The ion smoke sensor mainly used for fire alarm is shown in the figure. There are electrodes 2 and 3 in the net cover 1. A and B are connected to the power supply. 4 is a small piece of radioisotope americium 241, which can emit a kind of particles that can easily ionize the gas. Usually, the particles emitted by americium ionize the air between the two electrodes; a. When a fire breaks out, smoke enters the net cover, and the smoke particles absorb the ions in the air and the particles emitted by americium, causing the current to change. The circuit detects this change and gives an alarm A. Americium 241 emits α particles, and the current increases when there is smoke. B. americium 241 emits α particles, and the current decreases when there is smoke. C. americium 241 emits β particles, and the current increases when there is smoke. D. americium 241 emits β particles, and the current decreases when there is smoke

The ion smoke sensor mainly used for fire alarm is shown in the figure. There are electrodes 2 and 3 in the net cover 1. A and B are connected to the power supply. 4 is a small piece of radioisotope americium 241, which can emit a kind of particles that can easily ionize the gas. Usually, the particles emitted by americium ionize the air between the two electrodes; a. When a fire breaks out, smoke enters the net cover, and the smoke particles absorb the ions in the air and the particles emitted by americium, causing the current to change. The circuit detects this change and gives an alarm A. Americium 241 emits α particles, and the current increases when there is smoke. B. americium 241 emits α particles, and the current decreases when there is smoke. C. americium 241 emits β particles, and the current increases when there is smoke. D. americium 241 emits β particles, and the current decreases when there is smoke

The radioisotope americium 241 can emit a kind of particle which can easily ionize the gas. It is known that the particle is alpha particle. In case of fire, the smoke enters into the net, and the smoke particles absorb the ions in the air and the particles emitted by americium, which makes the current weaken. So B is correct, a, C and D are wrong. So B is selected