Question

When first discovered α, β and γ radioactivity were referred to as α−rays, β-rays and γ- rays. Now we refer to α-particles and β-particles, but still use the term γ-rays. What type of particles are α and β commonly known as? What type of ray is γ commonly known as? What are the signs of the charges on the three forms of radiation?

Answer 1

1. Helium nucleus and electron/positron

- An
`\alpha` decay is a decay in which an
`\alpha` particle is produced.

An
`\alpha` particle consists of 2 protons and 2 neutrons: therefore, in an alpha-decay, the nucleus loses 2 units of atomic number (number of protons) and 2 units of mass number (sum of protons+neutrons).

The alpha-particle consists of 2 protons of 2 neutrons: so it corresponds to a nucleus of helium, which consists exactly of 2 protons and 2 neutrons.

- There are two types of
`\beta` decay:

-- In the
`\beta^-` decay, a neutron decays into a proton emitting a fast-moving electron and an anti-neutrino:

`n \rightarrow p + e^- + \bar{\\u}`

and the
`\beta` particle in this case is the electron

-- In the
`\beta^+` decay, a proton decays into a neutron, emitting a fast-moving positron and a neutrino:

`p \rightarrow n + e^+ + \\u`

and the
`\beta` particle in this case is the positron.

2) Gamma ray

A
`\gamma` decay occurs when an unstable (excited state) nucleus decays into a more stable state. In this case, there are no changes in the structure of the nucleus, but energy is released in the form of a photon:

`X^* \rightarrow X + \gamma`

where the wavelength of this photon usually falls in the part of the electromagnetic spectrum corresponding to the gamma ray region.

So, the
`\gamma` ray is commonly known as gamma radiation.

3)

The sign of the three forms of radiation are the following:

-
`\alpha` particle: it consists of 2 protons (each of them carrying a positive charge of +e) and 2 neutrons (uncharged), so the total charge is

Q = +e +e = +2e

-
`\beta` particle: in case of
`\beta^-` radiation, the particle is an electron, so it carries a charge of

Q = -e

in case of
`\beta^+` radiation, the particle is a positron, so it carries a charge of

Q = +e

-
`\gamma` radiation: the
`\gamma` radiation consists of a photon, and the photon has no charge, so the charge in this case is

Q = 0