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RE: Gamma Ray Constant for F-18
It's not just semantics. For a good discussion on the distinction between
the two quantities, and for a list of a few nuclides where the confusion can
make a significant difference, see Attix (Introduction to Radiological
Physics and Radiation Dosimetry). The symbol given there for the exposure
rate constant is capital gamma with lower-case delta subscript which denotes
the photon cut-off energy.
As an aside, I note also that Attix gives some information on the quantity
used by Unger and Trubey. I believe this was the source used by the
Radiological Health Handbook, and this explains why you might have trouble
conveniently getting from those data to exposure rate constants. As I
mentioned in a previous post, the handbook did not really specify, in
practical terms, the quantity being tabulated. There are significant
differences in muen/rho for tissue vs air.
There was also a thread on radsafe about a year ago, I believe, concerning
differences in the exposure rate constant variously quoted for Ra-226. I
offered a list of several reasons for the differences. One of these reasons
was the common confusion between the specific gamma-ray constant and the
exposure rate constant.
Bruce Heinmiller CHP
heinmillerb@aecl.ca
> ----------
> From: Boyce, Dale[SMTP:DBoyce@intiso.com]
> Reply To: radsafe@romulus.ehs.uiuc.edu
> Sent: Monday, January 31, 2000 5:35 PM
> To: Multiple recipients of list
> Subject: RE: Gamma Ray Constant for F-18
>
> I always thought it was semantics. The symbol for a dose constant
> is capital gamma. Folks sometimes call it gamma constant due to the
> symbol
> representing it. Most of the references I've run across include x-rays
> usually with a 10 or 20 kev cutoff. Afterall it is the dose or exposure
> due
> to photons that we are nominally interested in.
>
> Dale Boyce
> International Isotopes Inc
>
> > -----Original Message-----
> > From: Rosen_Jerry [SMTP:rosen@radsafe.pitt.edu]
> > Sent: Monday, January 31, 2000 3:42 PM
> > To: Multiple recipients of list
> > Subject: RE: Gamma Ray Constant for F-18
> >
> > You shouldn't be dubious. Exposure constatnts and gamma constants are
> two
> > different animals. Further annihilation photons are not gammas. They do
> > not
> > originate in the nucleus. Although publications like Kocher's,
> radioactive
> > decay tables, list annihilation photons as Gamma+-, they are
> specifically
> > separated from the gamma listings.
> >
> > -----Original Message-----
> > From: Heinmiller, Bruce [mailto:heinmillerb@aecl.ca]
> > Sent: Monday, January 31, 2000 3:45 PM
> > To: Multiple recipients of list
> > Subject: RE: Gamma Ray Constant for F-18
> >
> >
> > If they specified "gamma constant", I'm a bit dubious about a reference
> > that
> > talks at the same time about a gamma ray constant and which x-rays were
> > excluded! Many errors have been made (OK, maybe not with F-18)
> confusing
> > two related but quite different quantities - specific gamma constant and
> > specific exposure rate constant.
> >
> > Bruce Heinmiller CHP
> > heinmillerb@aecl.ca
> >
> > > ----------
> > > From: David Whitfill[SMTP:DWhitfil@kdhe.state.ks.us]
> > > Reply To: radsafe@romulus.ehs.uiuc.edu
> > > Sent: Monday, January 31, 2000 3:19 PM
> > > To: Multiple recipients of list
> > > Subject: Re: Gamma Ray Constant for F-18
> > >
> > >
> > >
> > > I just ran across a data sheet prepared by Mallinckrodt which gives
> the
> > > gamma constant for F-18 as 5.72905 R-cm^2 per h-mCi. There is a note
> > which
> > > says the calculations exclude all X-rays < 20 keV.
> > >
> > > ============================================
> > > The handbook of Health Physics and Radiological Health, 3rd ed., gives
> > > this
> > > value for F-18:
> > >
> > > 1.879E-04 mSv-m^2 per h-MBq = 6.95 rem-cm^2/h-mCi
> > >
> > > If you assume 1 rem = 1 rad = 1 R you're finished, but..
> > >
> > > X air, R = D tissue, rad/(0.87 rad/R) x (uen/p air)/(uen/p tissue)
> > >
> > > Using an energy of 500 keV (close to 511 keV), the energy-absorption
> > > coefficients are 2.966E-02 cm^2/g for air and
> > >
> > > 3.304E-02 cm^2/g for adipose tissue (RHH 5-24,25) and the correction
> > > factor
> > > with 1 rem = 1 rad is 1.03:
> > >
> > > 7.16 rem-cm^2/h-mCi
> > >
> > > =============================================
> > > >I am looking for the true Gamma Ray Constant for F-18 in the
> nostalgic
> > > units of R/hr-cm^2/mCi. There have been values reported in the range
> of
> > > 5.7 - 8. Can anyone pin it down for me?
> > > >
> > > Scott Dube
> > > sdube@queens.org
> > >
> > >
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