Number Of Nuclear Reactions Research Articles

Cross-section measurements to low-lying excited final states in the Mg24(α,p)Al*27(γ) reaction as an energy source for x-ray bursts

Energy production in Type Ia x-ray bursts depends on a number of nuclear reactions that become efficient in a hot environment (up to 2 GK). Model sensitivity studies have been performed in an effort to better identify the reactions that have the largest effect, but these efforts are hampered by the high level of complexity of the astrophysical model and large nuclear physics uncertainties. In a recent study, the $^{24}\mathrm{Mg}(\ensuremath{\alpha},p)^{27}\mathrm{Al}$ reaction was found to significantly affect the energy generation in x-ray bursts. This manuscript reports the first study of the $^{24}\mathrm{Mg}(\ensuremath{\alpha},{p}_{1,2}\ensuremath{\gamma})^{27}\mathrm{Al}$ reaction at energies relevant for x-ray bursts. The branches to the $^{27}\mathrm{Al}$ excited states increase to a small degree the estimates of the total astrophysical $^{24}\mathrm{Mg}(\ensuremath{\alpha},p)^{27}\mathrm{Al}$ reaction rate.

Application of Extraction Chromatography for the Preparation of High Purity 111In for Medical Use

Indium isotopes, mainly In‐111, are frequently used in nuclear medicine, both in therapeutics and diagnostics. Therefore the preparation of high‐purity In‐111 solutions from irradiated targets is of great interest. In‐111 can be produced by a large number of nuclear reactions, e.g. from cadmium targets, preferably from enriched Cd‐112 targets, by irradiation with protons or deuterons. Reliable methods for preparing In‐111 radioisotope solutions of high radiochemical and chemical purity are thus needed. This work illustrates a fast and convenient way for further purification of 111In solutions shortly before their use. Elution studies have been undertaken to examine the behavior of cadmium and indium isotopes on four commercially available SPE materials—TRU Resin®, Ln Resin®, and Ac Resin®—all of which are manufactured by Eichrom Technologies, Inc. These resins were found to be best suited for 111In separation. Reaching high yields of 111In with high chemical purity, i.e., very low concentration of unwanted elements (preferably below the limit of detection <10−8).

Unified model of nuclear mass and level density formulas

Nuclear ground and excited state properties are described by using parameter systematics on mass and level density formulas. The formulas are based on an analytical expression of the single-particle state density by introducing the shell-pairing correlation in a new way. Main features are the shell, pairing, and deformation effects on the droplet model near the ground state, which are washed out at higher excitation energies. The main aim of the paper is to provide in the analytical framework the improved energy dependent shell, pairing, and deformation corrections generalized to the collective enhancement factors, which offer a systematic prescription over a great number of nuclear reactions. The new formulas are shown to be in close agreement with not only the empirical nuclear mass data but also the measured slow neutron resonance spacings and experimental systematics observed in the excitation energy dependent properties.

Measurement of the Ion Temperature in Laser-Driven Fusion

Using the time-of-flight technique, energy distribution measurements were made of the $\ensuremath{\alpha}$ particles emitted from laser implosions of DT gas in glass microshells. The number of nuclear reactions was determined by an absolute measurement of the number of $\ensuremath{\alpha}$ particles. From the width of the energy distributions, upper limits of the plasma ion temperature have been inferred.

Recoil Properties ofSm142from Nuclear Reactions Induced by Heavy Ions. I. Samarium Compound Systems

By means of thin-target differential-range experiments, the average ranges and range straggling 72-min Sm/sup 142/ recoils from a number of nuclear reactions induced by heavy ions were measured. Beams of Li/sup 6/, Li/sup 7/, B/ sup 10/, C/sup 12/, and N/s up 14/ with kinetic energies up to 10.5 Mev per nucleon were used in conjunction with targets of Cs/sup 133/, Ba/sup 137/, Ba/sup 137/, Ba/sup 138 La/sup 139/, and Pr/sup 141/. A range-energy curve was obtained for Sm/sup 142/ in Al, covering the region 2- to 10-Mev recoil energy. Strong evidence for a pure compound nucleus reaction mechanism is provided by the uniqueness of the rangeenergy curve for all the reactions, Gaussian-range distributions, and direct comparison of the experimental ranges with stopping theory. The reaction Nd ( alpha ,4n)Sm/sup 142/ was studied by integral range methods, and the average ranges in Nd were found to be consistent with theoretical expectations when projected ranges were corrected to true ranges. The experimental straggling parameters are compared with theoretical predictions of straggling inherent in the stopping process. For Li/sup 6/ and Li/sup 7/ experiments, where the recoil velocities are smaller than the Bohr velocity (2.2 x 10/sup 8/ cm/sec), an attempt ismore » made to extract the range straggling due to the nuclear reaction. From this analysis, qualitative information is obtained about the average total energy removed by neutrons and photons. (auth)« less

Statistical emission of nucleons in reactions produced by 14 MeV neutrons

We have analysed a certain number of nuclear reactions for medium and light nuclei (10<Z<40), particularly (n, p) reactions with 14 MeV neutrons. The expressionn(ɛ)/ɛσ*, which is proportional to the nuclear level density, is represented fairly well, forɛ in the range (4÷10) MeV, by an exponential law of the kindee/θ, beingθ=(1÷1.2) MeV for medium nuclei (20<Z<40) andθ=1.45 for lighter nuclei.σ* has been calculated assumingr0=1.4·10−13 cm for neutrons andr0=1.6·10−13 cm for protons. On such a basis the ratioσ(n, p)/σ(n, nI) is in good agreement with the evaporative model when one considers theQ values of the reaction and the fact that the residual nucleus is even-even or odd-odd. From such ratio, calculated for evenA nuclei, it is possible to obtain values of the pairing energyA in good agreement with that calculated by Cameron. Also for (n, 2n), (n, np) and (p, n) reactions on medium nuclei, the evaporative model gives satisfactory results for the interpretation of the cross-section variations.

The Evolution of the Stars

PROF. G. GAMOW has recently discussed in NATURE1 the consequences of recent developments in nuclear theory on the problem of stellar evolution. In the light of the exact knowledge that is now available of a large number of nuclear reactions, it is possible to decide which processes rise to importance at the densities and temperatures prevailing in the stars, and on this basis trustworthy estimates have been given for the rate of liberation of subatomic energy. These results, which are the outcome of laboratory investigations, furnish the mathematical theory of internal constitution of the stars with a new equation that enables the luminosity of a star to be calculated by direct methods. The information so obtained has been utilized to attempt to resolve the many paradoxes and discrepancies encountered in discussing the general problem of stellar evolution. All this recent work has been authoritatively summarized by Gamow with great clarity and understanding in the article referred to above. It is therefore with some surprise that we find that Prof. Gamow concludes his article with the impression that these now developments practically solve the problems of stellar evolution. This seems to us to be so far from being the case that some further discussion of the claims of nuclear theory as the main factor in stellar evolution would be desirable.

The energies of nuclear reactions

It has been shown in previous papers that the nuclei of the radioactive atoms probably have equally spaced energy levels so that the energies of the rays emitted by the nucleus are equal to multiples of a constant q = 3·85 × 10 5 electron volts. Several light elements also appear to have nuclear levels with differences equal to q within the rather large limits of error. We should therefore expect the energies set free in nuclear reactions to be equal to multiples of q . The electronic energies of the light elements are small compared with q , so that the observed energies should be multiples of q . The energies of considerable number of nuclear reactions have been measured, but only a few with sufficient accuracy to show whether they are or are not equal to multiples of q . The energies of the 17 nuclear reactions given in a recent paper by Oliphant, Kempton, and Rutherford are given in Table I. The energies are in atomic weight units equal to 9·315 ×10 8 electron volts. Some of the values have been increased slightly since they were not quite accurately calculated from the energies in electron volts.

Societies and Academies

LONDON Royal Society, March 14. M. L. E. OLIPHANT, A. E. KEMPTON and LORD. RUTHERFORD: The accurate determination of the energy released in certain nuclear transformations. If changes of mass are taken into account, the law of conservation of energy holds closely for the transformations of the isotopes of lithium when bombarded by ions of ordinary and of heavy hydrogen. The masses of Li6 and Li7 are found to be 6-0143 ± 0-0002 and 7-0148 ± 0-0002 respectively, in good agreement with the mass spectroscopic values 6-0145 ± 0-0003 and 7-0146 ± 0-0006 found by Bainbridge. By application of the laws of conservation of momentum and energy, the mass of the hydrogen isotope of mass 3 is found to be 3-0152 ± 0-0002. Attention is directed to the factors involved in determining the mean ranges of expelled particles and to the difficulties of interpretation when more than two particles are emitted in a single transformation. While there is good agreement in the case of lithium, which involves the masses of particles measured in terms of helium, a number of nuclear reactions in beryllium and other elements show large discrepancies on the accepted mass scale. These reactions, as well as those in lithium, can be brought into line by assuming a small error in the helium oxygen ratio. H. J. TAYLOR: The tracks of a-particles and protons in photographic emulsions, a-particles and protons give tracks in photographic emulsions, which are visible, after development, as rows of grains in straight lines. These tracks have been studied, using special emulsions more suitable for such work than those commercially obtainable. Exposure of a plate to a neutron source gives rise to well-defined tracks, which are due to the protons ejected by the neutrons in their passage through the gelatine of the emulsion. The method is, however, unsuitable for quantitative study of neutron energies.

The Evolution of the Stars

PROF. G. GAMOW has recently discussed in NATURE1 the consequences of recent developments in nuclear theory on the problem of stellar evolution. In the light of the exact knowledge that is now available of a large number of nuclear reactions, it is possible to decide which processes rise to importance at the densities and temperatures prevailing in the stars, and on this basis trustworthy estimates have been given for the rate of liberation of subatomic energy. These results, which are the outcome of laboratory investigations, furnish the mathematical theory of internal constitution of the stars with a new equation that enables the luminosity of a star to be calculated by direct methods. The information so obtained has been utilized to attempt to resolve the many paradoxes and discrepancies encountered in discussing the general problem of stellar evolution. All this recent work has been authoritatively summarized by Gamow with great clarity and understanding in the article referred to above. It is therefore with some surprise that we find that Prof. Gamow concludes his article with the impression that these now developments practically solve the problems of stellar evolution. This seems to us to be so far from being the case that some further discussion of the claims of nuclear theory as the main factor in stellar evolution would be desirable.