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The proton-reduced L X-ray spectrum of argon
Volume 42A, number 5
1 January 1973
PHYSICS LETTERS
THEPROTON-REDUCEDLX-RAYSPECTRUMOFARGON* R.C. DER, R.J. FORTNER and T.M. KAVANAGH Lawrence Livermore Laboratory, Livermore, Calif 94550, USA Received 8 November 1972 The argon L X-ray spectrum produced by 100 keV protons is presented. A new line, not observed in the electronproduced spectrum, appears at 262 eV is interpreted as a 3d + 2p transition. Since the 3d level is normally empty in argon, the data provide the first direct evidence from X-rays following proton bombardment of excitation of electrons to bound states.
In this note we discuss the spectrum of argon L Xrays produced by proton bombardment. The data show a new X-ray line, not seen for electron bombardment [ 1,2] , that we attribute to a transition involving the normally empty 3d level of argon. The data provide the first direct evidence, from X-rays following proton bombardment, of excitation of electrons to bound states (promotion) simultaneous with the creation of an inner-shell vacancy. The experimental technique has been described elsewhere. A Bragg spectrometer with a lead-stearate Mm as the diffracting element was used for observing the X-rays emitted at 90” to the direction of the incident beam; the detector was flow-mode proportional counter with an =S2000 A thick Parylene window. The target consisted of an argon gas cell with a small entrance aperture for the beam and a Parylene window for transmitting the X-rays; gas pressures were typically maintained at = 5 X 1O-2 torr. The data for 100 keV incident protons are shown in fig. 1. Three peaks are resolved in the spectrum, at approximately 210,221 and 262 eV. The first two peaks correspond to transitions seen in electron excited spectra [ 1,2] . The 221 eV transition is the normal 3s + 2p(LI,,) transition. The 210 eV transition is a “semi-Auger” process [ 1,2] , involving radiative decay of the 2p vacancy and simultaneous ionization or promotion of an M-shell electron. The transition at 262 eV is similar to lines seen in the argon L X-ray spectra produced by heavy ion bombardment [ 5,6] and has been interpreted as a 3d + 2p (L,&
* Work performed under the auspices of the U.S. Atomic Energy Commission.
transition (the 3d level is normally empty in argon). Since this line is not seen for electron excitation, it cannot be due to shake-up processes, but instead must represent additional excitation in the argon atom produced by the proton interaction. These observations are consistent with measurements of the argon L Auger spectra [7,8], though in that case the complexity of the spectra makes unambiguous interpretation very difficult. Studies on K X-ray satellite enhancement [9, lo] by light ion bombardment are related to, but fundamentally different than, these observations. In the studies of satellite enhancement, the interaction of the light ion produces L shell vacancies that accom1400-
p-) 100
1
I 290
I
I
220
I
I
Ar KeV
IIIIII 260
300
Energy (6v) Fig. 1. Argon L X-ray spectrum produced by 100 keV incident protons. The relative number of counts is plotted as a function of photon energy. 337
Volume 42A, number 5
PHYSICS LETTERS
pany the production of a K shell vacancy. The production of L shell vacancies can be explained as the result of a direct Coulomb interaction between the projectile and the L shell electrons [9]. In the theory of direct Coulomb interactions [ 11, 121 the electrons are usually assumed to be excited to the continuum and excitation to bound states is assumed to be negligible. However, the observations reported in this note can only be explained be electron promotion, in particular electron promotion to the 3d level. Quastmolecular considerations [ 12, 131, which are important in low velocity, heavy-ion collisions, are not expected to be important in this case since the velocity of the proton is greater than the velocity of the argon M shell electrons.
338
1 January 1973
References [l] R.C. Der et al., Rev. Sci. Instr. 41 (1970) 1797. [2] R.C. Der et al., Phys. Rev. A4 (1971) 556. [ 31 J.W. Cooper and R.E. LaVilla, Phys. Rev. Lett. 25 (1970) 1745. [4] L.O. Werme et al., Phys. Lett. 41 A (1972) 113. [S] M.E. Cunningham et al., Phys. Rev. Lett. 24 (1970) 931. [6] R.C. Der et al., Phys. Rev. I&t. 27 (1971) 1631. [7] D.J. Volz and M.E. Rudd, Phys. Rev. A2 (1970) 1395. [8] G.N. Ogurtsov, Rev. Mod. Phys. 44 (1972) 1. [9] A.R. Knudson, P.G. Burkhalter, D.J. Nagel, Proc. Int. Conf. Inner shell ion. phenomena, Atlanta, Georgia (1972) to be published. [IO] P. Richard, Proc. Int. Conf. Inner shell ion. phenemena, Atlanta, Georgia (1972) to be published. [ 1 l] E. Merzbacher and H.W. Lewis, Hand. der Phys. 34 (1958) 166. [ 121 J.D. Garcia, R.J. Fortner and T.M. Kavanagh, Rev. Mod. Phys., to be published. [13] M. Barat and W. Lichten, Phys. Rev. A6 (1972) 211.
1 January 1973
PHYSICS LETTERS
THEPROTON-REDUCEDLX-RAYSPECTRUMOFARGON* R.C. DER, R.J. FORTNER and T.M. KAVANAGH Lawrence Livermore Laboratory, Livermore, Calif 94550, USA Received 8 November 1972 The argon L X-ray spectrum produced by 100 keV protons is presented. A new line, not observed in the electronproduced spectrum, appears at 262 eV is interpreted as a 3d + 2p transition. Since the 3d level is normally empty in argon, the data provide the first direct evidence from X-rays following proton bombardment of excitation of electrons to bound states.
In this note we discuss the spectrum of argon L Xrays produced by proton bombardment. The data show a new X-ray line, not seen for electron bombardment [ 1,2] , that we attribute to a transition involving the normally empty 3d level of argon. The data provide the first direct evidence, from X-rays following proton bombardment, of excitation of electrons to bound states (promotion) simultaneous with the creation of an inner-shell vacancy. The experimental technique has been described elsewhere. A Bragg spectrometer with a lead-stearate Mm as the diffracting element was used for observing the X-rays emitted at 90” to the direction of the incident beam; the detector was flow-mode proportional counter with an =S2000 A thick Parylene window. The target consisted of an argon gas cell with a small entrance aperture for the beam and a Parylene window for transmitting the X-rays; gas pressures were typically maintained at = 5 X 1O-2 torr. The data for 100 keV incident protons are shown in fig. 1. Three peaks are resolved in the spectrum, at approximately 210,221 and 262 eV. The first two peaks correspond to transitions seen in electron excited spectra [ 1,2] . The 221 eV transition is the normal 3s + 2p(LI,,) transition. The 210 eV transition is a “semi-Auger” process [ 1,2] , involving radiative decay of the 2p vacancy and simultaneous ionization or promotion of an M-shell electron. The transition at 262 eV is similar to lines seen in the argon L X-ray spectra produced by heavy ion bombardment [ 5,6] and has been interpreted as a 3d + 2p (L,&
* Work performed under the auspices of the U.S. Atomic Energy Commission.
transition (the 3d level is normally empty in argon). Since this line is not seen for electron excitation, it cannot be due to shake-up processes, but instead must represent additional excitation in the argon atom produced by the proton interaction. These observations are consistent with measurements of the argon L Auger spectra [7,8], though in that case the complexity of the spectra makes unambiguous interpretation very difficult. Studies on K X-ray satellite enhancement [9, lo] by light ion bombardment are related to, but fundamentally different than, these observations. In the studies of satellite enhancement, the interaction of the light ion produces L shell vacancies that accom1400-
p-) 100
1
I 290
I
I
220
I
I
Ar KeV
IIIIII 260
300
Energy (6v) Fig. 1. Argon L X-ray spectrum produced by 100 keV incident protons. The relative number of counts is plotted as a function of photon energy. 337
Volume 42A, number 5
PHYSICS LETTERS
pany the production of a K shell vacancy. The production of L shell vacancies can be explained as the result of a direct Coulomb interaction between the projectile and the L shell electrons [9]. In the theory of direct Coulomb interactions [ 11, 121 the electrons are usually assumed to be excited to the continuum and excitation to bound states is assumed to be negligible. However, the observations reported in this note can only be explained be electron promotion, in particular electron promotion to the 3d level. Quastmolecular considerations [ 12, 131, which are important in low velocity, heavy-ion collisions, are not expected to be important in this case since the velocity of the proton is greater than the velocity of the argon M shell electrons.
338
1 January 1973
References [l] R.C. Der et al., Rev. Sci. Instr. 41 (1970) 1797. [2] R.C. Der et al., Phys. Rev. A4 (1971) 556. [ 31 J.W. Cooper and R.E. LaVilla, Phys. Rev. Lett. 25 (1970) 1745. [4] L.O. Werme et al., Phys. Lett. 41 A (1972) 113. [S] M.E. Cunningham et al., Phys. Rev. Lett. 24 (1970) 931. [6] R.C. Der et al., Phys. Rev. I&t. 27 (1971) 1631. [7] D.J. Volz and M.E. Rudd, Phys. Rev. A2 (1970) 1395. [8] G.N. Ogurtsov, Rev. Mod. Phys. 44 (1972) 1. [9] A.R. Knudson, P.G. Burkhalter, D.J. Nagel, Proc. Int. Conf. Inner shell ion. phenomena, Atlanta, Georgia (1972) to be published. [IO] P. Richard, Proc. Int. Conf. Inner shell ion. phenemena, Atlanta, Georgia (1972) to be published. [ 1 l] E. Merzbacher and H.W. Lewis, Hand. der Phys. 34 (1958) 166. [ 121 J.D. Garcia, R.J. Fortner and T.M. Kavanagh, Rev. Mod. Phys., to be published. [13] M. Barat and W. Lichten, Phys. Rev. A6 (1972) 211.