Applications In Nuclear Physics Research Articles

Recent Developments and Validation of Geant4 Hadronic Physics

In the past year several improvements in Geant4 hadronic physics code have been made, both for HEP and nuclear physics applications. We discuss the implications of these changes for physics simulation performance and user code. In this context several of the most-used codes will be covered briefly. These include the Fritiof (FTF) parton string model which has been extended to include antinucleon and antinucleus interactions with nuclei, the Bertinistyle cascade with its improved CPU performance and extension to include photon interactions, and the precompound and deexcitation models. We have recently released new models and databases for low energy neutrons, and the radioactive decay process has been improved with the addition of forbidden beta decays and better gamma spectra following internal conversion.As new and improved models become available, the number of tests and comparisons to data has increased. One of these is a validation of the parton string models against data from the MIPP experiment, which covers the largely untested range of 50 to 100 GeV. At the other extreme, a new stopped hadron validation will cover pions, kaons and antiprotons. These, and the ongoing simplified calorimeter studies, will be discussed briefly. We also discuss the increasing number of regularly performed validations, the demands they place on both software and users, and the automated validation system being developed to address them.

Radiopurity of a CeBr3 crystal used as scintillation detector

Cerium bromide (CeBr3) has recently been shown to exhibit several properties making it a suitable material as a scintillation detector in nuclear physics applications. The intrinsic activity of gamma-ray emitting radionuclides in a 38.1mm×38.1mm (diameter×height) crystal of CeBr3 was investigated. The measurements were carried out in the HADES underground laboratory located 225m underground. Two primordial radionuclides were detected; 227Ac (and its daughters) with massic activity of 0.30±0.02Bq/kg and 138La with massic activity of 7.4±1.0mBq/kg. Two activation products were also detected; 139Ce and 82Br. Their massic activities (assuming a homogeneous distribution in the crystal) just before taking the CeBr3 crystal underground were 4.3±0.3mBq/kg and 18±4mBq/kg correspondingly. None of the other common primordial radionuclides (40K, 226Ra, 228Ra, 228Th, and 235U) were detected and their detection limits were below 2mBq/kg except for 238U for which the upper limit was 135mBq/kg and 210Pb with an upper limit of 600mBq/kg.

Observation of the Deexcitation of theTh229mNuclear Isomer

The (229)Th nucleus possesses the lowest-energy nuclear isomeric state. Two widely accepted indirect measurements of the transition energy place it within reach of existing laser capabilities. Direct searches for the isomer deexcitation have proven elusive despite extensive effort over the past couple of decades. There is now a growing interest in finding this unique transition because of its potential applications in nuclear, atomic, condensed matter, and optical physics, quantum information, metrology, and cosmology, including the development of a new type of clock based on this nuclear transition. In this Letter we report the first direct observation of the deexcitation of the lowest-lying isomeric state in (229)Th. By collecting (229)Th recoils following the alpha decay of (233)U into MgF(2) plates and measuring the subsequent light emission, we have isolated the isomer deexcitation and measured the transition's half-life to be 6±1 h. Through comparison measurements with (235m)U isomer, we found that the observed (229m)Th deexcitation signal originates from photon emission rather than internal conversion electron emission. This discovery lays the groundwork for optical and laser spectroscopy of (229m)Th nuclear isomer and the development of a (229)Th nuclear clock.

Bound states at threshold resulting from Coulomb repulsion

The eigenvalue absorption for a many-particle Hamiltonian depending on a parameter is analyzed in the framework of non-relativistic quantum mechanics. The long-range part of pair potentials is assumed to be pure Coulomb and no restriction on the particle statistics is imposed. It is proved that if the lowest dissociation threshold corresponds to the decay into two likewise non-zero charged clusters then the bound state, which approaches the threshold, does not spread and eventually becomes the bound state at threshold. The obtained results have applications in atomic and nuclear physics. In particular, we prove that an atomic ion with the critical charge Zcr and Ne electrons has a bound state at threshold given that Zcr ∈ (Ne − 2, Ne − 1), whereby the electrons are treated as fermions and the mass of the nucleus is finite.

On the spectrum of the multigroup diffusion equations

The present work addresses the problem of the determination of the eigenvalue spectrum of the multigroup diffusion equation for nuclear reactor physics applications. The analytical determination of the multiplication eigenvalues is presented for the material homogeneous configuration case. The characteristics of the time eigenvalue spectrum is further considered and illustrated, highlighting the possibility of the appearance of complex eigenvalues and discussing their physical significance. Various results are presented for different material compositions and energy group structure. Some comparisons to reference results, obtained with highly detailed Monte Carlo evaluations, are also carried out. Such comparisons evidence the limits of the diffusive approach and of the energy group discretization.

Laser stabilization to an atomic transition using an optically generated dispersive line shape

We report on a simple and robust technique to generate a dispersive signal which serves as an error signal to electronically stabilize a monomode cw laser emitting around an atomic resonance. We explore nonlinear effects in the laser beam propagation through a resonant vapor by way of spatial filtering. The performance of this technique is validated by locking semiconductor lasers to the cesium and rubidiumD2 line and observing long-term reduction of the emission frequency drifts, making the laser well adapted for many atomic physics applications.

Remarks on the First Hundred Years of Superconductivity

On the occasion of centenary of superconductivity discovery I recall some facts from the first period and attempts to understand the phenomenon. It turns out that most famous physicists of the first half of XX century have tried to solve the puzzle. Bardeen, Cooper and Schrieffer succeeded in 1957. The BCS theory successfully described all known facts and offered new predictions, which soon have been confirmed experimentally contributing to the widespread acceptance of the theory. It have found applications in nuclear physics, theory of neutron stars and cold atomic gases. The discoveries of new superconductors in the last thirty years show that simple BCS model is not enough to understand new unconventional superconductors. The studies of superconductors develop vividly and still fascinate new generations of physicists working in such diverse fields as material science and string theory.

A simple model for calculating magnetic nanowire domain wall fringing fields

We present a new approach to calculating magnetic fringing fields from head-to-head type domain walls (DWs) in planar magnetic nanowires. In contrast to calculations based on micromagnetically simulated structures the descriptions of the fields are for the most part analytic and thus significantly less time and resource intensive. We begin with an intuitive picture of DWs, which is built upon in a phenomenological manner. The resulting models require no a priori knowledge of the magnetization structure, and facilitate calculation of fringing fields without any free parameters. Comparisons with fields calculated using micromagnetic methods show good quantitative agreement. We demonstrate that parameters key to atomic physics applications can easily be calculated with errors of around 10%. The model we present has greatest accuracy and hence utility for distances roughly greater than the width of the DW under consideration.

Recent progress on the superconducting ion source VENUS

The 28 GHz Ion Source VENUS (versatile ECR for nuclear science) is back in operation after the superconducting sextupole leads were repaired and a fourth cryocooler was added. VENUS serves as an R&D device to explore the limits of electron cyclotron resonance source performance at 28 GHz with its 10 kW gryotron and optimum magnetic fields and as an ion source to increase the capabilities of the 88-Inch Cyclotron both for nuclear physics research and applications. The development and testing of ovens and sputtering techniques cover a wide range of applications. Recent experiments on bismuth demonstrated stable operation at 300 eμA of Bi(31+), which is in the intensity range of interest for high performance heavy-ion drivers such as FRIB (Facility for Rare Isotope Beams). In addition, the space radiation effects testing program at the cyclotron relies on the production of a cocktail beam with many species produced simultaneously in the ion source and this can be done with a combination of gases, sputter probes, and an oven. These capabilities are being developed with VENUS by adding a low temperature oven, sputter probes, as well as studying the RF coupling into the source.

Covariant density functional theory and applications in nuclear physics and r-process

The covariant density functional theory (CDFT) with a few number of parameters allows a very successful description of the properties of nuclei all over the nuclear chart. The recent progress on the application of the CDFT as well as its extensions for a series of interesting and hot topics in nuclear structure and nuclear astrophysics are summarized. In particular, the newly proposed point-coupling parametrization PC-PK1 and the application of the CDFT to the single particle level of the radioactive neutron-rich doubly magic nucleus 132 Sn, the deformed halo in nuclei, and the β decay life-time of neutron rich nuclei are discussed in details.

Inverse scattering: applications in nuclear physics

Inverse scattering: applications in nuclear physics

Evaluation of inverse integral transforms for undergraduate physics students

We provide a simple approach to the analytical evaluation of inverse integral transforms that does not require any knowledge of complex analysis. The central idea behind our method is to reduce the inverse transform to the solution of an ordinary differential equation. We illustrate the utility of our approach by providing examples of the evaluation of transforms without the use of tables. We also demonstrate how the method may be used to obtain a general representation of a function in the form of a series involving the Dirac delta distribution and its derivatives, which has applications in quantum mechanics, semiclassical, and nuclear physics.

Applications of a 6.5T Superconducting Solenoidal Separator

A 6.5 Tesla superconducting gas-filled solenoid (SOLITAIRE) has been developed at the Heavy Ion Accelerator Facility at the ANU as a reaction product separator. Key features of the device allowing its application for precise measurement of heavy ion fusion cross sections are described. The physical separation of beam particles and the high efficiency (~80%) transport of heavy ion fusion products open up applications in nuclear structure physics, and in materials science. Finally, the developments to allow its application to providing beams of light radioactive isotopes (SOLEROO) are described.

Myths, symbols, society and nuclear energy

Today, can we really ascertain whether Humanity has effectively derived more good than evil from the discovery of radioactivity a century ago? The answer hinges on the judgement that we and our fellow–citizens make about the impact of the applications of nuclear physics, by reference to a number of fundamental values: the concern to preserve our planet, its inhabitants and its environment; the need to avoid the risk of conflicts; and the guideline of the development of all peoples. At the collective level, an ethic must enable every social group, every nation and, perhaps, humanity, to form a community of behaviours. This places us at the very heart of the nuclear debate.

Perturbative solution for analysis of coherent processes in a double-Λ atomic scheme

We solve optical Bloch equations (OBEs) for the atomic scheme that consists of four atomic levels which constitute double-lambda (DΛ) configuration i.e. two Λ systems sharing the same two ground levels. DΛ atomic scheme has being used as a basis for many interesting applications in atomic physics and nonlinear optics. It was studied in the context of electromagnetically induced transparency (EIT) Shpaisman et al. (2005) [1], four-wave mixing Baolong et al. (1998) [2], lasers without inversion Kocharovskaya et al. (1990) [3], etc. More recently, efficient application of DΛ scheme led to the development of phenomena like slow and stored light Eilam et al. (2008) [4], quantum mechanical entanglement of two beams of light Boyer et al. (2008) [5] and squeezed light Imad et al. (2011) [6].Typically, a numerical solution of OBEs is used in the theoretical treatment of atomic system of two Λ schemes. In this work, interactions of four laser fields driving a DΛ level scheme were analyzed by using perturbative method to solve OBEs Dimitrijević et al. (2011) [7]. Perturbative method produces simpler solutions such that analytical expressions can be obtained. The comparison of results obtained using lower-order corrections of perturbative method, and the exact calculations using optical Bloch equations is presented. Analytical expressions provide valuable information about processes that occur in the DΛ atomic system. These informations cannot be deduced from the numerical solutions of the OBEs for the same atomic scheme.

Family relationship among power-law multi-term potentials in extra dimensions

The extended transformation method is applied to construct a family relationship among the exactly solvable quantum mechanical potentials. The bound state solutions of the Schrödinger equation for specific multi-term potentials are obtained in any chosen dimensional space, which may find applications in atomic, molecular, nuclear and particle physics. An advantage of this method is that the wave functions of the generated quantum system are almost always normalizable. Explicit expressions for the energy eigenvalues and eigenfunctions of various potentials are found.

The atomic nucleus: Nuclear technology

Two applications of nuclear physics have given it a bad name: energy and bombs. But the properties of nuclei can also heal us and tell us about the far past

Chaotic motion in axially symmetric potentials with oblate quadrupole deformation

By computing the Poincaréʼs surfaces of section and Lyapunov exponents, we study the effect of introducing an oblate quadrupole in the dynamics associated with two generic spherical potentials of physical interest: the central monopole and the isotropic harmonic oscillator. In the former case we find saddle points in the effective potential, in contrast to the statements presented by Guéron and Letelier in [E. Guéron, P.S. Letelier, Phys. Rev. E 63 (2001) 035201]. The results we show in the second case have application in nuclear or atomic physics. In particular, we find values of oblate deformation leading to a disappearance of shell structure in the single-particle spectrum.

Quality of polyimide foils for nuclear applications in relation to a new preparation procedure

For more than 30 years thin polyimide foils have been produced at IRMM by in-situ polymerisation. The procedure consists of three steps, all performed under ambient atmosphere: preparation of a polycondensate solution used to form foil by spreading on a glass plate, removal of the solvent by thermal treatment for 4h at 100°C and final polymerisation at high temperature (350°C). Recently modifications of this procedure including preparation in an argon atmosphere and elimination of the time-consuming solvent removal were applied. The influence of these modifications on the quality of the foils was studied by testing the mechanical and thermal properties and the lifetime of the foil under a charged projectile beam. The influence of the modifications on the characteristics and on the level of impurities in the foils is presented as well. Comparative studies of parameters were performed for foils with an areal density between 20 and 80μgcm−2. This work showed that the foils prepared by the new fast preparation manner in a dry atmosphere have the best properties for nuclear physics applications.

A compact extended cavity laser using a micromachined silicon flexure for atomic spectroscopy

We report a novel compact extended cavity diode laser (ECDL) system for applications in atomic physics. It employs a 6.5 mm invar cavity, a volume holographic grating (VHG), and a micromachined silicon flexure integrated with a pair of piezoelectric transducer (PZT) actuators, and the overall laser system has a size of 26.3 mm × 20 mm × 20 mm. The advantages of using a silicon flexure are its high material rigidity and simple microfabrication process with designable displacement. The measured spring constant of the silicon flexure is 1.56 × 10 5 N/m, and its deflection is 157.45 nm. This displacement alters the laser cavity length, leading to a frequency tuning range of 9.31 GHz. A frequency tuning range of 11.6792 GHz can also be achieved by changing the VHG temperature, providing another fine tuning mechanism. The laser wavelength was swept between 780.2533 and 780.2344 nm, covering the rubidium D 2 absorption peaks.