NGHI6NCCfU TRflOBOI NGHIEN CUV CHE TAO PHO KE GAMMA XACH TAY DUNG DE DO UEU VA NHAN DIEN DONG V| PHONG XA NGUYIN oufc TUAN V\Sn Khoa hoc va Ky thu i t H^t nhii Vign Nang lirang Nguyen W Viat Nam, 66 K[.]
NGHI6NCCfU-TRflOBOI NGHIEN CUV CHE TAO PHO KE GAMMA XACH TAY DUNG DE DO UEU VA NHAN DIEN DONG V| PHONG XA N G U Y I N oufc TUAN V\Sn Khoa hoc va Ky t h u i t H^t nhii Vign Nang lirang Nguyen W Viat Nam, 66 KH&CN Pho ke gamma xach tay co cau tao g6'm mat kh6'i da'u tIa gamma ntfi b§n ngoal vdl mpt kho'i xiif ly Da'u nha'p nhay Nal(TI) co dp nhay cao diroc slii dung de ph|n bd' nSng lifdng cua bi}c xa gamma, sud't lid'u moi trirdng xung quanh (theo phifdng phap chuy§'n li§'u), tim va nh|n dl^n d£ng vj phdng xa Ngoai ra, cdn cd d'ng dem Geiger-Muller difdc tfeh hdp khd'i xiif ly d§' sud't lilu gamma d dai iid'u cao Khd'i xiil ly difa trdn vi xur ly bao gdm cac mach di$n tilf xiif ly xung, phan tich da kdnh, lifu trif dif iidu, hien thj LCD, ban phim, giao tid'p theo ehud'n ethernet va pin sac Li-ion Ph^ k§' gamma xach tay cd the suf dung difdc d phdng thi nghiem cung nhu dieu kidn hidn trifdng Chdc ndng chinh cua thid't bj ndi chung la nhdn didn dd'ng vj phdng xa ma khong can phai ke't nd'i vdi may PC Nhiing chdc nang khac cua thie't bj la dd tim ngudn phdng xa va sud't lidu Phd' kd' rd't phu hop cho cac dng dung nhu kie'm soat phdng xa moi trifdng, kiem soat chd't thai phdng xa, kl^m soat vi|c budn ban bat hdp phap cac ngud'n va vdt lidu phdng xa, k i l m seat phdng xa phd'lidu kim loai; cdng nghidp hat nhdn, y hgc hat nhan va i7ng phd sir cd'bdc xa TH khoa: ke gamma Mfftfau DESIGN AND CONSTDUCTION OF THE PORTABLE GAMMADAY 6PECTP0METED FOD ENViDONMENTAL D E DATE MEA6UDEMENT AND DADI0I60T0PE IDENTIFICATION Summary The portable gamma ray spectrometer is composed of an external gamma radiation detection unit and a processing unit Highly-sensible Nal(TI) scintillation detector is used for measurement of gamma radiation energy distribution, ambient gamma radiation dose rate equivalent (spectrum-dose conversion method), search and Identification of radionuclides GeigerMuller counter tube is integrated into the processing unit for measuring higti gamma dose rate The microprocessor-liased processing unit comprises of pulse processing electronics, multi-cbannel analyzer, data storage, LCD display, keypads, ethernet interface, and Li-ion rechargeable battery Portable multifunction scintillation gamma spectrometers can be used in laboratories as well as for working in field conditions It's main spectrometer function is radionuclide identification without connection to a PC Additional functionalities are search and detection of radioactivity sources and dose rate measurement This spectrometer is Ideally suited for radioactive environment monitoring, radioactive waste monitoring, illicit trafficking monitoring of radioactive source and materials, radiation monitoring of metal scrap; nuclear industry, nuclear medicine and emergency Keywords: gamma spectrometer ^" CdNCNCHEVIETNiSf ^ ° ' ' " ^ ' " ' ° ^ ^ „ ^ „ , ^ „ , ,„ ,,„ , Pho ke gamma xach tay la mdt cdng eg can thilt dung d l "^gn dien d^ong vj phdng xa viec kiem tra an ninh, an todn bflc xg, khao sat mdi trfldng cung nhu cae flng dyng khac khoa hpc va cdng nghi§p Thilt bj thu ttigp va phan tich dO' lieu dat dUdc tfl dau dd phdng xg phu hdp Nhflng skn ph^m thfldng mai hien ed cua ke gamma cdn bao gom nhilu chflc nang can thiet khac nen cd gia thdnh cao va khd tri bko dudng Do dd, viec thilt k l chi tao mdt ke vdi kich thfldc thu gpn d l cd the hoat dpng nhU mdt he thd'ng dpc lap dieu kien hien trudng ddp flng yeu cau flng dyng gpn nhe dupc dSt Cac ky thuat hidn dgi v l vi mgch to hpp tfldng tfl, bien doi tfldng tfl - Sd chat Ifldng cao va vi xfl ly da dfldc ap dung vi$c nghidn cflu phat triln thilt bi NGHIEN CLfU-TRRO DOI Thiet ke che tao Dong vj phdng xg qua trinh phan phat tia gamma vdi nang Ifldng dac trflng Cac kieu dau dd bflc xa gamma nhfl logi tinh t h i nhap nhay Sodium Iodide (Nai), hay tinh the ban ddn nhu Cadmium - Zinc - Telluride (CdZnTe) hoac High Purity Germanium (HPGe) d i u cd the ghi nhan nang IUdng cua tia gamma Trong cdc dau dd nay, bflc xg gamma tao eae xung anh sang hoae dien tich ty Id vdi ddng nang cfla bflc xa Cac khdi dien tfl hgt nhan bao gdm tiln khuech dgi, khulch dgi, bien dli tfldng tfl - sd (ADC) va phan tich da kenh (MCA) se hinh viec khuech dgi va tao dang tin hieu tfl diu dd, chuyin doi tUdng tU sang sd va phan chia cac xung d i n theo bien dp ty le vdi nang lupng Sfl phan bd dat dflpc gifla so d i m xung theo nang Iflpng chinh la gamma Nai Scintillation Detection Unit (1): to hpp dau dd nhap nhay Nai cd kich thfldc 2,48 x 2,48 inches bao gom cdc phan cd ban nhfl "tinh the nhap nhay Nal(Tl) - dng nhan quang dien PMT" va cac mgch tiln khulch dai, khulch dgi hinh xung ehuin Id'i de cd t h i dfla thang den Id'i vdo cija bd phan tich da kenh MCA, ngudn nudi cao ap cho dau dd vk he thd'ng on dinh dfla tren den LED vdi chflc nang bu trfl anh hfldng eua nhiet dp -I-500V High Voltage (2): khd'i ngudn nudi cao ap cho dau Geiger-Muller Internal GM Detector (3): dau dd Geiger-Muller tich hdp de dai lieu cao GM Pulse Shapper (4): khd'i hinh xung cho dau dd Geiger-Muller Sample & Hold (5): khoi lay mau va gifl dinh xung /VD converter (6):kh6\ chuyen doi tfldng tfl - sd Yeu cau thilt k l cd bcin ddi vdi ke xach tay Embeded Microprocessor (7): vi xfl ly thflc hien logic phai dgt dupc la mflc tieu thu cdng suat tha'p Thilt bj phai cd cau trflc nhd gpn de cho phep sfl dung dieu khien vk thu thap dfl lidu; chuyin doi ky thuat so khoang thdi gian mpt ch? vdi mdt bd ngudn tfl phd' sang lieu; bd nhd IUu trfl ham chuyin doi G(E) pin nhd D l dat dfldc dilu ndy, cac linh kidn dien va cac chflc nang khac tfl cdng sua't tha'p dflpc chpn Ifla cho viec sfl dung Real Time Clock module (8): khd'i thdi gian thuc khoi MCA va cac thiet k l maeh dien tfl dfldc Graphic LCD Display (9): khoi hien thj graphic LCD tdi gian din mflc cd the nhflng van dam bao nhflng Functional Keypad (10): khd'i ban phim chflc nang tinh nang ci!ia bd MCA danh cho nhflng flng dung GPS module (11): khdi thu nhan tin hieu GPS hien trudng Thiet ke cung sfl dung nhflng mach tieh hpp chflc nang cao vdi gid thap cho phep de EEPROM storage (12): khd'i bd nhd Iflu trO dang sfla chfla, nang cap can thilt RS-232, Ethernet Interface (13): khoi giao tilp theo Sd khdi cua thie't bi dflpc eh! d hinh 1, gom chuan RS-232 va Ethernet cac khd'i dien tfl chflc ndng nhfl sau: Li-ion Battery Power Supply (14): khoi nguon nuoi bang pin Li-ion DC-DC Converter (15): khoi chuyen doi nguon DCDC trang thai hoat ddng, xung den tfl khdi dau dfldc dfla den khoi lay mlu vd gifl dlnh xung Mdi xung dfldc dfldc lay mau va bie'n doi mpt chu trinh ADC mat 1,5 i^s va sau dd tgo ngdt dfla din vi xfl ly de khdi tao chflc nang IUu trfl dfl lieu, Nhung xung de'n tiep theo se dUdc xfl ly chu trinh IUu trfl vao bp nhd hoan Cac module ehfldng trinh chflc nang cija vi xfl ly dflpc vilt bang ngdn ngfl C51 cho viec thu nhgn va thflc hien cac phep tinh Ngoai ra, mpt cdng cy phan mem dflpc phat triln dfla tren Labview de hd trp k l giao tiep vdi may PC Phan tich va nhan dien dong vi phdng xa Hinh 1: sd dS khdi cua phS k§ gamma xich tay Chuan nang lut/ng Ckc ham sd hieu chuan mac djnh (kenh theo nang Ifldng va phan giai nfla chilu cao theo Top cM KHOA HO J S6 19 nam 2013 (jdNC NGHE VIET SkK NGHISN CLfu - TRFIO DOI P^ = a, + a,.E + aj.E^ va FWHM = c, + c^.E + c,.e nang IUdng) ducfc xac dmh bang each khdp ham Trong do, E la nang IUdng tUdng Ung vdi dinh giOa cac dinh gamma doi vdi ham Gauss Phep hieu chuan dUdc thUc hien vdi cac nguon gamma cua dong vj va a,, a^, ajla cacjie sd hieu chuan; •'»»Cd(89 keV), "Co(122 keV), "'Ba(356 chuan dUdc IUu glO thiet bj Khi thi^t bj keV), "'Cs(662 keV), »'Na(1274 keV) va "00(1173 che dp thu nhan, no se tim toan bp cac dinh co thu vien khoJng thdi gian giSy rnpt lan keVva 1332 keV) Viec hieu chuan nham xac dmh cac he so hi§u Thij tuc chi tiet cho viec tim dinh ddi vdi mdi ddng chuan a,, a,, a,, b,, b,, b, va c,, c^, c, cho cac ham vj dUdc cu the hda theo cac budc dudi dfiy Hinh the hien mpt dinh phd co kenh la P„, sd d^m C^, cac hieu chuan sau: Kenh theo nang vi tri kenh trai ROI, va phai ROI, cua vung quan tam chn = a, + a^.E + aj.E' ROI luijng (E CO don vi la keV) E = b, + bj.chn + bj.chn' Nang IUdng theo kenh {E c6 ddn vi la keV) FWHM = c,+ c,.E + C3.E2 Dp phan giai nOa chieu cao theo nang luong (E va FWHM cd ddn vi la keV) Thu vien dong v| phdng xa phan mem cCia thiet bl cd the bao gom dong vi phdng xa cd ban nhu bang Dong vj NangIUdng (keV) Cd-109 88 Co-57 122 U-235 185 1-131 364 Cs-137 662 Mn-54 835 Co-60 1173 Na-22 1274 Cac ham so' hieu chuan dudc tich hdp phan mem cua thiet bi nhu la phep hieu chuan mac dinh Khi thiet bj hoat dong, phan mem si!f dung cac ham de xac dinh vi tri cua dmh phd gamma Ngudi sCf dung cd the dung nguon ^^^Cs(662 keV) de kiem tra phep hieu chuan mac djnh Neu vi tri dinh 662 keV khong trung vdi kenh nhu da dUdc tinh toan phep hieu chuan mac djnh thi phan mem se thay ddi cac he so' khuech dai a va b^ de bu trU vao su thay ddi Phep hieu chuan mdi se trd phep hieu chuan mac dinh Tim dinh tudgng va nhan di$n dong vj Thu vien ve dong vi phdng xa cua thie't bi cd chCfa sSn dong vj Mdi thu vien hay phep hieu chuan nang IUdng bi thay ddi, thie't bj se tu tinh iai vj tri kenh cua dinh P^ va rong dinh (FWHM) cho mdi logi ddng V! trdng thu vien theo cac ham sau: " CONCNOHEVIETNlftf ^o 19 nam 2013 Hinh 2: vung quan tam ROI Budc Lam trdn dO lieu thd cija phd thu nhan theo diem iien tie'p nhau: Smodth[ii] = (-3.raw[ii-2] + 12.raw[ii-1 ] + 17.raw[iil + 12.raw[ii+1] - 3.raw[ii+2])/35 Trong dd, raw[ii] la sd dem tai kenh ii Budc Til gia tri kenh cua dinh P„ tinh dudc theo nang IUdng d cong thdc tren, tim kenh cija dinh C,,, bang each tim kenh cd sd dem cue d?i dO iieu da dUdc iam trdn dai (P,, ± 0,5.FWHM) Bade Thiet lap cac vi trf kenh toan cue cua vung quan tam ROI theo vi tri k§nh eua dlnh C, tim thay d tren theo eac cong thUc sau: L^ = P,_- 1,5.FWHM va R^ = P„ + 1,5.FWHM BMc Thie't I4p cac vi tri kenh trai ROI|Va phSi ROUhuc sU cho vung quan tam ROI: - Gia trj kenh trai ROi, dUde xac djnh bang viSc tim gia tri nho nha't dO lieu lam trdn dSi to kenh L^ den kenh (P„ - 0,5.FWHM) - Gia trj kenh phai ROI, dUdc xae djnh bang viSc tim gia trj nho nha't dO liSu lam trdn dJi NGHIEN CLOJ-TRflO BO tu kenh (P,, + 0,5.FWHM) den kenh R,^ Toan bd cac phep tinh tong sd dim dupc tinh tfl Budc Tinh ctfa sd dd rong kenh cua vung quan kenh ROI, den kenh ROI^ tSm ROI: W = ROI,-ROi,+1 , {NET.Gf Budc Thiet lap gia tr; m theo P,^, m la sd kenh \NET\'\G[ dupc si^ dung de tinh gia trj trung binh eua phdng khoang ROi Trong dd: NET.G = ^nei[ii]G[ii'\ vk bien dp: Ne'uO