Nuclear Physics: Understanding Nuclei, Nuclear Reactions, and Radioactivity, Slides of Physics

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nuclear

physics

Nuclear

binding

energies

Radioactivity

Nuclear

reactions

What

do

you

think

of

when

you

hear

the

phrase

nuclear

reaction?

A.

Clean

energy

source

B.

Radiation

danger

C.

Nuclear

weapons

D.

No

opinion

Constituents

of

the

nucleus

MeV

J

mc

27 .

938

10

50 .

1

299792458

10

67263 .

1

:

proton

for

Example

10

2

27

2















X

A

Z

Nuclear

notation:

Some

examples:

U

Fe

C C

Some

isotopes

of

C:

Natural

abundance

Natural

abundance

Z

Atomic

number

(number

of

protons)A

A

Nucleon

number

Z

A

Mass

of

nucleus:

M

sum

=

Zm

p

(A

‐

Z)m

n

Zm

e

=

u



M

=

u

mass

of

neutral

atom



includes

Z

electrons

What should we do with this mass deficit?(A) Chalk it up to inaccuracy of my calculator.(B) Figure that NIST made a mistake.(C) Give up on physics as a quantitative science.(D) Find some meaning associated with

M.

Z

A

Mass

of

nucleus:

M

sum

=

Zm

p

(A

‐

Z)m

n

Zm

e

=

u



M

=

u

=

MeV

/c

2



M/A

=

MeV

/c

2

/nucleon



energy

associated

with

nuclear

“binding”

Another

example:

mass

of

neutral

atom



includes

Z

electrons



M/A(

4

2

He)

=

MeV/c

2

/nucleon



M/A(

3

2

He)

=

MeV/c

2

/nucleon

Nuclear

binding

energies

per

nucleon







 

n Z A H Z X

:

energy

binding

NuclearA

Z







Neutral

atom

with

Z

electrons

and

Z

protons

Neutral

H

atom

Neutrons

Nuclear

forces

are

so

strong

that

within

the

nucleus,

mass

can

be

converted

to

energy

and

visa

versa:

E

mc

2

There

must

be

a

strong

attraction

between

nuclear

particles

fm

‐

15

m

Not

all

nuclei

are

stable:

Some

types

of

nuclear

decay





He

++

Ex:

238

92

U

234

90

Th

e



or

e

Ex:

14

6

C

14

7

N

e



photon)

Ex:

12

5

B

12

6

C*

e



ν

Measure

of

radioactive

decays:

t

t

e

N

t

dt dN

e

N

t

N

N

dt dN

λ

0

λ

0

λ

Solution

λ

rate

Decay





Example:

Suppose

that

you

have

a

sample

of

23

14

6

C

nuclei

each

of

which

has

a

half

life

of

years.

How

many

Curies

of

radiation

is

this?

Ci

decays/s

λ

decays/s

λ

λ

λ

ln

23

12

12

2 1

2 1





N

dt dN

T

T

Ci

s

Ci

s

N

T

N

T

dt dN

T

t

ln

ln

ln

10

7

6

23

2 / 1

0

2 / 1

2 / 1

Some

RBE

factors

Radiation type

RBE



rays

1



particles

1-1.

n (slow)

4-

n & p (fast)

10



particles

10-

heavy ions

20

Some

typical

values

of

dose

Source

Dose

Background radiation

0.13 rem/year

Recommended limit

0.5 rem/year

Diagnostic chest X-ray

0.01 rem

Mammogram

0.1 rem

Fatal dose

400-500 rem