MeV 14N Ions Research Articles

The Effect of 147 MeV 84Kr and 24.5 MeV 14N Ions Irradiation on the Optical Absorption, Luminescence, Raman Spectra and Surface of BaFBr Crystals

Today, BaFBr crystals activated by europium ions are used as detectors that store absorbed energy in metastable centers. In these materials, the image created by X-ray irradiation remains stable in the dark for long periods at room temperature. As a result, memory image plates are created, and they are extended to other types of ionizing radiation as well. Despite significant progress towards X-ray storage and readout of information, the mechanisms of these processes have not been fully identified to date, which has hindered the efficiency of this class of phosphors. In this study, using photoluminescence (PL), optical absorption (OA), Raman spectroscopy (RS), and atomic force microscopy (AFM), the luminescence of oxygen vacancy defects to BaFBr crystals irradiated with 147 MeV 84Kr and 24.5 MeV 14N ions at 300 K to fluences (1010–1014) ion/cm2 was investigated. BaFBr crystals were grown by the Shteber method on a special device. Energy-dispersive X-ray spectroscopy (EDX) analysis revealed the presence of Ba, Br, F, and O. The effect of oxygen impurities present in the studied crystals was considered. The analysis of the complex PL band, depending on the fluence and type of ions, showed the formation of three types of oxygen vacancy defects. Macrodefects (tracks) and aggregates significantly influence the luminescence of oxygen vacancy defects. The creation of hillocks and tracks in BaFBr crystals irradiated with 147 MeV 84Kr ions is shown for the first time. Raman spectra analysis confirmed that BaFBr crystals were amorphized by 147 MeV 84Kr ions due to track overlap, in contrast to samples irradiated with 24.5 MeV 14N ions. Raman and absorption spectra demonstrated the formation of hole and electron aggregate centers upon swift heavy ions irradiation.

Hardening of reduced activation ferritic/martensitic steels under the irradiation of high-energy heavy-ion

In order to study the irradiation responses of reduced activation ferritic/martensitic (RAFM) steels which are candidates for fusion reactors, a reduced activation steel is irradiated at a terminal of HIRFL (heavy ion research facility in Lanzhou) with 63 MeV 14N ions and 336 MeV 56Fe ions at -50 ℃. The energies of the incident N/Fe ions are varied from 0.22 MeV/u to 6.17 MeV/u by using an energy degrader at the terminal, so that a plateau region of an atomic displacement damage (0.05-0.2 dpa) is obtained from the near surface to a depth of 24 μm in the specimens. Nanoindentation technique is used to investigate the nano-hardness changes of the samples before and after irradiation. The constant stiffness measurement is used to obtain the depth profile of hardness. The Nix-Gao model taking account of the indentation size effect (ISE) is used to fit the measured hardness and thus a hardness value excluding ISE is obtained. Consequently, the soft substrate effect for lower energy ion irradiation is effectively avoided. It is observed that there seems to be a power function relationship between the hardness and damage for the RAFM steel. The hardness initially increases significantly with the increase of irradiation damage, then increases slowly when the damage reaches to about 0.2 dpa. Positron annihilation is performed to investigate the defect evolution in the material. The positron annihilation lifetime spectra show that the long-lifetime proportion of the RAFM steel increases significantly after being irradiated. This means vacancy clusters are produced by the irradiation, resulting in the change of mechanics property. Even at low irradiation dose, point defects with high density are generated in the steel specimens, and subsequently aggregate into defect clusters, thereby suppressing the dislocation slip.The defect concentration in the material increases continuously with the increase of irradiation damage, which leads to the obvious irradiation hardening phenomenon. When the damage is higher than 0.1 dpa, the increment of mean lifetime gradually decreases due to the existence of a large number of vacancies and dislocations, and it eventually tends to be saturated, which explains why the irradiation hardening increment rate decreases with the increase of irradiation damage in the material.

Depth profiles of indentation hardness and dislocation mobility in MgO single crystals irradiated with swift 84Kr and 14N ions

The depth dependence of damage and modification of micromechanical properties in MgO single crystals irradiated with 150 MeV 84Kr and 24.5 MeV 14N ions (specific energy 1.75 MeV/u) at fluences up to 1015 ions/cm2 has been studied. The effects of ion-induced increase in hardness and reduction in dislocation mobility, magnitude of which varies along the ion range, were observed. These effects are related to ion-induced dislocations which were revealed by chemical etching. The results confirm a joint contribution of electronic excitations and atomic displacements by elastic collisions in the structural damage of MgO. The excitation mechanism in hardening dominates in the incoming part of ion range (up to the Bragg’s maximum), while the role of impact mechanism becomes dominant only at the end of ion range.

Energy loss in polycarbonate and polyethylene terephthalate by 2.0–6.5 MeV 14N, 31P and 75As ions

Energy loss for 2.0–6.0MeV 14N ions, 3.0–6.5MeV 31P ions and 3.0–6.5MeV 75As ions in thin foils of polycarbonate and polyethylene terephthalate were measured by means of a transmission technique using a half-covered silicon surface barrier detector. During the measurement, the charged particle count rates were kept below 100cps in order to minimize dead time and radiation damage in the system. The obtained data are compared with the SRIM 2003 calculation and the ICRU Report 73. Most of the measurement results compare quite favorably with the ICRU Report 73.

Experimental isotopic effects in comparison to statistical prescriptions for fragment production in 32A MeV and 14A MeV 14N + 112,124Sn reactions

Results on isotopic effects in the production of light fragments in reactions of 14A and 32A MeV 14N ions with 112Sn and 124Sn are presented. The data are discussed in the frameworks of classical Weisskopf evaporation and an alternative Fermi gas prescription. The source isospin dependence of the production rates is consistent only with the latter prescription. It is emphasized that similar data from p-nucleus reactions and from projectile-like fragments in 40Ar induced reactions behave in the same way.

Neoplastic Cell Transformation by Heavy Ions

We have studied the induction of morphological transformation by heavy ions. Golden hamster embryo cells were irradiated with 95 MeV 14N ions (530 keV/microns), 22 MeV 4He ions (36 keV/microns), and 22 MeV 4He ions with a 100-microns Al absorber (77 keV/microns) which were generated by a cyclotron at the Institute of Physical and Chemical Research in Japan. Colonies were considered to contain neoplastically transformed cells when the cells were densely stacked and made a crisscross pattern. It was shown that the induction of transformation was much more effective with 14N and 4He ions than with gamma or X rays. The relative biological effectiveness (RBE) relative to 60Co gamma rays was 3.3 for 14N ions, 2.4 for 4He ions, and 3.3 for 4He ions with a 100-microns Al absorber. The relationship between RBE and linear energy transfer was qualitatively similar for both cell death and transformation.

Angular Momentum Transfer in Reactions Induced by 14N Ions on 154Sm

The angular momentum input in reactions induced by 151 MeV 14N ions on 154Sm has been investigated by measuring the gamma-ray multiplicity in coincidence with emitted charged particles. The average multiplicity of gamma-ray cascades following the emission of protons, deuterons and tritons in reactions leading to 158Er amounts to 17.5 which is far below the value 31, earlier reported for a bombarding energy of 167 MeV. Predictions by Wilczynski's sum-rule model for complete and incomplete fusion reactions combined with statistical evaporation of particles are in good agreement with the present results.

Fission of medium mass elements induced by 126 MeV 14N ions

Ni, Se, Mo, Ag, Ho and Au targets were bombarded by 126 MeV 14N ions in order to study compound nucleus fission. The large angular momentum brought in by the projectile implies much greater fission probabilities than those obtained when the same compound nuclei are created with light projectiles. We employed two surface-barrier detectors. The results obtained are fission cross sections, angular correlations and kinetic energy and mass distributions. Fissilities are found to decrease exponentially with the ratio Z 2/ A of the fissioning nucleus until Z 2/ A = 19 (molybdenum) and then to increase again for lower Z 2/ A. The calculations of fissilities performed with the fission barrier of Myers and Swiatecki, and including angular momentum effects in evaporation-fission competition, gives the same variation of fissilities as the experimental one, but the results obtained are lower than the experimental values. The total kinetic energies measured are higher than the predictions of the liquid drop model by around 10 MeV (Nix). The shapes of the mass distributions indicate that the value of x BG (Businaro-Gallone point) is lower than 0.4 (silver).

Mesure de faibles sections efficaces de fission à l'aide de détecteurs à barrière de surface

The use of surface barrier detectors for the detection of fission fragments is difficult when the number of fragments is small relative to a large number of other charged particles, which may produce other coincidence events (random or true). It is especially difficult when the fragments kinetic energies do not differ very much from those of the other charged particles. From the measured kinetic energies of the coincident particles and the kinematics of fission in the laboratory system, we can calculate (1) the time-of-flight from the target to the detector for each particle, and (2) the difference in time-of-flight for each coincident event. If this event is due to fission and the fragment energies are correctly measured, this calculated difference must be equal to the measured time-of-flight difference. We applied this selection method to the fission of medium targets induced by 128 MeV 14N ions, and it proved to be very effective and easy to handle. In addition, this method eliminates most of the random coincidence events. The remaining part of random events is lower by an order of magnitude than it would have been with the usual fast coincidence method; moreover, this part is easily measured.

The cross sections for different channels in heavy ion nuclear reactions

Estimates have been made for the critical value lc of the orbital angular momentum above which a complete fusion nucleus cannot be formed. The results have been obtained by measurements of cross sections for noncompound inelastic processes (inelastic scattering, transfer. reactions, α particle emission) when Ag targets were bombarded by 86 MeV 12C ions and by 78 and 113 MeV 14N ions. The average value of lc was found between 38 and 45 ħ. A short discussion is given on the range of angular momenta at which transfer reactions occur. It is shown that quasi elastic single and multi-nucleon transfer reactions are possible only for large values of l called lT. When the bombarding energy is high enough, theses values lT are larger than lc and there is a region of l between l c and lT where a very inelastic mechanism takes place. A model called « fusion prompt scission » process is proposed. It is suggested that a deformed shape for the two fissioning nuclei is temporarly formed and breaks off very shortly after.

Mechanism of single-nucleon and multi-nucleon transfer reactions in grazing collisions of heavy ions on silver

A large number of products of transfer reactions has been identified when bombarding natural Ag and 109Ag by 86 MeV 12C and by 78 and 113 MeV 14N ions. From the analysis of angular and energy distributions, it has been shown that both multi-nucleon and single-nucleon transfer processes are ruled by two different mechanisms. (i) When the products are formed at the ground state or at relatively low excited states, the angular distribution can be interpreted in terms of a DWBA analysis of a quasi-elastic scattering. This first mechanism is responsible for the preferential emission at a particular angle which depends on the bombarding energy. (ii) When the products are formed with a very large defect of kinetic energy (more than 10 MeV), they are observed at very small angles. A qualitative explanation of this “grazing” process is tentatively given. The relative importance of the second mechanism is higher for a large number of transferred nucleons than for single-nucleon transfers and increases with the bombarding energy.

Effects of L.E.T. and temperature in the radiolysis of cyclohexane. Part 1 .—Experimental results and comparison with predictions of diffusion kinetic models

For low dose (∼3 × 1019 eV g–1) irradiations of liquid cyclohexane at room temperature, G values of hydrogen, bicyclohexyl and cyclohexene were measured, using a number of different kinds of radiation, viz. 60Co γ-rays, 4He ions of energy 58, 23, 8, 7, 3.03, 2.13, 1.53 MeV, 115 MeV 14N ions, and 22 MeV 20Ne ions. The effect of changing temperature was determined for 60Co γ-rays and for 3 MeV 4He ions. A search for high-molecular-weight products, determined by weighing, was also made in high-dose (1–9 × 1021 eV g–1) irradiations at high dose rate (1021–1022 eV g–1 s–1), using 7 MeV 4He ions and 115 MeV 14N ions; initial G values of 0.65 and 0.80 respectively for conversion to polymer were found. In some experiments, G values of minor products, ethane, ethylene, acetylene, propane, propene, butane, butenes, n-hex-1-ene, and cyclohexyl-cyclohexenes were also measured. Attempts were made to correlate our results for changing L.E.T. and temperature, and the results of others using scavengers, with two diffusion models, in which the effect of L.E.T. is due to the competing reactions of thermal hydrogen atoms and excited molecules respectively. The latter model, in which L.E.T. effects are due to events prior to radical formation, was the more successful. G values for 115 MeV 14N ions were higher than expected on the basis of their overall mean L.E.T.; an analysis in terms of secondary electrons suggested that only a small part of the discrepancy was due to energetic secondary electrons, so that other radial track effects may occur with high-energy heavy ions.

Light radioisotopes of platinum formed in the interactions of tantalum with nitrogen ions

Decay characteristics of light radioisotopes of platinum formed in the interactions of tantalum with 140 MeV 14N ions have been investigated. Values for the half-lives and gamma ray energies as determined by scintillation spectrometry are as follows: Principal γ-rays S. no. Nuclide Half-life (MeV) 1. 189Pt 11 hr 0·140 2. 187Pt 2·1 hr 0·110, 0·180, 2·01 3. 186Pt 2·8 hr 0·065, 0·140, 0·190, 0·68, 1·140 4. 185Pt 60 min 0·035, 0·63, 1·56 5. 184Pt 42 min 0·68, 1·72, 1·85 Most of the γ-rays reported to be associated with the daughter iridium isotopes have also been confirmed.

Isomeric yield ratios of 44Sc produced by the 14N bombardment of 32S and 31P

Thick targets of red phosphorus and zinc sulphide were bombarded with 27·5 MeV 14N ions accelerated in the Oak Ridge 63 in. Cyclotron. Cross sections, as a function of the bombarding energy, were measured for the production of 43Sc, 44 m Sc, and 44 g Sc from 31P and 32S. The irradiated materials were γ-counted, and the radioactive products were identified by their characteristic γ-rays and half-lives. From the cross sections, the isomeric yield ratios of 44m Sc 44g Sc were found. For 31P the isomer ratio varied from 0·68 at 23·5 MeV to 1·68 at 27·0 MeV, while for 32S it varied from 0·12 at 20·5 MeV to 1·15 at 27·0 MeV. This increase in the ratio for both reactions is consistent with a compound nucleus formation mechanism for 44Sc at all energies considered. Accordingly, the higher ratio in the phosphorus reaction than in the sulphur reaction may be attributed to the smaller amount of angular momentum taken off by the single proton emitted from the 31P reaction than by the two protons emitted in the 32S case.