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Unit 7: Astrophysics Page 52

Activities, Experiments, Projects

Lesson 1: Particle Physics

Note: This section is an abbreviated overview of the experiments online.

Experiment: Alpha Particle the way and blocks the alpha
particles from reaching the
Detector
detector, you hear the smoke
alarm scream.
Here is another way to detect
cosmic rays, only this time you’ll
Alpha particles are actually high
actually see the thin, threadlike
speed helium nuclei (which is two
vapor trails appear and disappear.
protons and two neutrons stuck
These cobwebby trails are left by
together). They were named long
the particles within minutes of
before we knew what they were of,
creating the detector.
and the name stuck. Alpha
particles are pretty heavy and
In space, there are powerful
slow, and most get stopped by just
explosions (supernovas) and
rapidly-spinning neutron stars about anything, a sheet of paper or
(pulsars), both of which spew out your skin. Because of this, alpha
particles are not something people
high energy particles that zoom
get excited about, unless you
near the speed of light. Tons of
these particles zip through our actually eat the smoke detector.

atmosphere each day. There are
Both brick buildings as well as
three types of particles: alpha,
people emit beta particles. Beta
beta, and gamma.
particles are actually high speed
electrons or positrons (a positron is
Did you know that your household
smoke alarm emits alpha particles? the antimatter counterpart to the
electron), and they are quick, fast,
There’s a small bit (around
and light. You can stop a beta
1/5000th of a gram) of Americium-
particle by holding up a thin sheet
241, which emits an alpha particle
of plastic or tinfoil.
onto a detector. As long as the
detector sees the alpha particle,
When you hold the jar in your
the smoke alarm stays quiet.
hands, you warm it slightly and
However, since alpha particles are
cause the air inside to get
easy to block, when smoke gets in

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