Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal
Spectra of coherent bremsstrahlung and radiation spectra of the electron moving near the axis and plane of diamond crystal have been measured using the electron beam of low intensity with 0.8 GeV energy. Experimental data are compared with calculations based on the coherent bremsstrahlung theory.
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2000
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| Цитувати: | Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal / V.B. Ganenko, Yu.V. Zhebrovskij, L.Ya. Kolesnikov, А.L. Rubashkin // Вопросы атомной науки и техники. — 2000. — № 2. — С. 51-53. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-822712016-04-15T13:32:49Z Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal Ganenko, V.B. Zhebrovskij, Yu.V. Kolesnikov, L.Ya. Rubashkin, A.L. Electromagnetic radiation Spectra of coherent bremsstrahlung and radiation spectra of the electron moving near the axis and plane of diamond crystal have been measured using the electron beam of low intensity with 0.8 GeV energy. Experimental data are compared with calculations based on the coherent bremsstrahlung theory. 2000 Article Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal / V.B. Ganenko, Yu.V. Zhebrovskij, L.Ya. Kolesnikov, А.L. Rubashkin // Вопросы атомной науки и техники. — 2000. — № 2. — С. 51-53. — Бібліогр.: 9 назв. — англ. 1562-6016 PACS: 29.27.Fh http://dspace.nbuv.gov.ua/handle/123456789/82271 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
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English |
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Electromagnetic radiation Electromagnetic radiation |
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Electromagnetic radiation Electromagnetic radiation Ganenko, V.B. Zhebrovskij, Yu.V. Kolesnikov, L.Ya. Rubashkin, A.L. Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal Вопросы атомной науки и техники |
| description |
Spectra of coherent bremsstrahlung and radiation spectra of the electron moving near the axis and plane of diamond crystal have been measured using the electron beam of low intensity with 0.8 GeV energy. Experimental data are compared with calculations based on the coherent bremsstrahlung theory. |
| format |
Article |
| author |
Ganenko, V.B. Zhebrovskij, Yu.V. Kolesnikov, L.Ya. Rubashkin, A.L. |
| author_facet |
Ganenko, V.B. Zhebrovskij, Yu.V. Kolesnikov, L.Ya. Rubashkin, A.L. |
| author_sort |
Ganenko, V.B. |
| title |
Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal |
| title_short |
Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal |
| title_full |
Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal |
| title_fullStr |
Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal |
| title_full_unstemmed |
Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal |
| title_sort |
spectra of coherent bremsstrahlung and radiation formed by 0.8 gev electrons moving near the axis and plane of diamond crystal |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2000 |
| topic_facet |
Electromagnetic radiation |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/82271 |
| citation_txt |
Spectra of coherent bremsstrahlung and radiation formed by 0.8 GeV electrons moving near the axis and plane of diamond crystal / V.B. Ganenko, Yu.V. Zhebrovskij, L.Ya. Kolesnikov, А.L. Rubashkin // Вопросы атомной науки и техники. — 2000. — № 2. — С. 51-53. — Бібліогр.: 9 назв. — англ. |
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Вопросы атомной науки и техники |
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E L E C T R O M A G N E T I C R A D I A T I O N
SPECTRA OF COHERENT BREMSSTRAHLUNG AND RADIATION
FORMED BY 0.8 GEV ELECTRONS MOVING NEAR THE AXIS
AND PLANE OF DIAMOND CRYSTAL
V.B. Ganenko, Yu.V. Zhebrovskij, L.Ya. Kolesnikov, А.L. Rubashkin
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
Spectra of coherent bremsstrahlung and radiation spectra of the electron moving near the axis and plane of
diamond crystal have been measured using the electron beam of low intensity with 0.8 GeV energy. Experimental
data are compared with calculations based on the coherent bremsstrahlung theory.
PACS: 29.27.Fh
1. INTRODUCTION
The beams of coherent bremsstrahlung (CB) found
broad application in experiments on nuclear and
elementary particles physics [1]. These beams are
generated by relativistic electrons in monocrystalline
photon targets when the electron incidence angle
towards crystal axes are rather large, ψ>>ψc (ψc- is the
critical angle of axial channeling. For the diamond
crystal and electron energy E0∼1 GeV ψc≈0.3 mrad).
Owing to periodicity of atom positions in a crystal
lattice there appear interference peaks in CB spectra in
which the radiation intensity significantly exceeds that
of electrons in an amorphous substance. Besides the
radiation in the region of the peak has rather high linear
polarization. Due to a high Debye temperature, perfect
crystal lattice and small atomic number the
monocrystalline targets from diamond crystals ensure
the highest operational parameters of CB beams [1].
The spectra of CB radiation and polarization are
well described by the theory based on the Born
approximation [2,3]. According to the theory the CB
cross section can be presented as a sum:
dσkti = dσcoh + dσam ,
where dσcoh is the coherent part of the CB cross section
depending on the crystal orientation towards the
direction of the electron beam; dσam is the non-coherent
(amorphous) part of the cross section which does not
depend on the crystal orientation. So, the CB spectrum
consists a sum of two parts: coherent part Iint with
interference peak and usual bremsstrahlung Iam. The
interference peak has a sharp upper bound and it is
reduced smoothly in the low energy area. The radiation
intensity in the peak drops with increasing angle ψ, and
its position displaces into the area of high energies and
for a rather large ψ the peak is not observed.
There are also other crystal orientations towards an
incoming electron beam, with which the generation of
intensive gamma radiation is observed, for example,
when the channeling modes or above-barrier electron
movement are realized [4,5]. So, if incoming electrons
drop onto the crystal along crystalline planes, but at
large angles to crystal axes, ψ>>ψc, the electron
movement in the crystal is determined by an average
interplanar potential. Then the conditions for channeling
or above- barrier electron movement near the plane of
crystal take place. This results in appearance of an
interference maximum in the low-energy area of
radiation spectrum, ~7-10 MeV, for the energy of
incoming electrons E0~1 GeV. Its intensity for a non-
collimated radiation is ∼3-5 times higher, than the
radiation intensity in amorphous medium [6]. The
emergence of this maximum is conditioned by the
periodicity of electron movement in the average
potential of crystal planes. As the period corresponding
to the electron movement in the interplanar potential
does not depend on the angle ψ, the position of this
interference peak does not depend on ψ too. Radiation
of this type usually is called as plane channeling
radiation.
One more possibility for generation of the intensive
gamma radiation is opened, when the electrons drop
onto the crystal along one of the main close-packed
axes, ψ≤ψc. In this case also observed is the significant
enhancement of radiation intensity in the range of low
energies. It is connected with effects of axial channeling
or axial above-barrier electron movement. The spectrum
of this radiation also has a maximum which takes place
in the region of ~ 20-30 MeV for the energy of
incoming electrons E0 ~ 1 GeV and its intensity is ~20
times higher than the radiation intensity in amorphous
medium [6]. When the angle of incidence towards the
axis increases, the emission power in this energy range
drops. Radiation of this type usually is called as axis
channeling radiation. The movement of ~1 GeV
electrons in the crystal and their radiation spectra in
these cases can be described within the framework of
classical electrodynamics [4,5].
Research on spectral characteristics of radiation, for
orientations corresponding to CB generation, planar or
axial channeling, was conducted, as a rule, in diverse
experiments using the crystals of a various thickness and
different atomic number. It is useful to compare spectral
characteristics of these types of radiation obtained in the
same experimental conditions. In the present paper the
results of such measurements are given for the incoming
electron energy E0= 0.8 GeV and diamond crystal
0.03 cm thick.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2000, №2.
Серия: Ядерно-физические исследования (36), с. 51-53.
51
2. EXPERIMENTAL LAYOUT
The measurements were carried out on the electron
beam of low intensity at the Kharkov 2 GeV linear
accelerator. The layout of the experiment is shown in
Fig. 1. After passing through the crystal target (1) the
electrons were deflected by a cleaning magnet (2) and
entered a beam dump (3). The photon beam, produced
in the crystal, was passed through a formation system
composed of three rectangular lead collimators (5,6,9)
and cleaning magnets (2,7,10). In front of the last
collimator (9) a filter (8) from LiH 1.7X0 thick was
placed. The collimation angle of the gamma radiation
was θk≈0.3θγ (θγ=m/E0, m -is the electron mass) and
ensured a size of a gamma beam on a detector (11)
3x3 cm.
2 7 9 11
1 5 6 8 10
3
4
e-
Fig. 1. Experimental layout: 1-diamond crystal;
2,7,10- cleaning magnets; 3-beam dump; 4-shielding;
5,6,9- collimators; 8-LiH filter 1.7X0 thick; 11- NaJ
detector.
The photons were detected in an counting mode by
the NaJ(Tl) counter 20 cm in diameter and 20 cm in
thickness. The intensity of the electron beam was
selected such that the load of the detector did not exceed
10 counts/s. The system of producing and forming the
electron beam of a low intensity and controlling its
parameters, as well as the procedure of measurements
were described in [6,7].
The measurements of CB spectra were carried out
for orientations, when the main contribution to the CB
cross section was introduced by one point of the
reciprocal lattice (2,2,0). The angles of crystal
orientation θ and α, respective to direction of the
electron beam, unambiguously determine the energy of
the interference peak Eγ
p in the CB spectrum. θ is the
angle between the electron momentum and axis
B1=<110> of diamond crystal, α is the angle between
planes (P0,B1) and (B1,B2), where the axis B2=<110>.
In experiment the values of angles θ and α were selected
in such a manner that the interference maxima
corresponded to energies Eγ
p=30, 60, 100, 140 MeV.
The values of the relative energy X=Eγ/E0 are 0.0375,
0.075, 0.125 and 0.175, respectively. The planar
orientation was obtained when values of the angles were
α=0 and θ=75 mrad that corresponded to electron
movement in the plane (001) of the diamond crystal.
The axial orientation was obtained for the angle θ=0,
that corresponded to the electron movement along the
axes <110>.
3. RESULTS
In Fig. 2 the CB spectrum measured in the range of
photons energies 0.02 ≤ X ≤ 0.75 for the peak energy Eγ
p=100 MeV is shown. The interference peak with the
half-width ~38 MeV has a sharp upper bound with
smooth lowering in the low-energy area practically up to
zero energies as it is predicted by the CB theory. For
energies higher than 250 MeV the interference part does
not give any more contribution and the spectrum in this
area has a form of a bremsstrahlung spectrum in
amorphous substance. Usually, the intensity of the CB is
evaluated by the excess β of radiation intensity in the
CB maximum over the intensity of non-coherent part of
radiation spectrum:
β=(dσint+dσam)/dσam=(Iint+Iam)/Iam.
For spectrum in Fig. 2 the excess is β∼6 and it is well
described by the CB theory.
0 100 200 300 400 500 600
0
20
40
60
80
100
120
Eγ
dN
γ/d
Eγ
, a
rb
itr
ar
y
un
its
Eγ , MeV
Fig. 2. CB spectrum for the 100 MeV energy peak.
The curve is the calculation under the CB theory.
0 50 100 150 200 250 300
0
50
100
150
200
250
6
5
4
3
2
1
Eγ
dN
γ/d
E
γ,
ar
bi
tra
ry
u
ni
ts
Eγ , MeV
Fig. 3. CB spectra for energies of interference
peak: 140 MeV (1), 100 MeV (2), 60 MeV (3), 30 MeV
(4). (5)- planar orientation. (6)- Shiff spectrum. The
curves are calculated under the CB theory.
In Fig. 3 the results of CB spectra measurements in
the photon energy range 0.01 ≤ X ≤ 0.375 for energies
of interference maxima Eγ
p=30, 60, 100, 140 MeV are
shown. For comparison the spectra were normalized at
the photon energy 300 MeV, where the radiation is
52
determined only by the non-coherent part, and the
intensity does not depend on the crystal orientation.
It is seen, that the radiation intensity in CB maxima
increases with decreasing energy of interference
maxima. The magnitude of exceeding the maximum
above the amorphous level increases from β≈3.5 to 10
with decreasing peak energy from Eγ
p=140 MeV
(X=0.175) to 30 MeV (X=0.0375). The high values of β
are due to the strong collimation of the gamma radiation.
In Fig. 3 shown are also the calculations of the CB
spectra under the theory [2,3]. The theory describes well
the experimental data for X ≥ 0.1. For lower X the
agreement is worsened because the angles of electron
incidence onto the plane of crystal become already
comparable with the critical angles of channeling. The
results of calculation for the CB polarization under these
conditions are shown in Fig. 4. It is seen, that the
polarization of radiation is rather significant, namely
85% for Eγ
p=30 MeV and 75% for 140 MeV. The large
values of polarization are caused also by the strong
collimation of radiation.
In Fig. 3 also shown is the spectrum for the case
when incoming electrons drop onto the crystal along the
crystalline plane (001) at large angle, ψ=75 mrad, to the
crystalline axis <110>. For this orientation the
maximum radiation is observed at the photon energy Eγ
~7-8 MeV and the value β increases up to 12.5. This
maximum is not broad. At the energy Eγ~40 MeV the
radiation intensity decreases yet up to the amorphous
level. This orientation gives a slightly larger intensity in
the maximum, than CB. The radiation in the maximum
at this orientation is also strong polarized, up to 80 %
for the incoming electron energy E0~1 GeV [8].
0 50 100 150 200 250 300
0
20
40
60
80
100
4
32
1
Po
la
riz
at
io
n,
%
E , MeV
Fig. 4. Calculation of CB polarization for interference
peak energies 30 (1), 60 (2), 100 (3), 140 (4) MeV.
The significant increase of the radiation intensity in
the range of low energies is observed for axial
orientation, when the electron beam drops onto the
crystal along the axis <110>, Fig. 5. For conditions of
the given experiment the intensity maximum takes place
at the photon energy Eγ~20 MeV. The exceeding above
the amorphous level is about β≈70, that is 5-6 times
higher, than that of CB and planar orientation in this
energy range. The radiation spectrum is broader and
gets the amorphous level at Eγ~140 MeV, however, the
radiation in the maximum has not polarization.
Thus, the experimental measurements show that
there is a wide variety of possibilities to obtain intensive
and polarized photon beams for studying photonuclear
reactions in the area extended up to the pion threshold.
The radiation intensity at the axial orientation exceeds
the radiation intensity of other types of orientations by
the order of magnitude. An essential circumstance is that
the exceeding of the emission intensity in the maximum
above the emission in amorphous medium at the axial
orientation weakly depends on a thickness of crystal in
the range up to 0.3X0 [9]. Therefore there is a possibility
to increase the intensity of photon beams by increasing
the crystal thickness.
0 50 100 150 200 250 300
0
200
400
600
800
1000
1200
1400
65
4
3
2
1
Eγ
dN
γ/
dE
γ,
ar
bi
tra
ry
u
ni
ts
Eγ , MeV
Fig. 5. Radiation spectra for various orientations:
(1)- axial; (2)- planar; (3,4,5,6) CB spectra, for peak
energies, 30, 60, 100 and 140 MeV, respectively.
REFERENCES
1. G.D. Kovalenko et al. Topics in Current Physics
38. Coherent Radiation Sources. P. 33-60.
Springer-Verlag Berlin Heidelberg, 1985.
2. U. Timm. Coherent bremsstrahlung of electrons in
crystals. Preprint DESY, 69/14, 1969.
3. M.L Ter-Mickaelyan. Influence of a medium on
lectromagnetic processes at high energies.
Yerevan: Izd. AS Arm. SSR. 1969, 457 p. (in
Russian).
4. M.A. Kumakhov. Radiation of channeling particles
in crystals. M. Energoatomizdat, 1986, 161 p. (in
Russian).
5. A.I. Achiezer, N.F. Shulga. Electrodynamics of high
energies in substance. M. Nauka, 1993, 344 p. (in
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6. V.B. Ganenko et al. Radiation spectra of relativistic
electrons in diamond and silicon single crystals //
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7. V.B. Ganenko et al. Investigation of spectral
characteristic of the interference part of coherent
electron bremsstruchlung in diamond crystal.
Preprint KIPT 90-57, Kharkov. 1990.
8. V.B. Ganenko et al. Investigation of linear
polarization of radiation emitted by planar
channeling relativistic electrons in diamond crystal
// Yad. Fiz., 1997, v. 60, p. 223-229.
53
9. A.P. Antipenko et al. Research distribution of
gamma qwanta emitted by GeV electrons in a thick
crystals // Phys. Lett. 1991, v. A158, p. 176-181.
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