- Email: [email protected]
Corpuscular bombardment and N2+ radiation
100s
RESFARCH
NOTES
9. V. I. KRMWVSKY, N. N. SHEFOVand V. I. YARIN, J. Atmos. Terr. Phys. 21,46 (1961). 10. F. KAUFMAN, Private communication. 11. P. JACQUINOT, J. Phys. Radium, 19,223 (1958). 12. J. COGS, Revue SOpique, 40,4.5,116,1?1 and 231 (1961). 13. E. A. LYTLEand J. HAMPSON, Nature, Land. 202,76 (1964).
Planet. SpaceSci.1965,
Vol.
13,pp. 100sto 1009.
CORPUSCULAR
Pergamm
Press Ltd.
Printed
BOMBARDMENT
in Northern
Xreland
AND Na+ RADIATION
(Received 22 Jtine 1965) The axsrgy flux of a beam of fast electrons absorbed by the atmosphere can be derived from the resulting intensity of the first negative system of molecuIar nitrogen. (I2 The procedure is based upon the observation that the variation with impact energy E of the cross section for the production of the upper state of the first negative system by electron impact with N,‘B*8t e + N,(XIC,+) -+ e -i- N,+(BaX%,+)+ e
(1)
is very similar to that of the total ionization cross section’4-8’ e + N,(XG,+}
-+ e + CN*,f + e
(2)
and the further observation that the mean energy expended in the production of an ion pair by a beam of discrepancy between fast electrons absorbed in nitrogen is a constant of about 35 eV (@).There is a ~~i~~nt the efbciency derived from the cross section measurements of Stew~t~~l and of Hayakawa and Nishimura~a~ and the ethciency measured directly by Hartman and Hoerlin’**” (cf. Dalgarnoun). New more precise m~~rnents of the cross sections for (1) have been presented resently by Latimer and McConkey W) which largely remove the discrepancy, The ratio of the cross section for the production of an ion pair@-@ to the cross section for the production of a 3914 8, photon’12) is shown in Fig. 1 for electron impact energies uu to 300eV. The ratio is very nearlv constant and we adopt a value of 17 for it. The ef&iency wi?h w&h kinetic energy is transfor&ted inio 3914 A photon energy when an electron beam is absorbed in nitrogen is accordinelv 5.0 x 1W and for an electron beam absorbed in air it is 4-O x IO+. The value for air Measured by H&&ran and HoerlW”) is 3.3 x 1W. A mean value of 3.7 X lo-% appears to be an acceptable compromise. It is within the experiments error quoted by McConkey and Latimeroa). The value of the energy conversion coefficient appropriate to the upper atmosphere depends upon the
18
1
1
loo Electron FIG.
1.
RELATIVE
,
300
200
IOMZATION
energy, CROSS
eV
SECTIONS
IN
NITRWEN.
RESEARCH
1009
NOTES
TABLE 1 Parameter
Intensities of visual auroras International II I
Green line (kR) 3914 A (kR) Energy flux (erg cm-%eci) Ionization (cm-%ec-‘) Rates of ionization (cm-%ec-‘) Electron density
1 0.5 0.6 10’0 3 x 103 105
brightness coefficient III
10 5 6 10” 3 x 104 3 x 105
100 50 60 10’2 3 x 105 106
IV 1000 500 600 10’3 3 x 106 3 x 106
fractional content of N, at the altitude at which the electrons are absorbed. If we ignore the possibility of large fluxes of soft electrons with energies less than 1 keV, then a flux of 5 erg cm-%ec-’ gives rise to at least 500 5 rayleighs of 3914 8, emission. O’Brien, Allum and Goldwire observed that the mid-latitude intensity of 3914A radiation above 85 km was 5 rayleighs in July 1964 so that the possible flux of energetic electrons was less than 1 x 1O-2 erg cm-%ec-‘. The number of Na+ ions produced per photon of 3914 A radiation is also a useful parameter. Its variation with energy is shown in Fig. 1. It is nearly constant at a value of 14. The difference between the two ratios is due to the production of N+ and N,++ ions. Dalgarnoo4) has presented a table which summarises some quantitative information about typical auroras. It should be modified to the table given above. A. DALGARNO I. D. LATIMER The Queen’s University of Belfast Belfast, N. Ireland J. W. MCCONKEY REFERENCES
1. A. O~~HOLT,Geophys. Pablikasj. 20, 1 (1959). 2. D. T. STEWART,Proc. Phys. Sot. A 69,437 (1956). 3. S. HAYAKAWAand H. NISHIMURA,J. Geomag. Geoelect. 16, 72 (1964). 4. S. H. TATE and P. T. SMITH,Phys. Rev. 39,270 (1932). 5. W. L. FITE and R. T. BRACKMAN,Phys. Rev. 112,815 (1959). 6. J. R. PETERSON,Atomic Collision Processes (editor M. R. C. McDowell). North Holland, Amsterdam (1964). 7. R. L. SCHOEN,F. J. DE HEER, M. J. VANDER WIEL and J. KISTEMAKER, Ph_ysica 31, 94 (1965). 8. P. ENGLANDER-GOLDEN and D. RAPP, Unpublished report (1964). 9. J. M. VALENTINEand S. C. CURRAN, Rep. Progr. Phys. 21, 1 (1958). 10. P. L. HARTMANand H. HOERLIN,BUN. Amer. Phys. Sac. 11, 69 (1962). 11. A. DALGARNO,Ann. Gkophys. 20, 65 (1964). 12. I. D. LATIMERand J. W. MCCONKEY,Proc. Phys. Sot. 86,463 (1965). 13. B. J. O’BRIEN, R. ALLUM and H. C. GOLDWIRE,J. Geophys. Res. 70, 161 (1965). 14. A. DALGARNO,Aurorai Phenomena. Experiments and Theory (editor M. Walt). Stanford University Press, Stanford, Calif. (1965).
RESFARCH
NOTES
9. V. I. KRMWVSKY, N. N. SHEFOVand V. I. YARIN, J. Atmos. Terr. Phys. 21,46 (1961). 10. F. KAUFMAN, Private communication. 11. P. JACQUINOT, J. Phys. Radium, 19,223 (1958). 12. J. COGS, Revue SOpique, 40,4.5,116,1?1 and 231 (1961). 13. E. A. LYTLEand J. HAMPSON, Nature, Land. 202,76 (1964).
Planet. SpaceSci.1965,
Vol.
13,pp. 100sto 1009.
CORPUSCULAR
Pergamm
Press Ltd.
Printed
BOMBARDMENT
in Northern
Xreland
AND Na+ RADIATION
(Received 22 Jtine 1965) The axsrgy flux of a beam of fast electrons absorbed by the atmosphere can be derived from the resulting intensity of the first negative system of molecuIar nitrogen. (I2 The procedure is based upon the observation that the variation with impact energy E of the cross section for the production of the upper state of the first negative system by electron impact with N,‘B*8t e + N,(XIC,+) -+ e -i- N,+(BaX%,+)+ e
(1)
is very similar to that of the total ionization cross section’4-8’ e + N,(XG,+}
-+ e + CN*,f + e
(2)
and the further observation that the mean energy expended in the production of an ion pair by a beam of discrepancy between fast electrons absorbed in nitrogen is a constant of about 35 eV (@).There is a ~~i~~nt the efbciency derived from the cross section measurements of Stew~t~~l and of Hayakawa and Nishimura~a~ and the ethciency measured directly by Hartman and Hoerlin’**” (cf. Dalgarnoun). New more precise m~~rnents of the cross sections for (1) have been presented resently by Latimer and McConkey W) which largely remove the discrepancy, The ratio of the cross section for the production of an ion pair@-@ to the cross section for the production of a 3914 8, photon’12) is shown in Fig. 1 for electron impact energies uu to 300eV. The ratio is very nearlv constant and we adopt a value of 17 for it. The ef&iency wi?h w&h kinetic energy is transfor&ted inio 3914 A photon energy when an electron beam is absorbed in nitrogen is accordinelv 5.0 x 1W and for an electron beam absorbed in air it is 4-O x IO+. The value for air Measured by H&&ran and HoerlW”) is 3.3 x 1W. A mean value of 3.7 X lo-% appears to be an acceptable compromise. It is within the experiments error quoted by McConkey and Latimeroa). The value of the energy conversion coefficient appropriate to the upper atmosphere depends upon the
18
1
1
loo Electron FIG.
1.
RELATIVE
,
300
200
IOMZATION
energy, CROSS
eV
SECTIONS
IN
NITRWEN.
RESEARCH
1009
NOTES
TABLE 1 Parameter
Intensities of visual auroras International II I
Green line (kR) 3914 A (kR) Energy flux (erg cm-%eci) Ionization (cm-%ec-‘) Rates of ionization (cm-%ec-‘) Electron density
1 0.5 0.6 10’0 3 x 103 105
brightness coefficient III
10 5 6 10” 3 x 104 3 x 105
100 50 60 10’2 3 x 105 106
IV 1000 500 600 10’3 3 x 106 3 x 106
fractional content of N, at the altitude at which the electrons are absorbed. If we ignore the possibility of large fluxes of soft electrons with energies less than 1 keV, then a flux of 5 erg cm-%ec-’ gives rise to at least 500 5 rayleighs of 3914 8, emission. O’Brien, Allum and Goldwire observed that the mid-latitude intensity of 3914A radiation above 85 km was 5 rayleighs in July 1964 so that the possible flux of energetic electrons was less than 1 x 1O-2 erg cm-%ec-‘. The number of Na+ ions produced per photon of 3914 A radiation is also a useful parameter. Its variation with energy is shown in Fig. 1. It is nearly constant at a value of 14. The difference between the two ratios is due to the production of N+ and N,++ ions. Dalgarnoo4) has presented a table which summarises some quantitative information about typical auroras. It should be modified to the table given above. A. DALGARNO I. D. LATIMER The Queen’s University of Belfast Belfast, N. Ireland J. W. MCCONKEY REFERENCES
1. A. O~~HOLT,Geophys. Pablikasj. 20, 1 (1959). 2. D. T. STEWART,Proc. Phys. Sot. A 69,437 (1956). 3. S. HAYAKAWAand H. NISHIMURA,J. Geomag. Geoelect. 16, 72 (1964). 4. S. H. TATE and P. T. SMITH,Phys. Rev. 39,270 (1932). 5. W. L. FITE and R. T. BRACKMAN,Phys. Rev. 112,815 (1959). 6. J. R. PETERSON,Atomic Collision Processes (editor M. R. C. McDowell). North Holland, Amsterdam (1964). 7. R. L. SCHOEN,F. J. DE HEER, M. J. VANDER WIEL and J. KISTEMAKER, Ph_ysica 31, 94 (1965). 8. P. ENGLANDER-GOLDEN and D. RAPP, Unpublished report (1964). 9. J. M. VALENTINEand S. C. CURRAN, Rep. Progr. Phys. 21, 1 (1958). 10. P. L. HARTMANand H. HOERLIN,BUN. Amer. Phys. Sac. 11, 69 (1962). 11. A. DALGARNO,Ann. Gkophys. 20, 65 (1964). 12. I. D. LATIMERand J. W. MCCONKEY,Proc. Phys. Sot. 86,463 (1965). 13. B. J. O’BRIEN, R. ALLUM and H. C. GOLDWIRE,J. Geophys. Res. 70, 161 (1965). 14. A. DALGARNO,Aurorai Phenomena. Experiments and Theory (editor M. Walt). Stanford University Press, Stanford, Calif. (1965).