scholarly journals The emission of secondary electrons and the excitation of soft X-rays

1928 ◽  
Vol 119 (783) ◽  
pp. 531-542 ◽  
Keyword(s):  
Secondary Electron Emission ◽  
Good Deal ◽  
Metal Plate ◽  
Considerable Proportion ◽  
X Rays ◽  
Low Velocity ◽  
Secondary Electrons ◽  
A Value ◽  
Primary Electrons ◽  
Made In

Experiments I have recently made in collaboration with Dr. F. C. Chalklin on the one hand and with Mr. F. S. Robertson on the other, together with some observations not yet published made in the Wheatstone Laboratory by Mr. E. Rudberg, taken in conjunction with Krefft’s results for the secondary electron emission from baked tungsten, throw a good deal of light on the mechanism of the generation of secondary electrons at the surfaces of solids, particularly in the range where the energy of the primary electrons is sufficient to generate soft X-rays. I shall first consider what are the chief essential facts from this point of view as to what happens when a beam of electrons falls on a conductor. In 1908 I found that a considerable proportion of slowly moving electrons was reflected by a metal plate; in the particular case of the electrons coming from a hot platinum strip under no applied electric force on to a brass plate, I estimated the proportion reflected at roughly 30 per cent. A similar result with electrons of 2, 4 and 8 volts, equivalent energy was obtained independently about the same time by von Baeyer. Since that time a number of investigations of electron reflection at conductors have been published. Speaking broadly, it appears that with increasing energy of the primary electrons the proportion reflected, increases to a maximum, at a value which is in the neighbourhood of 11 volts for a number of metals, falls to a minimum at a value which is comparable to 30 volts, rises to a second maximum at a value which is of the order of 200 volts, and then falls off slowly and continuously with further increase in the energy. These results vary to some extent with the nature and treatment of the metal surfaces, but it is important to observe that there is generally some range of voltage in which the number of secondary exceeds the number of primary electrons. This is usually in the region in which the soft X-ray emission becomes important. Farnsworth examined the electrons emitted from a nickel plate and found that with primary electrons having 9 volts energy or less, a large proportion of the secondary electrons had an amount of energy nearly equal to that of the primary electrons, and but a small proportion had a velocity of 1 volt or less. As the energy of the primary electrons was increased above 9 volts, the proportion of low velocity electrons steadily increased and the proportion of secondary electrons having energy close to that of the primary electrons steadily fell to a very small percentage at 110 volts, a result previously obtained by Davisson and Kunsman.

scholarly journals Total secondary electron emission from polycrystalline Nickel

1930 ◽  
Vol 128 (807) ◽  
pp. 41-56 ◽  
Keyword(s):  
Electron Emission ◽  
Secondary Electron ◽  
Secondary Electron Emission ◽  
Considerable Proportion ◽  
Secondary Beam ◽  
X Rays ◽  
Applied Potential ◽  
Polycrystalline Nickel ◽  
Low Velocity ◽  
Secondary Electrons

The importance of secondary electron emission in its relation to the excitation of soft X-rays has been pointed out in a recent paper by Prof. O. W. Richardson. He has shown that at every potential where there is an increased excitation of soft X-rays, there is correspondingly an increase in the emission of secondary electrons, and has discussed at some length the mechanism of the generation of secondary electrons. It was therefore felt that a much clearer idea of the phenomenon of soft X-ray excitation from metallic surfaces could be had by studying the secondary electron emission from polycrystalline and single crystal faces. As early as in 1908 Richardson showed that slowly moving electrons are reflected in considerable proportion from metallic plates. Davisson and Kunsman, in a series of papers commencing from 1921, showed that at low voltages up to about 9 volts most of the secondary electrons were purely reflected electrons with velocities the same as the incident electrons. The percentage of the reflected electrons fell rapidly as the applied potential was increased above 9 volts, while that of low velocity electrons increased steadily. Farnsworth, with improved apparatus, added much valuable information regarding the generation of secondary electrons and the conditions operating in such cases. These observers showed that the total emission of secondary electrons from a metal surface depended on the applied potential, the nature of the surface and the previous heat treatment of the metal. They also found that the ratio of the secondary beam to the primary increases with applied potential and becomes greater than 1 after a certain potential, depending on the nature of the bombarded metal, is reached.

scholarly journals The efficiency of secondary electron emission

1933 ◽  
Vol 139 (838) ◽  
pp. 436-447 ◽  
Keyword(s):  
Velocity Distribution ◽  
Electron Emission ◽  
Secondary Electron ◽  
Secondary Electron Emission ◽  
Inelastic Collisions ◽  
Secondary Beam ◽  
X Rays ◽  
Secondary Electrons ◽  
The Third ◽  
Primary Electrons

The velocity distribution of the secondary electrons produced by bombarding a metallic face with a stream of primary electrons has been a matter of interest ever since the beginning of the study of secondary electron emission. As early as in 1908, Richardson and von Baeyer independently showed that slow moving electrons were copiously reflected from conducting faces. Farnsworth showed that for primary electrons having velocities less than 9 volts, most of the secondary electrons had velocities equal to the primary. As the primary potential was increased, the percentage of the reflected electrons decreased gradually but was appreciable at 110 volts. Davisson and Kunsman obtained reflected electrons even at primary potentials of 1000 and 1500 volts in the cases of some metal faces. At higher potentials we have also the electrons that undergo the Davisson and Germer scattering from the many crystal facets on the bombarded targets. As the potential is increased, the number of electrons with low velocities increases steadily and at large applied potentials, we have a large percentage of these in the secondary beam. These conclusions followed as a result of the work of Farnsworth who studied the distribution of velocities of the secondary electrons by the retarding potential method. He did not actually calculate the energy distribution from his curves but has drawn attention to the above conclusions. A careful investigation of the velocity distribution of the secondary electrons from various conducting faces was made by Rudberg at primary potentials ranging up to about 1000 volts. He adopted a magnetic deflection method similar to the one used in the analysis of the β rays and of the electrons excited by X-rays. The method had indeed been used by previous workers for the study of secondary emission, but Rudberg improved the technique considerably and obtained better focussing conditions. His results suggest that there are three groups of electrons in the secondary beam. The first group contains electrons returning with the same velocity as the primary. In the second group of electrons, we have those which undergo inelastic collisions with the orbital and structure electrons and hence are returned with some loss of energy. Richardson has drawn attention to the well-marked minimum between the two groups in Rudberg’s curves and infers that free electrons are not involved in the collisions. Finally there is the third group which contains the slow secondary electrons. The second and the third groups appear to be definitely connected with each other since they are both predominant at high primary potentials and become negligible at low primary potentials. Richardson suggests that the third group is the result of the excitation accompanying the inelastic collisions.

scholarly journals Critical potentials for the excitation of soft x-rays from iron

1930 ◽  
Vol 126 (803) ◽  
pp. 661-674 ◽  
Keyword(s):  
Velocity Distribution ◽  
Secondary Electron ◽  
Secondary Electron Emission ◽  
Target Surface ◽  
Photoelectric Effect ◽  
Secondary Emission ◽  
X Rays ◽  
Secondary Electrons ◽  
Current Voltage ◽  
Primary Electrons

The results of the various investigations which have been carried out during the last few years on the critical potentials for the excitation of soft X-rays, and for the production of secondary electrons, from solids, have shown that the effects occurring at solid surfaces under electronic bombardment in vacuo are more complex than was anticipated when this line of investigation was begun, and that they cannot be interpreted in any simple way in terms of the displacements of electrons within the atoms of the target. The work of various investigators* on the distribution of velocities among the electrons leaving a surface subjected to bombardment by primary electrons of known energy, has shown that a certain number of the electrons leaving the bombarded surface have energies practically equal to that of the primary stream, suggesting that a readily detectable proportion of the primary electrons is scattered or reflected at the target surface without appreciable loss of energy. The proportion of such electrons is greatest for small bombarding energies, e.g ., about 10 volts, and decreases as the voltage accelerating the primary electrons increases. The other marked feature in the velocity distribution curves, for bombarding voltages up to about 1000, is a group having a sharp maximum at about 10 volts. Apart from these features the distribution is a more or less continuous one, the number of electrons having a given velocity increasing as that velocity increases, except that after achieving a small maximum at about 25 volts less than the primary voltage, the curve falls to a minimum before rising to the very sharp peak indicating true reflection There are no indications of maxima for electron energies differing from the primary by amounts corresponding to those required to effect characteristic electron transitions within the atoms of the target. Moreover, there appears to be nothing in the velocity distribution curves for the secondary emission to correspond to the discontinuities which have been found by various investigators to occur in the current-voltage curves of the secondary electron current from a bombarded surface, or in the current-voltage curves of the photoelectric effect of the soft X-radiation excited by the bombardment. As regards the latter effect an explanation is to hand on the view that the proportion of the primary electrons whose energy is converted, in part, to photoelectrically active radiation is so small that indications of the various different energy transfers suggested by the critical potential curves are swamped in the velocity distribution curves of the secondary electrons. It is, however, more difficult to reconcile the absence of any correlation between the discontinuities which have been observed in the current-voltage curves for secondary electron emission, and the velocity distribution of the latter.

scholarly journals The emission of secondary electrons and the excitation of soft X-rays

1930 ◽  
Vol 128 (807) ◽  
pp. 63-74 ◽  
Keyword(s):  
Energy Distribution ◽  
Secondary Electron Emission ◽  
Continuous Distribution ◽  
Average Energy ◽  
Great Majority ◽  
Metal Plate ◽  
Inelastic Collisions ◽  
Common Mechanism ◽  
X Rays ◽  
Secondary Electrons

As a result particularly of experiments carried out by Miss Andrewes, Mr. Ramachandra Rao and myself at King’s College and by Dr. Rudberg in Stockholm, we now have much more information about these phenomena than we had when I discussed this question two years ago. The experiments of Whiddington as well as of Rudberg have removed much of the vagueness which was then necessary as to the nature of the first process which occurs when an electron strikes a solid. It is evidently either reflected without loss of energy, as in Davisson’s experiments, or it undergoes an inelastic collision of such a kind that it loses a substantial amount of energy. This is shown by the well-marked minimum in the energy distribution curve for the reflected and secondary electrons between the peak corresponding to the Davisson effect and lower energy values. In fact in important cases the density at this minimum is practically zero. This shows that in such cases there is no appreciable number of secondary electrons which have come back as a result of encounters with free electrons; since this process would give rise to a smooth and continuous distribution of velocities which should have an appreciable density at the place where the minimum occurs. The velocity distribution curves for the secondary electrons show, in addition to the two already mentioned, a third group having a low average energy. This group is closely connected with the group which has undergone inelastic collisions, since both groups are almost absent when the energy of the primary electrons is low. The electrons which form this group are to be regarded as the true secondary electrons originating in some way as a result of the excitation accompanying the inelastic collisions. This is very definitely supported by the fact that the energy loss in the inelastic collisions corresponds to definite level differences which are independent of the energy of the exciting electrons and at the same time the energy distribution in this third group is very insensitive to changes in the primary voltage. It is, in fact, very similar to the energy distribution among the photoelectrons of low energy which are generated when the soft X-rays which accompany these electron emissions fall on a metal plate. This similarity suggests that these photoelectrons and the third group of secondary electrons originate in a common mechanism or at least in mechanisms of very similar type. This is indeed required by the fact that the total secondary electron emission, i. e ., the sum of the three groups, and the X-ray emission both show a series of discontinuous increases at the same primary voltage. These discontinuities are very numerous and it is now abundantly clear that the great majority of them have nothing directly to do with the Bohr levels which govern the structure of the atoms of the bodies concerned.

MAXIMUM SECONDARY ELECTRON YIELDS FROM SEMICONDUCTORS AND INSULATORS

2016 ◽  
Vol 24 (04) ◽  
pp. 1750045 ◽  
Author(s):  
A. G. XIE ◽  
Z. H. LIU ◽  
Y. Q. XIA ◽  
M. M. ZHU
Keyword(s):  
Electron Emission ◽  
Secondary Electron ◽  
Maximum Yield ◽  
Secondary Electron Emission ◽  
High Energy ◽  
Secondary Electrons ◽  
Backscattered Electrons ◽  
Universal Formula ◽  
Yield Formula ◽  
Primary Electrons

Based on the processes and characteristics of secondary electron emission and the formula for the yield due to primary electrons hitting on semiconductors and insulators, the universal formula for maximum yield [Formula: see text] due to primary electrons hitting on semiconductors and insulators was deduced, where [Formula: see text] is the maximum ratio of the number of secondary electrons produced by primary electrons to the number of primary electrons. On the basis of the formulae for primary range in different energy ranges of [Formula: see text], characteristics of secondary electron emission and the deduced universal formula for [Formula: see text], the formulae for [Formula: see text] in different energy ranges of [Formula: see text] were deduced, where [Formula: see text] is the primary incident energy at which secondary electron yields from semiconductors and insulators, [Formula: see text], are maximized to maximum secondary electron yields from semiconductors and insulators, [Formula: see text]; and [Formula: see text] is the maximum ratio of the number of total secondary electrons produced by primary electrons and backscattered electrons to the number of primary electrons. According to the deduced formulae for [Formula: see text], the relationship among [Formula: see text], [Formula: see text] and high-energy back-scattering coefficient [Formula: see text], the formulae for parameters of [Formula: see text] and the experimental data as well as the formulae for [Formula: see text] in different energy ranges of [Formula: see text] as a function of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] were deduced, where [Formula: see text] and [Formula: see text] are the original electron affinity and the width of forbidden band, respectively. The scattering of [Formula: see text] was analyzed, and calculated [Formula: see text] values were compared with the values measured experimentally. It was concluded that the deduced formulae for [Formula: see text] were found to be universal for [Formula: see text].

scholarly journals The shape of the continuous β -spectrum of thorium C. C'

1937 ◽  
Vol 162 (910) ◽  
pp. 391-403 ◽  
Author(s):  
H. O. W. Richardson ◽  
Alice Leigh-Smith ◽  
James Chadwick
Keyword(s):  
Low Energy ◽  
Considerable Proportion ◽  
Secondary Electrons ◽  
Fast Electrons ◽  
Low Energies ◽  
Ionisation Chamber ◽  
Pass Through ◽  
Slow Electrons ◽  
Primary Electrons ◽  
Apparent Conflict

The theories of β -decay based on the neutrino hypothesis predict that a considerable proportion of the electrons emitted from a heavy nucleus will have low energies, owing to the Coulomb attraction between the electron and the nucleus. This prediction has been in apparent conflict with most experimental curves (Madgwick 1927; Scott 1935 ), which show the ordinate of the energy distribution falling to zero at the origin or even before it, thus even indicating a low energy end-point below which no β -rays are emitted. It is, however, probable that the experimental uncertainties in the methods which have been used are such that no definite conclusion can be drawn from them about the shape of the low energy end of the spectrum. In these methods the source is deposited on a solid mounting and the emitted β -particles pass through a window in entering the detecting apparatus, which may be a counter, a cloud chamber or an ionisation chamber. The window stops all β -particles below a certain energy, while those which pass through are reduced in energy and considerably scattered. These effects, which are well shown in curves given by Eddy (1928), produce a marked falling off in the observed number of β -particles of low energy. The use of a solid mounting for the source introduced opposite effects giving an increased number of slow electrons; for firstly, the fast electrons will eject slow secondary electrons from the solid mounting and, secondly, if the mounting is thick, a considerable reflexion of the primary electrons will occur with varying losses of energy inside the solid, so that the reflected spectrum will contain relatively more low energy rays.

HIGH DENSITY DIAMOND WHISKER FABRICATION AND SUPPRESSION OF SECONDARY ELECTRON EMISSION BY WHISKERS

2002 ◽  
Vol 01 (05n06) ◽  
pp. 431-436
Author(s):  
D. JEON ◽  
S. W. LEE ◽  
Y. J. BAIK
Keyword(s):  
Electron Emission ◽  
Diamond Film ◽  
Secondary Electron ◽  
Metal Clusters ◽  
Secondary Electron Emission ◽  
Narrow Gap ◽  
Secondary Electrons ◽  
Parallel Direction ◽  
Emission Yield ◽  
Primary Electrons

Diamond whiskers were formed by etching diamond thin films using metal clusters as a shadow mask, which were deposited on the diamond film before or during etching. The whiskers were as thin as 100 nm and the density was as high as 1010/ cm 2. The secondary electron emission yield of the diamond whiskers was significantly reduced as compared to the initial diamond film. The decrease in the yield was more significant if the primary electrons were impinged in parallel direction with the whiskers. We suggest that absorption of the secondary electrons in the narrow gap between the whiskers was the reason for the decreased yield.

food was presented by McLaughlin and collaborators (29). Glover’s review (30) is less detailed but more recent. Dosimetry for food irradiation processing has reached a high level of perfec­ tion. Many standards for this purpose have been issued by the American Society for Testing and Materials (31,32). The role of dosimetry in good radiation processing practice is described in the Recommended International Code of Practice for the Operation of Irradiation Facilities Used for the Treatment of Foods (see Appendix II) and in a series of Codes of Good Irradiation Practice issued by ICGFI (International Consultative Group on Food Irradiation) (see Appendix III). With some food items, such as whole eggs (33) and ground com (34), it may be possible to use the food itself as a dose meter. This will be discussed in more detail in Chapter 5. As mentioned earlier, electron beams, on the one hand, and gamma rays and x-rays, on the other hand, differ greatly in their ability to penetrate matter. This has important consequences for the dose distribution in the irradiated medium. Since many foods consist mostly of water, the penetration of radiation in water is shown in Figure 14. When an electron beam penetrates an aqueous medium the dose somewhat below the surface is higher than at the surface. This is due to the formation of secondary electrons which, because of their lower energy, are more effectively absorbed than the primary electrons. Also, scattering causes some secondary electrons to escape from the surface in the direction opposite to that of the beam of primary electrons. Thus a 10-MeV electron beam giving a dose of 10 kGy at the surface will deposit about 12.5 kGy at 2 cm below the surface. As more and more primary electrons lose their energy by interacting with water molecules, the absorbed dose decreases with increasing depth and at about 5 cm the limit of penetration is reached. In contrast, the dose delivered by gamma rays decreases continuously. The rate of decrease is faster with 137Cs gamma radiation than with 60Co gamma radiation. With x-rays it depends on the energy of the x-ray-producing electrons. For practical purposes the penetration of 5-MeV x-rays is comparable to that of 60Co gamma rays. Two-sided irradiation permits processing of thicker packages with more uni­ form dose distribution, as indicated in Figure 15. If the density of the irradiated medium is less than that of water, e.g., in fatty foods or in dehydrated or porous foods, the depth of penetration is correspondingly greater. The 10-MeV electron beam, which barely reaches a depth of 5 cm in water, will reach approximately 10 cm at a density of 0.5g/cm3. From Figures 14 and 15 it is clear that an absolutely uniform dose distribution cannot be obtained, even if a material of uniform density is irradiated. If dose

1995 ◽  
pp. 52-52
Keyword(s):  
Electron Beam ◽  
Gamma Radiation ◽  
Gamma Rays ◽  
Dose Distribution ◽  
Food Irradiation ◽  
X Rays ◽  
Secondary Electrons ◽  
60Co Gamma ◽  
American Society ◽  
Primary Electrons

NEUTRINO AND UHECR SPECTRA FROM MRK 421

2014 ◽  
Vol 28 ◽  
pp. 1460206
Author(s):  
MARIA PETROPOULOU ◽  
STAVROS DIMITRAKOUDIS ◽  
APOSTOLOS MASTICHIADIS
Keyword(s):  
Spectral Energy Distribution ◽  
High Energy ◽  
Spectral Energy ◽  
Synchrotron Emission ◽  
X Rays ◽  
Ultra High Energy ◽  
Secondary Electrons ◽  
Charged Pions ◽  
Tev Gamma Rays ◽  
Primary Electrons

We present the neutrino and UHECR spectra obtained from a detailed fitting of the spectral energy distribution (SED) of Mrk 421 (March 2001) using two variations of the leptohadronic model. In particular, while the low-energy component (optical to X-rays) of the SED is fitted by synchrotron emission of primary electrons in both models, the high-energy one (GeV-TeV gamma-rays) is synchrotron emission attributed either to ultra-high energy protons (LHs model) or to secondary electrons produced by the decay of charged pions (LHπ model). In the LHπ case we find that the produced neutrino spectra are sharply peaked at Eν ~ 30 PeV with a peak flux slightly below the IC-40 sensitivity limit for Mrk 421. In the LHs model, on the other hand, the neutrino spectra fall well outside the PeV energy range, but the calculated E ~ 30 EeV — UHECR flux at earth is close to that observed by HiresI, Telescope Array and Pierre Augere experiments.

THE FORMULAE FOR PARAMETERS OF THE SECONDARY ELECTRON YIELD OF INSULATORS FROM 10 keV TO 30 keV

2013 ◽  
Vol 27 (32) ◽  
pp. 1350238 ◽  
Author(s):  
AI-GEN XIE ◽  
QING-FANG LI ◽  
YUN-YUN CHEN ◽  
HONG-YAN WU
Keyword(s):  
Energy Band ◽  
Secondary Electron ◽  
Secondary Electron Emission ◽  
Average Energy ◽  
Surface Barrier ◽  
Secondary Electrons ◽  
Secondary Electron Yield ◽  
Electron Yield ◽  
Mean Escape Depth ◽  
Primary Electrons

Based on the formula for the average energy required to produce an internal secondary electron (ε) in emitter, the energy band of insulator and the assumption that the maximum exit energy of secondary electron in insulator is reverse to the width of forbidden band, the formula for ε in insulator is deduced. On the basis of the formula for the number of internal secondary electrons produced in the direction of the velocity of primary electrons per unit path length, the energy band of insulator and the characteristic of secondary electron emission, the formula for the probability of secondary electrons passing over the surface barrier of insulator into the vacuum (B) is also deduced. According to some relationship between the parameters of secondary electron yield from insulator, the formula for the mean escape depth (1/α) is successfully deduced. The formulae for ε and 1/α are experimentally proven, respectively, and thereafter the formula for B is indirectly proven to be true by the experimental results. It is concluded that the formulae for ε, B and 1/α are universal to estimate ε, B and 1/α under the condition that primary electrons from 10 keV to 30 keV hit on an insulator, respectively.

Sign in / Sign up

Export Citation Format

Share Document