Lab 12: RadiationOnly 0 more labs to go!!

Nuclear reactions involve changes in the nucleus of an atom. Chemical reactions involve changes in the electron structure around the atom.

Chemical reactions the same atoms are involved:

Nuclear reactions the nucleus changes, resulting in an entirely new atom:

There are three types of nuclear reactions we will talk about:

1. Alpha Decay ( - decay) – A reaction whereby a parent atom releases an particle. An particle consist of 2 protons and 2 neutrons. An particle is basically a Helium nucleus

NaClClNa

HeThU 42

23490

23892

HeYX AZ

AZ

42

42

HePbPo 42

20682

21084

atomic weightisotope

#

Atomic #

# of protons

2. Beta Decay ( - decay) – A reaction whereby a parent atom releases a -particle. particles aresimply free electrons. Since electrons have a charge of –1 proton a beta decay will have the following form:

011 YX AZ

AZ

019039

9038 YSr

In lab today we will look at the - decay of Strontium – 90:

3. Gamma Decay ( - decay) – A reaction whereby a parent atom releases a -particle. - decay is usually a result of an atom decaying from a higher energy state to a lower one.The emission of a - particle is a mechanism by which an atom can get rid ofexcess energy. The neat thing about - particles is that they are massless, itis a very high energy electromagnetic wave. Because of the high energy of the - particle it also removes an electron from an atom.

011YX A

ZAZ

01

6028

6027 NiCo

In lab today we will look at the - decay of Cobalt – 60:

As these atoms undergo the nuclear reactions they will emit the radiation. Today we will measurethis radiation using the Geiger counters.

Also, we will look at how this radiation is affected by shielding. When dealing with radiation shielding we talk in terms of half-thickness – which is the thickness of a certain material that will stop half of the incident radiation.

2/1

2ln

0x

x

eII where, I0 is the unshielded intensity, x is the thickness and x1/2 is thehalf-thickness

We can rearrange this equation:

The equation that relates the intensity of the transmitted radiation to the thickness of the material is:

thickness of shielding

cou

nts

N

N/2

x1/2

xxI

I

2/10

2lnln

Similar to the half-thickness there is a time when the original atom has been reduce by half. This is called it’s half-life.

Let’s say I start with 100 g of some radioactive material with a half-life of 100 years.

Remaining mass Time Time

100 g 0 0

50 g 1 half-life 100 years

25 g 2 half-lives 200 years

12.5 g 3 half-lives 300 years

6.25 g 4 half-lives 400 years

time

rem

ain

ing

am

ou

nt

N

N/2

t1/2

Mass – Energy:

01147

146 NC

Let’s say we start with 100 grams of C-14, after one half-life it decays through the followingreactions:

How much C-14 do you have? 50 grams

How about N-14?

It turns out that you will wind up with less than 50 grams of N-14 because some of this massis converted to energy