TIME OF COMPLETION______________

TIME OF COMPLETION_______________ &nb= sp; NAME____SOLUTION= _________________________

<= span style=3D'font-family:"Times New Roman"'>&nb= sp; = &nb= sp; = DEPARTMENT OF NATURAL SCIENCES

PHYS 3650, Exam 3 = &nb= sp; = &nb= sp; = &nb= sp; = &nb= sp; Section 1

Version 1 &nb= sp; = &nb= sp; = &nb= sp; = &nb= sp; = November 21, 2008

Total Weight: 100 points

1. = Check your examination for completeness prior to starting. There are a total of nine (9) prob= lems on six (6) pages.

2. = Authorized references include your calculator with calculator handbook, and the Refere= nce Data Pamphlet (provided by your instructor).

3. = You will have 50 minutes to complete the examination.

4. = The total weight of the examination is 100 points.

5. = There are six (6) multiple choice and three (3) calculation problems. Work five (= 5) multiple choice and three (3) calculation problems. Show all work; partial credit will= be given for correct work shown.

6. = If you have any questions during the examination, see your instructor who will=

be located in the classroom.

7. = Start: &= nbsp; 10:00 a.m.

Stop: &= nbsp; 10:50 a.m

&= nbsp; &nbs= p; PROBLEM

&= nbsp; &nbs= p; POINTS

&= nbsp; &nbs= p; CREDIT

&nbs= p; &= nbsp; 1-6

&nbs= p; &= nbsp; 25

&= nbsp;

&nbs= p; &= nbsp; 7

&nbs= p; &= nbsp; 25

&= nbsp;

&nbs= p; &= nbsp; 25

&= nbsp;

&nbs= p; &= nbsp; 9

&nbs= p; &= nbsp; 25

&= nbsp;

&= nbsp; &nbs= p; TOTAL

&= nbsp; &nbs= p; 100

&= nbsp; PERCENTA= GE

CIRCLE THE SINGLE BEST ANSWER FOR ALL MULTIPLE CHOICE QUESTIONS. IN MULTIPLE CHOICE QUESTIONS WHICH REQUIRE A CALCULATION SHOW WORK FOR PARTIAL CREDIT.

1. Radioactive decays into . Which of these particles is released in the decay?

&nbs= p; a. A proton.

&nbs= p; b. An electron.

(5)

&nbs= p; c. A positron. <= /o:p>

&nbs= p; d. A neutron.

2. = The activity of a radioactive sample (with a single radioactive nucleus) decrea= ses to 1/8 of the initial value in a time interval of 96 days. What is the half-life of the nucleus?

&nbs= p; a. 6 days.=

&nbs= p; b. 12 days.

(5)

&nbs= p; c. 24 days.

&nbs= p; d. 32 days.

3. Which of the following statements concerning the nuclear force is false?

&nbs= p; a. The nuclear force is very short-ranged.

&nbs= p; b. The nuclear force is very weak and m= uch smaller in relative magnitude than the electrostatic and gravitational forc= es.

(5)

&nbs= p; c. The nuclear force is attractive and not repulsive.

&nbs= p;

&nbs= p; d. The nuclear force acts on both protons and neutrons.

&nbs= p;

4. Which of these is appropriate unit for the decay constant l?

&nbs= p; a. s.

&nbs= p; b. rem.

(5)

&nbs= p; c. 1/s.

&nbs= p; d. MeV.

5. Complete the following radioactive decay form= ulas:

&nbs= p; a. = &nb= sp; =

&nbs= p; b. = &nb= sp;

(5)

&nbs= p; c. = &nb= sp;

6. A gamma ray is also known as

&nbs= p; a. An electron. =

&nbs= p; b. A positron. <= /o:p>

(5)

&nbs= p; c. A helium nucleus. =

&nbs= p; d. A photon.

A 60.0-kg patient about to hav= e a brain scan is injected with 20.0 mCi of the technetium-99, . The superscript m stands for metastable. The metastable state decays= to the ground state with a half-life of 6.00 h. The nucleus decays by emitting a 143-keV photon.

How many nuclei were injected= ?

l =3D ln (2) / T_1/2 =3D ln(2)/(6 x 3600 s) =3D 3.21 x 1= 0^-5 1/s

&nb= sp;

R= _{o<=
/sub> =3D l N_o}

N= _{o<=
/sub> =3D R_o/ l =3D (20.0 x 1=
0^-3Ci)(3.70 x 10¹⁰ Bq/Ci)/(3.21 x 10^-51/s) =3D 2.31
x 10¹³}

Assuming that half of these p= hotons escape the body without interacting, what is the absorbed dose in rad? Assume that all of the nuclei decay while in the body.

E =3D (N_o/2)(143 keV) =3D (1.16 x 10¹³)(143 x 10³⁼eV)(1.60 x 10^-19J/eV) =3D 26.4 x 10^-2 J

Dose (rad) =3D E/m =3D (26.4 x 10-2 J)/(60.0 kg) =3D 0.440 rad

The RBE factor for these phot= ons is 0.970. What is the absorbed dose in rem?

Dose (rem) =3D Dose (rad) x RBE

Dose (= rem) =3D 0.440 rad x 0.970 =3D 0.427 rem=

8.&n= bsp; The half-life of is 9.965 min.

a. &n= bsp; If a sample contains 3.20 x 10¹² <= sub>nuclei at t = =3D 0, how many nuclei are present 40.0 min later?

l =3D ln (2)/T_1/2 =3D ln(2)/(9.965 min) =3D 0.0696 mi= n^-1 =3D 0.001159 s^-1

N =3D N_oe^-^l^t

N =3D (3.20 x 10¹²)e^(-0.0696^{=
min-1)(40.0 min)}⁼

&= nbsp;

N =3D 1.98= x 10¹¹<= /o:p>

b. &n= bsp; What i= s the activity at= t =3D 0?

R= _{o<=
/sub> =3D l N_o}

R= _{o<=
/sub> =3D (0.001159 s^-1)(3.20 x 10¹²) =3D 3.71
x 10⁹ Bq}

&= nbsp;

c. &n= bsp; What is the activity at= t =3D 40.0 min?<= /p>

R =3D l N

R =3D (0= .001159 s^-1)(1.98 x 10¹¹) =3D 2.30 x 10⁸ Bq

&= nbsp;

&nb= sp;

9. The first several = decays in the series are a, b^-, b^-, a, a, a, a, b^-. Deter= mine the resulting intermediate daughter nuclei.

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