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Problem 1 (20 points) : Explain the following biological effects of radiation

Solution

(a) somatic vs. hereditary vs. in-utero effects (5 points)

□ Somatic effects : The effects on somatic cells of exposed individual itself

□ Hereditary effects : The effects on germ cells and the effects appear on ones descendants

□ In-utero effects : The effects on fetus/embryo cells

( They are not hereditary effects even though the effects appear on ones descendant but rather a special case of the somatic effect )

(b) acute vs. chronic effects (5 points)

□ Acute effects : The fast responses due to mostly high radiation exposure

□ Chronic effects : Latent effects

(c) deterministic vs. stochastic effects (5 points)

□ Deterministic effects

: non-stochastic effects and proportional to the severity of the effects with threshold

□ Stochastic effects

: probabilistic effects with no threshold and proportional to probability of occurrences

(d) detrimental vs. hormesis effects (5 points)

□ Detrimental effects : The harmful effects of radiation

□ Hormesis effects : The beneficial effects of radiation, mostly from low level exposure

( There consider : growth stimulation, reproduction increase, suppression of diseases and death rates, and life extension as the radiation hormesis. )

Problem 2 (20 points) : Compute ALI and DAC of I-131 through inhalation

Data :

□[eqn: bold{SEE(thyroid←thyroid) `=` 10`MeV/kg/t}] (controlling)

□[eqn: bold{f_thy}] = fraction uptake to the thyroid after inhalation = 0.2

□ radiological half-life = 8.05 days

□ biological half-life of iodine in the thyroid = 138 days

Solution

The effective half-life of I-131 is, [eqn: T_E `=`{T_R times T_B} over {T_R + T_B} `=` {8.05times138} over {8.05+138} `=`7.61``days]

And, the effective elimination constant of I-131 is,

[eqn: lambda_E (thyroid`;`I-131) `=`ln2 over 7.61days `=`0.091 day^-1 `=`1.05times10^-6 `sec^-1]

The effective committed dose equivalent to thyroid is given by :

[eqn: H_{50,thyroid} `=`1.6times10^-10 ``U_thyroid ``SEE(thyroid larrow thyroid)_{I-131}]

The number of nuclear transformations over 50 years in thyroid per unit intake (1 Bq) of I-131 is,

[eqn: U_thyroid `=` {q_thyroid `(0) `f_thy} over {lambda_E `(thyroid)} `=`{1times 0.2} over {1.05times10^-6} `=`1.91times10^5 "transformations"/Bq]

Therefore, [eqn: H_{50,thyroid} `=`(1.6times10^-10 )``(1.91times10^5 ) ``(10times10^-3 ) `=`3.06times10^-7 ``Sv/Bq]

□ limit on effective dose equivalent (5 rem/year)

- [eqn: ALI``(stochastic) `=`{0.05`Sv/yr} over {0.03 times (3.06times10^-7 ) ``Sv/Bq} `=`bold{5.45times10^6 `Bq/yr}]

- [eqn: DAC `=`ALI over {2000times60times0.02}`=`{5.45times10^6 `Bq/yr} over{2.4times10^3 `m^3 /yr} `=`bold{2.27times10^3 `Bq/m^3}]

□ limit on organ dose (50 rem/year)

- [eqn: ALI``(non-stochastic) `=`{0.5`Sv/yr} over {3.06times10^-7 ``Sv/Bq} `=bold{`1.63times10^6 `Bq/yr}]

- [eqn: DAC `=`ALI over {2000times60times0.02}`=`{1.63times10^6 `Bq/yr} over{2.4times10^3 `m^3 /yr} `=`bold{6.79times10^2 `Bq/m^3}]

Problem 3 (10 points) : Explain the functions of the followings of a cell :

Solution

(a) Membrane (3 points)

The cell is bounded by a surface known as the semi-permeable □membrane□ which is about 10-6 cm thick. The membrane regulates the movement of water, nutrients, electrolytes in and out of the cell.

(b) Cytoplasm and mitochondria (3 points)

Within the membrane, the cell consists of two main parts : □cytoplasm□ and nucleus. □Mitochondria□ are distributed in the cytoplasm as small rod-like structures, and control the metabolism of the cell such as manufacture of molecules and production energy.

(c) Chromatin and chromosome (4 points)

The nucleus of the cell contains □chromatin□ which contains the hereditary material of the cell.

Mitosis is a process of cell division. In the process of cell division, at the early stage (called prophase) the chromatin resolves into a definite number of thread-like objects known as □chromosomes□.□

The genetic material of the cell is in the chromatin. The genetic information is carried in the genes which are embodied in the chromosomes. A single chromosome may carry thousands of genes. Each gene has a specific location (called locus) in the chromosome.

Problem 4 (20 points) : Explain three main syndromes of acute exposure of radiation.

Solution

(1)	hemopoietic syndrome (blood changes)

(2)	gastro-intestinal (GI) syndrome (nausea, vomiting, diarrhea)

(3)	central nervous system syndrome (convulsion, malaise & fatigue, epilation,

temperature rise, sore throat)

Problem 5 (20 points) :

(a) What are the radiation risk factors for carcinogenesis and hereditary effects?

(b) Derive the annual limits of radiation exposure for radiation workers and general public?

Solution

(a) (10 points)

□ for carcinogenesis effects (fatal cancer) = 4.0×10-2 / Sv

□ for adverse hereditary effects = 1.0×10-2 / Sv

(b) (10 points)

ICRP-60 Recommendations are as follows :

	Radiation Workers	Public
Annual acceptable risk	8.0×10-4 / year	5.0×10-5 / year
Radiation risk factor	4.0×10-2 / Sv	4.0×10-2 / Sv

Therefore,

□ annual limit of radiation exposure for radiation workers is

[eqn: {8.0times10^-4 `/yr} over {4.0times10^-2 `/yr} `=`2.0times10^-2 `Sv/yr `=`bold{20`mSv/yr}]

□ annual limit of radiation exposure for general public is

[eqn: {5.0times10^-5 `/yr} over {5.0times10^-2 `/yr} `=`1.0times10^-3 `Sv/yr `=`bold{1`mSv/yr}]

Problem 6 (10 points) : Explain the objectives of radiation protection recommended by ICRP-26.

Solution

1) Justification of practice  (3 points) : adopt no practice unless produces a net positive profit

2) Limits of exposure  (3 points) : prevent detrimental deterministic effects of radiation

3) Optimization of protection  (4 points) : keep the probability of stochastic effects ALARA