digiBASE-E High Performance, Digital Gamma Spectrometer

The digiBASE-E is a complete spectroscopy solution for most scintillation detectors. It comprises, high voltage, digital signal processing of the detector pulse stream and high performance MCA functionality all within a standard 14-pin PMT base. Connection to the controlling PC is easy; the integral Ethernet RJ45 connector features Power-over-Ethernet (PoE) allowing a simple single cable connection. A flexible system of gating logic facilitates configuration of multiple units as part of an integrated system where time synchronicity is needed. The digiBASE-E is therefore ideal for remote monitoring applications and detector networks and arrays. Various scintillators can be used with the digiBASE-E. NaI(Tl) detectors have been historically the most popular, but digiBASE-E is also compatible with the newer “lanthanum halide” scintillators such as LaBr3(Ce), which are growing in popularity.

Flexible Acquisition Modes
Both the familiar Pulse Height Analysis (PHA) acquisition mode and List Mode Acquisition are provided in the digiBASE-E.

In list mode, each (gamma ray interaction) event is recorded both with energy (as in PHA mode) and with time of occurrence (not recorded in PHA mode). This mode of data collection means that the data set can be sorted on the basis of both time and energy. This has proven invaluable in many applications such as homeland security, where, for example, a source is moving relative to a detector. Data without the source present may be discarded on the basis of time of occurrence, potentially enhancing signal-to-noise. 

In addition to PHA and List Mode an external input allows the digiBASE-E to perform as a 32-bit counter.

Flexible Gating
In measurement systems employing multiple detectors, there is often a need to synchronize data acquisition (for example in a mobile gamma-ray search system the data from all detectors must be correlated to correctly map out the activity distribution over an area). DigiBASE-E provides flexible gating features; events from multiple spectrometers may be correlated to within <100-milliseconds. 

This is achieved by the use of a gate input and a gate output.

The gate input can accept multiple signal types, which can be enabled from the MAESTRO MCA emulation program (supplied) or from a user program. (Command syntax is provided in the documentation.) Gate input modes are:

1. Coincidence Gate mode. In this mode, during acquisition, the gate is only open to the passage of data when this input is “True.”
2. Trigger mode (“ACQ gate”). In this mode, application of a “True” pulse to the gate will start data acquisition.
3. EVENT GATE mode. Here, when in PHA mode the presence of a “True” level will result in data being routed to an alternate spectral memory. 
4. List Mode Event Gate. In this mode the presence of a TRUE level at the gate input will result in the associated list mode event(s) receiving a data tag.

The gate output is a bridged version of the gate input. It provides the “master output” for use with “slave” digiBASE-E instruments in a multi-detector system. In this mode, the master gate out connects to the slave gate(s) in.

The gate input can additionally operate as a 32-bit event counter for LVTTL pulses. The counter may be read through the MAESTRO MCA emulation software or user program.

Spectral Stabilization
NaI(Tl) detectors have a gain that is sensitive to changes in the ambient temperature and magnetic fields. DigiBASE-E incorporates a gain stabilizer to significantly diminish this sensitivity. It works by monitoring the centroid of a designated peak in the energy spectrum. The fine gain is automatically and continuously adjusted to maintain the centroid of the peak at its desired position.

PERFORMANCE

Conversion Gain	Range of 256 to 2048 channels. Optional 1024 or 512 selectable in MAESTRO software.
Coarse Gain	Jumper selectable for X1, X3 or X9.
Fine Gain	0.33 to 1.0.
Integral Nonlinearity	<±0.05% over the top 99% of the range.
Differential Nonlinearity	<±1% over the top 99% of the range.
Dead Time Accuracy	<5% error up to 50k cps input count rate. Dead time is measured with a Gedcke-Hale Livetime clock.
Detector Bias Voltage	0 to +1200 V in steps of 1.25 V under computer control.
Offset Drift	<50 ppm of Full-scale range per °C.
Gain Drift	<150 ppm per °C.
Presets	Live Time  Up to 8.5 x 107 seconds in steps of 20 ms. Real Time  Up to 8.5 x 107 seconds in steps of 20 ms.
Trapezoid Shaping	Rise/Fall Time  600 ns minimum to a maximum of ≤2 µs. Flat Top Time  40 ns minimum to a maximum of ≤2 µs.
Throughput	Maximum throughput with the appropriate scintillator is 196k cps with a 532k cps input rate. Note that peaking time (Rise Time + Flat Top) should not be less than ~4 X the light collection time of the scintillator; i.e. NaI should not be less than about ~1 µs.
Synchronous Operation	Operation of up to 12 each model digiBASE-E systems with one Master and all other devices slaved to the Master for time correlation of no more than 100-ms between all units.
List Mode Acquisition	Each valid event is converted to a digital value and transmitted to the computer along with a time stamp accurate to 160 ns.
Histogram Mode Acquisition	Data is presented as a histogram inside the digiBASE-E. Data channels are 32-bits. Most significant bit is ROI bit.
Spectrum Transfer	Transfer of any single spectrum to require ≤15 ms. This transfer is independent of the acquisition and does not create dead time for the acquisition of additional data.
Spectrum Stabilizer	The digiBASE-E features a built-in gain and offset stabilization circuit. Stabilization is performed by providing a reference peak in the spectrum which the MCA can monitor, should drift be detected, the gain and offset of the system are adjusted automatically to correct for the drift. The stabilizer can correct for 10% of Full-Scale Reading (FSR) error in offset and uses the full-range of the Fine Gain to correct for gain errors.

Inputs and Outputs

A-In	SMA input connector accepts LVTTL signals (+3.3 V) that function depending on the MAESTRO software GATE setting. Input impedance is 1-kΩ to +3.3 V protected to ±5 V.
Coincidence Gate	When input is low (false), real-time and live-time operate normally, but no counts are stored in memory. When high (true), normal acquisition occurs (cannot be used with R-TIME SYNC).
ACQ Gate	When input is low (false) real-time, live-time, and data acquisition is stopped. When high (true), real-time, live-time, and data acquisition is enabled (cannot be used with R-TIME SYNC).
Route Gate	Routes input to spectrum 1 when high (true) and spectrum 0 when low (false). In List Mode this adds a flag to data events generated when this gate is present (cannot be used with R-TIME SYNC).
Event	Rising edges are counted by a 32-bit event counter. The contents of the counter can be monitored on the Status tab in MAESTRO software (cannot be used with R-TIME SYNC).
Trigger In	Input rising edge starts the acquisition.
R-Time Sync	When multiple digiBASE-E instruments are in List Mode and one digiBASE-E must be designated the R-Time source (Master Timer) for the other systems connected, the B-output will provide a real time synchronizing pulse that will connect to the A-input of the second digiBASE-E. The B-out will be a bridged output to provide this same real time signal to the A-input to a third digiBASE-E and so on for up to 12 digiBASE-E instruments. The final digiBASE-E should connect the B-output back to the R-Time source (master timer).
B-Out	A second SMA connector with nominal 100-Ω output Z labeled “B” provides a bridged output for the input provided to the A-IN input. This output provides the Master Sync if this digiBASE-E is designated the “Master Sync.”
Interface	Ethernet provides Power-over-Ethernet (PoE). RJ45 connection.

Electrical, Mechanical, and Environmental

Dimensions	2.51 in. (6.38 cm) diameter x 4.7 in. (11.94 cm) length.
Weight	Net  0.79 lbs. (0.36 kg).   Shipping  ~5 lbs (2.27 kg).
Power Requirements	≤3 watts from PoE.
Ambient Operating Environment	–10 to +60 °C at 0 to 80% non-condensing humidity.
CE	Conforms to CE standards for radiated and conducted emissions, susceptibility and low-voltage power directives
NRTL	Certification verifies, through OSHA-approved NRTL certification authority TÜV SÜD, that the product meets U.S. electrical safety standards (UL/ANSI).