-optimized low-cost TDPAC spectrometer using a versatile routing/coincidence unit

M. RENTERÍA, A.G. BIBILONI, G.N. DARRIBA, L.A. ERRICO, E.L. MUÑOZ, D. RICHARD, AND J. RUNCO

Foz de Iguazú, Brasil

Conferencia; 14th International Conference on Hyperfine Interactions & 18th International Symposium on Nuclear Quadrupole Interaction; 2007

UNLP, UNCor, USP, CBPF, UFES

A highly accurate, stable and low-cost − TDPAC spectrometer, PACAr, using a versatile EPROM-based routing/coincidence (RC) unit, optimized for 181 Hf-implanted low-activity samples is presented. It is based, in addition, on 4 BaF2 detectors, 8 home-made fast constant-fraction differential discriminators (CFDD) [1], a TAC and an 8KMCA-card (Nucleus PCAII-8000) hosted in a 486 Intel-processor PC, connected in a fast-fast coincidence logic [2].The BaF2 crystals are truncated conical-caped cylinders of 30 mm height with 90 full cone angle, being their shape chosen to optimize “the signal (anisotropy) to relative accuracy (statistical error) ratio” assuming the use of a sample holder/oven of °=20mm and relevant energies of 181 Hf, but also of 111 In and 99 Mo TDPAC probes [3]. A serious limitation of a great number of commercial MCA cards is their impossibility to address events to different memory groups during acquisition, i.e., one can only select a memory group when the acquisition is stopped and it remains fixed during acquisition. Although the routing technique is very well-known, for face to these cases we developed a RC unit where the internal signals of the MCA that normally determine a particular memory group are replaced by the specific combination of logic signals produced in the coincidence circuit of the RC unit [4]. This procedure enables the time events storage in different memory groups, during continuous data acquisition, depending on the specificcoincidence validated in the RC unit. A compact instrumentation of this idea was presently developed and imple-mented, replacing the mentioned circuits by an EPROM (erasable programmable read-only) memory programmed to know which combination of input logic signals the MCA needs to route the event to a certain memory group. If the replacement of the MCA card by a different one is needed, the RC unit can be quickly adapted with no costreprogramming the EPROM. The excellent energy resolution, high efficiency and “information gain”, and very good timing resolution of PACAr are analyzed and compare with advanced and already tested fast-fast [2] and slow-fast [3] PAC spectrometers.We gratefully acknowledge T. Butz, R. Vianden, and A.F. Pasquevich for fruitful suggestions and advice during the design of the detectors.[1] Constructed upon a modification of a fast CFD (Dissertation Th. Schaefer, Univ. of Bonn, 1987, based on acircuit suggestion by J. Pouthas and M. Engrand, NIM 161 (1979) 331) adding a 3rd comparator to perform pulseenergy selection, N. Mart´ınez, G. Renzi and A.F. Pasquevich (1988), private communication.[2] A. Bartos etal., Nucl. Instr. and Meth. A330, 132 (1993).[3] T. Butz etal., Nucl. Instr. and Meth. A284, 417 (1989).[4] Our first RC unit is a modification of those described in many PhD Thesis done before 1987 at the H-ISKP(Univ. of Bonn).