Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator
Comparison is made between the calculated and experimental doses absorbed by complex density-inhomogeneous objects during their radiation processing. The process of fast electron passage through the object and depth dose formation has been simulated by the Monte Carlo technique with the use of the...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2009
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| Series: | Вопросы атомной науки и техники |
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| Cite this: | Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator / O.A. Demeshko, S.S. Kochetov, L.A. Mahnenko, I.V. Melnitsky, O.A. Shopen // Вопросы атомной науки и техники. — 2009. — № 5. — С. 85-89. — Бібліогр.: 1 назв. — англ. |
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irk-123456789-965122016-03-18T03:02:40Z Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator Demeshko, O.A. Kochetov, S.S. Mahnenko, L.A. Melnitsky, I.V. Shopen, O.A. Ядернo-физические методы и обработка данных Comparison is made between the calculated and experimental doses absorbed by complex density-inhomogeneous objects during their radiation processing. The process of fast electron passage through the object and depth dose formation has been simulated by the Monte Carlo technique with the use of the licensed program package PENELOPE. The calculated and experimental data are found to be in good agreement (≈30 %). Preliminary simulation of the process of object irradiation at given conditions provides the necessary information when developing the methods for a particular group of objects. This is of particular importance at performing bilateral irradiation, when an insignificant density variance of different objects may lead to appreciable errors of dose determination in the symmetry plane of the object В статтi наводяться результати обчисленого та експериментального визначення поглинутої дози при радiацiйнiй обробцi складних неоднорiдних за щiльнiстю об’єктiв. Моделювання процесу проходження швидких електронiв крiзь об’єкт та формування глибинної дози виконано за методом Монте-Карло з використанням пакету лiцензiйних програм PENELOPE. Обчисленi та експериментальнi данi добре спiвпадають мiж собою (≈ 30 %). Виконання попереднього моделювання процесу опромiнювання об’єктiв у заданих умовах дає необхiдну iнформацiю при розробцi методики для певної групи об’єктiв. Це особливо важливо при проведеннi двухстороннього опромiнювання, коли незначнi вiдхилення щiльностi рiзних об’єктiв можуть призводити до помiтних помилок визначення дози в площiнi їх симетрiї. В статье приводятся результаты расчетного и экспериментального определения поглощенной дозы при радиационной обработке сложных неоднородных по плотности объектов. Моделирование процесса прохождения быстрых электронов через объект и формирования глубинной дозы выполнено методом Монте-Карло с использованием пакета лицензионных программ PENELOPE. Расчетные данные находятся в хорошем согласии с экспериментальными (≈ 30 %). Выполнение предварительного моделирования процесса облучения объектов в заданных условиях дает необходимую информацию при разработке методики для конкретной группы объектов. Это особенно важно при проведении двухстороннего облучения, когда незначительные отклонения плотности разных объектов могут приводить к заметным ошибкам определения дозы в плоскости их симметрии. 2009 Article Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator / O.A. Demeshko, S.S. Kochetov, L.A. Mahnenko, I.V. Melnitsky, O.A. Shopen // Вопросы атомной науки и техники. — 2009. — № 5. — С. 85-89. — Бібліогр.: 1 назв. — англ. 1562-6016 PACS: 87.80.+s, 87.90.+y http://dspace.nbuv.gov.ua/handle/123456789/96512 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Ядернo-физические методы и обработка данных Ядернo-физические методы и обработка данных |
| spellingShingle |
Ядернo-физические методы и обработка данных Ядернo-физические методы и обработка данных Demeshko, O.A. Kochetov, S.S. Mahnenko, L.A. Melnitsky, I.V. Shopen, O.A. Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator Вопросы атомной науки и техники |
| description |
Comparison is made between the calculated and experimental doses absorbed by complex density-inhomogeneous
objects during their radiation processing. The process of fast electron passage through the object and depth dose
formation has been simulated by the Monte Carlo technique with the use of the licensed program package PENELOPE.
The calculated and experimental data are found to be in good agreement (≈30 %). Preliminary simulation of the
process of object irradiation at given conditions provides the necessary information when developing the methods for a
particular group of objects. This is of particular importance at performing bilateral irradiation, when an insignificant
density variance of different objects may lead to appreciable errors of dose determination in the symmetry plane of
the object |
| format |
Article |
| author |
Demeshko, O.A. Kochetov, S.S. Mahnenko, L.A. Melnitsky, I.V. Shopen, O.A. |
| author_facet |
Demeshko, O.A. Kochetov, S.S. Mahnenko, L.A. Melnitsky, I.V. Shopen, O.A. |
| author_sort |
Demeshko, O.A. |
| title |
Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator |
| title_short |
Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator |
| title_full |
Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator |
| title_fullStr |
Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator |
| title_full_unstemmed |
Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator |
| title_sort |
radiation processing of inhomogeneous objects at the 300 mev electron linear accelerator |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2009 |
| topic_facet |
Ядернo-физические методы и обработка данных |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/96512 |
| citation_txt |
Radiation processing of inhomogeneous objects at the 300 MeV electron linear accelerator / O.A. Demeshko, S.S. Kochetov, L.A. Mahnenko, I.V. Melnitsky, O.A. Shopen // Вопросы атомной науки и техники. — 2009. — № 5. — С. 85-89. — Бібліогр.: 1 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
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| first_indexed |
2025-07-07T03:43:55Z |
| last_indexed |
2025-07-07T03:43:55Z |
| _version_ |
1836958180026875904 |
| fulltext |
RADIATION PROCESSING OF INHOMOGENEOUS
OBJECTS AT THE 300 MeV ELECTRON LINEAR
ACCELERATOR
O.A. Demeshko, S.S. Kochetov ∗, L.A. Mahnenko, I.V. Melnitsky,
O.A. Shopen
National Science Center ”Kharkov Institute of Physics and Technology”, 61108, Kharkov, Ukraine
(Received July 26, 2007)
Comparison is made between the calculated and experimental doses absorbed by complex density-inhomogeneous
objects during their radiation processing. The process of fast electron passage through the object and depth dose
formation has been simulated by the Monte Carlo technique with the use of the licensed program package PENELOPE.
The calculated and experimental data are found to be in good agreement (≈30 %). Preliminary simulation of the
process of object irradiation at given conditions provides the necessary information when developing the methods for a
particular group of objects. This is of particular importance at performing bilateral irradiation, when an insignificant
density variance of different objects may lead to appreciable errors of dose determination in the symmetry plane of
the object.
PACS: 87.80.+s, 87.90.+y
1. INTRODUCTION
The expediency of using this or that irradiation
technique is determined with consideration for opti-
mum combination of productivity and quality of the
given process, which is characterized by the ability to
form the radiation field that provides the necessary
uniformity of absorbed energy distribution through-
out the irradiated object.
The absorbed dose built up on the object surface
(in the superfine layer of the material) is determined
by the incident electron flux density. In our case, the
sweeping magnets are absent, and the output beam
has the Gaussian distribution of flux density in the
cross section. Therefore, the highest flux density on
the object is found on the optical axis of the beam,
and its root mean square (r.m.s.) radius is dependent
on the initial electron energy, on the material and
thickness of the foil of the exit window of the chan-
nel, and also on the distance to the object. These
initial parameters are chosen in each particular case,
depending on the vertical dimensions of the object
and the permissible dose variations at the edges (e.g.,
no more than ≈ 30%).
2. SHORT DESCRIPTION OF THE
FACILITY PARTS AND THEIR
FUNCTIONS
The sterilization facility consists of three main parts:
− accelerated electron source with a horizontal
beam layout;
− extraction, beam-shaping and beam property
diagnostic channel;
− conveyor for object transfer to the irradiation
area (see. Fig.1).
1
2
3
4
5
6
7
8
9
LINAC
CONVEYOR
THE CHANNEL OF AN
EXTRACTION OF PARTICLES
Fig.1. The lay-out diagram of inventory of the
sterilization stand (plan view)
The accelerated electron accelerator presents a pulsed
two-section travelling-wave linear accelerator with
adjustable parameters of the beam (mean electron
energy 5...25 MeV , half-width ∼ 10%, average beam
current 1...100µA). It is a complicated setup that in-
corporates a unique pulse and high-frequency equip-
ment of total power ∼ 90 kw.
The extraction channel includes a dc magnet (1)
that deflects the electron beam through 35◦ in the
horizontal plane relative to the accelerator axis. In
∗Corresponding author. E-mail address: kochetoff@mail.ru
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, 2009, N5.
Series: Nuclear Physics Investigations (52), p.85-89.
85
the focus of the magnet there is a particle monochro-
mator (4) intended to analyze beam energy charac-
teristics.
At the channel output, a Faraday cup (6) with a
remotely introduced absorber is installed to measure
the total beam current. The quadrupole-lens doublet
(2) provides beam shaping of r.m.s. radius 0.5 cm
at the channel output. A two-pole electromagnetic
corrector of horizontal/vertical deflection (3) serves
for beam displacement within small limits (approxi-
mately 1.5 cm) relative to the optical axis of the ex-
traction channel in the conveyor plane. The shape,
lateral dimensions and position of the beam during
pretuning of the accelerator in the specified operat-
ing conditions are controlled with the help of the tele-
vision facility (8) through the use of the fluorescent
screen (7). The refinement of both the beam position
and the vertical current density distribution directly
on the object at the final adjustment of the operating
conditions and further on in the process of the whole
irradiation run of the accelerator is realized with the
help of the ionization detector (9). In this case, the
beam current is continuously controlled by means of
an induction transit-time pickup (5), a charge inte-
grator and a digital voltmeter pre-calibrated against
the full-absorption Faraday cup (6).
The conveyor presents a horizontal shelf, 25 cm in
width and 8.25 m in length. It is assembled from thin
plates and duralumin L-shaped elements and is check
clamped to four separate carriages movable on rolls
along a straight monorail. The asynchronous motor
connected with the carriages via a double-reduction
worm-gear unit, pinion and chain drives, a lead drum
and a haulage line serves as a driving actuator. Irre-
spective of charging by weight, the conveyor is mov-
ing at a constant velocity of 5.1 cm/s.
The conveyor performs the number of total cycles
or half-cycles (odd number of passes) assigned by the
operator through the use of the controlling system in
the autoreverse mode at the beginning and the end of
one-direction pass, which makes 9.1 m at most. De-
pending on the conveyor occupancy with objects, the
pass length can be regulated. After the assigned pro-
gram is completed, the beam is switched off and the
conveyor stops.
The facility is provided with safety locks for the
cases of unforeseen beam switching-off (the conveyor
is then stopped) or conveyor stop (in this case the
beam is switched off). In case of these unforeseen
stoppages, the data are recorded on the number of
passes made, the current condition of the conveyor
and the direction of its motion at the moment of stop-
page. This permits the conveyor restart after trou-
bleshooting with keeping the control over the process
of necessary dose buildup by the objects under irra-
diation.
3. CHARACTERIZATION OF OBJECTS
UNDER IRRADIATION
The surgical suture materials (polished catgut,
silk suture) are the principal items for treatment. The
Customer supplies them for irradiation in the form
of ampoules or packets. Separate items are placed in
cardboard panels, i.e., boxes, which are then linked in
paired units - irradiation objects. The object is char-
acterized by a molecular composition of component
mixture, overall dimensions, the average density and
density distribution uniformity in the volume. The
catgut blocks in ampoules, the lower part of which
(without a cardboard box) has an average density of
∼ 1.07 g/cm3 (air, glass, solution, catgut) and the
upper part has a density of ∼ 0.43 g/cm3 (air, glass),
present more complex objects for irradiation. The
irradiation technique under development must take
into account these circumstances.
4. DETERMINATION OF AVERAGE
DENSITY AND MASS BRAKING POWER
OF THE OBJECT
The mass braking power of the object, which in-
volves energy losses dE as a result of collisions and
radiation on the path dl (ionization and radiation
losses) is the quantitative characteristic of the in-
teraction between the accelerated electrons and the
substance of density ρ that is responsible for the ab-
sorbed dose. In the case, where the nuclear reactions
can be neglected, the total mass braking power of the
substance is represented by two components:
εtot =
1
ρ
· (dE
dl
)tot =
1
ρ
· (dE
dl
)col +
1
ρ
· (dE
dl
)rad . (1)
There are corresponding detailed tables [1] for
the data. However, as mentioned above, the
task difficulty in our case lies in the fact
that we are dealing with a complex multi-
component composition of the object under irra-
diation (air, glass, spirit aqueous solution, catgut).
2
1
r
A BD
O
C
E
F
G H
h
Fig.2. Element of volume
86
Therefore, when estimating the absorbed dose at
the given point of the object we must use certain
averaged values of energy losses and density.
For averaging of εav we single out the element of
volume in the form of a cube with a side 2r (r is the
outer radius of the ampoule, see Fig.2). Then, it can
be written down the following:
Vi = Si · 2r-partial volume of the i-th component
of the object (where Si- is the cross section);
mi = Vi · ρi-partial mass of the i-th component;
M =
∑
Vi · ρi-the total mass of volume element
(over all 4 components);
ρav = M
(2r)3 = 1
2r
∑
∆li · ρi-average volume of the
object (were ∆li = S
i
2r -is the reduced layer thickness
of the i-th component in the volume element)
∆Ei = εi ·ρi ·∆li-electron energy losses in the i-th
layer;
The average mass braking power of the object
takes on the form:
εav =
1
ρav
· 1
2r
·
∑
εi · ρi ·∆li . (2)
The procedure of determining Si and ∆li can be
understood from the geometrical constructions pre-
sented in Fig.2, which shows the cross section of the
volume element (one of possible variants). The cal-
culated εav values enable one to calculate the surface
dose distribution on the objects by the following for-
mula:
D ≈ n · I0 · ε√
2π · e · σ · νn
· exp(− y2
2σ2
) , (3)
were I0-is the average beam current; e-is the electron
charge; σ-is the r.m.s. beam radius; νn = ν · cos α-is
the velocity of the cross motion of the object relative
to the beam; n-is the number of conveyor passes; ν-is
the linear velocity of conveyor motion; α-is the angle
between the beam axis and the normal to the plane
of object motion; y-is the vertical coordinate of the
reference point of the object.
5. OBJECT SURFACE/DEPTH
DISTRIBUTIONS OF THE DOSE
Figure 3,a shows the vertical surface-dose dis-
tribution at irradiation of density-uniform object,
namely, packeted catgut, 10 cm in height. The r.m.s
beam radius on the near plane of the object is ∼ 6 cm,
the irradiation is bilateral.
A more complicated task relates to the determi-
nation of depth dose of the object, particularly if the
medium is inhomogeneous. The depth dependence
of the absorbed dose is determined by the elemental
composition and the average density of the irradiated
object, and also by the initial electron energy.
Figure 4,a shows the calculated absorbed dose
as a function of depth at energies of 2, 5, 10,
15 and 20 MeV in the elementary case for parallel
and uniform-in-the-cross section electron flux inci-
dent perpendicularly (α = 0) on the semi-infinite
medium of density 1.07 g/cm3, which was chosen to
be equal to the effective density of the lower part of
the object (catgut in ampoules).
a)
sm
10
D
o
s
e
,
M
ra
d
10
sm
D
o
s
e
,
M
ra
d
b)
a b
c)
sm
a b
δ
10
3.5
D
o
s
e
,
M
ra
d
Fig.3. Height dose distribution at bilateral
irradiation of objects: a) density-uniform, b)
nonuniform, c) nonuniform with beam
displacement by the optimum value relative to
the middle of the object
The process of fast-electron passage through the ob-
ject and the depth dose formation were simulated by
87
the Monte Carlo technique with the use of the li-
censed program package PENELOPE.
PENELOPE provides simulation of arbitrary
electron-photon showers in complex material struc-
tures (mixtures). In the process, consideration is
given to the following types of interaction: elastic
and inelastic scattering of electrons and positrons,
bremsstrahlung by electrons and positrons, positron
annihilation, coherent scattering, Compton scatter-
ing of photons, electron-positron pair production.
It can be seen from Fig.4,a that the dose increase
in the depth medium due to the production of sec-
ondary particles is dependent on energy, the dose be-
coming lower with energy increase.
a)
2
5
10
15
20 MeV
T
h
e
a
b
s
o
rb
e
d
d
o
s
e
,
M
ra
d
Depth of medium, sm
1
2
3
4
Depth of object, sm
T
h
e
a
b
s
o
rb
e
d
d
o
s
e
,
M
ra
d
b)
Fig.4. Depth dose distribution
To irradiate objects, we have chosen the
(15...16)MeV energy range, where the dose differ-
ence within the object is about ∼ 30%, and the
extrapolated path of electrons in the medium (R)
varies between 7.3 and 7.8 cm.
To equalize the dose in the depth of the object and
to improve the efficiency of the irradiation process,
the known bilateral irradiation method is used.
Figure 4b shows the plots of calculated depth
dose formation in this case for electron energy of
16 MeV and the above-specified initial conditions
(i.e., parallel uniform flux). Calculation was carried
out for 6 passes of the standing on the conveyor ob-
ject, at a current of a beam of electrons I = 73 µA.
The optimum thickness of the object, at which dose
balance is provided both on its surface and inside, is
∆ ≈ 13.5 cm. Curves 1 illustrate the data about ob-
ject irradiation on each side, curve 2 shows the total
characteristic.
All other conditions being equal, the dose accu-
mulated in the unit layer of the object is determined
by the mass braking power of the object substance
and by the density of electron flux passing through
it. In our case, the braking powers of materials differ
insignificantly. Thus, the decisive role in dose for-
mation belongs to the electron flux passing through
the unit layer of the object. At bilateral irradiation
conditions, the denser part of the object is irradiated
once, while the part of lesser density is irradiated
twice in view of its transparence. Hence, at bilateral
irradiation the accumulated dose in the part of lesser
density of the object is higher than that observed in
the denser part.
It is obvious that in the plane of symmetry of the
object (this may be the boundary line in the 2-box
block) there may be both the lack of dose in relation
to the dose accumulated in the thin surface layer Ds,
and the excess dose if the real thickness and average
density deviate from the optimum values at the set
electron energy value.
The same figure also shows the data on the dose
field formation in the upper part of the object that
has the effective density ∼ 0.43 g/cm3 (curves 3 show
the bilateral irradiation data, curve 4 represents the
total dose). It can be seen that owing to a relative
transparence of the block in this section to acceler-
ated electrons, the absorbed dose substantially ex-
ceeds the dose value in the lower, practically non-
transparent part that has a higher density (in the fig-
ure, the dose curves show only an insignificant step
(∼ 2 %) due to the occurrence of braking gamma-
radiation.
Taking into account the facts that the electron
flux is divergent, and the current density distribution
on the object is nonuniform in the cross section, then,
by displacing the optical axis of the beam by a cer-
tain δ value vertically downward with respect to the
middle of the block, it appears possible to attain the
dose equality at the points close to the upper (a) and
lower (b) boundaries of the block. (see Figs.3,b,c).
This procedure also leads to some increase in the ir-
radiation efficiency and to the decrease in dose strag-
gling directly in the thread field. In this case, the
necessary displacement value is determined through
88
calculations and is adjusted experimentally for each
type of objects (δ = 1.5...2.5 cm).
Since the beam is incident on the object at an
angle α = 55◦, the geometric thickness of the block
must be smaller than the above-mentioned ∆ value
by a factor of 1/ cosα ≈ 1.74. So, at an ampoule
outer diameter of 1.1 cm, the actual optimum block
thickness will be equivalent to approximately 8 lay-
ers of closely packed ampoules, i.e., each box must
contain 4 layers.
From the above reasoning it is recommended that
in the manufacture of the ampoule catgut special care
should be taken to control that the spirit solution
fully covers the catgut thread in the vertical position
of the ampoule. Otherwise, during bilateral irradi-
ation, the part of thread bundle projecting over the
solution will receive an excessive dosage by virtue of
a considerably lower effective density of the object in
this section.
6. CONCLUSION
The computations of the surface absorbed dose by
formula (3) and depth dose distribution with the use
of the simulation programs PENELOPE are in good
agreement between themselves and with the measure-
ment results, the divergence being no more than 30%.
(The absorbed dose was measured by the known tech-
nique through the use of Type SO PD(F)-5/150 film
dosimeters and Type SF-46 spectrophotometer).
The preliminary simulation of the process of ob-
ject irradiation at given conditions provides the infor-
mation required when developing the technique for a
specific group of objects. This is of prime importance
in the performance of bilateral irradiation, when an
insignificant variation in the density of different sam-
ples may lead to appreciable errors in dose determina-
tion in the symmetry plane of the object (see Fig.4,b).
References
1. Report of the 35-th International Commissions
on Radiation Units and Measurements ”Radia-
tion dosimetry: electron beams of energies rang-
ing from 1 to 50 MeV (Russian translation).
Moscow: ”Energoatomizdat”. 1988, p.16-22, 28-
34.
ОСОБЕННОСТИ РАДИАЦИОННОЙ ОБРАБОТКИ НЕОДНОРОДНЫХ ОБЪЕКТОВ
НА 300-МэВ - ЛИНЕЙНОМ УСКОРИТЕЛЕ ЭЛЕКТРОНОВ
О.А. Демешко, С.С. Кочетов, Л.А. Махненко, И.В. Мельницкий, О.А. Шопен
В статье приводятся результаты расчетного и экспериментального определения поглощенной дозы
при радиационной обработке сложных неоднородных по плотности объектов. Моделирование процесса
прохождения быстрых электронов через объект и формирования глубинной дозы выполнено мето-
дом Монте-Карло с использованием пакета лицензионных программ PENELOPE. Расчетные данные
находятся в хорошем согласии с экспериментальными (≈ 30%). Выполнение предварительного мо-
делирования процесса облучения объектов в заданных условиях дает необходимую информацию при
разработке методики для конкретной группы объектов. Это особенно важно при проведении двухсто-
роннего облучения, когда незначительные отклонения плотности разных объектов могут приводить к
заметным ошибкам определения дозы в плоскости их симметрии.
ОСОБЛИВОСТI РАДIАЦIЙНОЇ ОБРОБКИ НЕОДНОРIДНИХ ОБ’ЄКТIВ НА
300-МеВ - ЛIНIЙНОМУ ПРИСКОРЮВАЧI ЕЛЕКТРОНIВ
О.А. Демешко, С.С. Кочетов, Л.О. Махненко, I.В. Мельницький, О.О. Шопен
В статтi наводяться результати обчисленого та експериментального визначення поглинутої дози при
радiацiйнiй обробцi складних неоднорiдних за щiльнiстю об’єктiв. Моделювання процесу проходження
швидких електронiв крiзь об’єкт та формування глибинної дози виконано за методом Монте-Карло
з використанням пакету лiцензiйних програм PENELOPE. Обчисленi та експериментальнi данi добре
спiвпадають мiж собою (≈ 30%). Виконання попереднього моделювання процесу опромiнювання об’єк-
тiв у заданих умовах дає необхiдну iнформацiю при розробцi методики для певної групи об’єктiв. Це
особливо важливо при проведеннi двухстороннього опромiнювання, коли незначнi вiдхилення щiльно-
стi рiзних об’єктiв можуть призводити до помiтних помилок визначення дози в площiнi їх симетрiї.
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