- Email: [email protected]
Light emission from thin carbon foils bombarded with medium velocity heavy ions
Nuclear Instruments and Methods in Physics Research B67 (1992) 616-619 North-Hollatad
Nuclear Instruments & Methods in Physics Research section B
Light emission from thin carbon foils bombarded with medium velocity heavy ions H i s a o K o b a y a s h i a, N o b u o O d a b, F u m i o N i s h i m u r a
c, J a n g S i c k P a r k ~ a n d T o s h i h i r o I c h i m o r i c
a Institute for Atomic Energy, Rikkyo Unirersity, 2-5-1 N,~gasaka, Yokosuka, Kanagawa, Japan 240-01 t, Seitoku Unh'ersity, 531 Sagamidai, Matsudo, Chiba, Japan: 271 c Research Laboratory for Nuclear Reactors, Tokyo Institute .,f Technology, Ookayama, Meguro-ku, Tokyo, Japan 162 d ULVAC Japan, Ltd., 2500 Hagisono, Chigasaki, Kanagawt,, Japan 253
The rela~tive photon intensities of the continuum spectra emitted from the tilted carbon foils have been measured in the wavelength region 300-800 nm by 60 keV/amu Ne + impact at +30 ° tilt angles. This result was compared with our previous observations for H + and He + impacts. It was found that, while the photon emission intensities for H + and He + are approximately proportional to the first and second power of the electronic stopping powers, respectively; for Ne + it is proportional to a higher power of the stopping power. 1. Introduction Previously we measured photon spectra emitted from tilted carbon foils for 0.3-0.8 M e V / a m u H,+, (n = 1-3) impacts [1,2], where the continuum and line spectra were observed in the visible region (300-800 nm). It was found that the continuum radiation originates from the carbon foil itself. Later, measurements were extended to a wider energy range of H + ions (0.6-2.0 MeV: (4.9-9.0)t'0) and to He ÷ impact (0.150.6 M e V / a m u : (2.4-4.9)r 0) [3], where the photon intensities for H + and He + ions were compared with the electronic stopping powers, S e, of carbon for both ions. It was fou~nd that the photon intensity tor H + ions is linearly proportional to S¢, whereas that for He + ions is approximately proportional to the square of S¢. From the above result, it is interesting to see how the shapes and intensities of the continuum photon spectra depend on the type and S~ of the impact ion species. These experimental data would be very useful for elucidation of the emission mechanism of continuum photons from solid carbon. In order to study this situation more extensively, in the present work, photon spectra have been measured from the carbon foil (10 Irg/cm 2) bombarded with Ne + ions (60 k e V / a m u : 1.6v 0) and the photon intensity for Ne + ion is compared with those for H + and He + ions,
2. Experimental The details of the experimental apparatus used in the present work have been described previously [1-4].
The H + and Ne + ions, with energies 0.3-2.4 MeV, were produced from a duoplasmatron ion source and a Pelletron accelerator, and directed onto thin carbon foils (10 t~g/cm 2) at tilt angles ( + 3 0 °), positive and negative signs for the angles mean that the optical system views the exit and incident sides, respectively, of the tilted foils with respect to the direction of the projectiles. The target chamber was evacuated to less than 1 × 10 - s Torr during the measurements. The ion beam was collimated to 2.3 mm in diameter at the target foil. The beam currents were kept to 0.2-1.5 IrA (5-36 ixA/cm 2) for the H + ion and to 0.01-0.03 IrA (0.2-0.7 I r A / c m 2) for the Ne ÷ ion. The limit of current density of Ne + was selected empirically, so as to protect the foil against thickening and breakdown. Spcctral measurements were made using a modified Czerny-Turner type grating monochromator equipped with a photomultiplier (Hamamatsu R649) cooled to - 3 0 ° C . Both the entrance and exit slits of the monochromator were set to 0.1-5 mm in width, resulting in a wavelength resolution of 0.25-12.5 nm. The optical axis of the lens-monochromator system was placed perpendicularly to the beam and was in the plane defined by the beam and the normal to the tilted target surface. Relative photon intensities were derived using the relative photon detection efficiency in our optical system, which was calibrated by a standard tungsten lamp. To compare the photon emission intensity with S e, the observed photon intensity emitted from the surface of carbon target was converted to the photon emission intensity per ion per unit beam pass length by correcting for the optical attenuation in the carbon foil whose
0168-583X/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
617
H. Kobayashi et aL / Light emission from thin carbon foils .1
attenuation constant has been measured as a function of wavelength by Kobayashi and Oda [2]. To estimate the photon emission intensity per ion at the exit of the carbon foil, the information on the equilibrium charge state of Ne at the exit is needed. The beam current after passing through the carbon foil was measured and compared with the current without the foil for the same Ne + beam. The ratio of the two current intensities was found to be 3.05 + 0.24 at the incident energy of 60 k e V / a m u and it is regarded as the equilibrium charge state. The above ratio agrees well with the equilibrium charge estimated by interpolation from published data [5-8], which is 2.9 + 0.1 for 54 k e V / a m u Ne, this latter figure corresponding to the energy of a 60 k e V / a m u incident energy after passing through a 10 ixg/cm 2 carbon foil.
10" ~
I
I Clll
I C-foil l'0/~g/cm'- I tilt angle=30° 1
c.,
cII
|
h, l0 s
l .... I
•"m
|
Nell
8~0
H,II
i_1
s.~P"
3. Results and discussion
Fig. 1 shows the measured spectra of the relative photon emission intensities per unit charge per unit beam pass length in the wavelength region from 300 to 800 nm observed for 60 k e V / a m u Ne ÷ ions incident on the carbon foil at (a) + 3 0 ° and (b) - 3 0 ° tilt angles, (c) for 1.2 MeV He ÷ at - 3 0 °, and (d) for 2.0 MeV H ÷ at + 3 0 °. The slit widths of Ne ÷, He ÷ and H ÷ data were adjusted to be 2, 5 and 5 mm, respectively, which correspond to spectral resolutions of 5, 12.5, and 12.5 nm, respectively. The measured photon intensity is proportional to the square of the slit width and easily converted to the value for an arbitrary slit width. It can be seen that for Ne ÷ bombardments line spectra are superimposed on the continuum spectrum. The line spectra were identified from the high resolution spectra as lines from projectiles (Ne I / I I ) , Balmer lines from sputtered hydrogens (H,~, HI3), sputtered carbon lines ( C I / I I / I I I / I V and C 2 Swan band), and unidentified lines with relatively low intensities. A few strong lines were observed for the exit side ( + 3 0 °) spectra and the strongest line was ten times greater than the continuum light (fig. la). Furthermore, there is a possibility of the presence of unresolved continuum background light originating from the sputtered particles in addition to the continuum light from carbon foil itself. The nuclear stopping power is estimated for the 60 k e V / a m u Ne ÷ bombardment to be 0.05 M e V / (rag/era 2) which equals 0.8% of S e. The average range in carbon of carbon atoms hit by 60 k e V / a m u Ne + is of the order of 100 p,g/cm 2. Thus, the sputtering yield from the 10 i~g/cm 2 carbon foil should be much less than 0.3, which is the sputtering yield from bulk carbon for the same ion bombardment [9]. For a thin foil, the probability that carbon atoms recoiled by the incident
10"
"
10' 300
o
I 400
I 500
~ o o
I 600
WAVELENGTH.
I 700
800
nm
Fig. 1. Spectra of photon intensity per unit charge per unit path length emitted from the 30 ° tilted carbon foil (10 p.g/cm 2) bombarded by (a) 1.2 MeV Ne + (o: measured at the exit side), (b) 1.2 MeV Ne + (o: incident), (c) 1.2 MeV He + (.: incident), and (d) 2.0 MeV H + (o: exit). Some identified lines are noted only for Ne + impact.
ions can escape to the incident side of the foil through multiple scattering is so small that most recoil atoms are emitted at the exit side. In other words, for a thin foil, the sputtering yield to the incident side is much lower than that for the exit side. It is possible for photons emitted from atoms sputtered into the exit side to penetrate through the foil with a tilt angle of - 3 0 ° and be observed in the incident side of the foil. However, since the transmission probability of photons through the foil is only 4%, the contribution of the photons emitted from the exit side to the spectra observed on the incident side may be negligibly small. This feature may be understood by comparing curve (a) with curve (b) in fig. 1. For the above reasons, for Ne + impact only the intensity from the incident side was used to analyze the emission from the carbon foil itself. For H + and He + impacts intensities averaged over all incident and exit spectra were used, because the shape and intensity of IX. SECONDARY EMISSION
H. Kobayashi et al. / Light emission from thin carbon foils
618
I U,,::.0,./o ...... h,',. l-
'
'
'
k=42~1)-428am /
|
i ,o.~- ~ .'o.3.:.oM~v
-/
[..
/I
I 0~
//
regarded as the continuum photon intensity per ion per unit path length at 420 nm and is denoted by I. In fig. 2, electronic stopping powers, S e, for H + and He + are from Andersen and Ziegler [10] and Ziegler [11], respectively, and for Ne + can be calculated by the empirical formula of Garnir-Monjoie et al. [12]. Fig. 2 shows that the slope of the log-log plot of the I vs S e curve changes from the value of 1 in the low Se region, which includes all H + data, to 2 for S e > 1.6 M e V / ( m g / c m 2 ) , the He + data. The slope becomes much steeper for Ne +. Using fig. 2, we can express the relation between I and S¢ as follows: In l = n
-r~
In S ¢ + k ,
(1)
where n and k are both slowly varying functions of S~. The n values are determined from the data in fig. 2 in the three different S e regions by regression analysis: (1) In the region for S~ <~ 1.6 M e V / ( m g / c m 2) for H + impact,
/lingcm')
n = 0.97 + 0.09.
(2a)
(2) In the region for 1.6 ~
I
I0
n = 2.04 + 0.30.
(2b)
ELECTRONIC STOPPING POWER, MeV/(mg/cm-') Fig. 2. Stoppiing power dependence of the relative photon emission intensities per ion per unit path length in the 420-428 nm range. The intensity in the wavelength region for Ne ÷ impact is derived from the intensity in the 398-414, 476-482, and 558-564 nm ranges, where no lines are observed (see text in detail), o: H + impact, e: He +, Q: Ne +.
(3) In the region for S e >/1.6 M e V / ( m g / c m 2 ) , there are only two experimental results, that is, one point for S~ = 2.6 M e V / ( m g / c m 2) for He + impact and another for S e = 6.7 M e V / ( m g / c m 2) for Ne + impact. Estimating from the above two points, we obtain
the continu~lm spectra do not depend on tilt angles ( + 1 5 °, _+30 °, _+45°, and +55 ° ) within the experimental uncertainty [1-3]. In our previous studies [2,3], the photon intensities for H + and He + impacts were compared at the 420-428 nm wavelength region. However, for Ne: + impact, the continuum spectrum is overlapped with the line spectrum in this wavelength range. Therefore, the continuum photon intensity at the 420428 nm region for Ne + impact was estimated as follows: i) There are three continuum regions at wavelength ranges of 398-404, 476-482, and 558-564 nm where no line is observed (fig. 1 curves (a) and (b)). ii) As shown in fig. 1, the shapes of all the continuum spectra for Ne + agree well with those for H + and He + within _+17% except for the spectra measured at the exit side for Ne +. iii) Combining the results (i) and (ii), three values for the photon intensity at the 420-428 nm region were derived for Ne + impact, whose average value is shown in fig. 2 together with previously measured values for H + and He +. This average value is
From the above results for n, one may conclude that the graph of the intensity photon as a function of the electronic stopping power S e has a slope which becomes steeper with the increase of S e. It is not clear at the present time whether the photon intensity is a function of S~ only or whether the photon intensities are different for different ion species with the same Se. This question requires further investigations over a wider range of S e for H +, He +, and Ne + impacts.
n = 2.6.
(2c)
References [1] H. Kobayashi and N. Oda, Nucl. Instr. and Meth. B2 (1984) 248. [2] H. Kobayashi and N. Oda, Nucl. Instr. and Meth. B13 (1986) 189. [3] J.S. Park, F. Nishimura, T. Ichimori, H. Kobayashi and N. Oda, Nucl. Instr. and Meth. B48 (1990) 635. [4] H. Kobayashi and N. Oda, Phys. Rev. 30 (1984) 1924. [5] R.Girardeau, E.J. Knystautas, G. Beauchemin, B. Neveu and R. Drouin, J. Phys. B4 (1971) 1743. [6] A.B. Wittkower and H.D. Betz, Atom. Data 5 (1973) 113.
H. Kobayashi et al. / Light emission from thin carbon foils [7] W.N. Lennard, D. Phillips and D.A.S. Walker, Nucl. Instr. and Meth. 179 (1981) 413. [8] K. Shima, N. Kuno, M. Yamanouchi and H. Tawara, Nat. Inst. Fusion Sci. Res. Report NIFS-DATA-10 (Nagoya, Japan, 1991). [9] H.H. Andersen and H.L. Bay, in: Sputtering Yield Measurements, Sputtering by Particle Bombardment I, ed. R. Behrisch (Springer, Berlin, 1981) p. 145. [10] H.H. Andersen and J.F. Ziegler, Hydrogen Stopping
619
Powers and Ranges in All Elements, vol. 3 of The Stopping and Ranges of Ions in Matter, ed. J.F. Ziegler (Pergamon, New York, 1977). [11] J.F. Ziegler, Helium Stopping Powers and Ranges in All Elements, vol. 4 of The Stopping and Ranges of Ions in Matter, ed. J.F. Ziegler (Pergamon, New York, 1977). [12] F.S. Garnir-Monjoie, H.P. Garnir, Y. Baudinet-Robinet and P.D. Dumont, J. Phys. (Paris) 41 (1980) 599.
IX. SECONDARY EMISSION
Nuclear Instruments & Methods in Physics Research section B
Light emission from thin carbon foils bombarded with medium velocity heavy ions H i s a o K o b a y a s h i a, N o b u o O d a b, F u m i o N i s h i m u r a
c, J a n g S i c k P a r k ~ a n d T o s h i h i r o I c h i m o r i c
a Institute for Atomic Energy, Rikkyo Unirersity, 2-5-1 N,~gasaka, Yokosuka, Kanagawa, Japan 240-01 t, Seitoku Unh'ersity, 531 Sagamidai, Matsudo, Chiba, Japan: 271 c Research Laboratory for Nuclear Reactors, Tokyo Institute .,f Technology, Ookayama, Meguro-ku, Tokyo, Japan 162 d ULVAC Japan, Ltd., 2500 Hagisono, Chigasaki, Kanagawt,, Japan 253
The rela~tive photon intensities of the continuum spectra emitted from the tilted carbon foils have been measured in the wavelength region 300-800 nm by 60 keV/amu Ne + impact at +30 ° tilt angles. This result was compared with our previous observations for H + and He + impacts. It was found that, while the photon emission intensities for H + and He + are approximately proportional to the first and second power of the electronic stopping powers, respectively; for Ne + it is proportional to a higher power of the stopping power. 1. Introduction Previously we measured photon spectra emitted from tilted carbon foils for 0.3-0.8 M e V / a m u H,+, (n = 1-3) impacts [1,2], where the continuum and line spectra were observed in the visible region (300-800 nm). It was found that the continuum radiation originates from the carbon foil itself. Later, measurements were extended to a wider energy range of H + ions (0.6-2.0 MeV: (4.9-9.0)t'0) and to He ÷ impact (0.150.6 M e V / a m u : (2.4-4.9)r 0) [3], where the photon intensities for H + and He + ions were compared with the electronic stopping powers, S e, of carbon for both ions. It was fou~nd that the photon intensity tor H + ions is linearly proportional to S¢, whereas that for He + ions is approximately proportional to the square of S¢. From the above result, it is interesting to see how the shapes and intensities of the continuum photon spectra depend on the type and S~ of the impact ion species. These experimental data would be very useful for elucidation of the emission mechanism of continuum photons from solid carbon. In order to study this situation more extensively, in the present work, photon spectra have been measured from the carbon foil (10 Irg/cm 2) bombarded with Ne + ions (60 k e V / a m u : 1.6v 0) and the photon intensity for Ne + ion is compared with those for H + and He + ions,
2. Experimental The details of the experimental apparatus used in the present work have been described previously [1-4].
The H + and Ne + ions, with energies 0.3-2.4 MeV, were produced from a duoplasmatron ion source and a Pelletron accelerator, and directed onto thin carbon foils (10 t~g/cm 2) at tilt angles ( + 3 0 °), positive and negative signs for the angles mean that the optical system views the exit and incident sides, respectively, of the tilted foils with respect to the direction of the projectiles. The target chamber was evacuated to less than 1 × 10 - s Torr during the measurements. The ion beam was collimated to 2.3 mm in diameter at the target foil. The beam currents were kept to 0.2-1.5 IrA (5-36 ixA/cm 2) for the H + ion and to 0.01-0.03 IrA (0.2-0.7 I r A / c m 2) for the Ne ÷ ion. The limit of current density of Ne + was selected empirically, so as to protect the foil against thickening and breakdown. Spcctral measurements were made using a modified Czerny-Turner type grating monochromator equipped with a photomultiplier (Hamamatsu R649) cooled to - 3 0 ° C . Both the entrance and exit slits of the monochromator were set to 0.1-5 mm in width, resulting in a wavelength resolution of 0.25-12.5 nm. The optical axis of the lens-monochromator system was placed perpendicularly to the beam and was in the plane defined by the beam and the normal to the tilted target surface. Relative photon intensities were derived using the relative photon detection efficiency in our optical system, which was calibrated by a standard tungsten lamp. To compare the photon emission intensity with S e, the observed photon intensity emitted from the surface of carbon target was converted to the photon emission intensity per ion per unit beam pass length by correcting for the optical attenuation in the carbon foil whose
0168-583X/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
617
H. Kobayashi et aL / Light emission from thin carbon foils .1
attenuation constant has been measured as a function of wavelength by Kobayashi and Oda [2]. To estimate the photon emission intensity per ion at the exit of the carbon foil, the information on the equilibrium charge state of Ne at the exit is needed. The beam current after passing through the carbon foil was measured and compared with the current without the foil for the same Ne + beam. The ratio of the two current intensities was found to be 3.05 + 0.24 at the incident energy of 60 k e V / a m u and it is regarded as the equilibrium charge state. The above ratio agrees well with the equilibrium charge estimated by interpolation from published data [5-8], which is 2.9 + 0.1 for 54 k e V / a m u Ne, this latter figure corresponding to the energy of a 60 k e V / a m u incident energy after passing through a 10 ixg/cm 2 carbon foil.
10" ~
I
I Clll
I C-foil l'0/~g/cm'- I tilt angle=30° 1
c.,
cII
|
h, l0 s
l .... I
•"m
|
Nell
8~0
H,II
i_1
s.~P"
3. Results and discussion
Fig. 1 shows the measured spectra of the relative photon emission intensities per unit charge per unit beam pass length in the wavelength region from 300 to 800 nm observed for 60 k e V / a m u Ne ÷ ions incident on the carbon foil at (a) + 3 0 ° and (b) - 3 0 ° tilt angles, (c) for 1.2 MeV He ÷ at - 3 0 °, and (d) for 2.0 MeV H ÷ at + 3 0 °. The slit widths of Ne ÷, He ÷ and H ÷ data were adjusted to be 2, 5 and 5 mm, respectively, which correspond to spectral resolutions of 5, 12.5, and 12.5 nm, respectively. The measured photon intensity is proportional to the square of the slit width and easily converted to the value for an arbitrary slit width. It can be seen that for Ne ÷ bombardments line spectra are superimposed on the continuum spectrum. The line spectra were identified from the high resolution spectra as lines from projectiles (Ne I / I I ) , Balmer lines from sputtered hydrogens (H,~, HI3), sputtered carbon lines ( C I / I I / I I I / I V and C 2 Swan band), and unidentified lines with relatively low intensities. A few strong lines were observed for the exit side ( + 3 0 °) spectra and the strongest line was ten times greater than the continuum light (fig. la). Furthermore, there is a possibility of the presence of unresolved continuum background light originating from the sputtered particles in addition to the continuum light from carbon foil itself. The nuclear stopping power is estimated for the 60 k e V / a m u Ne ÷ bombardment to be 0.05 M e V / (rag/era 2) which equals 0.8% of S e. The average range in carbon of carbon atoms hit by 60 k e V / a m u Ne + is of the order of 100 p,g/cm 2. Thus, the sputtering yield from the 10 i~g/cm 2 carbon foil should be much less than 0.3, which is the sputtering yield from bulk carbon for the same ion bombardment [9]. For a thin foil, the probability that carbon atoms recoiled by the incident
10"
"
10' 300
o
I 400
I 500
~ o o
I 600
WAVELENGTH.
I 700
800
nm
Fig. 1. Spectra of photon intensity per unit charge per unit path length emitted from the 30 ° tilted carbon foil (10 p.g/cm 2) bombarded by (a) 1.2 MeV Ne + (o: measured at the exit side), (b) 1.2 MeV Ne + (o: incident), (c) 1.2 MeV He + (.: incident), and (d) 2.0 MeV H + (o: exit). Some identified lines are noted only for Ne + impact.
ions can escape to the incident side of the foil through multiple scattering is so small that most recoil atoms are emitted at the exit side. In other words, for a thin foil, the sputtering yield to the incident side is much lower than that for the exit side. It is possible for photons emitted from atoms sputtered into the exit side to penetrate through the foil with a tilt angle of - 3 0 ° and be observed in the incident side of the foil. However, since the transmission probability of photons through the foil is only 4%, the contribution of the photons emitted from the exit side to the spectra observed on the incident side may be negligibly small. This feature may be understood by comparing curve (a) with curve (b) in fig. 1. For the above reasons, for Ne + impact only the intensity from the incident side was used to analyze the emission from the carbon foil itself. For H + and He + impacts intensities averaged over all incident and exit spectra were used, because the shape and intensity of IX. SECONDARY EMISSION
H. Kobayashi et al. / Light emission from thin carbon foils
618
I U,,::.0,./o ...... h,',. l-
'
'
'
k=42~1)-428am /
|
i ,o.~- ~ .'o.3.:.oM~v
-/
[..
/I
I 0~
//
regarded as the continuum photon intensity per ion per unit path length at 420 nm and is denoted by I. In fig. 2, electronic stopping powers, S e, for H + and He + are from Andersen and Ziegler [10] and Ziegler [11], respectively, and for Ne + can be calculated by the empirical formula of Garnir-Monjoie et al. [12]. Fig. 2 shows that the slope of the log-log plot of the I vs S e curve changes from the value of 1 in the low Se region, which includes all H + data, to 2 for S e > 1.6 M e V / ( m g / c m 2 ) , the He + data. The slope becomes much steeper for Ne +. Using fig. 2, we can express the relation between I and S¢ as follows: In l = n
-r~
In S ¢ + k ,
(1)
where n and k are both slowly varying functions of S~. The n values are determined from the data in fig. 2 in the three different S e regions by regression analysis: (1) In the region for S~ <~ 1.6 M e V / ( m g / c m 2) for H + impact,
/lingcm')
n = 0.97 + 0.09.
(2a)
(2) In the region for 1.6 ~
I
I0
n = 2.04 + 0.30.
(2b)
ELECTRONIC STOPPING POWER, MeV/(mg/cm-') Fig. 2. Stoppiing power dependence of the relative photon emission intensities per ion per unit path length in the 420-428 nm range. The intensity in the wavelength region for Ne ÷ impact is derived from the intensity in the 398-414, 476-482, and 558-564 nm ranges, where no lines are observed (see text in detail), o: H + impact, e: He +, Q: Ne +.
(3) In the region for S e >/1.6 M e V / ( m g / c m 2 ) , there are only two experimental results, that is, one point for S~ = 2.6 M e V / ( m g / c m 2) for He + impact and another for S e = 6.7 M e V / ( m g / c m 2) for Ne + impact. Estimating from the above two points, we obtain
the continu~lm spectra do not depend on tilt angles ( + 1 5 °, _+30 °, _+45°, and +55 ° ) within the experimental uncertainty [1-3]. In our previous studies [2,3], the photon intensities for H + and He + impacts were compared at the 420-428 nm wavelength region. However, for Ne: + impact, the continuum spectrum is overlapped with the line spectrum in this wavelength range. Therefore, the continuum photon intensity at the 420428 nm region for Ne + impact was estimated as follows: i) There are three continuum regions at wavelength ranges of 398-404, 476-482, and 558-564 nm where no line is observed (fig. 1 curves (a) and (b)). ii) As shown in fig. 1, the shapes of all the continuum spectra for Ne + agree well with those for H + and He + within _+17% except for the spectra measured at the exit side for Ne +. iii) Combining the results (i) and (ii), three values for the photon intensity at the 420-428 nm region were derived for Ne + impact, whose average value is shown in fig. 2 together with previously measured values for H + and He +. This average value is
From the above results for n, one may conclude that the graph of the intensity photon as a function of the electronic stopping power S e has a slope which becomes steeper with the increase of S e. It is not clear at the present time whether the photon intensity is a function of S~ only or whether the photon intensities are different for different ion species with the same Se. This question requires further investigations over a wider range of S e for H +, He +, and Ne + impacts.
n = 2.6.
(2c)
References [1] H. Kobayashi and N. Oda, Nucl. Instr. and Meth. B2 (1984) 248. [2] H. Kobayashi and N. Oda, Nucl. Instr. and Meth. B13 (1986) 189. [3] J.S. Park, F. Nishimura, T. Ichimori, H. Kobayashi and N. Oda, Nucl. Instr. and Meth. B48 (1990) 635. [4] H. Kobayashi and N. Oda, Phys. Rev. 30 (1984) 1924. [5] R.Girardeau, E.J. Knystautas, G. Beauchemin, B. Neveu and R. Drouin, J. Phys. B4 (1971) 1743. [6] A.B. Wittkower and H.D. Betz, Atom. Data 5 (1973) 113.
H. Kobayashi et al. / Light emission from thin carbon foils [7] W.N. Lennard, D. Phillips and D.A.S. Walker, Nucl. Instr. and Meth. 179 (1981) 413. [8] K. Shima, N. Kuno, M. Yamanouchi and H. Tawara, Nat. Inst. Fusion Sci. Res. Report NIFS-DATA-10 (Nagoya, Japan, 1991). [9] H.H. Andersen and H.L. Bay, in: Sputtering Yield Measurements, Sputtering by Particle Bombardment I, ed. R. Behrisch (Springer, Berlin, 1981) p. 145. [10] H.H. Andersen and J.F. Ziegler, Hydrogen Stopping
619
Powers and Ranges in All Elements, vol. 3 of The Stopping and Ranges of Ions in Matter, ed. J.F. Ziegler (Pergamon, New York, 1977). [11] J.F. Ziegler, Helium Stopping Powers and Ranges in All Elements, vol. 4 of The Stopping and Ranges of Ions in Matter, ed. J.F. Ziegler (Pergamon, New York, 1977). [12] F.S. Garnir-Monjoie, H.P. Garnir, Y. Baudinet-Robinet and P.D. Dumont, J. Phys. (Paris) 41 (1980) 599.
IX. SECONDARY EMISSION