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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.

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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?

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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.

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

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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.

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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?

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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.

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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.

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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?

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Questions & Answers

Suppose that a grandfather clock is running slowly; that is, the time it takes to complete each cycle is longer than it should be. Should you (@) shorten or (b) lengthen the pendulam to make the clock keep attain the preferred time?
Aj Reply
I think you shorten am not sure
Uche
discuss under damped
Prince Reply
resistance of thermometer in relation to temperature
Ifeanyi Reply
how
Bernard
that resistance is not measured yet, it may be probably in the next generation of scientists
Paul
Is fundamental quantities under physical quantities?
Igwe Reply
please I didn't not understand the concept of the physical therapy
John Reply
physiotherapy - it's a practice of exercising for healthy living.
Paul
what chapter is this?
Anderson
this is not in this book, it's from other experiences.
Paul
please I have probably with calculate please can you please and help me out
John Reply
Sure
Gift
What is Boyce law
Sly Reply
how to convert meter per second to kilometers per hour
grace Reply
Divide with 3.6
Mateo
multiply by (km/1000m) x (3600 s/h) -> 3.6
Muhammad
2 how heat loss is prevented in a vacuum flask
Abdullah Reply
what is science
Helen
logical reasoning for a particular phenomenon.
Ajay
I don't know anything about it 😔. I'm sorry, please forgive 😔
Adarsh
due to non in contact mean no conduction and no convection bec of non conducting base and walls and also their is a grape between the layer like to take the example of thermo flask
Abdul
dimensions v²=u²+2at
Lagben Reply
what if time is not given in finding the average velocity?
Alan Reply
the magnetic circuit of a certain of the flux paths in each of the long and short sides being 25cm and 20cm reprectielectrove. there is an air gap of 2mm long in one the long sides if a flux density of 0.8weber/m is to produce in the magnet of 1500 turns..
Daniel Reply
How do you calculate precision
Sacky Reply
what module is that?
Fillemon
Chemisty 1A?
Fillemon
No it has something to do with measurements bro... What we did today in class
Sacky
Tah bra honestly I didn't understand a thing in that class..when re your Tutorials?
Fillemon
Friday bro... But the topics we did are in this app... Just try to master them quickly before the test dates... Are you done with the Maths sheet
Sacky
I eat ass
Anderson
I'll work on the maths sheet tomorrow bra @Sacky Malyenge but I'll try mastering them
Fillemon
I'll eat your mom's ass with a side of tendies
Anderson
@Fillemon Nanwaapo
Anderson
lol, hush
Emi
There are very large numbers of charged particles in most objects. Why, then, don’t most objects exhibit static electricity?
Bilkisu Reply
Because there's an equal number of negative and positive charges... objects are neutral in nature
NELSON
when a ball rolls on a smooth level ground,the motion of its centre is?
Mary Reply
what is electro magnetic field?
Mary
electromagnetic field is a special type of field been produced by electric charges..!!! like the word electro from Electricity and the word magnetic from Magnetism.. so it is more of a join field..!!!
NELSON
Electromagnetic field is caused by moving electric charge
Muhammad
when a ball rolls on a smooth level ground,the motion of its centre is?
Mumeh
Practice Key Terms 8

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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