60 MeV/u 18O离子同天然铀反应钡同位素截面的测定

通过60MeV/u18O离子照射天然铀靶产生Ba放射性同位素,使用BaCl2沉淀法从大量铀和其它反应产物混合物中分离出Ba.通过离线γ谱学方法测量了Ba样品的γ射线单谱,根据Ba同位素特征γ射线峰的强度及其它相关数据计算了Ba同位素的生成截面.发现在厚铀靶的情况下,缺中子Ba同位素仍有较高的截面. The radioactive Ba isotopes were produced by 60 MeV/u~(18)O ion bombardment of natural uranium. Ba was separated from U and the reaction product mixture by BaCl_(2) precipitation. The Ba fraction was measured by off-line γ-ray spectroscopy. The cross sections of the individual Ba isotope were calculation based on the intensities of the character γ-ray peaks of Ba isotopes and other relative information. It was found that the n-deficient Ba isotopes have higher cross sections using the thick uranium targets.     

Production cross-section of 230Ra in the reaction of 60 MeV/u 18O ions with 238U

A thick natural uranium target was bombarded with a 60 MeV/u ¹⁸O beam. The neutron-rich isotope ²³⁰Ra as the target residue was produced through the multinucleon transfer reaction(²³⁸U-4p-4n). The barium and radium fraction as BaCl₂ precipitate were radiochemically separated first from the mixture of uranium and reaction products. Then, the radium fraction was separated from BaCl₂ precipitate by using cation exchange technique. The γ-ray spectra of the Ra fraction were measured using an HPGe detector. The production cross sections of ²³⁰Ra were obtained by a combination of the radiochemical separation technique and off-line γ-ray spectroscopy. The cross section of ²³⁰Ra has been determined to be 66±20 μb.     

Fragment correlations in the reaction 9.03 MeV/u238U+natU

Kinematically almost complete correlation studies on heavy fragments in the reaction 9.03 MeV/u²³⁸U+^natU were performed using metaphosphate-glass detectors in a 2π-geometry technique. Absolute data for the total reaction cross-section and the partial cross-sections for the three-, four-, and five-body reaction channels were measured. The tracks of correlated particles were measured and converted into masses and energies. The reaction mechanism of each individual event was studied in terms of the separation velocities of correlated fragment pairs. Sequential fission following inelastic collision is found to account for all analysed events with more than two heavy nuclei in the exit channel. The masses, scattering angles, and energies of the first reaction step were reconstructed event by event.     

Fission following complete or incomplete fusion of 135 MeV16O and238U

From measurements of the laboratory angular distribution and the projected range distribution for each of 26 individual radioactive fission products from the interaction of 135 MeV¹⁶O on²³⁸U, we have determined for each product quantities including the average velocity,ν, of the parent fissioning system and the anisotropy,ω, of the fission angular distribution. We have interpreted the results in terms of two competing mechanisms: complete fusion and a process involving transfer of anα-particle from projectile to target followed by fission of²⁴²Pu. The values ofν lie betweenν _cn, the complete fusion value, and 0.3ν _cn, and can be taken as a measure of the relative importance of the two processes competing in populating each observed product. These two contributions to each measured product yield can then be separated, and understood using a simple model of the fission process. The data suggest that approximately 24% of the overall fission yield is due to incomplete fusion processes. The anisotropy,ω, is strongly correlated with the value ofν, indicating anisotropies of 1.4 and 2.8 for the two individual processes.     

Target Residues from the Interaction of Copper with 40MeV/u 40Ar Ions

Cross Sections and average forward recoil range FW were measured for target residues from the interaction of Cu with 40MeV/u ⁴⁰Ar ions using off-line y-ray spectroscopy.The mass yield distribution was obtained with assumption of charge distribution.The linear momentum transfer was calculated from FW values.A comparison with similar results of ¹²C+Cu and ²⁰Ne+Cu reactions indicates that the fractional linear momentum transfer,corresponding to central collisions,decreases with increasing projectile mass at the same energy per nucleon. However,the excitation energy of the composite system created from the collisions of Cu with ⁴⁰Ar ions reached the value of 5.3MeV /u and was higher than those from the collisions with ¹²C and ²⁰Ne ions.     

π− Production in16O +27Al at 38, 65 and 93 MeV/u

Negative pion production cross-sections are measured at 38, 65 and 93 MeV per nucleon in O + Al reaction. Rough estimations of the total cross sections are given and compared to previous neutral pion data. Double differential cross sections at 93 and 65 MeV/u show enhancement for pions with velocity close to the beam. At variance no effect is observed at 38 MeV, where π^? and π⁰ distributions are identical. Fewπ ⁺ detected at 38 MeV support this result. This indicates that at the lowest incident energy nearly the whole projectile participates in the production reaction.     

Investigation of the 40Ar + 197Au, 238U systems at 44 MeV/u

We have measured the angular correlation between two fragments emitted in the reactions Ar + Au and Ar + U at 44 MeV/u at GANIL. The aim was to investigate the amount of initial linear momentum transferred from the projectile to a fissioning nucleus. It turned out that this amount is much smaller than can be extrapolated from previous experiments. Furthermore, the probability of forming a fissioning nucleus is very small.     

Neutral pion production in subthreshold heavy ion collision with16O (38 MeV/u) and20Ne (200 MeV/u) beams

Inclusive production of neutral pions has been studied in¹⁶O +²⁷Al,¹⁹⁷Au reactions at 38 MeV/u and²⁰Ne +²⁷Al reaction at 200 MeV/u. A setup of 10 Pb glass Cherenkov detector telescopes was used to detect the twoγ rays from theπ ⁰ decay.     

Mass Yield Distribution of Target Residues from the Interaction of Iron with 135MeV/u 12C Ions

The formation cross sections of target residues have been measured from the interaction of iron with 135MeV/u ¹²C ions.With the help of assumption of Gaussian charge distribution,the mass yield distribution was obtained.We found that the yield in mass region of A＜30 were notably increased and the products got away to neutron-excessive.The experimental results were compared with calculations based on the statistical fusion fragmentation model and on the sequential binary decay model,respectively. It seems to indicate that the multifragmentation decay mode was the dominant reaction mechanism responsible for production of the fragments with mass number A＜30 in the produce process of target residues under the condition of the higher incident projectile energy.     

Fission and emission of H and He in the reactions of 215 MeV16O with181Ta,208Pb and238U

The reactions of 215 MeV¹⁶O with¹²C,¹⁸¹Ta,²⁰⁸Pb and²³⁸U have been studied. Inclusive measurements for⁴He emission are given from each target, and for fission and^1,2,3H from Ta, Pb and U. For H/He a high-energy, forward-peaked component is observed with characteristics similar to those reported by others. At backward angles a low-energy, nearly-isotropic component is also observed for⁴He that cannot be accounted for by emission from fully accelerated fission products. The spectral shapes for this evaporative component are compared with statistical model calculations, and information is obtained concerning the effective barriers to emission. For the reactions of¹⁶O with¹²C, complete fusion seems to be overwhelmed by incomplete fusion. Fission angular distributions and cross sections are also presented and discussed.     

Range and energy-loss of 16.34 Mev/u 238U in kapton polyamide

Abstract

The range and energy-loss of 16.34 MeV/u ²³⁸U in Kapton-polyamide plastic have been measured by the nuclear track technique. The experimental ranges are compared with two sets of theoretical values. It has been observed that ranges obtained from the computer code ‘DEDXT’ are found to be 5–8% lower as compared to measured ones whereas those from Northcliffe and Schilling are about 10–15% overestimated above 8 MeV/u.     

Evidence of complete fusion in the subbarrier 16O+238U reaction

Evaporation residue cross sections in the ¹⁶O+²³⁸U reaction were measured for the energy range from above-to extreme subbarrier. We used a He-gas-jet system to transport the fusion products, and the α decay of the evaporation residues was measured by using a rotating wheel system. The measured cross sections for ^248,249,250Fm are reproduced by a statistical model calculation, for which partial cross sections are calculated by a coupled-channel model taking into account the prolate deformation of ²³⁸U. We conclude that complete fusion is the main process in the subbarrier energy region, and quasifission is not an important channel. The text was submitted by the authors in English. On leave from China Institute of Atomic Energy, Beijing, China.     

Evidence of complete fusion in the sub-barrier 16O+238U reaction

Evaporation residue cross sections in the 16O+238U reaction were measured for the energy range from above- to extreme sub-barrier. The cross sections are reproduced by a statistical model calculation, for which partial cross sections are calculated by a coupled-channel model taking into account the prolate deformation of 238U. Complete fusion was observed in the collision of the projectile with the tips of the 238U target, in the same way as the side collision.     

Study of Yields for Target Fragments From the Reaction of Iron With 80MeV/u 16O Ions

Produchon yields were determined for 25 abet fragments produced from the reaction of iron with 80 MeV/u ¹⁶O ions. From these data, charge distribution and mass yield distribution have been deduced. The experimental results are compared with those reported from our previous work. It is found that the width parameter σ_z and the most probable charge Z_p of the charge distribution increase slowly with increasing bombarding energy. The mass yield distribution is discussed in terms of the concepts of limiting fragmentation and factorization.     

Production of medium-weight isotopes by fragmentation in 750 A MeV 238U on 208Pb collisions

Projectile fragmentation of ²³⁸U in a lead target was investigated at a bombarding energy of 750 A MeV. Isotopic production cross sections of about 250 different projectile fragments in the element range Z= 30–53 were measured with the FRagment Separator (FRS). The magnetic selection and the kinematical analysis of the measured isotopes allowed to disentangle fission and fragmentation residues. The mass loss of these residues indicates a violent collision where a large amount of energy is dissipated. The position of the fragmentation corridor defined by the measured residues was used to determine an effective proton-evaporation barrier. Received: 3 October 1997 / Revised version: 27 February 1998     

Energy Dependence of the Most Stable Nuclei Production in Proton-Induced 238U and 232Th Fission

Using the available experimental data, production cross sections of the most stable nuclei have been calculated for the proton-induced fission of ²³⁸U and ²³²Th at 12, 20, 35, 50, 96 MeV in case of ²³⁸U and at 8, 9.3, 12, 19.55, 32.2, 44.7, 53 MeV for ²³²Th. The analysis has been carried out for the fission fragment mass ranges corresponding to N/Z ratios in the ranges 1.33 ± 0.09 and 1.32 ± 0.08 for ²³⁸U and ²³²Th respectively. Results have been compared with the ones generated indirectly by employing GEF nuclear reaction code, version 2017/1.1. From the production cross sections point of view, for the same energy, ²³²Th is found to be a better target than ²³⁸U for producing nuclei A around the symmetric mass peak, while ²³⁸U comes out to be a better one than ²³²Th for producing the fission fragments around the asymmetric peaks of the mass distribution.

     

Spallation Yield of Neutrons Produced in Thick Lead Target by 400 MeV/u Carbon Ions

Measurement of the neutron yield is performed at a primary energy of 400 MeV/u carbons for the Pb target.Water-bath activation-foil method is used in a moderation measurement with Au foils to detect the moderated neutrons. The neutron yield is determined to be 18.4±2.1 per carbon by integrating the neutron flux over the entire water volume. The corresponding simulation values are performed by Geant4 code with three models to compare with the experimental results. The comparison shows that the calculated result with the INCL model is in good agreement with the experimental data.     

Neutron multiplicity in the fission of 238U and 235U with neutrons up to 200 MeV

Prompt-fission-neutron multiplicities were measured for 238U(n,f) and 235U(n,f) from 0.4 to 200 MeV. The data are of great importance in connection with accelerator-coupled nuclear reactor systems incinerating actinides. We report that fission induced by 200 MeV neutrons produces approximately 10 more prompt neutrons than fission induced by reactor neutrons. Most neutrons are evaporated from the fission fragments and the prefission compound nucleus, as the preequilibrium emission of energetic neutrons accounts for a maximum of 15% of the prompt neutrons at 200 MeV.     

Tracks of 18·56 MeV/u 40Ar ions in Lexan polycarbonate detector

Latent damage tracks of energetic⁴⁰Ar ions (18·56 MeV/u) have been recorded in Lexan polycarbonate detector. Bulk and track-etch parameters are evaluated under successive chemical etching. Our results show a linear correlation between the measured track-etch rate along the track and the corresponding total energy-loss rate and predict a threshold value of 5·0 MeV mg⁻¹ cm² for track registration. Maximum etchable track lengths of⁴⁰Ar ions as a function of energies have also been measured and compared with three different sets of theoretical ranges.