Indian Journal of Pure & Applied Physics Vol. 42, June 2004, pp. 387-389 Determination of live-time efficiency of a photonuclear experiment I Akkurt Slileyman Demirel University Fen-Edebiyat Fak. Fizik Bol. Isparta, Turkey Received /0 Jmlllar), 2003; revised 12 Jail/tal)' 2004; accepted 3 March 2004 The live-time efficiency has been calculated and corrected to obtain the absolute magnitude of the experimental yield. The percentage efficiency of the data acquisition system used in a photoneutron experiment at Maxlab in Lund (Sweden) has been determin ed. IPC Code: G OIT [Keywords: Data acquisition. Photo nuciear experiment, Live-time] 1 Introduction Nuclear structure physics close to hundred years old , is still one of the most difficult areas of physics. To investigate nuclear structure photonuclear reactions can always be used as the photon is relatively weaker than other probes (electron, proton, neutron etc) and electromagnetic interaction is very well-known by quantum electrodynamics (QED) theory. A photonuclear reaction is characterised by a photon incident on a target, with one or more products of the reaction being knocked-out (p, n, d, t, h etc) and detected. As all information such as pulse height, time and scaler, from detectors is required to convert into digital words to be stored and analysed, the electronics system is a vital part of the measurement. A typical photonuclear experiment at Maxlabl.2 involves the collection of two types of data; event type data, from Analog-to-Digital Converters (ADC) and Time-to-Digital Converters (TDC), and scaler type data. The data acquisition system is effectively dead for} min whenever it carries out a read/clear procedure. Thus if a second event arrives within } min of the original event, it will be ignored by the data acquisition system. However, the collection of the scaler data is not affected by such dead times. Thus, to calculate the correct integrated dose for the number of events that the data acquisition system was able to collect, the scaler data has to be multiplied by a factor which represents the fraction of ev ent type data that collected, i.e, the live-time efficiency. The live-time is the fraction of all event type data that the data acquisition system is able to collect. 2 Experimental Details During a normal photonuclear experiment at Maxlab, the output of 2 oscillators has been recorded as a scaler data. One is free running, the other is inhibited by the data acquisition system, i.e, it only counts when the data acquisition system is not busy and is ready to accept an event. Thus, to first order, a comparison between the data from these oscillators gives the live-time, inhibited oscillator C(o"e ) = --- --- ------- free running oscillator ... (I) However, this is only true if the duty factor (d r ) of the beam is 100%. Figure I is the shematic view of duty factor beam. For a pulsed beam, duty factor is defined as the ratio of the pulse duration (t in Fig. I) to the time interval between pulses ("C in Fig. I). In the more realistic case of a reduced duty factor, the results of a calculation using Eq. (I) will always overestimate Electron-Beam Time Structure Ii t }ll- IIr-- Miaotrorl =i u duty = 0.05% duty = tit Stretcher duty> 50% Fig. I-Shematic view of the pulsed (above) and stretched beam (below)