Manuscript number RINP_2019_566 Title Complementary dosimetry for relativistic electron beams Articletype FullLength Article Abstract… [618413]

Manuscript Details
Manuscript number RINP_2019_566
Title Complementary dosimetry for relativistic electron beams
Articletype FullLength Article
Abstract
Severaldosimetry methods are employed for a 6 MeV pulsed electron beam at 53 Hz frequency. A comparative study
ofthese systems is presented showing the advantages of each method. Calorimetry is performed using a graphite
calorimeter made in our laboratory. Electron beam fluence per pulse determined using a Faraday cup ranged from
10^9to10^15 e-/cm2 and it. Radiochromic films (RCF), scintillating screens (LANEX) and imaging plates (IP) methods
showedsimilar results. The dark spots on RCF were processed using Image J while for IP dedicated scanner and
software were necessary
Keywords Electron beam; dosimetry; calorimetry;radiochromic films; LANEX; Imaging
Plates.
Corresponding Author ticosdorina
Corresponding Author's
Institutioninflpr
Orderof Authors ticosdorina, Adrian Scurtu, Mihai Oane, Constantin Diplasu, Georgiana
Giubega, Ion Cosmin Calina, Catalin Ticos
Suggested reviewers ancascarisoreanu, Feras M. O. Al-dweri, Noramaliza Mohd Noor, liviu neagu
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1Dear Results in Physics Editor,
Please find attached the manuscript titled “Complementary dosimetry for relativistic
electron beams” by D. Ticoș, A. Scurtu, M. Oane, C. Diplasu, G. Giubega, I. Calina and C.M.
Ticoș, submitted for publication in Results in Physics. The manuscript contains the file
“Complementary dosimetry_Ticos_2019” which has 7 figures included in the text: Fig. 1, Fig. 2,
etc., and 15 references. The corresponding author is the first author of the paper.
We report on complementary dosimetry employed for a 6 MeV pulsed electron beam. We
used a graphite calorimeter made in our laboratory, radiochromic films EBT-3 and HD-V2,
LANEX fast screen, imaging plate. For fluence determinations we used a Faraday cup. We varied
exposure times from 1 to 10 ms and used a Pb brick and to lower the electron flux. We showed
that for short irradiation time or pulse by pulse irradiation film based dosimetry is more
appropriate. Also, Faraday cup can be very easily adapted to short electron beam pulse encountered
in hyper intense lasers interactions. To the best of our knowledge such a comparison hasn’t been
made before.
The electron beam was pulsed at a frequency of 53 Hz with a pulse length of 4
microseconds. We evaluate the average dose through calorimetry. We integrated the beam fluence
per pulse and also over higher exposure times up to 10 minutes. Electron beam fluence ranged
from 109 to 1015 e-/cm2 depending on the filament voltage of the accelerator. For the film based
dosimetry we used a set-up consisting of a screening Pb brick, a magnetic spectrometer and the
RCF/Lanex/imaging plates. The image acquisition for LANEX was made using a CCD PointGrey
camera with an objective with focal distance of 50 mm. The signal obtained on the exposed
LANEX is shown for different values of electron beam fluence. We show the RCF for different
exposure times and a blackening distribution along one of the spots obtained. We show the spots
on the Imaging Plates obtained using DURR NDT HD-IP PLUS scanner. The blackening
distribution for one of the spots on the imaging plates is in good agreement with the distribution
on RCF..
This is a new submission, which has not been previously discussed with any Results in Physics
Editorial Board member.
Sincerely,
Dr. Dorina. Ticoș
National Institute for Laser, Plasma and Radiation Physics
409 Atomistilor Str., PO Box MG 36,
Postcode 077125
Magurele-Bucharest,

2Romania
Tel/Fax: +40 021-457 4550
Email: toaderdorina@yahoo.com
Email #2: dorina.toader@inflpr.ro

Complementary dosimetry for relativistic electron beams
D. Ticos, A. Scurtu, M. Oane, C. Diplasu, G. Giubega, I. Calina, C.M. Ticos
National Institute for Lasers, plasma and radiation, P.O.Box MG-36, RO-077125 Bucharest-Magurele, Romania,
E-mail: dorina.toader@inflpr.ro
A B S T R A C T
Several dosimetry methods are employed for a 6 MeV pulsed electron beam at 53 Hz frequency. A comparative study
of these systems is presented showing the advantages of each method. Calorimetry is performed using a graphite
calorimeter made in our laboratory. Electron beam fluence determined using a Faraday cup ranged from 109 to 1015 e-
/cm2 and it. Radiochromic films (RCF), scintillating screens (LANEX) and imaging plates (IP) methods showed
similar results. The dark spots on RCF were processed using Image J while for IP dedicated scanner and software
were necessary.
Keywords: Electron beam, dosimetry, calorimetry, RCF, LANEX, Imaging plates, high power laser acceleration
1. INTRODUCTION
The effect produced in an irradiated material is given by the absorbed dose. Dosimetry is a technique used to
control the irradiation process. Several important aspects have to be taken into account in order to choose the adequate
dosimetry system, such as: its detection limit (minimum, maximum, dose rate), the radiation dose range, dosimeter
dependence on energy, temperature effect during the irradiation process, response stability, spatial scale, resolution,
price, etc. Dosimetry is important for any irradiation facility but also for a routine control of the irradiation technology.
Typical dosimetry systems for electron beam irradiation are graphite calorimeters [1], radio-chromic films (RCF)
[2,3,4], cellulose triacetate films [5], polyvinyl chloride [6], plane parallel chambers [7], single mode optical fibre
[8,9], alanine and chemical solutions such as dichromate, Fricke, ceric-cereous, ferrous sulphate – copper sulphate
[10]. New dosimetry methods [11] were developed for laser-plasma accelerated electron beams that have particular
characteristics like very short pulse duration (picoseconds to tens of femtoseconds), various energy distributions, low
particle fluxes. Therefore their detection is very challenging. Also, in the interaction chambers of the facilities with
ultra-intense laser systems the space is often quite limited. In the followings, several dosimetry systems, i.e.
calorimetry, Faraday cup [12], RCF, imaging plates (IP) and LANEX fast screen scintillation detectors, will be
comparatively described. The methods based on film detectors (RCF, IP and LANEX) were tested in combination
with a magnetic spectrometer, in order to meet the requirements specific to high power laser accelerated electron
beams. All determinations were made at the ALID-7 facility that is a travelling wave linear electron accelerator. The
electron beam energy was 6 MeV while the beam pulse duration was 4 µs at a frequency of 53 Hz.
2. RESULTS AND DISCUSSIONS
2.1 Graphite Calorimeters Dosimetry
Calorimetry is based on the determination of the energy deposited by the electron beam in the irradiated sample
as heat through inelastic interaction with the detection material. Calorimeters are typically made of a low-Z material
(graphite, polystyrene or water), a temperature sensor (thermistor), and a heat insulator disposed around the material
absorber. The graphite calorimeters used for these measurements were made in our laboratory [1]. They have a
sensitivity of ≈ 0.75 kGy /°C. The minimum and maximum doses that can be measured are 0.5 kGy and 30 kGy,
respectively with an absorbed dose rate <10 Gy/s. The electrolytic graphite disk used for the calorimeter is 130 mm
in diameter, 18 mm thick and has a mass m = 0.423 kg. The calorimeter is inserted into an insulating polystyrene box
with the sizes 300 x 300 x 100 mm that weighs 0.179 kg and it is shown in Fig. 1.

Fig. 1 – Graphite calorimeter used at the Electron Accelerator ALID-7
The absorbed dose is given by the relation (Gy) where E (J) is the energy absorbed in the calorimeter 𝐷=𝐸/𝑚
and m is the calorimeter mass. Assuming that all the absorbed energy E is converted into heat, the temperature increase
is ΔT [K] = E /mC p where C p [J/kg K] is the heat capacity of the graphite. Thus, the absorbed dose can be calculated
as D = C p · ΔT. Table 1 shows the average and nominal absorbed dose obtained for different exposure times while
keeping the beam parameters constant.
Table 1: Absorbed dose measured with the graphite calorimeter in the range 1-30 kGy
Doses obtained with the calorimeter (kGy) Average dose (kGy) Exposure time (s)
0.97 1.00 1.02 0.99 18
5.20 5.05 4.98 5.07 86
10.10 10.00 10.10 10.06 140
15.20 15.20 14.90 15.10 309
20.50 20.40 20.00 20.30 359
25.30 25.8 24.90 25.33 410
2.2 Faraday Cup
The Faraday cup can be used to determine electron beam fluence and flux which is an important parameter for
the irradiation process. We used a RadiaBeam Faraday Cup, shown in Fig. 2a), that can measure electron fluxes in the
energy range 1 to 120 MeV. The Faraday cup produces an electrical pulse that is directly proportional to the electrical
charge of the beam pulse and can be visualized on the oscilloscope screen in real time. An example of a pulse is given
in Fig. 2b). The Faraday cup signal is in units of Volts. For signal conversion we use the Faraday cup impedance of
50 Ohm and we integrate the area under the curve.

Fig.2 – a) Faraday cup for fluence measurements; b) Single electron beam pulse.
Electron beam fluence and flux measurements are given in tables 2 and 3 for various values of the filament
voltage that generates the free electrons in the accelerator. Results in Table 2 were determined at the exit window of
the electron accelerator. For the determinations given in Table 3 we used a Pb brick with cross-section 50 X 50 mm
and length 100 mm. The brick had a cylindrical cut of 5 mm diameter and 100 mm length through its center. The
electron beam flux was measured after passing through hole of the Pb brick.
Table 2: Electron beam fluence and flux at the exit window of the ALID 7 accelerator
Filament
voltage (kV)Electron beam fluence /pulse
(el/cm2)Electron beam flux /pulse
(el/cm2 ·s)Exposure time (min) /
Fluence (el/cm2)
12 9.5 ×10102.4 ×101610 3.0 ×1015
11 6.6 ×10101.7 ×101610 2.1 ×1015
10 4.5 ×10101.1 ×101610 1.4 ×1015
9 1 ×10102.5 ×101510 3.2 ×1014
8 2.6 ×1096.5 ×101410 8.3 ×1013
Table 3: Electron beam fluence and flux after passing through a 5 mm hole in a Pb brick at the ALID 7 electron accelerator
Filament
voltage (kV)Electron beam fluence /pulse
(el/cm2)Electron beam flux /pulse
(el/cm2 ·s)Exposure time (min) /
Fluence (el/cm2)
12 2.1 ×1095.3 ×10141 1.1 ×1011
11 9.1 ×1082.3 ×10141 4.8 ×1010
10 3.8 ×1089.5 ×10131 2.0 ×1010
9 1 ×1082.5 ×10131 5.3 ×109

2.3 RCF film
Radiochromic films (RCF) are solid state detectors which undergo a structural change when exposed to
radiation [2,6,13]. Radiochromic dosimeters do not require chemical processing. Image formation occurs as a dye-
forming or a polymerization process, in which the radiation initiates color formation through chemical changes [14].
Fig. 3 shows the sketch and a picture of the experimental set-up which uses RCF film as dosimeter implemented at
ALID-7 accelerator. Below the exit window of the accelerator the electron detection system. It consists of a screening
Pb brick, a magnetic spectrometer and the RCF film.
Fig. 3 – (a) Sketch of the experimental set-up; (b) Picture of the experimental set-up which uses RCF film as electron
detector, implemented at ALID-7.
At the exit of the Pb brick the electron beam is passed through a magnetic spectrometer shown in Fig. 4a.
This is made up of Nd permanent magnets positioned in front of each other forming a 10 cm long and 0.5 cm wide
channel. A transverse magnetic field is produced inside the channel. The electron beam is deflected by the magnetic
field with a relatively constant value of 0.6 T. The electron beam is deflected towards the RCF. The Pb brick filters
the X-ray flux and allows the RCF to darken only under the influence of electrons. The deviated electron beam creates
a dark spot on the RCF at a certain distance from the spectrometer entrance which is proportional to the electron beam
energy. For 6 MeV electrons the black trace on RCF is positioned at a distance of ≈ 23 mm from the entrance slit of
the spectrometer as shown in Fig. 5.
a)
b)
c)
Fig. 4 – a) Magnetic spectrometer, b) RCF (HD-V2) film impressed at different exposure times (1s to 4s – left to right), c) EBT-
3 type of RCF film overexposed (at 1 and 5 s).

Fig. 5. – Dark spots created by the 6 MeV deviated electrons on HDV-2 RCF film. Image J plot of the blackening distribution
along one of the spot.
Fig. 4 b) shows the effect of electron beam exposure on RCF HD-V2 type for different values of fluence.
The exposure time is 1, 2, 3 and 4s from left to right. The exposure time of 1 s corresponds to a fluence of 1.1×1011
el/cm2 while 4s corresponds to el/cm2. The relation between the dose and the fluence is D=Φδ where 4.4×1011
δ=(1/ρ)(dE/dx) is the mass stopping power. Fig. 4c) shows the electron beam trace on a EBT-3 type of RCF film
obtained after 1 and 5 s of exposure. Being more sensitive to radiation the EBT-3 film looks as overexposed. Is is
clear from these images that the optical density (blackening) of the RCF film is directly proportional to the radiation
dose. For similar doses, the EBT-3 film shows a more pronounced darkening than the HD-V2 films as illustrated in
Fig. 4 for an exposure of 1 s. After radiation exposure, the RCFs are scanned and the obtained digital image shown in
Fig. 5 are analysed with different image processing tools. A plot of the optical density distribution along one of the
spots, marked with yellow line is also given in Fig. 5.
2.4 LANEX screen
Real-time dosimetry can be made using scintillating screens, containing luminescent materials which absorb
its energy and scintillate when irradiated with ionizing radiation. LANEX is a type of “fast screen” having a small
response time to electrons. The LANEX is placed on the magnetic spectrometer as shown in Fig. 6a) and emits a
luminous flux due to the interaction with the electron beam as shown in Fig. 6b)-f). The intensity of the luminous
signal of the LANEX depends on the electron beam fluence. The accelerator filament voltage has been set at 8, 9, 10,
11 and 12 V in Fig. 6b) to Fig. 6f), respectively.
a)
b)
c)
d)
e)
f)
Fig. 6 – a) LANEX covering the magnetic spectrometer b) LANEX exposed to electron beam passed through the magnetic
spectrometer at a filament voltage of 8V c) 9V, d) 10 V, e) 11V, f) 12 V.
The image acquisition was made using a CCD PointGrey FL3-U3-13E4C camera with an Edmund Optics
objective with a focal distance of 50 mm at a frame rate of 60 frames/second. The exposure time of the camera is 16.6
ms which is shorter than the duration between pulses (18.8 ms). The electron beam pulse duration is 4 µs. This way
the luminescence variation with the electron beam fluence can be observed. Fig. 6(f) shows the saturation of the

LANEX film obtained at a filament voltage of 12 V. The illuminated trace is larger than the trace on saturated RCF.
Therefore LANEX film are most suitable for low electron beam fluence with short pulse durations such as the beams
produced by hyper intense lasers interaction with gas or solid targets [11].
2.5 Imaging Plates
Imaging Plates (IP) are also film-like radiation detectors, based on the luminescence of special phosphors
[15]. We used IP DURR NDT HD-IP PLUS in a set-up similar with the one used for RCF films. We irradiated the IP
at two exposure times, of 1 s and 2 s. After irradiation, the IP was scanned with a dedicated scanner DURR NDT HD-
CR 35 NDT. The image obtained is presented in Fig. 7a), where two black spots, corresponding to the two electron
irradiations, can be seen. A blue analysing mask and line along Y and X axis, respectively, is used for the spot
corresponding to 1 s exposure time as shown in Fig.7a). The value distributions, given in Fig.7b) are proportional to
the radiation dose and are obtained through image processing within the chosen area. The path of the electrons in the
magnetic field that depends on the electron energy is almost ~ 23 mm. As it can be seen, in the case of 2s exposure
time, the intensity is too high for the IP detectors since the intensity profile is saturated.
a)
b)
Fig. 7. Left: Electron spots on IP at two exposure times of 2s and 1 s; Right: (1s) The blackening distribution along the spot
obtained at 1s exposure time, (2s) The blackening distribution along the spot obtained at 2s exposure time.
3. CONCLUSSIONS
Several dosimetry techniques were tested, each of them having its own advantages. For high exposure times of
the order of minutes calorimetry is the most suitable. For short irradiation times of the order of seconds and for pulse
by pulse irradiation film based dosimetry RCF, IP or LANEX are more appropriate. LANEX screens are more
sensitive than RCF but they can be used for real-time observations of the electron beam intensity as long as the electron
beam flux /pulse do not exceed an approximate value of ≈1014 el/cm2 ·s. EBT-3 film is more sensitive than HD-V2
and should be used for lower electron beam flux. IP detectors can give information on the radiation dose after scanning
and processing the signal. Faraday Cup measurements of electron beam flux are suitable and necessary for all types
of irradiations since they can be adapted to very short electron beam pulse duration encountered in the field of hyper
intense lasers interactions. They provide a precise determination of the beam flux which is one of the most important
parameters to be determined when working with electron beams since it directly influences the absorbed dose.
Choosing a proper dosimetry system needs to take into account the electron beam parameter such as energy, flux,

frequency as well as the characteristics of the irradiation that will be performed (required dose, irradiated material,
beam focus).
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Acknowledgements:
Work financed by The Ministry of Education through PN. 18.13.01.01 Programme, IIN Programe and ELI-RO
program, project nb. 24/ 2016