# Uranium238 vs U235, which are true?

• Kibbel
In summary, the question is whether the speed of sound in a bar of U238 is higher, lower, or the same compared to U235. The answer is that the speed is the same due to the identical number of protons and electrons in both isotopes, which determines the interatomic distance and effective stiffness of the interatomic bond. The difference in mass does not affect these parameters.
Kibbel

## Homework Statement

Uranium-238 (U238) has three more neutrons than uranium-235 (U235). Compared to the speed of sound in a bar of U235, is the speed of sound in a bar of U238 higher, lower, or the same? There are several factors that play a role.

(a) Chemically, the atoms of these two isotopes behave in essentially identical ways, since the number of protons (92) is identical and the clouds of 92 electrons are nearly identical. The interatomic distance, and the effective "stiffness" of the interatomic bond, both depend on the chemical properties of the atoms. Therefore, which of the following statements are true?

1. The interatomic distance is the same for the two isotopes, because it depends on the size of the electron cloud, not the nuclear mass.

2. An atom with more mass in the nucleus is bigger, so the distance between neighboring atoms is larger.

3.The effective stiffness of the interatomic "spring" is the same in the two isotopes, since this "spring" is a model for the interactions of the outer electrons, which are the same for different isotopes of the same atom.

4.The effective stiffness of the interatomic "spring" is greater for U238 because the mass is greater.

none

## The Attempt at a Solution

I thought it was that the interatomic distance in between the two are the same, (#1). I am not sure whether it has to do with the electron, but I was pretty sure that it doesn't have to do with the mass. this is why i didn't check 2 or 4 either. Because I know two things can have the same mass, but they don't neccissarily have to be bigger, because the density might be different. Or maybe the entire thing is different on the microscopic level?

can someone help me out?

Think of the atoms comprising the metal as little balls connected to other little balls with springs. What two parameters determine the speed at which a vibration travels through this mass/spring web?

As is pointed out, in the case of U235 and U238 there is no difference in "spring" constant, only a difference of mass.

AM

## 1. What is the difference between Uranium-238 and Uranium-235?

Both Uranium-238 and Uranium-235 are isotopes of the element uranium, meaning they have the same number of protons but different numbers of neutrons. Uranium-238 has 92 protons and 146 neutrons, while Uranium-235 has 92 protons and 143 neutrons.

## 2. Which isotope is more commonly found in nature?

Uranium-238 is more commonly found in nature, making up about 99.3% of all naturally occurring uranium on Earth. Uranium-235 makes up the remaining 0.7%.

## 3. Can both isotopes be used to create nuclear energy?

Yes, both Uranium-238 and Uranium-235 can be used to create nuclear energy through the process of nuclear fission. However, Uranium-235 is the preferred isotope for nuclear energy production due to its higher fissile properties.

## 4. Is one isotope more radioactive than the other?

Yes, Uranium-238 is more radioactive than Uranium-235. This is because Uranium-238 has a longer half-life, meaning it takes longer for half of the atoms in a sample to decay. This longer half-life results in a slower rate of radiation emission.

## 5. Can Uranium-238 be converted into Uranium-235?

Yes, Uranium-238 can be converted into Uranium-235 through a process called enrichment. This involves separating the two isotopes using a centrifuge or other methods. However, this process is expensive and is heavily regulated due to the potential for creating nuclear weapons.

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