(d,p) with RIBs

ORRUBA

(d,p gamma)

Ion Source Development

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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.
 

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.

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.

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