Background

2

The large area solar gamma-ray spectrometer (LASGA) is a high-energy radiation detector that consists of anti-coincidence detectors and calorimeter. The calorimeter is composed of 5 orthogonal LaBr

3

(lanthanum bromide) layers. Each layer includes fourteen 25 mm×25 mm×400 mm LaBr

3

crystals. To achieve large dynamic range

each LaBr

3

crystal matches with two independent readout elements with different gains. High gain readout uses a photomultiplier tube (PMT) while the low gain uses photodiode (PD). Since PD has no amplification capability for photoelectrons

the LASGA readout system requires a low-noise readout electronics system to achieve a high signal-to-noise ratio (SNR).

Purpose

2

This study aims to design an electronics prototype system with high dynamic range and low noise properties.

Methods

2

A 64-channel charge sensitive ASIC (VA140) produced by the IDEAS Inc. was used in front-end electronics board. And an Altera cyclone field-programmable gate array (FPGA) (EP3C25Q240C8) was employed to control the ASIC

analog to digital converter (ADC) and digital to analog converter (DAC) chips in data acquisition board. The digitalized detector signal was packaged in field-programmable gate array (FPGA) and sent to personal computer (PC) for processing.

Results

2

The performance of the electronics prototype was tested

while the minimum ionizing particles (MIPs) response of LaBr

3

with cosmic ray muon was carried out as well. The test results showed that the noise level of the electronics system (@0 pF) and the detection system (connected with PD) at room temperature was about 600 e

-

and 1800 e

-

respectively. And there was a good linearity in the range of 0-200 fC. The integral nonlinearity (INL) of 126 channels in the range of 0-180 fC was better than 3%.

Conclusion

2

Single bromide lanthanum unit can measure the energy deposited linearly up to 250MeV. The dynamic range and SNR of the prototype system could fully meet the project's requirements.