MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_NextPart_01C942AF.BA6DFC50" This document is a Single File Web Page, also known as a Web Archive file. If you are seeing this message, your browser or editor doesn't support Web Archive files. Please download a browser that supports Web Archive, such as Microsoft Internet Explorer. ------=_NextPart_01C942AF.BA6DFC50 Content-Location: file:///C:/60545C93/Phys3650L.Betas.htm Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii" PHYS 3650L - Modern Physics Laboratory

PHYS 3650L= - Modern Physics Laboratory

Laboratory Advanced Sheet

Absorption of beta parti= cles

 =

 

1. Objectives. The objective of this laboratory is to inve= stigate the absorption of beta particles.

 

2. Theory.

 Charged partic= les have a definite range in matter. The range of a charged particle in an abso= rber is the

= average depth of penetration of the charged particle i= nto the absorber before it loses all of its kinetic energy

= and stops. The energy of the particle, which is a function of the mass of the particle and its velocity, and the

= electrical charge of the particle affect the range of the charged particle in a material. The atomic density

(number of atoms per cubic centimeter) and the atomic number (Z) of the shielding material also affect range.

Generally, the highe= r the electrical charge and the higher the mass, the shorter the range of the cha= rged

= particle. Conversely, the lighter the mass and the smal= ler the electrical charge, the longer the range.

 

The factor that affe= cts the range of a charged particle in any material is a unit called density-thickness.

Density-thickness ca= n be calculated by multiplying the density of a material in milligrams per cubic centimeter

(mg/cm3) = by the distance the particle traveled in that material in centimeters. The product= is density-thickness

= in units of milligrams per square centimeter (g/c= m2). Density-thickness can be considered a cross-sectional target

= for a charged particle as it travels through the material. Although materials may have different densities and

= thicknesses, if their density-thickness values are the sam= e, they will attenuate beta radiation in a similar

= manner. For example, a piece of Mylar used as a detec= tor window with a density of 7 mg/cm2 will attenuate

= beta radiation similar to the outer layer of dead s= kin of the human body which has a density-thickness of 7

= mg/cm2. The density of soft human tissue is equal to = 1,000 milligrams per cubic centimeter (mg/cm3).

Therefore, the density-thickness values for the skin, lens of the eye and whole body are 7 milligrams per square centimeter (mg/cm2),

= 300 mg/cm2 and 1,000 mg/cm2.

Beta particles have a range in air of about 10 feet per MeV of kinetic energy. Beta particles can penetrate

= the dead layer of skin if they possess more than 0= .07 MeV of kinetic energy.

 

There exists an approximate empirical relationship between range and energy for low energy electrons:<= /span>

 

 <= /o:p>

 

 

 

where r is in cm, E is in MeV, and r is the density of the sto= pping material in g / cm3.

Note that the density of Aluminum is 2.702 g / = cm3.

 

 

3. Apparatus and experimental proce= dures.

a. Equipmen= t.

 

        &= nbsp;           1)=        Geige= r-Müller tube with sample holder.

 

        &= nbsp;           2)=        Radia= tion counter.

 

        &= nbsp;           3)=        Radio= active sources.

 

        &= nbsp;           4)=         Absorber set.

b. Experime= ntal setup. To be provided by the student.

c. Capabili= ties. To be provided by the student.

d. Procedur= es. Detailed instructions are provided in paragraph 4 below.

4. Requirements.

a. In the laboratory.

1) Your instructor will introduce you to the experiment.

2) Perform the background count measurement.

4) Perform the count measurements for different absorption thickness for two radioactive isotops.

b. After the laboratory. The items listed below = will be turned in at the beginning of the next laboratory period. A complete laboratory report is not required for this experiment.

Para 3.= Apparatus and experimental procedures.

1) Provide a figure of the experimental apparatus (para 3b).

2) Provide descriptions of the capabilities of equipment used in the experimen= t (para 3c).

Para 4.= Data. Data tables are included at Annex A for record= ing measurements taken in the laboratory. A copy of these tables must be includ= ed with the lab report. Provide the items listed below in your report in the f= orm a Microsoft ExcelTM sprea= dsheet showing data, calculations and graphs. The spreadsheet will include:=

1) Operating potential, resolving time, and counting= time for the absorption measurements.  = ;         =

2) Background count measurement (per 400 s).

3) A table with columns for absorber code, absorber thickness, corresponding u= ncorrected count, and corrected count for each isotope.

4) A graph of the counts vs. absorber thickness for each isotope.

5) Estimated value of a range of beta particles for each isotope.

 

 =

Para.<= /span> 5.  Results and Conclusions.

 

        &= nbsp;           a.=        Resul= ts.

 

        &= nbsp;           1)=        A sta= tement of the experimental and estimated range of beta particles for each isotope.=

 

 

        &= nbsp;           b.=        Concl= usions.

 

        &= nbsp;           1)=        Do yo= ur experimental results agree with the empirical formula? If not, what are the possible rea= sons?

 

 

 

Annex A
Data

      = ;    Counting time:  &nb= sp;      50 s.

 

      = ;            &n= bsp; Operating potential: _________________________= _____ V

 

        =             Resolving time:__________________________= ____ s

 

        =             &nb= sp;  Background count/ 400 s:_________________= _____________

 

 

1.       Absor= ption measurements. Isotope 1 __________________________

 <= /p>

 

  

   = Absorber code

 

 

Absorber thickness (mg/cm2)<= /span>

 

   =    counts/50 s

Absorber code

 

           &nbs= p;  

Absorber thickness (mg/cm2)<= /span>

 

   =    Counts/50 s

       &nbs= p;     A

 

 

K

 

 

B

 

 

L

 

 

C

 

 

M

 

 

D

 

 

N

 

 

E

 

 

O

 

 

F

 

 

P

 

 

G

 

 

Q

 

 

H

 

 

R

 

 

I

 

 

S

 

 

J

 

 

T

 

 

 

 

2.       Absor= ption measurements. Isotope 2 ____________________________

 

 

 

 

  

   = Absorber code

 

 

Absorber thickness (mg/cm2)<= /span>

 

   =    counts/50 s

Absorber code

 

           &nbs= p;  

Absorber thickness (mg/cm2)<= /span>

 

   =    Counts/50 s

       &nbs= p;     A

 

 

K

 

 

B

 

 

L

 

 

C

 

 

M

 

 

D

 

 

N

 

 

E

 

 

O

 

 

F

 

 

P

 

 

G

 

 

Q

 

 

H

 

 

R

 

 

I

 

 

S

 

 

J

 

 

T

 

 

 

      = ;            &n= bsp;

 

 =

 =

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