Video Transcript
Which of the following statements
about the deflection of a stream of ionized radiation containing 𝛼 particles, 𝛽
particles, and 𝛾 rays in a magnetic field is true? (A) 𝛼 particles and 𝛽 particles
are deflected in the same direction. (B) 𝛽 particles are not deflected
by an electric field. (C) 𝛽 particles can be deflected
back toward the emitter. (D) 𝛼 particles are only deflected
by a small amount compared to 𝛽 particles. Or (E) 𝛾 rays are deflected in the
same direction as 𝛽 particles.
Ionizing radiation is radiation
that carries enough energy to remove electrons from atoms. Common examples of ionizing
radiation include 𝛼 particles, 𝛽 particles, and 𝛾 rays. In order to understand how these
types of ionizing radiation will be affected by a magnetic field, it’s important to
understand their structure.
An 𝛼 particle consists of two
protons and two neutrons and is comparable to a nucleus of a helium atom. An 𝛼 particle has a mass of four
unified atomic mass units and an overall charge of two plus, as it contains two
positively charged protons. A 𝛽 particle, more specifically, a
𝛽 minus particle, is a high-energy electron. These particles are significantly
smaller than 𝛼 particles and have a mass of approximately one divided by 1800
unified atomic mass units. As electrons carry a negative
charge, a 𝛽 minus particle similarly has an overall negative charge.
𝛾 rays, also called 𝛾 radiation,
are a form of electromagnetic energy. As such, 𝛾 rays have no mass and
no charge. When each of these types of
radiation passes through a magnetic field, they may or may not be deflected by the
positive and negative poles of the field. As 𝛾 rays do not have a charge,
they will not be affected by a magnetic field and will continue to travel along the
same path.
𝛽 minus particles are negatively
charged. Since opposite charges attract, the
𝛽 minus particles will be attracted to the positive pole. 𝛼 particles, on the other hand,
are positively charged, so they should be attracted to the negative pole. As the magnitude of the charge of
an 𝛼 particle is two times that of a 𝛽 minus particle, we might expect an 𝛼
particle to be deflected more in a magnetic field. However, the mass of an 𝛼 particle
is over 7000 times greater than the mass of a 𝛽 particle. As 𝛼 particles are much more
massive than 𝛽 particles, they will be deflected to a lesser extent.
With this understanding in mind,
let’s take a look at the answer choices. Answer choice (A) cannot be correct
because 𝛼 and 𝛽 particles are deflected in opposite directions. Answer choices (B) and (C) cannot
be correct because 𝛽 particles are deflected by an electric field and are not
deflected back towards the emitter. Answer choice (E) is incorrect
because 𝛾 rays are not deflected by a magnetic field. This leaves us with answer choice
(D). 𝛼 particles are deflected to a
lesser extent than 𝛽 particles.
So, the true statement about the
deflection of a stream of ionized radiation in a magnetic field is answer choice
(D): 𝛼 particles are only deflected by a small amount compared to 𝛽 particles.
