SOLUTIONS RADIOLOGICAL FUNDAMENTALS PRACTICE PROBLEMS FOR TECHNICAL MAJORS

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1 SOLUTIONS RADIOLOGICAL FUNDAMENTALS PRACTICE PROBLEMS FOR TECHNICAL MAJORS Noe: Two DOE Handbooks are used in conjuncion wih he pracice quesions and problems below o provide preparaory maerial for he NPS Radiological Fundamenals Subjec. DOE HANDBOOK: GENERAL EMPLOYEE RADIOLOGICAL TRAINING Par 3 of 3 Suden s Guide, Pars A hrough E 1. Define ionizing radiaion and lis he four basic ypes of ionizing radiaion. Ionizing radiaion has enough energy o remove elecrons from elecrically neural aoms. There are four basic ypes of ionizaion radiaion: Alpha paricles Bea paricles Neurons Gamma rays. 2. Define radioacive conaminaion. Conaminaion is unconained radioacive maerial in an unwaned locaion. 3. Describe he difference beween radiaion and radioacive conaminaion. Exposure o radiaion does no resul in conaminaion of he worker. A worker s clohes or skin can only become conaminaed if i comes in conac wih radioacive conaminaion. Page 1 of 7

2 4. Wha are he wo basic sources of radiaion? Give examples of each. Naural background sources: Cosmic radiaion Radon Terresrial radiaion Maerials presen in our bodies. Man-made sources: Medical uses such as X-rays and nuclear medicine reamens Tobacco producs Building maerials Domesic waer supply. 5. Describe an individual s risk associaed wih occupaional exposure o radiaion. The risks associaed wih occupaional doses are very small and considered accepable when compared o oher occupaional risks. 6. Describe he risk of heriable effecs associaed wih occupaional exposure o radiaion. The risk of heriable effecs from ionizing radiaion is considered o be very small when compared o oher naurally occurring heriable effecs and is difficul o deec over he naural background rae of birh defecs. 7. Describe he basic pracices used o mainain exposure o radiaion ALARA. Time reduce he amoun of ime spen near a source of radiaion Disance say as far away from he source as possible Shielding Shielding is placed beween workers and he source. 8. Wha are he annual radiaion dose esimaes for he following occupaions? Airline fligh crew member Nuclear power plan worker Medical personnel mrem 300 mrem 70 mrem Page 2 of 7

3 DOE HANDBOOK: NUCLEAR PHYSICS AND REACTOR THEORY-VOLUME 1 OF 2 Module 1 - Aomic and Nuclear Physics Topic 5 Radioaciviy 1. Define aciviy, curie, radioacive decay consan, and radioacive half-life. Include equaions where applicable. Aciviy: he rae of nuclear decay of a subsance. A = λ N. Curie (Ci): uni of aciviy equal o 3.7 x disinegraions per second Radioacive decay consan: The probabiliy ha a nuclide will decay per uni ime. I is a consan for a given radioacive nuclide. λ = ln 2. Radioacive half-life: he amoun of ime required for he aciviy (or aomic concenraion) of a sample o reach half is iniial value Wha is he curie conen of 1 mg of Mn-56? The half-life of Mn-56 is hrs. A = λn = ( ) = 1, 000 mg 56 g 1 mole 23 1g 1 mole 6.02x10 aoms 19 N 1mg 1.075x10 aoms ln hr 1min λ = = = 7.469x10 sec hrs 60 min 60 sec Ci 4 A = ( 7.469x10 sec )( 1.075x10 aoms) 2.17x10 Ci 10 aoms = 3.70x10 sec Page 3 of 7

4 3. A sample of Co-60 in a 250 ml sample bole is known o have an aciviy of 3.4 Ci. Wha is he concenraion of Co-60 in he bole, expressed as g/l? The half-life of Co-60 is yrs. A A = λn N= λ 10 aoms 3.70x yrs sec ( 365)( 24)( 3600) sec = ( ) = ln 2 1Ci 1 yr N [ Co-60] = V x10 aoms 1mole 60 g 1,000 ml [ Co-60] = = 0 g. 250 ml 6.02x10 aoms 1mole 1L L 19 N 3.4 Ci 3.017x10 aoms 4. Calculae he aciviy of 1 Ci of N-16 (half-life is 7.13 sec) afer one, wo, hree, four, five, six, and seven half-lives. A wha ime (expressed in halflives and seconds) is he aciviy essenially zero? ln 2 # of half lives 12 λ = o = o A A e A e or or 2 2 ( ) A (Ci) ( / 1/2 ) (sec) The aciviy is essenially zero a approximaely 5 1/2 or sec. 5. Define radioacive equilibrium. Radioacive equilibrium exiss when he producion rae of a radioacive subsance equals he removal rae of he subsance. Page 4 of 7

5 Topic 6 Neuron Ineracions 1. Describe scaering of neurons wih nuclei in general. Then describe elasic scaering and inelasic scaering of neurons. Neuron scaering occurs when a nucleus is bombarded by a neuron and hen emis a neuron. The iniial and final neurons do no have o be he same, and he ne effec is ha a neuron will appear o have bounced off he nucleus. Elasic scaering: A neuron bombards a nucleus, a neuron is released from he nucleus, bu no gamma ray is emied. Inelasic scaering: A neuron bombards a nucleus, a neuron is released from he nucleus, bu a gamma ray is emied. Topic 9 Ineracion of Radiaion wih Maer 1. Wha is he difference beween charged paricle ineracions and uncharged paricle ineracions? A charged paricle ineracs wih surrounding nuclei by elecric field ineracions. The charged paricle can compleely remove elecrons from surrounding aoms in a process called ionizaion. An uncharged paricle can only ionize surrounding aoms by direc collision since hey have no elecric field. A phoon, which is also uncharged, can undergo phooelecric effec, Compon scaering, or pair producion o ionize surrounding aoms. 2. Describe an alpha paricle. How does i inerac wih maer? Why does i have a shor range in maer? Wha can sop alpha paricles? Would a flux of alpha paricles inciden upon a person be a risk o he person s inernal organs if he source was exernal? Why or why no? An alpha paricle is he nucleus of a helium aom. I is produced by an unsable nucleus ha undergoes alpha-decay. I consiss of wo proons and wo neurons. I has a +2 charge. Since an alpha is charged, i undergoes charged paricle ineracions, specifically ionizaion. For each ineracion an alpha undergoes, i loses some finie amoun of energy. Page 5 of 7

6 Because of is high mass and relaively high charge, an alpha paricle s ionizing power is very high. Alphas herefore lose heir energy in a very shor disance as hey ravel hrough maer. A few cenimeers of air or a piece of paper sop alpha paricles. A person exernally exposed o alpha paricles would no experience any damage o his/her inernal organs because he range of alphas in he body (or any maer) is exremely small (only a few microns in he body; a micron is a millionh of a meer, or a housandh of a millimeer). The ouer layer of skin (which is mainly dead skin cells) would compleely absorb he energy from he alpha paricles. However, if he person inhaled or ingesed he source of alpha paricles (e.g., radon gas), he person could experience damage o his/her inernal organs. 3. Describe a bea-minus paricle. How does i inerac wih maer? Compare is range o an alpha paricle s range. Wha can sop bea-minus paricles? A bea-minus is an elecron ha has been ejeced a a high velociy (and herefore, high energy) from an unsable (radioacive) nucleus. I has a very iny mass compared wih an alpha paricle which has a mass more han 7,000 imes larger han he mass of a bea. The bea-minus has a charge of 1e, where e is he fundamenal charge on an elecron. A bea-minus undergoes charged paricle ineracions, such as ionizaion. The range of bea-minus paricles is longer han he range of alphas, bu is much shorer han he range of gammas or neurons. A few mm of a ligh meal such as aluminum foil will sop bea-minus paricles. 4. Describe a neuron. Wha is he ypical source of neurons? How does a neuron inerac wih maer? Compare is range o an alpha paricle s range. Wha ype of maerial is more effecive a aenuaing neurons? Neurons are uncharged paricles wih almos he same mass as a proon. Neurons primarily come from nuclear fission bu can also come from decay of unsable (radioacive) nuclei. Neurons undergo elasic scaering, inelasic scaering, and absorpion. Neuron absorpion can, in urn, resul in radiaive capure, paricle ejecion, or fission. Page 6 of 7

7 Since i is uncharged, a neuron s range is much, much longer han an alpha paricle s range. Neuron radiaion is considered peneraing radiaion. I will damage he inernal organs of a person exernally exposed. Hydrogenous maerials (i.e., maerials which conain H as par of he chemical formula) are he bes a aenuaing neurons. Examples include waer, oil, and paraffin (polyehylene). 5. Describe a gamma ray. How does i inerac wih maer? Compare is range o an alpha paricles range. Wha maerial can aenuae gamma rays? How much maerial is required? Gamma rays are elecromagneic radiaion, jus like microwaves, radio and TV waves, or visible ligh, bu wih much higher energy. Gamma rays are indisinguishable from X-rays excep for heir source: gamma rays come from nuclear decays or nuclear reacions (like fission) and X-rays come from de-exciing or deacceleraing elecrons. Gamma rays have no mass and no charge. Gamma rays inerac wih maer by he Phooelecric Effec, Compon Scaering, and Pair Producion. A gamma ray s range is much, much longer han an alpha s range. Gamma radiaion is also considered o be peneraing radiaion. Several fee of concree, several meers of waer, or several inches of lead will aenuae gamma radiaion. Page 7 of 7