54223660
The program LISE: a simulation of fragment separators
This paper describes the program LISE which simulates the operation of fragment separators used to produce radioactive beams via fragmentation. Various aspects of the physical phenomena involved in the production of such radioactive beams are discussed. They include fragmentation cross-sections, energy losses in materials, ionic charge-state distributions, as well as ion optics calculations and acceptance effects. This program is highly user-friendly, and is designed not only to forecast intensities and purities for planning future experiments, but also for beam tuning during experiments where its results can be quickly compared to on-line data. In addition, several general-purpose tools such as a physical parameters calculator, a database of nuclear properties, and relativistic two-body kinematics calculations make it useful even for experiments with stable beams. After a general description of fragment separators, the principles underlying the calculations are presented, followed by a practical description of the program and its features. Finally, a few examples of calculations are compared to on-line data, both qualitatively and quantitatively.
118725362
Isotopic distribution of fission fragments in collisions between 238U beam and 9Be and 12C targets at 24 MeV/u
Inverse kinematics coupled to a high-resolution spectrometer is used to investigate the isotopic yields of fission fragments produced in reactions between a 238U beam at 24 MeV/u and 9Be and 12C targets. Mass, atomic number and isotopic distributions are reported for the two reactions. These informations give access to the neutron excess and the isotopic distribution widths, which together with the atomic-number and mass distributions are used to investigate the fusion-fission dynamics.
41501572
Production cross sections from 82Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line
Production cross sections for neutron-rich nuclei from the fragmentation of a 82 Se beam at 139 MeV/u were measured. The longitudinal momentum distributions of 126 neutron-rich isotopes of elements 11 Z 32 were scanned using an experimental approach of varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including several isotopes first observed in this work. These are the most neutron-rich nuclides of the elements 22 Z 25 ( 64 Ti, 67 V, 69 Cr, and 72 Mn). One event was registered consistent with 70 Cr and another one with 75 Fe. The production cross sections are correlated with Qg systematics to reveal trends in the data. The results presented here confirm our previous results from a similar measurement using a 76 Ge beam and can be explained with a shell model that predicts a subshell closure at N = 34 around Z = 20. This is demonstrated by systematic trends and calculations with the abrasion-ablation model that are sensitive to separation energies.
118688563
Isotopic fission fragment distributions as a deep probe to fusion-fission dynamics
During the fission process, the atomic nucleus deforms and elongates up to the two fragments inception and their final separation at the scission deformation. The evolution of the nucleus energy with deformation defines a potential energy landscape in the multidimensional deformation space. It is determined by the macroscopic properties of the nucleus, and is also strongly influenced by the single-particle structure of the nucleus, which modifies the macroscopic energy minima. The fission fragment distribution is a direct consequence of the deformation path the nucleus has encountered, and therefore is the most genuine experimental observation of the potential energy landscape of the deforming nucleus. Very asymmetric fusion-fission reactions at energy close to the Coulomb barrier, produce well-defined conditions of the compound nucleus formation, where processes such as quasi-fission, pre-equilibrium emission and incomplete fusion are negligible. In the same time, the excitation energy is sufficient to reduce significantly structural effects, and mostly the macroscopic part of the potential is responsible for the formation of the fission fragments. We use inverse kinematics combined with a spectrometer to select and identify the fission fragments produced in 238U+12C at a bombarding energy close to and well-above the Coulomb barrier. For the first time, the isotopic yields are measured over the complete atomic-number distribution, between Z=30 and Z=63. In the experimental set-up, it is also possible to identify transfer-induced reactions, which lead to low-energy fission
40441323
Status report on the NSCL RF fragment separator
The Radio Frequency Fragment Separator (RFFS) proposed in [1] is now operational at the National Superconducting Cyclotron Laboratory (NSCL). The RFFS is an additional purification system for secondary beams at the NSCL after the existing A1900 fragment separator and will primarily be used to purify beams of rare neutron deficient isotopes. A similar device is already in use at RIKEN [2]. The RFFS uses an rf kicker to angularly separate unwanted particles from the desired ion beam, a pi/2 phase advance cell to rotate the beam in phase space before the beam reaches a collimating aperture for purification, and a final pi phase advance cell to transport the desired beam to the experiment. The final design for the rf kicker and the focusing system is presented and a status report on the building and commissioning effort is given.
123615222
New neutron-rich microsecond isomers observed among fission products of U-238 at 80 MeV/nucleon
Eight new isomeric states in neutron-rich nuclides have been discovered in fission fragments produced by the reaction of an 80 MeV/nucleon {sup 238}U beam with a {sup 9}Be target and separated in-flight using the A1900 fragment separator. The experiment was conducted at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. Gamma rays were detected in a high-purity germanium detector located at the focal plane within a time window of 20 {mu}s following ion implantation. In some cases the isomers were observed to decay into previously reported states, allowing us to assign the initial decay from the isomeric state. Among the outcomes, the results suggest that many studies on the nuclear structure of medium-mass neutron-rich nuclei are feasible at projectile fragmentation facilities using induced fission.
14723337
Functional equations for one-loop master integrals for heavy-quark production and Bhabha scattering
Abstract The method for obtaining functional equations, recently proposed by one of the authors [O.V. Tarasov, Phys. Lett. B 670 (2008) 67, arXiv:0809.3028 [hep-ph] ], is applied to one-loop box integrals needed in calculations of radiative corrections to heavy-quark production and Bhabha scattering. We present relationships between these integrals with different arguments and box integrals with all propagators being massless. It turns out that functional equations are rather useful for finding imaginary parts and performing analytic continuations of Feynman integrals. For the box master integral needed in Bhabha scattering, a new representation in terms of hypergeometric functions admitting one-fold integral representations is derived. The hypergeometric representation of a master integral for heavy-quark production follows from the functional equation.
118467843
Analytic result for the one-loop scalar pentagon integral with massless propagators
The method of dimensional recurrences proposed by Tarasov (1996, 2000) [1] ;  [2] is applied to the evaluation of the pentagon-type scalar integral with on-shell external legs and massless internal lines. For the first time, an analytic result valid for arbitrary space–time dimension d and five arbitrary kinematic variables is presented. An explicit expression in terms of the Appell hypergeometric function F3F3 and the Gauss hypergeometric function F12, both admitting one-fold integral representations, is given. In the case when one kinematic variable vanishes, the integral reduces to a combination of Gauss hypergeometric functions F12. For the case when one scalar invariant is large compared to the others, the asymptotic values of the integral in terms of Gauss hypergeometric functions F12 are presented in d=2−2ed=2−2e, 4−2e4−2e, and 6−2e6−2e dimensions. For multi-Regge kinematics, the asymptotic value of the integral in d=4−2ed=4−2e dimensions is given in terms of the Appell function F3F3 and the Gauss hypergeometric function F12.
119292876
Finding new relationships between hypergeometric functions by evaluating Feynman integrals
Several new relationships between hypergeometric functions are found by comparing results for Feynman integrals calculated using different methods. A new expression for the one-loop propagator-type integral with arbitrary masses and arbitrary powers of propagators is derived in terms of only one Appell hypergeometric function F1. From the comparison of this expression with a previously known one, a new relation between the Appell functions F1 and F4 is found. By comparing this new expression for the case of equal masses with another known result, a new formula for reducing the F1 function with particular arguments to the hypergeometric function 3F2 is derived. By comparing results for a particular one-loop vertex integral obtained using different methods, a new relationship between F1 functions corresponding to a quadratic transformation of the arguments is established. Another reduction formula for the F1 function is found by analysing the imaginary part of the two-loop self-energy integral on the cut. An explicit formula relating the F1 function and the Gaussian hypergeometric function 2F1 whose argument is the ratio of polynomials of degree six is presented.
118380334
Color-kinematic duality for form factors
A bstractRecently a powerful duality between color and kinematics has been proposed for integrands of scattering amplitudes in quite general gauge theories. In this paper the duality proposal is extended to the more general class of gauge theory observables formed by form factors. After a discussion of the general setup the existence of the duality is verified in two- and three-loop examples in four-dimensional maximally supersymmetric Yang-Mills theory which involve the stress energy tensor multiplet. In these cases the duality reproduces known results in a particularly transparent and uniform way. As a non- trivial application we obtain a very simple form of the integrand of the four-loop two-point (Sudakov) form factor which passes a large set of unitarity cut checks.