Further study of CdWO4 crystal scintillators as detectors for high sensitivity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si122.gif" overflow="scroll"><mml:mn>2</mml:mn><mml:mi mathvariant="normal">β</mml:mi></mml:math> experiments: Scintillation properties and pulse-shape discrimination