A smoke and particle ionization detector using tritiated amorphous silicon film as the radiation source is demonstrated. The ion chamber design includes both bipolar and unipolar region; the unipolar region is defined as the volume space extending beyond the range of ionizing particles. Attachment of ions to particulate matter in the unipolar region considerably reduces the mobility of the carriers, thus forming a space charge cloud accompanied by a reduction in the electrical field strength, thereby enhancing the particulate detection responsivity. Tritium s have a maximum range of about 6 mm in air, which makes the detector compact. Owing to the potential of increased specific activity, it results in a gamma-free detector with improved sensitivity. The results show that this gamma-free detector is several-fold to forty-fold more responsive than traditional ionization detectors using Am-241. In addition, this ion chamber can function as a dual detector having both photoelectric and ionization detector responsivities.