Tapered Optical Fiber- based Detection of Charged Particle Irradiation in Space Exploration and Nuclear Reactors Manoj K. Rajbhar Basudeba Maharana Shyamapada Patra and Shyamal

2025-05-02 0 0 1.63MB 22 页 10玖币

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Tapered Optical Fiber-based Detection of Charged Particle

Irradiation in Space Exploration and Nuclear Reactors

Manoj K. Rajbhar, Basudeba Maharana, Shyamapada Patra and Shyamal

Chatterjee*

School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Jatni, 752050, India

*Corresponding Author E-mail: shyamal@iitbbs.ac.in

Abstract:

In this work, we demonstrate the use of tapered optical fibers (TOF) to detect charged particle

(ions), irradiated at various energies, fluences and species. The single mode tapered optical

fiber has been used in various sensing applications in recent times. Here, tapered optical fibers

have been exposed to two different ion species namely Ar+ and N+ at different energies and

different fluences, respectively. The optical spectrum analyser (OSA) detects the changes in

the free spectral range (FSR), period, and transmission power loss from the ion beam irradiated

TOFs. The change in the refractive index of the cladding material due to the implanted ions

influences the transmission spectra of the TOFs and we could able to detect ions of energy as

low as 80 keV. COMSOL simulation results are employed to explain the observed changes in

spectra. The ion beams induced surface modification and defect formation as well as the

implantation in TOF have been predicted using Monte Carlo based 3D TRI3DYN ion-solid

interaction simulation and corroborated with other experimental studies such as scanning

electron microscopy and Raman scattering spectroscopy. Such tapered optical fiber-based

detection technique will help to develop portable device to detect charged particles in space

exploration and in nuclear reactors.

Key Words: Tapered Optical Fiber (TOF), Ion beam irradiation, COMSOL, TRI3DYN,

Optical Spectrum Analyser (OSA), Ion detection

1. Introduction:

Radiation detectors must be light, portable, and highly sensitive to radiation sources that are

smaller and more difficult to detect [1]. There are three basic types of radiation detectors: gas-

filled detectors, solid-state detectors, and detectors that use scintillators [2]. Ionization

chambers, proportion counters, and Geiger-Mueller (G-M) tubes are examples of gas-filled

detectors [3]. All of these detecting methods operate on the same concept; the key difference

is the voltage supplied across the detectors. Gas-filled detectors are ionisation chambers of ion

chambers that register only primary ions at lower voltages (in actuality pair of ions created: a

positively charged ion and a free electron). However, one significant disadvantage of such gas

ionisation chambers is that they are unable to distinguish between different types of radiation

and their energy levels [4]. This is overcome by proportional counters, which are highly useful

for spectroscopy since they react differently at different energies, allowing them to distinguish

between different types of radiation [5,6]. The second major radiation detection technology is

based on solid-state or semiconducting materials and employs a p-n junction [7]. The radiation

traverses the depletion area, which generates an electron-hole pair and an analogue signal [8].

In a position sensitive detector which is one kind of photodetector, the energy and position of

a light spot can be determined after signal processing. The scintillation detectors are the type

of detectors that detects the amount of light produced in some specific crystalline materials

when exposed to ion irradiation [9]. Due to its great effectiveness in detecting charge particles

and photons, modern scintillation detectors based on optical fiber have efficiently and reliably

worked in many high-energy physics experiments [10] [11]. Scintillating fibers are widely used

as detectors to measure beam luminosity and charge particle time flight separation. The fiber

structure enables efficient light collection and transmission via total internal reflection in the

cladding region. The transmission loss during light propagation along the fiber surface is

caused by Rayleigh scattering, which is caused by inhomogeneities, radiation damage, and self-

absorption [12]. The upgradation of large hadron collision beauty spectrometer is planned to

replace the silicon microstrip and gas drift tubes detector by scintillating fiber of diameter 250

µm due to their high homogeneity and low materials cost [13]. Radiation tests by the fiber

carried out on the different particles (proton, gamma ray, X-ray irradiation) of different

energies show that the expected yield loss is nearly about 40 percentage. The major features of

the detector measured by the 2.4 m long SCSF-78MJ fiber using pion/proton beams at CERN

and electron beam at DESY shows the detection efficiency 99 percentage with spatial

resolution 70 µm [13]. The effects of irradiating the fiber with the same fluence at high power

(short time) or low power (long time) are not well understood. The effect of irradiation fluence

rate on fiber and their recovery after irradiation has been investigated in some research [14–

20]. According to these studies, radiation damage in optical fibers increases with decreasing

radiation fluences. The recovery time of an optical fiber detector is nearly 100 times faster than

the recovery time of a scintillator and fiber detector. The optical fibers based on the new

Nanostructured Organosilicon Luminophores (NOL11 & NOL19) have a high

photoluminescence quantum light yield and a very short delay time (1.34ns and 1.18 ns) [21].

In recent years, optical fiber based techniques in conjunction with nanotechnology have

emerged as successful and efficient platform for developing sensing devices [22,23]. Sensors

based on tapered optical fiber (TOF) have versatile performance. Due to its small size and the

enhanced evanescent field distribution at the tapered region, the TOFs have been implemented

for detection of molecules and nanoparticles [24], [25]. Optical fibers are used in several

studies to develop radiation sensors. Depending on operating principles, there are several well-

known methods used for radiation sensing. For instance, detection of radioluminescence,

Cerenkov radiation or analysis of change of refractive index of optical fibers and optical

absorption analysis due to radiation are used for detection of electrons and gamma rays. Other

popular methods involve scintillating materials, thermoluminescence and optically simulated

luminescence materials. Some of the most used techniques include refractive index sensing

[26], Rayleigh scattering loss/transmission monitoring [27], fluorescence labelling [28], intra-

fiber modal interference [29], Raman spectroscopy-based sensor [30], chemiluminescence

[31], surface plasmon resonance [32], Fiber Bragg Gratings (FBG) [33]. Lee et al., developed

an optical fiber-based dosimetry for detection of electron irradiation using Cherenkov radiation

method [34]. Arvidsson et al., measured ionizing fluence of photon irradiation using hard and

multimode index multimode fibers [35]. A real time scintillating fiber based dosimeter was

developed by Bartesaghi et al., for measurement of fluences of neutron and gamma ray during

radio therapy [36]. Brichard et al worked on improving radiation hardening of optical fibers

used in plasma diagnostics [37]. Alfeeli et al., embedded scintillating material within a holey

optical fiber structure and used Cherenkov radiation to detect gamma rays [38]. However, use

of tapered optical fibers to detect heavier charged particles is handful at this stage.

In this work, we show ion irradiation detection capacity of tapered optical fiber (TOF)

by wavelength interrogation technique. The TOF has been irradiated with nitrogen and argon

ions at two different energies of 80 and 100 keV and at different fluences, respectively. The

comparison of optical spectra from pristine and the irradiated fibers are clear indicatives of

implantations and irradiation induced defects in the fibers. The ion implantations and induced

defects have been predicted by Monte Carlo based simulation of 3D structures of the fiber and

corroborated with scanning electron microscopy and Raman scattering studies respectively.

We have used COMSOL simulation to predict the change of optical spectra due to irradiations.

2. Principles:

2.1 Tapered Fiber:

The tapered fiber, which is made by drawing the fiber uniformly when it is heated to a certain

temperature to reduce its diameter to less than 10 µm. It has three regions; untapered region,

which retains the diameter of the original fiber taken, the conical taper transition region with

gradually changing diameter, and taper waist segment, which has a very small and uniform

diameter. Due to heating and drawing, at the taper waist region the core and cladding diameters

decrease resulting in much smaller core and cladding regions (shown in the supplementary

figure S1). Due to lower core region, the guided modes redistribute resulting in excitation of

higher order modes along with fundamental mode. The higher order modes of TOF have greater

overlap over the cladding region that allow for interaction of light with the cladding region.

Moreover, these modes have different effective indices and the difference between these

indices can be represented as Δn. These modes overlap and interfere about the waist region

such that the transmitted intensity can be given as:

=++ 2.cos()

Where,  and  are the intensities of HE11 and HE12 mode, respectively and the phase shift:

 = 2.

, here, L is the length of taper waist,  is the wavelength of light. The condition

for constructive interference is  = 2, where m is an integer. So, the wavelength value

about the interference peak can be written as:

=.



The fringe spacing of the interference pattern termed as free spectral range (FSR) can be

expressed as  =

. that depends on length of the waist region. The fringe spacing can be

varied by varying the taper waist length.

An important parameter in any modal interferometer is visibility for different sensing

applications. Higher visibility is needed to get an accurate measurement as the signal-to-noise

ratio will be more. The general expression for V is: =

, which can be simplified as

defined as [39]:

=2

1 + 

Here, =

. In this work, we have expressed visibility in terms of fringe contrast (FC) (in

dBm) that can be defined as  =10log (1  ).

2.2 Ion Beam Irradiation:

Ion beam irradiation is a very well-developed field of study for materials modification,

analysis, in semiconductor industry and for radiation therapy. The space is full of such particle

radiation, which is harmful for living beings and equipment for space explorations.

Furthermore, there are irradiations build up in nuclear reactors. These charged particles or ions

interact with matter via nuclear and electronic stopping interactions. Such interactions lead to

surface modifications, defect generations and thermal spike in a material. The consequence

may lead to change of crystal phase, surface roughening or patterning, atomic mixing, change

of chemical state, mechanical and structural changes to name a few. Usually, low energy ions

lose energy in solid via nuclear stopping and high energy ions lose through electronic stopping

interactions. Nuclear stopping causes displacement of atoms in a solid and creates defects apart

from implantation of the ions. Electronic stopping causes excitation and ionization of electrons

in a solid leading to generation of thermal spike and lattice heating. In this study the

aforementioned ion irradiation effects in tapered optical fibers are exploited to detect the

irradiation.

3. Experimental Details:

3.1 Fabrication of Taper Fiber:

Single-mode fibers (SMF-28) with core/cladding diameters of 8/125 μm were used in this

study. The protective coating was removed from a 5 mm long section of the SMF along the

length. The TOF was fabricated by flame and brush technique in which the fiber section is

heated to nearly its melting point and pulled from both sides to cause lowering of diameter.

The diameter of waist region and the length of the microfiber was kept at 10 μm and 7.5 mm,

respectively [40]. Multiple such TOFs were fabricated and their transmission spectrum was

recorded using spectrum analyser before and after the irradiation. The fringe spacing and

visibility parameters of each of the TOF was evaluated.

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TaperedOpticalFiber-basedDetectionofChargedParticleIrradiationinSpaceExplorationandNuclearReactorsManojK.Rajbhar,BasudebaMaharana,ShyamapadaPatraandShyamalChatterjee*SchoolofBasicSciences,IndianInstituteofTechnologyBhubaneswar,Jatni,752050,India*CorrespondingAuthorE-mail:shyamal@iitbbs.ac.inAbstract...

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Tapered Optical Fiber- based Detection of Charged Particle Irradiation in Space Exploration and Nuclear Reactors Manoj K. Rajbhar Basudeba Maharana Shyamapada Patra and Shyamal

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