Production of Fast Neutrons With a Plasma Focus Device

Moshe Gai

Laboratory for Nuclear Science at Avery Point and

Yale University and

DIANA-HiTECH, LLC, North Bergen, NJ

1. The Plasma Focus Device. (History, Physics) 2. Neutron, X-Ray, Radioisotopes 3. Applications: Radioisotopes Neutron interrogation (Interstellar propulsion)

Cape town, April 6, 2006

The Laboratory for Nuclear Science At Avery Point

Developments of Plasma Foucs 1. Discovery of Plasma Foucs in Late 1950’s early 1960’s by Filippov and Mather. J.W. Mather; Physics of Fluids 8, 336(1965). N.V. Filippov, T.I, Filippova, and V.P. Vinogradov IAEA Nuclear Fusion Suppl. 2, 577(1962). 2. PF developed mostly in (Poland) Eastern Europe 1970’s Transferred to Italy 1980’s (Jan Brzosko). 3. Transferred to USA, Stevens Tech, Hoboken, NJ. Knife Edge Discovered (Vittorio Nardi, Jan Brzosko). J.S. Brzosko, V. Nardi; Phys. Lett. A155, 162(1991). 4. Discovery of Accelerated Ions. 5. Los Alamos, Weapons simulations Sandia National Lab, Z-machine 1 MJ achieved 6. Future? Brazil, Poland…

Plasma Focuse Neutron generator (1013 n/pulse)

DIANA-HITECH, LLC (PF-50 x 2)

X-RaysNeutronsIons (<5 MeV/u)(Backward Emission)

J.S. Brzosko, K. Melzaci, C. Powell, M. Gai, R.H. France III, J.E. McDonald, G.D. Alton, F.E. Bertrand, and J.R. Beene; Amer. Inst. Phys. CP576(2001)277

DIANA's PF-25

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Similar results are applicable to the gross pinch of the plasma focus in other gases such as Argon, Neon and Xenon. Generally for these other gases rmin < 0.1a. The difference in the computation involves the value of γ. Scaling these parameters of the focus to the anode radius a is extremely useful for understanding and for applications. We have carried out exhaustive series of experiments [7,10], using TEA nitrogen laser nanosecond shadowgraphy (see Fig 3), which confirm these theoretical results. Agreement is also observed with more recent detailed computation [1].

Fig 3. Sequence of compression in UNU/ICTP PFF at 4.0 mbar deuterium [20]

III: Drive parameter S is constant over range of machines We next return to discuss the drive parameter S: (Ip/a)ρ-1/2 . We had surveyed [5] the drive parameter for a range of machines, from large to small, as compiled in Table 1.

Device/Author [Reference] V (kV)

W (kJ)

p (torr D2)

Ip (kA)

a (cm)

Ip/a/p½ (kA/cm/[torr D2]½)

DPF-78 [24] 60 28 5 550 2.5 98.4

SPEED 2 [25] 183 70 4 1000 6 83.3

PF-360 [18] 21 60 3 750 5 86.6

Mather [19] 17.3 13.5 6.5 537 2.5 84.3

UMPF [20] 14 6 6.5 300 1.25 94.1

UNU/ICTP-PFF [23] 14 2.9 3.5 172 0.95 96.8

Bernstein [21] 27 8 820 3.9 74.3

POSEIDON [22] 60 280 3.8 1200 6.55 94.0

Table 1 Actual-shot data of some neutron-optimized Mather-type plasma focus devices and their calculated drive parameter. The mean value and the corresponding standard deviation of the drive parameter are 89.0 and 7.7 kA/cm/(torr D2)½ respectively. In this compilation care is taken that the data represent actual neutron-optimized shots as published. Actual-shot data needs to be distinguished from machine data which may give maximum current capability of a machine or design current which when combined with the pressure of an actual shot may give a misleading drive parameter since the actual shot is usually carried out not at the maximum or designed current. Thus much published data of machines could not be used in this compilation because of uncertainty over actual shot data. In Table 1 the value of the peak current Ip flowing into the focus tube is used as this value is more usually quoted than the plasma current and thus using the peak current more actual shot data points are available. Table 1 shows that the drive parameter S for a range of neutron-optimized plasma focus devices is 89±8 kA/cm per (torr)½ of deuterium. The standard deviation of less than 10% is quite remarkable since the machines in the

*

. ‘i l

All these studies [3] -suggest the following Reaction Yield fromHot-Magnetized Plasma-Target

empirical formula fJ% 2 0.1 MeV): of the Plasma Focus

d@i/a CC tern (2 I m I 3) (1) Similar (as in E!q. 1) spectral dependence for the trapped and reacting in plasma ions was drawn by unfolding of the D(d,n) neutron spectra The data provide evidence that the fast beam yields (0;) as well as reaction yields &I plasma (Yp> and/or on external targets (YJ scale with the square of the energy (W) stored in the capacitor bank [4], i.e.

ylpulse - I I t

eyoFd 3:: 1:: 12C(3He.n)140; 12C(3He,4He)ll C;

w,,kJ 5:: 14N(3He,4tte)l3N;

2:: 4:: 12C(3He.d)13N; 14N(3He.d)150;

7:: 160(3He,4He)150; 6:: 160(3He,p)l8F;

9:: 12C(d,n)13N; 10:: 8:: lOB(d,n)llC;

11: 16O(d,n)l7F; 14N(d,n150;

13:: D(d.n)3H; 15:: 22Ne(d,p)23Ne;

E(11) - 16::76Se(d,2n)76E!f;

Q oCW2; YpoCW2; Yt cl;w2 (2) In addition to direct ion-beam observation, the activation methods have also been broadly used. In such approaches energy threshold reactions leading to formation of radioactive species in externally positioned solid targets (exposed to D” irradiation) have been used as PF-diagnostics. Under these conditions, radioisotopes such as “C, ‘lN, 150, “F, **Al, &Cu have been observed and are reported elsewhere.

410)

w9)

The scope of this paper is to evaluate/demonstrate of potential of the PF device as a breeder of radioactive isotopes that can be utilized for the production of exotic and/or radioactive ion beams for radioactive ion beam applications and/or for medical imaging (PET) and biomedicine a@ications.

- ~-- 49 49

Calct4ated ReactionYkM, Y

W=7kt5O.%HZ&%?%LZ; P-W*2

2. NUCLEAR REACTIONS INDUCED IN THE MAGNETIZED PLASMA-TARGET

FIGURE 2. Compilation of experimental data measured with a PF (W= 7 kJ) filled with a mixture of HZ and LZ gases. The box sizes are represez@ive of standard deviations (vertically) obtained by averaging many experimental points (discharges) and model uncertainties (ho&&al). For convenience experimental data are adjusted (see Eq. 3 and 4) to n&n= = la3hLz=l.

BY FAST IONS TRAPPED IN THE TARGET

In this section, the experimental evidence and discussion is oriented to the situation where fast ions are trapped in domains of magnetized plasma Such fast ions can induce nuclear reactions by collisions with nuclei in the background plasma To produce a selected nuclear reaction and as a result, produce a specific radioisotope, one has to create a dense, magnetized plasma composed of two isotopes with different atomic numbers and an appreciable population of high-energy (fast) ions. The cross-section for the production of the radioisotope of interest (reaction product) has to be sufficiently large (a 2 100 mb) at the ion-projectile energy of 0.5 MeV/nucleon.

A summary of these experiments is shown in Fig2. From Fig2 it is clear that a broad range of radioisotopes, with large yield, can be produced in a PF device. A relatively small PF-machine, operated at a discharge power of W= 7 kJ, can produce x106 to 5x 10’ radienuclei per pulse, while with a medium size machine, operated at discharge power of, W = 70 kJ, one can expect a hundred times higher yields.

The semi-empirical model assumes: fij the instantaneous creation of a magnetized plasma domain, containing fast trapped-ions, (i:i) a domain stability pera z = 0.5-5 ns, and (iii) an instantaneous domain destabilization, causing fast ions to be ejected out of the pinch zone. For briefness, and demonstration of trends, a simplified formula (instead of full theory [5]) for (HZ- LZ) radioisotope production is used here:

Only one experimental group has achieved high efficiency (yield per kJ af stored energv) for the production of short-lived radioisotopes in a plasma environment [5]. The experiments reported here were carried out with a Mather-type PF device with a capacitorbankenergyofW=7kJ(V=lSkV)and&a total gas mixture pressure of p = 5 Torr. Gas mixtures were composed of low-Z (LZ) isotopes (H, D, %e) mixed with high-Z (Hz) isotopes.

Yp= XI~XTX@~

In the Eq.3, dQr,/dE, (see Eq. 1) is normalized to the range, E. _< E 5 h; Qpa is the total number of the projectile ions that are accelerated and trapped in the plasma; nm is the numeric density of plasma nuclei that serve as target during radioisotope productioq a(E) is

108Ag: t = 2.41 min110Ag: t = 24.6 sec

the reaction cross section and M is the qss of the LZ ion. E!q. 3 neglects stopping powers of fast ions .in the plasma domain and considers -only LZ as projectiles inducing nuclear reactions. IQ.3 simplifies further if one assumes that: (i) the density of Hz particles in the plasma target, nm is proportional to the atomic density, m,, of the HZ in the filling gas (constant plasma compression), Le., nm a pm; (ii) the number of accelerated LZ ions is proportional to the abundance of such ions in the plasma target, i.e., G$, cc nr,r ct p~z. As a result, Eq. 3 converts to the following form:

The identification of isomers, is based on their lifeiime$ @;j Gd. ;iaon’ Y&& are. &~/-&g22~-~;om

i&ial~‘“radmactivity of the component (associated with the identified radioisotope) and the efficiency (solid , I .1* , . angle included) of the detection system.

Yp cc zx~xp~~x 7 cs(E)~E-*‘~xdE (4) 0

The theoretical values (in Fig2) are calculated by use of Eq. 3. The beam yield in the plasma was assumed to be the same as those activating the external targets. The nxz product wns taken from Ref. 13. __ Eq. 4 agrees well with experimental results (see Fig2).

‘3. EXPE$&j3$J$N’Y&‘AL TESTS OF . .-I-, *~,.“.4,a..c*,~~~-*;c~.,.” .,( RADIOISOTOPES PRODUCTION IN

THE PF-PLASMA

Plasma origin of the radioisotopes breeding is supported by three observations; (A) For PF discharges with a chamber Ta-clad and filled with a mixture of deuterium and one HZ component (r*C, or 14N and/or 160) only one T1/, , as expected from (d,n) reaction product, is observed; no radioactivity occurs for pure Dz fillings. @I$) Whenever the PF-chamber is filled with different relative compositions of HZ and LZ gases while keeping the total atomic density constant - the resulting radioactivity changes proportionally to the product of puxxpu as expected from Eq.4. m In experiments with Al or Cu external targets and the chamber filled with HZ and LZ gases, two radioisotopes are produced: one ti the plasma and one @ the target Fig4 demonstrates complete disappearance of the plasma radioactivity when the chamber is instantly evacuated during measurements of the decay curve. . /*I..” .a.- <_. ~I .~

Radioactivity (&cay curve) is measured by use of a thin-wall, cylindrical Geiger-Muller counters (GM) havirig walls (cathode) made of high resistivity metal alloy (no Al or Cu). GM counters were used because they can survive an electromagnetic shock and jets of plasma emitted during PF operation. In the course of experiments, various geometrical set-ups were used [5], one of which is shown in Fig 3. GM

15 cm couuter

AlorCuI

279

TIME ]sj FIGURE 4. Au example of the decay curves each c0~0sed of two half-lives: TX = 1.1 miu (“F) and 5.1 min ( %). Three min after the discharge @azjmz = O.l), the chamber was pumped-out (radioactive gas evacuation) after which the plasma-induced radioactivity 0% = 1.1 min) di~app~md. A decay curve, measured after mother discharge and witho& gas

evacuaticsu, is shown for comparison.

4. PLASMA FOCUS AS AN EFFICIENT BREEDER OF SHORT IXQ

RADIOISOTOPES FOR ACCELERATORS AND BIOMEDICINE

FIGURE 3. Au exp esimeatal s&-up used for simultaneous measurement of radioactivity induced in the plasma and on the target foils (Al or Cu). Each set of the four @Is is .c~~ected in pral.lel to a multi-scaler counter and counting begins 10 s after the PFdis&arge is completed The chamber walls are clad with Ta.

PF devices have the capability of producing radio- nuclei m external targets and ti the plasma This second application is addressed here. Data, such as shown in Fig4, replicate results where the external target is assumed to be solid 160, accounting for differences in the ion. stopping power, cross-sections, efficiency and considering a pdpu = 1 plasma In such cases, the production of “F radionuc!ei & the plasma

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May 8, 2005 NY Times WASHINGTON, May 7 - After spending more than $4.5 billion on screening devices to monitor the nation's ports, borders, airports, mail and air, the federal government is moving to replace or alter much of the antiterrorism equipment, concluding that it is ineffective, unreliable or too expensive to operate.

Wednesday, July 24, 2002FOR IMMEDIATE RELEASECONTACT:Rebecca Hanks 202/224-2182

McCain Voices Opposition to FY'02 SupplementalAppropriations Bill

Washington, DC – U.S. Senator John McCain (R-AZ) today entered the followingstatement into the Congressional Record regarding the FY'02 SupplementalAppropriations Bill:

Other questionable provisions regarding the TSA should also be mentioned. For example,in the Statement of Managers, the appropriators have earmarked money for the fieldtesting of a particular security technology referred to as Pulsed Fast Neutron Analysis(PFNA). There is only one company that has developed this technology: AncoreCorporation of Santa Clara, California. Unfortunately, earlier this month, the NationalResearch Council (NRC) concluded that PFNA is not ready for airport deployment ortesting. Even though the main role for PFNA is the detection of explosives in full cargocontainers, the appropriators are directing money for field testing on checked bags. Thisearmark could be a total waste of critical research money that should be contributing toour effort to increase aviation security.

1. The Plasma Focus Device, pulsed source: Neutron: 1011, 1013 /pulse @ 2.5, 14 MeV

20-50 nsec pulse duration (up to 5 Hz) X-Ray Radioisotopes Accelerated ions Safe (Can be turned off) 2. It’s a pity it will not be developed further. 3. It’s a pity we will not know if it is

applicable for HLS etc.

Cape Town, April 6, 2006