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Science Question I got wrong...

Diamond

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Jun 2, 2003
Messages
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What type of radiation is used in a smoke detector?

a) Infrared
b) Alpha
c) Beta
d) Gamma

What is your answer and why?
 
I chose "Alpha", because it's the correct answer ;) - or rather, it's probably the answer they're expecting.
 
None of the above: It uses tachyon pulses generated by the fire's main deflector dish.
 
Diamond said:
What type of radiation is used in a smoke detector?

a) Infrared
b) Alpha
c) Beta
d) Gamma

What is your answer and why?
Click to expand...

Aren't there two different major kinds of smoke detectors?

Photoelectric detectors use (mostly) infrared radiation. Ionizing detectors use alpha particles (generated by americium, IIRC).
 
Diamond said:
What type of radiation is used in a smoke detector?

a) Infrared
b) Alpha
c) Beta
d) Gamma

What is your answer and why?
Click to expand...

Alpha, of course. Smoke detectors use Americum which undergoes spontaneous alpha decay.

I remember a news story some years back about a high-school kid to tried to build a nuclear reactor using the strips from smoke detectors. It didn't work, of course, but the result was hot enough that the guys in the bulky suits had to come take it away.
 
epepke said:
Alpha, of course. Smoke detectors use Americum which undergoes spontaneous alpha decay.

I remember a news story some years back about a high-school kid to tried to build a nuclear reactor using the strips from smoke detectors. It didn't work, of course, but the result was hot enough that the guys in the bulky suits had to come take it away.
Click to expand...

I didn't realise that smoke detectors used americium (or even that they were radioactive).
 
epepke said:
Alpha, of course. Smoke detectors use Americum which undergoes spontaneous alpha decay.

I remember a news story some years back about a high-school kid to tried to build a nuclear reactor using the strips from smoke detectors. It didn't work, of course, but the result was hot enough that the guys in the bulky suits had to come take it away.
Click to expand...


You refering to this?
http://www.dangerouslaboratories.org/radscout.html
 
epepke said:
Alpha, of course. Smoke detectors use Americum which undergoes spontaneous alpha decay.
Click to expand...

Americum is also a fissile material. I did once work out how many fire alams you would need to get enough material to build a bomb. It was a lot.
 
There are two types of smoke detectors: optical and ionization.

The optical detector sends a beam of light through a detection area, and has a light sensor offset from the direction of the beam. If smoke particles enter the detection area, they scatter the light, causing some of it to fall on the detector. When the detector detects light, it sets off the alarm.

The ionization detector uses alpha particles from Americium-241 to ionize gas within a tube, permitting an electric current to flow through the gas. The detection area is between the alpha source and the tube; if smoke enters the detection area, it scatters the alpha particles and reduces the ionization of the gas in the tube, which restricts the electric current. The reduced electric current sets off the alarm.

Quite likely, either of these answers would have been correct and justifiable, but the answer the test was looking for was probably the second.
 
Schneibster said:
There are two types of smoke detectors: optical and ionization.
Click to expand...

Welcome to the fora, Schneibster.

I don't know about modern optical smoke detectors, but I installed one in 1976. Of course, I took it apart first. It definitely used mostly visible light, generated from a grain-of-wheat bulb. The test button was connected to a plastic needle with white paint that was introduced into the chamber.
 
Thanks, epepke, and thanks for inviting me. It's interesting here.

Yes, that white painted plastic needle would scatter light onto the sensor and set it off.
 
I got 8/10. Wiring colors and smoke alarms. I know of another 2nd rate physicist who got the same...
 
We use optical smoke detectors in big ventilation ducts you could probably walk inside. I've never seen one in a house.

Otherwise, alpha particles and the americium. You might know this if you ever replaced the batteries and read the warning label. CHANGE THOSE BATTERIES! :)
 
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