# Homework Help: Products of nuclear reaction

1. Aug 11, 2006

### Amith2006

# Neutrons bombard nuclei of N(14,7) converting it into Li(7,3). The process is accompanied by the emission of:
1)4 protons and 4 neutrons
2)6 protons and 2 electrons
3)1 alpha particle, 2 protons and 1 neutron
4)2 alpha particles and gamma ray photon
I get 2 solutions here.
N(14,7) + n(1,0) ---> Li(7,3) + 4p(1,1) + 4n(1,0)
N(14,7) + n(1,0) ---> Li(7,3) + 2(alpha particles)

Is it right? When a N(14,7) is bombarded with a neutron, is the emission of 2 different particles possible? Here N=nitrogen, Li=Lithium, n=neutron, p=proton.

2. Aug 11, 2006

### Chi Meson

The answer likes in the additional information of the gamma ray. Does the element Iron have any meaning regarding fission for you?

3. Aug 12, 2006

### Amith2006

Sorry I forgot to include the gamma ray emission. I didn't get you. Could you please be more clear?

4. Aug 12, 2006

### jubba

Iron has the most nuclear stability. Atoms will lose energy as they undergo fusion or fission to form Iron. i.e Atoms with atomic number less than iron will not release energy in fission.

5. Aug 12, 2006

### Amith2006

So, do u mean that,
N(14,7) + n(1,0) ---> Li(7,3) + 2(alpha particles) + (gamma rays)
is not possible?

6. Aug 12, 2006

### jubba

Well thats what i think

7. Aug 12, 2006

### Chi Meson

Almost, but not quite.

[Edit: Oh I see what you meant; you're quite right]

Elements lighter than iron will release enery when undergoing fusion (specifically, is they fuse to form elements lighter than iron). In order to make the lighter elements undergo fission, a lot of energy is required to be put in. In this sample reaction, it will be the kinetic energy of the bombarding neutrons. There is no way that there would be so much excess KE that it must be released as gamma rays.

Elements heavier than iron will release excess binding energy in the form of gamma rays when fissing; but they will require energy (lots of it) to fuse into these heavier elements. There is one correct answer to your question.

Last edited: Aug 12, 2006
8. Aug 12, 2006

### Astronuc

Staff Emeritus
There are two possible solutions based on the balance of protons and neutrons.

The more particles produced requires more initial energy in the reaction, so more particles are a less likely outcome.

The initial reaction is more likely $^{14}_7N\,+\,^1_0n\,\rightarrow\,^{15}_7N\,+\,\gamma$ - prompt gamma.

Now 15N is stable, so there should be a threshold for a fission/spallation reaction.

One can calculate the neutron energy required to form the products by calculating the mass defect (or binding energy).

8Be is unstable with a half-life of 6.7E-17 s, splitting into 2 alpha particles.

Last edited: Aug 12, 2006
9. Aug 12, 2006

### Amith2006

I saw in a book that lead is the most stable heavy element. That is why all radioactive series ends in lead. But you say that iron has the most nuclear stability. Please clarify.

10. Aug 12, 2006

### Chi Meson

Does this mean that the answer should be "two alpha particles plus gamma?" Would the decay of 8Be emit a gamma with it? I'm thinking it wouldn't, but it has been so long since my atomic physics class (1986). Is this question intended to be that advanced, do you think?

11. Aug 16, 2006

### Astronuc

Staff Emeritus
Response to last two posts
By virtue of the binding energy per nucleon, Fe is the most stable element.
http://hyperphysics.phy-astr.gsu.edu/Hbase/nucene/nucbin.html#c2
http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin2.html

and - http://en.wikipedia.org/wiki/Binding_energy

binding energy = (mass (reactants) - mass (products))c2
If mass is in amu (atomic mass units) one can use conversion of 931.494 MeV/amu (used without the multiplication of c2. If mass is in kg, the c is in m/s, and energy is in J, and 1.6 x 10-13 MeV/J.
http://www.tpub.com/content/doe/h1019v1/css/h1019v1_41.htm
http://www.eh.doe.gov/techstds/standard/hdbk1019/h1019v1.pdf (source of above html pages)
http://www.eh.doe.gov/techstds/standard/hdbk1019/h1019v2.pdf

http://www.antonine-education.co.uk/Physics_A2/Module_4/Topic_11/topic_11.htm [Broken]

Bismuth 209 is the heaviest stable isotope.
Lead (Pb) could be considered heaviest most stable element since it has several isotopes which are stable - Pb 204, 206, 207 and 208, but Bi 209 still beats for heaviest stable nuclide.
http://www.nndc.bnl.gov/chart/reCenter.jsp?z=83&n=126 (Click on 1 under Zoom on right)
from http://www.nndc.bnl.gov/chart/ (sometime unaccessible)
Alternatively - http://wwwndc.tokai-sc.jaea.go.jp/CN04/index.html [Broken] (which is sometimes unavailable)
Also - http://wwwndc.tokai-sc.jaea.go.jp/CN03/index.html [Broken] (if 2004 version not available). If they are on the same server, then both may be unavailable

As for Be-8, as far as I know, it splits into 2 alpha particles without gamma decay.

Last edited by a moderator: May 2, 2017