Linear Energy Transfer Spectrometer Research Articles

Scintillation Efficiency and Position Sensitivity for Radiation Events in Plastic Scintillators

Plastic scintillators (PLSs) are potential materials for the development of a dosimeter based on linear energy transfer (LET) measurement for mixed radiation fields, such as the surroundings of accelerator facilities and in space because PLSs are composed mainly of hydrocarbon molecules, and have the effective atomic number and density similar to those of water and human tissues. In addition, PLSs have a wide range of application in particle physics experiments, owing to their response to all types of radiation (photon, neutron, and charged particles). To use PLSs in designing and constructing an LET spectrometer, essential characteristics of PLSs, such as light yields as a function of deposited energy and radiation species, and the position sensitivity to observe trajectories of incident radiation must be studied. Previously, we performed a procedure for determining the energy deposited in a PLS (EJ-200) for gamma rays from a 137Cs radiation source using Compton Coincidence Technique. In that measurement, the scintillation efficiency, which was determined as a function of Compton electron energy, approaches a saturation value in the high-energy region and decreases in the low-energy region. The decrease in efficiency possibly suggests the nonproportionality between the light yield and deposited energy. In this paper, the scintillation efficiencies, as well as the absolute light yield of PLSs (EJ-200, EJ-212, and EJ-252) are investigated. In addition, the position sensitivity characteristic is studied by using a PLS rod, and photomultiplier tubes (PMTs) are attached to both ends of the rod, and the position of radiation incidence in the rod can be evaluated by using signals from the PMTs.

Dosimetry and microdosimetry of 10–220 MeV proton beams with CR-39 and their verifications by calculation of reaction cross sections using ALICE, TALYS and GEANT4 codes

Abstract High- and intermediate-energy protons are not able to directly form a track in a CR-39 etch detector (TED). Such detectors, however, can be used for the detection and dosimetry of the beams of these particles through the registration of secondary charged particles with sufficiently high values of linear energy transfer (LET). High-energy protons (72–220 MeV) and Intermediate-energy protons (10–30 MeV) with low LET values ranging from 1.1 down to 0.4 keV/μm and 5.87 down to 2.40 keV/μm, respectively are considered in this study. It seems to be sufficient to create secondary particles, although the LET values are low. This phenomenon can modify the characteristics of the energy transfer process due to these particles, which should be taken into account when such particles are used for radiobiology studies or for radiotherapy. The importance of these secondary particles was investigated experimentally by means of an LET spectrometer based on a chemically etched track detector in which the tracks of the primary protons are not revealed. Experiments were performed with proton beams available at the Nuclear Research Center for Agriculture and Medicine (NRCAM) in Karaj, Iran and at the National Cancer Center (NCC) in Seoul, Korea with protons of primary energies of about 10–30 MeV and 72–220 MeV respectively. The contribution of the secondary particle dose increases as the proton energy decreases. The origin of the secondary particles in interactions with protons having high and intermediate energies due to various nuclear reactions was calculated by the both ALICE and TALYS computer codes. The secondary microdosimetry doses were also calculated by GEANT4 code. There is large discrepancy between experimental and calculated results in low proton energies. It has been verified that there is a good correlation between the experimentally obtained results and the reaction cross sections predicted by ALICE and TALYS codes.

Spectrometry of linear energy transfer and dosimetry measurements onboard spacecrafts and aircrafts

There are only a few methods of dosimetry which can estimate the contribution of different particles to onboard spacecraft and/or aircraft exposure. This contribution describes an attempt to estimate the contribution of different components to the exposure level using MDU-Liulin energy deposition spectrometer and thermoluminescent detectors (TLD’s), in combination with a spectrometer of linear energy transfer (LET) based on track etch detectors. This equipment was exposed onboard: the International Space Station for a long period and two shorter shuttle missions and a commercial subsonic aircraft for several long-term monitoring periods from 2001 to 2006. The data obtained are analyzed from several points of view and the obtained results are presented, analyzed, and discussed.

Spectrometry of linear energy transfer and its use in high-energy particle beams

A new method to determine the spectra of linear energy transfer (LET) based on track-etch detectors has been developed. It is based on chemically etched polyallyldiglycolcarbonate (PADC) track detector. LET spectra are calculated using the track parameters measured with an automatic optical image analyzer. This method has been recently improved; the calibration curves have been upgraded on the basis of evaluating the detectors exposed in heavier high-energy charged particle beams. The LET spectrometer has been used to determine LET spectra and integral dosimetry characteristics along the range of protons, resp. 12C ions with primary energies of 205 MeV, resp. about 480 MeV/amu; and to study the importance of the fragmentation and nuclear reactions in carbon and other heavier ion beams. The results obtained are analyzed and discussed; the possible advantages of this type of equipment are outlined.

Upgrading of some instrumentation devoted to increase space radiation environment understanding

Three methods permitting to characterize space and onboard spacecraft radiation environment have been developed and/or upgraded in our laboratories: MDU equipment with a semiconductor detector as sensitive element devoted to register energy deposition spectra in the Si-diode; a spectrometer of the linear energy transfer (LET) based on chemically etched polyallyldiglycolcarbonate (PADC) track etch detectors (TED); and thermoluminescent detectors (TLDs) with different dependences of relative TL yield on the LET of particles transferring their energy in them. We have used all these types of dosimetry equipments onboard spacecrafts since several years and succeeded to treat directly read data in terms of both quantitative and qualitative dosimetry characteristics and deduce from them related radiation risk. During last few years all these three types of detectors have been intensely studied to understand still better their possibilities to characterize space radiation fields. Particularly: 1. Both PADC TED LET spectrometer and TLDs have been exposed in heavier ion beams with LET in water ranging from 1 to about 700 keV/μm with the goal to upgrade their calibration curves; 2. A new method of MDU directly read data has been developed, permitting to measure not only dose in Si-detector, but also to estimate radiation protection quantities and the neutron contribution to the onboard exposure level; 3. All three methods have been tested onboard spacecrafts during several missions. Contribution presents, analyses and discusses the results obtained in items 1–3 and, also, the possibilities of these detectors to help in characterizing radiation fields during longer space missions, above 1 year.

To the spectrometry of linear energy transfer in charged particle beams by means of track-etch detectors

The contribution describes the methodology of linear energy transfer (LET) spectrometry based on the chemically etched track detectors and results of some experimental studies. Three types of polyallyldiglycolcarbonate (PADC) material have been used in our laboratory: Page—with a thickness of 0.5 mm and Tastrak with thicknesses of 0.5 and 1 mm. This LET spectrometer is able to detect charged particles with LET above the registration threshold (around 10 keV / μ m , depending on the used material), both primary and secondary, created through nuclear interactions in the detector itself or in the surroundings. During several years the detectors were irradiated by various particles with LET in water up to about 600 keV / μ m . In these studies, primary heavy ions had LET above the registration threshold and so they can be directly detected. However, also some fragments and products of nuclear reactions of the primary particles are registered in the detector, especially behind various absorbers. LET spectrometer calibration curves and also the importance of secondary particles in heavy ion beams and their contribution to the absorbed dose are presented and discussed.

LET spectrometry with track etch detectors—Use in high-energy radiation fields

For assessing the risk from ionizing radiation it is necessary to know not only the absorbed dose but also the quality of the radiation; radiation quality is connected with the physical quantity linear energy transfer (LET). One of the methods of determination of LET is based on chemically etched track detectors. This contribution concerns with a spectrometer of LET based on the track detectors and discusses some results obtained at: • high-energy radiation reference field created at the SPS accelerator at CERN; and • onboard of International Space Station where track-etch based LET spectrometer has been exposed 273 days during “Matrjoshka – R” experiment. Results obtained are compared with the results of studies at some lower-energy neutron sources; some conclusions on the registrability of neutrons and the ability of this spectrometer to determine dose equivalent in high-energy radiation fields are formulated.

Dependence of thermoluminescent detectors relative response on the linear energy transfer; some examples of use

The relative response (RR) of the most thermoluminescent detectors (TLDs) decreases with increasing linear energy transfer (LET) of particles depositing energy in a TLD. Three TLDs have been mostly studied: Al–P glasses, Al 2 O 3 : C , and CaSO 4 : Dy . They have been exposed, since several years, to high energy charged particles with energies up to 1 GeV/amu, and LET up to 600 keV / μ m in water. The RR of TLDs as a function of LET is presented. In two cases, the sets of obtained data permitted us to regress them and obtain general LET dependences of RRs for Al–P glasses and Al 2 O 3 : C and for their ratios. These functions, in combination with LET spectra established by means of track etch based LET spectrometer were also used to appreciate their ability to establish total dosimetric characteristics in some high-energy radiation beams and fields, also those usable for hadron therapy.

Contribution of secondary particles to the dose in 12C radiotherapy and other heavy ion beams

The results of experimental studies performed in a radiotherapy (12)C ion beam with a nominal energy of 500 MeV/amu and in (16)O and (56)Fe ion beams with a nominal energy of 1 GeV/amu have been described. Linear energy transfer (LET) spectra have been established by means of an LET spectrometer based on a chemically etched track detector, and the measured results were also compared with theoretical calculations obtained using the program Stopping and Range of Ions in Matter (SRIM). It was observed that with increasing depth in a beam, the LET spectra are shifted towards higher values of LET; one can also observe an important widening of the spectra along the range, as well as an increasing amount of nuclear reaction products and/or of fragments in the spectra. The relative contribution of these secondary particles to the total absorbed dose was assessed.

Doses and LET spectra in the beam of 12C with energy 500 MeV amu−1

This paper describes the results of experimental studies performed at the Joint Institute for Nuclear Research (JINR) in a (12)C ion beam with the primary nominal energy 500 MeV amu(-1). Data measured by means of a diamond detector and a spectrometer of linear energy transfer (LET) based on chemically etched track detectors are presented, analysed and discussed. LET spectra are also calculated by program SRIM.

Monitoring of onboard aircraft exposure to cosmic radiation: May–December 2005

Onboard aircraft exposure to cosmic radiation has been monitored during the period May–December 2005. Mobile Dosimetry Unit (MDU) Si-spectrodosimeter has been used as an active measuring equipment, it has been installed onboard of an A310–300 aircraft. Some passive detectors were placed on the body of MDU. Three types of thermoluminescent detectors (TLD) were used as well as track etch detectors (TEDs). TEDs were treated both as a neutron dosimeter and as a spectrometer of linear energy transfer. Available navigation data permitted us also to calculate onboard exposure during more than 400 individual flights. MDU established and calculated data for each individual flight are compared and analyzed, from the data conclusions as to aircrew exposure are outlined. Particular attention is devoted to the influence of: • geomagnetic characteristics and flight altitude on the calculated and MDU-Liulin measured dosimetry characteristic of onboard radiation field; • some solar events (Forbush decreases) registered by MDU-Liulin on the level of aircraft crew exposure during monitoring period. Integral data on the exposure due to non-neutron and neutron-like component obtained on the base of MDU and calculated data are compared with the data obtained by TLDs and TEDs, respectively. Total effective dose during the period mentioned (494 flights and 2940 h between taking offs and landings) was found to be about 11–12 mSv for. Results obtained by means of different approaches are analyzed and discussed, it was found that in general good agreement of all data sets could be stated.

Dosimetry and microdosimetry using LET spectrometer based on the track-etch detector: radiotherapy bremsstrahlung beam, onboard aircraft radiation field

The spectrometer of linear energy transfer (LET) based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector was developed several years ago in our institute. LET spectra are estimated through track parameters determination carried out by an automatic optical image analyzer LUCIA G. This LET spectrometer enables determining LET of particles approximately from 10 to 700 keV/µm. From the LET spectra, dose characteristics can be calculated. This contribution presents the use of this spectrometer in some applications – studies in 18 MV radiotherapy bremsstrahlung beam and investigation onboard a commercial aircraft during more than 6 months long exposure. The LET spectra obtained in both experiments represent mainly the contribution of secondary or tertiary particles created through the nuclear reactions of photons (bremsstrahlung beam) or neutrons and neutron-like reacting particles (onboard aircraft) in the detector itself or in the surroundings material. The dose due to the photoparticles represents about 3 × 10-4 of the photon dose; for the dose equivalent this value is about 2 × 10-3 Sv/Gy. Regarding the onboard aircraft exposure, the results obtained using LET spectrometer were compared with those achieved with other methods and a reasonable agreement were stated.

Upgrading of LET track-etch spectrometer calibration: Calibration and uncertainty analysis

The spectrometer of linear energy transfer (LET) was developed several years ago. It is based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector. LET spectra are determined through track parameters determination and analysis by an automatic optical image analyser LUCIA G. For the past few years, we have used three materials, Page, 0.5 mm thick and Tastrak, 1 and 0.5 mm thick. To upgrade and determine their calibration curves, we have performed irradiation in high-energy heavier charged particle beams at Dubna, Russia and at Chiba, Japan. We were able to irradiate detectors by means of particles from 12 C to 56 Fe with LET in water from 7.9 to 200 keV / μ m . Upgraded calibration curves were obtained through a regression analysis, including systematic uncertainty estimation. The results obtained were combined with statistical uncertainty treatment and were used to analyse recently and previously obtained data. Examples of the results are presented and analysed.

Response of a track-etch-based LET-spectrometer to high-energy protons

The spectrometer of linear energy transfer (LET) was developed. It is based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector. LET spectra are estimated through track parameter determination and analysed by an automatic optical image analyser LUCIA G. Three PADC materials were used: 0.5 mm thick Page, 0.5 and 1 mm thick Tastrak; they were exposed to protons with energies up to 1000 MeV. Such energetic protons are generally not directly registrable in any of PADCs mentioned; the tracks observed correspond mostly to secondary particles created through nuclear interactions of primary protons. LET spectra permit to calculate the dose absorbed in the detector due to these secondary particles and to compare it with the ionization collision dose of primary protons. It is observed that the dose due to secondary particles represents a few percent of the ionization collision dose. Their ratio varies slightly with proton energy, and some differences between the three PADCs used were also observed. The importance of results obtained for on-board spacecraft dosimetry is analysed and discussed.

An empirical approach to the measurement of the cosmic radiation field at jet aircraft altitudes

Researchers at the Royal Military College of Canada have accumulated extensive dose measurements performed at jet altitudes on over 160 flights and with a wide variety of detectors including a tissue equivalent proportional counter (TEPC), a smart wide energy neutron detection instrument (SWENDI), bubble detectors, thermoluminescent detectors (TLD) and an ion chamber. The summation of the individual low and high LET results from the latter equipment compared successfully to those from the TEPC on each flight. The data from these numerous worldwide flights have been encapsulated into a program that calculates the radiation dose for any flight in the world at any period in the solar cycle. This experimentally based program, Predictive Code for AIRcrew Exposure (PCAIRE) has been designed to be used by the airline industry to meet national dosimetry requirements. In Canada, for example, such a code can be used, supported by periodic measurements. With this latter requirement in mind and a desire to decrease equipment size, the silicon-based LIULIN-4N LET (linear energy transfer) spectrometer has been assessed to determine its suitability as a mixed field instrument and possible code verification tool. Data obtained from the LIULIN and TEPC in ground-based experiments at the CERN-EC Reference-field Facility (CERF) and on 42 jet-altitude flights have been compared. Analysis of these data has resulted in two different mathematical correlations which can be used to determine the ambient dose equivalent, H ∗(10), from the LIULIN absorbed dose output. With either calibration factor, the LIULIN instrument could now be used as a simple, compact and portable detector for routine monitoring.

Dosimetry and microdosimetry characteristics measured on board the MIR station during the 28th basic expedition

Three types of detectors were used onboard the MIR station during the 28th base expeditions to characterise the radiation field: a linear energy transfer (LET) spectrometer was used to establish the LET spectrum between 7 and 700 keV/ μm corresponding mostly to secondary charged particles; a set of thermoluminescent detectors was used to characterise the low LET component of the onboard radiation field; and Si-diodes were installed to determine the contribution to the exposure due to fast neutrons. It was found out that the LET spectrum from secondary particles between 7 and 700 KeV/ μm does not depend on the external radiator; the average quality factors for the region mentioned are about 6.0 with ICRP 26 quality factors and about 6.8 with ICRP 60 quality factors. Both differential and integral LET spectra are presented for some typical cases, not only for particle number but also for the dose characteristics like dose and dose equivalent. The spectra obtained also permitted us to calculate the total doses and dose equivalents due to secondary particles with the LET values between 7 and 700 keV/ μm . It was found out that these quantities are higher for the case of detectors placed in the less shielded area, both for the LET spectrometer (high LET part) as well as for TLDs measuring the low LET component. Total dosimetric characteristics obtained as a sum of both components mentioned are a little lower than previously reported.

Microdosimetric characteristics of the clinical proton beams at JINR, Dubna.

High-energy proton radiotherapy beams give rise to secondary heavy charged particles with elevated linear energy transfer (LET), which contribute to the dose in a patient. This contribution to the characteristics of radiotherapy proton beams was experimentally studied by means of a LET spectrometer based on a track detector. The spectrometer permits LET spectra to be established in the region above 10 keV.micron-1 in tissue. Sets of track detectors were exposed in the various depths of a phantom irradiated with protons of two energies, 150 and 205 MeV. It was observed that the contribution of particles with the values of LET mentioned increases with the depth, representing from about 2 (at the surface) up to few tens% close to Bragg peak region of the total dose. There, some of primary protons contribute also above 10 keV.micron-1. Using the 'biological weighted function' proposed, the clinical RBE was calculated, it could approach 1.3. This effect has to be taken into account during the clinical beam production and the radiotherapy.

Dosimetric and microdosimetric characteristics of high energy proton beams

High energy (⩾50 MeV) protons can be considered, when their ionization losses stopping power is taken into account, as the radiation with low (<5 keV/ μm) linear energy transfer (LET). However, their energy is already sufficient to create, through the nuclear reactions in irradiated matter, secondary particles with much higher LET. This phenomenon can modify the characteristics of the energy transfer process due to these particles, which should be taken into account when such particles are used for radiobiology studies and/or for radiotherapy. The importance of these secondary particles was studied experimentally by means of the LET spectrometer based on a chemically etched track detector, in which the tracks of primary protons are not revealed. The studies were performed in proton beams available at the Joint Institute of Nuclear Research (JINR) at Dubna, Russia, with protons of primary energies of about 200 MeV and 1 GeV . The microdosimetric distribution of secondary particles mentioned are presented and compared and their contribution to primary proton ionization losses absorbed dose is estimated. This contribution increases relatively with the proton energy, and also changes with the depth of penetrated material. The importance of this phenomenon to some applications is discussed.

Detection, dosimetry and microdosimetry using high energy 12C beams

Samples of polyallyldiglycolcarbonate (PADC) track etch detectors (TED) were exposed to high energy 12C nuclei at the particle beam of the Dubna synchrophasotron. The energy of 12C nuclei varied between 0.1 and 1.5 GeV per amu. At the low studied energies the linear energy transfer (LET) of these nuclei is higher than the detector threshold value. Then, the primary particle tracks are directly etched in the detector surface. The detection efficiency approaches to 100% at perpendicular incidence. Their LET has been established by means of standard authomatized procedure recently developed. The LET values found here are in good agreement with theoretical ones. At 1.5 GeV per amu (LET ∼ 8.4 KeV μm −1) the secondary particle tracks were evaluated in all the exposed detectors. The energy deposited by these particles was compared to the energy deposited through primary ionization losses. It was found out that its contribution to the total dose is relatively lower than for protons of comparable energies. In some of these samples even the tracks of the primary nuclei were observed. It follows that the detection threshold of the developed LET spectrometer should be below 10 keV μm −1.