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Stopping powers of 0.5–8.3 MeV protons in Havar, Nickel, Kapton and Mylar
130
Nuclear Instruments and Methods in Physics Research B35 (1988) 130-134 North-Holland,
STOPPING
POWERS OF 0.543
E.RAUHALA University
MeV PROTONS
Amsterdam
IN HAVAR, NICKEL, KAPTON AND MYLAR
and J. ~~ISANEN
of Helsinki, Accelerator Laboratory
Hiimeentie
100, SF-00550 Helsinki,
Finland
Received 27 May 1988 and in ievised form 24 August 1988
Stopping powers of 0.5-8.3 MeV protons have been determined in transmission geometry for Havar, Ni, Kapton and Mylar. The experimental data are compared with calculated values obtained by Bragg’s additivity rule and by the Andersen-Ziegler parameters for proton stopping. Comparisons are made with the limited data from the literature.
1. Introduction
2. Experimental
Stopping of protons in matter has been of considerable interest due to their wide use in various applications. However, in the case of composite materials such as Havar, Kapton and Mylar, the stopping of protons has not been studied adequately. The knowledge of ion stopping in such materials is also interesting from the theoretical point of view. For Kapton, only the energy loss measurements by Foroughi et al. 111 for 1.26-4.43 MeV protons, and those determined in our laboratory [2] for 0.45-2.4 MeV protons, can be found in the literature. Ishiwari et al. [3] have determined the stopping power of 6.92 MeV protons for Mylar. L’Hoir and Schmaus [4] have measured the stopping powers of 0.3-2.0 MeV protons in Terphane, which is a very similar material to Mylar. Duder et al. [5] have measured the stopping powers of 2.9-6.0 MeV protons in Havar. The energy loss values of protons in Havar have been determined by Foroughi et al. [l] (1.26-4.43 MeV) and in our previous study (0.45-2.4 MeV) [2]. A disagreement of about 10% in the stopping powers of refs. [l] and [5] at around 3 MeV is observed. The purpose of the present study was to determine the stopping powers of 0.5-8.3 MeV protons in Havar, nickel, Kapton and Mylar by the transmission technique. Nickel was chosen as a reference material to check for any systematic errors, and for comparison purposes. The nickel stopping power data for proton energies over a few hundred keV may be found in refs. [6-111. The stopping power values at the low energy region (Er I 2.4 MeV) have been determined from the energy loss data presented in our earlier study [2]. An incorrect composition of the Kapton foil given in that study is corrected. The present work is a continuation of our systematic study for obtaining stopping powers in composite materials 112-161.
The proton beams were obtained from 5 MV EGPlo-11 tandem and 2.5 MV Van de Graaff accelerators. The stopping power measurements were performed in transmission geometry. A thick gold target, or a 56 nm thick gold film on a SiO, substrate, was used as a scatterer to reduce the ion flux to a reasonable level. The experimental setup and measuring geometry is described in detail in references [2] and [12]. The most probable energy loss of the protons in the foils was determined from the shift of the backscattering signal, induced by the foil. The detector used was a 50 mm2 (area), 1000 urn (sensitive depth) silicon surface barrier detector, and the energy resolution of the detection system was 18 keV at Ep = 8.5 MeV.
0168-583X/88/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
3. Measurements and results In the determination of the stopping power from the energy loss, the knowledge of the foil thickness (or areal density) is essential. In the present study, the average foil thicknesses were determined by weighing a circular (la 20 mm) piece from the foils. The mass densities of 8.30, 8.91, 1.42 and 1.39 g/cm3 for Havar, nickel, Kapton (C2,H,,0,N2) and Mylar (C,,H,O,), respectively, were assumed. The possible local foil thickness variations were checked by 1.4 MeV proton backscattering measurements from several points ( 0 0.5 mm) of the foils. All foils except Kapton were found homogeneous within experimental error limits of f 1%. The determination of the true thickness of Kapton was found to be more problematic. Thickness variations over 6% were observed. Therefore, the thickness of the Kapton foil was further investigated by several independent methods. Signs of variations in the foil thickness
131
E. Rauhala, J. Riiisiinen / MeVproton stopping in Havar, Ni, Kapton and Mylar Table 1 The stopping power values [keV cm2/mg] of protons in Havar, nickel, Kapton and Mylar EWeV)
Havar
WMeV)
Ni
WMeV)
Kapton
E(MeV)
Mylar
0.510 0.630 0.857 1.074 1.288 1.498 1.705 1.912 2.119 2.322 2.88 3.37 3.87 4.33 4.37 4.82 5.33 5.82 6.31 6.81 7.30 7.79 8.29
188 169 142 125 112 102 94.2 87.3 80.8 77.8 67.4 62.7 57.0 52.5 53.2 48.8 44.4 42.9 39.9 37.5 36.6 33.9 31.8
2.85 3.35 3.85 4.29 4.34 4.78 5.29 5.78 6.28 6.78 7.27 7.76 8.26
68.5 60.9 57.0 51.8 52.5 49.2 45.4 42.6 40.7 37.9 36.5 34.9 32.8
0.512 0.582 0.831 1.057 1.276 1.488 1.698 1.908 2.112 2.318 2.87 3.37 3.86 4.31 4.35 4.80 5.31 5.81 6.80 7.29 7.78 8.28
385 352 273 232 200 182 165 149 143 132 116 101 91.4 80.4 82.5 76.5 69.0 63.9 57.4 55.1 53.1 49.6
0.336 0.393 0.457 0.509 0.525 0.648 0.730 0.879 0.940 1.096 1.148 1.311 1.355 1.519 1.552 1.725 1.762 1.933 1.966 2.136 2.339 2.370 2.84 2.91 3.34 3.41 3.84 3.90 4.28 4.35 4.40 4.77 5.28 5.78 6.27 6.77 7.27 7.76 8.26
462 a) 432 a) 410 b, 370 *) 374 b, 325 b, 288 * 260 b, 247 a) 224 b, 214 ‘) 194 b, 187 a) 176 ‘) 173 =) 163 b, 158 a) 146 b) 142 a) 139 b) 131 b) 127 * 114 d, 115 O) 104 d, 102 =) 93.8 ‘) 91.7 c, 81.5 e, 85.4 d, 81.3 ‘) 77.1 e, 69.9 e, 67.9 =) 62.2 =) 57.3 =) 55.5 =) 51.3 =) 44.8 =)
MyIar a) From 3.50 pm thick foil data, ref. 121.
b, From 6.64 pm thick foil data, ref. [2]. ‘) From 3.26 pm thick foil data. ‘) From 12.21 pm thick foil data. ‘) From 24.38 pm thick foil data. Nickel 2.85-4.34 MeV: from 2.82 pm thick foil data. 4.29-8.26 MeV: from 5.56 pm thick foil data. Kapton 0.512-2.318 MeV: from 8.73 pm thick foil data, ref. [2] 2.87-4.35 MeV: from 8.86 pm thick foil data. 4.31-8.28 MeV: from 18.17 pm thick foil data. Havar 0.510-2.322 MeV: from 2.43 pm thick foil data, ref. [2]. 2.88-4.37 MeV: from 2.02 pm thick foil data. 4.33-8.29 MeV: from 4.02 pm thick foil data.
132
E. Rauhala, J. R&ken
/ MeVproton stopping in Havar, Ni, Kapton and Mylar
were observed in the interference spectrum obtained by a 580 nm wavelength ring dye laser beam of about 10 mm in diameter. The surface profile of the foil was also determined by a profilometer, which showed similar behavior. No reliable absolute thickness values, however, were obtained by these methods. Since the effective foil area (approximately 10 mm’) used in the actual stopping power measurements is too small to yield accurate areal densities directly by weighing, an indirect method was chosen to determine the “weighed local” Kapton foil thickness at exactly the spot exposed to the scattered proton beam. This was accomplished by using proton beams to determine reference thicknesses of the foil: an average thickness over a large foil area and a local thickness at the spot where the stopping power experiments were performed.For these reference values standard proton stopping powers from ref. [17] used in conjunction with Bragg’s rule were assumed. An agreement better than 1% was found when both 1.4 MeV proton backscattering and the present energy loss data at 3.0-4.0 MeV were used for computing the local reference thickness. The average reference thickness obtained by 1.4 MeV proton backscattering from 20 different spots (00.5 mm) over the whole weighed foil area of 20 mm in diameter, was taken to correspond to the thickness obtained by weighing. The ratio of the weighed thickness to this average was found to be 1: 1. The local reference thickness from proton measurements, at the spot where the stopping power experiments were per-
formed, thus represents the final correct “weighed local” Kapton foil thickness. An accuracy of 3% was estimated for the determined Kapton foil thickness and 2% for the other foil thicknesses. Multiple foils were formed by stacking and were used at the higher proton energies, since the energy losses were too small for the thinner foils and would have increased the relative errors in the stopping power values depicted. The foil thicknesses used were: Havar 2.02 and 4.02 pm, Kapton 8.86 and 18.17 pm, nickel 2.82 and 5.56 pm, Mylar 3.26, 12.21 and 24.38 pm. The obtained stopping power values for the foil materials are given in table 1. The method for obtaining the stopping power values from the measured energy loss data is described in detail in refs. [13] and [14]. Below 2.4 MeV the energy loss data from ref. [2] were used. The incorrect composition of the Kapton foil material given in table 1. of ref. [2] should be corrected as C,,H,,O,N,. The resulting thickness given in ref. [2] is corrected in the data of table 1 of the present study. Taking into account the possible experimental error sources, the uncertainties of the stopping powers are expected to fall below 3%. However, for Kapton the possible errors are larger due to the local thickness variations of the foils. The given values for Kapton should include errors smaller than 4%. Figs. l-3 show the experimental data, together with calculated predictions obtained by using Bragg’s rule in conjunction with the proton stopping parameters given in ref. [17]. The limited data from the literature is also given for com-
. o
0.01
present work Foroughi et al. [I Duder et al. [51
1
I
I
1.0
2.0
3.0
proton
LO
energy
5.0
6.0
7.0
8.0
(MeVl
Fig. 1. Stopping powers of protons in Mylar. The solid lines have been fitted to the present experimental data to guide the eye. The calculated dashed curves were obtained by using Bragg’s rule with stopping power values from ref. [17]. Data from the literature are also presented for comparison.
E. Rauhala, J. Riiisiinen / MeVproton
133
stopping in Havar, Ni, Kapton and Mylar
present work L'Hoir 8, Schmaus 141 Ishiwari etal. [31 ____calculated . o 0
I-
1.0
,2.0
3.0
4.0
proton energy
5.0
_
6.0
_
7.0
c 8.0
(MeV)
Fig. 2. As in fig. 1, but for Kapton and Havar.
parison. The values for Kapton and Havar presented in fig. 2 obtained by Foroughi et al. [l] have been calculated from their energy loss data using an appropriate procedure.
4. Discussion Our data may be compared with both existing experimental data from the common energy intervals, and with semiempirical predictions. Over the entire 0.5-8.3 MeV energy region used in the present study the maximum deviation of our values from the semiempirical stopping power values is less than 5% in all cases.
3.0
4.0
proton
5.0 energy
6.0
7.0
IMeW
Fig. 3. As in fig. 1, but for nickel.
8.0
For the light composite Mylar foil, previous measurements cover the energy region below 2 MeV [4]. One data point at 6.92 MeV has also been presented [3]. Our data are in good agreement with both these experimental data and with the semiempirical tabulations of ref. [17]. In the light of the results of the present work this may also be considered as an indication of the good quality of Mylar foils in that they have no significant variations in foil thickness. For Kapton the present stopping power data agree well with the semiempirical values, but differences of the order of 15% between the data of Foroughi et al. [l] and our data are found. As described in the previous section, the large local thickness variations of Kapton make it extremely difficult to reliably determine the thickness of the foil at exactly the position of the stopping power measurements. The different method in determining the foil thickness in ref. [l] could partly explain the difference between the experimental data. Foroughi et al. quote an experimental accuracy of 15-208. It may be noted that the stopping powers for Mylar and Kapton are very close to each other. Two groups have earlier experimented on Havar. Between the range 3 and 6 MeV, Duder et al. [5] present data that fall l-22 below our data. The results computed from the energy loss data of Foroughi et al. [I], however, show a clear deviation from our stopping power values below 2 MeV, also suggesting a different stopping power curve shape from that in ref. [5] and from that in the present study. All the data mentioned, however, fall within the 20% error limits of ref. [l].
134
E. Rauhala, J. Riiisiinen / MeVproton
For nickel it may be noted that our data are in very good agreement with the mutually consistent experimental data in the literature. However, all the data fall systematically slightly higher than the calculated semiempirical predictions. As at our energies no theoretical evidence exists for a difference between proton and deuteron stopping powers at identical velocities [17], deuteron stopping data may also be drawn into comparison. For Havar Duder et al. [5] have determined the stopping powers of 0.8-4 MeV deuterons (corresponding to proton energies 0.4-2 MeV) and Shepard and Porter [18] of 4.6-5.1 MeV deuterons. These literature deuteron data are in very good mutual agreement. Compared to the proton stopping powers they lie about 1.5% below the semiempirical calculated curve, whereas the present values are about 2-3% above the calculated values at energies below 1 MeV. With increasing energy the present data approach gradually the calculated predictions coinciding with them at 1.5 MeV. At 1.5 MeV the deuteron data lie about 3% below the calculations but coincide with them at about 2 MeV. In view of the experimental accuracies the overall agreement between all data is good. To the knowledge of the authors, no experimental deuteron stopping powers for Kapton and Mylar may be found in the literature. The support acknowledged.
from
the Academy
of Finland
is
stopping in Hauar, Ni, Kapton and Mylar
References [l] F. Foroughi, B. Vuilleumier and E. Bovet, Nucl. Instr. and Meth. 159 (1979) 513. [2] E. Rauhala and J. RZis&ren, Nucl. Instr. and Meth. B12 (1985) 321. 131 R. Ishiwari, N. Shiomi and N. Sakamoto, Phys. Rev. A25 (1982) 2524. [41 A. L’Hoir and D. Schmaus, Nucl. Instr. and Meth. B4 (1984) 1. 151 J.C. Duder, J.F. Clare and H. Naylor, Nucl. Instr. and Meth. 123 (1975) 89. WI H.H. Andersen, C.C. Ha&e, H. Simonsen, H. Sorensen and P. Vajda, Phys. Rev. 175 (1968) 389. [71 A.B. Chilton, J.N. Cooper and J.C. Harris, Phys. Rev. 93 (1954) 413. PI R. Ishiwari, N. Shiomi, S. Shirai, T. Ohata and Y. Uemura, Bull. Inst. Chem. Res. Kyoto Univ. 49 (1971) 390. t91 R. Ishiwari, N. Shiomi and N. Sakamoto, Phys. Lett. 75A (1979) 112. WI N.N. Pucherov and T.D. Chesnokova, Ukr. Phys. J. 24 (1979) 372. WI L.P. Nielsen, K. Dan. Vidensk. Selsk. Mat. Fys. Medd. 33 (1961) no. 6. WI J. Rls’ben and E. Rat&ala, Phys. Rev. B35 (1987) 1426. 1131 E. Rauhala and J. R;iis;inen, Nucl. Instr. and Meth. B24/25 (1987) 362. P41 J. RZis&nen and E. Rat&ala, Phys. Rev. B36 (1987) 9776. 1151 E. Rauhala and J. R%isSinen,Phys. Rev. B37 (1988) 9249. WI J. R;iisS;nen and E. RauhaIa, Radiat. Eff., in press. P71 H.H. Andersen and J.F. Ziegler, The Stopping and Ranges of Ions in Matter, vol. 3 (Pergamon, New York, 1977). WI C.L. Shepard and L.E. Porter, Phys. Rev. B12 (1975) 1649.
Nuclear Instruments and Methods in Physics Research B35 (1988) 130-134 North-Holland,
STOPPING
POWERS OF 0.543
E.RAUHALA University
MeV PROTONS
Amsterdam
IN HAVAR, NICKEL, KAPTON AND MYLAR
and J. ~~ISANEN
of Helsinki, Accelerator Laboratory
Hiimeentie
100, SF-00550 Helsinki,
Finland
Received 27 May 1988 and in ievised form 24 August 1988
Stopping powers of 0.5-8.3 MeV protons have been determined in transmission geometry for Havar, Ni, Kapton and Mylar. The experimental data are compared with calculated values obtained by Bragg’s additivity rule and by the Andersen-Ziegler parameters for proton stopping. Comparisons are made with the limited data from the literature.
1. Introduction
2. Experimental
Stopping of protons in matter has been of considerable interest due to their wide use in various applications. However, in the case of composite materials such as Havar, Kapton and Mylar, the stopping of protons has not been studied adequately. The knowledge of ion stopping in such materials is also interesting from the theoretical point of view. For Kapton, only the energy loss measurements by Foroughi et al. 111 for 1.26-4.43 MeV protons, and those determined in our laboratory [2] for 0.45-2.4 MeV protons, can be found in the literature. Ishiwari et al. [3] have determined the stopping power of 6.92 MeV protons for Mylar. L’Hoir and Schmaus [4] have measured the stopping powers of 0.3-2.0 MeV protons in Terphane, which is a very similar material to Mylar. Duder et al. [5] have measured the stopping powers of 2.9-6.0 MeV protons in Havar. The energy loss values of protons in Havar have been determined by Foroughi et al. [l] (1.26-4.43 MeV) and in our previous study (0.45-2.4 MeV) [2]. A disagreement of about 10% in the stopping powers of refs. [l] and [5] at around 3 MeV is observed. The purpose of the present study was to determine the stopping powers of 0.5-8.3 MeV protons in Havar, nickel, Kapton and Mylar by the transmission technique. Nickel was chosen as a reference material to check for any systematic errors, and for comparison purposes. The nickel stopping power data for proton energies over a few hundred keV may be found in refs. [6-111. The stopping power values at the low energy region (Er I 2.4 MeV) have been determined from the energy loss data presented in our earlier study [2]. An incorrect composition of the Kapton foil given in that study is corrected. The present work is a continuation of our systematic study for obtaining stopping powers in composite materials 112-161.
The proton beams were obtained from 5 MV EGPlo-11 tandem and 2.5 MV Van de Graaff accelerators. The stopping power measurements were performed in transmission geometry. A thick gold target, or a 56 nm thick gold film on a SiO, substrate, was used as a scatterer to reduce the ion flux to a reasonable level. The experimental setup and measuring geometry is described in detail in references [2] and [12]. The most probable energy loss of the protons in the foils was determined from the shift of the backscattering signal, induced by the foil. The detector used was a 50 mm2 (area), 1000 urn (sensitive depth) silicon surface barrier detector, and the energy resolution of the detection system was 18 keV at Ep = 8.5 MeV.
0168-583X/88/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
3. Measurements and results In the determination of the stopping power from the energy loss, the knowledge of the foil thickness (or areal density) is essential. In the present study, the average foil thicknesses were determined by weighing a circular (la 20 mm) piece from the foils. The mass densities of 8.30, 8.91, 1.42 and 1.39 g/cm3 for Havar, nickel, Kapton (C2,H,,0,N2) and Mylar (C,,H,O,), respectively, were assumed. The possible local foil thickness variations were checked by 1.4 MeV proton backscattering measurements from several points ( 0 0.5 mm) of the foils. All foils except Kapton were found homogeneous within experimental error limits of f 1%. The determination of the true thickness of Kapton was found to be more problematic. Thickness variations over 6% were observed. Therefore, the thickness of the Kapton foil was further investigated by several independent methods. Signs of variations in the foil thickness
131
E. Rauhala, J. Riiisiinen / MeVproton stopping in Havar, Ni, Kapton and Mylar Table 1 The stopping power values [keV cm2/mg] of protons in Havar, nickel, Kapton and Mylar EWeV)
Havar
WMeV)
Ni
WMeV)
Kapton
E(MeV)
Mylar
0.510 0.630 0.857 1.074 1.288 1.498 1.705 1.912 2.119 2.322 2.88 3.37 3.87 4.33 4.37 4.82 5.33 5.82 6.31 6.81 7.30 7.79 8.29
188 169 142 125 112 102 94.2 87.3 80.8 77.8 67.4 62.7 57.0 52.5 53.2 48.8 44.4 42.9 39.9 37.5 36.6 33.9 31.8
2.85 3.35 3.85 4.29 4.34 4.78 5.29 5.78 6.28 6.78 7.27 7.76 8.26
68.5 60.9 57.0 51.8 52.5 49.2 45.4 42.6 40.7 37.9 36.5 34.9 32.8
0.512 0.582 0.831 1.057 1.276 1.488 1.698 1.908 2.112 2.318 2.87 3.37 3.86 4.31 4.35 4.80 5.31 5.81 6.80 7.29 7.78 8.28
385 352 273 232 200 182 165 149 143 132 116 101 91.4 80.4 82.5 76.5 69.0 63.9 57.4 55.1 53.1 49.6
0.336 0.393 0.457 0.509 0.525 0.648 0.730 0.879 0.940 1.096 1.148 1.311 1.355 1.519 1.552 1.725 1.762 1.933 1.966 2.136 2.339 2.370 2.84 2.91 3.34 3.41 3.84 3.90 4.28 4.35 4.40 4.77 5.28 5.78 6.27 6.77 7.27 7.76 8.26
462 a) 432 a) 410 b, 370 *) 374 b, 325 b, 288 * 260 b, 247 a) 224 b, 214 ‘) 194 b, 187 a) 176 ‘) 173 =) 163 b, 158 a) 146 b) 142 a) 139 b) 131 b) 127 * 114 d, 115 O) 104 d, 102 =) 93.8 ‘) 91.7 c, 81.5 e, 85.4 d, 81.3 ‘) 77.1 e, 69.9 e, 67.9 =) 62.2 =) 57.3 =) 55.5 =) 51.3 =) 44.8 =)
MyIar a) From 3.50 pm thick foil data, ref. 121.
b, From 6.64 pm thick foil data, ref. [2]. ‘) From 3.26 pm thick foil data. ‘) From 12.21 pm thick foil data. ‘) From 24.38 pm thick foil data. Nickel 2.85-4.34 MeV: from 2.82 pm thick foil data. 4.29-8.26 MeV: from 5.56 pm thick foil data. Kapton 0.512-2.318 MeV: from 8.73 pm thick foil data, ref. [2] 2.87-4.35 MeV: from 8.86 pm thick foil data. 4.31-8.28 MeV: from 18.17 pm thick foil data. Havar 0.510-2.322 MeV: from 2.43 pm thick foil data, ref. [2]. 2.88-4.37 MeV: from 2.02 pm thick foil data. 4.33-8.29 MeV: from 4.02 pm thick foil data.
132
E. Rauhala, J. R&ken
/ MeVproton stopping in Havar, Ni, Kapton and Mylar
were observed in the interference spectrum obtained by a 580 nm wavelength ring dye laser beam of about 10 mm in diameter. The surface profile of the foil was also determined by a profilometer, which showed similar behavior. No reliable absolute thickness values, however, were obtained by these methods. Since the effective foil area (approximately 10 mm’) used in the actual stopping power measurements is too small to yield accurate areal densities directly by weighing, an indirect method was chosen to determine the “weighed local” Kapton foil thickness at exactly the spot exposed to the scattered proton beam. This was accomplished by using proton beams to determine reference thicknesses of the foil: an average thickness over a large foil area and a local thickness at the spot where the stopping power experiments were performed.For these reference values standard proton stopping powers from ref. [17] used in conjunction with Bragg’s rule were assumed. An agreement better than 1% was found when both 1.4 MeV proton backscattering and the present energy loss data at 3.0-4.0 MeV were used for computing the local reference thickness. The average reference thickness obtained by 1.4 MeV proton backscattering from 20 different spots (00.5 mm) over the whole weighed foil area of 20 mm in diameter, was taken to correspond to the thickness obtained by weighing. The ratio of the weighed thickness to this average was found to be 1: 1. The local reference thickness from proton measurements, at the spot where the stopping power experiments were per-
formed, thus represents the final correct “weighed local” Kapton foil thickness. An accuracy of 3% was estimated for the determined Kapton foil thickness and 2% for the other foil thicknesses. Multiple foils were formed by stacking and were used at the higher proton energies, since the energy losses were too small for the thinner foils and would have increased the relative errors in the stopping power values depicted. The foil thicknesses used were: Havar 2.02 and 4.02 pm, Kapton 8.86 and 18.17 pm, nickel 2.82 and 5.56 pm, Mylar 3.26, 12.21 and 24.38 pm. The obtained stopping power values for the foil materials are given in table 1. The method for obtaining the stopping power values from the measured energy loss data is described in detail in refs. [13] and [14]. Below 2.4 MeV the energy loss data from ref. [2] were used. The incorrect composition of the Kapton foil material given in table 1. of ref. [2] should be corrected as C,,H,,O,N,. The resulting thickness given in ref. [2] is corrected in the data of table 1 of the present study. Taking into account the possible experimental error sources, the uncertainties of the stopping powers are expected to fall below 3%. However, for Kapton the possible errors are larger due to the local thickness variations of the foils. The given values for Kapton should include errors smaller than 4%. Figs. l-3 show the experimental data, together with calculated predictions obtained by using Bragg’s rule in conjunction with the proton stopping parameters given in ref. [17]. The limited data from the literature is also given for com-
. o
0.01
present work Foroughi et al. [I Duder et al. [51
1
I
I
1.0
2.0
3.0
proton
LO
energy
5.0
6.0
7.0
8.0
(MeVl
Fig. 1. Stopping powers of protons in Mylar. The solid lines have been fitted to the present experimental data to guide the eye. The calculated dashed curves were obtained by using Bragg’s rule with stopping power values from ref. [17]. Data from the literature are also presented for comparison.
E. Rauhala, J. Riiisiinen / MeVproton
133
stopping in Havar, Ni, Kapton and Mylar
present work L'Hoir 8, Schmaus 141 Ishiwari etal. [31 ____calculated . o 0
I-
1.0
,2.0
3.0
4.0
proton energy
5.0
_
6.0
_
7.0
c 8.0
(MeV)
Fig. 2. As in fig. 1, but for Kapton and Havar.
parison. The values for Kapton and Havar presented in fig. 2 obtained by Foroughi et al. [l] have been calculated from their energy loss data using an appropriate procedure.
4. Discussion Our data may be compared with both existing experimental data from the common energy intervals, and with semiempirical predictions. Over the entire 0.5-8.3 MeV energy region used in the present study the maximum deviation of our values from the semiempirical stopping power values is less than 5% in all cases.
3.0
4.0
proton
5.0 energy
6.0
7.0
IMeW
Fig. 3. As in fig. 1, but for nickel.
8.0
For the light composite Mylar foil, previous measurements cover the energy region below 2 MeV [4]. One data point at 6.92 MeV has also been presented [3]. Our data are in good agreement with both these experimental data and with the semiempirical tabulations of ref. [17]. In the light of the results of the present work this may also be considered as an indication of the good quality of Mylar foils in that they have no significant variations in foil thickness. For Kapton the present stopping power data agree well with the semiempirical values, but differences of the order of 15% between the data of Foroughi et al. [l] and our data are found. As described in the previous section, the large local thickness variations of Kapton make it extremely difficult to reliably determine the thickness of the foil at exactly the position of the stopping power measurements. The different method in determining the foil thickness in ref. [l] could partly explain the difference between the experimental data. Foroughi et al. quote an experimental accuracy of 15-208. It may be noted that the stopping powers for Mylar and Kapton are very close to each other. Two groups have earlier experimented on Havar. Between the range 3 and 6 MeV, Duder et al. [5] present data that fall l-22 below our data. The results computed from the energy loss data of Foroughi et al. [I], however, show a clear deviation from our stopping power values below 2 MeV, also suggesting a different stopping power curve shape from that in ref. [5] and from that in the present study. All the data mentioned, however, fall within the 20% error limits of ref. [l].
134
E. Rauhala, J. Riiisiinen / MeVproton
For nickel it may be noted that our data are in very good agreement with the mutually consistent experimental data in the literature. However, all the data fall systematically slightly higher than the calculated semiempirical predictions. As at our energies no theoretical evidence exists for a difference between proton and deuteron stopping powers at identical velocities [17], deuteron stopping data may also be drawn into comparison. For Havar Duder et al. [5] have determined the stopping powers of 0.8-4 MeV deuterons (corresponding to proton energies 0.4-2 MeV) and Shepard and Porter [18] of 4.6-5.1 MeV deuterons. These literature deuteron data are in very good mutual agreement. Compared to the proton stopping powers they lie about 1.5% below the semiempirical calculated curve, whereas the present values are about 2-3% above the calculated values at energies below 1 MeV. With increasing energy the present data approach gradually the calculated predictions coinciding with them at 1.5 MeV. At 1.5 MeV the deuteron data lie about 3% below the calculations but coincide with them at about 2 MeV. In view of the experimental accuracies the overall agreement between all data is good. To the knowledge of the authors, no experimental deuteron stopping powers for Kapton and Mylar may be found in the literature. The support acknowledged.
from
the Academy
of Finland
is
stopping in Hauar, Ni, Kapton and Mylar
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