# HELP!! Radioactive decay bmatWatch

Thread starter 4 years ago
#1
Hi guys

Could someone please explain the following question to me....

The correct answer is B.

I think I understand that the first phase of the decay is the emission of an alpha particle (hence the -2 (neutrons) and -2 (protons) from the element) but I cannot understand what is happening in the second stage!? has a positron been emitted? How would I know that to be the case from the question, rather than say, a beta particle?

Im probably missing something fundamental but if someone could assist me that would be amazing! Thanks!
0
reply
4 years ago
#2
(Original post by juicedesuccess)
Hi guys

Could someone please explain the following question to me....

The correct answer is B.

I think I understand that the first phase of the decay is the emission of an alpha particle (hence the -2 (neutrons) and -2 (protons) from the element) but I cannot understand what is happening in the second stage!? has a positron been emitted? How would I know that to be the case from the question, rather than say, a beta particle?

Im probably missing something fundamental but if someone could assist me that would be amazing! Thanks!
Three types of decay exist:

1. Alpha decay (top number decreases by 4, while bottom by 2)
2. Beta decay (top number decreases by 0, while bottom number increases by 1)
3. Gamma decay (no change)

In beta decay, a neutron is converted into a proton and an electron, and the electron is emitted. Therefore the number of protons, that is the bottom number, increases by 1. The total number of protons and neutrons however remains constant, since 1 neutron has been lost.

So to solve the question we have to look at what is given and deduce if process 1,2 or 3 is taking place.

Initially it is given that X decays to Y, reducing the bottom number by 2. We can thus deduce this is alpha decay, and therefore P = N-4.

Next we see that Y decays to Z, but the top number doesn't change. This means that it cannot be alpha decay, since otherwise the top number would have changed. This leaves either beta or gamma decay. Gamma decay doesn't really change the atom at all, so if we assume Y is different to Z, then it must be beta decay, and therefore the bottom number must increase by 1 from R-2 to R-1.

Therefore the correct answer is B.
1
reply
Thread starter 4 years ago
#3
Amazing explanation, thank you so much!
0
reply
X

Write a reply...
Reply
new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• Cranfield University
Cranfield Forensic MSc Programme Open Day Postgraduate
Thu, 25 Apr '19
• University of the Arts London
Open day: MA Footwear and MA Fashion Artefact Postgraduate
Thu, 25 Apr '19
• Cardiff Metropolitan University
Undergraduate Open Day - Llandaff Campus Undergraduate
Sat, 27 Apr '19

### Poll

Join the discussion

#### Have you registered to vote?

Yes! (129)
38.62%
No - but I will (19)
5.69%
No - I don't want to (25)
7.49%
No - I can't vote (<18, not in UK, etc) (161)
48.2%

View All
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.