Table of Contents

## How long does it take a 100 gram sample of uranium-235 to decay to a mass of 50 grams?

700 million years

Since the problem is asking for the time for U-235 to decay to 1/2 its original mass (100 grams to 50 grams) then the decay time is 1 half-life, or 700 million years.

**How long does it take uranium-235 to decay?**

Uranium-235 has a half-life of just over 700 million years. Uranium-234 has the shortest half-life of them all at 245,500 years, but it occurs only indirectly from the decay of U-238. In comparison, the most radioactive element is polonium.

**What is the half-life of 700 million years?**

The much scarcer, fissionable isotope of uranium, U-235, has a half-life of 700 million years, indicating that its present abundance is only about 1 percent of the amount present when the solar system was born.

### How long will it take for 10 of a 1000 gram sample of uranium-235 to decay?

How long will it take for ten percent of a 1000-gram sample of uranium-235 to decay? Ten percent of 1000 grams is 100 grams….Solving Applied Problems Using Exponential and Logarithmic Equations.

Substance | Use | Half-life |
---|---|---|

carbon-14 | archeological dating | 5,715 years |

**What is the measure of radioactive decay rate?**

Curies

The rate of decay is often referred to as the activity of the isotope and is often measured in Curies (Ci), one curie = 3.700 x 1010 atoms that decay/second. By knowing the amount of radioisotope and the activity of the sample, the rate constant can be determined.

**How much will remain after 800 years?**

The quantity of radioactive nuclei at any given time will decrease to half as much in one half-life. For example, if there are 100g of Cf-251 in a sample at some time, after 800 years, there will be 50g of Cf-251 remaining; after another 800 years (1600 years total), there will only be 25g remaining.

#### Why is U 235 better than U 238?

U- 235 is a fissile isotope, meaning that it can split into smaller molecules when a lower-energy neutron is fired at it. U- 238 has an even mass, and odd nuclei are more fissile because the extra neutron adds energy – more than what is required to fission the resulting nucleus.

**What has the longest half-life?**

The data helped the collaboration make the first definitive measurement of xenon-124’s half-life: 18 billion trillion years. “This is the longest lifetime that we have ever directly measured.” This decay process is called two-neutrino double electron capture.

**Is radioactive decay first order?**

Since the rate of radioactive decay is first order we can say: r = k[N]1, where r is a measurement of the rate of decay, k is the first order rate constant for the isotope, and N is the amount of radioisotope at the moment when the rate is measured.

## How do you calculate half-life decay?

The time required for half of the original population of radioactive atoms to decay is called the half-life. The relationship between the half-life, T1/2, and the decay constant is given by T1/2 = 0.693/λ.

**What is the half life of uranium 235?**

Uranium-235 (U-235) Half-life: 700 million years Uranium-238 (U-238) Half-life: 4.47 billion years

**What are the chemical properties of uranium uranium?**

Chemical properties: Weakly radioactive, extremely dense metal (65% denser than lead) What is it used for? Uranium “enriched” into U-235 concentrations can be used as fuel for nuclear power plants and the nuclear reactors that run naval ships and submarines. It also can be used in nuclear weapons.

### What does uranium look like in a nuclear reactor?

Uranium is an extremely heavy metal. Enriched uranium can be in the form of small pellets that are packaged in the long tubes used in nuclear reactors. What does it look like? When it has been refined and enriched, uranium is a silvery-white metal. How can it hurt me?

**How is uranium not harmful to the human body?**

When it has been refined and enriched, uranium is a silvery-white metal. How can it hurt me? Because uranium decays by alpha particles, external exposure to uranium is not as dangerous as exposure to other radioactive elements because the skin will block the alpha particles.