Potential Correlations between Unexplained Experimental Observables and Hot Projectile-Like Fragments in Primary Interactions above ECM/u ≈ 150 MeV

doi:10.4236/wjnst.2013.34026

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World Journal of Nuclear Science and Technology, 2013, 3, 155-161

http://dx.doi.org/10.4236/wjnst.2013.34026 Published Online October 2013 (http://www.scirp.org/journal/wjnst)

Potential Correlations between Unexplained Experimental

Observables and Hot Projectile-Like Fragments in

Primary Interactions above ECM/u ≈ 150 MeV

Eberhard Ganssauge1, Wolfram Westmeier2,3*, Reinhard Brandt2

1Fachbereich Physik, Philipps University, Marburg, Germany

2Fachbereich Chemie, Philipps-University, Marburg, Germany

3Dr. Westmeier GmbH, Ebsdorfergrund, Germany

Email: *[email protected]

Received July 22, 2013; revised August 25, 2013; accepted September 11, 2013

cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

An enhanced neutron production and an enhanced nuclear destruction due to secondary fragments have been observed

in very thick targets irradiated with high energy ions. This enhancement is beyond theoretical calculations and it is an

unresolved problem. It is observed only when primary ion interactions exceed an energy threshold (ECM/u ≈ 150 MeV).

Investigations using nuclear emulsions for very high-energy nuclear reactions suggest that two distinctly different

classes of relativistic projectile-like fragments are emitted in primary interactions: a “cool” channel with a temperature

of (T(p)cool ≈ 10 MeV), and a “hot” channel with (T(p)hot ≈ 40 MeV. This second reaction class may induce the above

mentioned enhanced reactions of secondary fragments, thus being responsible for unresolved problems. This assump-

tion should be studied in further experiments. Nuclear interactions of secondary particles in thick targets are of interest,

in particular in view of radiation protection needs for high energy and high intensity heavy ion accelerators. Many basic

ideas of this paper go back to the late Professor E. Schopper (Frankfurt).

Keywords: Very High Energy Projectile; Hot Projectile Fragments; Cool Target Fragments; Unresolved Problems

1. Introduction

Since around 1950, researchers have been unable to re-

solve problems in explaining observed phenomena in nu-

clear reactions at high energies in very thick targets.

In a recent publication on “Correlations in nuclear in-

teractions between ECM/u and unexplained experimental

observables” [1] it is pointed out that these observations

are restricted to high energy interactions induced by pri-

mary ions in medium and heavy element target nuclei

above a threshold of ECM/u ≈ 150 MeV for the primary

nuclear interaction. Enhanced neutron emission and en-

hanced nuclear destruction of target nuclei in secondary

reactions are observed which significantly exceed model

calculation. The concept of “limiting fragmentation” in

spallation reactions does not hold in these thick target in-

teractions any longer. In a preceding publication the en-

hanced “Neutron production in thick targets irradiated

with high energy ions” [2] and radiochemical spallation

yields were analyzed using advanced computer simula-

tions such as MCNPX 2.7a. The authors concluded that

enhanced neutron production (quote) “may have an im-

pact on radiation safety protection issues for future heavy

ion accelerators” under construction. A systematic re-

view on “Interactions of relativistic heavy ions in thick

heavy element targets and some unresolved problems” [3]

has been published earlier.

In 1996, the late Professor E. Schopper (Frankfurt) in-

formed the Marburg group in a private letter that Baum-

gardt, Friedlander and Schopper had shown in 1984 [4]

that two distinctly different exit channels had been ob-

served in the reaction of 100 GeV 56Fe ions with nuclear

emulsion. Fifteen years later, we are following up on Prof.

Schopper’s suggestion to continue our work in this direc-

tion. One channel was “cold” and consistent with well-

known spallation reactions. The other channel was “hot”

and not compatible with any model calculation. This ob-

servation was confirmed by several experimentalists.

However, it was in the following completely ignored by

all scientists, even by Friedlander himself. We will re-in-

vestigate the phenomena observed in [4]. Our interest is

*Corresponding author.

E. GANSSAUGE ET AL.

156

focused on the FIRST nuclear interaction of 100 GeV

56Fe observed in nuclear emulsions, following a sugges-

tion of the late Professor Schopper:

“Is this ‘hot’ channel in the 1st interaction responsible

for the observation of unresolved problems due to inter-

actions of secondary fragments?”

Projectile fragments emitted in the “hot” exit channel

of the first interaction will induce secondary interactions

in thick targets which may be the source of unresolved

problems. The situation will be described, but no definite

solution can be given yet.

2. Primary Interactions Produce “Cool” and

“Hot” Relativistic Projectile-Like

Fragments

Detailed investigations with nuclear emulsions of pri-

mary interactions where ECM/u exceeds 150 MeV are

available only for irradiations with either 100 GeV 56Fe

or 72 GeV 40Ar projectiles. These reactions were studied

about three decades ago [4-10]. For all relevant interac-

tions with target atoms in emulsion (107,109Ag, 79,81Br, 16O,

14N, 12C), but not with protons, the energy threshold of

ECM/u ≈ 150 MeV is clearly exceeded.

Baumgardt, Friedlander, and Schopper [4] showed that

all heavy target elements in nuclear emulsion with a mass

A ≥ 12 amu are involved in primary interactions. How-

ever, they studied only those nuclear interactions, (ob-

served under an optical microscope as a “star” in a nu-

clear emulsion) where target-like products, visible as a

number of heavy tracks, either black or grey, could be se-

parated experimentally in a clear manner from relativistic

projectile-like fragments moving forward as minimum-

ionizing ions (visible as thin tracks). An example of such

an event is shown in Figure 1. The authors of [4] restric-

ted their analysis further to such events having at least

one projectile-like fragment with Z ≥ 3 and at least one

projectile-like helium-ion (Z = 2). They measured the

pseudo-rapidity (related to the transverse-momentum Pt)

only for these helium-ions and treated the angular distri-

bution of the He projectile fragments within the frame-

work of thermodynamic models. The results are presented

in convenient parameter space like squared transverse mo-

menta per nucleon using a quantity Q, defined as



QPA



(1)

where A = 4 is the mass of the outgoing particle.

In their analysis the transverse momentum, Pt, for each

relativistic α-projectile fragment was determined by the

measurement of its polar angle Θ with respect to the

beam direction. Assuming beam velocity for the He frag-

ments they introduced as a good approximation



22 2

1sin

QqM



  (2)

with γ being the Lorentz factor of the projectile, Mp is the

Figure 1. An example of an Ar-induced interaction “star”

(or event) in Ilford G5 nuclear emulsion. The relativistic

Ar-ion enters from the right and moves to the left. Clearly

seen are two different types of fragments. The target-like

products are emitted more or less isotropically from a point

source as black or grey prongs. The projectile-like frag-

ments are emitted as minimum-ionizing particles leaving

tracks into a small forward cone [5].

proton mass and Θ is fragment’s polar angle. In nomen-

clature and analysis the authors of [4] follow a long-

standing tradition of scientists in the field of nuclear

emulsion studies. The interested reader may consult the

textbook of Powell et al. [6]. If the emission of the He

fragments in the projectile frame is a Maxwellian distri-

bution with some temperature T, then for an integral fre-

quency distribution the logarithm of F(>Q) is











/2/ p



nFQAMq T (3)

Linearity of such a plot is a strong evidence for a single

temperature T describing this type of interaction. The

authors of [4] continued: “We selected events with nα ≥ 2

[nα being the number of alphas in one specific event] in

which at least one He fragment had a transverse momen-

tum exceeding some threshold value Qth,

Qth = Q0 = 0.02 [(GeV/c)/nucleon]2, chosen so that it

corresponds to practical extinction of a T = 10 MeV

component. The trigger particle with the highest q [trans-

verse momentum of trigger particle] was excluded from

the analysis and the remaining alpha particle momenta

were plotted. In the same way we proceeded with those

events in which no α particles occurred with a momen-

tum q > Q0.

The results are shown in Figure 2. The surprising

finding is that the residual particles from the tagged events

appear to constitute a homogeneous group corresponding

to a temperature of T(p)hot = 40 MeV (hot events; Figure

2(a)). When events in which the highest q of a He particle

lies below Q0 are plotted in the same way one finds a quite

different but again homogeneous distribution correspond-

ing to a much lower T(p)cool ≈ 10 MeV, which is ap-

proximately the boiling temperature of the nucleus (cool

events; Figure 2(b)).

One observes about 80% of all events in the “cool

group” and about 20% in the “hot group”.

Ganssauge et al. [7,8] reproduced the essential results

of Baumgardt et al. [4] with an independent study of nu-

E. GANSSAUGE ET AL. 157

Figure 2. Normalized integral frequency distribution F(>q)

for He projectile fragments, omitting the trigger particles:

(a) qtrigger > Q0 = 0.02 [(GeV/c)/nucleon]2, (hot events, T(p)hot

≈ 40 MeV, ~20%). (b) qtrigger ≤ Q0 (cool events, T(p)cool ≈ 10

MeV, ~80%). The dashed line in (a) depicts the distribution

from (b).

clear emulsions irradiated with 100 GeV 56Fe ions. Joseph

et al. [9] did the same with nuclear emulsions irradiated

with 72 GeV 40Ar ions, and Aggarwal et al. [10] studied

also the same interactions as the two preceding groups.

All groups started their investigations with new irradia-

tions of nuclear emulsion. The number of analyzed nu-

clear events was always substantially larger in [7-10] than

in [4]. All groups confirmed the central observation of

Baumgardt et al.:

There Are Two Independent Kinds of

Interactions Observed for Projectile-Like

Fragments

In about 80% of all events one observes nothing exciting,

these are “cool” interactions. In about 20% of all interac-

tions one observes a “hot” source emitting projectile frag-

ments. Both channels are clearly separated.

As an example of the other independent measurements,

the normalized frequency distribution for He projectile

fragments showing two independent reaction channels is

depicted in Figure 3. The data are taken from [8] where

the authors followed the procedure of [4] in their separa-

tion of “cool” from “hot” events. Of particular interest is

the indication of a third and even “hotter” temperature

component within the “hot” regime (<10%). Actually, all

three groups observed this phenomenon within the “hot”

distribution, but omitted a more detailed and quantitative

analysis [7-10].

Joseph et al. [9] summarized their results: “This high

statistics study based on the analysis of 3308 relativistic

alphas gives clear evidence of two distinctly different

Figure 3. Normalized integral frequency distribution F

(>{[pt/A2][GeV/c]2}) for residual He projectile fragments,

omitting the trigger particles: right, hot events (T(p)hot ≈ 43

MeV, ~20%); left, cool events (T(p)cool ≈ 10 MeV, ~80%) [8].

temperatures in the fragmentation region.” Aggarwal et al.

[10] reached similar conclusions.

3. In Primary Interactions ONLY ONE

TYPE of Target-Like Fragments Is

Produced

The complementary partners to projectile-like fragments

in these interactions are the target-like fragments appear-

ing as heavy tracks. They are isotropically emitted in the

lab system (see Figure 1). T he authors of [4] dis-

cussed this only shortly and did not publish all relevant

details. In the context of questions discussed in this paper,

there exists only one experiment—the irradiation of nu-

clear emulsions with 100 GeV 56Fe—where the number of

heavy tracks, Nh, coming from target-like fragments has

been studied systematically. Ganssauge and his group in-

vestigated target-like fragments for “cool” and “hot” events

[7,8] and presented a normalized frequency distribution of

the target-like fragment multiplicity Nh for “cool” and

“hot” reaction channels (Figure 4).

The average h

N is for “cool” events:



hcool

N =

(9.1 ± 0.5) tracks/event, and for “hot” events:





hhot

= (11.4 ± 1.4) tracks/event.

A more detailed analysis shows that “hot” events are

found slightly more often due to interactions with Ag- or

Br-target nuclei as compared to “cool” interactions, as it

was observed already in [4]. Only on heavy target nuclei

(Ag and Br) one can find reactions with more than 8 tracks

(Nh ≥ 9). Table 1 gives a summary of relevant experi-

mental results for Nh-distributions from [8].

According to semi-empirical standard procedures in

uclear emulsion experiments, such as described in the n

E. GANSSAUGE ET AL.

158

Table 1. Number of black prongs, Nh, in a nuclear emulsion irradiated with 100 GeV 56Fe.

h ≤ 8 Nh ≥ 9 Nh ≥ 0 (Nh ≥ 9)/(Nh ≤ 8)

“cool”, nα ≥ 2 222 events (62%) 136 events (38%) 358 events (100%) 0.61 ± 0.07

<Nh> = 3.0 ± 0.3 <Nh> = 19.0 ± 1.7 <Nh> = 9.1 ± 0.5 6.3 ± 0.5

“hot”, nα ≥ 2 38 events (49%) 40 events (51%) 78 events (100%) 1.05 ± 0.22

<Nh> = 3.3 ± 0.6 <Nh> = 19.1 ± 3.1 <Nh> = 11.4 ± 1.3 5.8 ± 1.0

02468101214

T(MeV)

< N

> (stars)

T(MeV) = f(<N

T(cool)

T(hot)

Figure 4. Normalized integral frequency distribution F(>Nh)

for target-like fragments in the “cool” (kalt) and “hot” (heiß)

reaction channels [8].

Figure 5. Increase of the nuclear temperature T with the

number <Nh> of heavy prongs according to equation 6.

Taking the experimental values for <Nh> from Table 1, one

obtains only a “cool” temperature of T(cool) ≈ 12 MeV, but

there is NO WAY to reach a source temperature of T(hot) ≈

40 MeV.

textbook of Powell et al. [6], one can correlate the average

number of heavy tracks <Nh> with a nuclear heat U as

follows:

similar integral frequency distribution F(>Nh) in interact-

tions induced by cosmic rays in nuclear emulsions. The

primary energy of cosmic rays observed in these nuclear

emulsions extended up to 2000 GeV.



UN124 N30 MeV (4)

and U is connected with the nuclear temperature T as:





10U NMeVTA (5)

Combining Equations 4 with 5 yields:





10124 N+30MeVTA (6)

Not surprisingly, Friedlander and Friedmann never-

theless observed only well-known “cool” phenomena in

their h

N distributions in [11], as also reported in [4].

The authors of [11] simply did not study projectile-like

fragments so they could not see the hot regime.

It was shown in [1] that the threshold of Ecm/u ≈ 150

MeV applies for all hadronic (protons and heavier ions)

primary interactions. All cosmic rays with energy above

about 30 GeV should therefore induce “unresolved prob-

lems” in emulsion.

Using these formulas, one obtains for the “cool” and

“hot” target-like fragments about the same nuclear tempe-

rature:

 

cool hot

N12 MeVTT (7)

This temperature of 12 MeV is based on the assumption

of an average mass A = 80 of the target atoms within the

nuclear emulsion. Therefore this temperature is only a

rough estimate. However, the essential result of equation

7 remains valid: The nuclear temperatures in both chan-

nels, the “cool” and “hot” target-like sources, must be

quite similar. Actually, this is the temperature of a “cool

source”.

4. “Hot” Relativistic Projectile Fragments

Are an Unresolved Problem

The essential results of this article shall be repeated:

For projectile-like fragments one observes two kinds of

reactions with distinctly different temperatures T(p) in the

“cool” and “hot” reaction channels:

T(p)cool ≈ 10 MeV, T(p)hot ≈ 40 MeV.

For target-like fragments one observes from both reac-

tion channels:

Experimental results of derived temperatures vs. h

are shown in Figure 5.









cool hot

N12 MTT

It is of interest to note, that the behavior of h

N as

observed in this paper, has been known for a long time. As

early as 1967, Friedlander and Friedman [11] measured a

This has been considered an unresolved problem al-

E. GANSSAUGE ET AL. 159

ready in 1987 [8]:

“The strong increase of projectile-like temperatures

from ‘cool’ events to ‘hot’ events has no correspondence

on the target-like side”.

The unresolved problem shows up in primary ion in-

teractions above the threshold given earlier (ECM/u ≈ 150

MeV)—as far as the limited experimental evidence allows

definition. The authors of this paper have no problem to

understand the “cool” reaction path, as these classical

spallation reactions have been studied for decades using

well-known concepts of nuclear science [3]. However, we

are not aware of any model calculation, which yields such

a strong difference in ONE nuclear interaction leading to

rather conventional temperatures in the target-like re-

siduals and simultaneously to exceedingly high tempera-

tures for 20% of the projectile-like fragments. There ap-

pears to be a problem with classical concepts, which al-

ways request an increase in entropy for reactions in iso-

lated systems. One should remember: the volume for this

interaction has only a tiny radius (approx. 10−12 cm) and

the reaction time is very short (approx. 10−20 s).

In this situation it might be allowed to recall a historical

paper of L. Szilard, published in Berlin in 1929: “Über die

Entropieverminderung in einem thermodynamischen Sys-

tem bei Eingriffen intelligenter Wesen.” [12].

Instead of trying a translation, we employ a description

of the essence of this article as given by Szilard’s friend E.

Teller in his Memoirs [13]:

“Szilard proposed that the rules of thermodynamics

remain valid, if one includes the demon in the system

rather than talking exclusively about the state of disorder

(entropy). He assigned a value of entropy (or of order) to

pieces of information received by the demon. Szilard’s

work gave rise to a practical and famous branch of science,

called information theory, important today in transmitting

information at minimum cost.”

This ansatz with an active demon interfering with a

nuclear reaction system may turn out be useful or not—it

should at least be mentioned. Obviously, information the-

ory and physics of high energy nuclear interactions are

quite different fields. In this nuclear application, the de-

mon will not receive information, but the demon may in-

troduce information into a nuclear system and thus create

a new experimental situation, i.e. the separation of “hot”

projectile-like fragments from “cool” target-like residuals.

(One may ask: is the demon introducing some “Ord-

nung”?). One might investigate if the ideas of Szilard

could be fruitful even in this new field.

Future experiments with heavy ion induced reactions

above the threshold of (ECM/u ≈ 150 MeV) will answer the

questions: Is the “hot” channel in the first interaction

responsible for producing unresolved problems in con-

secutive second interactions? So far, this problem has not

been settled in a definite and conclusive experiment. Do

“hot” projectile-like He-fragments produced in 100 GeV

56Fe interactions show in their 2nd interactions within the

same nuclear emulsion any specific particular character-

istics, for example enhanced Nh yields? Such studies can

also be done in nuclear emulsions irradiated with 72 GeV

40Ar ions. Preliminary studies of the 2nd interactions in

nuclear emulsions irradiated with 72 GeV 22Ne have been

mentioned in [3]. Their results could not answer the ques-

tions at stake in a conclusive manner. However, this last

study did not consider specifically He-like “hot” projectile

fragments.

Are “hot” He-like projectile fragments responsible for

secondary interactions inducing the enhanced neutron

emission and enhanced nuclear destruction reported ear-

lier in [1-3]? This problem cannot be studied directly with

radiochemical methods or neutron yield measurements,

but results from these two independent experimental tech-

niques would be useful to obtain a complete picture of this

new nuclear process. In a recent conference contribution

[14] “Suggested investigations to understand experimen-

tal observables” more experimental studies were proposed.

Among others, these experiments are geared towards ans-

wering the question of the origin of various unexplained

experimental results, such as e.g.:

1) The extremely large neutron fluence at a distance of

over 240 meters from the 20 cm THICK Cu target irradi-

ated with 72 GeV 40Ar ions at the BEVALAC in Berkeley

(USA) in March 1987 (see Appendix), or the 3-fold in-

crease of the neutron fluence generated with 44 GeV 12C

onto 20 cm Cu (or Pb) at the JINR accelerator in Dubna

(Russia) as compared to most recent calculations.

2) Radiochemical spallation yields in THICK Cu tar-

gets irradiated with the same ions as above show an en-

hanced nuclear destruction beyond standard model ex-

pectations.

These questions are directly connected with the design

of radiation protection shielding in high energy heavy ion

accelerators presently under construction.

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Appendix

Figure A1. Sketch of parts of the Lawrence Berkeley National Laboratory (California). with its former BEVALAC (High-

Energy Heavy Ion Accelerator) and the position “P”, where a 20 cm thick copper target was irradiated for 44 minutes with

72 GeV 40Ar-ions ( ~5 × 108 ions/second) on March 10, 1987. The health physics neutron monitoring measurements at the

SUPERHILAC, at a distance of about 240 m from “P”, forced the operators to announce: “There is a large neutron dose

above the warning threshold within the entire laboratory”. No further information about the actually measured neutron dose

was ever released.