Nuclear Power

Fission à breaks apart heavy nuclides, resulting in typically “hot” radioactive by-products Fusion à the sun, fuses two hydrogens together · Alpha à α à essentially ionized helium atom originating from nucleus after fission · Betas à β^- à an electron · a neutron decays to a proton and electron and the electron is ejected from nucleus · Positron, β^+ à positive electron, this is very rare, typically a high energy cosmic ray imparts energy to “make-up” the mass difference.  A proton absorbs energy, converts to mass and “decays” to a neutron and positive electron · Gamma à γ à high energy “light” from above electromagnetic spectrum (rainbow) from above https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php

What are some common household items that have radioactive parts….

What about older smoke detectors…Americium 241, an alpha emitter.  Also anything with potassium like bananas, or potatoes….because the natural K, includes 0.012% K-40.

Example 1

How many neutrons are ejected from the U-238 nucleus on disintegration?

Solution; only focus on neutrons

146 à 85  +   55 +   x

6 neutrons are ejected

Note:  if a beta particle is also ejected, does that effect neutrons?

· Power generation

o U-235 is about 5 to 6.5%

§ (so U-238 is about 93 to 95%)

o Yellow cake is about 99.3% U-238, so U-235 must be enriched.

The enrichment process involves uranium hexafluoride gas and centrifuges.

How are U-235 and U-238 separated in a centrifuge?

· If enrichment is beyond 8 or 9%, only one purpose.  Weapons.

o Weapons grade starts ~ 40% of U-235

USA à   PWR and BWR,

outside of US, many breeder reactors

USA

· we don’t re-process

· Outside of US, reprocess the spent fuel rods. 

In reactors: 

· U-235 has roughly ½ of initial remaining after “spent” (Starts at ~5% U-235, removed at ~2.5%)

· Most reactors are research and for diagnostics both industry and hospitals.

What do we notice about the mass of the neutron? 

Also what is the charge of a neutron?

AMUs

(x 10^-30) kg

Referring to our homework, E = mc²

What is mass difference between?

m_p    + m_e + E     ≈      m_n

(1672.6 + .91 + E    ≈ 1674.9)x10^-30

E ≈ 1.4 x 10^-30    c²

E = 1.4 x 10^-30 (3x10⁸)² = 1.26 x 10^-13 Joules

 1.26 x 10^-13 Joules (1 eV / (1.602e-19 J)

      Or 7.9 x 10⁵ eV    or    0.79 MeV

Neutron

Proton  (+)

Electron (-)

1.00866

1.00728

0.00055

1674.9

1672.6

0.91

What is an eV (electron Volt)?

The energy an electron gains being accelerated through a potential

difference   of 1 Volt through 1 meter

https://sciencenotes.org/printable-periodic-table/ Free Printable Periodic Tables (PDF and PNG)

An element is defined by # of protons.

As element become more massive, for geometric reasons (spacing the positive protons further apart) and the strong nuclear force (hold the neutrons together), more neutrons are required to be stable.

The four forces

· Gravity   (F = G M m / r²)

· Weak      (nuclear)

· Electro-magnetic (F = k Q q / r²)

· Strong    (nuclear)

What if….

Question 1    (92 p+, 140 n)   

U-242 undergoes beta decay, what is it?

242	U		=	242	?		+	β
92		150		93		149

Question 2    (93 p+, 139 n)

Np-242 undergoes a beta decay, what is it?

242	Np		=	242	?		+	β
93		149		94		148

Question 3    (94 p+, 138 n)

Pu-242 undergoes an alpha decay, what is it?

242	Pu		=	4	α		+	238	?
94		148		2		2		92

Question 4    (92 p+, 136 n)

A proton in U-238 absorbs a high energy cosmic ray

(gamma), what does it emit and what is it?

Hint:  undergoes positron emission

238	U		=	238	?		+	β^+
92		146		91		147

Look at U-235 (0.72%) and U-238 (99.27%; T_½ = 4.5 billion year (half-life)) which we discussed the other day.    We discussed forming uranium hexafluoride, a gaseous form, with U-238 being 3 AMUs more massive than U-235 and centrifuges

(also improperly named, remember chalk board pushing you without you initially pushing the board)

Any uranium dust over 7-8%

U-235, only purpose is for weapons grade uranium…

Question 5    (91 p+, 137 n)

Pa-238 undergoes fission and emits one neutron, and one alpha and one beta; if one fission fragment is Tc-103 (43p⁺, 60n), what is the other fragment?

During beta emission a neutron decays into a proton and electron (with neutrino).  So the right side of the equation loses a neutron, and gains a proton, so 92 protons, and 146 neutrons

238

Pa

=

103

Tc

+

p+n

?

+

β

+

4

α

+

n

91

147

43

60

p+

n

2

2

Easiest way to do this…evaluate the the beta particle FIRST, then do the new problem.

So how to get a β à   neutron decays to p⁺ and  β ;     Thus Pa-238 à U-238

238	U		=	103	Tc		+	128	Ag		+	+	4	α		+	n
92		146		43		60		47		83			2		2

After (due to positron emission)----CHECK this…is this correct??????????

Due to conservation:   Left side = right side  or Left side - right side = 0

Protons:   92 – 43 – p⁺ -2 = 0 à p⁺ = 47

Neutrons:  146 – 60 – n – 2 – 1 = 0  à n = 83

Question 6    (92 p+, 136 n)

A proton in Magnesium-23 absorbs a high energy cosmic ray (gamma), what does it emit and what is it?

Hint:  undergoes positron emission

23	Mg		=	23	Na		+	β^+
12		11		11		12

 Note:  the emitted neutrino, v_e, is neglected

Question 7

If high pressure and temperature fuse two hydrogen atoms together, what is this called?..... this is rhetorical, the answer is in the question, Fusion.