Energy spectrum of iron nuclei measured inside the MIR space craft using CR-39 track detectors

We have exposed stacks of CR-39 plastic nuclear track detectors inside the MIR space craft during the EUROMIR95 space mission for almost 6 months. Over this long period a large number of tracks of high LET events was accumulated in the detector foils. The etching and measuring conditions for this experiment were optimized to detect tracks of stopping iron nuclei. We found 185 stopping iron nuclei inside the stack and identified their trajectories through the material of the experiment. Based on the energy-range relation the energy at the surface of the stack was determined. These particles allow the determination of the low energy part of the spectrum of iron nuclei behind shielding material inside the MIR station.     

Calibration studies and the application of nuclear track detectors to the detection of charged particles

This paper describes calibration studies of solid state nuclear track detectors (SSNTDs) of he CR-39/PM-355 type. A dozen or so PM-355 detector samples were cut out from detector sheets delivered at different times and were irradiated with mono-energetic protons, deurerons and helium ions of energy ranging up to a few MeV. After that, the samples were etched and track opening diameters were determined as a function of particle energy and detector etching time. These studies were motivated by the application of the detectors in fusion experiments to measure energetic ions which escape high-temperature plasmas. The calibration diagrams obtained enable us to compare the relative sensitivities of detectors from different batches and to use these detectors in an optimal way.     

The experimental and simulated LET spectrum and charge spectrum from CR-39 detectors exposed to irons near CRaTER at BNL

Human will be sooner or later return to the moon and will eventually travel to the planets near Earth. Space radiation hazards are an important concern for human space flight in deep space where galactic cosmic rays (GCR) and solar energetic particles are dominated and radiation is much stronger than that in LEO (Low Earth Orbit) because in deep space there is no magnetosphere to screen charged particle and no big planet nearby to shadow the spacecraft.Research indicates that the impact of particle radiation on humans depends strongly on the particles' linear energy transfer (LET) and the radiation risk is dominated by high LET radiation. Therefore, radiation research on high LET should be emphasized and conducted systematically so as to make radiation risk as low as reasonably achievable (ALARA) for astronauts.Radiation around the moon can be measured with silicon detectors and/or CR-39 plastic nuclear track detectors (PNTDs). At present stage the silicon detectors are one of the preferred active dosimeters which are sensitive to all LET and CR-39 detectors are the preferred passive dosimeters which are sensitive to high LET (≥5 keV/μm water). CR-39 PNTDs can be used as personal dosimeters for astronauts. Both the LET spectrum and the charge spectrum for charged particles in space can be measured with silicon detectors and CR-39 detectors.Calibrations for a detector system combined with the silicon detectors CRaTER (Cosmic Rays Telescope for the Effects of Radiation) from Boston University and Massachusetts Institute of Technology, and the CR-39 PNTDs from JSC (Johnson Space Center) – SRAG (Space Radiation Analysis Group) were conducted by exposing the detector system to the accelerator generated protons and heavy ions. US space mission for the radiation measurement around the moon using CRaTER was carried out in 2009.Results obtained from the calibration exposures indicate an excellent agreement between LET spectrum and charge spectrum measured with CR-39 detectors and simulated with PHITS (Particle and Heavy Ion Transport System).This paper introduces the LET spectrum method and charge spectrum method using CR-39 PNTDs and the Monte Carlo simulation method for CR-39 detectors, presents and compares the results measured with CR-39 PNTDs and simulated for CR-39 detectors exposed to heavy irons (600 MeV/n) in BNL (Brookhaven National Laboratory) in front and behind the CRaTER.     

Calibration of CR-39 with atomic force microscope for the measurement of short range tracks from proton-induced target fragmentation reactions

We studied the track response of CR-39 plastic nuclear track detectors (PNTD) for low (<6 MeV/n) and high (>100 MeV/n) energy heavy ions using the atomic force microscope (AFM). CR-39 PNTD was exposed to several heavy ion beams of different energy at HIMAC (Heavy Ion Medical Accelerator in Chiba). For AFM measurement, the amount of bulk etch was controlled to be ∼2 μm in order to avoid etching away of short range tracks. The response data obtained by AFM for ∼2 μm bulk etch was in good agreement with data obtained by the conventional optical microscope analysis for larger bulk etch. The response data from low energy beams (stopping near the surface) was also consistent with the data from high energy beams (penetrating the detector) as a function of REL (restricted energy loss) with the δ-ray cut off energy of ω₀ = 200 eV. We experimentally verified that REL (ω₀ = 200 eV) gives a universal function for wide energy range in CR-39 PNTD. This work has been done as part of a basic study in the measurement of secondary short range tracks produced by target fragmentation reactions in proton cancer therapy fields.     

Measurement of LET distribution and dose equivalent on board the space shuttle STS-65

Space radiation dosimetry measurements have been made on board the Space Shuttle STS-65 in the Second International Microgravity Laboratory (IML-2). In these measurements, three kinds of detectors were used; one is a newly developed active detector telescope called “Real-time Radiation Monitoring Device (RRMD)” utilizing silicon semi-conductor detectors and others are conventional detectors of thermoluminescence dosimeters (TLDs) and CR-39 plastic track detectors. Using the RRMD detector, the first attempt of real-time monitoring of space radiation has been achieved successfully for a continuous period of 251.3 h, giving the temporal variations of LET distribution, particle count rates, and rates of absorbed dose and dose equivalent. The RRMD results indicate that a clear enhancement of the number of trapped particles is seen at the South Atlantic Anomaly (SAA) without clear enhancement of dose equivalent, while some daily periodic enhancements of dose equivalent due to high LET particles are seen at the lower geomagnetic cutoff regions for galactic cosmic ray particles (GCRs). Therefore, the main contribution to dose equivalent is seen to be due to GCRs in this low altitude mission (300 km). Also, the dose equivalent rates obtained by TLDs and CR-39 ranged from 146.9 to 165.2 μSv/day and the average quality factors from 1.45 to 1.57 depending on the locations and directions of detectors inside the Space-lab at this highly protected orbit for space radiation with a small inclination (28.5°) and a low altitude (300 km). The LET distributions obtained by two different detectors, RRMD and CR-39, are in good agreement in the region of 15–200 keV/mm and difference of these distributions in the regions of LET < 15 keV/mm and LET > 200 keV/mm can be explained by considering characteristics of CR-39 etched track formation especially for the low LET tracks.     

Energy spectrum of 50-250 MeV/nucleon iron nuclei inside the MIR space craft

Stacks of CR-39 plastic nuclear track detectors were mounted inside the MIR spacecraft during the EUROMIR95 space mission for a period of 6 months. This long exposure time resulted in a large number of tracks of HZE-particles in the detector foils. All trajectories of stopping iron nuclei could be reconstructed by optimizing the etching conditions so that an automatic track measurement using image analysis techniques was possible. We found 185 stopping iron nuclei and used the énergy-range relation to calculate their energies at the stack surface. The measured spectrum of iron nuclei inside the MIR station is compared to results of model predictions considering the effect of the solar modulation for the mission period, the geomagnetic shielding effect for the MIR orbit and the shielding by material of the spacecraft walls and its instrumentation.     

Determination of the range of alpha particles in SSNTD by optical density method

A technique based on the optical density (D) measurement of the etched track is useful for charged particles spectroscopy using SSNTD. It was shown that the stopping power of alpha particles in CR-39 is proportional to D. We measured the optical density and derived an expression to estimate the range of alpha particles in CR-39 detector as a function of the bulk etching rate and etching time. The relation between the etching time, track parameters (depth, radius) and D for different alpha particles energy and etching conditions were studied. A relation describing D as a function of track size is proposed.     

Modification of optical, chemical and structural response of CR-39 polymer by 50 MeV lithium ion irradiation

CR-39 polymer samples were irradiated with 50 MeV lithium ion beam; the fluence was varied in the range 10¹¹–10¹³ ionscm⁻². Irradiation effects were studied using UV–visible, FTIR spectroscopic and X-ray diffraction techniques. The observation of the recorded spectra shows that the detector is sensitive to swift ions irradiation and its UV absorption is influenced by the stopping power (dE/dx)_e. The FTIR spectra does not show any considerable changes due to the irradiation indicating that the detector is chemically stable. No appreciable change in the diffraction pattern of CR-39 polymer after irradiation upto the fluence level of 10¹³ ionscm⁻² is observed, showing its structural stability also.     

DIP angle dependence on track formation sensitivity in antioxidant doped CR-39 plates

Recently, space radiation dosimetry measurements were made by passive and active detectors inside the Spacelab [STS-47 (FMPT): 300km, 57°, STS-65 (IML-2 mission): 300km, 28.5°]. The LET distributions obtained by antioxidant doped CR-39 inside the Spacelab were compared with those measured by the tissue equivalent proportional counter (TEPC) and the real time radiation monitoring device (RRMD) consisting of eight silicon detectors. While both distributions by CR-39 are in good agreement with those obtained by active detectors over the region of LET of several tens to 200 keV/μm, a significant difference in the LET region of smaller than several tens keV/μm is seen. It is considered to be caused by the dip angle dependence of track formation sensitivity in CR-39. The track formation sensitivity for different dip angle were measured for several high heavy energy ions. Using these results, the correction for the dip angle was made for the LET distribution. The corrected result is consistent with the results obtained by active detectors.     

Determination of Z/β for strange quark matter candidates with CR-39 track detector

In order to confirm the existence of strange quark matter (SQM) in cosmic rays, a series of international balloon flights with a hybrid system combining active counters and passive detectors was conducted under the collaboration between Japan and Italy. In this report, the methodology of how to detect SQM with the hybrid system and how to determine Z/β with CR-39 track detectors are presented.     

Techniques to investigate the characteristic of CR-39 detectors using Am---Be neutron source

Two techniques have been developed to investigate the characteristic of the sensitivity of CR-39 (polyallyldiglycol carbonate) track detector using Am---Be neutron source. The firstis to measure volume track density created by fast neutrons in CR-39 detectors. The second is to measure areal asymptotic track density on the surface of CR-39 sheets. Two types of CR-39—SY-2 CR-39 made in China and another made in USA were calibrated using the techniques. It shows that the two types of CR-39 detectors have nearly the same sensitivity to detect fast neutrons. The techniques developed in this work can be applied to calibration of other track detectors.     

CR-39核径迹探测器及其在核科学等研究领域中的应用

介绍了一种核径迹探测器ＣＲ－３９塑料的特性,这种探测器对逞电粒子非常灵敏,它还具有稳定、透明等特点,可记录ｐ、ａ粒子,裂变碎片和其他带电粒子,它是现有固体核径迹探测器中能量沉积密度探测阈最低的材料,介绍了ＣＲ－３９对带电粒子的响应,给出了各种带电粒子的ｖＴ对限定能量损失（ＲＥＬ）的响应曲线,利用ＣＲ－３９与转换屏的组合还可测定能量范围广的中子能谱,可作为方便的个人中子剂量计,介绍了ＣＲ－３９在研究     

Total charge-changing and partial cross-section measurements in the reaction of 110 MeV/u C with paraffin

We have measured the total and partial charge-changing cross-sections (Z=5) after the passage of a 110 MeV/u ¹²C beam through an assembly consisting of CR-39 thin detectors and paraffin targets. These experimental cross-sections were compared to the predictions of known models. It was found that the measured total cross-sections agree with the model calculations to within about 8% or even less, while, depending on a model, discrepancies of up to a factor 1.2 higher and up to a factor 2.7 lower values of cross-sections for the production of fragment with Z=5 were observed.     

Abundance of actinides in cosmic radiation

Ultra heavy (UH) cosmic rays of Z65 are produced either by s- or r-process of nucleosynthesis. Since these two processes occur under different astrophysical environments, the relative abundances of UH ions could be an important parameter in finding their source and origin. Data analysis is carried out on four detector stacks exposed in space by UH cosmic ray experiment on board LDEF. Scanning and analysis of 0.21 m² detector area resulted in finding of 72 UH ions (68Z96) including two actinides (88Z100). The ratio of actinides to that of sub-actinides is found to be 0.034±0.024, which is well within the observational limits of other experiments. Results suggest possible sources, which predominantly ejects r-process synthesized material.     

FT-IR spectroscopy of carbon dioxide in CR-39 and SR-90 track detectors irradiated with ions and gamma-rays at different energies and fluences

Two types of polymeric track detectors CR-39 and SR-90 were irradiated with protons, alpha particles, heavy ions and gamma-rays at different energies and fluences. After irradiation these detectors were analyzed with an FT-IR spectrometer of Jasco type 5300 in transmission and ATR modes. We have found that CO₂ is produced not only by irradiation but also by polymerization. The amount of CO₂ in the detector material is closely related to the latent track formation.     

LET calibration for CR-39 detectors in different oxygen environments

High LET (linear energy transfer) radiation is the main contributor to the radiation field in low Earth orbit (LEO) in terms of dose equivalent. CR-39 plastic nuclear track detectors (PNTDs) can measure the LET spectrum and charge spectrum for the complicated radiation field in space. Previous research indicated that the sensitivity of CR-39 is different for CR-39 PNTDs working in different oxygen environments. LET calibration for CR-39 detectors in different oxygen environments is needed. Almost all the previous LET calibration work was carried out for CR-39 detectors in good-oxygen condition, LET calibration work for CR-39 in poor-oxygen condition has not been conducted until our work. Systematic LET calibrations were carried out by JSC-SRAG (Space Radiation Analysis Group) for CR-39 detectors working in different oxygen environments and abundant results of LET calibrations were obtained. This paper introduces the method for CR-39 LET calibration, presents and discusses the calibration results and some applications.     

Dosimetry of 40 and 70 MeV/n O beams

Using CR-39 plastic track detectors the range values of ¹⁶O ions at two different energies (initially in the beam line, 39.97 MeV/n and 69.98 MeV/n) were measured after escaping the beam pipe and found to be (3050 ± 40) μm and (8210 ± 90) μm, respectively. The longitudinal and projected angular spread of oxygen ions of an initial energy of 69.98 MeV/n in the region of the Bragg peak was derived from the measured geometrical parameters of tracks. Based on a calibration curve (etch rate ratio vs total linear energy transfer in CR-39) and the measured track length distribution at the range end of oxygen ions, the complete depth dose profile of a 67.7 MeV/n ¹⁶O beam in CR-39 (plateau, extended Bragg peak and residual ionization caused by projectile like fragments) was obtained.     

Study of projectile fragmentation in the reaction (158 A GeV) Pb + Pb using CR-39

The fragmentation of Pb ions at 158 A GeV energy produced in the interaction with Pb target has been studied using a CR-39 track detector. A stack comprising of 64 detectors was prepared such that a target of 1 cm thickness was sandwiched between the sheets of CR-39. The purpose of this exposure geometry was to calibrate CR-39 with respect to relativistic heavy ions as well as to study the fragmentation of Pb ions at 158 A GeV energy. The exposure was carried out at the SPS beam facility of CERN at normal incidence with a fluence of . Two detectors from the exposed stack have been selected for this study: one before and the other after the target material. After etching, the detectors were scanned using an optical microscope and the etched track lengths and the diameters of the track openings were measured manually. Considering that the lengths of tracks provide the best charge resolution for Z>65, we have measured track lengths for a sufficiently large number of fragments to identify individual charge states for 65<Z<83. The total charge-changing cross section has also been determined.     

Investigation of response of CR-39, PM-355 and PM-500 types of nuclear track detectors to energetic carbon ions

Samples of CR-39, PM-355, and PM-500 plastic detectors were irradiated with carbon ions of energy ranging from 0.9 MeV to 14.7 MeV. After the irradiation the detector samples were etched for a period from 2 hrs to 10 hrs. Dependence of track diameters on the ion energy values for different etching times, and dependence of V_T/V_B as a function of incident carbon-ion energy, are presented.     

A CR-39 based thermal neutron dosimeter

Both chemically and electrochemically etched CR-39 detectors are used for the detection of fast neutrons. In practical situations, fast neutrons are always accompanied by thermal neutrons. Therefore, the response of the CR-39 based dosimeter has to be extended to thermal neutrons. To do so, a radiator/converter like LiF is introduced in front of the CR-39 detector and an optimum thickness of the LiF film is determined so that a response similar to that of the fast neutrons is achieved. Thin films of natural LiF were prepared and the response of the CR-39 detector was studied as a function of the film thickness.