Nuclear Physics Micro-world Macro-world Lecture 16.
-
date post
15-Jan-2016 -
Category
Documents
-
view
224 -
download
0
Transcript of Nuclear Physics Micro-world Macro-world Lecture 16.
![Page 1: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/1.jpg)
Nuclear Physics
Micro-world Macro-world
Lecture 16
![Page 2: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/2.jpg)
Neutron
By 1930, the charge and masses of many differentnuclei were known. The charges were found to be Qnucleus = Z x proton charge & the masses wereMnucleus = A x proton mass
Z is always an integer A is nearly an integer
But, except for hydrogen where A=Z=1,A & Z are different.
![Page 3: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/3.jpg)
Electrons in the nucleus?
One idea was that the nucleus contained A protonsand A-Z electrons.
But Heisenberg’s uncertainty principle forbids this:
Suppose x= 1x10-14m typical size of a nucleus
px > 6.6x10-34Js1x10-14m
= 6.6x10-28kgm/s
vx > px me
6.6x10-28Js9x10-31kg
= >speed of light
non-relativistic calculationis invalid
Correct calculation gives Eelectron > 2x106 eV,such electrons would not stay inside a nucleus
![Page 4: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/4.jpg)
Discovery of the neutron
James Chadwick
Po
Be
n detector
detectorsource
No electric charge; mass ≈ proton mass
![Page 5: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/5.jpg)
Nucleons (protons & neutrons)
proton neutron
mass 1.672x10-27kg 1.675x10-27kg
mc2 938.27 MeV 939.57 MeV
Charge +1.6x10-19 C 0
+
![Page 6: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/6.jpg)
Isotopes
Same chemistry; very different nuclear physics
![Page 7: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/7.jpg)
Light isotopes
AX
Chemical symbol
A = number ofprotons + neutrons
ZZ=# of protons
![Page 8: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/8.jpg)
All elements have isotopes
238
92U
235
92U
![Page 9: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/9.jpg)
Nuclear force
++
The very powerful electrical repulsion (100’s of Newtons)
must be counteractedby some other verystrong attractive
force
This new force is called the Strong Nuclear force
![Page 10: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/10.jpg)
Strong Nuclear force
Forc
e
Distance (x10-15m) 1.0 2.0 3.0 4.0 5.0
Attractive nuclear force
repulsive electrical force
attraction isstronger here
repulsion isstronger here
![Page 11: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/11.jpg)
Strong Nuclear Force
• It is very strong– It overcomes the electrical
repulsion between positively charged protons that are only 10-
15m apart.
• It acts over a very short range– It is not felt by nucleons when they
are more than 10-15m apart.
• It is selective– It is felt by neutrons & protons, but
not by electrons
![Page 12: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/12.jpg)
Nuclei can’t be too large
+++
++
+
+
+
+
+
+
++
++
A proton feelselectrical repulsionfrom every protonin the nucleus
It feels a Strong Nuclearattraction only to nearby nucleons
In larger nuclei, the electricalforce is bigger while the nuclear force stays the same.
There are no stable nuclei above Z=82 (Lead)
+
+
++
++
+++
Eventually, the electrical repulsionoverwhelms the nuclear attraction
![Page 13: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/13.jpg)
Discovery of radioactivity
![Page 14: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/14.jpg)
Different types of radiation
Marie Curie
---
+++
neutral
- charged
+ charged
![Page 15: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/15.jpg)
decayZY Z-2X + 2A A-4 4
![Page 16: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/16.jpg)
Conservation of energy in decay
ZY Z-2X + 2A A-4 4
parent daughters
Energy of parent= Energy of daughters
![Page 17: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/17.jpg)
Conserv. of energy in decay
ZY Z-2X + 2A A-4 4
parent daughters
v
= MXc2 + Mc2 + KEMYc2KE = MYc2 - MXc2 - Mc2
![Page 18: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/18.jpg)
Energy balancepar
ent d
aughte
rs
the mass difference,times c2, becomes KE
![Page 19: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/19.jpg)
KE = Mparentc2 – (Mdaughters c2)
-particle Kinetic Energy
Some mass is changed into Kinetic Energy
All the a particles havethe same Kinetic Energy
![Page 20: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/20.jpg)
ZY Z+1X + e-A A
n p + e-
Beta () decay
+ e-
6C147N14
+
++
+
++ +
++
+
+
++7p
7n6p8n
![Page 21: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/21.jpg)
88Ra 89Ac + e-228 228
Other beta decays
![Page 22: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/22.jpg)
1H 2He + e-3 3
Tritium Beta decay
+ e-
3H 3He+ +
+
![Page 23: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/23.jpg)
Energy balance in beta decay
14C160 keV
14N+e-
1 keV = 1000 eV
![Page 24: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/24.jpg)
Electron energy in 14C beta decay
160 keV KEe-
KEe-
None of the electrons have160 keV of kinetic energy they all have less than that amount
What has happened to the “missing” energy??
![Page 25: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/25.jpg)
Pauli’s “desperate solution”
no chargeno mass
Another “unseen” particle isemitted in decay process
![Page 26: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/26.jpg)
6C 7N + e- + 14 14
14C decay revisited
e-6C14
7N14
![Page 27: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/27.jpg)
1H 2He + e- + 3 3
3H decay revisited
e-3H 3He
![Page 28: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/28.jpg)
Energy balance in beta decay
parent KEe- + KE
daughters
![Page 29: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/29.jpg)
Cosmic gallNEUTRINOS, they are very small. They have no charge and have no mass And do not interact at all. The earth is just a silly ball To them, through which they simply pass, Like dustmaids down a drafty hall Or photons through a sheet of glass. They snub the most exquisite gas, Ignore the most substantial wall, Cold shoulder steel and sounding brass, Insult the stallion in his stall, And scorning barriers of class, Infiltrate you and me! Like tall and painless guillotines, they fall Down through our heads into the grass. At night, they enter at Nepal and pierce the lover and his lass From underneath the bed-you call It wonderful; I call it crass.
John Updike
![Page 30: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/30.jpg)
Radioactive half-life
N = N0 ( ½ )n
Number ofremaining atoms
Initial numberof atoms number
of halflives
![Page 31: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/31.jpg)
Some half-lives
3H (3He + e- + ) 12.3 yrs14C(14N + e- +) 5730 yrs238U(234Th +) 4.5x109 yrs235U(231Th + ) 7.1x108 yrs226Ra(222Rn + ) 1600 yrs28Mg(28Al + e- + ) 21 hrs213Po(209Pb + ) 4x10-6 s
T1/2
![Page 32: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/32.jpg)
Carbon-14 dating
![Page 33: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/33.jpg)
14C content
![Page 34: Nuclear Physics Micro-world Macro-world Lecture 16.](https://reader034.fdocuments.in/reader034/viewer/2022051018/56649d4d5503460f94a2b7b7/html5/thumbnails/34.jpg)
Shroud of Turin