Data-Acquisition Systems for Neutron-Induced Cross-Section Measurements at TUNL

J.H. Kelley1, A. Hutcheson2, C.T. Angell3, G. Rusev2, A.P. Tonchev2, W. Tornow2

1Triangle Universities Nuclear Lab & North Carolina State University2Triangle Universities Nuclear Lab & Duke University

3Triangle Universities Nuclear Lab & UNC at Chapel Hill

With SSAA support the Triangle Universities Nuclear Laboratory has undertaken an array of cross section measurements for neutron-induced transitions that take advantage of the high neutron fluxes available using the pulsed and quasi-monoenergetic beams available on-

sight in the FN Tandem Lab. To carry out these measurements we have adapted both custom and commercial data-acquisition systems.

NNSA Group in-beam Daq V.1.0 with scripted Spectrodaq/SpecTcl system

• Dual Processor PC (2.8+ GHz XEON)

• PCI-VME card (SBS bit-3 620)

• CAEN 700 series digitizers (ADC/TDC 32 Channels)

• 4. CAEN 568 16-ch Spectroscopic Amplifier

5. CAEN 812 16-ch Constant Fraction Discriminator

Software is freely available from www.sourceforge.net

• Pre-packaged NSCL Knoppix/Debian distribution

• Data acquisition and analysis software are contained in self installing files.

• Online documentation is available at http://docs.nscl.msu.edu

A program to measure partial cross sections for (n, xn ) reactions on nuclei in the actinide region is well underway. In the TUNL Shielded Neutron Source Area, a detector array comprising various combinations of four Canberra segmented HPGe detectors and a pair of planar detectors is used to carry out in-beam, prompt -ray measurements. At present we take advantage of the 2-fold quadrant segmentated clover detectors. This gives a modestly high number of ADC and TDC data channels in typical experiments.

Supported in part by the NNSA under the Stewardship Science Academic Alliances Program DOE grant #DE-PS52-05NA25930, and by

DOE DE-FG02-97ER41033 (Duke) and DE-FG02-97ER41042 (NC-State).

In-beam “prompt -ray” measurementsSpectrodaq/SpecTCL

NNSA Group in-beam Daq V.2.0 with scripted Spectrodaq/SpecTcl system

• Dual Processor PC (2.2 GHz AMD Opteron)

• VME-USB2 card (WIENER)

• CAEN CFD’s/Digitizers/etc.

• Debian Etch distribution

Software from www.sourceforge.net

• Enhanced NSCL Spectrodaq/SpecTcl system withevent buffering in the VME crate

Since 2002 the NNSA group at TUNL has made good use of the Spectrodaq/SpecTCL data acquisition system, however live times have been somewhat limited by event-by-event data transfers across the PCI-to-VME interface. In the next generation of this software, the SBS bit-3 PCI-VME interface is replaced with a WIENER USB-VME interface, and multiple event buffers are accumulated prior to transfer across the USB-VME interface. As a result, we anticipate ~30% improvements in livetime, as well as greatly improved performance as we move to 13+-bit ADC’s where numerous digitizer modules will be readout in each event.

Out-of-beam neutron activation measurementsGenie 8000

Throughout 2006-2007 the NNSA group at TUNL carried out measurements of the 241Am(n,2n) cross section using activation techniques. During the irradiation periods, the neutron beam flux was monitored using online neutron detectors, as well as, a broad selection of witness foils with known activation cross sections. Cross sections were measured from threshold (~7.5 MeV) up to 15 MeV.

A Genie 2000 special system, with 14-bit resolution, was purchased to facilitate these measurements. The Genie system permits independent measurements on any one of six channels, with accurate dead-time correction. The system provides high livetime and simple functionality.

Following irradiation, the 241Am foils and the witness foils were carried to a low-background counting area where induced -ray activity was measured. Three different counting stations were configured to permit simultaneous sample counting. Measurements continued for at least 3 half-lives.