(d,p) with RIBs

ORRUBA

(d,p gamma)

Ion Source Development

People

Publications



The Center of Excellence for Stewardship Science is a collaboration between Rutgers University, UNIRIB/ ORAU with ORNL , Tennessee Technological University, Colorado School of Mines, University of North Carolina and the NNSA Lawrence Livermore and Los Alamos National Laboratories.The Center is involved with experiments at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory . The aim of the Center is to provide nuclear structure input on unstable species of importance to nuclear structure, nuclear astrophysics and science-based stockpile stewardship.
 
Attendees of the Stewardship Science Academic Alliance Symposium
Thomas P. D’Agostino (center) is Deputy Administrator for Defense Programs in the Department of Energy’s (DOE) National Nuclear Security Administration (NNSA). Deputy Administrator D’Agostino leads NNSA’s weapons programs, which maintain the reliability of our nation’s nuclear weapons stockpile. Pictured with him at the Stewardship Science Academic Alliance (SSAA) Symposium held at the Carnegie Intuition in Washington, DC, February 26-28, 2008 are: Cara Jost, ORAU and University of Mainz; Travis Bray, Auburn University; Kelly Chipps, Colorado School of Mines; Sean Liddick, University of Tennessee; Steven Padgett, University of Tennessee; Catalin Matei, ORAU; Patrick O’Malley, Rutgers; William Peters, Rutgers; Jolie Cizewski, Rutgers.Also attending, but not pictured, was Ken Carter, (ORAU), Robert Hatarik (Rutgers) and Steven Pain (ORNL/UT).

Neutron Transfer Measurements

Single-neutron transfer reactions, such as (d,p), provide information which is useful for nuclear structure, astrophysics and stewardship science studies. These reactions, with stable, light ion beams, have been used for decades to extract information about the spins and parities as well as single-particle properties of nuclei resulting from reactions of stable beams on targets of stable or long-lived isotopes. Now with sufficient Radioactive Ion Beam (RIB) intensities it is possible to perform (d,p) reactions in inverse kinematics, using a heavy radioactive species as the beam and a deuterated polyethylene target, allowing us to study nuclei away from the valley of stability.

At the HRIBF, we use RIBs produced from proton-induced fission on a uranium carbide target. This production mechanism supplies many species of neutron-rich nuclei, including those close to the shell closures at N=50 and N=82. The 25-MV tandem Van de Graaff accelerator is capable of accelerating beams to around the Coulomb barrier, a favorable energy regime for transfer reactions. The protons resulting from the (d,p) reaction are measured in various silicon detectors including the SIDAR array and silicon strip detector telescopes. The beam-like recoil particles are detected in an ion counter . The program to date has had a number of successes, including the first spectroscopic measurement of the r-process nucleus 83Ge and a measurement of another N=51 neutron-rich isotone, 85Se. We have recently performed three (d,p) measurements on nuclei near the double shell closure at 132Sn - 130Sn(d,p) 131Sn, 132Sn(d,p)133Sn and 134Te(d,p)135Te.

ORRUBA

Measurements using radioactive beams require efficient detector arrays, due to the relatively low beam intensities currently obtainable (compared to stable beams) . The Oak Ridge Rutgers University Barrel Array (ORRUBA) is a large solid angle silicon detector array, capable of providing energy, angle and particle identification information. ORRUBA is comprised of two rings of 12 position-sensitive silicon detector telescopes, symmetrically covering angles forward and backward of 90 degrees (relative to the target location). Each telescope consists of a thin (65um or 140um) transmission (dE) detector, and a thick(1000um) stopping (E) detector, enabling particle identification and measurement of the energy of particles of interest. Each detector is ~8cm long, and its width is divided into four 1cm wide resistive strips, oriented parallel to the beam axis. Readouts from both ends of each strip allow measurement of the position of the interaction, allowing determination of the emission angle of the detected particles. ORRUBA is currently in its design phase. The prototype detectors are being manufactured by Micron Semiconductors Ltd, and a new chamber is being constructed to accommodate the array.

 


(d,p gamma)

The Q-value resolution of (d,p) reactions in inverse kinematics is limited by the kinematic conditions. However, it is possible to measure the excitation levels of excited states populated in the reaction, as well as others in the subsequent cascade, using the emitted gamma-rays.Gamma-ray cascades also give information on the spin-parities of the states, thus yielding important nuclear structure information. Tagging on the gamma-rays can help to clarify the proton spectra and reduce background. As the energy resolution is now independent of the reaction it is possible to use thicker targets to increase the yield. It is important, at the same time, to use arrays of high resolution detectors in close geometry.

The Stewardship Collaboration will test the feasibility of (d,p gamma) measurements at the HRIBF at ORNL. Currently, a chamber is being built to house pre-existing detection systems such as SIDAR, silicon telescopes and germanium clover detectors. SIDAR, in the lamp shade configuration, will cover "back angles" between 120 degrees to 160 degrees in the lab frame. Four silicon telescopes, 5cm by 5cm position sensitive strip detectors, will cover 90 degrees and back to 120 degrees in the lab frame. Finally, four germanium clovers will be mounted at 90 degrees in the CARDS configuration. The efficiency of the system is dictated by the efficiency of the clovers, which is 4% at 1.333 MeV. The initial test will utilize a stable 88Sr beam. This beam was chosen because of its close proximity to unstable nuclei of interest to the stewardship center. Radioactive nuclei in the Sr region will be examined using the proton-gamma coincidence method upon successful completion of the stable run. In the future the ORRUBA system will be combined with gamma-ray coincidence capabilities to be used with RIB experiments.

 

 

Ion Source Development

Radioactive Ion Beams (RIBs) at the HRIBF are produced via the ISOL method, where a thick target is bombarded with light ions, such as protons, deuterons or alpha particles. The radioactive species produced in the reaction has to diffuse out of the production target and is transported to the ion source where it is ionized and accelerated. These steps are highly dependent on the chemistry of the isotope. Neutron-rich beams are produced at the HRIBF via the fission of uranium. In this case, isotopes of many different elements are produced simultaneously. Hence, it is often necessary to perform chemical separation in addition to mass separation. This chemical separation has to performed in-situ and on0line by using chemical properties for the element of interest. Many beam are available at the HRIBF, however in some cases the purity or intensity needs to be improved before they can be used for transfer reactions. For instance, for some very short lived isotopes, the time required to extract and transport the ion can be long compared with the nuclear half life, leading to significant losses in intensity. The RIB development team of the Center of Excellence is working to understand all the processes which take place in a target-ion source and to optimize each of them in order to purify beams and increase their intensities. The Center of Excellence is also interested in experiments on proton-rich isotopes which are relevant to radiochemical detectors for stewardship science. This involves the development of new beams. Different target materials are under investigation for fast release of reaction products.

People

Jolie Cizewski, Principle Investigator, Rutgers University

Ken Carter, Co-Principle Investigator, ORAU/UNIRIB 

Dan Bardayan, ORNL Staff Member

Jeffrey Blackmon, ORNL Staff Member

Ryan Fitzgerald, Graduate Student, University of North Carolina, Chapel Hill

Patty Gulyas, Secretary, Rutgers University

Micah Johnson, Post doc, ORAU

Kate Jones, Post doc, Rutgers University

Ray Kozub, Professor, Tennessee Technological University

Andreas Kronenberg, Post doc, ORAU

Jake Livesay, Graduate Student, Colorado School of Mines

Zhanwen Ma, Graduate Student, University of Tennessee

Caroline Nesaraja, Post doc, ORNL

Steve Pain, Post doc, Rutgers University

Charles Reed, Technician, ORAU/UNIRIB

Gene Spejewski, Consultant, ORAU/UNIRIB

Jeffry Thomas, Grad Student, Rutgers University

Dale Visser, Post Doc, University of North Carolina, Chapel Hill

Ally Wright, Administrative Assistant, ORAU/UNIRIB

Publications

Coming soon.