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*ORETICAL METHODS IN THE Dosimersy of High- NERGY PA. . . . . . .
J. E. Turner
Health Physics Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee
October, 1965
* Research sponsored by the United states Atomi
º º © c Ene © e •
contract with Union Carbide Corporation *gy Commission undez
* - L E G Al NOT ICE
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A. Males anywarranty or representation, expressed or implied, with respect to the aegu-
racy, completeness, or usefulness of the latermatica contained in this report, or that the use
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use of any infºrmation, apparatus, methºd, or precess diselesed in this report,
As used in the above, "person acting on behalf of the Commission” tasiades any em-
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with the Commission, or his employment with such centraster, - h


THEORETICAL METHODS IN THE DOSINTETRY
OF HIGH-ENERGY PARTICLES*
J. E. Turner *
Health Physics Division, Oak Ridge National Laboratory
, Oak Ridge, Tennessee -
Abstract
From the standpoint of the health physicist, the dosimetry of high-
energy particles (e.g., protons, neutrons, pions) involves an understanding
of the various interactions that these radiations undergo with matter and,
particularly, with tissue. In addition to energy losses by atomic excitation
and ionization, the most important processes are nuclear cascade reactions
in which a high-energy particle striking a nucleus produces a number of
secondary nucleons and pions. From the detailed properties of the inter-
actions, the physical quantities to be determined that are of . Aterest in
assessing biological effect are the absorbed dose and the spectrum of linear
energy transfer (LET) in tissue. Specific nuclear reactions relevant to
high-energy particle dosimetry will be described in terms of these physical
quantities and the results of several calculations of dose at high energies
will be reviewed. For health physics personnel monitoring under normal
operating conditions in the vicinity of a high-energy accelerator, neutrons,
gamma photons, and mudns will generally constitute the most important
radiation outside shields. The reactions that give rise to these radiations
are described.
A summary will be given of an ICRP task group report on the estimation
of absorbed dose and dose-equivalent for nucleons with emergies up to
400 Mev. The report is in final preparation for publication. It is based in
large measure on work done at Oak Ridge National Laboratory utilizing
computer codes for Monte Carlo calculations developed by the Neutron
Physics Division of the Laboratory. The calculations treat explicitly nuclear
cascade and evaporation processes and multiple nuclear interactions arising
from secondary and higher-order reaction products. Pion production has not
been treated and hence the calculations have been applied to nucleons with
energies not above 400 Mev. The new estimated flux densities of protons
that deliver 2.5 millirem/hr are, for normally incident protons, lower than
those given in the Report of ICRP Committee IV (1953-1959) for energies
lower than about 215 Mev. At higher emergies the newer flux densities for
normal incidence are greater than the older ones by factors of about 2 to 3.
The newer and older estimates agree well for isotropically incident protons. ,
"M.
*Research sponsored by the United States Atomic Energy Commission
under contract with Union Carbide Corporation.

2
For neutrons the newer estimates give fluxes that are greater than those
given in the previous report by factors of 2 to 3. Figures summarizing these
results have been prepared. The differences in the older and rewer estimates
are attributed to the use of newer cross section data and to the increased
refinement and detail of the newer calculations.
A study is being made of the possible change in absorbed áość and dose
equivalent from high-energy nucleons at an interface of soft tissu- a.d bone.
Some preliminary results from this work are presented.
I. INTRODUCTION
Radiation protection planning, the specification of exposure standa:ás
and criteria, routine day-to-day health physics operations, and tº basic
principles of dosimetry are all based on concepts of absorbed dose (rad) and
dose equivalent (rem). This implies that the relevant physical quantities to
be determined in dosimetry are (1) the absorbed energy per unit mass (absorbed.
dose) in exposed individuals and (2) the linear energy transfer, or LET, spect:urn
of radiation. The latter quantity describes the zºº. …ive amounts of absorse:
dose that occur in different ranges of linear energy transfe: (e.g., kev pe:
micron in water); it is the basis for the assignment of quality factors for Čose
equivalent. Beyond the immediate needs of dosimetry, however, it is impo. Cart
to have as complete a description as possible of radiation penetration in matter.
Our understanding of radiation effects phenomena is formulated in terms of
the way in which radiation interacts with matter, the specific reactions that
appear to be important, the origins of the physical properties that are observed
to correlate with biological responses, and so on. In addition, the design of
dosimeters and the interpretation of their responses are based on the physics
of the interaction of radiation with raatter.
Some of the physics relevant to dosimetry in radiation fields arc...i
high energy accelerators is reviewed below. While this paper will deal primarily
with theory, it is emphasized at the start that the real test of what is said
is experiment. Unfortunately, the details one would like to know are exceedingly
numerous and experiments with high-energy particles are difficult and costly;
thus we have today only certain base points with which the theory has been
checked. Dr. Alsmiller in the preceding paper has described some of these
important checks. Fortunately, theory is in a refined enough state that sorºe
predictions can be made and some understanding can be achieved in advance of
experiments. Indeed, both experiment and theory are brought to bear on solving
the problems at hand. In the following section sources of the most abundant
* 3
particles coming from high-energy accelerators will be describeſ. The terrº.
"high-energy" as used here means energies up to tens of Gev. The particles
may include those of a primary accelerated beam as well as products arising,
from reactions of the beam with a target and the numerous secondary and
higher-order products produced in shielding materials. In Section III particle
interactions of importance in dosimetry will be reviewed and physical models
for calculating absorbed dose and LET spectra described. Section IV will
describe some dose calculations in the high-energy region. The contents of a
forthcoming ICRP task group report will be described in Section V and some
preliminary results of dose studies at a soft tissue-bone interface given in
Section VI. f
*
II. SOURCES OF PARTICLES
&
There are over 30 known kinds of particles and anti-particles produce:
either directly or indirectly from high-energy interactions. The ºnajority of
these particles are produced in such small numbers that they contribute
negligibly to absorbed dose. Others, notably neutrinos and anti-neutrinos,
have almost no interaction with matter and hence also contribute negligibly
to absorbed dose. The remaining particles that are significant for accelerator
radiation dosimetry are listed in Table 1: neutrons, protons, pions, photons,
electrons, and mudns. Probably next in importance are K mesons, or kaons,
which are produced in strong interactions (mucleon-nucleon and pion-rucleon)
above laboratory threshold energies of 1 to 2 Gev. Kaon production rates,
however, are a fraction of pion production rates” and so these particles will
not be included in this discussion.
e
The photon-electron cascade was described in the previous paper and will
not be discussed further here. As Dr. Alsmiller has stated, the theory gives a
good accounting of what goes on and should be adequate for the needs of the
present and the immediate future. Photons are also produced in radiative
transitions of nuclei to their ground states following nuclear cascades, in
capture processes such as (n, Y) reactions, and by the disintegration of the
neutral pion into two photons. Because some of these precursors to gamma rays
are neutral particles that can penetrate large distances through matter, some
gamma radiation will generally always be present outside shields.
Of the remaining types of particles listed above, protons, neutrons, and
pions interact strongly with matter and muons weakly. The first three are
produced in significant numbers, therefore, by the action of nuclear or "strong"
forces in nuclear interactions. Under the mechanism proposed by Serber,” a
high-energy incident nucleon (neutron or proton) undergoes individual collisio: s

4.
with other nucleons inside a nucleus. (The de Broglie wavelength of high-cnergy
nucleons is of the order of the internucleon separation within the nucleus.)
These collisions are governed by the free-particle nucleon-nucleon cross sections
modified by the application of the Pauli exclusion principle to the nuclear systern.
The multiple encounters inside the nucleus can knock other nucleons out, and &
series of secondary, lower-energy nucleons escape in cascade from the nucleus.
When the incident nucleon has enough energy, pions are produced. The observed.
nucleon-nucleon reactions producing pions and the threshold energies in the
laboratory system are shown in Table 2. In addition to these, one has in the
cascade model n + n reactions assumed on the basis of the charge independence
of nuclear forces. A typical collision of a 1.8 Gev proton with a copper nucleus
(**Cu), based on the calculations of Metropolis et al., *, * gives, on the average,
the numbers of cascade products listed in Table 3. Thus a typical collision
gives about eight secondary cascade nucleons and one pion. As pointed out by
Metropolis et al., pion production is rather insensitive to the nuclear raass
number, probably because the increase in production with increased nuclear
size is balanced by the increased absorption within the nucleus. The cascade
ends when the total available energy in the nucleus drops below some cut-off
value. Additional low-energy nucleons and larger pieces of nuclear matter can
then be emitted by the evaporation that follows the cascade. This is discussed
below.
Secondary nucleons and pions can, of course, travel through raatter and
strike other nuclei to initiate cascades. The problem of the transport of high-
energy radiation through matter is very greatly complicated by both the variety
and extent of processes that take place. It is a problem that is suitable for
analysis by Monte Carlo techniques.
The remaining particle from Table 1, the muon, can arise from the
radioactive decay of pions (and kaons). The T has a lifetime of only ~107* 2-3
and decays almost immediately after its creation into two 70 Mev photons.
The tº live -10° sec and can be slowed down to rest before decay if they have
no further nuclear interactions. Thexe is a high probability that a stopped 7"
will be absorbed by a nucleus before it has a chance to decay, giving rise to two
70 Mev nucleons in the nucleus. These nucleons can initiate additional cascades.
The mº, however, is held away from the positively charged nucleus by electro-
static repulsion, and this particle will decay into a positively charged mudn
and a neutrino, m* ~ * + v. This is practically the only source of muons. The
** are thus created in a two-body decay and therefore have a unique energy,
which is about 4 Mev. They slow down to rest in matter by ionization and other
electronic energy losses and with negligible nuclear interaction. The pit chen
decays into a positive electron and two neutrinos, at - e” + 29, the positrox,
having a continuous energy spectrum up to about 50 Mev.
To summarize this section, neutrons, gamma photons, and muons will
probably make the most important contributions to absorbed dose and dose
equivalent outside shields around high-energy accelerators with the accelerator
beam on. Neutrons arise directly in nuclear cascade and evaporation. …actio:3;
photons from electron-photon cascades, Bremsstrahlung, and nuclear reactic:3;
and muons from the decay of pions produced in cascades. One can interpret
measurements with these general characteristics in mind. Mr. Sullivan showed
a figure earlier in this symposium” summarizing studies of radiation that
penetrated shielding above a target in the high-energy CERN pro-, ... synchrotror.
With the methods used, this radiation was found to give dose equivalents of
which up to about 90% was due to high-energy particles (neutrons and protons
with energies greater than 20 Mev), 10-30% to £ast neutrons, about 1% to
thermal neutrons, and less than 10% to combined gamraa photons and c.arge.
particles. Most of the high-energy component was contributed by neutrors
since the total ionization component, which included high-energy protons, did
not exceed about 10%. Presumably the ionization component consists of gamma
photons and muons, with a small contribution from protons.
III. QUANTITATIVE DESCRIPTION OF PARTICLE
INTERACTIONS FOR DOSIMETRY
6 7
Extensive calculations for nuclear cascades by Bertini ’ and for the
transport of high-energy particles through matter by Kinney” have been cazzied
out during the past few years in a continuing program of the Neutron Physics
Division at Oak Ridge National Laboratory. Dr. Alsmiller has described ... Sw
results from their computer code programs have been compared with experiment,
and he has given the results of some calculations using them. Under the heading
of theoretical dosimetry some of the details of these calculations as they
pertain not to shielding but to the determination of absorbed dose arid dose
equivalent in persons will be discussed here. To this end let us consider a nig.-
energy nucleon that has come out of a shield or some other source and strikes a
tissue target.
In Bertini's cascade model for incident nucleons and charged pions, the
nucleus is divided into three regions by concentric spheres. The prº on density
in each region is chosen to fit electron-nucleus scattering data” for charge dis-
tribution, and the neutron density is chosen in the same three regions to have a
constant neutron-proton density ratio. The nucleon energy distribution is based
on the Fermi gas model of the nucleus. The resulting nucleon momen sum
distribution is then approximately gaussian with a mean energy - 15 Niev. The
most loosely bound nucleon is assumed to have a binding energy of 7 Mev and an

ô
incident pion interacting with a nucleon is assumed to moº. ... the 3..… pcte: i.e.:
as the nucleon. The point of collision of an incident particia in … …:2u2, -3.c
type of struck particle, and its rºom.cntum are dc corminad ºatia, c.c.1
sampling procedures. A cascade is then ini-...ted on the basis of the ircd-
particle scattering cross sections.
c
To be specific, let us consider a £C0 Nºv groto: º, c 3-c.:33 - -of-- 3:2-...-
target consisting of the elements hydroger, carºo.1, ri:2:3:1, … oxygen. 2:-
collision in the actual Monte Carlo calculations occurred tº £ollows. Tra ºro Q:-
penetrated the tissue to a depth of 2.83 cra wacze it screes ºf oxyge: …ac. ---.
In slowing down through this depth, the proton had an are:gy C.; 332 ...& a 2 - .
eace red the nucleus. The slowing dowa, of course, took 1-c3 in accortance ºf:
the Bethe formula for stopping power, - diº/dx. The cascadic groduced an
emergent 246 Mev proton and an 85 Mev neutron, both at ºr...as incar 50° v.i.
respect to the incident proton direction, and it left a nucleus of oxyge: wi... …
excitation energy of 53 Mev. The cascade reaction was this as show... i. T-c.c. :
where the star denotes an excited nucleus. From the conscrvatio. of ºor...….
the recoil energy of the **O” nucleus was estimated to be only about . Mev.
S.
• *, º -tº-
A large portion of the excitation 3:37 of the residual **O” …cleus
following the cascade is spent in the evaporation of nucleors and ....claaz frº -
ments of small mass number. ** A code was written by L. Dresne of the
Neutron Physics Division at Oak Ridge National Laboratory chât allowed, tr.
evaporation of fragments of various mass numbers. ** I: tº specific colli:::::
being described the **O" nucleus gave off a single neutro. of exergy C. 97 is:-y
and two alpha particles with a total energy of 23 Miev. Tº Gwagoration of cºase
products is shown in the second line of Table 4. The resić….. bery..…. nucleus
was left with an excitation energy of 6 MeV. This energy ....y 32 exhieved in the
form of gamma radiation or, as in the case of unstable *E.2, it raay become
distributed among additional disintegratio:, products. O: tº a groiucts sho.... ...
the two reactions in Table 4, only the proton and the two neutrons & osit 2:... .
non-locally, i.e., in a region away from the location of the initial collision & ....
The history of these particles is traced further by means of the transport c. . .”
IV. REVIEW OF DOSE CALCULATIONS FROM HIGH-ENERGY P. RTICLES
In this section we discuss how these physical processes are put together
so that an assessment of absorbed dose and dose equivalent can be made.
Some data for a uniform beam of protors incident normally on a 30 c. c...cx
homogeneous tissue slab of infinite lateral extent are shown in Table 5. * T.
• -
$.
wº
a .9
7
data were generated for 2000 incident protons at each c.crgy ºy a vio.t.c C----
calculation using the programs of the Neutron Physics Divisio. . . Cak Kidſ,a
National Laboratory. At 400 Mev, which, is clºc energy of the proto-, -3Gd i. e.t.
example above, 64% of the primary collisions (i. e., those between a grimary
proton and an atomic nucleus) occur with oxyger, 19% wit... carbon, 1... wit:
hydrogen, and 3% with nitrogen. The total autºber of 3riºry collis.J.3 was 533,
indicating that about 72% of the pro cons went all the way tºrough tº 30 crº. --->
witi, only clectronic cincrgy losses. There were 218 ačditional collision3 bcº, &c.,
muclei and secondary mucleons with energics greater than 50 X.av. Froz. t.32-
data and from the detailed collisio: with oxygen described above, orie can a...alyze
tºe various contributions to absorbed dose à:á čoce &cuivale: i:
rºcleons below emergies where pion production is irºportarº. Tº
appear to be summarized by the following statements. (..
dose comes from ionization since about 3 out of 4 protons gigs tºzoº, the sia:
* * * > •ke .º. * . . . •º e.e. *", w
be de's, “… • **- & 9
* ** . .
* , **, *, *, * * * * ... As * = , º, ºr
§§: ºº cloiſ, C-: *...**
without nuclear collisions. (2) Recoil mucici, such as **, C* ... -, i.e...oug:
they have a high LET, contribute little to ºbscrbed dose ox-ºriº, a... a cău::::::
quality factor not exceeding 20-to dose cºuivalent because àeir cº-gies are so
small. (3) High-LET evaporation products, such as the two heliu.º. º.clai as ove,
occur rarely and contribute negligio’y to dose ar.á čose equivalent. (..., The
residual energy following evaporatica, ever, waci, considered as deposited lo-fi.
at high LET, also has a small effect.” For incidenc ºutrons, however, there
is no primary particle ionization dose and the high-LET muclear products make a
large contribution to dose equivalent.
These findings are summarized in Figures 1 and 2, which are taken ::::::::
the work of Zerby and Kinney. ** The curves show c.3 àose and dose cºaivaia:
averaged over a 30 cm thick soft tissue s.ao for .cº.ily incident gro cons = < ..
function of their energies. The contributions froz. griºnary and geco.iiary 2-oxºs
are shown separately. Above 215 May the groton range exceeds 33 cº, aid so… of
the primary proton energy is lost through, ºne back of the slab. The error in
making first-collision dose estimates can 22 seen by comparing tº primary à:...
secondary proton dose curves. They are about an order of magnitude apart below
200 Mev, indicating that a first-cc.ilision estimate is reliable. At +30 MeV the
primary and secondary absorbed doses and dose equivalents are about 2 to 1. The
heavy particle curves include all of the contributions from :ecoil nuclei (other
than hydrogen) and evaporation products other than nucleons. For dose equivalent,
energies of these particles were assumed to be absorbed at the point of the
collision and a quality factor QF = 20 was assigned.”
Figure 2 shows the total dose and dose equivalent for mornº incident
protons and neutrons averaged over the slab. The proton rad and ~... curve = <re
the sums of primary and secondary proton curves from Fig. 1. The protor. .…
absorption curve is calculated simply by assuming that the proton bears is tot---y
absorbed in the slab. This, of course, results in a large over-estimate of tº:
dose above 215 Mev, the energy at which the proton range exc. : is 33 cºm. S...ce
much of the dose from incident protons co...... from proton ionizatio: it emergies
above 10 - 15 Mev (QF = 1), the proton rad and rem curves & O not differ much.
The over-all quality factor fox incident protons is seen from Fig. 2 to be

8
about 1.4 In the case of aormally inc. -nt :wu crons Zerºy -- Kandy found that
about 11% of the dose was due to cnc heavy particles. With the assigned QF = 20
these contributed more to dose equivalent tºan the secondary protors ...,erated
by the neutrons. Zerºy and Kinney suggested that an over-all QF = 3 yr.gºt oc
appropriate for incident neutrons. e
- t
l
Both shielding and dose calculations can be simplified gro... cºy by usin, .
scraight-ahead approximation. In this approximation the actual angular distric--ion
o: cascade products is replaced by a distribution that is peaked in the forwazd
direction. Specifically, secondary products are assumed to have the earne directivº.
as that of the incident particle that initiates a nuclear reaction. From the
physical point of view, this means that contributions to the total morrºr, cur:
o: the secondary particles from all directions czcept forward (i. e., the direct-o:
of travel of the incident particle) are so small that they can be added to the
<orward one. Processes initiated by high-energy particles are characterized &
just this circumstance. A large total momentum vector in the forward directio:
is supplied initially by the incident particle and must be conserved in the collis.c..
independently of any details of the interaction.
The validity of the straight-ahead approximation has been demonstrate: ºy
Alsmiller, Irving, Kinney, and Moran.” They performed calculations with the
nucleon transport coda” replacing the actual angular distributions of secondary
particles by the straight-ahead distribution. Their results for 400 Mev protc..s
incident isotropically on a 30 g/cm" thick slab of aluminum followed by a 30 cº,
thick soft tissue slab are shown in Fig. 3. The solid curves show the actual
absorbed doses as a function of depth in the cissue from the detailed ca.culatiºs,
and the marked points show the doses in the straight-ahead approximation.
Primary protons and secondary protons and meutrons refer to particles that woul-
& ºverge from the aluminum shield in the absence of the tissue backing. For th
grimary proton ionization dose (curve 1), the exact and the approximate calculations
give the same result, since these protons always travel straight ahead. For the
does from secondary particles produced by primary protons (curve 2), the
approximate dose is somewhat low in the first few centimeters of the tissue
but thereafter agrees with the exact dose. For the secondary protons and
nextrons (curves 3 and 4), the doses in the straight-ahead approximation are
slightly highez, than the exact results. The backscattered dose (curve 5) repr-.....ts
ti.at from particles produced in the tissue the E cross back into the aluminum.
These particles are, of course, missing in the approximate calculations, but
their contribution to the absorbed dose is very small. From this figure it is
seen that the straight-ahead approximation gives quite reliable results for the
major contributions to absorbed dose.
The results of the straight-ahead approximation in the calcula c.o.m. of dose
equivalent under the same conditions as those used in obtaining Fig. 3 are shown
in Fig. 4. The exact and the approximate resu.es agree about as well for
dose equivalent as for absorbed dose. Similar calculations by Alsmillerand.
t
9
co-workers for incident proton energies of 100 Mev also gave good agreement. **
These calculation; provide an important verification of the validity of the
straight-ahead approximation in the cases studied.
V. RECOMMENDATIONS FOR MAXIMUM PERMISSIBLE NUCLEON FLUXES
Calculations of absorbed dose and dose equivalent from nucleons with
energies of up to 1 iſ ... . . . . . . . . ºry and iſ and were incorporated
in Publication 4 of , ..., cºrra ciortú V. ºr ... .sadiological Protection.”
Maximum permis Jie mucleon fluxes were adopted by the Commission in 1962 with
revisions in 19 J.
An upper bound to dose was first obtained by Neary and Mulvey by assuming
that the entire energy from an incidcat nucleon striking a nucleus is absorbed
locally with a quality factor of 20. More realistic assumptions, based on
available experimental data on nuclear interactions, were then made and numbers
and average energies of cascade and evaporation particles were estimated. For
nucleon transport with primary nucleons incident on the body, Neary and Mulvey
used a model with the following properties. (1) The body is represented as a
24 cm thick slab on which primary particles are incident normally. (2) Nucleons
with energies less than 30 Mev are absorbed locally with a quality factor of 10.
(3) Higher-energy secondary particles travel straight ahead and have 24 cm in
which to interact. (4) Higher-energy tertiary particles have 12 cm in which to
interact and higher-energy quaternary particles escape with no further
interaction. The effective QF values for protons were found to increase from
near unity at 40 Mev to about 4 at 1 Gev, while that for neutrons decreased
from about 8 to 4. The calculated flux densities giving a dose equivalent of
2.5 millirem/hour as a function of nucleon energy are shown in Fig. 5. *” The
flux values are for primary nucleons assumed to be in equilibrium with secondary
particles as a result of passage through shields. We see, for example, that
at higher energies the neutron and proton curves merge and that a flux density of
around 2 particles/cm”/sec gives 2.5 mrem/hr. The neutron curve at lower
emergies is joined smoothly to data of Snyder.”
During the past year a Task Group headed by J. Neufeld has completed a
report for the ICRP on the calculation of radiation dose from protons and neutrons
to 400 Mev, * The report is based largely on the Monte Carlo cascade and transport
calculations already described, and was undertaken as part of a program of
continuing reappraisal of the subject as new information is published. Dose
equivalent was calculated on the basis of the QF-LET relationship for routine
operational exposure, ** allowing a maximum QF of 20 for contributions to
absorbed dose made with an LET greater than 175 kev/micron in water.
10
* .
Figure 6 shows the new calculated flux densities from isotropically and
normally incident neutrons on a soft tissue slab of 30 cm thickness as a
function of energy. The earlier ICRP values” are also shown. The new
estimates give neutron fluxes that are a factor of 2 or 3 greater than the
older. Figure 7 shows the corresponding curves for isotropically and normally
incident protons. For isotropic protons the new and old results are the same
below about 215 Mev and agree to better than a factor of 1.6 at the higher
energies up to 400 Mev. For normally incident protons the new flux de...sities
are lower below 215 Mev and higher above. The small flux density below 215 Mev
is the result of the pronounced peak that occurs within the slab at the end of the
proton range. (The range of a 2.15 MeV proton in soft tissue is 30 cm). The flux
density is limited by the dose equivalent of 2.5 mrem/hr in the peak. The
abrupt increase above 215 Mev is due to the very idealized conditions (e.g.,
exactly monoenergetic protons) assumed in the calculations. The values of
quality factors from the new neutron calculations range from about 5 at 60 Mev
to about 3 at 400 Mev, as compared with values of almost one unit higher in the
older work. The QF values from the newer proton calculations are almost
constant at about 1.2, which is slightly below the values in the older work, **
VI. PRELIMINARY RESULTS FOR DOSE BUILD-UP AT
A SOFT TISSUE-BONE INTERFACE
In connection with previously published depth-dose curves for protons
in soft tissue,” it was suggested” that we investigate possible build-up in
absorbed dose due to enhanced nuclear contributions from radiation in passing
from soft tissue into bone. By way of obtaining preliminary information we
calculated absorbed dose and dose equivalent from 400 Mev protons in a
parallelepiped phantom of dimensions 2 cm x 3 cm x 8 cm. The protons were
incident perpendicular to the long dimension of the phantom, simulating
rotation of the target about its longest axis in a broad beam of particles. T.e
phantom consisted of a parallelepiped of bone with dimensions 1 cm x 1.5 cm × 8 cm
surrounded laterally with soft tissue. In this single case that we have run, the
absorbed dose and dose equivalent were virtually the same in the soft tissue and
bone. Since most of the dose in this phantom is due to ionization by the primary
protons, this result was anticipated. Calculations are now underway for incident
neutrons and for protons at lower emergies, where more discrimination between
dose in soft tissue and in bone might be expected.
9.
10.
ll.
12.
13.
14.
15.
16.
17;
11
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R. Hofstadter, Rev. Mod. Pye. as: as assº -
V. F. Weisskopf, Phys. Rev. , 52: 295 (1937).
L. Dresner, ORNL-CF-61-12-30, Oak Ridge National Laboratory, 1961.
J. E. Turner, C. D. Zerby, R. L. Woodyard, H. A. Wright, W. E. Kinney,
W. S. Snyder, and J. Neufeld, Health Phys. , 10: 783 (1964).
C. D. Zerby and W. E. Kinney, Nuclear Instr. and Meth., to be published.
Cf. Report of the RBE Committee to the International Commissions on
Radiological Protection and on Radiological Units and Measurements
(ICRP and ICRU), Health Phys. , 9: 357 (1963).
R. G. Alsmiller, Jr., D. C. Irving, W. E. Kinney, and H. S. Moran, in
Second Symposium on Protection Against Radiations in Space, Gatlinburg,
Tennessee, October 12-14, 1964, NASA SP-71, 1965.
G. J. Neary and J. Mulvey, Maximum Permissible Fluxes of High-Ener
Neutrons and Protons in the Range 40 to 1000 Mey. Unpublished manuscript.
ICRP Publication 4, Report of Committee IV (1953-59), Macmillan, New
York, 1964. -

18.
19.
20.
to be published. - -
12
W. S. Snyder, cf. , National Bureau of Standards Handbook 63, Washington,
D. C., 1957. f
J. Neufeld, W. S. Snyder, J. E. Turner, and H. A. Wright, "Calculation
of Radiation Dose from Protons and Neutrons to 400 Mev, "Healtr, Phys. ,
G. V. Dalrymple, Brooks Air Force Base, personal conversation.
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
13
FIGURE CAPTIONS
Average Dose and Dose Equivalent in a 30 cra Soft Tissue Slab
as a Function of Energy from Normally Incident Protons
(from Zerby and Kinney, Ref. 13).
Average Dose and Pose Equivalent in a 30 cra Soft Tissue Slab
as a Function of Energy from Normally Incident Protons and
Neutrons (from Zerby and Kinney, Ref. 13). -
Comparison of Absorbed Doses in Straight-ahead Approximation
with Results from Detailed Calculation for 400 Mev Protons
Incident Isotropically on a 30 g/cmº Aluminum Slab Followed by
30 cm Soft Tissue Slab (from Alsmiller et al., Ref. 15).
Comparison of Dose Equivalents in Straight-ahead Approximation
with Results from Detailed Calculation for 400 Mev Protons
Incident Isotropically on a 30 g/cmº Aluminum Slab Followed by
30 cm Soft Tissue Slab (from Alsmiller et al., Ref. 15).
Flux Densities of Neutrons and Protons for Dose Equivalent of
2.5 Millirem/Hour (from Ref. 17). O - &
Neutron Flux Density for Dose Equivalent of 2.5 Millirem/Hour
(from Neufeld et al., Ref. 19). *
Proton Flux Density for Dose Equivalent of 2.5 Milliram/Hour
(from Neufeld et al., Ref. 19). * - -
Table 1
Particles of High-Energy Dosimetry
Neutron n
Proton P
Pion m”. n°
Photon Y
Electron ©"
+
Muon |A
Table 2
Laboratory Threshold Energies for
Pion-Producing Reactions
Laboratory Threshold
Reaction Energy (Mov)
p + p - p + p + " 263
p + n - p + p + wº 287
+
p + p → p + n + m 292

Table 3
Average Cascade Products for 1.8 Gav
Proton Incident on *cu Nucleus”
4.33 Neutrons
ſ 3, 67 Protons
p + *cu sº { 0, 48 n°
0.31 *
0.26 Tr"
*From Metropolis et al., Ref. 4.
ºt-
Table 4
Actual Cascade and Evaporation Products in a Single
Collision from a 400 Mev Proton Incident on Soft Tissue
1P + 39 an) 1P + o” + a’ (cascade)
OW - '." + 2 T. He # .Be" (evaporation)

Fri - - -y ºr ºllision Da: "…: 2000 Protons Incid, at Normally on 30 cm Tissue Slab
‘t’.1: "...? 5
** * -ºº º * - - -º-ºº-ººººººººº-, * = < * ... - tº-ºº." -
* ...
- *** - sº - -
tº ident ºft: ºr Collisions Col l ; ; ; ) is Collisions ſlot W is ions Percent Percent Percent Percent
* roton of : ; ; th vº i th with vii th of of of of
<rtergy Collisions ... sen Car": cin Hydrogen ::i trojo Collisions Collisions Collisions Collisions
(Fºev) with with with with
sº Oxygen Carbon Hydrogen Nitrogen
...6) E35 362 #09 ° 78 16 64 19 14 3
350 567 362 | 15 78 12 64 20 14 2
300 511 314 * {}3 68 21 61 21 13 4.
250 577 339 107 65 16 67 19 | | 3
200 514 303 124 70 17 59 24 14 3
150 343 212 63 53 10 62 20 15 3
* 30 150 89 35 23 3 59 23 15 2
Average: 62 21 14 3
ſ
:
iº
*~e?
#
–7 OF MIL-DVJG 64 - 1790
1O
- PRIM. T.Y
Af PR C. JS
/ to- —
|
o -., -ses ºf
* ºr -
2
*
HEAVY PARTICLES, , , ,
Y9 m / /
10-8 `-y Zº -
SECON DARY PROTONS, rem
SEcoMDARY PROTONs, rod T
HEAVY PARTICLES, rad
to-10
O |OO 2OO 3OO 4OO 5OO
Æ ( MeV)
! Fig. 1


T
l
:
i
;*=º
OF, NL - C \','3 & 4 - . T &
5x1OT7
PROTONS, TOTAL -
ABSORPTION (rce
2 g
10-7 *ens PROTONS, rem
PROTONS, rod
NEUTRONs, rem
2 -
NEUTRONs, rad
10-8
5xto"?
O 1OO 200 3OO 4 OO 5 OO
INCIDENT ENERGY (Mev)
Fig. 2

1100 MEW
f oxNi DWG
PROTONS INCIDENT ON 30 GM. ZSQ. C.M. (JF RL+TISSUE.
. 64-9309
PRIMARY PROTON |ONIZAT;ON DOSE
5–
2. PRIMARY PROTONS, OTHER DOSE
3. SECONDARY PROTON DOSE
2– 4, SECONOARY NEUTRON DOSE
5. BACKSCATTERED DOSE
10." O PRIMARY PROTON |ONIZATION DOSE
A PRIMARY PROTONS, OTHER DOSE STRAIGHTAHEAD
5 + SECONDARY PROTON DOSE APPROXIMATION
|- D X SEconDARY NEUTRON Dose
2–
•!!
4–
2–
•12 - -
10”! -l | | | -
0 5.0 10 15 20 25 30
-- - - - - - -
DEPTH IN TISSUE, CM.
Fig. 3


:
#
**
É
i
u
É
ORNL DWG. &4-93 l l
-1-
t FTL: ! +
2. 1. *Many protonionization boss - Liſ" + -L -
hºmº- ºr ſº 2. PRIMARY PROTONS, OTHER DOSE - - + T
, --8 3. SECONDARY PROTON DOSE . 3 |
4 ** * 4. SECONDARY NEUTRCN DOSE *
5. BACKSCATTERED DOS5
§ – O PRIMARY PROTON ONIZATION DOSE
| A PRIMARY PROTONS, OTHER DOSE STRA;GHTAHEAD
2. + SECONDARY PROTON DOSE APPROXIM,”,TION
– X SECONDARY NEUTRON DOSE m
•10
10 H
H
5–
2– 5
10” + ;
5–
2—
10”! – | | | l
0 5.0 10 15 20 25 &J - 35
DEPTH IN TISSUE, CM.
Z"
i
i
. - Fig. 4 :
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