positron decay

[DrMattOglesby]

Advertisement - Members don't see this ad

positron decay...AKA beta(+) decay:
what exactly is changing into what and what happens to the A and Z values??

 

[bluemonkey]

positron decay...AKA beta(+) decay:
what exactly is changing into what and what happens to the A and Z values??

A proton decays into a neutron, positron (the antiparticle to an electron), and a neutrino (which isn't really important for the MCAT). The positron gets ejected from the atom while the neutron remains. Because neutrons and protons weight the same, the atomic weight remains the same (minus the positron which is insignificant in terms of mass). Because you "lose" a proton, however, the atomic number decreases by one.

 

[TawMus]

positron decay...AKA beta(+) decay:
what exactly is changing into what and what happens to the A and Z values??

A stays same
Z goes down 1

 

[DrMattOglesby]

.

 

[DrMattOglesby]

and so Beta(-) decay is thus:

Neutron --> proton + electron

• where the electron is emitted and the proton stays in the nucleus.

This means that:

• the mass stays the same (neutron = proton in terms of weight).
• the overall charge goes up by one (proton = +1 charge)

2 Questions

1. is that a correct understanding?
2. the A and Z values are constant in Gamma Decay...right?

 

[bluemonkey]

and so Beta(-) decay is thus:

Neutron --> proton + electron

• where the electron is emitted and the proton stays in the nucleus.

This means that:

• the mass stays the same (neutron = proton in terms of weight).
• the overall charge goes up by one (proton = +1 charge)

2 Questions

1. is that a correct understanding?
2. the A and Z values are constant in Gamma Decay...right?

You're right on for beta decay! As you said, a neutron splits into a proton plus an electron. The Z value increases by one and the A value remains constant.

You're also solid with gamma production. The mass stays the same. All that is taking place here is a nucleon is going from a high energy state to a lower energy state emitting a high energy photon (gamma ray). This often takes place in conjunction with alpha and beta decays (both + & -) where one of the daughter nuclei may be in a high-energy state.

Rock on!