lecture 25.2- nuclear transformations

BELLWORK

1. What is the symbol for an alpha particle?2. Write the nuclear equation for the alpha

decay of Uranium-238.3. What is the symbol of a beta particle?4. Write the nuclear equation for the beta

decay of Carbon-14.5. Write the symbol for gamma radiation.6. Why is gamma radiation often not included

in a nuclear equation?

Lecture 25.2- NuclearTransformations

Radon-222 is aradioactive isotope thatis present naturally inthe soil in some areas. Ithas a constant rate ofdecay. You will learnabout decay rates ofradioactive substances.

25.2

The nucleus is held together by the strong nuclear forceThe strong nuclear force is thestrongest force known

Protons and neutrons are very closetogether

They exchange a teeny bit of mass backand forth.

When disrupted, the mass is convertedto energy according toE=mc2

The mass is tiny.The energy is immense.

Protons and neutrons experience the strongnuclear force if close enough

Because protons repel each other thenucleus needs a certain proton to neutronratio for stability

More than 1,500 different nuclei are known. Ofthose, only 264 are stable and do not decay orchange with time. These nuclei are in a regioncalled the band of stability.

25.2

Nuclear Stability and Decay

The neutron-to-proton ratiodetermines thetype of decaythat occurs.

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A half-life (t1/2) is the time required forone-half of the nuclei of a radioisotopesample to decay to products.

After each half-life, half ofthe existing radioactiveatoms have decayed intoatoms of a new element.

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Stable Isotope

The ratio of Carbon-14 tostable carbon in theremains of an organismchanges in a predictableway that enables thearchaeologist to obtain anestimate of its age.

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for Sample Problem 25.1

The conversion of an atom of oneelement to an atom of anotherelement is called transmutation.

Transmutation can occur byradioactive decay.

Or

when particles bombard thenucleus of an atom.

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The first artificial transmutation reaction involvedbombarding nitrogen gas with alpha particles.

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The elements in the periodic table withatomic numbers above 92, the atomicnumber of uranium, are called thetransuranium elements.

• All transuranium elements undergotransmutation.

• None of the transuranium elementsoccur in nature, and all of them areradioactive.

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Transuranium elements aresynthesized in nuclear reactors andnuclear accelerators.

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25.2 Section Quiz.

1. During nuclear decay, if the atomic numberdecreases by one but the mass number isunchanged, the radiation emitted is

a. a positron.

b. an alpha particle.

c. a neutron.

d. a proton.

25.2 Section Quiz.

2. When potassium-40 (atomic number 19)decays into calcium-40 (atomic number 20),the process can be described as

a. positron emission.

b. alpha emission.

c. beta emission.

d. electron capture.

25.2 Section Quiz.

3. If there were 128 grams of radioactivematerial initially, what mass remains after fourhalf-lives?

a. 4 grams

b. 32 grams

c. 16 grams

d. 8 grams

25.2 Section Quiz.

4. When transmutation occurs, the ________always changes.

a. number of electrons

b. mass number

c. atomic number

d. number of neutrons

25.2 Section Quiz

5. Transmutation occurs by radioactive decayand also by

a. extreme heating.

b. chemical reaction.

c. high intensity electrical discharge.

d. particle bombardment of the nucleus.