Photofission Of Uranium Research Articles

First Observation of Electron Scattering from Online-Produced Radioactive Target.

We successfully performed electron scattering off unstable nuclei which were produced online from the photofission of uranium. The target ^{137}Cs ions were trapped with a new target-forming technique that makes a high-density stationary target from a small number of ions by confining them in an electron storage ring. After developments of target generation and transportation systems and the beam stacking method to increase the ion beam intensity up to approximately 2×10^{7} ions per pulse beam, an average luminosity of 0.9×10^{26} cm^{-2} s^{-1} was achieved for ^{137}Cs. The obtained angular distribution of elastically scattered electrons is consistent with a calculation. This success marks the realization of the anticipated femtoscope which clarifies the structures of exotic and short-lived unstable nuclei.

Charting Terra Incognita at Alto and S3

Charting Terra Incognita is a project grant that brings together the IPN Orsay, CSNSM Orsay and Irfu-SPHN laboratories around the common development of knowhow, equipment and techniques for mass spectrometry and nuclear spectroscopy at the low-energy branch of the new S3 spectrometer at Ganil, where likewise the Reglis set-up for intrajet laser spectroscopy is entering its final phase of construction. At the same time its concerted action initiates and sets the pace for the corresponding precursor physics programme at the Alto on-line isotope-separation facility, based on the photofission of uranium. We also collect a review of the Alto laser ion source, which is an essential instrument at any low-energy facility for the production of purified isotopic beams.

Simulation of delayed γ-ray emission following photofission reactions induced by pulsed bremsstrahlung x-rays using MCNPX and experimental validation

There is a great demand to develop non-destructive techniques to identify and quantify Special Nuclear Materials (SNM) in homeland security and nuclear safeguards applications. Passive assay could be extremely challenging in some scenarios. Active interrogation technique based on photofission has been identified as one of the promising approaches. In radiation detection system design based on such technique, it is highly desired to have abilities to accurately and efficiently simulate delayed γ-rays emitted from photofission reactions. In this work, simulation results were compared with measurement outcomes to demonstrate the capabilities and limitations of the code MCNPX 2.7.0 in the simulation of delayed γ-rays from photofission of uranium and plutonium samples. First, high-energy delayed γ-rays (Eγ~2.7–4.5MeV) from photofission of 238U were simulated and validated against the energy spectra measured in between linac pulses. Second, low-energy delayed γ-ray spectra (Eγ~0.6–2.7MeV) measured with a list-mode system after irradiation of 239Pu were used in the validation.

Electron-beam-driven RI separator for SCRIT (ERIS) at RIKEN RI beam factory

We constructed a radioactive isotope (RI) separator named ERIS (electron-beam-driven RI separator for SCRIT) for the SCRIT (Self-Confinement RI Target) electron scattering facility at RIKEN RI Beam Factory (RIBF). In ERIS, production rate of fission products in the photofission of uranium is estimated to be 2.2×1011fissions/s with 30g of uranium and a 1-kW electron beam. During the commissioning of ERIS, the mass resolution and overall efficiency, including ionization, extraction, and transmission, were found to be 1660 and 21%, respectively, using natural xenon gas. The preparation of uranium carbide (UC2) RI production targets is described from which a 132Sn beam was successfully separated in our first attempt at RI production.

A technique for measuring the quadrupole deformation parameter of transuranium nuclei

A method for determining the quadrupole deformation parameter of transuranium nuclei is presented. This method is based on giant dipole resonance splitting in the photofission cross section. The experimental setup containing an avalanche counter of fission fragments, as well as a method for reconstructing the cross section from the measured dependence of the photofission reaction yield on the endpoint energy of the bremsstrahlung spectrum, are described. The setup was tested on the bremsstrahlung beam of the MT-25 microtron at the Flerov Laboratory for Nuclear Reactions of the Joint Institute for Nuclear Research. The test results—in particular, the measured excitation function of the uranium photofission reaction—are presented.

Determination of uranium photofission fragment (Xe, Sn, Sb, Te) yields over chlorine in on-line

In the framework of the Project DRIBs (Dubna Radioactive Ion Beams) the photofission reaction 238U(γ, f) has been studied at the FLNR (JINR) in view of producing beams of neutron-rich radioactive nuclei 132Sn and 142Xe using the MT-25 microtron [1].

RIB production with photofission of uranium

The process of uranium photofission with electron beams of 20–50 MeV is considered in terms of the production of fission fragments. It is shown that in the interaction between an electron beam (25 MeV in energy and 20 μA in intensity), produced by a compact accelerator of the microtron type, and a uranium target of about 40 g/cm 2 in thickness, an average of 1.5×10 11 fission events per second is generated. According to the calculations and test experiments, this corresponds to the yield of 132Sn and 142Xe isotopes of approximately 2×10 9/s. The results of experiments on the optimal design of the U-target are presented. Problems are discussed connected with the separation of isotopes and isobars for their further acceleration up to energies of 5–18 MeV A. The photofission reactions of a heavy nucleus are compared with other methods of RIB production of medium mass nuclei.

00/02555 Observation of uranium photo-fission by 16N decay gamma rays from water activated by D-T fusion neutrons

00/02555 Observation of uranium photo-fission by 16N decay gamma rays from water activated by D-T fusion neutrons

Observation of uranium photo-fission by 16N decay gamma rays from water activated by D-T fusion neutrons

Radioactive 16N is generated in pure water (H 2O) which has been exposed to D-T fusion neutrons with energies near 14 MeV. The principal neutron-activation reaction is 16O(n,p) 16N. Decay by β emission (100%) of the 7.13±0.02 s 16N activity is accompanied by production of energetic gamma rays (most of them with energies>6 MeV) that are associated with the prompt radiative de-excitation of various elevated energy levels of 16O populated through the process 16N( β-) 16O. The dominant gamma-ray emission branch energies (intensities) are 6.129 MeV (67.0±0.6%) and 7.115 MeV (4.9±0.4%). A particular given intensity refers to the percent of 16N decays that produce the indicated gamma ray. Both photons possess energies that are above the photo-fission threshold for the naturally occurring isotopes of uranium, namely, 234U, 235U, and 238U. This paper reports on an experiment that demonstrated 16N decay gamma-ray induced photo-fission in a commercial fission detector that contained 0.14 g of depleted uranium (predominantly 238U with a small trace of 235U). This detector was placed near a tubing system containing circulating water that had been activated by neutron bombardment as it passed near to the target of an intense D-T fusion neutron generator. The fission detector was situated in a shielded location remote from the source of primary D-T neutrons. Other possible mechanisms leading to the generation of the observed detector events were considered. Among these were natural background radiation (e.g., cosmic rays), delayed neutrons from the decay of 17N and 18N also produced in water by D-T neutrons, secondary neutrons from ( γ,n) reactions in materials near the detector, and electronic noise or pulse pileup. All of these alternative possibilities were ultimately rejected as significant contributors to the experimental detector counts by a detailed examination of the pertinent nuclear data and by specific measurements carried out in the present study. Photo-fission of 238U remained as the predominant source of the recorded fission-detector events after elimination of these other possibilities as significant contributors of observed counts. The anticipated photo-fission yield was calculated based on consideration of the experimental setup, tabulated cross sections, and other pertinent nuclear data. This analysis yielded results which were found to be consistent with the present experimental observations to within the combined — rather large — uncertainties. This outcome further supports the conclusion that photo-fission events were indeed observed in this experiment. Some engineering implications of this investigation, and potential applications for the observed phenomenon in contemporary nuclear fusion technology, are also discussed.

A Comment on the High-energy Photofission of Uranium

The peak-to-valley ratio in the bremsstrahlung induced fission of 238U has been measured at Emax = 800 MeV. The value obtained, 1.95±0.15, is in good agreement with earlier measurements at this laboratory. Current data on the peak-to-valley ratios at different maximum photon energies are presented and the discrepancies existing above 100 MeV discussed.

Angular distributions in photofission of uranium

The angular distributions in photofission of natural uranium have been measured. Bremsstrahlung with maximum energies of 10 and 20 MeV and monoenergetic gamma radiation of 6.1, 6.9 and 7.1 MeV energy were used as photon sources. The fission fragments were detected in two ways. One method was to irradiate nuclear emulsions containing uranium. In the other method a scintilation counter was used to detect the fission fragments. The first method is more tedious but has a considerably better angular resolution. The two methods give results which agree very well. The following results have been obtained: The angular distribution at 6.1 MeV is of the form 0.07+sin 2θ+0.37 sin 2 2θ. At 6.9 MeV the distribution 1+0.70 sin 2θ+0.05 sin 2θ was obtained. The distribution at 7.1 MeV is similar but somewhat more isotropic. The angular distribution obtained by 10 MeV bremsstrahlung is of the form 1+0.85 sin 2θ+0.13 sin 2 2θ. Irradiation with 20 MeV bremsstrahlung gives an isotropic angular distribution. The results of the present work are compared with the theory of A. Bohr. They agree very well with this theory. It is also possible to use these results to separate the photonuclear absorption at 6 MeV into a dipole and a quadrupole part. The quadrupole absorption in particular is discussed and compared with theoretical estimates.

121. The angular distribution of fission fragments in the photofission of uranium

121. The angular distribution of fission fragments in the photofission of uranium

Photo-Fission of Uranium with Possible Emission of a Beryllium Nucleus

IN the study of the slow-neutron ternary fission of uranium-235, there is evidence that short-range particles of greater mass than α-particles are emitted. Dewan and Allen1 have reported ionization chamber experiments indicating the emission of particles of mass 13 ± 4 having ranges less than 1 cm. of air, and Titterton2 has recorded events in photographic plates which suggest the emission of nuclei heavier than α-particles having ranges up to 3 cm. air equivalent. An example of such an event is given in Fig. 1, from which it will be seen that, owing to the short range of the third fragment, certain interpretation cannot be made.

Evidence for the Photo-Fission of Uranium into Three Charged Fragments

Evidence for the Photo-Fission of Uranium into Three Charged Fragments

X-Ray Yield Curves forγ−nReactions

Yield curves for the reactions ${\mathrm{C}}^{12}(\ensuremath{\gamma},n){\mathrm{C}}^{11}$ and ${\mathrm{Cu}}^{63}(\ensuremath{\gamma},n){\mathrm{Cu}}^{62}$ have been taken with x-rays up to 100 Mev. The induced radioactivity at each energy is plotted per unit x-ray intensity as measured by a $r$-meter thimble jacketed by ⅛ in. of Pb. Both yield curves are similar to the photo-fission yield curves, the x-ray yield increasing to a maximum and then slowly decreasing as the x-ray energy is increased. With simple assumptions regarding the generation of ionizing secondaries in the Pb walls of the monitor and assumption of a constant intensity x-ray spectrum, these curves can be analyzed. The relative cross section is found to have a maximum at approximately 22 Mev for ${\mathrm{Cu}}^{62}$ and 30 Mev for ${\mathrm{C}}^{11}$, decreasing to negligible values at high quantum energies. This decrease in cross section can be attributed to competition from multiple disintegrations. These reactions provide detectors sensitive only to part of the x-ray spectrum. Absorption curves have been taken in Pb using uranium photo-fission and in Cu and Pb using the ${\mathrm{Cu}}^{63}(\ensuremath{\gamma},n){\mathrm{Cu}}^{62}$ reaction as detectors. The resulting absorption coefficients compare favorably with theoretical values.

Threshold Measurements on the Nuclear Photo-Effect

The high voltage x-radiation from the betatron has been employed to produce ($\ensuremath{\gamma},n$) reactions in several elements of atomic number up to 47, the reaction observed by detection of induced radioactivity. The peak x-ray energy was controlled by integrating the voltage on the main coils with an RC circuit, which actuated the orbit expander at a predetermined electron energy. Upon irradiating samples at sequences of energies, measuring their activity with beta-counters, and plotting activities against peak energy, smooth curves were obtained from which thresholds were estimated. The accuracy of the method is limited by low activity in almost all cases and by uncertainties in energy output. The following thresholds in Mev have been measured: ${\mathrm{C}}^{11}$, 18.7 to 19.4; ${\mathrm{N}}^{13}$, 11.1\ifmmode\pm\else\textpm\fi{}0.5; ${\mathrm{O}}^{15}$, 16.3\ifmmode\pm\else\textpm\fi{}0.4; ${\mathrm{Fe}}^{53}$, 14.2\ifmmode\pm\else\textpm\fi{}0.4; ${\mathrm{Cu}}^{62}$, 10.9\ifmmode\pm\else\textpm\fi{}0.3; ${\mathrm{Zn}}^{63}$, 11.6\ifmmode\pm\else\textpm\fi{}0.4; ${\mathrm{Se}}^{79\phantom{\rule{0ex}{0ex}}\mathrm{o}\mathrm{r}\phantom{\rule{0ex}{0ex}}81}$, 9.8\ifmmode\pm\else\textpm\fi{}0.5 for the lower, short period isomer; ${\mathrm{Mo}}^{91\phantom{\rule{0ex}{0ex}}\mathrm{o}\mathrm{r}\phantom{\rule{0ex}{0ex}}93}$, 13.5\ifmmode\pm\else\textpm\fi{}0.4; ${\mathrm{Ag}}^{108}$, 9.3\ifmmode\pm\else\textpm\fi{}0.5; ${\mathrm{Ag}}^{106}$, 9.5. The first three are in fair agreement with other data, but because of exceptionally weak activities are not sufficiently reliable to afford a test of the method. Rough measurements on the uranium photo-fission threshold are also reported. Since the radiation from the betatron is continuous and its spectral distribution is unknown, the excitation curves are not susceptible to interpretation, and cross sections for the above reactions cannot be estimated at present.

Photo-Fission of Uranium and Thorium Produced by the γ-Rays of Lithium and Fluorine Bombarded with High Speed Protons

Photo-Fission of Uranium and Thorium Produced by the γ-Rays of Lithium and Fluorine Bombarded with High Speed Protons

Radioactive Barium and Strontium from Photo-Fission of Uranium

Radioactive Barium and Strontium from Photo-Fission of Uranium