Comparison of Cobalt-60 Exposure Determinations by Calorimetry and by Ionization Chamber Techniques

Petree, B.; Humphreys, J.C.; Lamperti, P.; Loftus, T.; Weaver, J.T.

doi:10.1088/0026-1394/11/1/004

Cited by 7 publications

(4 citation statements)

References 11 publications

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“…This is consistent with other reported results of accumulated absorbed dose up to 620 kGy [8]. In another investigation [9] an accumulated absorbed dose of 4.3 MGy at a rate of 25 kOy/min from 3 MeV electrons produced a resistance change of only about 0.01 percent. A possible cause may have been a gradual release of strains within the thermistors as a result of their manufacture or handling their delicate leads during the fabrication of the temperature probes.…”

Section: Thermistor Calibrationsupporting

confidence: 92%

A sealed water calorimeter for measuring absorbed dose

Domen¹

1994

J. RES. NATL. INST. STAN.

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The NIST sealed water calorimeter is intended for direct measurement of absorbed dose to water. This calorimeter was used for a series of approximately 3700 measurements to investigate the so-called heat defect, that is, anomalous endothermic or exothermic effects caused by dissolved gases. The three systems investigated were "high-purity" water saturated with N2, H2, and mixtures of H2/O2. The repeatability of the measurements of absorbed dose rates for the '*"Co teletherapy beam was studied with different water fillings and accumulated absorbed dose. Measurements with the H2/O2 system varied with accumulated absorbed dose. Based on the measurements and theoretical considerations, it appears that the H2-saturated system is the best choice for eliminating the heat defect. Measurements with both the N2-and H2-saturated systems are in good agreement with those determined with a graphite and graphite-water calorimeter (for which there is no heat defect).

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Section: Thermistor Calibrationsupporting

confidence: 92%

A sealed water calorimeter for measuring absorbed dose

Domen¹

1994

J. RES. NATL. INST. STAN.

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“…Mo reover, th e agreement of the new exposure s tandard for 60CO with other standards [12] and other physical meas ure me nts [13] is within 0.4 perce nt.…”

Section: Discussionmentioning

confidence: 57%

“…The preceding discussion is based on ratios of chamber readings at different times in different radiation fields_ The percentage difference between the free-air chamber and the cavity chamber for these gamma-ray energies should be considered as an estimate_ Since the high-pressure free-air chamber is no longer available, confidence in the validity of the cavity-chamber determinations of exposure rate is derived from intercomparisons with other standards [12] and comparisons of cavity-chamber ionization measurements with other physical measurements such as source power [13]. Such comparisons have shown agreement in exposure-rate determinations to within several tenths percent.…”

Section: Relationship Of Cavity-chamber Andfree-air-chamber Source Mementioning

confidence: 99%

Standardization of 60Co and 137Cs gamma-ray beams in terms of exposure

Loftus

Weaver

1974

J. RES. NATL. BUR. STAN. SECT. A.

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At th e Na tion a l Burea u of S ta nd ard s (N BS), th e ex pos ure-ra te s ta nd ard s fo r ""Co a nd mcs ga mm a rays we re based fo r a numbe r of yea rs o n a we ig ht ed ave ra ge of meas ureme nt s usin g a cy lin d ri ca l ionizati o n cha mbe r a nd a gro up of s m ail s phe ri ca l c ha mbe rs . Comp lex se tu p co ndition s for th e cy lindrica l c hamb e r. diffe re nces be t wee n th e cy lindri ca l a nd s ph e ri ca l c ha mbe r d a ta, a nd recogniti o n th a t th e in stituti o n of th is we ight e d ave rage ex pos ure-ra te sta nd a rd increased th e diffe re nce be t wee n freeair-c ha mbe r a nd c av it y-ch a mbe r meas ure me nts, le d to th e de velopm e nt of new s ph e ri ca l c h a mbers. All co rrecti o n fa c to rs for ex pos ure-rate meas ure me nt we re in ves ti ga ted a nd upd a ted _ Exce ll e nt ag ree me nt was a c hi eved be t wee n ind e pe nd ent ex pos ure-rate me as urc mc nt s for s ix s ph e ri ca l c ha mbe rs a nd , as of May 1, 1972 , th e e xpos ure sta ndard s we re redu ce d 0. 7 pe rce nt for ""Co a nd 0.6 pe rce nt fo r ""Cs ga mm a ra ys. Reca lc ul a tion of cor rec ti o n fa c to rs s in ce th a t ti me indi ca tes th at th e s ta ndard ':J'Cs s ho u ld be furth e r redu ced b y 0. 2 perce nt , a nd thi s adju s tm e nt wa s mad e o n Jul y 1. 1974.Th e un ce rt a inties associated with eac h of th e qu a ntiti es e nt er in g int o th e de termin a ti o n of e xpo s ure rate we re tabul a te d a nd th e ove ra ll un ce rt a int y of th e ex pos ure ra tes use d for in s trum e nt ca librati o ns a t NBS was fo und to be abo ut 0.7 percen t for add iti on in qu adrature_ Key word s : Cav it y io ni za ti on c hamb e r; ex po s ure; gamma rays ; IWCO; ''''Cs; sta nd a rds. Introduct ionThe s tand ard in strum e nt e mployed for ex pos ure meas ure m e nts, for x-rays ge nerate d b y pote nti als from te n up to a fe w hundred kil ovo lts, is th e free -air ionizati o n c hamb e r [1 , 2, 3).1 Expe ri me nt al di ffi c u Iti es e nco unter ed with this in s trum e nt at hi gh e nergi es, in fulfillin g th e re quire me nt that all ionizin g particles be stopped in air , cause stand a rd s labo ratories 10 have reco urse to another me thod of s tan dardiza tion . Thi s alternate me thod , which obviates the necess ity of a free-air c hamb er operated at hi gh pressure , or with large pla te s pac in g, e mploys cavity io nizati o n chambers and relies o n th e prin ciples of th e Bragg-Gray th eo ry [4] for its validity.Th e expos ure, X, is th e quoti e nt of dQ by dm where dQ is th e absolute value of th e total c harge of th e ions of one sign produ ced in air wh e n all electrons libe ra te d by photon s in a volume ele me nt of ai r havin g mass dm are co mpletely s topped in air [51. Th e special unit of expos ure is th e roe ntge n whi c h is e qual to 2.58 X 10-4 C· k g-I.Durin g 1959, Wyc ko ff [6] meas ured a 60 CO so urce and a 13iCS source, in roe ntge ns, usin g a press urize d free-air c hamb e r. Fo r co mpari so n, the exposure rates we re also m...

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“…The activity measurement of a B°Co source of about 1 c'i 15 as performed at BIPM and the results are given in the preceding paper [l]. The power measurements were made at XBS by calorimetry with a source identical to the one used at BIPM: they are reported in [ 2 ] . The two sources were prepared at the Kational Research Council of Canada (XRC) [3].…”

Section: Comparison Proceduresmentioning

confidence: 99%