radioactive decay

A threory of nuclear astrophysics is that all the heavy elements like uranium are formed in supernova explosions of massive stars, which immediately release the elements into space. If we assume that at the time of the explosion there were equal amounts of 235U and 238U, how long ago were the elements that formed our Earth released, given that the present 235U/238U ratio is 0.007? (The half-lives of 235U and 238U are 0.70 x 10^9 yr and 4.47 x 10^9 yr, respectively)

positrons and other antiparticles

A photon with an energy of 2.00 GeV creates a proton-antiproton pair in which the proton has a kinetic energy of 95.0 MeV. What is the kinetic energy of the antiproton?

use of Bohr's model

Using Bohr Model determine: 1. energy loss when electron moves from orbit n=3 to n=1 2. calc wavelenght of the light when electron moves orbit from n=3 to n=1

Calculate the energy levels

Use the equation attached to calculate the energy of E1, E2, E3 and E energy levels of the hydrogen-like boron ion... (refer to attachment)

Calculate the energy of the photons of the hydrogen-like boron ion

Calculate the energy of the photons of the hydrogen-like boron ion... see attached