From: Alberto Fasso' (fasso@SLAC.Stanford.EDU)
Date: Tue Jan 02 2007 - 20:11:30 CET
Maurizio Pelliccioni has sent me privately some interesting information
about the issue I raised concerning conversion coefficients for
photons of very low energy. With his permission, I will copy it here.
He says that to produce a new set of coefficients suitable for
low-energy synchrotron radiation, it is necessary to decide the
dosimetric quantity of interest and the geometry of irradiation.
Before we possibly engage in such an enterprise, I hope that FLUKA users
with an interest in synchrotron radiation will express their opinion.
>From Maurizio.Pelliccioni@lnf.infn.it Tue Jan 2 10:31:20 2007
Date: Tue, 2 Jan 2007 13:54:59 +0100 (MET)
The problem with the conversion coefficients for low energy photons is just
what dose quantity should be used.
1) Effective dose should be ok. However a more significant quantity should
be the skin dose.
2) According to ICRP-ICRU, the operational quantity should be H'(0.07,
angle), depending on the photon energy and on the angle of incidence.
3) So, first, it should be necessary to settle the irradiation geometries
significant for radiation protection purposes.
Here was my answer:
Maurizio, would you mind to send this mail to the fluka-discuss list?
The purpose of my mail was indeed to trigger a discussion on the points
you have mentioned.
There is another aspect to consider: what would inspecting authorities
expect in different countries? After all, the purpose of all our calculations
is to satisfy some legal requirements.
It would be nice to hear what other people think.
Still another aspect is that of measurement, that I mentioned in my mail to the
list. H*(10), if I am not wrong, was invented to "represent" the response of a
typical survey instrument. I thought, perhaps naively, that H*(0.07) could
correspond to the response of the same instrument with a thin window and the
cap off. But to what would H'(0.07,angle) correspond?
Maurizio's answer to my answer:
1) If you like, forward my e-mail to the list
2) What local authorities think does not matter much: they follow ICRU-ICRP
with some short or long delay. Anyway, in Europe they do mostly as indicated
in my e-mail. It could be interesting to know what the USA do.
3) H'(0.07, angle) also in my opinion has little practical meaning.
Difficult to calculate and even more to measure. I was just pointing out
the official opinion of ICRP-ICRU.
We will discuss the matter further. In the meantime, try to think which
irradiation geometries should be considered (for instance, I don't think
that isotropic exposure would be meaningful).
A possible simplification (or complication) could be derived from what
we mean by "skin dose": the dose received by 100 cm2 of skin surface (if
I remember correctly). But perhaps that wouldn't help.
H'(0.07, angle) mimics the fact that at low energies the instrument response
depends on the angle at which radiation hits the window. Indeed the
direction of the instrument should be rotated until a maximum is found.
On Mon, 1 Jan 2007, Alberto Fasso' wrote:
> Hi Stefan,
> writing this technical note was really a very good idea (I would like
> to get a copy, please).
> I would like to take this opportunity to stimulate a discussion with the FLUKA
> user community on an issue with which I am struggling since a long time.
> On the experimental floor of synchrotron radiation facilities, the radiation
> field is composed mainly of low-energy photons. FLUKA can be used to
> calculate photon spectra down to 1 keV, but conversion coefficients are
> available only for energies > 50 keV or > 10 keV, depending on the type
> of dose of interest (effective dose, ambient dose equivalent).
> What should one do? As a very crude patch, I have modified your fluscw.f
> routine and I have extended the tables to 1 keV using fluence-to-tissue kerma
> conversion coefficients. This is equivalent to what I was doing many years ago,
> when I was calculating photon dose by scoring energy deposition in a thin tissue
> region. This solution is conservative, but I have got objections that it is
> _too_ conservative.
> I realize that my question goes far beyond FLUKA calculations: the actual
> question should be "What dose quantity should we use in radiation protection
> around this kind of facilities?". Effective dose should be ok, but there
> are no conversion coefficients. H*(10) is clearly not suitable, since most of
> the energy is deposited at thicknesses much smaller than 1 cm.
> In practical radiation protection, one uses an instrument with a very thin
> window. Shall we use H*(0.07) or H*(3)? But again, no conversion coefficients
> are available.
> I would like to hear from my colleagues who work at photon sources what they
> think we should do. If we agree on the dosimetric quantity we want, maybe we
> can convince Maurizio Pelliccioni to prepare a special set of conversion
> coefficients for synchrotron radiation calculations...
> On Wed, 20 Dec 2006, Stefan Roesler wrote:
> > Dear FLUKA-users,
> > Some of you are using the routine deq99c.f (a special fluscw.f
> > user-routine) to convert fluence into dose equivalent. I have now managed
> > to complete a Technical Note which I would kindly ask you to cite if you
> > publish dose results based on that routine in the future. In addition,
> > please continue to cite also the original work by M.Pelliccioni:
> > Stefan Roesler and Graham R. Stevenson, "deq99.f - A FLUKA user-routine
> > converting fluence into effective dose and ambient dose equivalent",
> > Technical Note CERN-SC-2006-070-RP-TN, EDMS No. 809389 (2006)
> > M. Pelliccioni, "Overview of fluence-to-effective dose and
> > fluence-to-ambient dose equivalent conversion coefficients for high
> > energy radiation calculated using the FLUKA code", Radiation Protection
> > Dosimetry 88 (2000) 279-297
> > If you are interested in either of the two papers and you do not have
> > access or if you are interested in the routine itself please do not
> > hesitate to contact me directly.
> > Best regards,
> > Stefan
-- Alberto Fasso` SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025 Phone: (1 650) 926 4762 Fax: (1 650) 926 3569 firstname.lastname@example.org
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