X-RAY DIFFRACTION RADIATION SAFETY INFORMATION

Transcription

1 APPENDIX - XI X-RAY DIFFRACTION RADIATION SAFETY INFORMATION The fllwing infrmatin shuld be read by all users f x-ray diffractin units. The frm at the end f this sectin shuld be signed by each user and respnsible Principal Investigatr, and frwarded t Radiatin Safety. I. Hazards f Operating Machine Surces f X-Rays The radiatin frm x-ray machines can be very dangerus, and such danger shuld nt be minimized. On the ther hand, there is n reasn t be afraid t perate these machines after receiving prper training and instructins. The peratr f an analytical x-ray machine shuld never becme cmplacent r vercnfident abut the ptential danger frm an x-ray beam. Numerus safety devices may be prvided, but the user shuld nt depend t heavily n these safety devices lest he becme vercnfident. If a safety device shuld fail unnticed, serius injury may result. Adequate safeguards must be prvided, but these can never replace cnstant vigilance and alertness t pssible danger. Prper training in the peratin f these machines shuld teach the nature f the hazards s that the user can be prperly alert and vigilant. The wavelengths f the x-rays used mst cmmnly in x-ray diffractin and flurescent x-ray spectrscpy fall in the range frm apprximately 0.5 t 10A. These are s-called "sft" x-rays which are readily absrbed in matter. A thickness f nly a few mm r less f Al, Fe, r Pb is required t reduce the intensity f the transmitted beam t 1/10 that f the initial intensity even fr x-rays with a wavelength f 0.5A. The 1.54A wavelength crrespnds t CuKa radiatin, and 1.93A is the wavelength f FeKa radiatin. These are cmmnly used surces in x-ray diffractin wrk. It is apparent that nly relatively thin layers f shielding are required t prtect against this radiatin, but it is this same prperty that makes these x-rays very dangerus. They are highly absrbed in sft tissue, and severe burns can result frm expsure f the hands, arms, skin r eyes t the direct r diffracted beams. The maximum permissible dse f radiatin fr varius parts f the bdy are shwn in Table I. Fr cmparisn, x-ray intensities that may be btained with high-pwer tubes and strngly diffracting crystals are als shwn in Table I. It is apparent that a dse f 100 t 500 times the permissible yearly dse may be btained frm a 1-secnd expsure t the mst intense direct beam. Even a strng diffracted beam can deliver the maximum permissible yearly dse t the eye in less than 10 minutes. 81

2 II. Bilgical Effects f Intense X-Ray Beams It is pssible t prvide a general classificatin f the kind f changes that inizatin radiatin can prduce in skin. It is useful t categrize these effects int three areas. 1. Reversible changes. 2. Cnditinal reversible changes. 3. Irreversible changes A. Reversible Changes The mst cmmn and earliest reversible change is the prductin f reddening f the skin r erythema. If the dse and energy is lw enugh that mst f the radiatin is absrbed in the superficial layers f the skin, reddening ccurs, then disappears apparently with n future effects. Anther reversible change is the lss f hair r epilatin. It is pssible t give a dse f radiatin that will stp cell divisin in the epithelial cells s that hair ceases t grw temprarily and falls ut. With a lw dsage, the hair will begin t grw after a perid f time, with n apparent permanent ill effects. A third system that shws reversible effects are the sebaceus glands (ilprducing glands in the skin) which are temprarily affected t prduce less sebum (il secretin f these glands in the skin). B. Cnditinal Reversible Changes Pigmentatin f the skin is nt a ttally reversible change. If a large area f skin is irradiated, erythema and pigmentatin will ccur with the pigmentatin eventually fading. It has been shwn that the resulting skin is nt nrmal and has sme "memry f the injury." Future dses f the same area d nt prduce the same skin respnse. C. Irreversible Changes If enugh radiatin f the prper energy is absrbed in the skin this will result in permanent destructin f either hair r sweat glands, r whle skin, with a resulting scar. The irreversible changes are categrized in the heading f: 1. Radiatin Dermatitis 2. Chrnic radiatin dermatitis 3. Radiatin cancer A summary f the varius effects t be expected after given acute dse t lw energy x-rays and the time f expsure t receive the dse in the beam are given in Table II n page

3 Surces f Expsure 1. The primary beam. 2. Leakage f primary beam thrugh cracks in shielding. 3. Penetratin f primary beam thrugh shutters, cameras, beam stps, etc. 4. Secndary emissin (flurescence) frm a sample r shielding material. 5. Diffracted rays frm crystal. 6. Radiatin generated by rectifiers in the high vltage pwer supply. TABLE 1 NRC OCCUPATIONAL EXPOSURE LIMITS* WHOLE BODY 5000 SKIN OF THE WHOLE BODY EXTREMITY LENS OF EYE MINORS (PERSONS UNDER THE AGE OF 18) 500 YEARLY LIMIT (mrem) FETAL EXPOSURE 500/Nine mnths *Nte: State f Cnnecticut expsure limits vary slightly. Fr mre infrmatin cntact Radiatin Safety. TYPICAL X-RAY BEAM INTENSITIES Primary Beam: Diffracted Beam: 400,000 Rem/min., 2.4 x 10 7 Rem/hr 80 Rem/hr. It shuld be nted that in x-ray diffractin bth the primary beam and the diffracted beam are small and well cllimated, which increases the pssibility f receiving severe burns n very lcalized areas f the fingers, hands, eyes, r arms if inadvertently expsed. Leakage f the primary beam r scattered radiatin thrugh cracks r small penings in the shielding likewise may give rise t small but intense beams which may escape detectin in general area radiatin surveys unless the survey is carried ut carefully. The penetratin f the primary beam thrugh shutters n cmmercial equipment may result if the shutter becmes defective r des nt clse prperly. Imprperly designed shielding can itself be a hazard if it excited t flurescence and the radiatin is allwed t scatter int the rm. The rectifiers in the high-vltage pwer supply cnstitute a frequently unsuspected surce f hazardus radiatin. When they becme gassy they functin like x-ray tubes, and due t the high vltages that may be impressed acrss them, they can emit penetrating radiatin. It is essential that adequate shielding be prvided arund the rectifier tubes t prevent this radiatin frm escaping int the rm. 83

4 TABLE II Effect Cmments Dse, Rem Primary Beam *Expse time, sec erythema Appear in ne day, disappears and recycles -- lasts days epilatin 350 Temprary 1200 permanent acute dermatitis chrnic radiatin dermatitis Over Time, ulceratin, tumrs, thin skin Thusand f rem ver many years in small dses. NA skin cancer Median time between x-ray expsure and prductin is years. Receive small dses ver a lng perid f time t get a ttal large dse rem/wk. fr 5-7 years. NA * assuming an in-beam dse rate f 400,000 rem/min. IT SHOULD BE POINTED OUT THAT A ONE (1) SECOND EXPOSURE OF AN EXTREMITY IN THE PRIMARY X-RAY BEAM COULD RESULT IN A DOSE OF OVER 6,000 REM! 84

5 III.Precautinary Measures General precautinary measures t be taken t prtect against accidental expsure t x-radiatin are: 1. Effective shielding 2. Check tubes r shield tubes in high vltage rectifier 3. Interlck switches and warning lights 4. Radiatin mnitring, film badges 5. Physical exam f any suspected injury 6. Radiatin surveys by the Radiatin Safety Sectin and peratr. T be effective, the shielding must prevent any stray radiatin frm escaping int areas where it can be intercepted by persnnel in the rm. Care shuld be taken t avid cracks r small penings which may g unnticed. Tube status indicatrs shuld be prvided bth at the n-ff switch and near the tube head s that the peratr will be reminded whenever the x-ray beam is n. In additin, a light r ther signal shuld be prvided t indicate when the shutter is pen, and this shuld be augmented by interlck switches and lights r manual cntrl devices that will prevent access t the beam area when the shutter is pen. It is advisable t cnduct a regular maintenance prgram scheduled and checked by the Principal Investigatr in rder t insure that these safety devices are always in prper wrking rder. Radiatin mnitring is f tw types. On the ne hand, the intent is t determine hw much radiatin a persn may have received in a given perid f time. Fr this purpse a film badge is wrn, but this usually indicates nly the general level f radiatin in the rm, r the level f whle-bdy radiatin. Radiatin surveys arund the tube head and assciated equipment shuld be cnducted by the peratr and radiatin safety persnnel t check the adequacy f the shielding. This shuld be dne peridically with a detectr which is sensitive t the x-ray wavelengths being used r generated. A survey shuld als be cnducted whenever the gemetrical arrangement r design f the equipment is changed in rder t accmmdate new experiments r prcedures. Recrds shuld be kept f the survey results. Beam detectin with flurescent screens shuld be dne with the screen placed n a lng device t insure that n expsure t the primary beam is pssible. Fr experiments taking lng perids f time, the peratr shuld leave the area, securing it fr unauthrized access. 85

6 IV. Accidents If yu feel yu may have been expsed t the primary beam, r if yu feel cnditins n yur unit have changed significantly, yu shuld call Radiatin Safety at If yu cannt reach anyne in Radiatin Safety, call Campus Plice at 111 r (accidents and emergencies nly). Campus Plice will then cntact the apprpriate Radiatin Safety persnnel Detach, sign and mail t: Radiatin Safety 135 Cllege Street New Haven, CT I have read the cntents f this x-ray diffractin radiatin safety guide and have been instructed as t the prper peratin prcedures in using the unit(s) lcated in: User Signature: SIGNATURE and TYPED NAME Trainer: SIGNATURE and TYPED NAME Respnsible Principal Investigatr Signature: SIGNATURE AND TYPED NAME Date: 86

7 V. X-ray Diffractin Unit Safety Guidelines AUTHORIZED PERSONNEL ONLY - Yu must have department apprval and prper equipment rientatin training prir t using x-ray equipment. A Radiatin Safety infrmatin handut is available as a resurce. See the equipment supervisr r call the Radiatin Sectin at T insure yur safety, d nt attempt any unauthrized repair f x-ray unit. D nt allw hands, fingers r ther bdy parts t enter the x-ray beam. Be sure the beam is ff and shutter is clsed prir t sample changing r ther activity. Check all warning lights prir t placing hands near the beam line. Use a GM radiatin survey instrument t cnfirm beam ff cnditins. Use the shielding and interlcks prvided. D nt bypass interlcks. X-ray units need rutine shutter maintenance t prevent shutter failure and resulting safety hazard. See equipment supervisr. Shuld any safety related interlck r device fail, the unit shuld be taken ut f service until such time as effective repairs have been made. Failure f beam shutter(s) must be reprted t the Radiatin Safety Sectin. A heath physicist may physically inspect the unit prir t use, after such repairs have been made. If yu are having prblems with the equipment, ask fr assistance. In case f emergency r accident ntify yur supervisr and Radiatin Safety immediately at Prevent further use f the unit until a safety evaluatin is dne. 87