A possibility to measure the linear polarization of photons by using triplet photoproduction
A review of currently available high-energy photon polarimeters, which use the effect of asymmetry of recoil electron yield during triplet photoproduction, is presented. The influence of both multiple scattering of electrons and d-electron production in the target medium on the decrease of the exper...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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| Цитувати: | A possibility to measure the linear polarization of photons by using triplet photoproduction / V.F. Boldyshev, Yu.P. Peresunko, E.A. Vinokurov // Вопросы атомной науки и техники. — 2001. — № 1. — С. 63-65. — Бібліогр.: 14 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859644725701640192 |
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| author | Boldyshev, V.F. Peresunko, Yu.P. Vinokurov, E.A. |
| author_facet | Boldyshev, V.F. Peresunko, Yu.P. Vinokurov, E.A. |
| citation_txt | A possibility to measure the linear polarization of photons by using triplet photoproduction / V.F. Boldyshev, Yu.P. Peresunko, E.A. Vinokurov // Вопросы атомной науки и техники. — 2001. — № 1. — С. 63-65. — Бібліогр.: 14 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | A review of currently available high-energy photon polarimeters, which use the effect of asymmetry of recoil electron yield during triplet photoproduction, is presented. The influence of both multiple scattering of electrons and d-electron production in the target medium on the decrease of the experimentally observed asymmetry is considered. The graphs of effective asymmetry and the figure of merit versus target thickness are given.
|
| first_indexed | 2025-12-07T13:26:04Z |
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E X P E R I M E N T A L M E T H O D S A N D C O M P U T A T I O N S
A POSSIBILITY TO MEASURE THE LINEAR POLARIZATION OF
PHOTONS BY USING TRIPLET PHOTOPRODUCTION
V.F. Boldyshev, Yu.P. Peresunko , E.A. Vinokurov
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
A review of currently available high-energy photon polarimeters, which use the effect of asymmetry of recoil
electron yield during triplet photoproduction, is presented. The influence of both multiple scattering of electrons and
δ-electron production in the target medium on the decrease of the experimentally observed asymmetry is considered.
The graphs of effective asymmetry and the figure of merit versus target thickness are given.
PACS: 29.27.Hj 29.90. +r.
1. GENERAL CHARACTERISTICS OF
THE METHOD
The possibility of measuring the linear photon-beam
polarization by measuring the asymmetry of recoil elec-
tron yield in the process of triplet photoproduction γ+e–
→ e– + e– + e+ has first been indicated by the KIPT group
[1–4]. The cross section for the recoil electron yield has
the form:
)2cos1(2cos2 1
)(
1
)()(
1
ϕσϕσσ
ϕ
σπ Λ+=+= PP
d
d tlt , (1)
where )(tσ is the total cross section for unpolarized
photons, σ(l) is a part of cross section due to the photon
polarization, P is the degree of linear photon-beam po-
larization, )()( / tl σσ=Λ is the asymmetry of the yield
of recoil electrons for P=1, ϕ1 is the azimuthal angle.
The detailed analysis of this process and the devel-
opment of a new method, which, in principle, allows
measuring the linear photon-beam polarization in a wide
range of photon energies from 25 MeV to several TeV,
been performed in [5]. Possibilities of constructing
tracking devices and high-speed counters for these mea-
surements have been discussed.
About 90% of recoil electrons detectable at the ex-
periment momentum mcqq 10 ≈≥ have a polar angle Θ1≥
20°, that makes it possible to determine reliably their az-
imuthal angle ϕ1. The values σ(t) and σ(l) increase, and
the asymmetry Λ slightly decrease and tend to the
asymptotical value with an increase in the photon ener-
gy ω. It is possible to choose such a region of kinemat-
ics’ variables, where σ(t) and σ(l) are of the order of sev-
eral mbn and the asymmetry is not less than Λ~0.11.
2. THE USE OF THE TRACKING DEVICES
The tracking devices have a slow rate of statistics
acquisition. To measure the photon-beam linear polar-
ization by these devices, one should use all the range of
allowed values for recoil electron moment with q > q0..
The helium-filled streamer chamber SK–600 has
been used in the course of a trial experiment [6] to mea-
sure the degree of linear polarization of a beam of co-
herent bremsstrahlung (CB) with an electron energy of
600 MeV in the LUE–2000 with a photon energy of
60 MeV at the coherent peak. The method developed
was used in this experiment for the first time.
The photon polarization determined by means of the
asymmetry method gives P=0.68±0.94.
For the determination of photon polarization by the
least-squares method (LSM) and by the maximum like-
lihood method (MLM), two sets of events were used.
The first one contained events with all θ1 and the second
contained events with θ1< 60•. With these sets the fol-
lowing P values were obtained:
P=0.53±0.45 and P=0.59±0.83 (LSM),
P=0.66±0.54 and P=0.66±1.18 (MLM).
All five values for the degree of polarization, ob-
tained by the method of asymmetry of recoil electrons
of triplets, agree with P=0.65±0.15 determined on the
basis of the coherent bremsstrahlung theory.
These results mean that the method under considera-
tion can be used for measuring the photon-beam polar-
ization. At the same time, it is clear that tracking de-
vices cannot be effective monitors of the polarization of
photon beams. For this purpose short-response time de-
tectors should be used.
3. THE USE OF HIGH–SPEED COUNTERS
The polarimeters based on the method considered
have been developed in Japan [7-8], Germany [9], and
USA [10]. The scintillation counters with short response
times were used for registration of both the recoil elec-
trons and the e+e–-pairs [7-8], [10]. Plastic plates of dif-
ferent thickness were used as targets. By the method un-
der discussion the Tokyo group [11] measured the ener-
gy spectra of observed asymmetry (PΛ product) in the
range of photon energies from 240 to 620 MeV with the
use of a polarimeter, which was installed in the CB
beam. This experiment has corroborated the validity of
the method.
The mentioned experiments show that in the real
case the observable asymmetry value of the yield of re-
coil electrons is less than the values predicted in [1-5].
Actually, the important effects which reduce the observ-
able asymmetry of recoil electron yield in the polarime-
ter considered are the multiple scattering of slow elec-
trons and the δ-ray production by fast particles of the
e+e– pair produced in the medium of target, air, and
counters.
The multiple scattering of charged particles in the
matter is described by the Moliere theory [12]. Accord-
ing to this theory, for a rather thick layer of medium the
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2001, № 1.
Series: Nuclear Physics Investigations (37), p. 63-65.
63
Gauss approximation to the angular distribution of parti-
cle deviation from the initial direction is valid
2
0
2 /2/1)2
0()( ΘΘ−−Θπ=Θ eF , (2)
where
0
20
15
X
x
E
MeV
β
=Θ , E is the particle energy in
MeV, β is the particle velocity , X0 is the radiation
length, x is the particle path length in the matter.
After averaging the initial distribution (1) taking into ac-
count (2) we get
).12cos1()(
))1(2cos)()()((
1
2
2
0 ϕΘ−Λ+σ=
ϕ−ϕσ+σϕϕ=
ϕ
σπ ∫
ePt
lPtFd
d
d
(3)
The macroscopic cross section for the yield of recoil
electrons produced by the photon at the point x after
these electrons traversed the target layer of thickness
(L-x), is given by
).2cos1)((
)2cos1(),(
1
)(
)(
1
)()(
1
1
ϕσρ
ϕσρ
b
ePxL
A
ZN
ePdx
A
ZNLx
bxL
t
A
L
x
xLbt
Atr
−−
−−
−Λ+−=
Λ+=Σ ∫
(4)
Here
0
2
2
115
XE
MeVb
=
β
, L is the target thickness in
cm, AZN A /ρ is the number of electrons in 1 cm3 (ρ -
density, NA – Avogadro number, AZ , – averaged
atomic number and atomic weight of medium, respec-
tively). Considering that points of triplet production are
uniformly distributed inside the target with the probabil-
ity density )()(1)(1 xLx
L
xF −ΘΘ= , and averaging over
the target thickness L, we shall obtain the following ex-
pression for the macroscopic cross section:
.12cos)1(2)(
21
2
)(
),()(1)(
ϕ−+−Λ+σρ=
Σ=Σ ∫
LbLbe
Lb
PLt
A
Z
AN
dxLxtrxFLtr
(5)
As regards the production of δ-rays, they are mainly
due to the Moliere and Bhabha scattering of fast parti-
cles from the e+e–-pair by the electrons of the target. The
total cross section for this process is given to an accura-
cy of 1/γ [13,14] as
2
2
0
)( 12
β
πσ
cut
ee
t
r= , (6)
where r0 is the classical radius of electron, m is the
electron mass, ;1/ −= mEt cutcut , 22 1 −−= γβ
mE /1=γ , 1E is the initial particle energy , Ecut is the
minimal detectable energy of δ-electrons. The number
of e+e– pairs which are produced at the point x of the tar-
get with an average charge Z , is
)()( )( Z
A
xNx pair
Apair σρ=Σ . Each particle of the pair
can produce the following number of δ–electrons in the
remaining layer (L-x) of the target::
)()()( ee
A A
ZNxLx σρδ −=Σ . Taking into account that
photons are producing e+e–-pairs inside the target uni-
formly with the probability density F1(x), and averaging
over x, we shall get the expression for the quantity of δ-
electrons produced by each photon in the target of thick-
ness L:
.
3
2
)()()(
)()()(12
LZpair
AANee
A
Z
AN
xpairxxdxF
σρσρ=
ΣδΣ=δΣ ∫
(7)
In the experiments considered, the events of triplet
photoproduction and the events of e+e–-pair photopro-
duction followed by δ-electron knocking-out cannot be
distinguished. Therefore the effective macroscopic cross
section will be equal to the sum of macroscopic cross
sections of these two processes:
( )ϕδ 2cos1)(
eff
t
efftreff PΛ+Σ=Σ+Σ=Σ , (8)
where
( )LDL
A
ZN t
A
t
eff +=Σ 1
2
)()( σρ (9)
and the effective azimuthal asymmetry equals
LD
Lbe
Lb
Lb
eff +
−+Λ=Λ
−
1
1
)(
2
2 (10)
Here the parameter D is:
)(
)(
)( )(
3
2
t
pair
A
ee Z
A
ND
σ
σρσ= . (11)
The parameters b and D entering into expressions
(8)–(11) are strongly dependent on the minimal observ-
able momentum of electron, q0. For the following esti-
mations it is reasonable to set E and Ecut entering, re-
spectively, into (2) and (6), equal to
22
0 mqEE cut +== . In our numerical calculations
we shall use the approximation from [14] for σ(pair)(Z)
and the asymptotic expression from [4, 5] for σ(t). We
assume that the target is a plastic plate (polystyrene,
C8H8, ρ=1.032 g cm-3, X0=42.4 cm, 13/7/ ≈AZ ) of
different thickness.
Fig. 1 shows the effective asymmetry Λeff (Eq. (10))
as a function of target thickness. Curves 1to 3 corre-
spond to different minimal observable moments of the
electron, q0.. The dashed curves 1a to 3a correspond to
the case, where the effect of δ-electron production
(D=0) with the same q0 values as for curves 1 to 3 was
neglected. The difference between solid and dashed
curves shows the importance of taking into account the
δ-electron production effect. It can be seen that the se-
lection of the events with a greater q0 value is appears
more effective for measuring the photon-beam polariza-
tion by the method under consideration.
65
0,0 0,1 0,2 0,3 0,4 0,5
0,00
0,02
0,04
0,06
0,08
0,10
0,12
0,14
0,16
3a
2a
1a 32
1
E
ffe
ct
iv
e
as
ym
m
et
ry
Target thickness, cm
Fig. 1. Effective asymmetry as a function of
polystyrene target thickness. Curve 1 corresponds to
q0=1 MeV/c, 2 – q0=2 MeV/c, 3 – q0=5 MeV/c. The
dashed curves (1a to 3a) correspond to the D=0 case
with the same q0 values as for curves 1 to 3
An important characteristic of the experiment is the
figure of merit, effeffF ΣΛ= 2 . It is well known that rela-
tive error of the measurements is minimal if the figure
of merit is maximal.
Fig. 2 shows the figure of merit as a function of tar-
get thickness for different q0 values. The units used are
the number of recoil electrons and δ-electrons emerging
from the target per initial photon. It is evident that for
the most of experiments [7,8,11], where the scintillation
counters of recoil electrons were tuned to register the
events with q>1 MeV/c, it would be more effective to
use the target with a thickness of about 1 mm.
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
0,0
0,0
0,0
0,0
0,0
0,0
0,1
0,1
0,1
0,1
3
2
1
F
ig
u
re
o
f
M
e
ri
t,
e
ve
n
t/
p
h
o
to
n
*1
0
8
Target thickness, cm
Fig. 2. Figure of merit, 2)(
eff
tr
eff ΛΣ , as function of
polystyrene target thickness. The curve 1 corresponds
to q0=1 MeV/c, 2–q0=2 MeV/c, 3–q0=5 MeV/c
In conclusion, we would like to note that up till now
no sequential analysis of the whole set of effects which
are accompanying the measurements of photon-beam
linear polarization by the method considered has not
been performed. This task demands for numerous calcu-
lations to be done with the help of the GEANT code.
So, the present work should be regarded as information
on only preliminary results of the study.
ACKNOWLEDGMENT
The authors would like to thank W.J. Briscoe,
G. Feldman, and G.V. O’Rielly for helpful discussion of
the test experiment results before publication. One of us,
Yu.P., thanks for hospitality during his visit in George
Washington University.
REFERENCES
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576).
2. V.F. Boldyshev, Yu.P. Peresun’ko. On determina-
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6. V.F. Boldyshev, E.A. Vinokurov, V.I. Voloschuk et
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using the asymmetry of the recoil electrons in photo-
production of triplets // Yad.Fiz. 1992. v. 58, p. 43-
49.
7. I. Endo et al. Detection of recoil electrons in the
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energy photons. Annual Report 1986, Institute for
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8. I. Endo et al. Detection of Recoil Electrons in Triplet
Photoproduction // NIM, 1989, v. A 280, p. 144-146.
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12.Moliere Z. Theorie der Streung schneller geledener
Teilchen I: Einzelstreuung am abgerschmitten
Coulomb-Field // Z. Naturforsch. 1947, Bd. 2a,
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ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2000, №2.
Серия: Ядерно-физические исследования (36), с. 3-6.
64
V.F. Boldyshev, Yu.P. Peresunko , E.A. Vinokurov
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
PACS: 29.27.Hj 29.90. +r.
1. GENERAL CHARACTERISTICS OF THE METHOD
2. THE USE OF THE TRACKING DEVICES
3. THE USE OF HIGH–SPEED COUNTERS
acknowledgment
REFERENCES
|
| id | nasplib_isofts_kiev_ua-123456789-78449 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T13:26:04Z |
| publishDate | 2001 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Boldyshev, V.F. Peresunko, Yu.P. Vinokurov, E.A. 2015-03-17T12:14:11Z 2015-03-17T12:14:11Z 2001 A possibility to measure the linear polarization of photons by using triplet photoproduction / V.F. Boldyshev, Yu.P. Peresunko, E.A. Vinokurov // Вопросы атомной науки и техники. — 2001. — № 1. — С. 63-65. — Бібліогр.: 14 назв. — англ. 1562-6016 PACS: 29.27.Hj 29.90. +r. https://nasplib.isofts.kiev.ua/handle/123456789/78449 A review of currently available high-energy photon polarimeters, which use the effect of asymmetry of recoil electron yield during triplet photoproduction, is presented. The influence of both multiple scattering of electrons and d-electron production in the target medium on the decrease of the experimentally observed asymmetry is considered. The graphs of effective asymmetry and the figure of merit versus target thickness are given. The authors would like to thank W.J. Briscoe, G. Feldman, and G.V. O’Rielly for helpful discussion of the test experiment results before publication. One of us, Yu.P., thanks for hospitality during his visit in George Washington University. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Experimental methods and computations A possibility to measure the linear polarization of photons by using triplet photoproduction Возможности измерения линейной полятизации фотонов при использовании фоторождения триплетов Article published earlier |
| spellingShingle | A possibility to measure the linear polarization of photons by using triplet photoproduction Boldyshev, V.F. Peresunko, Yu.P. Vinokurov, E.A. Experimental methods and computations |
| title | A possibility to measure the linear polarization of photons by using triplet photoproduction |
| title_alt | Возможности измерения линейной полятизации фотонов при использовании фоторождения триплетов |
| title_full | A possibility to measure the linear polarization of photons by using triplet photoproduction |
| title_fullStr | A possibility to measure the linear polarization of photons by using triplet photoproduction |
| title_full_unstemmed | A possibility to measure the linear polarization of photons by using triplet photoproduction |
| title_short | A possibility to measure the linear polarization of photons by using triplet photoproduction |
| title_sort | possibility to measure the linear polarization of photons by using triplet photoproduction |
| topic | Experimental methods and computations |
| topic_facet | Experimental methods and computations |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/78449 |
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