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The neutron rich $$^{123}$$ Ag nucleus was populated via induced photofission of UC $$_x$$ at the ALTO ISOL facility. Its $$\beta $$ -decay properties were studied by means of detecting $$\beta $$ -delayed $$\gamma $$ and neutron activities. The measured half-life T $$_{1/2}$$ = 0.350(20) s agreed with the earlier data; the $$\beta $$ -delayed neutron emission branching P $$_{1n}$$ = 1.01(24)% was reestablished using $$\gamma $$ and neutron counting.

Photofission fragments mass yield for $$^{232}\hbox {Th}$$ , $$^{234,238}\hbox {U}$$ , $$^{237}\hbox {Np}$$ , and $$^{239,240,242}\hbox {Pu}$$ isotopes are investigated. The calculations are done using a developed approach based on Gorodisskiy’s phenomenological formalism. The Gorodisskiy’s method is developed to be applied for the neutron-induced fission. Here we revised it for application to photofission. The effect of emitted neutron prior to fission on the fission fragment mass yields has also been studied. The peak-to-valley ratio is extracted for the $$^{240}\hbox {Pu}$$ isotope as a function of energy. Obtained results of the present formalism are compared with the available experimental data. Satisfactory agreement is achieved between the results of present approach and the experimental data.

At ELI-NP, high-power lasers together with a very brilliant γ beam are the main research tools. The high-power laser system (HPLS) and the γ beam system (GBS) of ELI-NP are presented. The expected performance of the electron accelerator and production lasers of the GBS, and the targeted operational parameters of the γ beam are described. Possible laser-induced fission and γ beam photofission experiments which are under preparation at ELI-NP, and the different set-ups and instrumentation, are designed for these experiments, are presented.

An ISOL post-accelerator type of RIB facility is being developed at Variable Energy Cyclotron Centre (VECC), Kolkata, India. In this scheme, Rare Ion Beams (RIBs) will be produced using light ion beams (p, α) from the K=130 cyclotron, the RIB of interest will be separated from the other reaction products and accelerated up to about 2 MeV /u using a number of linear accelerators. Recently, a few RIBs have been produced and accelerated using this facility. As an extention of this effort, another RIB facility – ANURIB will be developed in a new campus as a green-field project. ANURIB will have two driver accelerators – a superconducting electron LINAC to produce n-rich RIBs using photofission route and a 50 MeV proton cyclotron for producing p-rich RIBs. In this paper, the status of the RIB facility in the present campus and future plans with the ANURIB facility will be discussed.

The ratio of the probabilities of population of the isomeric and ground states, so called the isomeric ratio is closely connected to the angular momentum of the initial fission fragments that is dissipated at the later stages of gamma ray cascade. This ratio also provides important information on the nuclear level structure as well as the nuclear reaction mechanism involved. In this work, the isomeric ratio in fission fragment 135Xe from photofission of 233U induced by 23.5 MeV bremsstrahlung has been determined by the method that uses inert gaseous flow. The results have been discussed and compared with that of other authors.

Fission fragment angular distribution measurements of even-even (232Th) and odd mass (237Np) nuclei were carried out using bremsstrahlung radiation in the energy range 7.4 to 9.2 MeV from variable energy microtron at Mangalore University. In the present work SSNTD lexan polycarbonate films were used to detect the fission tracks from both even-even (232Th) and odd mass (237Np) nuclei. From the knowledge of track density formed from photofission reaction of 232Th and 237Np, angular distribution of fission fragments was measured. The results obtained are discussed on the basis of Age Bohr theory in this paper.

Nuclear waste management cost at CEA is a heavy budget share. Therefore, it is important, in order to minimize that cost, to select the most suitable repository for the waste. Significant cost savings are obtained, for example, whenever a medium activity waste drum initially filed to end up in a geological repository can be measured accurately enough to be accepted by the Centre de Stockage de l’Aube (CSA). Photofission can be used as a non-destructive technique to measure the actinide content embedded in a nuclear waste drum. It can even be applied when the waste is packaged in its heavy concrete shielding. It is equally sensitive to non-fissile nuclear material. However, the present state of art suffers from a lack of sensitivity to be able to help redirecting the waste to the proper repository. A new program called INPHO is proposed at CEA Saclay aiming at enhancing the sensitivity sufficiently to be applicable for waste characterization.

The perspectives for photonuclear experiments at the new Extreme Light Infrastructure - Nuclear Physics (ELI-NP) facility are discussed in view of the need to accumulate novel and more precise nuclear data. The parameters of the ELI-NP gamma beam system are presented. The emerging experimental program, which will be realized at ELI-NP, is presented. Examples of day-one experiments with the nuclear resonance fluorescence technique, photonuclear reaction measurements, photofission experiments and studies of nuclear collective excitation modes and competition between various decay channels are discussed. The advantages which ELI-NP provides for all these experiments compared to the existing facilities are discussed.

We have calculated the fission probabilities for 237-Np, 233,235,238-U, 232-Th, and nat-Pb following the absorption of photons with energies from 68 MeV to 3.77 GeV using the RELDIS Monte-Carlo code. This code implements the cascade-evaporation-fission model of intermediate-energy photonuclear reactions. It includes multiparticle production in photoreactions on intranuclear nucleons, pre-equilibrium emission, and the statistical decay of excited residual nuclei via competition of evaporation, fission, and multifragmentation processes. The calculations show that in the GeV energy region the fission process is not solely responsible for the entire total photoabsorption cross section, even for the actinides: ~55-70% for 232-Th, \~70-80% for 238-U, and ~80-95% for 233-U, 235-U, and 237-Np. This is because certain residual nuclei that are created by deep photospallation at GeV photon energies have relatively low fission probabilities. Using the recent experimental data on photofission cross sections for 237-Np and 233,235,238-U from the Saskatchewan and Jefferson Laboratories and our calculated fission probabilities, we infer the total photoabsorption cross sections for these four nuclei. The resulting cross sections per nucleon agree in shape and in magnitude with each other. However, disagreement in magnitude with total-photoabsorption cross-section data from previous measurements for nuclei from C to Pb calls into question the concept of a ``Universal Curve'' for the photoabsorption cross section per nucleon for all nuclei.

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].

Some of the most noticeable resonance structures in the energy dependence of nuclear cross sections and other reaction characteristics, for example, the kinetic energy and angular anisotropy, of fission fragments are correlated for different nuclei irrespective of the parity of their atomic number and mass number. The resonance structures in the neutron cross sections can also correlate with the structure of the cross sections of photonuclear reactions with equal wave length of the neutron and γ radiation. These correlations could be due to the diffraction of waves by the spatial structures of a nucleus, for example, isolated nuclear shells.

Recoil properties and yields of radionuclides formed in the photofission of 197Au and 209Bi by bremsstrahlung of end-point energies (E0) from 300 to 1100 MeV have been investigated using the thick-target thick-catcher method. The kinetic energies T of the residual nuclei were deduced based on the two-step vector model and discussed by comparing with the reported results on protoninduced reactions as well as those on photospallation. The charge distribution was reproduced by a Gaussian function with the most probable charge Zp expressed by a linera function of the product mass number A and with the A-independent width FWHMCD. Based on the charge distribution parameters, the symmetric mass yield distribution with the most probable mass Ap of 92 m.u. and the width FWHMMD of 39 m.u. was obtained for 197Au at E0≥600 MeV. The Ap value for 209Bi was larger by 4 m.u. than that for 197Au and the FWHMMD was smaller by 6 m.u. A comparison with the calculations using the Photon-induced Intranuclear Cascade Analysis 3 code combined with the Generalized Evaporation Model code (PICA3/GEM) was also performed.

An experimental setup for transporting fission fragments by a gas flow with aerosols is described. The results of tests of the setup on fragments of 238U photofission by bremsstrahlung from a microtron are presented. The parameters of the setup obtained experimentally (the transport efficiency reaches 70%, and the transport time reaches 0.1 s to a distance of 1 m) make it possible to successfully use it in experiments on the fission of heavy nuclei and study of properties of fission fragments

A theoretical approach to describe electro- and photofission processes at intermediate energies was worked out. Photopion reabsorption mechanisms by two and three nucleons (2NA and 3NA) were incorporated in the calculations. The comparison with electrofission data for preactinides showed that a substantial 3NA component should be added in the pion absorption to fit the data near photopion threshold, in accordance with a recent theoretical estimate. It was also shown that the shape of the fission response curve is sensitive to detailed aspects of the pion mean free path.

Fission of the even-even nuclei 232Th, 236,238U and even-odd nuclei 233,235U by linearly polarized photons has been studied at excitation energies in the region of a giant dipole resonance. The performed investigations unambiguously showed the existence of the fragment mass dependence of the cross section azimuthal asymmetry in the photofission of 236U and 238U. In addition, the obtained results provided the first evidence for the possible difference between the asymmetry values in asymmetric and symmetric mass distribution regions in the case of 236U. The measured cross section azimuthal asymmetry of the fission of 232Th does not show any fragment mass dependence. In the even-odd nuclei 233U and 235U the difference between the far-asymmetric and other mass distribution regions was also observed but with the statistical uncertainty not small enough for definitive conclusion.

The empirical-phenomenological quasi-deuteron photofission description is theoretically justified within the semiclassical, intermediate statistics model. The transmutational fermion (nucleon) - boson (quasi-deuteron) potential plays an essential role in the present context and is expressed in terms of thermodynamical and of microscopical quantities, analogous to those commonly used in the superfluid nuclear model., Comment: 7 pages, RevTex, to appear in Zeit. f. Phys. A

The measurements of the {sup 231}Pa yield and cross section photofission in the energy range 7-9 MeV are presented. These measurements are a continuation of similar measurements performed for the {gamma}-ray energy range 4.8-7 MeV. The entire collection of experimental data which combine the results obtained in the present work and in Ref. 1 was analyzed.

The total photofission cross section σγ,F for235U and238U has been measured in the energy range 50≤E γ≤800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4π arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section σγF , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections σγ,F normalized to the atomic numberA for both isotopes coincide, and agree in theΔ-resonance region, within the systematic errors, with the socalled“Universal Curve” σγ,T /A of the total photon absorption cross section σγ,T . At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there isno resonance-like shape near the D13 resonance (at ≈710 MeV) as observed for the free proton. This complete suppression of the D13 resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.

Neutron-induced fission and photon-induced fission are techniques that can be used to determine fissionable isotopes of uranium, thorium, plutonium, and other actinides in a number of matrices. The purpose of this work is to compare the advantages and disadvantages of those techniques based on theoretical and experimental considerations.

The photofission and photoneutron cross-sections of233U have been measured by using monochromatic and discrete photons produced by thermal neutron capture gamma-rays in several targets placed at the core of the IEA-R1 reactor in the energy interval from 5.43 MeV to 9.72 MeV. The evaluation of the total photoabsorption cross-sections and the parameters: single fission barrier, relative fissionability, fission probability, neutron emission/fission competition, nuclear temperature are also presented.

The yields of products originating from {sup 238}U photofission are measured at the bremsstrahlung endpoint energies of 50 and 3500 MeV. Charge and mass distributions of fission fragments are obtained. Symmetric and asymmetric channels in {sup 238}U photofission are singled out on the basis of the model of multimode fission. This decomposition makes it possible to estimate the contributions of various fission components and to calculate the fissilities of {sup 238}U in the photon-energy regions under study.

An analysis of the photofission reactions in the quasi-deuteron energy range of photonuclear absorption (∼30–140 MeV) has been performed for209Bi and238U nuclei. Experimental cross section data available in the literature have been compared with calculated values obtained from a model in which the incoming photon is assumed to be absorbed by a neutron-proton pair (Levinger's quasi-deuteron photoabsorption), followed by a mechanism of evaporation-fission competition for the excited residual nuclei. The model has been shown to reproduce the main experimental features of209Bi and238U photofission cross section, although unexplained differences still remain in the case of238U-fission by 30– 50 MeV incident photons.

Photofission cross sections of209Bi,238U and232Th are very different, both in magnitude and in their dependence on the incident photon energy. In fact, in the quasi-deuteron energy region,σf (Bi)

Photofission and electrofission cross sections for fissionable isotopes of uranium, thorium, plutonium and other actinides have been known for several decades. Published data on electrofission and photofission reactions for energies lower than 60 MeV indicate that the238U cross sections range from a fraction of one mbarn up to about 2.0 mbam for the first of these reactions, and for the second is about 150 nbarn. However, the use of photofission and electrofission as analytical tools to measure uranium, thorium, plutonium and other fissionable actinides is still quite recent. This work examines the potential use of photofission and electrofission to measure thorium, uranium, neptunium, plutonium, americium and curium in environmental and biological samples.

The isomeric yield ratios for134I, for the photofission of232Th and238U with 25-MeV bremsstrahlung have been determined using radiochemical techniques and γ-spectrometry. Angular moment a of the corresponding fission fragments, Jrms, were calculated by the statistical procedure of Huizenga and Vandenbosch. We have discovered a significant proton odd-even effect on Jrms values, and demonstrated its dependence on the nuclear structure of fragments.

Samples of Al, Ti, Co, Zr, Nb, Ag, In, Nd, Sm and Ta elements in contact with solid-state nuclear track detectors were exposed to (0.8÷1.8) GeV bremsstrahlung beams at the 2.5 GeV electron synchrotron of the Bonn University. The detectors were processed to produce visible fission tracks for track analysis with optical microscopes. Absolute mean cross-sections per photon and fissility were evaluated. Results are discussed and compared with other photofission data as well as with estimates from the current fission models. A broad minimum found for nuclear fissility of 10−4÷10−3 covering the range 15≲Z 2/A≲25 seems to confirm the predictions from the models. For Al and Ti nuclei the probability of fission amounts to ∼ 10−1.

The pronounced "forward" direction (along the electron beam) that is specific to bremsstrahlung is an advantage in some cases but a disadvantage in others. In particular, this feature entails difficulties extending the previous approach to measurements to a wider energy range, which are the subject of this article. It has turned out these difficulties can in fact be overcome easily within the framework of the same formulation of the experiment, making relative instead of absolute measurements of the fission yield. We report the results of some methodological studies as well as data on the photofission yields and cross sections of 233U and 23SU, measured with respect to the same characteristics for 23SU.

The recoil energies of24Na produced in Cu, Ag and Au and of a series of fragments produced in Cu irradiated with 800 MeV bremsstrahlung have been measured in directions forward, backward and perpendicular to the beam using the thick target-thick catcher method. Comparison of the measured values with theoretical calculations indicates that24Na is produced through fission in Ag and Au and that fission is competing with spallation even in Cu.

Energy correlation measurements were performed for the photofission of238U with 100, 140, 180, 200, 230 and 260 MeV bremsstrahlung photons using silicon surface barrier detectors. Overall fragment mass and energy distributions were deduced. The behaviour of the total fragment yield and kinetic energy and average total kinetic energy as a function of the fragment mass and of the bremsstrahlung maximum energy were studied. The symmetric fission contribution was extracted from the contour plot of the two-dimensionalE1-E2 array giving an identification without any constraint on the variance of the distribution itself. The symmetric-to-asymmetric fission yield ratioYs/Ya was studied as a function of the end-point bremsstrahlung energy. The results were compared with all the relevant data on the238U photofission and interpreted in terms of the two component picture of the fission process of Fairhallet al.

The photofission yields of Re, W and Ta induced by a coherent bremsstrahlung beam from 1000 MeV electrons striking a diamond single crystal have been measured. The experiment has been performed at eighteen different energies of the main peak of the photon spectrum, in the energy range between 220 MeV and 550 MeV, by detecting the fission fragments with glass sandwiches. The behaviour of the photo-fission cross-section has been deduced from the experimental yields by using an appropriate unfolding method. The obtained curves clearly show a first resonance centred at a photon energyk≃350 MeV with a FWHM≃145 MeV, while there is a hint of a second resonance atk≃750 MeV. Information on the energy dependence of the nuclear fissility from 100 MeV to 1000 MeV has been deduced from the comparison of the estimated photofission cross-section with the total photon interaction cross-section. It has been found that the photomesonic model of the fission process permits to explain the energy dependence of our photofission cross-sections if a nuclear fissility increasing with photon energy is assumed.

The photofission yields of Bi induced by the quasi-monochromatic photon beam from in-flight annihilation of positrons of the Frascati linac were measured. The experiment was performed at sixteen different positron energies, from 120 MeV up to 280 MeV, by collecting the annihilation photons at angles 0.5° < θ < 1°. Fission fragments were detected with glass sandwiches. Photofission cross-section values were deduced by means of an appropriate unfolding method.

The formalism for fragment angular distributions in photofission with unpolarized and linearly polarized photons is summarized. First experiments on232Th using linearly polarized bremsstrahlung are described. The results for the analyzing power show for the first time in a model independent way that the low energy photofission can be explained byelectric dipole excitation. The possibilities of this new method are discussed, in particular when using monoenergetic tagged photons, which are available soon at new high duty cycle electron accelerators.

The cross-section per equivalent quantum in the fission induced in238U by a quasi-monochromatic photon beam has been measured. The photon beam was obtained by coherent bremsstrahlung from 1000 MeV electrons striking a diamond single crystal. In the experiment the energies of the main peak of the photon spectrum assumed sixteen different values in the range from 220 MeV to 500 MeV. The fission fragments have been detected by means of glass sandwiches containing thin targets of UF4. The cross-section per photon from 100 MeV to 1000 MeV has been deduced from the experimental yields applying an appropriate unfolding method after having subtracted from the yields the contribution due to photons with energies below 100 MeV. The obtained cross-section clearly shows a resonance centred at a photon energy 320 MeV with a FWHM ⋍125 MeV and a peak value of 70 mb. This resonance is in good agreement with the first baryon resonance in pion photoproduction. The energy dependence of the photofission cross-section for238U can be explained by both assuming that the photomesonic absorption mechanism prevails over the quasi-deuteron interaction in producing fission above 150 MeV and that the nuclear fissility increases with the energy.

Measurements of photofission fragment angular distributions of238U between 5.1 and 6.0 MeV are presented. As γ-source the intense bremsstrahlung beam from the Catania University Microtron is used. The results are analysed within the framework of the double-humped barrier model with a potential constructed with three smoothly joined parabolae and a damping term in the second well. The values of the fission barrier parameters for the involved 2+0, 1−0 and 1−11 channels are extracted and a comparison with the theoretical predictions and experimental results in the literature is made. Delayed-fission contributions for the involved channels are taken into account in the 1−1 channel parameter determination.

The photofission yields of Bi, Pb, Au, Pt, Re, W and Ta have been measured by using a bremsstrahlung photon beam at maximum energies from 300 MeV to 1000 MeV. The fission fragments have been detected by means of glass sandwiches. The behaviour of the photofission cross-section has been deduced by applying an appropriate unfolding method to the results of the present experiment and to the data of previous measurements performed by a coherent photon beam. The cross-sections obtained for all the seven studied elements clearly show a first resonance at a photon energyk ≃ 340 keV and a second one centred atk ≃ 720 MeV, in good agreement with the position of the baryon resonances in the pion photoproduction. The resonant behaviour of the photofission cross-section is explained by assuming a photomesonic model of the photofission process and a nuclear fissility increasing with photon energy.

The authors proposed a method for calculating the effect of photofission of U and Th, which is based on the well-known laws of physics of photofission and methods for calculating the activity of fission products. The authors compared the results of numerical calculations of the gamma spectra of photofission products with the measurements performed with a Ge (Li) detector with the spectra from activated model samples of U and Th. The method developed enables calculating the coefficients of interference and is also applicable to the solution of the problems of optimization of gamma activation analysis taking into account U and Th fission.

Fragment energy correlation measurements have been made for238U,232Th and209Bi with bremsstrahlung of 600 MeV maximum energy. The study was performed with silicon surface barrier detectors. Distributions of kinetic energy as a function of fragment mass are presented. The results are compared with earlier photofission data and, in the case of bismuth, with calculations based on the liquid drop model.

An unfolding method is discussed and improved in its application. Unfolded solutions result to be reliable even if the registration errors of the integral yields are large. Bremsstrahlung photofission angular-distribution measurements on238U were analysed. This procedure was also applied to a particle distribution multiplicity reconstruction.

The LEALE quasi-monochromatic photon beam, produced by positron annihilation, was used to measure the238U photofission yields. Measurements were performed at 17 positron energies, from 120 MeV up to 280 MeV, and collecting the annihilation photons at an angle ≈1o. Fission fragments were detected with glass plates. The fission cross-section, deduced by means of an appropriate unfolding method, agrees very well with the results of a recent tagged-photon experiment. The calculated nuclear fissility results constant as a function of energy and equal to 0.87±0.13.

The photofission yields of Bi, Pb, Au and Pt induced by a coherent bremsstrahlung beam from 1000 MeV electrons striking a diamond single crystal have been measured. The experiment has been performed at sixteen different energies of the main peak of the photon spectrum, in the energy range between 220 MeV and 500 MeV, by detecting the fission fragments with glass sandwiches. All the photon spectra have been measured simultaneously to the exposures of the fissionable samples by means of a magnetic pair spectrometer and a real-time acquisition system with an on-line computer. An appropriate unfolding method was developed in order to deduce the behaviour of the photofission cross-section from the experimental yields. The estimated cross-section curves clearly show a first resonance at a photon energy of about 320 MeV with a FWHM ≈125 MeV, whilst there is only a hint of a second broad resonance centred atk≈750 MeV. The very good agreement between the position of the first resonance put in evidence in the present experiment and the energy of the first baryon resonance in the pion photoproduction is attributed to a predominance of the photomesonic mechanism in the photofission process of the investigated elements.

The theory of nuclear fission is reconsidered by introducing the charge asymmetry in the asymmetric two-centre shell model as a dynamical collective coordinate. The quantum-mechanical fluctuations which are accompanied with the collective motion are responsible for the mass distributions in fission. Numerical calculations are carried out for the mass distributions and charge dispersions for the nuclear fission of the236U and238U nuclei. Also, the cross-sections of the photofission of the236U and238U nuclei are numerically calculated as a function of the photon energy. The present obtained theoretical calculations are in good agreement with the experimental measurements.

Measurements are presented for the mass and energy distributions of fragments from the photofission of232Th,235U,238U and239Pu. The experiments were performed for bremsstrahlung endpoint energies between 15 and 55 MeV, using silicon surface barrier detectors. The results are discussed with respect to the competition between the symmetric and asymmetric fission modes.

Deep subthreshold photofission data of238U are analysed. Spectroscopic properties of highly deformed states from experiments in the literature are introduced into a model calculation based on the doorway state formalism which is extended to fission at energies as low as the isomeric level. It is shown that starting from the results of a detailed analysis of the photofission measurements near the top of the fission barrier it is possible to describe the process in the energy range covered by the intermediate well in the double-humped deformation potential. In particular, the so-called “shelf effect” in the low energy photofission is reproduced in terms of delayed isomeric fission through a few undamped vibrational states localised in the pairing gap region above the isomer.

A measurement of the angular distribution and yield of fission fragments from photofission of238U has been performed between 5.2 MeV and 6.4 MeV. Asγ-source the bremsstrahlung from a microtron has been used. For the detection of the fission fragments, solid state track detectors were used. The yield data were evaluated to approximate cross sections. The data were analyzed within the framework of the double hump barrier model.

Nuclear emulsions impregnated with thoriumnitrate solution were exposed to the 15·8 MeV bremsstrahlung of the Tubingen betatron. Fission tracks were identified by ionization and range, and their angular distribution relative to the incomingγ-rays was measured. As the origin of fission was unknown, the distributions obtained extend from 0‡ to 90‡ only. All tracks with a dip angle less than 50‡ were accepted, giving a total of 1726 events. The preponderance of fragment emission under 90‡ is pronounced even in the distribution of projected angles. After some calculation and correction also the distribution of true, spatial angles could be obtained from the data. Although a three constants formula gave the best fit to the distribution observed, the quadrupole term was found not to be statistically significant. We therefore conclude the angular distribution to be of pure dipole form with an anisotropyα=0·55± 0·12. This is in agreement with previous counter experiments. The anisotropy is interpreted in terms of the A. Bohr model, some of the implications of which are discussed. Extension of the measurements to 180‡ might be feasible by utilizing the ionization properties of fission tracks near the origin.

The deuteron photodisintegration matrix element, which exhibits, in the relativistic case, anomalous thresholds is studied in the nonrelativistic case, where the nucleons interact through a superposition of Yukawa or exponential potentials. For simplicity all spins are taken to be zero. A double dispersion relation is derived, in agreement with the latest results ofEdenet al. The treatment is easily extended to electrodisintegration.