The fission systematics of (15.9 MeV/u) Au ions in polymer CR-39

It has been demonstrated that high-energy heavy ions undergo fission while propagating in dielectric solids. Since these materials act as particle detectors because of their ability to retain primary ionization damage that can be fixed and enlarged with chemical etching, therefore, in principle, a complete kinematical analysis of fission events is possible. The crucial point in this regard is the availability of a well-calibrated range-energy relation, which is necessary for mass identification. We have developed an analytical method to convert the geometrical parameters of fission fragment tracks into physical parameters using an equation that expresses velocity as a polynomial of mass and range. A set of nine different polynomials was used to represent small regions of mass and range in order to improve accuracy. In the case of (15.9 MeV/u) Au ions incident normally on CR-39, we have found about 200 events which could be categorized as in-flight fission of Au ions inside the body of the detector. Mass distributions and cross sections of fission events have been calculated.     

Projectile fragmentation of silicon ions at 490 A MeV

Fragmentation cross sections are essential input parameters for propagation calculations which describe the effect of shielding against cosmic ray heavy nuclei by the walls of spacecraft or planetary habitat. Cross sections for the breakup of different elements are needed for different types of target material and for a wide range of energy.

For this purpose, we have extended our studies of projectile fragmentation. By using stacks containing CR-39 track detectors and targets ranging from CH₂ to Pb we have measured total and elemental fragmentation cross sections for fragments with charges Z_F>5, for silicon projectiles with energies of 490 AMeV. These new data sets allow us to improve our knowledge about the target and energy dependence of fragmentation cross sections.     

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.     

Track etch rates along the trajectories of nitrogen and oxygen ions in CR-39

Experimental studies on track etch rates in CR-39 performed with protons, deuterons and alpha particles as well as ⁷Li, ¹¹B and ¹²C ions were extended to ¹⁴N and ¹⁶O ions. The results are compatible with the general systematics found for the dependence on the kind of ion and its initial energy. Analysing the etch rate ratios as function of the restricted energy loss (REL), the non-existence of a unique relationship has been confirmed. However, assuming a dependence of the etch rate ratio not only on REL, but also on the depth within the detector where a given REL value occurs, all experimental data could be adjusted. The experiments with ¹⁴N and ¹⁶O ions allow extension of the REL range studied up to about 14 000 MeV/cm. The whole area relevant to neutron-induced charged particles generated within the CR-39 detectors is covered thereby. Having added the data for ¹⁴N and ¹⁶O ions, the array of curves for the etch rate ratio could be expanded up to 14 000 MeV/cm without inconsistencies, demonstrating the compatibility of the new data set also quantitatively.     

Projectile fragmentation of O and S at 3.65 GeV/n on several targets

We investigate the charge changing collisions for ¹⁶O and ³²S beams at 3.65 GeV/n on several targets, by using Solid State Nuclear Track Detectors (SSNTD). Track measurements were performed by an automatic measurement system. We determined the total charge changing cross sections and the elemental cross sections for the production of fragments of charge 9 ≤ Z ≤ 14. Comparison with theoretical models as well as with experimental data are given.     

Comparison of responses of CR-39 and PM-355 track detectors to fast protons, deuterons and He ions within energy range 0.2–4.5 MeV

The paper presents new results of the calibration of the standard CR-39 and super-grade PM-355 plastic detectors, which are applicable for the registration of the protons, deuterons, and ⁴He-ions. The calibration diagram show track diameters vs particle energy for different etching times.     

氦,氖,氩气体压力对氖光谱和能级填充的影响

以＾２３８Ｐｕ为激发源，测量了不同压力下Ｎｅ、Ｈｅ－Ｎｅ、Ｈｅ－Ｎｅ－Ａｒ体系的氖光谱，并以此为基础计算了Ｎｅ的２ｐ＾５３ｐ的１０个２ｐ能级的辐射率Ⅰ、相对集居数Ｎ、填充率Ｗ，总结出相应的Ｎｅ压力、Ｈｅ压力和Ａｒ压力对Ｎｅ的５８５．２ｎｍ谱线强度和１０个２ｐ能级填充的影响规律。     

The fragmentation of 20Ne at 400 A MeV

The total charge-changing cross sections and partial cross sections for the production of projectile fragments are measured in the interactions of 400 A MeV ²⁰Ne with aluminum, carbon and polyethylene targets sandwiched with CR-39 plastic nuclear track detectors. The measured total charge-changing cross sections are compared with the predictions using the Bradt-Peters semi-empirical formula, and the NUCFRAG2 and PHITS models. It is shown that the measured experimental results are in good agreement with the theoretical model prediction and other experimental results, and it can be clearly seen that the partial cross sections for fragment production show obvious odd-even effects.     

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.     

Investigation of free radicals induced by light ions in CR-39 using ESR spectroscopy

In previous investigations the formation of radicals induced by γ-irradiation in CR-39 samples has been studied by electron spin resonance (ESR) spectroscopy. On the other hand, all attempts fail to detect radicals in samples irradiated by particles (p, and neutrons). The present work succeeded in detection of radicals produced by charged particle radiation in CR-39 (TASTRAK). The detectors were irradiated with protons of 7 MeV and -particles of 3 MeV with fluences in the order of 10¹¹–10¹² particles/cm². The observed ESR signal is composed of at least four different resonance lines for each of which we determined the amplitudes, g-factors, lifetimes and the G-value. The amplitude of the total ESR signal decreases rapidly with a short and a longer lifetime. About 5 days after irradiation the ESR intensity decreased to an undetectable value. The lowest detectable dose (LDD) is of the order of 1 kGy.     

Fragmentation of 370 MeV/n 20Ne and 470 MeV/n 24Mg in light targets

Total charge-changing cross sections and cross sections for the production of projectile-like fragments were determined for fragmentation reactions induced by 370 MeV/n ²⁰Ne ions in water and lucite, and 490 MeV/n ²⁴Mg ions in polyethylene, carbon and aluminum targets sandwiched with CR-39 plastic nuclear track detectors. An automated microscope system and a track-to-track matching algorithm were used to count and recognize the primary and secondary particles. The measured cross sections were then compared with published cross sections and predictions of different models. Two models and the three-dimensional Monte Carlo Particle Heavy Ion Transport Code System (PHITS) were used to calculate total charge-changing cross sections. Both models agreed within a few percent for the system ²⁴Mg + CH₂, however a deviation up to 20% was observed for the systems ²⁰Ne + H₂O and C₅H₈O₂, when using one of the models. For all the studied systems, PHITS systematically underestimated the total charge-changing cross section. It was also found that the partial fragmentation cross sections for ²⁴Mg + CH₂ measured in present and earlier works deviated up to 20% for Z = 6–11. Measured cross sections for the production of fragments (Z = 4–9) for ²⁰Ne + H₂O and C₅H₈O₂ were compared with predictions of three different semi-empirical models and JQMD which is used in the PHITS code. The calculated cross sections differed from the measured data by 10–90% depending on which fragment and charge was studied, and which model was used.     

Computation of etched track profiles in CR-39 and comparison with experimental results for light ions of different kinds and energies

Computation of etched track profiles needs the knowledge of the variable track etch rates along the ion trajectories. Using the depth-dependent track etch rates experimentally determined for perpendicularly incident protons, deuterons and alpha particles as well as ⁷Li, ¹¹B, ¹²C, ¹⁴N and ¹⁶O ions of different energies simulations of the track development were performed. Two models of track etching were applied for that purpose recently published in literature. Although the models are based on the same physical fundamentals the results are slightly different. The reasons of the discrepancies were found by analysing the algorithms in detail. Comparison of the calculated track profiles with those determined experimentally from longitudinal sections of the etch pits showed good agreement for non-overetched as well as overetched tracks. The consistency of the whole experimental data set was checked by analysing the correlation of the track etch rates with geometric track parameters for all kinds of ions and etching times covered by the experiments.     

Observation of the reaction products formed in the interaction of 3.65 A GeV O ions with thick copper target at wide angles

Experiments have been carried out to study the ‘heavy fragments’ emitted at wide angles in the interaction of 3.65 A GeV ¹⁶O ions with a thick Cu target, using a stack of CR-39 track detectors. Diametric distribution in a stack registering ¹⁶O-beam halo are compared with diameters observed in a stack placed downstream at an angle of 25°. There is a strong indication that the heavy fragments are scattered at large angles.     

Extension of alpha particles in CR-39-etched track depth model to heavier ions

In this paper, the previous modeling of protons and alpha particles tracks depth in CR-39 nuclear track detectors was extensively extended to describe tracks of heavier ions. These ions include deuteron, lithium, boron, carbon, nitrogen and oxygen. Based on a compilation of published experimental results related to these ions, a set of empirical fitted model parameters is obtained for each type of ion. The A dependence of these model parameters is obtained.     

MeV氢微团簇离子与固体介质的电荷交换

利用静电加速器提供的0.6—1.8MeV的H⁺，H⁺₂，H⁺₃离子，轰击不同厚度的碳膜，分别测量这些离子通过碳膜后各种产物的产额. 得到了不同能量的H⁺通过碳膜后中性原子H和负离子H^-的产额随入射质子速度的变化关系；分别得到能量为1.2MeV,1.8MeV的H⁺₂，H⁺₃团簇离子通过不同厚度碳膜的透射产额及其与团簇离子在碳膜中驻留时间的关系；对结果进行了理论分析与讨论. 关键词： 团簇离子 电荷交换     

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.     

Fragment angular correlation in the breakup of 16O ions at 95 MeV/A

Fragment angular correlations in projectile breakup reactions are very sensitive to interference between different multipolarities entering in the excitation-dissociation process of the projectile. In particular, it was proposed to disentangle L = 1 and L = 2 contributions in direct breakup reactions of ¹⁶O with low relative energy between the α and ¹²C fragment, which are of astrophysical interest. We studied the experimental aspects of extracting those angular correlations in extreme kinematical conditions usually encountered in breakup experiments of astrophysical interest. The breakup of 95 MeV/A ¹⁶O projectiles induced by a ²⁰⁸Pb target was measured using the high-resolution spectrometer SPEG at Ganil for the coincident detection of the fragments. Sequential breakup via the 12.53 MeV level of ¹⁶O is analyzed in this framework and it favors an one-step M2 excitation of this level.     

Measurement of target fragments produced by 160 MeV proton beam in aluminum and polyethylene with CR-39 plastic nuclear track detectors

Production of target fragments from reactions of 160 MeV proton beams in aluminum and polyethylene was measured with CR-39 plastic nuclear track detectors (PNTD). Due to the detection limit of PNTD, primary protons cannot be detected; only low-energy short-range target fragments are registered. As a feasibility study, a so called “two step etching method” was employed to get the linear energy transfer (LET) spectra, absorbed dose, and dose equivalent. This method is discussed in this paper, together with the measured results.