<< Chapter < Page Chapter >> Page >

Collisions

Conservation of energy and momentum often results in energy transfer to a less massive object in a collision. This was discussed in detail in Work, Energy, and Energy Resources , for example.

Different types of radiation have different ranges when compared at the same energy and in the same material. Alphas have the shortest range, betas penetrate farther, and gammas have the greatest range. This is directly related to charge and speed of the particle or type of radiation. At a given energy, each α , β , or γ will produce the same number of ionizations in a material (each ionization requires a certain amount of energy on average). The more readily the particle produces ionization, the more quickly it will lose its energy. The effect of charge is as follows: The α size 12{α} {} has a charge of + 2 q e , the β has a charge of q e size 12{ - 2q rSub { size 8{e} } } {} , and the γ size 12{γ} {} is uncharged. The electromagnetic force exerted by the α size 12{α} {} is thus twice as strong as that exerted by the β size 12{β} {} and it is more likely to produce ionization. Although chargeless, the γ size 12{γ} {} does interact weakly because it is an electromagnetic wave, but it is less likely to produce ionization in any encounter. More quantitatively, the change in momentum Δ p size 12{Δp} {} given to a particle in the material is Δ p = F Δ t , where F size 12{F} {} is the force the α , β , or γ exerts over a time Δ t size 12{Δt} {} . The smaller the charge, the smaller is F size 12{F} {} and the smaller is the momentum (and energy) lost. Since the speed of alphas is about 5% to 10% of the speed of light, classical (non-relativistic) formulas apply.

The speed at which they travel is the other major factor affecting the range of α size 12{α} {} s, β size 12{β} {} s, and γ size 12{γ} {} s. The faster they move, the less time they spend in the vicinity of an atom or a molecule, and the less likely they are to interact. Since α size 12{α} {} s and β size 12{β} {} s are particles with mass (helium nuclei and electrons, respectively), their energy is kinetic, given classically by 1 2 mv 2 size 12{ { {1} over {2} } ital "mv" rSup { size 8{2} } } {} . The mass of the β size 12{β} {} particle is thousands of times less than that of the α size 12{α} {} s, so that β size 12{β} {} s must travel much faster than α size 12{α} {} s to have the same energy. Since β size 12{β} {} s move faster (most at relativistic speeds), they have less time to interact than α size 12{α} {} s. Gamma rays are photons, which must travel at the speed of light. They are even less likely to interact than a β size 12{β} {} , since they spend even less time near a given atom (and they have no charge). The range of γ size 12{γ} {} s is thus greater than the range of β size 12{β} {} s.

Alpha radiation from radioactive sources has a range much less than a millimeter of biological tissues, usually not enough to even penetrate the dead layers of our skin. On the other hand, the same α radiation can penetrate a few centimeters of air, so mere distance from a source prevents α size 12{α} {} radiation from reaching us. This makes α size 12{α} {} radiation relatively safe for our body compared to β and γ size 12{γ} {} radiation. Typical β radiation can penetrate a few millimeters of tissue or about a meter of air. Beta radiation is thus hazardous even when not ingested. The range of β size 12{β} {} s in lead is about a millimeter, and so it is easy to store β sources in lead radiation-proof containers. Gamma rays have a much greater range than either α size 12{α} {} s or β size 12{β} {} s. In fact, if a given thickness of material, like a lead brick, absorbs 90% of the γ s, then a second lead brick will only absorb 90% of what got through the first. Thus, γ s do not have a well-defined range; we can only cut down the amount that gets through. Typically, γ size 12{γ} {} s can penetrate many meters of air, go right through our bodies, and are effectively shielded (that is, reduced in intensity to acceptable levels) by many centimeters of lead. One benefit of γ size 12{γ} {} s is that they can be used as radioactive tracers (see [link] ).

This figure shows four images of a skeleton of a human. Different parts of the body show bright spots wherever the bone cells are most active, indicating bone cancer.
This image of the concentration of a radioactive tracer in a patient’s body reveals where the most active bone cells are, an indication of bone cancer. A short-lived radioactive substance that locates itself selectively is given to the patient, and the radiation is measured with an external detector. The emitted γ size 12{γ} {} radiation has a sufficient range to leave the body—the range of α size 12{α} {} s and β size 12{β} {} s is too small for them to be observed outside the patient. (credit: Kieran Maher, Wikimedia Commons)

Phet explorations: beta decay

Watch beta decay occur for a collection of nuclei or for an individual nucleus.

Beta Decay

Section summary

  • Some nuclei are radioactive—they spontaneously decay destroying some part of their mass and emitting energetic rays, a process called nuclear radioactivity.
  • Nuclear radiation, like x rays, is ionizing radiation, because energy sufficient to ionize matter is emitted in each decay.
  • The range (or distance traveled in a material) of ionizing radiation is directly related to the charge of the emitted particle and its energy, with greater-charge and lower-energy particles having the shortest ranges.
  • Radiation detectors are based directly or indirectly upon the ionization created by radiation, as are the effects of radiation on living and inert materials.

Conceptual questions

Suppose the range for 5 . 0 MeV α size 12{5 "." "0 MeV" α} {} ray is known to be 2.0 mm in a certain material. Does this mean that every 5 . 0 MeV α size 12{5 "." "0 MeV" α} {} a ray that strikes this material travels 2.0 mm, or does the range have an average value with some statistical fluctuations in the distances traveled? Explain.

Got questions? Get instant answers now!

What is the difference between γ size 12{γ} {} rays and characteristic x rays? Is either necessarily more energetic than the other? Which can be the most energetic?

Got questions? Get instant answers now!

Ionizing radiation interacts with matter by scattering from electrons and nuclei in the substance. Based on the law of conservation of momentum and energy, explain why electrons tend to absorb more energy than nuclei in these interactions.

Got questions? Get instant answers now!

What characteristics of radioactivity show it to be nuclear in origin and not atomic?

Got questions? Get instant answers now!

What is the source of the energy emitted in radioactive decay? Identify an earlier conservation law, and describe how it was modified to take such processes into account.

Got questions? Get instant answers now!

Consider [link] . If an electric field is substituted for the magnetic field with positive charge instead of the north pole and negative charge instead of the south pole, in which directions will the α size 12{α} {} , β size 12{β} {} , and γ size 12{γ} {} rays bend?

Got questions? Get instant answers now!

Explain how an α size 12{α} {} particle can have a larger range in air than a β size 12{β} {} particle with the same energy in lead.

Got questions? Get instant answers now!

Arrange the following according to their ability to act as radiation shields, with the best first and worst last. Explain your ordering in terms of how radiation loses its energy in matter.

(a) A solid material with low density composed of low-mass atoms.

(b) A gas composed of high-mass atoms.

(c) A gas composed of low-mass atoms.

(d) A solid with high density composed of high-mass atoms.

Got questions? Get instant answers now!

Often, when people have to work around radioactive materials spills, we see them wearing white coveralls (usually a plastic material). What types of radiation (if any) do you think these suits protect the worker from, and how?

Got questions? Get instant answers now!

Questions & Answers

how lesers can transmit information
mitul Reply
griffts bridge derivative
Ganesh Reply
below me
please explain; when a glass rod is rubbed with silk, it becomes positive and the silk becomes negative- yet both attracts dust. does dust have third types of charge that is attracted to both positive and negative
Timothy Reply
what is a conductor
Timothy
hello
Timothy
below me
why below you
Timothy
no....I said below me ...... nothing below .....ok?
dust particles contains both positive and negative charge particles
Mbutene
corona charge can verify
Stephen
when pressure increases the temperature remain what?
Ibrahim Reply
what is frequency
Mbionyi Reply
define precision briefly
Sujitha Reply
CT scanners do not detect details smaller than about 0.5 mm. Is this limitation due to the wavelength of x rays? Explain.
MITHRA Reply
hope this helps
what's critical angle
Mahmud Reply
The Critical Angle Derivation So the critical angle is defined as the angle of incidence that provides an angle of refraction of 90-degrees. Make particular note that the critical angle is an angle of incidence value. For the water-air boundary, the critical angle is 48.6-degrees.
dude.....next time Google it
okay whatever
Chidalu
pls who can give the definition of relative density?
Temiloluwa
the ratio of the density of a substance to the density of a standard, usually water for a liquid or solid, and air for a gas.
Chidalu
What is momentum
aliyu Reply
mass ×velocity
Chidalu
it is the product of mass ×velocity of an object
Chidalu
how do I highlight a sentence]p? I select the sentence but get options like copy or web search but no highlight. tks. src
Sean Reply
then you can edit your work anyway you want
Wat is the relationship between Instataneous velocity
Oyinlusi Reply
Instantaneous velocity is defined as the rate of change of position for a time interval which is almost equal to zero
Astronomy
The potential in a region between x= 0 and x = 6.00 m lis V= a+ bx, where a = 10.0 V and b = -7.00 V/m. Determine (a) the potential atx=0, 3.00 m, and 6.00 m and (b) the magnitude and direction of the electric ficld at x =0, 3.00 m, and 6.00 m.
what is energy
Victor Reply
hi all?
GIDEON
hey
Bitrus
energy is when you finally get up of your lazy azz and do some real work 😁
what is physics
faith Reply
what are the basic of physics
faith
base itself is physics
Vishlawath
tree physical properties of heat
Bello Reply
tree is a type of organism that grows very tall and have a wood trunk and branches with leaves... how is that related to heat? what did you smoke man?
algum profe sabe .. Progressivo ou Retrógrado e Acelerado ou Retardado   V= +23 m/s        V= +5 m/s        0__>              0__> __________________________>        T= 0               T=6s
Claudia
Practice Key Terms 8

Get the best College physics course in your pocket!





Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics' conversation and receive update notifications?

Ask