870 1 880 1 890 *1 899,1 1 900 1 909.9 1 920 1 940 1 960 *1 968.6 1 980 2 000 2 020 2 040 2 060 2 080 2 100 2 120 2 140 2 160 2 180 2 200 2 250 2 300 2 350 2 400 2 450 2 500 N~ ~C 9st 5 460 5 470 5 490 5 555 5 605 95 630 5 635 5 655 5 745 5 960 6 130 6.180 6A90 6 203 5.220 6 235 6.250 6 255 6 255 6.270 6.280 6.300 6 235 6 340 6 345 6 365 6 390 6 410 6 435 6 455 6 520 6 695 6 890 7 115 7.330 7 485 8 035 8 545 9 050 9 510 10 005 10 490 Chem 9 12 (1972) 196 G. DECONNINCK, G. DEMORTIER: ANALYSIS OF ALUMINIUM These resonances are characterized by: (1) a c o n s i d e r a b l e i n c r e a s e in t h e r e l a t i v e i n t e n s i t y o f t h e e m i t t e d v-rays ( i n t e n s e resonance); (2) l o n g p l a t e a u o n b o t h sides o f t h e r e s o n a n c e ( i s o l a t e d r e s o n a n c e ) . F o r t h e analysis o f A I t o a q u i t e c o n s i d e r a b l e d e p t h (10 p m ) , p r o t o n s o f 2.5 M e V will b e u s e d w h i c h p r o d u c e a n i n t e n s i t y t e n t i m e s as b i g as t h o s e o f 1 M e V . T h e e n e r g y r e g i o n b e t w e e n 1 370 a n d 1 400 k e V w a s s c a n n e d in steps o f 0.3 k e V in o r d e r t o o b t a i n t h e best d e s c r i p t i o n o f t h e i n t e n s i t y b e h a v i o u r Nv(Ep). A r e s o n a n c e n o t q u o t e d in t h e l i t e r a t u r e w a s o b s e r v e d at 1 3 9 2 + 0 . 5 keV. T h e v a s t m a j o r i t y o f t h e o t h e r k n o w n r e s o n a n c e s w e r e o b s e r v e d in o u r m e a s u r e m e n t s . E x a c t r e s o n a n c e v a l u e s w e r e n o t m e a s u r e d in t h e c o u r s e o f t h e s e e x p e r i m e n t s ; t h e y a r e c o n t a i n e d in t h e l i t e r a t u r e ) ,4 P o s i t i o n s l o c a t e d in o u r e x p e r i m e n t s c o r r e s p o n d t o t h e v a l u e s p u b l i s h e d in t h e s e r e f e r e n c e s . O f t h e r e s o n a n c e s q u o t e d i n R e f . 4 o n l y t h o s e s i t u a t e d at 1 519 a n d 1 800 k e V a r e c l e a r l y visible. Table 3 Absolute intensities of the 843 keV ~*rays emitted under bombardment by protons from a thick target of pure AI. The errors in the absolute values are less than 15 ~o, and the errors in the relative intensities are less than 5 ~ . Intermediate values can be obtained by linear interpolation; * indicates the positions of the expected resonances Ep, keV 1 500 "1 502.3 1 510 1 518 *1 519.6 1 521 1 530 1 540 1 550 1 560 *1 565.5 1 570 *1 577.9 *1 588.2 1 590 1 600 1 610 1 620 1 630 1 640 *1 647.7 1 650 1 660 1 661 3". Radioanal. N7 186 186 186 186 1 490 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 2 890 I Ep, keV *1 662.2 *1 663 1 664 1 670 1 680 1 683 *1 683.9 1 685 1 690 1 700 *1 705.6 1 710 1 720 1 723 *1 724.4 1 726 1 730 1 740 1 747 *1 749 1 751 1 760 1 770 1 780 Chem. 12 (1972) ! N), [ ] 3 3 3 3 3 3 6 7 7 7 7 7 7 7 8 9 9 9 9 10 10 13 140 13 420 13 885 I Ep, keV 1 790 1 798 *1 799.9 1 803 1 810 1 820 1 830 1 840 "1 841.5 1 850 1 860 1 870 1 880 1 890 *1 899.1 1 900 1 908 *1 909.9 1 911 1 920 1930 1 940 1 950 1'960 w _ _ Ny ! [ [ Ep, keV 1 967 *1 968.6 1 970 1 980 1 990 2000 2 050 2 100 2 150 2 200 2 250 2 300 2 350 2 400 2 450 2 500 2 600 2 700 2 800 2 900 3 000 23145 23 480 N7 gC 9st 23 535 24 695 25 930 26 155 26 245 26 280 27 625 28 636 29 985 31000 34 370 15 115 67 315 102 400 148 225 225 150 577 250 913 800 1 086 000 1 384 000 1 880 000 G. D E C O N N I N C K , G. D E M O R T I E R : ANALYSIS OF A L U M I N I U M 197 The reaction ~TAl(p,p'?)27AI (E.e = 843 k e V ) The intensity o f the reaction was measured f r o m Ep = 1 500 to 2 500 keV. Fig. 4 shows the results for Or = 90 ~ The numerical values are listed in Table 3. ~2.105 z" Z~'Ai (p,p'3.) E1=8/43keV G =90 ~ ~3.10 ~ z 2.1(34 10 ~ (~ 1.6 1.7 1.8 1.9 2.0 Ep~,teV i 2.1 ; 2.2 I 2.3 I 2./, [ 2.5 Ep,MeV Fig. 4. Absolute intensities of the 843 keV 7-rays from the reaction 27Al(p, p'?)27A1. The photons are detected at 90~ with respect to the direction of the incident proton beam The intensity approaches zero for Ep < 1 520 keY. Beyond this energy it suddenly increases to a level stretch between 1 520 and 1 660 keV. Next, several resonances (quoted in Ref. 4) can be perceived at 1 662.2, 1 683.9, l 724.4, 1 749, 1 799.9, 1 899.1, 1 909.9 and 1 968.6 keV. The most considerable intensity increases are situated at Ep = 1 520, 1 684 a n d 1 800 keV. The reaction Z7Al(p,p'?)27Al (E 7 = l O13 k e V ) This reaction does not produce any appreciable intensities below Ep = l 600 keV. The intensity curve also displays stepwise increases, indicating the presence o f J. Radioanal. Chem. 12 (1972) 198 G. DECONNINCK,. G. DEMORTIER: ANALYSIS OF ALUMINIUM Table 4 Absolute 9 of the 1 013 keV 7-rays emitted under b o m b a r d m e n t by protons f r o m a thick target of pure AI. The errors in the alJsolute values are less than 15 %, a n d the errors in the r e l a t i v e intensities are less t h a n 5 %. Intermediate values can be obtained by linear interpolation; * indicates the positions of the expected resonances Ep, keV 1 660 *1 662.2 *1 663 1 680 1 700 *1 705.6 1 720 *1 724.4 1 740 *I 749 1 760 1 780 1 798 Ny 280 213 320 462 657 1 030 1 500 1 680 2 530 2 905 3 280 3 470 3 505 ED, keV *1 799.9 1 802 1 820 1 840 *1 841.5 1 860 1 880 1 895 *1 899.1 * 1 909.9 1 912 1 920 1 940 N7 Ep, keV ~ 4 O32 5 060 5 455 6 000 6 085 6 565 7 125 8 525 11 250 15 940 16 520 17 450 19 890 1 96O 1 965 *1 968.6 1 970 1 980 2 000 2 050 2 100 2 120 2 140 2 160 2 180 2 200 N~, Ep, keV 22 24 30 34 36 40 43 52 62 68 71 75 79 500 335 000 37O 575 135 200 600 030 560 135 090 010 2 2 2 2 2 2 2 2 2 2 3 N7 uC 9st 25O 109 300 152 350 222 400 297 450 372 500 445 600 661 700 874 800 1 669 900 1 2 360 3 472 000 000 200 000 000 100 000 300 300 000 000 000 resonances. It is interesting to note that between 1 895 and 1 915 keV the intensity of this reaction increases by a factor of 2. The measured intensity values are exhibited in Fig. 5 and Table 4, Beyond I 900 keV the intensity 'of this reaction exceeds those of all the others. Table 5 Absolute intensities of the 1 368 keV ;,-rays emitted under b o m b a r d m e n t by p r o t o n s f r o m a thick target of pure AI. The errors in the absolute values are less than 15 Yo, and the errors in the relative intensities are less t h a n 5 %. Intermediate values can be obtained by linear interpolation; * indicates the positions of the expected resonances Ep, k~V ~ Ny Ep, kov 1 660 *1 662.3 *1 663 1 680 1 700 *1 705.6 1 710 1 720 *1 724.4 1 730 1 740 1 747 *I 749 390 410 417 585 780 845 930 1640 2 665 3 995 4 030 4 065 4 745 1 75l 1 755 1 760 ' 1 780 *1 799.9 1 820 *1 841.5 1 860 1 880 1 890 1 895 *1 899.1 *i 909.9 J. RadioanaL Chem. 12 (1972) N~, Ep, ~ k~V 5 700 5 525 5 525 6 525 :51525 5 525 5 525 5 525 5 525 5525 5525 5720 6 165 1 912 1 920 1 940 1 960 *1 968.6 1 980 2000 2 020 2040 2 060 2 080 2 100 2 120 N~ ~:~t 6 200 6 370 6 370 6 370 7 090 8 255 9 750 10 330 11 010 11 800 12 580 13 460 14 240 Eo' koV 2 140 2160 2 180 2 200 2 220 2 240 2 260 2 280 2 300 2 350 2 400 2 450 2 500 N~, /~(2 9st 15 17 20 23 24 24 25 25 26 28 33 42 55 310 550 965 9 100 180 865 350 940 325 730 150 700 750 G. D E C O N N I N C K , G. D E M O R T I E R : ANALYSIS OF ALUMINIUM 199 z 4.10 s 27AI.(p.p.~,) EI=I013keY z 0 = 90 ~ 3.10 s 4 910 ~ 3.10 = 2-1~ 2. lOS I | i ! 17 18 1.9 2_0 2.1 22 2.3 2/, 2.1 E p.lvleV 2.5 Ep),,'.eV Fig. 5. Absolute intensities of the 1 013 keV >,-rays from the reaction -~ p'~0"TAI. The photons are detected at 90 ~ with respect to the direction of the incident proton beam The. reaction ~ ~?)~Mg (Er = 1 368 keV) The intensity o f this reaction was measured between 1660 and 2 500 keV. Below Ep = 1 600 keV, the intensity is unobservable. F o r the h i g h e r energies it reaches a value comparable to that o f the reaction ZrAl(p, 7)zsSi. We observed a flat region between 1 760 and 1 890 keV in the intensity curve. Details are given in Fig. 6 and Table 5. Interferences The interest in this method o f analysis is limited to p r o t o n energies less than 5 MeV. Beyond 5 MeV the damage to the sample m a y become considerable. In addition, because o f the considerable emission o f neutrons at these energies, a rapid destruction o f the Ge(Li) detector is to be feared. ]. Radioanal. Chem. 12 (1972) 200 G. D E C O N N I N C K , G. D E M O R T I E R : A N A L Y S I S OF A L U M I N I U M / 5.~04 Z~ ! 27AI(P'a'~) 5.~o3~ / / ~J _S (~ Q v/ ,.6 ! 1.7 18i 2, 2~ 2~ I ,.9I I 24 20I =,.. Ep,MeV 215 " E=.Meu Fig. 6. Absolute intensities o f the I 368 keV )J-rays from the reaction 27Al(p, ~7)==Mg. The photons are detected at 90 ~ with respect to the direction of the incident proton beam A complete study of interferences will not be possible until all the intensities of the y-rays emitted by the elements are known. Those which are described here are only the most important ones. The y-rays of 1 778 keV can be produced by inelastic scattering of protons on esSi and by the reaction 31p(p, ~y)~.ssi" The minimum energy required for the first reaction to be possible is 1 842 keV. The second has been extensively studied at LARN. s The y-rays of 843 and 1 013 keV can be produced b y t h e reaction 26Mg(p, y)ZTAl (reaction without threshold)' and by the reaction a~ ~y)27Al for proton energies greater than 3.3 MeV. The y-rays of l 368 keV can be produced by inelastic scattering of protons on ~4Mg and by the reaction 6 23Na(p, y)~Mg. Other reactions on light nuclei which can produce these y-rays have thresholds at energies greater than 5 MeV. To avoid the possibility of interference it is sometimes possible to work with incident protons of energy less than the threshold energy, if any. Nevertheless, J. Radioanal. Chem. 12 (1972) G. D E C O N N I N C K , G. D E M O R T I E R : ANALYSIS OF ALUM1NIUM 201 it is often m o r e interesting to test the presence o f interference nuclei b y the following method. W h e n samples c o n t a i n i n g elements such as N a , M g , P a n d Si are b o m b a r d e d with 2.2 MeV p r o t o n s , t h e y emit y-rays o f an energy different f r o m the c h a r a c teristic ones o f P. T h e relative intensities o f the p r i n c i p a l y-rays e m i t t e d u n d e r the b o m b a r d m e n t o f these f o u r nuclei are given in T a b l e 6. T h e existence o f one o r m o r e y-rays o f greater intensity t h a n the interfering one allows r a p i d detection o f the possibility o f interference. T h e m o s t useful y-ray for d i s c o v e r i n g the p o s s i b i l i t y o f interference in each case is u n d e r l i n e d in T a b l e 6. Table 6 Intensities of the y-rays emitted under bombardment with 2.2 MeV protons Bombarded element Na Possible interfering ?-rays E~, keV N~,/tzC 9 st Reaction Mg E~,, keV st Reaction N~,/#C Si " Ee, keV st Reaction Nv/tzC " E~,, keV st Reaction N,/IzC " 1 368 300 + 50 23Na(p, y)24Mg 803 1 080 + 200 ~6Mg(p, 7)27A1 1 778 400 __. 40 31p(p, :qv)zsSi O t h e r emitted ?-rays Ev, keV N~,/#C 9 st Reaction Mg E ; i k ~ V st l~eaction Si 1 368 11 100 + 500 '-'4Mg(p,p';c)24Mg l 778 <10 28Si(p, p'y)28Si Bombarded element Na 1 013 l 670___ 200 "6Mg(p, 9))27A1 E,~ keV N~/#C 9 st Reaction E~, keV N~,/#C 9 st Reaction 43...~9 1 9 0 0 0 0 0 + 10000 "aNa(p ' p" F)23Na 390 10560+ 500 eSMg(p, p'7)25Mg 1 630 442000 _ 5000 2aNa(p, ~q,)~ONe 586 4 8 4 0 0 + 2000 Z~Mg(p,p'7):,~Mg 976 9 900 + 500 '-'~Mg(p, p'y)25Mg 1 273 538 + 25 29Si(p, p';,)29Si l 266 4-200 __ 200 alp(p, p,7)~lp 2 237 2 200 __ 200 alp(p, 7)a.*S J.. Radioanal. Chem. 12 (1972) 202 G. D E C O N N I N C K , G. D E M O R T I E R : ANALYSIS OF A L U M I N I U M Practical method of analysis The choice of the acceleration eneryy for the protons and of the y-radiation to be detected The speed of analysis of the aluminium concentration in the surface layer of a sample is a function of the intensity of the emitted y-rays, of the correspondence between z (the number of y-rays counted in the peak) a n d f ( t h e number appearing in the continuous background at the peak site), and of the specific physical factors concerning each individual sample. Among these last-named are the characteristic interferences from y-rays of the element under analysis and those from other compounds in the sample, and the possible destruction of the sample under extensive bombardment (the effect of this complication can be reduced by using a revolving target). Disregarding these physical factors, the optimal acceleration energy of the protons can be predicted. When the sample consists mainly of light elements which usually emit few y-rays under proton bombardment, it will be advantageous to work at a fairly high energy. For an acceleration energy of the order of 2 000 keV, y-radiations of 843 or 1 013 keV are of comparable intensities. If interference by Mg is suspected, a proton energy of the order of 1 500 keV will be used and the y-radiation of 1 778 keV detected. When the sample consists mainly of heavy elements, a lower proton energy will be used. For the measurement of concentrations in the per cen t range, a choice of proton energy slightly higher than the resonance energy at Ep = 632 keV and the detection of the y-rays of 1 778 keV are recommended. For lower concentrations it is sometimes advantageous to select an energy Ep of 1 MeV (i.e. slightly higher than the intense and isolated resonance energy at 991.88 keV), where the y-rays are more intense than at 632 keV. This choice of energy is merely a recommendation. It will often prove interesting to generate the spectrum of the emitted y-rays at several energies Ep and select that one which produces the fastest results. Rapid identification of AI in a sample The analysis of a spectrum of y-radiations emitted by a sample subjected to proton bombardment permits the identification of A1 in a few minutes (for a beam intensity of the order of 1 /aA). The sample contains AI if y-rays of 843 and 1 013 keV of comparable intensities are observed under the bombardment with 2 MeV protons and if these two radiations disappear from the spectrum when the proton acceleration energy is diminished below 1 500 keV. This last procedure makes sure that the ~,-rays are not generated by a reaction with Mg. J. Radioanal. Chem. 12 (1972) G. DECONNINCK, G. DEMORTIER: ANALYSIS OF ALUMINIUM 203 If an accelerator of sufficient energy is not available for this method of analysis, the detection of the 1 778 keV y-rays produced by b o m b a r d m e n t with "protons of lower energy may be possible. This second procedure can prove more interesting than the first in the case where the sample consists mainly of heavy elements. I f these two tests for AI give a negative result, the sample does not contain more than 0.1% AI. Smaller quantities may be detected by longer exposures. Measurement of the average concenti'ation The stopping power ( S) of the sample is calculable. The prodecure to be followed consists of the steps below: - b o m b a r d with protons of selected energy (see previous section) a sample containing a known quantity of AI and arranged in the manner shown in Fig. 1 ; - count the number (Z) of y-rays emitted for a fixed number of pC; - replace this standard by the sample to be analysed and take care that all other conditions remain the same; - count the number (z) of y-rays emitted for the same number of pC. Repeat this measurement if the statistical error of computation is big and calculate the average value (:?); - apply the relation:' Yech Yst -- Z S9 Z Sst(E) (1) where Yech -- proportion of atoms being analysed in the sample, proportion of atoms in the standard, z (or :?) - number of y-rays detected during the b o m b a r d m e n t of the sample, Z - number of v-rays detected during the b o m b a r d m e n t of the standard, S - stopping power (this may be found in Ref.8). The value/~ is the value of Ep where Nr(Ep) is halfway along the ordinate, i.e. N~(E) = 1/2N~,(E,). This empirical rule gives results correct to approximately 1~/o. To begin with, it is assumed that Scch is dependent only on the known constituents. If Ycch is of the order of 1% or less, the assumption is valid. Ify~ch is bigger, an iteration calculation must be made by substituting into S~r the newly calculated value of Yech. The stopping power (S) cannot be calculated. The same procedure is followed as in the first case and eventually one of the methods described in Ref. t is applied. If the composition is unknown, a comparative analysis of another constituent can be executed. In the report LARN-705 an example of a comparative analysis of A I - N a is described. 6 Yst - - J Radioanal. Chem. 12 (1972) 204 G. D E C O N N / N C K , G. DEMORTIER: -ANALYSIS OF ALUMINIUM Remark: If the absence of interferences is definite, the detection and simultaneous counting of several characteristic ?-rays of the element under analysis allow a faster measurement. Eq. (1) is then written: Yeeh 272 Sech(J~) y~t ~ z ss,(E) Sensitivity o f the method According to convention, the limit of sensitivity a m is considered to be reached when the peak height of the characteristic ?-rays is equal to half of that of the average background noise recorded in the neighbourhood of the peak. By visualizing this peak as a triangle, the peak count will then equal 1/4 of the background count at the peak site. For the measurement of low concentration, it is important to decide with the greatest care on the acceleration energy of the protons and therefore also the characteristic y-radiation to be detected, basing the decision either on trials at various energies, or on the method described above for the rapid identification of A1. An accelerator of variable energy between 500 and 2 500 keV is indispensable for a complete critical analysis of the best energy of acceleration. Of course, the sensitivity improves with increasing bombardment time, but the bombardment of a sample with a beam of the order of 1/zA for several hours is accompanied by the risk of deterioration. This deterioration is manifested in the form of craters of depth equal to R(Ev), i.e. a few dozen microns. This mode of destruction is typical in a crystalline substance. It was observed during prolonged bombardment of silicon. 7 Preliminary applications The following applications were chosen for their specific characteristics, i.e. for the peculiar difficulties they present. Analysis o f AI in stainless steel Different samples of stainless steel were bombarded and different concentrations of AI were obtained, depending on the origin of the sample. The sensitivity limits (Ymi,) are a function of the detected ?-rays and of the energy of the protons employed for the bombardment. They were estimated for different practical conditions of analysis (Table 7). The analysis at Ep = 2 000 keV is therefore especially interesting where speed is essential. The analysis of A1 in stainless steel by the detection of ?-rays of 843 keV is impossible because of their proximity to the 847 keV ?-rays resulting from the reaction 56Fe(p, p'?)56Fe.9 d. RadioanaL Chem. 12 (1972) G. D E C O N N I N C K , G. D E M O R T I E R : ANALYSIS OF ALUMINIUM 205 Table 7 Bombardment INOX Ep, k e V E~,, k e V Time, min 650 1 000 2 200 1 778 ! 778 1 013 30 Beam intensity, /tA 2 2 0.2 30 3 Ymin, p p m 750 2 000 I 200 The accuracy of the determination is reduced by the limited knowledge of the S values and by computation statistics. For a particular analysis (stainless H. V. E.) it has been found that Yech = 3 110_ 120 ppm. The precision is of the order of 5 %. Analysis of Al in uranyl nitrate A sample of uranyl nitrate was bombarded by protons of 995 keV for 1 hr using a beam of 1.4 pA, and the count of emitted ),-rays was compared with that of a standard of pure A1. The experimental results are given below; the molecular weight of the sample [UO2(NO3)2.6 H20] equals 502. Under prolonged bombardment (1 hr) a progressive evaporation of water is possible. By assuming that the water evaporates rapidly, a molecular weight of 394 is computed and a new calculation of Seth has to be made. This complication can be surmounted either by cooling the sample to the temperature of liquid nitrogen, or by getting rid of the water beforehand. The uranyl nitrate sample contained Yech = 387• AI. The lower limit of the amount of A1 detectable is Yeeh,min : 75 ppm. For a sample containing less than 109 ppm the analysis is only qualitative. Analyses of rock samples containing Al and Na Samples of mairupt and muscovite were bombarded with protons of 1.4 MeV, and the ),-radiation of 1 778 keV was detected. The following compositions served as the basis for the calculation of S: Mairupt: NaA1Si3Os; Muscovite: KA1Si3010(OH)2. J. RadioanaL Chem. 12 (1972) 206 G. D E C O N N I N C K , G. D E M O R T I E R : ANALYSIS OF A L U M I N I U M Table 8 Comparison of the calculated and measured data Sample Mairupt Muscovite A1, ~ theoretical AI, found 10.4 7.8 13 _ I 5.96__+0.4 In Table 8 the measured percentages are compared with the percentages calculated for the theoretical compositions. The differences imply compositions different from those presumed. A comparative analysis of the A1 and Na concentrations in these substances (see report LARN-705) gives the results shown in Table 9. Table 9 The ratio of A1 to Na concentrations Na/AI (calculated), atoms Sample Mairupt Muscovite J I 1 0 NalAI (found), atoms 0.35 0.04 Analysis of Al in a heavy substance A finely powdered mixture of W and A120~ in the proportion of 104/1 was bombarded by protons of 1 and 2.2 MeV. The y-rays of 1 778 and 1 0 1 3 keV were recorded. The results are given in Table 10. During the b o m b a r d m e n t at I MeV and the detection of the 1 778 keV ),-rays, the limit defined above as the sensitivity of the method was attained. The method can be made more sensitive, detecting t0 ppm, by using protons of 2.2 MeV and by detecting the 1 013 keV y-radiation. It is not surprising that the results recorded at different energies of Ep should be different. It is rather difficult in fact to obtain a completely homogeneous mixture of substances in which the concentrations differ so much (104/1). Since the layers penetrated by the protons of 1.0 and 2.2 MeV are not the same, a difference in the measurements made on the same sample points to an inhomogeneous mixture W - A120~. J. Radioanal. Chem. 12 (1972) 207 G. D E C O N N I N C K , G. D E M O R T I E R : A N A L Y S I S O F A L U M I N I U M Table 10 Results recorded at different proton energies Ep, keV 1 000 2 200 E, keV 1778 1013 Yech, ppm Yeeh.mln, ppm Tirae, rain 120+ 5 15o+ 5 80 10 200 20 Beam intensity, /zA 2 0.5 Contrary to the rule, it is seen that maximum sensitivity is attained for the higher proton energies. Actually, each analysis depends on the specific sample. A critical analysis of ~-ray intensities at different proton energies is always to be preferred. Conclusions (1) When a thick target of pure A1 is bombarded by protons, 7-radiations o f 843, 1 013, ! 368 and 1 778 keV are produced, as well as some others of lower intensities (see Table 1). The intensities of these four v-rays as a function of the proton energy have been measured for incident energies between 500 and 2 500 keV. (2) The analysis of A1 in the surface of materials is possible to a depth of the order of 20 #m. (3) The possible interferences by Na, Mg, Si and P can be easily identified. (4) The sensitivity of the method is of the order of 10 to 1 000 ppm and depends on the sample. The limits given here were obtained at L A R N in practical trials on several samples and for measurements not exceeding 60 min. Concentrations of 1 000 ppm can be easily detected in samples consisting of solid organic matter. The assistance of Mr. F. BODART and Miss L. TH()NE in obtaining the results is gratefully acknowledged. Special thanks are also due to Mr. Y. MORCIAUX for the perfect functioning of the experimental apparatus, and to Miss NOLTE for the preparation of this manuscript. References 1. G. DECONNINCK, Analyse des surfaces par r6actions (p~ ~)) et (p, p'~). L A R N 702, 1970; Dosage des 616ments par r6action nucl6aire de basse 6nergie. Ann. Soc. Scient., Bruxelles, 83 (1969) 45. 2. G. DEMORTIER, Efficienceabsolue de deux d6tecteurs Ge(Li). L A R N 703, 1970; to b e published in the Proc. on P h o t o n detectors, Varna, 1971. 3. P. F. DAHL, D. G. COSTELLO, W. L. WALTERS, Nucl. Phys., 21 (1960) 109. 4. M. A. MEYER, N. S. WOLMARANS, D. RETMANN, Nucl. Phys., A 144 (1970) 261. J. Radioanal. Chem. 12 (1972) 208 G. DECONNINCK, G. DEMORTIER: ANALYSIS OF ALUMINIUM 5. G. DEMORTIER, F. BODART (in this Proceedings), J. Radioanal. C h e m . , 12 (1972) 209. 6. F. BODART, G. DEMORTIER, G. DECONNINCK, Dosage du N a par r6actions (p, ~,0, (P, P';') et (p, ~ ) . L A R N 705, 1970. 7. G. DEMORTIER, G. DECONNINCK, F. BODART, L. THONE, Dosage de l ' A l u m i n i u m par r6action (p, y), (p, p'y), (p, ct)J). L A R N 704, 1970. 8. C. F. WILLIAMSON, J. P. BOUJOT, J. PICARD, Tables of range and stopping power of chemical elements for charged particles of energy 0.05 to 500 MeV. 9. G. DECONNINCK, G. DEMORTIER, Dosage d'6chantiIIons m6talliques par r6actions atomiques et nucl6aires promptes. L A R N 725, 1972. J. Radioanal. Chem. 12 (1972)