Experimental and theoretical studies of nuclear reactions induced by high energy protons and heavier ions are included. Fundamental data needed in the shielding, dosimetry, and radiobiology of high energy particles produced by accelerators were generated, along with data on cosmic ray interaction with matter. The mechanism of high energy nucleon-nucleus reactions is also examined, especially for light target nuclei of mass number comparable to that of biological tissue

Shen, B. S. P.

English

NASA Technical Reports Server

Final Report
for
N.A.S.A. Research Grant
NGR-39-010-114
entitled "Nuclear Reactions Induced by
High-Energy Alpha Particles"
(1 July 1970 -- 30 September 1974)
(NASA-CR-138903) NUCLEAR REACTIONS N74-29155
INDUCED BY HIGH-ENERGY ALPHA PARTICLES
Final Report, 1 Jul. 1970 - 30 Sep.
1974 (Pennsylvania Univ.) 10 p HC $4.00 Unclas
CSCL 20H G3/24 43979
Principal Investigator:
B. S. P. Shen
Reese Flower Professor of
Astronomy and Astrophysics ' ,
University of Pennsylvania ;
The NASA Technical Officer for this grant is John W. Wilson,
NASA Langley Research Center.
https://ntrs.nasa.gov/search.jsp?R=19740021042 2020-03-23T06:39:29+00:00Z
INTRODUCTION
This is the final report for the research project entitled "Nuclear
Reactions Induced by High-Energy Alpha Particles", supported at the
University of Pennsylvania for the period 1 July 1970 to 30 September
1974 byN. A. S. A. research grant NGR-39-010-114.
The principal personnel at the University of Pennsylvania involved
in the project were:
B.S.P. Shen, Principal Investigator, A.B., A.M., D. Sc., Reese Flower
Professor and Chairman of Astronomy
M. Merker, Co-Principal Investigator, B.S., M.S., Ph.D., Assistant
Professor and Assistant Chairman of Astronomy
W.F. Schmitt, A.B., Ph. D., Research Associate
C.L. Ayres, A.B., Ph.D. . candidate
W.J. Nale.snik, B.S., M.S., Ph.D.
L. Skoski, B.S., M.S., Ph.D.
The following is a list of publications and reports made under this
project. Aspects of some of these publications were also supported in part
by other N.A.S.A. and A.E.C. contracts and grants.
a. W.J. Nalesnik, T.J. Devlin, M. Merker and B.S.P. Shen,
"Accelerator Measurement of the Spectra of Neutrons Emitted in
the Interaction of 3 GeV Protons with Several Elements", Proc-
eedings of the National Symposium on Natural and Manmade Radiation
in Space, NASA TMX-Z440, 523 (1972).
b. W. J. Nalesnik, "Energy and Angular Distribution of Neutrons
Emitted in the Interactions of 3-GeV Protons with Carbon, Aluminum
and Cobalt", Ph. D. Thesis, University of Pennsylvania (1972).
c. L. Skoski, M. Merker, "Neutron Spectra at 900 from 3 GeV Protons
on Carbon, Aluminum and Cobalt", Bulletin of the AmericanPhysical
Society 18, 692 (1973); abstract.
d. L. Skoski, "Energy Spectra of Neutrons Emitted in the Interaction
of High Energy Protons with Several Elements", Ph.D. Thesis,
New York University (1973).
e. L. Skoski, M. Merker and B.S. P. Shen, "Production Cross-Section
of 11C from Carbon Bombarded by High-Energy Heavy Ions", Bulletin
of the American Physical Society 17, 489 (1972); abstract.
f. L. Skoski, M. Merker and B.S.P. Shen, "Absolute Cross-Section
for Producing C from Carbon by 270 MeV-Per-Nucleon 14N Ions",
Physical Review Letters 30, 51 (1973).
g. E.S. Light, M. Merker, S.A. Korff, and R.B. Mendell, "Solar
Modulation of Atmospheric Neutron Flux; Experiment and Calculation"
Proceedings of the 12th International Conference on Cosmic Rays 3,
903 (1971).
h. M. Merker, "Energetic Neutrons Leaking from the Top of the
Atmosphere", Physical Review Letters 29, 1531 (1972).
i. M. Merker, E.S. Light, H.J. Verschell, R.B. Mendell, and S.A.
Korff, "The Time-Dependent World-Wide Distribution of Atmospheric
Neutrons and of Their Products, 1. Fast Neutron Observations",
Journal Geophysical Research 78, 2727 (1973).
3j. E.S. Light, M. Merker, H.J. Verschell, R.B. Mendell, and
S.A. Korff, "The Time-Dependent World-Wide Distribution of
Atmospheric Neutrons and of their Products, 2. Calculation",
Journal Geophysical Research 78, 2741 (1973).
k. R.B. Mendell, H.J. Verschell, M. Merker, E.S. Light, and
S.A. Korff, "The Time-Dependent World-Wide Distribution of
Atmospheric Neutrons and of Their Products, 3. Neutrons from
Solar Protons", Journal Geophysical Research 78, 2763 (1973).
1. M. Merker, "The Contribution of Galactic Cosmic Rays to the
Atmospheric Neutron Maximum Dose Equivalent as a Function of
Neutron Energy and Altitude", Health Physics 25, 524 (1973).
m. W.F. Schmitt, C.L. Ayres, M. Merker, and B.S.P. Shen, "A
Model for Astrophysical Spallation Reactions", Proceedings of
the 13th International Cosmic Ray Conference 1, 517 (1973).
n. C. L. Ayres, W. F. Schmitt, M. Merker, and B. S. P. Shen,
"Calculation of Astrophysical Spallation Reactions Using the RENO
Model", Proceedings of the 13th International Cosmic Ray Conference
1, 522 (1973).
o. C. L. Ayres, Ph. D. Thesis, expected Fall (1974).
4DESCRIPTION OF RESEARCH
The original objective of this research was to study experimentally
at the Princeton-Pennsylvania Accelerator (PPA) nuclear reactions
induced by high energy alpha particles. Due to the early shutdown of
the PPA and with the approval of N.A. S.A., we have included experimental
and theoretical studies of nuclear reactions induced by high-energy protons
and heavier ions.
The purpose of this research is
A. to generate fundamental data needed in the shielding, dosimetry,
and radiobiology of high-energy particles produced by accelerators,
B. to generate data needed in the study of the interaction of cosmic
rays with matter, e.g. with the earth's atmosphere, and with
biological tissue, and
C. to help elucidate the mechanism of high-energy nucleon-nucleus
reactions, especially for light target nuclei of mass number
comparable to that of biological tissue.
The research carried out under this grant can be divided into
the following three parts:
I. Experiments at the PPA to study high energy nuclear reactions.
II. Calculations of the atmospheric nucleonic cascade initiated by
the cosmic radiation.
III. Calculations of the intranuclear cascade and evaporation stages of
nuclear reactions induced by high-energy hydrogen, helium and
heavier nuclei incident upon light target nuclei, H through Al.
5Publications a through f report details and results of the experiments
conducted under part I. The experiments were of two types. In one,
(publications a through d) neutron spectra produced in the interaction of
3-GeV protons with several elements at several scattering angles were
determined by time-of-flight techniques. The results were consistent with
the theory of intranuclear cascade and evaporation.
In the other experiments (publications e and f), we measured the
production cross-section of 11C in targets of carbon bombarded by 270 MeV/
nucleon 14N ions. The data obtained were among the first measured results
using high-energy heavy-ions and demonstrated the effects of nuclear inter-
actions between high-energy heavier nuclei.
Publications g through 1 report our theoretical studies under part II
of our research. Atmospheric neutron fluxes and maximum dose equivalents,
element production including radiocarbon production rates, and albedo
neutron leakage rates were determined by Monte Carlo calculations simulating
the interaction of the cosmic radiation with the earth's atmosphere. The
results, which show close agreement with experimental measurements where
available, confirm the usefulness of this theoretical technique in difficult
transport calculations as well as determine important data of the nucleonic
cascade in the atmosphere.
Publications m through o describe our research under part III,
intended to study nuclear interactions among the lighter elements hydrogen
through aluminum using the RENO (Random Encounters between Nuclear
Objects) model. The RENO model simulates the intranuclear cascade and
evaporation stages of nuclearreactions by Monte Carlo techniques. The
original RENO model, a computer program developed principally by
W.F. Schmitt of our group and described in his dissertation ("A Monte
Carlo Calculation of Spallation Reactions of Astrophysical Interest in the
M Nuclei", Ph. D. Thesis, University of Pennsylvania (1970)), has been
modified to accommodate interactions at higher energies and between
heavier elements. A description of the modifications to the model follows:
The work has consisted of the development of an intranuclear cascade
simulation program capable of predicting the results of collisions between
light and medium nuclei at high energies. Although a number of programs
are available for the simulation of cascades produced by free nucleons
incident on nuclei, there have been few attempts to model collisions between
complex nuclei.
The model used in the program is based on that of Schmitt, which
represents nuclei as clusters of discrete point nucleons, instead of the usual
Fermi-sea probability distribution, an approach which greatly simplifies the
modeling of nucleus-nucleus interactions. However, a number of improve-
ments and extensions have been made over the original model. These include:
a) Generalization of the initial state.
Schmitt's original program has been rewritten and expanded from a
version which permitted only incident protons and alphas to one which
permits any light nucleus or pion as either the incident or the target
particle.
7b) Exact dynamics.
A number of dynamical approximations used by Schmitt have been
replaced by exact calculations. This becomes increasingly necessary
as higher energy collisions are considered, and the relativistic
effects become more pronounced. In addition, the nuclei are given
their known atomic masses in the calculations, rather than integral
multiples of the proton mass as in the earlier version.
c) Inclusion of pions.
The production of pions during collisions and their subsequent
interactions with other nucleons in the cascade have been included
in the model. This permits the simulation of collisions at higher
energies than before; it also makes possible cascades produced by
incident pions. The pion-production is based on the Sternheimer-
Lindenbaum model, in which the pions are produced via an inter-
mediate heavy-hyperon state of the nucleon or nucleons in the collision.
The hyperon has a variable mass, dependent on the energy available
in the collision - it then decays by the emission of a pion. By this
algorithm, up to two pions can be produced at each nucleon-nucleon
encounter, one at each pion-nucleon encounter, provided the energy
is sufficient. Empirical elastic and inelastic nucleon-nucleon and
pion-nucleon cross-sections and differential cross-sections are used
to model the individual interactions within a cascade.
d) Reformulation of the reaction-selection algorithm.
In the Schmitt model, selection of the mode of breakup resulting
.8
from a nucleon-nucleon collision was governed by an ad hoc
probability equation of the form:
1
P =
n a (E E )Yn +
n n
this being designed to resemble a resonance pattern around energy E
n
In the new version, a similar algorithm is used, butthe probability
expression has an additional term which will dominate at high
energies. It now reads:
1
P = + Y E.
n 2 na (E- E ) +
n n
The coefficients a and Y are chosen by trial and error to give the
n n
best results when compared with experiment. They may be entered
by the user as input if desired.
e) Generation of history file:
The program now generates a file on tape or disk as well as a
printed output. The secondary file contains the initial and final
states of all interacting cascades; it may be used as input to a
second program in order to generate additional statistics about
the run without repeating the simulation.
A series of runs is currently under way to obtain an optimal set of
the reaction-selection coefficients mentioned in paragraph (d) above.
The program in its present form will simulate bombardments in
which the incident and target particles may be pions, free nucleons, or any
light or medium nucleus, provided only that the sum of nucleons
in incident and target particles does not exceed 32. It will accom-
modate energies from a minimum of 20 MeV per nucleon (or per pion)
up into the GeV range; however, the model does not take into account
nucleon-antinucleon pair production or triple-pion production, which puts
an upper limit on the incident energies at which it can be useful. It
provides total elastic and inelastic cross-sections, nuclide production
cross-sections, and outgoing spectra for pions and free nucleons. In
conjunction with the secondary program which reads the output tape, it
can also provide outgoing spectra for any species of nucleus.
A detailed description of the modifications to the Schmitt model
and calculations using the model will be presented in publication o, the
dissertation of C. L. Ayres, which is expected to be completed this fall
and will be forwarded. In addition, we are providing our N.A.S.A.
technical officer, at his request, with a tape of RENO and auxiliary
programs, as well as a user's guide and a sample calculation.


Nuclear reactions induced by high-energy alpha particles

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